Room: 315B
Session Chairperson: TBA
8:00 am
PULSED LASER DEPOSITION OF ELECTRONIC CERAMIC THIN FILMS: D.B. Chrisey, J.S. Horwitz, P.C. Dorsey, L.A. Knauss, R.C.Y. Auyeung, U.S. Naval Research Laboratory, Washington, D.C., 20375-5345
Pulsed laser deposition (PLD) is a unique physical vapor deposition technique that is making available high quality thin films of complex, multicomponent materials for the design and fabrication of advanced electronic devices and protective coatings. Single phase and epitaxial thin films can be deposited in situ. by PLD. Recent applications of PLD include high temperature superconductors, ferroelectrics, magnetoresistive materials and ferrites. Ferroelectric thin films grown by PLD are currently being developed into low loss, frequency agile microwave electronics which exploit the electric field dependence of the dielectric constant. More recently, colossal magnetoresistance with DRH/RH=0 ~100,000% has been observed in thin films of rare earth manganites deposited by PLD. These materials have applications in magnetic field sensing and recording as well as electrodes in solid oxide fuel cells and room temperature microbolometers. This presentation will show recent examples applying PLD to high quality electronics ceramic thin films growth for next generation devices.
8:35 am
THERMAL BARRIER COATINGS FOR AIRCRAFT ENGINES--A PRATT AND WHITNEY PERSPECTIVE: S. Bose, Pratt and Whitney, 400 Main Street, East Hartford, CT 06108
The gas temperatures in the turbine section of Aircraft Gas Turbine Engines are hundreds of degrees higher than the melting point of the materials of construction. Exposure to such high temperatures would result in structural failure of the materials from a variety of mechanisms. Yet, in modern engines, the components, generally made a nickel and cobalt based superalloys, survive for extended periods of time. This is accomplished by devising efficient air cooling of the components and by applying Thermal Barrier Coatings (TBCs) to the substrate alloy to reduce metal temperatures to safer levels. Combustor TBCs are processed with air plasma spray (APS) ceramic on APS metallic bond coat. Vanes, exposed to higher temperature and thermal load, require electron beam physical vapor deposition (EB-PVD) ceramic on FE/A1 laminates of different layer thicknesses were produced by PVD. TEM studies showed that as deposited microstructure depends on the ratio of the nominal thicknesses of the FE and A1 layers and on the actual layer thickness. For dfe:da1=0.4mm the microstructure consisted of nanocrystals of Fe/A1 solid solution with A2 or B2 structure and A13Fe. For dfe:dA1»44nm or 2.1mm:0.7mm laminated structures were produced. The laminates consisted of layers of Fe(A2-bcc) and of solid solution of Fe in A1 with B2 (ordered bcc) structure which was formed by interdiffusion between the Fe and A1 layers. Thermodynamic modelling showed that interdiffusion and interface reaction in the as deposited materials are closely related to the overall heat of mixing. The mechanical properties of the laminates will be related to their microstructures low pressure plasma spray (LPPS) bond coat. These TBCs have allowed the components to be operated at high gas path temperatures to meet thrust, efficient and life requirements of Pratt and Whitney's gas turbine engines. Details of Pratt and Whitney's experience on various aspects of TBCs will be discussed.
9:10 am
ANALYSIS OF THERMAL SPRAY METHOD FOR COATING NANOSCALE MATERIALS: Schmuel Eidelman, Xiaolong Yang, Science Applications International Corporation, 1710 Goodridge Drive, McLean, VA
Thermal Spray (TS) system allows delivery of the plating materials to the substrates at high velocities (on the order of 1 to 1.5 km/sec) and high temperatures. The total pressure of the particle impinging on the surface can reach 10 Gpa for some of the TS systems. Lower sintering temperatures and higher ductility of nanoscale materials open a range of attractive and unique possibilities for high rate deposition of nanostructured coatings. We use a recently developed and validated three dimensional simulation capability to model the TS systems' gas and coating powder flow for the TS process analysis, to illustrate the roots of currently used TS systems' inefficiencies, and to optimize and control the coating process. Examples are given for the TS process designs with improved performance and system efficiency. The use of numerical simulation will be especially crucial for the plating with nanoscale powders.
9:30 am
ROLE OF INTERDIFFUSION AND HEAT TREATMENTS ON THE ADHESION OF PLASMA SPRAYED NiCrAlY COATINGS: C.S. Richard, G. Beranger, Universite de Technologie de Compiegne, Department de Genie Mecanique, URA 1505 du CNRS, 60206 Compiegne Cedex, France; J. Lu, Universite de Technologie de Troyes, Department de Genie des Systemes Mecaniques, 10000 Troyes, France
During service blades and vanes of stationary gas turbines are subject to different kinds of loadings like mechanical and thermal stresses as well as corrosion, oxidation and erosion. Against these phenomena, plasma spraying coatings are frequently used to protect the componenets in the hot parts of these engines. The layers are commonly deposited by Atmospheric Plasma Spraying (APS) and by Vacuum Plasma Spraying (VPS). One of the main parameters in quality of a coating is its adhesion on a Ni-based superalloy substrate. This study focused on a NiCrAlY metallic bonding layer and its adhesion on a Ni-based supralloy substrate. It looks at the influence of different spraying methods (APS and VPS) and the influence of a post heat treatment on the adhesion of the coatings. In order to determine the interface toughness, a Vickers interfacial indentation test, based on fracture mechanics method, was performed. In APS and VPS cases, the residual stresses were evaluated by a step-by-step drilling method and these were taken into account in the adhesion parameters. The results were supplemented by a microstructural study of the interface in order to understand the role of interdiffusion on adhesion.
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9:50 am
PLASMA SPRAYED ZIRCONIA BASED COATINGS FOR USE AS AN INSULATING LAYER IN DIE CASTING: M. Giannos, CAST, CSIRO Division Manufacturing Technology, Melbourne, Victoria, Australia
10:10 am
COATING PHASES OF COMMERCIAL GALVANNEALED COATINGS: Carlos Nelson Elias, Universidade Federal Pluminense, Av. Dos Trabalhadores 420, Vila Santa Cecilia 27260-740 Volta Redonda, RJ-BRAZIL, Jorge Alcala Vera, Institutio Militar de Engenharia, Pr General Tiburcio 80, 22290 270 Rio de Janeiro, RJ
Hot-dip galvannealed steel sheet has been increasingly used in the automotive industry and more recently it has been found that a zinc-iron alloy steel sheet, such as galvannealed would provide even better results. The galvannealed steel sheet is a product with good corrosion resistance, weldability and paintability. Therefore it has been used in the automotive and appliance industries. The properties of galvannealed steel are strongly influenced by the iron content of the coating, especially galling, corrosion resistance, welding and powdering. The galvannealed steel is predominately composed of delta phase. When the soft zeta phase is present in the surface of the coating, it adheres to the die and reduces the performance of steel sheet during deformation. When the hard and brittle gamma phase is at the interface steel-coating , the galvannealed coating fails by powdering. In this work we discuss the formation of Fe-Zn intermetallic compounds in the industrial galvannealed coating.
10:30 am BREAK
10:40 am
RECENT TRENDS IN ELECTROPLATING: Brian Am Manty, Concurrent Technologies Corporation, Johnstown, PA
This paper reports on recent trends and advances in electroplating as a surface finishing technology. It includes a description of environment and worker exposure regulations that have affected the industry. New developments in water and chemical recycling equipment and techniques have substantially reduced the amount of wastes generated during electroplating. Near-zero discharges are now technically and economically feasible for many electroplating shops. Several guidance documents are available to help electroplaters reduce wastes with simple, inexpensive techniques. Alternative electroplating processes and materials are also being developed for processes requiring the use of toxic materials. On-going programs within industry and the government are aimed at reducing the use of cadmium, chromium (hexavalent), lead and cyanide. There is a substantial increase in commercial formulations for alloy electrodeposits, especially where those alloys may be used as a substitute for more toxic coatings.
11:05 am
STRUCTURE AND PROPERTIES OF FUNCTIONALLY THICK CHROMIUM ELECTRODEPOSITS FROM A TRIVALENT ELECTROLYTE - A " GREEN " TECHNOLOGY: Christian E. Johnson, Jasper L. Mullen National Institute of Standards and Technology, Gaithersburg MD 20899
Chromium is widely used as an electrochemically applied coating on metal for wear resistance, to reduce friction, or for a desired appearance. In present commercial electroplating processes, the chromium is deposited from electrolytes in which it is in the hexavalent state. With recent interest in seeking alternatives to the toxic Cr6+, a process has been developed to deposit thick chromium coatings from a non-toxic trivalent electrolyte. The coatings deposited from this electrolyte are an alloy of chromium-carbon-oxygen-hydrogen having an amorphous structure, as-deposited. However, with heat treatment they are transformed to a crystalline structure of chromium carbide in a chromium matrix. The hardness and resistance to wear increase with the transformation of this coating after heat treatment. The structure of the electrodeposited coatings, will be discussed. Property measurements of microhardness, wear and coefficient of thermal expansion will be discussed for the as-deposited and heat treated coatings.
11:35 am
COPING WITH UNINTENDED Cu ENRICHMENT DURING CONVERSION COATING OF MICROSTRUCTURALLY COMPLEX ALUMINUM: R.G. Buchheit, Sandia National Laboratories, Albuquerque, NM 87185
Copper is a major alloying element in engineering aluminum alloys. Cu is concentrated in second phase particles distributed throughout the alloy. The interaction of these particles with conversion coating solutions can result in enrichment of Cu on the treated surface. This enrichment has serious negative consequences on subsequent corrosion and adhesion properties. Direct examination using high resolution SEM shows that in 2024-T# Cu is segregated into large (2-6 micrometer) Al2CuMg particles. During surface finishing these particles experience severe dealloying and produce a fine dispersion of Cu-rich clusters that are distributed across the alloy surface facilitating galavanic corrosion during testing or service. Since redistribution of Cu across the surface is possible without ever oxidizing the Cu, mitigation schemes based on Cu complexing agent additions alone may be inadequate. However, mitigation schemes that utilize a Cu complexing agent and a sufficiently oxidizing solution can successfully prevent Cu enrichment and produce significant improvements in corrosion resistance.
Room: 340B
Session Chairpersons: Prof. Leon L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; Prof. Carl C. Koch, Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695
8:30 am INVITED
PROCESSING OF CONTINUOUSLY REINFORCED Ti-ALLOY MMCS BY PHYSICAL VAPOR DEPOSITION: P. R. Subramanian, S. Krishnamurthy, and S. Keller, UES, Inc., Materials and Processes Division, 4401 Dayton-Xenia Rd., Dayton, OH 45432-1894
Fiber-reinforced titanium aluminide composites are of particular interest as candidate materials for aerospace structural applications at moderately high temperatures. Conventional techniques for fabrication of these composites pose many technical challenges, and serve as one of the barriers to the practical use of these composite systems. The present work deals with a novel vapor synthesis route, the matrix-coated fiber process, for producing Ti-alloy metal matrix composites (MMCs). In this process, the matrix alloy is directly deposited on continuous SiC fibers by hollow-cathode magnetron sputtering. The matrix-coated fibers are then consolidated to produce unidirectionally reinforced MMC panels. Details of the processing technique will be presented, along with results on microstructural evolution. Results from room-temperature mechanical evaluation of the MMC specimens will also be presented. This research is funded by the U.S. Air Force as a Small Business Innovative Research Program under Contract No. F33615-94-C-5214 . Program Monitor: Dr. Stephen W. Schwenker, USAF Wright Laboratory, Materials Directorate (WL/MLLM), Wright-Patterson AFB, OH 45433-7817.
9:00 am
COMBUSTION CHEMICAL VAPOR DEPOSITION (CCVD) OF LaPO4 MONAZITE ON ALUMINA FIBERS FOR CERAMIC MATRIX COMPOSITES: T.J. Hwang, M.R. Hendrick, H. Shao, H.G. Hornis, A.T. Hunt, Micro Coating Technologies, 430 Tenth Street, Suite N-108, Atlanta, GA 30318
It has been demonstrated that monazite compounds can serve as an oxidation protection and crack deflecting interface coatings to improve the strength and toughness in oxide-oxide ceramic matrix composite. In this study, lanthanum phosphate LaPO4 (monatize) was coated on alumina fibers (Nextel 610) using the combustion chemical vapor deposition (CCVDSM) method in the open atmosphere. This study has shown that the CCVD is feasible for applying a dense LaPO4 coating while moving the fiber tows through the deposition zone. A systematic stoichiometry study showed that monazite was the predominate phase in the film. Deposition temperatures were controlled to prevent degradation of fibers while maintaining an optimal deposition rate and coating quality. Several interlayer materials were investigated to minimize the reaction and recrystallization of the A12O3 fibers. Since a vacuum chamber is not required for the CCVD process, large scale, continuous coating of fibers is possible.
9:25 am
DENSE TITANIUM MATRIX COMPOSITE MONOTAPE FROM E-BEAM METAL COATED FIBERS: Herve Deve, Metal Matrix Composites Program, 3M Center, Bldg 60-1N-01, St Paul, MN 55144-1000
The high temperature specific strength and stiffness of titanium matrix composites (TMC's) make them very attractive for the next generation of jet engine components. Significant efforts are now underway at 3M to reduce the cost of TMC's; bring them to a production status; and offer the customer a TMC precursor that will be easy to integrate into titanium components. The recent advances in the production of metal coated fibers by electron beam evaporation have allowed the development of continuous dense monotape. Dense TMC monotape will facilitate the fabrication of complex curved parts such as rings. A dense monotape is a single composite ply made by roll-bonding cylindrical metal coated fibers. Continuous roll-bonding allows the low-cost fabrication of TMC tape that do not contain organic binders. Monotapes have been produced that are typically 200 =B5m thick by 10 mm wide and greater than 30 meter long. The flexible composite tape can be easily laid-up on flat or curved parts. Final bonding of the component requires a HIP or diffusion bonding cycle without the complex removal of organic binders. TMC rings with a nearly perfect fiber distribution were fabricated to illustrate the simplicity of use of TMC monotapes.
9:50 am
REACTIVE SPRAY ATOMIZATION AND DEPOSITION OF ALUMINUM ALLOYS: MODELING DISPERSOID VOLUME FRACTION AND SIZE DISTRIBUTION: J.-P. Delplanque, E.J. Lavernia, R.H. Rangel, Department of Mechanical and Aerospace Engineering, Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, California 92697-2575
Reactive spray atomization and deposition combines atomization, chemical reaction and consolidation into a single step. It offers a unique opportunity for in-situ, continuous control over alloy composition and chemical reaction between atomized droplets and reactive atomization gas. During reactive spray deposition a molten alloy is atomized by using a reactive gas mixture. The atomized droplets are subsequently deposited on a substrate. Chemical reactions occur between the matrix material and the reactive gas during both atomization and deposition. By carefully selecting alloying additive and reactive gas combinations on the basis of containing in-situ dispersoids such as carbides, nitrides, and oxides, leading to grain refinement. The volume frac tion and the size distribution of the dispersoids is critical to the grain refinement mechanisms. The primary goal of the present work is to define a model to estimate these characteristics. The materials considered are aluminum alloys while target dispersoids are primarily oxides. These may be obtained by the reaction of oxygen containing atomization gas mixtures with molten alloy droplets or with minor alloy additives which exhibit a high affinity for oxygen. Droplet position and velocity histories are obtained from the numerical solution of the one-dimensional equation of motion. The energy equation inside the droplet is solved numerically using finite-differences to predict the spatially resolved temperature field. The solid/liquid interface progression rate is estimated using a power law. The effect of the dispersiods on the achievable undercooling is included. This model is then used to determine the parameters controlling the volume fraction and the size distribution of the dispersiods.
10:15 am BREAK
10:25 am INVITED
PLASMA SPRAYED MULTI-LAYERED AND FUNCTIONALLY GRADED MATERIALS: H. Herman, Department of Materials Science and Engineering, State University of New York, Stony Brook, NY 11794
Multi-layered (MLM) and functionally graded (FGM) composites display discrete or continuously varying compositions of metals, ceramics and polymers and/or microstructures over definable geometrical orientations and distances. Plasma spray offers a flexible and economic means for producing non-uniform composites and is used to apply layered and graded deposits to enhance the survivability of thick ceramic coatings (e.g., TBCs). These "graded coatings" are primarily applied to reduce CTE mismatch-related failure. The versatility of plasma spray allows the processing of a wide range of high performance materials, including most metals and refractory ceramics, under a controlled atmosphere if desired. Using plasma spray, it is possible to deposit multiple constituents simultaneously, thus providing a unique means of producing FGMs. Plasma spray MLM/FGM production will be discussed and the characteristics and properties of two FGM systems, Ni-Al2O3 and NiCrAlY-ZrO2, will be presented. This research is supported by NIST-Caterpillar Advanced Technology Program and the INEL University Research Consortium.
10:55 am
SPRAY FORMING OF TiB2 REINFORCED GAMMA TITANIUM ALUMINIDE ALLOYS: B. Li, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA 92697-2575
Gamma titanium aluminide composite with a nominal composition of Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2 was spray formed using a skull melting technique. Microstructure characteristics of as-received and spray formed Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2, along with the oversprayed powders, were examined by optical microscope and SEM, and rationalized on the basis of numerical analysis.
11:20 am INVITED
SOL-GEL SYNTHESIS OF CERAMIC MATRIX COMPOSITES: E.D. Rodeghiero, E.P. Giannelis, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853
Sol-gel techniques provided new and powerful means by which to synthesize oxide-based ceramic matrix composites. The advantages of sol-gel approaches relative to conventional powder processing are numerous. First, sol-gel synthesis can achieve extremely fine (nanoscale) microstructures with high degrees of dispersion between the matrix and reinforcement phases. In addition, the chemical compositions of the various phases can be precisely controlled. Furthermore, gel-derived composites are also highly uniform, as a result of eliminating powder mixing and segregation problems. Finally, sol-gel synthesis can reduce consolidation temperatures significantly, leading to more efficient, economical processing. This talk will present the results of our work in synthesizing both Ni/
-Al2O3 metal-ceramic composites and SiC(whisker)/-Al2O3 ceramic-ceramic composites. The unique physical and mechanical properties of these composites in their various forms will be discussed, as well as their potential applications.
11:50 am
NANOCOMPOSITE MATERIALS VIA CHEMICAL ROUTES: Kenneth E. Gonsalves, X. Chen, Department of Chemistry & Institute of Materials Science, University of Connecticut, Storrs, CT 06269
The formation of an AlN/Polyimide (PI) nanocomposite was achieved by the rapid solidification of the precursor suspension, followed by compression molding. Such an approach for nanocomposites exhibits improved homogeneity with ultrafine fillers and allows a tailorable composition and property at the nanoscale level. AlN/PI nanocomposites with an increased ceramic loading up to 50% by volume were attained and their thermal and mechanical properties, along with the compositional effects, were investigated.
Sponsored by: LMD Aluminum Committee
Room: 230D
Session Chairman: Jean Doucet, Alcan International Limited, 1188 Sherbrooke Street West, Montreal, Quebec, Canada H3A 3G2
Program Organizer: F. S. Williams, Alcoa Alumina & Chemicals L.L.C., Point Comfort, TX 77978-0101
8:30 am
REDUCTION OF THE MOISTURE CONTENT IN MRN BAUXITE, BY TREATMENT WITH DEWATERING AID: Carlos Estevam da Silva, Marcos Fernando Dias Moreira, Mineracão Rio do Norte S.A. , Porto Trombetas, PA 68275-000 Brazil; Luis Gustavo Esteves Pereira, Mauro Pinto dos Reis, Nalco Brasil Ltda, Av. das Nacões Unidas, 17891 - 11o. Andar, Sao Paulo, - SP - 04795-100 - Brazil
MRN must sell their bauxite at a maximum of 12% moisture content to avoid paying a penalty. To meet this target it is necessary to mix dried and wet bauxite; however, that mixing is very costly because of the high drying cost. Thus MRN and NALCO BRASH have worked together to develop a chemical program to reduce the moisture content of wet bauxite. A large number of dewatering aid products were tested on a lab scale. Two products were selected and tried in pilot plant scale. Finally the product 95DW121 was selected and tried on an industrial scale. The industrial trial was run for three months in the fine and superfine plants with the results that the bauxite moisture was reduced around three percentage points with a dosage rate of 80 g/t.
8:55 am
BQUANT: COST-EFFECTIVE CALCULATIONS OF BAUXITE MINERALOGY: Frank M. Kimmerle, Frank Feret, Alcan International Ltd., Arvida Research and Development Centre, P. O. Box 1250, Jonquière, QC, G7S-4K8; Barbara Feret, BF Simulation, 3099 St. Patrick St., Jonquière
Routine elemental analysis of the major and minor oxides in alumina-bearing minerals, using modern XRF instrumentation yields better than 0.1% reproducibility at a rate exceeding 100 samples per day. However, the mineralogy required to evaluate the amount of recoverable alumina or other Bayer plant parameters has been far less readily accessible. Empirical fits between elemental composition and simulated plant digests are limited to narrow composition ranges in particular geological deposits. Interpretation of X-ray diffractograms is notoriously slow, influenced by crystallite size, amorphous phases, and preferred orientation effects. Instead, using non-linear programming, the BQUANT software provides quantitative phase analysis based on an elemental mass balance. It can even deal with overburden, clay bottoms and is independent of the exact nature of the geological deposit. Given its rapidity, it is particularly useful for estimating the potential of new deposits. Given its accuracy, it greatly facilitates mine exploitation control.
9:20 am
MONITORING OF HEAT EXCHANGER PERFORMANCE THROUGH THE SCALING FACTOR: Eugènio C. G. Azevedo Jr., Carlos Eduardo A. Batista, Alumar-Consórcio de Alumínio, BR 135 - Km 18, Distrito Industrial de Pedrinhas CEP 65095.050 - São Luis/MA - Brasil
The ALUMAR Refinery was designed to maximize heat recovery, and therefore minimize process steam requirements. Since the increase of alumina production from 0.5 to 1.2 million tons per year, the heat exchangers became a strategic point in the refinery performance. An objective has been to create a tool to improve the performance of the heaters. A continuous method of monitoring individual heaters was developed of calculating the scaling factor using the principles of the heat transfer theory. This paper describes the method and the steps to achieve a significant improvement in the identification and troubleshooting of heat transfer related problems. This method also proved to have a positive effect on the operation and maintenance planning of the heat exchangers in the refining.
9:45 am
THE PRECIPITATION MECHANISM OF SODIUM ALUMINOSILICATE SCALE IN BAYER PLANTS: J. Addai-Mensah, A.R. Gerson, K. Zheng, A. O'dea, R. St. C. Smart, Ian Wark Research Institute, University of South Australia, The Levels, Adelaide, 5095, Australia
During the dissolution of bauxite ores by caustic soda, a serious and unwanted downstream precipitation of sodium aluminosilicate may occur in heat exchangers, due to the presence of silica impurity dissolved in the Bayer liquor. To date, the mechanism of nucleation and growth of scale occurring on heat transfer surfaces is not fully known. This paper presents the results from studies carried out to investigate the mechanism of formation of sodium aluminosilicate scale on metallic surfaces under conditions close to those in alumina refineries. It is shown that the scale formation may involve two aluminosilicate dimorphs: sodalite and cancrinite. The extent of solution desilication and scale growth was observed to be strongly temperature and carbonate impurity concentration dependent.
10:10 am BREAK
10:30 am
ASPECT OF DEEP DESILICATION WITH LIME AGENT: Qingwei Wang, Gengyou Tian Zhengzhou, Light Metals Research Institute, Shangjie District, Zhengzhou City, Henan, 450041, China; Chongyu Yang, Central South University of Technology, Changsha City, Hunan, 410083, China
The formation of hydrogarnet (CAS) with low solubility is the essence of desilication of the sodium aluminate solutions with lime addition. The mechanisms of formation of hydrogarnet were studied. It is indicated that desilication with formation CAS is in a form of SCM-type model, i.e. the unreacted core model for spherical particles of unchanging size. The reaction is controlled by diffusion through outer layer. A mathematical model of the kinetics of the process has been developed.
10:55 am
A STUDY OF DESILICATION OF ALUMINATE SOLUTION WITH HCAC : Peng Zhihong, Li Xiaobin, Department of Metallurgy, Central South University of Technology, Changsha, Hunan, 410083, China
Because the sintering process is very important in the Chinese alumina industry, it is important to understand and improve on desilication of aluminate solutions from the sintering process. This paper presents a thorough study on a new method of desilication utilizing HCAC (4CaO·Al2O3·mCO2·mH2O) both in theory and practice. The reaction thermodynamics and kinetics study reveal the reaction laws during synthesis of HCAC and desilication with HCAC. All levels of tests and applications indicate that the desilication effect of HCAC is superior to lime. It can achieve lower silica concentrations in the purified solution under the same amount of lime addition. At the same target silica concentration it can decrease the amount of lime addition about 44% and reduce the loss of alumina about 30%. The new method has achieved satisfactory results in the plant after replacing the old method of desilication with lime in Shangdong Aluminium Corporation. It sets a new path for sintering processes in China by improving alumina product quality, decreasing energy consumption, and raising the target of technology and economy.
Room: 230A
Session Chairperson: Jerry Johnson, Alumax Inc., Intalco Plant, P.O. Box 937, Ferndale, WA 98248
8:30 am
COMMISSIONING OF ALUSAF HILLSIDE SMELTER REDUCTION POTS: Jean-Paul Aussel, Jean-Claude Frison, Aluminium Pechiney, Licensing Department, BP 7, FR-38340 Voreppe, France; Shaun Kroutz, Gideon Stander, Alusaf Hillside Smelter, P.O. Box 897, RSA 3900 Richards Bay, Republic of South Africa
From the 18th of June 1995 to the 21st of June 1996, Alusaf Hillside Smelter started the 576 AP30 reduction pots of its two potlines. The promising results achieved by the first stabilized pots allowed the Process management team to finely tune the potlines around 310 kA and to achieve current efficiency in excess of 95.5% and energy consumption very close to 13000 kWh/t during the first half of 1996. The results of these first 6 months of operation of the first full potline are discussed. It includes data on the raw materials, the organisation and the training programs of the Reduction Department which were all instrumental in engineering this success. The evolution of the Reduction Process parameters and results described in the paper will be updated for the final presentation with the available data of both potlines.
8:55 am
FROM 110 TO 175 kA: RETROFIT OF VAW RHEINWERK. PART I: MODERNIZATION CONCEPT: D. Vogelsang, I. Eick, M. Segatz, Ch. Droste, VAW Aluminium-Technologie, G.-v.-Boeselager-Str. 25, D-53117 Bonn, Germany
Modernization of the 210,000 tpy VAW Rheinwerk smelter includes installation of point feeder, alumina conveying system, state-of-the-art pot control system and forsees an increase in amperage of up to 175 kA. For the modernized pots, concepts for the potlining as well as for improvements of the busbar system were developed, based solely on computer simulations. For the layout of the potlining a new three-dimensional thermoelectric cell model was applied that allows prediction of side ledge countours as well as heat and voltage balances. Based on this model the choice of semi-graphitic vs. fully graphitized cathode blocks was evaluate with respect to the anticipated increase in system amperage. Temperature fields and side ledge contours predicted are in good agreement with measurements. The busbar system, designed originally for a current load of 110 kA, was improved in a very efficient manner to cope with the higher amperage. Magneto-hydrodynamic simulations predicted and plant measurements demonstrated significant improvements in cell stability and performance.
9:20 am
FROM 110 TO 175 kA: RETROFIT OF VAW RHEINWERK. PART II: CONSTRUCTION & OPERATION: J. Ghosh, A. Steube, B. Levenig, VAW Aluminium AG, Koblenzer Str. 122, D-41468 Neuss, Germany
Construction, start-up and operation of ten retrofitted 165 kA prebaked pilot cells in the Rheinwerk smelter are described. The excellent performance of these pots led to the DM 40 Mill. investment decision to retrofit all three potlines. The hot-change of cells during full potline operation minimizes production losses. The pilot cells are equipped with improved steel shells and lining, modified busbar system and modern pot controller and point-feeding system. To evaluate the most cost-effective solution with best performance, four cells are provided with two point feeders and six cells with three point feeders. The new-developed VAW-ELAS process controlling system with improved algorithms and a user-friendly graphical interface allows system atic surveillance and interpretation of all pot parameters and has a major contribution to the highly improved pot performance.
9:45 am
DEVELOPMENT OF A 200 kA REDUCTION CELL TECHNOLOGY - CD200: Geoff Bearne, Mark Dunn, Comalco Research Centre, P.O. Box 316, Thomastown 3074 Australia; Mike Roberts, Yousuf Ali Mohammed, Head of Technology Development Reduction, Dubai Aluminium Co. Ltd., P.O. Box 3627, Dubai, United Arab Emirates
In 1990, Comalco and Dubai Aluminium Co. Ltd. (Dubai) joined forces to develop a modern high amperage reduction cell design known as the CD200. This technology was aimed at the 190 to 200 kA operating range. It was designed to be compatible with future expansion plans at Dubai as well as at the Comalco managed New Zealand Aluminium Smelters Ltd. (NZAS) plant, while remaining within the scope of the present anode design. The cell incorporated a cathode lining design and alumina feeding technology which had been successfully demonstrated at NZAS. The bus bar system was developed using computer modelling at the Comalco Research Centre (CRC). Dubai provided the financial investment and operational experience as well as improvements in process control strategies. Five cells were installed in Dubai's potline 4 and these have operated since 1991. During the last five years, there have been changes to the bus bar design and cathode lining, introduction of larger anodes and further enhancements of the process control systems and operating practices. As a result, the operational performance and the power efficiency of the prototype cells have met or exceeded all targets. Subsequently, the technology has been selected for expansions at both NZAS and Dubai. NZAS has installed 48 cells to be operated at 190 kA, with commissioning from mid 1996. 2 is installing 240 cells to be operated at 195 kA, with start up scheduled in September 1996.
10:10 am BREAK
10:30 am
AN ANALYSIS OF THE ELECTRICAL PREHEAT TECHNIQUE BASED ON THE START-UP OF THE CD200 PROTOTYPES AT DUBAI ALUMINUM CO. LTD: Mark R. Dunn, Comalco Research Centre, P.O. Box 316, Thomastown 3074 Australia; Q.M.I. Galadari, Dubai Aluminum Co. Ltd., P.O. Box 3627, Dubai, United Arab Emirates
In 1991 the Dubai Aluminum Co. Ltd. And Comalco Research & Technology set up a joint project to develop a 200 kA cell in a facility attached to the end of Dubai's potline 4 (then under construction). One aspect of this project was the development and assessment of a suitable electrical preheat practice, based on Dubai's current methods. This paper reports on the process used and the extensive monitoring that took place during the preheats. The effect of current distribution control was also quantified in terms of cathode temperature variation.
10:55 am
ELECTRIC POWER CONTRACTS AND OTHER FACTORS AFFECTING SMELTER ECONOMICS: Nolan E. Richards, 117 Kingswood Dri., Florence, AL 35630; Helge O. Forberg, 8A Quail Ridge Court, Owensboro, KY 42303
The cost of electric power for smelters varies from less than 15% to more than 35% of operating costs. For a smelter with a high power rate, it becomes important to obtain a premium in the market for finished products, produce a higher proportion of premium grade metal, increase volume supplemented with purchased scrap, reduce other cost factors or negotiate a power contract that would allow power modulation. The large difference in cost of power demand between a peak period, normally between 6 p.m. and 10 p.m., and the no-peak period can give some smelters the opportunity to negotiate advantageous contracts for reductions in demand of 20-30% during the peak period. Provided the smelter can implement the changes necessary in the operating procedures to maintain control of potroom operations during the modulations, the decreased power rate can have a substantial beneficial affect on the plant's economics. Some of the strategies and major changes which could be considered for a reduction plant to improve economics are discussed in this paper.
11:20 am
CAPACITY CREEP - THE HIDDEN POTENTIAL GROWTH OF ALUMINIUM SMELTING CAPACITY: K. J. Driscoll, CRU International, Ltd., London WC1X 0AD, England
Given the lack of firm expansion plans for aluminium smelting capacity over the next few years, many people are expecting a smelter bottleneck to develop towards the end of the century. However, CRU believes that a potential source of capacity growth, which we call "capacity creep", is being ignored. As well as new greenfield and brownfield expansions which might fill the new capacity requirements, incremental production gains at existing smelters can be achieved through lower cost upgrades or improvements in operational efficiencies. Indeed, we believe that such capacity creep has historically added around 0.50-0.75% per year to industry capacity, although many of these capacity increases remain undocumented. This paper will present the results of an extensive study of the potential for growth in aluminium smelting capacity, in which we will review how and where capacity creep has occurred, and show that the potential for further capacity creep remains substantial.
11:45 am
ORGANISATION AND INFORMATION SYSTEMS: WHERE INTEGRATION COMES: S.A. Ferre, Aluminium Péchiney, 235 Avenue Alsace Lorraine, 73007 Chambery Cedex, France; P.W. Cowie, Alusaf Limited, 9 West Central Arterial, P.O. Box 897, Richards Bay 3900, Republic of South Africa
Managing an aluminium plant within a concurrential environment demands a greater use of leading edge technology. This technology is of course related to the smelting process but also deals with the organisation scheme and the information provided. During the engineering phase and the construction phase of the Alusaf smelter, Aluminium Pechiney has provided Alusaf with the AP30 technology and has elaborated an organisation with its SA partner. The design and the construction of the information systems have been done in partnership between AP and Alusaf. The information system is based on the use of the state-of-the-art technology and more important is really designed to fit the organisation and to evolve with it. It is built using the 4 classic levels of the CIM model. It takes advantage of packages as SAP R/3 and Microsoft Office Suite tools for routine processes and uses specific developments defined by AP and is used by Alusaf to implement value-adding processes.
Room: 232A
Session Chairs: S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; J. Chun, Dept of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
8:30 am
USE OF IMAGING PYROMETRY SENSOR IN METALLURGICAL PROCESSES: C. Lorenson, Quadtek, 14737 NE 87th St., Redmond, WA 98052
The Spyrometer imaging pyrometer brings a new dimension of imaging capabilities to temperature measurement technology by combining a high temperature video camera with scanning optical pyrometry. This gives operators the ability to observe process conditions while measuring the temperature of virtually any object or region in the field of view. Since the lens tube of the camera can be air or water cooled, it is possible to insert the optical lens tube inside furnaces giving very good view of many different types of metallurgical processes. Specific benefits in process knowledge and maintenance tasks for electric arc melting furnaces, anode furnace and casting wheels, flash smelters, reheat furnaces, and torpedo ladles in different types of metal industries will be discussed.
8:55 am
A COMPUTED TOMOGRAPHY SENSOR FOR SOLIDIFICATION IN METAL CASTING: J. Chun, N. Saka, M.H. Hytros, D. Kim, Dept. of Mechanical Engineering, R.C. Lanza, I.M. Jureidini, Dept of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
We have developed a novel method, using X-ray photons and computed tomography (CT), for distinguishing the solidification front in metal casting processes directly and nondestructively. Depending on the metal, the density of the liquid and solid phases may differ anywhere from 4 to 12%. Computed tomography provides an excellent means of mapping this density difference into a two- or three-dimensional image. Using a Co60 radioisotope and a NaI scintillation detector, CT image reconstruction was performed on pure tin metal in a two-phase state. In addition, CT image reconstruction was done using a 6 MeV linear accelerator and CdWO4 scintillation detector array on pure and alloyed aluminum metals while they underwent solidification. As the speed of the data acquisition and image reconstruction improves, this sensor technology offers the possibility of real-time performance and eventual feedback control for the metal casting process.
9:20 am
LASER ULTRASONIC SENSING OF SOLID-LIQUID INTERFACES DURING BRIDGMAN SINGLE CRYSTAL GROWTH: H.N.G. Wadley, Y. Lu, D.T. Queheillalt, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
Using a 3-D ray tracing methodology combined with laser ultrasonically measured elastic constant data near the melting point, ultrasonic propagation in cylindrical single crystal bodies containing either a convex or a concave solid-liquid interface have been simulated and used to design new sensing concepts. Ray paths, wavefronts, and time of flight (TOF) of rays that travel from a source to an arbitrarily positioned receiver have been calculated. Experimentally measured TOF data have been collected using laser generated/detected ultrasound on model systems with independently known interface shapes. Both numerically simulated data and experimental results have shown that the solidification (interfacial) region can be identified from ultrasonic transmission TOF data. Ultrasonic sensing in the diametral plane is the preferred sensing configuration. Since convex and concave solid-liquid interfaces result in distinctively different TOF data profiles, the interface shape (convex or concave) can be readily determined from the TOF data. When TOF data collected in the diametral plane are used in a nonlinear least squares algorithm, the interface curvature has been successfully reconstructed and ultrasonic velocities of both the solid and liquid obtained, the reconstruction errors were found to be less than 5%.
9:45 am
EDDY CURRENT SENSORS FOR MONITORING THE NUCLEATION AND GROWTH OF Cd0.96Zn0.04Te BULK CRYSTALS: Haydn N.G. Wadley, K.P. Dharmasena, Bill W. Choi, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
Non-contact eddy current sensing methods have been developed and applied to Cd0.96Zn0.04Te crystal growth to obtain a better understanding of the melt, solid nucleation, and the growth process. The application of this sensor approach relies on a large difference in liquid and solid electrical conductivities near the melting point and requires knowledge of the relationships between the electrical conductivity, melt composition, and temperature. Using a multi-frequency encircling eddy current sensor, the electrical conductivities of three different Cd1-yZnyTe (y = 0.00, 0.045, and 0.08) alloys were measured as a function of temperature in a laboratory-scale vertical Bridgman furnace. The measured solid and liquid electrical conductivities were then used in electro-magnetic finite element models to analyze the multifrequency responses of eddy current sensor designs during the simulated growth of a crystal. Three eddy current sensors were fabricated and installed in a vertical Bridgman furnace and used to monitor many Cd0.96Zn0.04Te growth runs One sensor was placed in the vicinity of the ampoule tip to detect undercooling/spontaneous nucleation and two other sensors ("absolute" and "differential" designs) placed to monitor the movement/curvature of the liquid-solid interface during crystal growth. The sensor data was used to characterize the initial melt state, detect the onset of nucleation, determine the growth velocity, and identify the shape of the interface.
10:10 am BREAK
10:20 am
ADVANCES IN SENSING COMPOUND SEMICONDUCTOR CRYSTAL GROWTH: J.P. Wallace, Casting Analysis Corp., RT 2 BOX 113, Weyers Cave, VA 24486
Monitoring compound semiconductor crystal growth using multifrequency eddy currents for sensing illustrates some of the extreme problems of measurement and interpretation of that are not often seen in metallic systems monitored through solidification. Using sensor arrays and scanning have produced a qualitative and quantitative basis for understanding some of the high temperature electrical conductivity mechanisms. The implications of these measurements of electrical conductivity variations are important in that they reflect the complex states of stress that will occur on cooling and heat treating following crystal growth. In particular, for the CdTe and the CdZnTe system, the measurements provide some proof of where the changes in majority defect types occur. The complex nature of the melt and the cooling solid coupled with the growth interface data provide a basis for analyzing the major events during growth and cool down.
10:45 am
GAUGING OF HOT TUBE, BAR, AND WELDS BY MULTIFREQUENCY EDDY CURRENT: J.P. Wallace, Casting Analysis Corp., C. Iheagwara, Magnetic Analysis Corp., RT 2 Box 113, Weyers Cave, VA 24486
Refinements in sensor design have produced low-cost rugged elements acting as loops coupled with stable detection hardware. This has allowed direct dimensional gauging of nonferrous and ferrous products above the curie point for absolute dimensions and electrical conductivities independently. The software was developed for the analysis of electrical conductivity profiles in CZ silicon crystal growth, then refined for the monitoring of bar properties, and then tube properties. Since in most metal working operations, speeds at the minimum of a few hundred feet per minute are encountered, the design of the gauge was optimized for a rapid measurement. Independently extracting electrical conductivity provides data in some metal system for determining the temperature of the monitored product. Applications in ferrous heat treatment will be discussed.
11:10 am
A REMOTELY OPERABLE SENSOR FOR PRECISION SURFACE MAPPING USING COHERENT FREQUENCY MODULATED (FM) LASER RADAR: M.M. Menon, R.E. Barry, P.T. Spampinato, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6305; A. Slotwinski, Coleman Research Corporation, Springfield, VA 22150; M.A. Dagher, Rockwell International Corporation, Canoga Park, CA 91303
A coherent FM laser radar based sensor is being developed for remote metrology of plasma facing material surfaces in the International Thermonuclear Experimental Reactor (ITER). The sensor is capable of three-dimensional mapping of the surface under examination, based on a series of precise range measurements. Sub-millimeter accuracy at large ranges (15 m) has been achieved. Other features that are being incorporated include the ability to operate under adverse environmental conditions involving a combination of very high gamma radiation (3x106 rad/h), ultra-high-vacuum (<10-7 torr), and high temperature (200°C). The paper will describe the basic principles of the sensor, together with experimental results obtained with the sensor. The paper will also outline the broad capabilities of the sensor, including its ability for remote rendering of "visual quality" images without the need for any external illumination. Research sponsored by the Office of Fusion Energy, U. S. Department of Energy, under contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp.
Room: 231A
Session Chairperson: R.S. Kunter, Advanced Sciences Inc., 405 Urban Street, Suite 401, Lakewood, CO 80228
8:30 am
THE USE OF FRACTAL DIMENSION WITH AN AGGREGATION MODEL TO CHARACTERISE COPPER ELECTRODEPOSITION IN THE PRESENCE OF THIOUREA: S.P. Fox, S.A. Godorr, A.W. Bryson, School of Process and Materials Engineering, Private Bag 3, Wits 2050, South Africa
This work is an extension of a previous investigation on the development of surface roughness during electrodeposition of copper. A comprehensive model based on diffusion and migration in a force field together with surface diffusion and sticking probabilities is used to generate profiles which are compared to those produced experimentally. The roughness is characterized by using the technique of fractal geometry which is shown to describe both qualitatively and quantitatively the development of surface morphology during electrodeposition. The work is extended to the deposition of copper in the presence of various concentrations of thiourea. The development of roughness is observed experimentally on the edge of a thin copper disc mounted between two glass plates. This enables photographs to be taken at various stages during growth. The surface outline is digitized using an image analyzer which enables the fractal dimension to be determined as growth proceeds. As expected the presence of thiourea at low concentrations produces a fractal dimension which is closer to unity (i.e. the surface becomes smoother). The original model is modified to include diffusion and migration of thiourea to the surface. It is postulated that the presence of thiourea on a surface site changes the sticking probability of discharged copper ions at this site. This results in increased surface diffusion of the copper, which in turn produces a smoother deposit. Extensive experimental results are presented which show that the model adequately predicts the effect of changes in thiourea concentrations over a wide range of conditions including those that are of relevance in electrorefining practice.
8:55 am
DIRECT RECOVERY OF METALS FROM LOADED ORGANIC SOLVENTS: A REVIEW OF RECENT METHODOLOGIES: L.M. Abrantes, A.P. Paiva, Universidade de Lisboa, Faculdade de Ciências, Departamento de Quimica, Lisboa, Portugal
The application of hydrometallurgical methods to the recovery of metal values from ores and concentrates has been receiving a growing interest, either from researchers or from the mining industry. For the concentration/purification of the relatively low concentrated metallic solutions resulting form the leaching of those raw materials, a well established technique often used is solvent extraction (SX); the loaded organic solvent is then conventionally contacted with a suitable aqueous medium, the metal in its final form being usually recovered form this solution by electrowinning. Methods dealing with the direct stripping of metals from loaded organic extractants have recently been investigated, as an efficient stripping is sometimes difficult to achieve for some solvents. Amongst these innovating processes, the electroreductive stripping (2-phase electrolysis) and cementation (galvanic stripping) must be emphasized, the related research works being cautiously reviewed in the present paper. Particularly, the possibility of use of a 2 phase electrolysis to recover basic and precious metals is more extensively discussed. Examples are given for the recovery of copper and silver from suitable organic media, namely by direct application of an electrical potential to a mixture of a silver loaded organic phase containing Cyanex 471X - obtained by SX - and a stabilized sodium thiosulfate solution. The overall efficiencies of these one-step techniques are analyzed and compared with the results obtained by conventional stripping procedures. The purity of the cathodic deposits is also considered. The recovery of silver by galvanic stripping involving iron and zinc powders is also preliminarly evaluated, using a similar organic solution as described above. The influence of temperature on the efficiency of the process is also studied, either for concentrated or more diluted organic silver solutions. The literature data and the results reported here on the application of both methods for direct metal recovery from organic phases show promising advantages over the conventional procedures, encouraging a research effort to optimize and establish these alternative processes.
9:20 am
KINETICS MECHANISM OF GOLD ELECTROWINNING: J.A. Garcia, Universidad Nacional de San Juan, Argentina, C. Hecker, Universidad de Concepcion, Chile, E. Larenas, Concepcion, Chile
To determine the kinetic reaction mechanism, electrochemical experimental techniques of stationary polarization, linear voltammetry and faradaic impedance were used. Gold electrodeposition experiments were realized using an electrolysis cell, provided by a rotary disk of vitreous carbon and or platinum counter electrode of platinum mesh and reference electrode. Using an automatic measurement system voltammograms and Nyquist faradaic impedance spectra were obtained. In this paper, responses for different cases were analyzed through faradaic impedance criteria, considering several kinds of diagrams obtained. The importance diffusion influence of aurocyanide ions and adsorption as controlling steps previous charge transfer was verified. A model of proposed mechanism is discussed.
9:45 am
AN INVESTIGATION ON GOLD ELECTROWINNING FROM ACIDIC THIOUREA SOLUTIONS: C.M. Juarez, A.J.B. Dutra, Federa University of Rio de Janeiro, Metallurgical and Materials Engineering Program, Rio de Janeiro, Brazil
The use of thiourea as a gold leaching reagent has been extensively studied by many researchers, and it has proved to be promising for some cases as refractory gold ores and electronic gold scraps. Otherwise, the recovery of gold from these solutions did not receive so much attention. In this paper, the electrowinning of gold in acidic thiourea solutions was studied by voltammetry, chronopotentiometry and electrochemical impedance in a conventional three-electrode cell with a rotating disc electrode. These electrochemical techniques can provide valuable kinetic information to electrowinning practice. Results have shown that gold electrowinning should be carried out at low current densities in order to avoid cathode passivation and side reactions, as formamidine disulfide reduction and hydrogen evolution at higher overpotentials.
10:10 am
ELECTROCHEMICAL ASPECTS OF THE DISSOLUTION OF GOLD IN CYANIDE ELECTROLYTES CONTAINING LEAD: D. Mussatti, J. Mager , G.P. Martins, Colorado School of Mines, Department of Metallurgical and Materials Engineering, Golden, CO 80401
The role of lead (Pb), at low concentrations in high pH cyanide electrolytes, on the dissolution behaviour of gold has now been a topic of scientific and industrial concern for over 50 years. The recent paper by Kondos et al at CANMET (1995) attests to this continuing interest and apparent importance. Nevertheless, the mechanism(s) by which this (and other heavy metal) component influences the electrodics of this electrochemical system has still not been unequivocally demonstrated. Instead, several plausible hypothesis, by pioneering researchers in this field, have been advanced and reiterated over the ensuing years. While it is generally accepted, based on electrode potential calculations, that co-reduction of lead on the gold surface may occur due to cementation (contact reduction) the cemented lead has never been characterized. The subject matter is confounded further when sulfide (or hydrosulfide) species are also a consitutent of the electrolyte. The work to be presented re- examines the role of lead and sulfide in this system, by considering the species distribution of these components and by conducting potentiodynamic studies in conjunction with surface analyses of a gold (and lead) electrode.
10:30 am
STUDY ON WASTEWATER TREATMENT OF CHEMICAL PLATING SOLUTION USING RECOVERING PROCESSES: Y. Kumagai, National Institute of Material & Chemical Research, Laboratory of Organic Materials, Tsukuba, Japan; F.A. Souza, Federal University of Minas Gerais, Department of Metallurgical Engineering, Belo Horizonte, Brazil
Electroless plating processes or chemical deposition processes, have been used in many fields such as automobile and electronic industries. These solutions must be disposed or treated even when the components already have high performance and concentrations. Commonly, in these kind of solution among others components, metal ions are in very high concentrations. The cost of the plating process becomes higher and is very difficult to keep the environmental regulations. The main objective of this study was to investigate the ways to recover the bath components, among them, the metal ion, in order to decrease the cost of the process as well as to meet the environmental regulations. Specifically, in this study was investigated the way to recover, from the exhausted bath, the nickel ion, sulfate ion, phosphite ion and organic compounds. In this case, was investigated a solution for electroless for nickel deposition. The metal ion was recovered from the wastewater by chemical plating onto mica powder surface. The phosphite and sulfate ions were recovered from the wastewater by precipitation as calcium salts. The organic acids were recovered by solvent extraction. These recovery process, used for the metal ion, is particularly important because many studies are investigating the use of mica coated with metal in the development of new composite materials.
10:55 am
THE EVALUATION OF FOAMING BEHAVIOUR OF SURFACTANTS FOR ACID MIST CONTROL IN METAL ELECTROLYSIS PROCESSES: A.M. Alfantazi, D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, B.C., V6T 1Z4, Canada; J. Synnott, M. Boissoneault, Falconbridge Ltd., Kidd Creek Division, P.O. Bag 2002, Timmins, Ontario, P4N 7K1 Canada
Acid Mist Generation is a major concern in zinc, copper and nickel electrowinning industry and there is a strong environmental drive to control its emission in the work environment. Foaming reagents are typically added to the electrolyte to alleviate this problem. In zinc electrowinning, licorice and saponin are examples of foaming reagents used for this purpose. In order for the foaming reagent to be effective, its foaming behaviour must be determined. In this work, a test procedure was developed to study the foaming characteristics of various surfactants for use as foaming agents to control acid mist in aqueous metal electrowinning. This new test was termed a "mini-flotation test" and it was used to study the foaming behaviour of a large number of reagents in an industrial zinc electrolyte under simulated zinc electrowinning conditions (gas sparging). In addition, the influence of important parameters such as current density, electrolyte temperature, reagent addition level and sulfuric acid concentration on the foaming characteristics of the electrolyte for each surfactant were investigated. This study has identified the most important factors that influence foam formation, growth and stability. This method could be used as a process control measure for reagent addition in the cellhouse by generating a calibration curve for the optimum electrolyte conditions.
11:20 am
ELECTROWINNING COBALT FROM SULPHATE SOLUTIONS: K.C. Lenthall, A.W. Bryson, Mintek, Private Bag X3015, Randburg, 2125, Republic of South Africa
The effects of operating parameters on cobalt electrowinning from sulphate solutions were investigated. Experiments were carried out in a divided five-litre cell holding two anodes and a single cathode (150 by 105 mm). The cell was operated in a continuous manner and the catholyte conditions (pH and temperature) were controlled. The following parameters were chosen as a base for the investigation: cobalt feed concentration 90 g/l, catholyte pH 2.5, temperature 65°C, current density 250 A/m2. The feed flow-rate was set to achieve a Co of 30 g/l. The cobalt concentration in the catholyte was varied from 25 to 65 g/l and the current efficiency was found to increase linearly from 90 to 96. Varying the catholyte pH from 2 to 2.75 caused efficiency to increase linearly from 91 to 98%, but above pH 2.75 the rate of increase slowed. Efficiency remained at 95% between 35 and 65°C. Cathodic current density was varied between 150 and 350 A/m2 and did not affect efficiency. Only temperature and catholyte H+ were found to affect the nature of the deposit. Below pH 2.5 many small pits occur. Above this pH, the deposit is shinier and has fewer, though larger, pits. The temperature of the catholyte has a marked effect on the deposit since pitting on the metal decreases dramatically below 50°C. In order to simulate realistic cell behaviour, control of catholyte pH was relaxed. The feed flow-rate was varied from 2.2 to 4.5 ml/min, corresponding to a Co of 30 to 60 g/l. The catholyte pH and cobalt concentration were both found to increase with increasing flow-rate, which caused an increase in efficiency from 82 to 99%. The cell is modeled by considering (i) the transport of H+ across the diaphragm, (ii) the effect of Co and H+ on efficiency using Wark's Rule, (iii) the overall mass balance across the cell.
Room: 230C
Session Chairperson: Lester Mc Coy, Great Lakes Carbon Corporation, P.O. Box "C", Port Arthur, TX 77640
8:30 am
CORRELATION OF COKE PROPERTIES, ANODE PROPERTIES, AND CARBON CONSUMPTION: C.T. Leach, D.G. Brooks, R.E. Gehlbach, Manufacturing Technology Laboratory, Reynolds Metals Company, 3326 East Second Street, Muscle Shoals, AL 35661-1258
Researchers often use calcined coke and anode core properties to predict carbon consumption in aluminum reduction cells. This study compared laboratory analysis data and production data from 1992 through 1995 at RMC's Lake Charles Carbon Company and Baie Comeau Reduction Plant. During this period, carbon plant operations produced anodes with a range of properties using various calcined cokes. The results indicate that calcined cokes having a relatively wide range of properties can produce quality prebake anodes that yield low, stable carbon consumptions. Some coke and anode properties that are considered important quality parameters had little or no detrimental effect on carbon consumption. Correlations exist between certain coke and anode properties during time periods where the properties changed significantly.
8:55 am
QUANTIFICATION OF THE INFLUENCE OF NICKEL ON REDUCTION CELL ANODES: Max Casada, Venco, P.O. Box 577, State Route 2, South Moundsville, WV 26041; Jeff Rolle, A.J. Edmond Co., 1530 West 16th Street, Long Beach, CA 90813; Chris Eppig, Dr. Steve Paspek, BP Oil Company, 4440 Warrensville Center Road, Cleveland, OH 44128-2837; Zeno DeMori, ORMET, P.O. Box 176/State Route 7, Hannibal, OH 43931; Gary Force, BP Oil Company, 200 Public Square, Cleveland, OH 44114; Jaime Mora, Juan Turpial, Venalum, CVG Industria Venezolana De Aluminio, C.A., Zona Industrial Matanzas, Estado Bolivar, Venezuela; David Hester, Conoco Inc., 1000 South Pine, Ponca City, OK 74602; Mirna Chirinos, Francisco Perez, Alcasa, CVG Aluminio Del Caroni S.A., Zona Industrial Matanzas, Estado Bolivar, Venezuela; Julio Velasco, Venco URB Villa Asia, Calle Bombay Manz. 27, #10, Puerto Ordaz, Bolivar, Venezuela; Eli Epstein, Don Pirolo, Venco, 600 N. Dairy Ashford, Houston, TX 77252
The concentration of various metallic compounds in crude oils and in the resulting petroleum coke has continued an upward trend as crude reserves continue to change and tend toward being increasingly heavy and sour. Traditionally labeled as a catalyst, nickel has been included with vanadium in the evaluation of its effects on anode reactivity. In 1995, a Task Force was formed to quantify the influence of nickel on reduction cell anodes as existing information in the literature did not address specifically the affects of varying concentrations of nickel on anodes. The task force prepared resid with identical properties with the exception of nickel content. These resids were then coked, calcined, and formed into anodes in as identical a process as possible. Finally, the anodes were baked and tested to determine the effects on their performance characteristics. The results and conclusions drawn from this process will be communicated in this paper.
9:20 am
VIBRATED BULK DENSITY (VBD) MEASUREMENT OF CALCINED COKE AND BINDER CONTROL IN PREBAKED ANODE PASTE : A CASE STUDY: Luc Duchesneau, Roland Lessard, André Gendron and Germain Brassard, Alcan International Limited, Arvida Research & Development Centre, 1955 Mellon Blvd, P.O. Box 1250, Jonquière, Québec, Canada G7S 4K8
Vibrated bulk density is used to establish the binder content in prebaked anode paste. Alcan adopted the calcined coke VBD analytical method from Collier Carbon in 1961 with slight modifications. Recent paste quality problems (sticking in baking furnaces) were associated with a lack of precision in the VBD. The apparatus was identified as the main cause of imprecision (irregular flow when feeding the cylinder with the vibrating spatula, increase of table vibration amplitude over time and cylinder holding system) and an improved semi-automatic version was constructed. This communication describes the critical parts of the apparatus and their impact on the quality of the results. It also discusses calibration approach, analytical performance achieved (a four-fold improvement in reproducibility sigma = 0.003) and the impact on the paste production control.
9:45 am
PETROLEUM COKE DEOILING FOR PROPERTIES DETERMINATION: R.E. Gehlbach, C.T. Leach, and V.A. Benoît, Reynolds Metals Co., 3326 E. Second Street, Muscle Shoals, AL 35661-1258
The presence of petroleum-based dedusting agents applied to calcined petroleum coke for control of fugitive dust precludes obtaining correct analytical results when certain tests are performed. Removal of various dedusting agents in commercial use is difficult and the process (es) employed may also affect the properties obtained. Results are presented for studies of thermal, solvent extraction, and vacuum deoiling methods and their effectiveness for several surface-sensitive tests. While all methods are observed to remove virtually all of the dedusting agents, different types of residues or decomposition products remain on the coke particles and adversely affect test results. Depending on the particular properties to be determined and the desired accuracy of the results, more than one technique may be required.
10:10 am BREAK
10:30 am
EFFECTS OF IRON AND SULPHUR ON THE AIR- AND CO2-REACTIVITY OF COKES: Trygve Eidet, Department of Electrochemistry, Norwegian Institute of Technology, Elkem ASA, Research, PO Box 8040 Vaagsbygd, N-4602 Kristiansand, Norway; Morten Sorlie, Elkem ASA, Research, PO Box 8040 Vaagsbygd, N-4602 Kristiansand, Norway; Jomar Thonstad, Department of Electrochemistry, Norwegian Institute of Technology, N-7034 Trondheim, Norway
The aim of this work was to investigate the effects of inorganic impurities on the reactivity of cokes and anode materials and at the same time to avoid the uncertainties that are introduced by the often complex background impurity content in industrial anode cokes. An aromatic distillate fraction from the production of coal tar pitch was used as coke precursor and cokes with controlled amounts of impurities were produced in a laboratory coker. Iron was added to the coke precursor as iron (III) acetylacetonate, and sulphur as dibenzothiophene. These organic substances dissolve in the precursor. The effects of iron and sulphur on the reactivities of cokes were measured in air at 500°C and in CO2 at 960°C. Surface studies (SEM, EDX) showed the topography of the surface, what iron phases were present and indicated the impact of iron and sulphur on the reaction.
Room: 230B
Session Chairperson: Stuart R. Thistlethwaite, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
8:30 am
AlTiB GRAIN REFINER - THE CONSISTENT INGREDIENT: P.C. van Wiggen, KBM Master Alloys
The use of AlTiB grain refiners for a precise control of the metallurgical cast structure has become an integral requirement in the manufacture of present day products. A permanent high standard in the quality and consistency of grain refiners is essential especially when considering their radical impact on the production result. This paper will discuss the consistency of grain refiners in terms of the composition, the production route and the required grain refiner properties. Particular attention will be given to an in-depth comprehension of the AlTiB microstructure. The above will be illustrated by microstructures and further supported by a selection of SPC data, process capabilities and (particle) distribution figures taken from various grain refiners. Information concerning recent advancements in the characterisation and process development of AlTiB grain refiners will also be incorporated in this paper.
8:50 am
EFFECTS OF TRANSITION METALS ON THE POTENCY OF TiBAl GRAIN REFINERS: A. Green, M.A. Kearns, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
TiBAl grain refiners are known to be susceptible to fading and poisoning phenomena which can limit their effectiveness in some practical situations.The long-term fading behaviour of good and bad TiBAl grain refiners in 99.7% Al is presented as a function of temperature in the presence of Zr and other transition metals. It is shown that fade occurs more rapidly at higher temperatures and that the effects of Zr and other transition metals display a complex behaviour as a function of temperature. The observations are explained in terms of recent theories on the behaviour of TiBAl grain refiners which propose that potent TiB2 nuclei have TiAl3 layers present on certain facets. It is shown that the reported behaviour is consistent with interactions occurring between transition metals and the potent aluminide layer. Results are discussed in terms of key stages in the production of TiBAl grain refiners and lessons for the use of TiBAl in the aluminium industry are highlighted.
9:10 am
DEVELOPMENT OF AN IMPROVED AlTiC MASTER ALLOY FOR THE GRAIN REFINEMENT OF ALUMINIUM: W. Reif, Institute of Material Science, Technical University Berlin, Str. des 17.Juni 135, D-10621 Berlin, Germany; A. Green, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England; P.C. van Wiggen, KBM Master Alloys B.V., Klosterlaan 2, 9936 TE Delfzijl, The Netherlands; W.Schneider, VAW aluminium AG, Research and Development, Georg-von-Boeselager-Str.25, D-53117 Bonn, Germany; D. Brandner, Hoogovens Aluminium-Walzprodukte GmbH, Carl-Spaeter-Str.10, D-56070 Koblenz, Germany
The commercial AlTiB master alloys for grain refinement of aluminium contain TiB2 particles, which can be coarse and have the tendency to agglomerate in the melt. As a result of this, quality problems in different products occur.In Zr and Cr containing alloys TiB2 interacts with these elements leading to inhomogenous grain structure. In order to avoid the above mentioned disadvantages of the grain refinement with TiB2, a co-operative research programme has been carried out, to develop an improved AlTiC grain refiner. The main objectives of the project were: Development of an efficient AlTiC master alloy. Fundamental research to understand the mechanism of an AlTiC grain refiner. Evaluation of test methods for determination of the grain refining efficiency and agglomeration behaviour of TiC as standard test methods. Production scale testing of the developed AlTiC master alloy. The paper presents the results with respect to the above mentioned objectives.
9:30 am
THE DEVELOPMENT OF A COMMERCIAL Al-3% Ti-0.15% C GRAIN REFINING MASTER ALLOY: A.J.Whitehead, S.A.Danilak, Shieldalloy Metallurgical Corporation, Newfield, NJ 08344; Douglas A. Granger, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069
An Al-3% Ti-0.15% C master alloy has been developed and is now being used for ingot grain refinement in Alcoa. A description is given of the development of the high ratio Al-6% Ti-0.02% C master alloy and the progression from this alloy to the more acceptable lower ratio Al-3% Ti-0.15% C alloy. Acceptance for commercial use came only after extensive metallurgical characterization and evaluation of the grain refining performance, including the impact of alloy type and the presence of tramp elements. Details of the production, testing and characterization of this new grain refining master alloy are discussed.
9:50 am
THE GRAIN REFINEMENT OF Al-Si FOUNDRY ALLOYS: J.A. Spittle, J.M. Keeble, IRC for Materials in High Performance Applications, Department of Materials Engineering, University of Wales Swansea, Swansea SA2 8PP, United Kingdom
Whereas small concentrations of Si have been shown to enhance the grain refinement of aluminium by addition of an Al-Ti-B master alloy grain refiner, increasing Si contents in excess of 2-3% result in a continuous increase in primary aluminium solid solution grain size. Two explanations of these observations have been proposed to date based on the influence of Si on either the nucleation or growth of the aluminium primary crystals. Neither of these explanations appears to fit all the available grain size data. In an attempt to further clarify the origin of the Si coarsening effect, grain size studies have been performed on Al-Si and Al-Zn alloys as a function of solute content. It appears that the coarsening is a result of the influence of the Si content on aluminium grain nucleation. A coarsening mechanism is suggested based on the coupled influence of Si level on melt undercooling and primary phase freezing range.
10:10 am BREAK
10:20 am
MODIFICATION OF SILICON IN EUTECTIC AND HYPER-EUTECTIC Al-Si ALLOYS: Ben Heshmatpour, Shieldalloy Metallurgical Corporation, 12 West Boulevard, P.O. Box 768, Newfield, NJ 08344
Refining of eutectic silicon in hyper-eutectic and eutectic Al-Si alloys is accomplished by using phosphorus-bearing additives. Commercially available copper-phosphorus (CuP) in a variety of forms and concentrations is widely used for this application. Large addition rates are needed for effective silicon modification via CuP. The recently developed ferro-phosphorus (FeP) based tableted product provides significant performance and cost advantages while requiring much smaller addition rates, lower alloy temperature, and short contact times. This paper compares the results for refinement of A390.1, B390.1, and 339.1 alloys using CuP and tableted FeP.
10:40 am
EFFECTS OF RESIDUAL TRANSITION METAL IMPURITIES ON ELECTRICAL CONDUCTIVITY AND GRAIN REFINEMENT OF EC GRADE ALUMINIUM: R. Cook, M.A. Kearns, P.S. Cooper, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
Removal of transition metal impurities is a key step in production of high conductivity EC grade Aluminium. Titanium and Vanadium in particular are generally removed by adding an excess of Boron to precipitate stable borides before decanting the treated metal. It is nevertheless advantageous to add sufficient grain refiner to avoid hot cracking of the cast bar without jeopardising electrical conductivity. We report here a study of the effects of residual Vanadium on the efficiency of different grain refining additives and electrical conductivity of the product. It is shown that Vanadium must be below a threshold figure to give adequate grain refinement at levels which do not compromise conductivity. The effects of residual Fe and Si impurities on grain refinement and conductivity are also described and their role is discussed in terms of constitutional supercooling effects. The relevance of the results to the manufacture of EC grade wire is discussed.
11:00 am
EXPERIMENTAL MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF ALUMINUM ALLOYS AT ELEVATED TEMPERATURES: Raphaël Craen, Nagy El-Kaddah, Department of Metallurgical & Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487-0202; Willem Loué, Péchiney CRV, Parc Economique Centr'Alp-BP27, 38340 Voreppe, France
The knowledge of the electrical conductivity of aluminum alloys is critical for the analysis and computer simulation of induction heating and melting operations as well as electromagnetic casters. While accurate conductivity data are available for pure aluminum, there is a paucity of data for aluminum alloys, particularly at elevated temperature. This paper describes an eddy current technique for measuring the electrical conductivity of metallic specimens at high temperatures. In this technique, which is based on measurement of the electric energy dissipation (Joule Heating), the electrical conductivity is determined from measurement of the heating rate of the specimen. The measurement is made by subjecting an insulated cylindrical specimen to a uniform axial alternating magnetic field, and measuring temperature of the specimen during heating. The method requires no contact with the specimen, and is capable of providing electrical conductivity data to the melting point of the specimen with an error of less than five percent. Upon validating the technique using pure aluminum, measurements have been conducted on Al-Mg (5182) and Al-Li (8090) wrought alloys, and on foundry and rheocast Al-Si (357) cast ingots. The results show that electrical conductivities of Si and Mg alloys are about one half of pure aluminum, and the microstructure of Al-Si 357 alloy has little effect on the electrical conductivity of the alloy. The Li containing alloy exhibited a much lower conductivity than Si and Mg alloys. Expressions are presented for the conductivities of these alloys up to 450°C.
11:20 am
DETECTION OF SOLIDIFICATION REACTIONS USING HEAT PIPE TECHNOLOGY
REPLACEMENT: Panel Discussion on Attic Grain Refiner
11:40 am
COMPUTER-AIDED COOLING CURVE ANALYSIS (CA-CCA), APPLIED TO AN Al-Si SYSTEM: M.A. Ramirez A., J.C. Escobedo B., A.H. Castillejos E., A. Flores V., F.A. Acosta G., Centro de Investigación y de Estudios Avanzados del IPN, Unidad Saltillo, P.O.Box 663, 25000 Saltillo, Coahuila, México
The computer-aided cooling curve analysis is a new method for thermal analysis that can be used in foundries of low budget and with small investment. This method tries to simulate the classic differential thermal analysis method (DTA) by using only an acquisition data system coupled to numerical methods in micro-computers. The kind of information provided by this technique includes thermodynamical and thermophysical data, heat transfer parameters, solidification kinetics, and microstructure features. All this information is more than that obtained with the classic DTA, and it is necessary in order to get a real comprehension of the solidification process. CA-CCA has been applied to the study of an Al-Si system to try to characterize it and to predict microstructure, because it is possible with this technique to obtain the evolution of solid during the solidification process and the segregation behaviour of this system.
Room: 330C
Session Chairperson: Robert Shull, NIST, Bldg. 223, Rm B152, Gaithersburg, MD 20899
9:00 am INVITED
STRUCTURE, MECHANICAL PROPERTIES, AND FRACTURE IN NANOPHASE SILICON NITRIDE: MILLION ATOM MOLECULAR DYNAMICS SIMULATIONS ON PARALLEL COMPUTERS: Rajiv K. Kalia, Aiichiro Nakano, Andrey Omeltchenko, Kenji Tsuruta, Priya Vashishta, Concurrent Computing Laboratory for Materials Simulations, Physics and Astronomy, Computer Science, Louisiana State University, Baton Rouge, LA 70803
Structure, mechanical properties, and dynamic fracture in nanocluster-assembled silicon nitride are investigated with molecular-dynamics (MD) simulations involving 1.08 million particles. The simulations reveal that intercluster regions in the consolidated nanophase Si3N4 are highly disordered with 50% undercoordinated atoms. These disordered interfacial regions deflect cracks and give rise to local crack branching. As a result, the nanophase system is able to sustain an order-of- magnitude larger external strain than the crystalline Si3N4. We also investigate the morphology of fracture surfaces in nanophase Si3N4. The MD results for roughness exponents are very close to experimental values [P. Daguier et al., Europhys. Lett. 31, 367 (1995)] even though the materials and length scales are very different.
9:30 am INVITED
THERMAL CONDUCTIVITY OF NANOPHASE CERAMICS: Paul G. Klemens, Physics, University of Connecticut, Storrs, CT 06269-3046
Heat conduction of insulators is by lattice waves (phonons), which have a wide frequency spectrum. The mean free path of phonons is limited by anharmonic intereactions and by scattering, principally scattering by point defects, and by grain boundaries and other etended imperfections. Point defects reduce the mean free path and the contribution to the conductivity of high frequency phonons; grain boundaries that of low frequency phonons. These reductions in conductivity will be discussed. They are additive in materials of micron-sized grains, but not in nanophase materials, where the frequency ranges of phonons affected by point defects and by grain boundary scattering may overlap. The effect of phonon scattering on the thermal conductivy will be discussed with reference to solutes, non-stoichiometry, grain size, and radiation damage.
10:00 am
A SIMULATION STUDY ON THE MELTING OF NANOCRYSTALLINE PLATES AND SPHERICAL CLUSTERS: J.K. Lee, Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931; B.K. Cheong, W.M. Kim, S.G. Kim, Materials Design Laboratory, Korea Institute of Science and Technology, Seoul, Korea
As an emerging mass-data storage technology, phase change (PC) optical recording makes use of the difference in reflectivity between the amorphous and crystalline state of chalcogenide thin films. The amorphous state is obtained via laser melting and subsequent rapid cooling. For a better understanding of the melting behavior of such nanocrystalline plates, a Lennard-Jonesian fcc solid is studied using the method of molecular dynamics. Unlike the bulk case, it is shown that a plate melting is accompanied by a gradual change in both the volume and enthalpy. The melting point of a plate decreases as a function of h**(-n), where h is the thickness and n is 0.7. If the thickness becomes 15 lattice parameters, the melting point reaches a plateau. (111) plates show slightly higher melting points than those for (100) plates. The melting points of spherical clusters with radii ranging from 1.4 to 6.4 lattice parameters show a r**(-n) dependence, where r is the radius and n is 0.75.
10:20 am BREAK
10:35 am
EVIDENCE FOR THERMODYNAMIC STABILIZATION OF GRAIN BOUNDARIES IN Pd1-xZrx: C.E. Krill, H. Ehrhardt, R. Birringer, Unversität des Saarlandes, FB10 Physik, Postfach 151150, Gebäude 43, D66041 Saarbrücken, Germany
The rate of grain growth in a crystalline material is proportional to both the mobility and energy of its grain boundaries. Standard techniques for hindering grain growth, such as solute drag, are kinetic in nature: that is, they aim to reduce the mobility term. A thermodynamic approach, however, should be just as effective: a reduction in grain-boundary energy would be accompanied by a corresponding decrease in the driving force for grain growth. According to the Gibbs adsorption theorem, grain-boundary energies can be reduced by introducing a component that tends to segregate to the grain boundaries. We have investigated ball-milled solid solution of Pd1-xZrz for signs of improved stability against grain growth with increasing Zr concentration; the growth rate is observed to drop to very low values for x greater than 0.2. Differential scanning calorimetry has been used to estimate the concentration dependence of the grain-boundary energy, thereby isolating the themodynamic contribution to grain-growth stability from that due to solute drag.
10:55 am
VIBRATIONAL DENSITY OF STATES OF NANOCRYSTALLINE Ni3Fe PREPARED BY HIGH ENERGY BALL MILLING: H. Frase, L.J. Nagel, J.L. Robertson, B. Fultz, California Institute of Technology, mail 138-78, Pasadena, CA 91125; Oak Ridge National Laboratory, Solid Sate Physics Division, P.O. Box 2008, Oak Ridge, TN 37831
We performed inelastic neutron scattering experiments on two states of Ni3Fe: 1) as-milled, when the material had a characteristic nanocrystallite size of 9 nm, and 2) annealed, when the material had a characteristic crystallite size of 30 nm. The nanophase material showed an enhancement by a factor of 2 in its density of states at energies below 15 meV, and some broadening of its longitudinal peak at 33 meV. The large enhancement in the density of states at these low energies appears to require coupling between inter- and intra-crystallite vibrational motions. The inter-crystalline modes would be associated with the vibrations of the crystallites themselves. These measured changes in vibrational DOS predict a difference in vibrational entropy of the bulk and nanocystalline Ni3Fe of about 0.18 kB/atom at high temperatures, with the nanocrystalline materials having the larger vibrational entropy. This work was supported by the U.S. Department of Energy under contract DE-FG03-86ER45270.
11:15 am INVITED
FUNCTIONAL CERAMICS USING NANOMETER-SIZED MATERIALS: Manu Multani, Tata Institute of Fundamental Research, Bombay 400 005, India
Working with a range of current ceramic materials with a wide variety of applications, it is shown that considerable improvements can be obtained when one starts with Small Solid State Systems (S4) Materials studied range from doped ZnO varistors, PZT piezoelectrics, YIG microwave materials, and the new superconductors. General principles underlying these changes are shown to be dependent on the dispersion relations of phonons and wavevectors (for ferroelectrics) and magnons and wavevectors (for ferromagnetics). Another S4 rule that we have found applicable for most oxides is the tendency towards higher symmetry and increasing unit-cell-volume with decreasing size of the S4s. These changes may usher in phase transformation(s) and size dependent phase transition temperatures.
Room: 340D
Session Chairperson: Anthony D. Rollett, Materials Science & Engineering Dept., Carnegie Mellon University, Pittsburgh, PA 15213
8:30 am INVITED
CURRICULUM DESIGN; INPUTS AND OUTPUTS: Richard Heckel, Dept. of Metallurgy and Materials Engineering, Michigan Technological Univ., 1400 Townsend Drive, Houghton, MI 49931
Undergraduate engineering curricula are designed by faculty committees in accord with accrediting guidelines for content, logical course sequencing and practical limitations for scheduling faculty and laboratory resources. Presently, engineering education is receiving intense scrutiny due to several decades of large tuition increases, continuous enrollment declines since the early '80s, constraints in external research support and decreases in the number of employment opportunities for graduates. These trends have already resulted in proposals for new curriculum designs which would, for example, reduce credits needed for graduation, sacrifice discipline-specific content and increase multidisciplinary activities. Presumably, such curricula would broaden appeal, increase engineering enrollments, widen the range of career opportunities and stimulate interest in industrial interactions. Can such curricula provide the optimum balance between the new educational boundary conditions and quality engineering education? To what extent should curriculum design emphasize graduate/employer feedback, student/parent expectations, instructional philosophy/methodology and general skill development (communication, self-directed learning, open-ended problem solving, ethical decision making, etc.)? Tradeoffs and opportunities associated with these issues will be discussed.
9:00 am
THE MATERIALS SCIENCE AND ENGINEERING CORE CURRICULUM AT VIRGINIA TECH: R.W. Hendricks, R.S. Gordon, Virginia Tech, MSE Dept., Blacksburg, VA 24061-0237
We have developed a core curriculum for an ABET-approved Materials Science and Engineering curriculum incorporating 8 required core courses, options in each of the 5 principle fields (ceramics, composites, electronic materials, metallurgy and polymers), and developed an integrated "across-the-curriculum" approach to writing and communication, ethics, and statistics. Our required core courses, each with laboratory, include physical ceramics, physical metallurgy, electronic materials, and polymer engineering. These "material specific" courses are supported by three material-independent courses including X-ray diffraction, thermodynamics and transport processes, and by a capstone engineering design course based on a research project. Oral, written, and graphical communication, statistics, and ethics and integrated in a manner such that the student is led from fundamental concepts through to sophisticated interpretation of each topic. The student is exposed to these "across-the-curriculum" topics during each semester of the three year program of study beginning with the sophomore year.
9:25 am
MATERIALS SCIENCE AND ENGINEERING: THE NEW UNDERGRADUATE CURRICULUM AT DREXEL UNIVERSITY: Alan Lawley, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104
In 1994 the new undergraduate Drexel Engineering Curriculum was implemented, emphasizing 'up front' engineering, computer and communication skills, life long learning and teamwork. This common core in the first two years reflects many of the tenets and the philosophy of the E4 experiment ('Enhanced Educational Experience for Engineering Students') which began in 1988. Concurrently, the Department of Materials Engineering has been proactive in the Gateway Coalition, a major component of which is to build on E4 by focusing on the upper level curriculum via the development of advanced engineering science courses. Our new undergraduate major, enacted in 1995, reflects the maturing of the E4 experiment into the core Drexel Engineering Curriculum and the integration of selected engineering science courses (developed under the Gateway Coalition) into the curriculum at the upper level. Evolution of the new curriculum is discussed, including the development of modules in materials education.
9:50 am
MATERIALS SCIENCE AND ENGINEERING CURRICULA; RETHINKING THE CORE CONTENT - THE CASE FOR A 128 HOUR CORE: Richard L. Porter, Campus Box 7904, North Carolina State University, Raleigh, NC 27695-7904
Most materials educators agree that three major components constitute the undergraduate materials science and engineering curriculum; that presented in the first 2-3 semesters (generally the basic sciences), the real "core," and finally the obligatory senior design or capstone experience. Scattered throughout will be the necessary humanities and social sciences, maybe a communications course or technical writing course. It is assummed that the mathematics, chemistry, physics, and writing have been properly and correctly introduced and students' have mastered the content. There are several problems with this approach; little if any experiential learning, little if any contextual learning for the basic sciences, little integration of engineering sciences with the basic sciences, and in many cases a disconnected core. Although all curricula meet and or exceed ABET criteria, there is little accountability for the actual content and methodology of presenting the material. This paper discusses the entire curricula in context with the intended outcome for materials science and engineering and encourages curricular designers to rethink the entire learning experience, not to simply add more courses for short term accomplishments. At North Carolina State University, our approach has been to introduce different models for first year engineering, ranging from a hands-on engineering experience linked with freshmen writing, an integrated approach pulling together math, chemistry, and physics, with a year year engineering overview, and recently a new freshmen course linked with the computer literacy course and including a weekly small-group problem solving session. Concurrently, we have administered an attitudes survey at the beginning of the year and again at the end of the semester and year. Students enrolled in these special courses report a greater interest in engineering as a problem solving discipline, they view engineering as an iterative process, and report a higher degree of satisfaction with their first year experiences. Finally, a curriculum will be presented and discussed that builds upon the fundamental basic sciences and integrates the curriculum rather than present it as a linear combination of sub-disciplines.
10:15 am INVITED
INDUSTRIAL EXPECTATION OF A MATERIALS EDUCATION: AN AUTOMOTIVE VIEW: R. Heimbuch, D. Mattis. J. Hall, General Motors, 30300 Mound Road, A/MD-36, Warren, MI 48090-9040
Competitive pressures have caused the automotive industry to critically examine and modify their engineering processes. The new engineering processes have put a higher value on certain skill sets than in the past. The need for technical competence has not changed - it is a given. The question for the Education Community is how to maintain a strong balanced technical framework while developing other critical skills. The goal should be to enhance the effectiveness of the student as he or she moves into and through their professional career. The authors will share their views around the critical question of "balance" and "critical skills".
10:45 am
RESTRUCTURING UNDERGRADUATE EDUCATION AT ILLINOIS INSTITUTE OF TECHNOLOGY; CASE STUDY: METALLURGICAL AND MATERIALS ENGINEERING PROGRAM: Marek Dollar, Mechanical, Materials and Aerospace Engineering Dept., Illinois Inst. of Technology, Chicago, IL 60616.
There is a broad recognition at IIT that we live in a time of revolutionary change in undergraduate education. In response, we are developing new ways to recruit and retain a diverse student body, seeking educational relationships with industry, experimenting with new approaches to teaching and learning, and positioning ourselves to meet ABET engineering criteria for the year 2000. The key elements of the undergraduate education restructuring will be presented. They include, but are not limited to, such initiatives as: Interprofessional Projects, project-oriented learning that teams students from different disciplines and professions and constitutes a new instructional tool though which students learn concepts of teamwork, communication and problem solving; Introduction to the Professions, a freshman-level course that in an innovative way bridges the gap between high school experience and the university's environment; Writing Across Curriculum, an institutional structure for integrating writing into engineering courses. Our attempts to increase computer competence, introduce multimedia in the classroom and create undergraduate research opportunities will also be discussed.
11:10 am
EFFECTIVE USE OF A SMALL FACULTY FOR MAINTENANCE OF A COMPREHENSIVE MATERIALS ENGINEERING PROGRAM: Jeffrey W. Fergus, Materials Research and Education Center, 201 Ross Hall, Auburn University, AL 36849
A recent analysis of the materials/metallurgical engineering programs at U.S. universities shows that these programs can be divided into three, approximately equal, groups in terms of faculty size. Specifically, there are 24 programs with 21-90 faculty, 23 programs with 13-20 faculty and 25 programs with 3-12 faculty. The small number of faculty in this latter group presents challenges in terms of maintaining a comprehensive (undergraduate, graduate, research) materials program. This presentation will relate experience with the materials engineering program at Auburn University, which has 7 full-time faculty, in meeting these challenges. In addition, the contribution of these small programs to the materials engineering discipline as a whole will be discussed.
11:35 am
TITLE TBA: Samuel Allen, Dept. of Materials Science and Engineering, Mass. Inst. of Technology, Cambridge, MA 02139
Room: 332
Session Chairpersons: Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304; James F. Maguire, Boeing Co., P. O. Box 3999, Defense & Space Systems Group, Mail Stop 3W-97, Seattle, WA 98124
8:30 am INVITED
DESIGNING WITH Pb-FREE SOLDERS: Walter L. Winterbottom, Reliability Consultant, 30106 Pipers Lane Court, Farmington Hill, MI 48331
As the global competition in the transportation industry intensifies, the focus on quality and time-to-market have become major driving forces in product design and dominant forces in the market place. Although the current design/development process as practiced in the industry provides a time tested path for new products, leadership in these areas seems to be elusive. A York Times article (March, 1991) notes that Consumers Report ranks the reliability of new American models at about the level of the average Japanese models. In 1988, the Material Systems Reliability Department was organized in the Materials Research Laboratory of Ford Research with the mission to evaluate existing, and develop if necessary, design methodologies capable of the task of providing world leadership in both quality and time-to-market. It was apparent from the outset that a life-cycle design approach must be used to contain reliability, cost, and environmental considerations in a time efficient manner. Further, it became increasingly apparent from the Department's failure mode/root cause identification and testing assistance activities that these issues have to be designed into a product rather than being assured by extensive prototype testing programs. A Design-for-Reliability methodology based upon the development of analytical prototypes which has the capability to fulfill the requirements for world leadership. The methodology is based upon the definition of system failure modes and mechanisms, system model development with verification capable of reliability prediction early in the design process prior to the building and testing of prototype hardware. This 'preventive' approach is based upon quantitative reliability estimates as a key design metric for use in assessing design alternatives. In simplest terms, the approach emphasizes the need to consider products as material systems whose reliability must be thoroughly understood early in the design and development process. The traditional 'build, test, and fix' design approach must be replaced with an approach that relies upon analytical prototypes leading to a single, optimized, prototype hardware build. In the presentation, the Design-for-Reliability approach will be illustrated using electronic packaging design with lead-free solder interconnects as example.
8:55 am INVITED
DESIGN OF NEW SOLDER ALLOYS THROUGH MICROSTRUCTURE CONTROL: Sungho Jin, Lucent Technologies, Bell Laboratories, Room 1A-123, 700 Mountain Avenue, Murray Hill, NJ 07974
The mechanical properties of solder alloys and reliability of solder joints are significantly affected by microstructural features such as grain size, phase distribution, and precipitate morphology. A finer grain size, smaller precipi tates, and a uniformity in phase, precipitate and grain size distribution are often beneficial for improving the strength and ductility as well as the resistance in fatigue and creep failures. The control of microstructure is accomplished by modifications in alloy chemistry and processing conditions. Several examples of microstructural control in lead-free solder systems will be discussed. More forward-looking approaches for further control of microstructure in solder alloys and composites, e.g., by distribution of nano-scale dispersoid particles will also be discussed.
9:20 am INVITED
LEAD-FREE SOLDERS FOR ELECTRONIC ASSEMBLY: Fay Hua, Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304
This paper gives an up dated literature review on the metallurgy of lead-free solders for electronic assembly. The review includes newly reported technical data on existing binary Sn-based eutectic alloys: Sn-Ag, Sn-Bi, Sn-Cu and Sn-In. It also reviews the newly developed multi-component solder alloys in following systems: Sn-Zn-In, Sn-Zn-Bi, Sn-Zn-Sb, Sn-Ag-Zn, Sn-Ag-Cu(-Sb), Sn-Ag-Bi, Sn-Ag-In(-Sb), Sn-Bi-In, and Sn-Bi-Sb. The characteristics of these alloys described are chemical composition, physical properties, microstructure, and mechanical properties. The manufacturability issues and applications of these lead-free solders in electronic assembly will be presented.
9:45 am INVITED
SUMMARY OF RECENT STUDIES OF THE EFFECT OF PROCESSING ON MICROSTRUCTURE OF SOME SOLDER ALLOYS: James Clum, E. Cotts, N. Jiang, Mechanical Engineering, Physics Department, State University of New York at Binghamton, Binghamton, NY 13902
A variety of solder alloys selected from the Sn-based, and In-based systems, have been examined to test for the interaction of composition with processing conditions in controlling alloy microstructure. Rate of solidification, amount of compressive strain, annealing temperature and time were the independent variable studied. Grain size, phase fraction and microhardness have been monitored as measures of microstructural changes. A simple factorially designed experimental plan has been used to conduct and interpret the tests. A major effect of solidification rate and a secondary effect of the interaction between deformation and annealing was observed for most alloys. The effect of alloy composition is reflected primarily in terms of the role of Tambient/Tm on microstructural stability. Some other processing related characteristics of these solder alloys will also be discussed such as creep and stress relaxation behavior. The role of microstructure in behaviors such as grain boundary sliding will be illustrated.
10:10 am
EVALUATION OF ALTERNATIVES TO LEAD SOLDERS FOR PRINTED WIRING APPLICATIONS: James F. Maguire, Boeing Co., P. O. Box 3999, Defense & Space Systems Group, Mail Stop 3W-97, Seattle, WA 98124
This paper describes the first phase of a three year program undertaken by Boeing to evaluate "no lead" materials as a potential replacement for solder in printed wiring assembly applications. This program is looking at a number of different potential replacements including both conductive adhesives and "no lead" solder materials. In addition, the impact of other environmentally driven process changes such as "no clean" soldering and lead free PWB finishes are being tested for compatibility with "no lead" attachment materials. The phases of this program are: Phase I: Initial materials evaluations, processability, stability of electrical performance in environmental exposure, sequential exposure to temperature/humidity cycling and thermal shock environments, compatibility with "standard" finishes (reflowed solder and "de-oxidized" copper), down Selection for Phase II testing; Phase II: detailed material performance testing, stability of contact and bulk resistance during environmental exposure, compatibility with high speed/RF applications, * Compatibility with existing PWA processes such as - pre-conformal coat cleaning, rework/repair, down selection for Phase III testing; Phase III: Development of design allowables and manufacturing processes. This paper will discuss the results of Phase I of this program which evaluated a total of 21 conductive adhesives and 8 commercially available solder alloys with control samples fabricated with Sn63 solder.
10:30 am
CREEP AND MECHANICAL PROPERTIES OF Sn-5%Sb SOLDER: Rao K. Mahidhara, K. Linga Murty and Fahmy M. Haggag, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; North Carolina State University, Raleigh, NC 27695; Advanced Technology Corporation, Oak Ridge, TN 37830
A knowledge of the mechanical and creep properties of solder materials is required both for alloy development and life-prediction. We report here tensile and creep properties of Sn-5%Sb which is one of the candidate materials for replacing lead-based solders in electronic packaging. The temperature and stress dependencies of the strain-rate are evaluated using both the tensile and creep tests. In addition, the recently developed Stress-Strain Microprobe (SSM) is used to evaluate the strain-rate dependence of stress through automated ball indentation (ABI) tests at ambient. An excellent correlation is noted between creep and ABI data. While creep tests covered low stresses, ABI corresponded to high stresses which revealed breakdown of the Norton-law noted at lower stresses. While creep tests took 5 months time, the ABI tests were completed in a matter of hours although they covered 3 orders of magnitude strain-rates. The utility of ABI technique in solder joints is clearly pointed out and such tests are planned on real joints. ABI tests at elevated temperatures were not performed to-date. Such a facility is now under development and future plans include testing at elevated temperatures on bulk as well as solder joints.
10:50 am BREAK
11:00 am
CHARACTERIZATION OF 58Bi-42Sn SOLDERED ON Sn-Pb COATED SURFACE: Zequn Mei, Fay Hua, Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304
As reported in our previous work, solder joints of 58Bi-Sn on 80Sn-20Pb coated surface failed prematurely in thermal cycles between -40°C to 100°C. The failure mechanism was identified to be the dissolving of Pb atoms into the 58Bi-Sn solder joint during soldering, which caused formation of the ternary eutectic 52Bi-30Pb-18Sn with melting point of 95°C. In this paper, study of three types of solder joints will be reported: (1) 58Bi-42Sn soldered on Cu surface, (2) 58Bi-42Sn solder on 80Sn-20Pb coated surface, and (3) 57.5Bi-41.5Sn-1Pb soldered on Cu surface. These solder joints were aged at 80°C and 110°C. The evolution of the grain or phase sizes and the degradation of mechanical properties will be characterized as function of aging time. Early results indicate that the grains grew much faster in the solder joints containing Pb atoms (types 2 and 3 above), which reduced mechanical strength and ductility, than the solder joints without Pb atoms (type 1). Detailed results will be reported in the meeting.
11:20 am
MICROSTRUCTURAL STABILITY AND MECHANICAL PROPERTIES OF TIN-SILVER-COPPER SOLDER JOINTS: Iver E. Anderson, Ozer Unal, Ames Laboratory, Iowa State University, 122 Metals Development Bldg., Ames, IA 50011
The properties of a Pb-free ternary eutectic solder alloy, Sn-4.7Ag-1.7Cu (wt.%), which was discovered in our laboratory have been evaluated. This patented alloy has a melting point of 217°C, a fine 3-phase eutectic microstructure, and a very good solderability. The primary goal of this investigation has been to enhance its microstructural stability for high temperature environments, greater than 125°C, and to improve its overall mechanical properties, especially for extended service. Thus, minor modifications were made in the base eutectic alloy to control microstructural aging without degrading solderability. Alloying effects on solder/Cu joints in the as-soldered and aged conditions were studied. Tensile strength and shear strength measurements were made using butt and lap shear joint configurations, respectively, under various loading conditions. The results will be presented and their implications will be discussed. Support from the DOE-BES-DMS under Contract No. W-7405-Eng-82 is gratefully acknowledged.
11:40 am
THERMAL AGING AND IN-BOARD PEEL TESTING OF PB-FREE SOLDERS FOR UNDERHOOD APPLICATIONS: Martin W. Weiser, Julie A. Kern, Celeste A. Drewien, Frederick G. Yost, Johnson Matthey Electronics, Spokane Assembly Products Group, 15128 E. Euclid Avenue, Spokane, WA 99216; University of New Mexico, Mechanical Engineering Department, Albuquerque, NM 87131; Sandia National Laboratories, Materials and Process Sciences Center, Albuquerque, NM 87185
The thermal aging and post aging joint strength of four Pb-free solder alloys on a Ag-Pt thick film metalization were studied as the last part of a larger evaluation of solder/flux/metalization systems for use in high temperature under hood automotive application. The solders were the Sn-Ag and Sn-Ag-Cu eutectics and a Bi modified version of each. Solder pastes were reflowed on metalized alumina in a commercial inert atmosphere belt furnace. Aging of both sessile drops and in-board peel test samples was conducted at 134 to 190°C for up to 1000 hours. Addition of Bi and/or Cu increased the intermetallic growth rate and decreased the in-board peel strength.
12:00 am
RATE-CONTROLLING MECHANISM DURING PLASTIC DEFORMATION OF 95.5Sn4Cu0.5Ag SOLDER JOINTS AT HIGH HOMOLOGOUS TEMPERATURES: Hans Conrad, Z. Guo and Y. H. Pao, Materials Science and Engineering Department, North Carolina State University, Raleigh, NC 27695; Ford Scientific Research Laboratory, Materials Systems and Reliability Department, 20000 Rotunda Drive, Dearborn, MI 48121
The effects of stress and temperature on the creep rate of 95.5Sn4Cu0.5Ag solder joints at 22°C to 168°C were investigated employing stress-change and temperature-change tests. The resulting plastic deformation kinetics are in accord with those obtained previously in constant strain rate tests. They are better described by an obstacle-controlled dislocation glide kinetics equation than the usual Dorn equation for diffusion-controlled mechanism. The Helmholtz free energy for overcoming the obstacles is 0.28µb3, where µ is the shear modulus and b the Burgers vector. The activation volume is of the order of 1000 b3. The plastic deformation kinetics are in reasonable accord with the intersection of dislocations as the rate-controlling mechanism. However, alternative mechanisms are not ruled out.
12:20 pm
ALLOY DESIGN OF Sn-Zn-X (X=In, Bi) SOLDER SYSTEM THROUGH PHASE EQUILIBRIA CALCULATIONS: Sueng Wook Yoon, Jeong Ryong Soh, Byeong-Joo Lee, Hyuck Mo Lee, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong 373-1, Yusung-Gu, Taejon, Korea 305-701; Materials Evaluation Center, Korea Research Institute of Standards and Science, P.O. Box 3, Taedok Science Town, Taejon, Korea 305-606
Thermodynamic studies of the Sn-Zn-X (X=In, Bi) system have been carried out in terms of phase equilibria to design Pb-free solder alloys which are drop-in replacement for Sn-37Pb alloy. Based on the result of phase equilibria calculations, several selected alloys were chosen and analyzed by DSC, XRD and EPMA techniques. Microstructures of as-cast and heat-treated alloys were examined as well as the interface between solder joint and Cu substrate by optical microscopy and SEM. Spreading area test and preliminary mechanical test were performed to investigate the possibility as an alternative of eutectic Pb-Sn-solder.
12:40 pm
ALLOY DESIGN OF Sn-Ag-In-Bi-Sb SOLDER SYSTEM USING THERMODYNAMIC CALCULATIONS: Byeong-Joo Lee and Hyuck Mo Lee, Materials Evaluation Center, Korea Research Institute of Standards and Science, Yusong P.O. Box 102, Taejon 305-600, Korea; Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusong-Dong 373-1, Yusong-gu, Taejon 307-701, Korea
Room: 340C
Session Chairs: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139
8:30 am INVITED
GRAIN GROWTH IN POLYCRYSTALLINE THIN FILMS: C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139
Polycrystalline thin films are used in a wide variety of applications, especially in electronic and magnetic devices and systems. In these applications, the properties, performance and reliability of polycrystalline films are strongly affected by the average grain size, grain shapes, the way in which grain sizes are distributed and the distribution of grain orientations. These vary with deposition technique and with deposition conditions, and can also be modified through post-deposition processing. The factors which affect the structure and crystallographic texture of polycrystalline films will reviewed and categorized. Approaches for process development for application-specific optimized structures will be outlined.
9:10 am
NEW MICROSTRUCTURAL CHARACTERISTICS OF POLYCRYSTALLINE GOLD THIN FILMS: Alexander H. King, Varun Singh, Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275
We have made detailed observations of unsupported gold thin films, using transmission electron microscopy. These films embody a strong [111] fiber texture, as found in many FCC metal thin films. Rotations of individual grains about the [111] surface normal are observed and we present a simple model that mimics this behavior, providing a reasonable explanation for it. We will also present an analysis of the triple junctions in the films showing that symmetry is the most significant factor in determining the energy associated with a triple junction. We will show that supposed "U-lines" do not embody the disclinations that are expected on the basis of Bollmann's analysis. Acknowledgment: This work is supported by the National Science Foundation, under grant number DMR-9530314.
9:30 am
MODELING OF GRAIN GROWTH IN THIN FILMS WITH TEXTURE: Harold J. Frost, Johan Grape, Thayer School of Engineering, Dartmouth College, Hanover, NH
We have developed our two-dimensional simulation of grain growth to include several effects which apply for the case of large-grained polycrystalline thin films in which the grains completely traverse the film thickness and the grain boundaries are all nearly perpendicular to the plane of the film. To properly include the effects of texture we must include the following factors which differ among individual grains based on crystallographic orientation: surface energies for the film-substrate and film-covering interface; elastic compliances, and the related strain-energy densities when elastic strains are imposed; yield stresses, which limit the elastic strains and strain-energy densities. In this paper we will expand on previous treatments by explicitly allowing for variations in grain boundary energy and mobility, based on the relative misorientation of neighboring grains. In this case, the grain growth evolution favors pairs of grains separated by low angle (low energy) grain boundaries. Such low energy boundaries generally separate grains of the same texture component. Other effects, such as pinning by surface grooving, pinning by precipitate particles or holes in the film, and solute drag may also be included in the simulations.
9:50 am
POST-PATTERNING MICROSTRUCTURE EVOLUTION OF Al-Cu INTERCONNECT LINES: D. P. Field, TexSEM Laboratories, Inc., 226 W. 2230 N., Provo, UT 84604
Optimization of microstructural features in interconnect lines for integrated circuits is becoming increasingly important for device reliability as the minimum feature size continues to shrink. Recent efforts have clearly demonstrated that not only grain size and precipitate morphologies are affected by the patterning and subsequent anneal, but also the crystallographic texture and grain boundary structure evolve during this process. For narrow lines, the (111) fiber texture sharpens and the near-bamboo grain structure is controlled by interface area minimization and grain boundary energy minimization. The current work describes the competing energetics associated with the process. Experimental results using orientation imaging microscopy as the analysis technique on Al-1% Cu interconnect lines are shown to support the analyses.
10:10 am BREAK
10:30 am INVITED
CRYSTALLOGRAPHIC TEXTURE EVOLUTION DURING FILM FORMATION AND ANNEALING IN SPUTTERED Al ALLOY/Ti AND Al ALLOY/TiN/Ti LAYERS: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; P.R. Besser, J. Williams, Advanced Micro Devices, Sunnyvale, CA 94088; D.K. Knorr, Rennselaer Polytechnic Institute, Troy, NY 15128
Ti, TiN and Al alloy thin films comprise the basis for patterned metallization interconnects in advanced integrated circuit devices. Ti in particular has been shown to provide increased reliability of the primary Al conductor against electromigration-induced failures. A proposed mechanism is for this improvement is increased Al (111) film fiber texture due to the presence of the Ti underlayer. A review of extensive Al texture characterization by x-ray diffraction methods will be presented for various Ti, TiN, and Al layering schemes and sputter deposition conditions. Factors such as substrate surface energy, substrate roughness, Al grain growth, and "texture inheritance" between layers will be discussed. Deposition and processing schemes for improved Al (111) texture and improved interconnect reliability will be provided.
11:10 am
THE EFFECT OF MICROSTRUCTURE AND LOCAL MICROSTRUCTURE VARIATIONS ON ELECTROMIGRATION FAILURE DISTRIBUTIONS: Dirk D. Brown, AMD, Sunnyvale, CA 94088; John E., Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; Matt A. Korhonen, Che-Yu Li, Cornell University, Ithaca, NY 14850
In narrow metal lines used for chip level interconnects, the electromigration reliability is affected by variations in the microstructure. Electromigration failure distributions were obtained experimentally for six different Al-Cu interconnect widths, ranging from 1mm to 8mm. Or each of these line widths, the microstructure was characterized (using TEM) and the initial stress distribution was calculated. This information was used, with a flux divergence model, to simulate the entire failure distribution for each line width. These simulations, when compared to the experimental failure distributions, were used to quantify important material parameters, such as atomic diffusivities and failure criteria. This information, in turn, can be used to accurately extrapolate electromigration data. A detailed failure analysis was carried out on the simulated lines to study the effect of microstructure variations on electromigration failure.
11:30 am
LOCAL GRAIN BOUNDARY STRUCTURE CHARACTERIZATION IN VOIDED COPPER INTERCONNECTS: R.R. Keller, National Institute of Standards and Technology, Materials Reliability Division, 325 Broadway, Boulder, CO 80303; J.A. Nucci, Cornell University, School of Electrical Engineering, Phillips Hall, Ithaca, NY 14853; D.P. Field, TexSEM Laboratories, Inc., 226 West 2230 North #120, Provo, UT 84604
We have characterized grain boundary structures and local textures in oxide passivated copper lines which had undergone thermal stress-induced voiding. Grain boundary misorientations and the crystallographic character of boundary planes were determined for individual grain boundaries using electron backscatter diffraction in the scanning electron microscope as well as focussed ion beam images. We have summarized the data for a number of boundaries immediately adjacent to voids and made direct comparisons to boundaries from regions which remained intact. These data were acquired from the same lines, and so represent measurements from material with identical thermal histories. The results suggest that significant variations in local structure exist in narrow lines, and that those local regions associated with more favorable kinetics are more susceptible to void formation and growth.
Room: 330E
Session Chairpersons: James C. Williams, GE Aircraft Engines, 1 Neumann Way, Evendale, OH 45215; Young-Won Kim, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432
8:25 am OPENING REMARKS
8:30 am INVITED
PROCESSING-PROPERTY-MICROSTRUCTURE RELATIONSHIPS IN TiAl-BASED ALLOYS: M H. Loretto, D. Hu, A. Godfrey, T.T. Cheng, I.P. Jones, P.A. Blenkinsop, IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston B15 2TT, UK
A range of TiAl-based alloys has been p