THE 1994 HOWE MEMORIAL LECTURE
Alternative Studies in Iron and Steelmaking
PAUL E. NILLES
The first Howe Memorial Lecture, which was delivered 70 years ago, in 1924, was entitled "What is Steel?" This title may seem surprising in view of the very diversified use of steel already achieved at that time. It is obvious that the particular event constituted by the creation of this lecture invited the author to look back on what had been achieved and to try to forecast future developments. The turn of the millenium, due in 6 years, induces similar initiatives in numerous fields. As far as the steel industry is concerned, some of the questions most frequently asked are:
- How much steel will the world consume during the first part of the 21st century?
- What are the raw material requirements and availabilities?
- Which will be the geographical repartition of the production facilities?
- What will be the optimum size and layout of a steel plant?
- Will the future have large integrated steel plants?
During this lecture, I would like to address these two topics: 1) Are the present production technologies still appropriate or do new processes have to be developed for meeting the future needs of the steel industry? and 2) Which research strategy is required for bringing the new processes and new products to maturity and to industrial application?
HYDROMETALLURGY
A Study of Solid-Aqueous Equilibria by the Speciation Approach in the Hydronium Alunite-Sulfuric Acid-Water System at High Temperatures
B.C. BLAKEY and V.G. PAPANGELAKIS
An experimental and theoretical investigation of the aqueous equilibria of hydronium alunite-sulfuric acid-water systems at saturation and under pressure leaching conditions was conducted. To this end, pure hydronium alunite was synthesized through an in situ dissolution-precipitation reaction sequence. A nonideal chemical equilibrium model was then developed to predict the behavior of the system at high acidities (pH25°C < 1) and high temperatures (230°C to 270°C). The model was based upon the most recent thermodynamic data available for all known aluminum-oxy-hydroxyl-sulfate-bisulfate species, as well as experimentally determined solubility data for hydronium alunite. System behavior was characterized by speciation diagrams which illustrated the relative concentrations of aqueous species and acidity as functions of total sulfate concentration. This type of investigation was found to give valuable insight into the equilibrium behavior of high-temperature systems that would be otherwise inaccessible.
The Mineralogical Deportment of Germanium in the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc.
J.E. DUTRIZAC, T.T. CHEN, and R.J. LONGTON
A mineralogical study was carried out on the neutral leach residue and weak acid leach residue generated from Gordonsville zinc concentrate at the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc. The intent was to characterize the mineral forms and associations of germanium. The Gordonsville zinc concentrate consists mostly of sphalerite which has a solid solution Ge content of ~400 ppm; the sphalerite is the dominant, if not only, Ge carrier in the concentrate. The neutral leach residue consists principally of iron gel-silica gel, ZnO, and basic zinc sulfate, (Zn,Cu)4(SO4)(OH)6·4H2O, together with minor amounts of ZnFe2O4, sphalerite, Zn2SiO4, Zn-Fe-Pb silicate, and PbSO4, as well as traces of quartz, silicates, Pb-K jarosite solid solution, Fe2O3, and FeO·OH. The major Ge carrier is the iron gel-silica gel phase, but modest amounts of Ge are present in the ZnO, ZnFe2O4, sphalerite, and Zn-Fe-Pb silicate phases. The weak acid leach residue consists mostly of iron gel-silica gel, ZnFe2O4, PbSO4, Pb-K jarosite, Zn-Fe-Pb silicate, and quartz. The major Ge carrier is the iron gel-silica gel phase which contains up to 1.7 pct Ge and accounts for ~70 pct of the total Ge content of this residue. The remaining Ge is carried by the Zn-Fe-Pb silicate, ZnFe2O4, and some of the rare Mn-Pb-Fe oxide phases.
Preparation of Fine Copper Powders from Organic Media by Reaction with Hydrogen under Pressure: Part I. Experimental Study
R. SARRAF-MAMOORY, G.P. DEMOPOULOS, and R.A.L. DREW
In this work, a novel method of preparing copper powder having the required properties for thick film applications was investigated. This method involves the precipitation of copper powder by hydrogen reduction under pressure from Kelex 100-decanol-Versatic 10-kerosene media. The parameters studied were temperature (453 to 573 K), hydrogen pressure (1.03 to 3.79 MPa) time, use of additives, solvent composition, etc. Powders with the following excellent properties were produced: d50=1 µm; 80 pct spread - 1.3 + 0.7 µm; specific surface area = 1 ± 0.2 m2/g, spheroidal shape; and 0.056 wt pct oxygen content.
Preparation of Fine Copper Powders from Organic Media by Reaction with Hydrogen under Pressure: Part II. The Kinetics of Particle Nucleation, Growth, and Dispersion
R. SARRAF-MAMOORY, G.P. DEMOPOULOS, and R.A.L. DREW
The kinetics of very fine copper powder (1 to 2 µm) production by hydrogen reduction of solvent extracted copper chelates have been determined. The Avrami-Erafeer model for nucleation growth processes has been found to best describe the precipitation kinetics. The model parameters were correlated with reasonable success to the morphology of the copper powder. The chemically controlled particle formation process was found to exhibit 30 to 58 kJ/mol activation energy depending on the temperature range and a complex dependency (from first order to fractional/zero order) on hydrogen pressure. A steric stabilization model has been advanced to interpret the cooperative action of decanol and Versatic 10 in stabilizing the very fine copper powder dispersion.
PYROMETALLURGY
Chemical Potentials of Components of the System CaO+P2O5+FexO at 1673K
HIDEAKI HOSHINO and MASANORI IWASE
Electromotive force (emf) measurements were conducted with a solid oxide galvanic cell of the type
Mo/Mo+MoO2/ZrO2 (MgO)/Fe (s)+FexO (in slag)/Ag/Fe
at 1673K in order to obtain the activities of FexO in CaO+P2O5+FexO ternary slags. By using the Gibbs-Duhem integration, the activities of P2O5 and CaO were also obtained.
Formation of Aluminum-Silicon Alloys from Feldspars--Determination of Silicon, Light, and Heavy Elements in Silumin by Scanning Electron Microscopy
A. OLSEN, J.R. STUBERGH, and T. VINSAND
Silumin has directly been deposited from feldspars by thermal reduction with aluminum metal at 1000°C. The six analyzed samples of silumin alloys contained 10.8 to 15.3 mass pct silicon in aluminum. The amount of iron deposited was 0.17 to 0.40 mass pct, magnesium was in the range of 0 to 1.8 mass pct, and sodium was 0.35 to 0.55 mass pct. The amounts of titanium, calcium, and potassium were quite close to the detection limit for these elements, which is proposed to be 0.0 to 0.1 mass pct. The sulfur and phosphorous concentrations were too low to be measured by scanning electron microscopy. Analyses were made by scan plot and spot tests of both the aluminum matrix and silicon crystals.
ELECTROMETALLURGY
Fundamental Studies of Copper Anode Passivation During Electrorefining: Part II. Surface Morphology
XUAN CHENG and J. BRENT HISKEY
Passivation of commercial copper anodes and pure copper has been previously analyzed by performing electrochemical measurements. Chronopotentiometry results revealed four characteristic regions involving I-active dissolution, II-prepassivation, III-passivation onset, and IV-passivation, for commercial copper anodes, while only active dissolution was observed for pure copper under the conditions employed. In order to establish the relationship between surface morphology and passivation response, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS) were applied to characterize morphology of the product layers formed on a commercial copper anode surface for the distinctive electrochemical regions. The morphology studies suggested that the formation and stability of copper oxide surface films are critical to the onset and development of passivation. The structure and porosity of the slimes layer present in the outer layer of the anode influence the stability of copper oxide surface films which dominantly control the passivation response.
TRANSPORT PHENOMENA
Intermixing Model of Continuous Casting During a Grade Transition
XIAOQING HUANG and BRIAN G. THOMAS
To investigate the composition distribution that develops in continuously cast
steel during a grade change, an efficient, accurate, and user-friendly
computational model has been developed. The model is fully transient and
consists of three submodels, which account for mixing in the tundish, mixing in
the liquid core of the strand, and solidification. The first submodel of mixing
in the tundish consists of two plug flow zones, two back-mixing boxes, and two
dead volumes. The second submodel solves a one-dimensional (1-D) diffusion
equation in series with two back-mixing boxes to calculate concentration
histories in the strand, and the third submodel transforms these histories into
slab compositions. The model was calibrated using both concentration histories
measured on tundish water models and calculations from a three-dimensional
(3-D) model. It was then verified with several sets of composition measurements
along the surface and centerlines of slabs. The model is capable of tracking
mixing phenomena for arbitrary tundish filling and casting speed histories. It
has been used to compare the effects of different grade change procedures on
the amount of intermixed steel, including standard sequence casting, flying
tundish change, and insertion of grade separators. Mixing in the strand was
found to be very important. Without a grade separator, a flying tundish change
had very little benefit on reduced intermixing, for the typical conditions
considered.
Experimental Study of Splash Generation in a Flash Smelting Furnace
LIOW JONG-LENG and NEIL B. GRAY
A survey of previous studies of splash formation in metallurgical vessels revealed that little information is available to characterize and describe the processes involved in splash formation. An experimental study of splash formation by top submerged gas injection was carried out in the settler region of the nickel flash smelting furnace at the Kalgoorlie Nickel Smelter (KNS) both to obtain some visualization of the splash mechanisms that occur on a plant scale and to measure the amount of splash being formed. Video images taken of the splashing showed that large sheets of melt were formed by the escaping gas and subsequently thinned into ligaments which then broke up into large splash drops. The video could only resolve a minimum size of 2 cm. The large splash drops visible on video have an initial velocity between 1 and 2 m/s, are unstable, and fall back into the bath after traveling a short distance. The analysis identified two major splash forming mechanisms. First, the gas injected resulted in the bulk movement of the melt to form a cavity and large sheets of melts being thrown around the point of injection. The area affected by this splash mechanism can be predicted successfully by using an energy balance between the removal of the melt in the cavity and the energy of the gas being injected. Second, the slag free surface within the cavity is highly unstable, and through the Kelvin-Helmholtz instability mechanism, small splash droplets are generated which are carried into the furnace's top space. A model proposed for the formation of the smaller splash droplets predicted that the splash collected decreases exponentially with increasing height above the slag free surface from the point of splashing, and this is in agreement with the experimental results obtained.
Communication: Cold Model Study of the Surface Profile in a Continuous Slab Casting Mold: Effect of Second Phase
DHARMENDRA GUPTA and A.K. LAHIRI
Communication: A Unified Representation of the Two-Phase Plume Characteristics in Gas-Stirred Ladle Systems
VELURU SUDHAKAR and DIPAK MAZUMDAR
PHYSICAL CHEMISTRY
Controversy on the Free Energy of Formation of CaO--Additional Evidence in Support of Thermochemical Data
K.T. JACOB and VIJI VARGHESE
The standard free energies of formation of CaO derived from a variety of high-temperature equilibrium measurements made by seven groups of experimentalists are significantly different from those given in the standard compilations of thermodynamic data. Indirect support for the validity of the compiled data comes from new solid-state electrochemical measurements using single-crystal CaF2 and SrF2 as electrolytes. The change in free energy for the following reactions are obtained:
CaO+MgF2 
MgO+CaF2
G° = -68,050 - 2.47 T (±100) J mol-1
SrO+CaF2 SrF2+CaO
G° = -35,010 + 6.39 T (±80) J mol-1
The standard free energy changes associated with cell reactions agree with data in standard compilations within ±4 kJ mol-1. The results of this study do not support recent suggestions for a major revision in thermodynamic data for CaO.
Thermodynamics of Sulfur in the BaO-MnO-SiO2 Flux System
TATSUO KOBAYASHI, KAZUKI MORITA, and NOBUO SANO
The sulfide capacity of the molten BaO-MnO-SiO2 system was determined by measuring the sulfur partition ratio between the oxide and an Ag-S alloy in a controlled CO-CO2-Ar gas mixture at 1573K for two purposes. One is to develop highly basic fluxes which can extensively desulfurize manganese-based alloys, and the other is to examine the effect of BaO addition on thermodynamic properties of sulfur in the MnO-SiO2 melts from which MnS precipitates functioning as the nucleus for subsequent 
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transformation of steel. The sulfide capacity of the BaO-MnO-SiO2 system strongly depends on the composition, and MnO has been found to enhance sulfide capacity to a greater extent than BaO at less basic compositions.
Use of Solid-Electrolyte Galvanic Cells to Determine the Activity of CaO in the CaO-ZrO2 System and the Standard Gibbs Free Energies of Formation of CaZrO3 from CaO and ZrO2
JUN TANABE and KAZUHIRO NAGATA
The activity of CaO in the CaO-ZrO2 system has been measured at 1572 to 1877K with a Galvanic cell composed of 4CaO·P2O5 as the solid electrolyte. The activity ZrO2 was calculated from the activity of CaO by integrating the Gibbs--Duhem relation. From the activities of CaO and ZrO2, the standard Gibbs free energy of formation of CaO·ZrO2 was determined as follows:
Gf0/J mol-1 = -25,200 (±150) - 17.58 (±0.085) T (1633 to 1873K)
Communication: Discussion of "Representation of Mixed Reactive Gases on Free Energy (Ellingham-Richardson) Diagrams"
D.R. GASKELL
Communication: Author's Reply
C.V. ROBINO
Communication: Viscosity of Superalloy 718 by the Oscillating Vessel Technique
R.A. OVERFELT, C.A. MATLOCK, and M.E. WELLS
Communication: M23C6 Carbide Equilibria in the Fe-Cr-C System
J. SOPOUSEK and J. VRESTAL
SOLIDIFICATION
Solidification of Particle-Reinforced Metal-Matrix Composites
G.S. HANUMANTH and G.A. IRONS
The solidification behavior of ceramic particle-reinforced metal-matrix composites (MMCs) is different from that of the bare matrix, not only because of the presence of the ceramic particles, but also due to their redistribution in the melt that results in nonhomogeneous thermophysical properties. The MMCs comprised of 10- to 15-µm SiC particles of varying volume fractions, dispersed uniformly in a modified aluminum A356 alloy by the melt stirring technique, were solidified unidirectionally in a thermocouple-instrumented cylindrical steel mold. The cooling rates were continually monitored by measuring temperatures at different depths in the melt, and the solidified MMCs were sectioned into disks and chemically analyzed for SiC volume fraction. The results point out that the cooling rate increased with increasing volume fraction of SiC particles. A small increase in the bulk SiC volume fraction of the cast MMC was observed due to particle settling during solidification. A one-dimensional enthalpy model of MMC solidification was formulated, wherein particle settling occurring in the solidifying matrix was coupled to the enthalpy equation by means of the Richardson--Zaki hindered settling correlation. A comparative study of simulations with experiments suggested that the thermal response of SiC particles used in this study was similar to that of single crystals, and their presence increased the effective thermal conductivity of the composite.
Communication: Radioscopic Visualization of Isothermal Solidification of Eutectic Ga-In Alloy
R. DEREBAIL and J.N. KOSTER
MATHEMATICAL MODELING
Flow and Thermal Behavior of the Top Surface Flux/Powder Layers in Continuous Casting Molds
R.M. McDAVID and B.G. THOMAS
Steady-state finite-element models have been formulated to investigate the coupled fluid flow and thermal behavior of the top-surface flux layers in continuous casting of steel slabs. The three-dimensional (3-D) FIDAP model includes the shear stresses imposed on the flux/steel interface by flow velocities calculated in the molten steel pool. It also includes different temperature-dependent powder properties for solidification and melting. Good agreement between the 3-D model and experimental measurements was obtained. The shear forces, imposed by the steel surface motion toward the submerged entry nozzle (SEN), create a large recirculation zone in the liquid flux pool. Its depth increases with increasing casting speed, increasing liquid flux conductivity, and decreasing flux viscosity. For typical conditions, this zone contains almost 4 kg of flux, which contributes to an average residence time of about 2 minutes. Additionally, because the shear forces produced by the narrowface consumption and the steel flow oppose each other, the flow in the liquid flux layer separates at a location centered 200 mm from the narrowface wall. This flow separation depletes the liquid flux pool at this location and may contribute to generically poor feeding of the mold-strand gap there. As a further consequence, a relatively cold spot develops at the wideface mold wall near the separation point. This nonuniformity in the temperature distribution may result in nonuniform heat removal, and possibly nonuniform initial shell growth in the meniscus region along the wideface off-corner region. In this way, potential steel quality problems may be linked to flow in the liquid flux pool.
Communication: Prediction of Dendrite Arm Spacing for Low Alloy Steel Casting Processes
M. EL-BEALY and B.G. THOMAS
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