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Session Chairperson: TBA
ELECTRODEPOSITED Ni-Al PARTICLE COMPOSITE COATINGS: D.F. Susan, K. Barmak, A.R. Marder Department of Materials Science and Engineering, Lehigh University Bethlehem, PA 18015-3195
Electrodeposited metal matrix/metal particle composite coatings (EMMC's) were deposited, heat treated, and characterized. Nickel matrix/aluminum particulate coatings deposited on a nickel substrate was chosen as a model system. The microstructure of the as-plated and heat treated coatings was characterized using light optical microscopy (LOOM), SEM, quantitative image analysis (QIA), and EPMA. A schematic model is presented for coating morphological development during codeposition of small, electrically conducting particles. The heat treated coatings consist of a two phase mixture of y solid solution and Ni3Al (gamma-prime) with small Kirkendall voids also present. The hardness of the heat treated coatings increased with increasing Ni3Al content and remained constant with extended heat treatment time. Oxidation tests were performed isothermally in air at 800, 900, and 1000°C for up to 900 hrs. and the depth of the oxidation attack was determined. Throughout the investigation, the Ni-Al coatings were compared to conventional pure Ni coatings deposited under similar conditions.
FORMATION OF THIN COLORED FILM ON STAINLESS STEEL: G.S.Gupta, Dept. of Mining, Minerals and Materials Engineering, The University of Queensland, St.Lucia, Queensland - 4072, Australia
Formation of colored film on type 304 stainless steel has been studied using chromic acid and potassium dichromate solutions. Permanent colors have been obtained using immersion and electrolytic (potentiostatic) methods. The effect of different parameters on the coloring process including temperature, coloring methods, solution composition, stirring, surfactant etc., have been noted. Moderate temperature of the solution, electrolytic method, use of surfactant and stirring of the solution were found to enhance the coloring process. A coloring solution which is strongly oxidized and acidic in nature is recommended. It is advisable that after the extended use of the coloring solution, fresh solution should be used.
TRICATIONIC PHOSPHATE COATING ON GALVANNEALED STEEL SHEET: Carlos Nelson Elias, Mila Marques Justo, Escola de Engenharia Metaurgica de Volta Redonda, Av dos Trabalhadores 420, 27260 740 Volta Redonda, RJ - Brazil
The galvannealed compared to galvanized steel sheet has excellent paint adhesion, weldability and corrosion resistance after painting. However, the coating tends to cause exfoliation when undergoing severe deformation. This coating is used in the automobile industry. Since the mass loss is very large, it accumulates on the metal mold and results in severe damage to the surface quality of the formed panel affecting press workability and damaging the tool. Nevertheless, phosphating is the most widely used pretreatment, since it serves as an excellent paint base, increases corrosion resistance to metal paints, aids in cold forming of steel and increases the lubricant power of oil applied to the pieces subjected to friction and wear. The influence of galvannealed morphology on the phosphate crystal feature is not well understood. In this work, a tricationic phosphate coating was applied to a surface of a low carbon steel and an interstitial free steel with galvannealed coating. Our paper will discuss the structural and mechanical properties resulting from this treatment.
PROGRESS TOWARD THE DEVELOPMENT OF DENDRIMER-BASED PROTECTIVE COATING: Larry A. Milco, Donald A Tomalia, Michigan Molecular Institute, 1910 W. St. Andrews Road, Midland, MI 48640-2696
There is a considerable demand for thin film coatings to which other substances will not stick. Coatings are required to protect surfaces from soils, stains, ice, graffiti, insects, oils, corrosion and chemical and biological contaminants. Moreover, as legislative pressures to remove volatile organic solvents from coating formulations persist, the demand for alternative water-borne systems continues to increase. The incorporation of dendritic polymers in non-stick coating formulation is a highly viable approach to overcoming the limitations associated with conventional polymer systems. Non-stick coatings were prepared by crosslinking dendrimers with linear polymers. The high advancing and receding contact angles and low contact angle hysteresis of water and hexadecane on the coatings are indicative of the non-stick (low adhesion) properties of these surfaces.
PULSED LASER DEPOSITION OF COLLAGEN AND APATITE/COLLAGEN COMPOSITE BIOCOMPATIBLE THIN FILMS: J.A. Conklin, C.M. Cotell, Surface Modification Branch, Code 6671, U.S. Naval Research Laboratory, Washington, D.C. 20375
Thin films comprising either collagen or a composite of hydroxyapatite (HA) and collagen were deposited by pulsed laser deposition (PLD) on various substrates. Films were deposited using either a KrF (248nm) or ArF (193nm) excimer laser and the substrates were maintained at room temperature. Collagen films were characterized by SEM, Fourier transform infrared (FT-IR) spectroscopy and gel electrophoresis. The functional groups on the collagen molecule remained intact through the laser ablation process, but there was evidence for some loss of secondary structure. In addition, the surface morphology was a function of the laser fluence and the gas environment during PLD. Less denaturation of the molecule was observed when the ablation was at 193nm than at 248nm. For the composite films, the target material consisted of a 70/30 (by weight) mixture of apatite/collagen, the same ratio found in bone. The resulting composite films were a homogenous mixture of amorphous collagen and highly crystalline apatite.
3:40 pm BREAK
PROTEINS FROM OYSTER SHELL AS MODELS FOR BIODEGRADABLE COMMERCIAL POLYMERS: A.P. Wheeler, Department of Biological Sciences, Clemson University, Clemson, SC 29634
Virtually all minerals formed by organisms are composites, containing an organic phase (matrix) which enhances the mechanical properties of the inorganic phase and which presumably controls mineral growth. The matrix of the CaCO3 shell of oysters contains soluble, highly anionic proteins which in vitro adsorb to mineral and in so doing alter mineral growth. Based on the surface reactive properties of these proteins, synthetic analogs have been made which have properties that make them candidates as inhibitors for mineral scale and corrosion and as dispersants. Synthesis of a simple matrix protein analog, polyaspartic acid, is possible on a significant scale using dry thermal polymerization and aspartic acid as the only reactant. Thermal polyaspartic acid is highly biodegradable when compared to polymers currently used for commercial surface reactive applications.
THE APPLICATION AND SUBSEQUENT CROSS-LINKING OF A BIOLOGICAL POLYMER ON ALUMINUM METAL: Douglas C. Hansen, Naval Research Laboratory, Washington, D.C. 20375-5343
Biological polymers that are used by organisms in the formation of structural materials and protective coatings are widespread in nature. An example of such a polymer is the protein utilized by the blue mussel Mytilus edulis as a varnish coating on its byssal threads. This protein is of high molecular weight (>100,000) and is unique in containing the catecholic amino acid L-dopa. This protein exhibits high affinity for metals and acts as a substrate for the enzyme catechol oxidase, which catalyzes the two electron oxidation of catechol to o-quinone. This reaction is essential in the formation of a two component sclerotized resin. The adsorption of this protein onto pure aluminum (99.99999%) and subsequent cross-linking of the adsorbed protein results in a significant shift in the critical pitting potential and polarization resistance of the treated aluminum. Atomic Force Microscopy (AFM) measurements clearly show that treatment of the protein adsorbed onto Highly Ordered Pyrolytic Graphite (HOPG) with catechol oxidase results in a stable, varnish-like coating.
ADSORPTION OF ADHESIVE PROTEINS FROM THE MARINE MUSSEL, MYTILUS EDULIS, ON POLYMER FILMS IN THE HYDRATED STATE USING ANGLE DEPENDENT XPS AND AFM: A.M. Baty, P.K. Leavitt, C.A. Siedlecki, B. J.Tyler, P.A.Suci, R.E. Marchant, G.G.Geesey. Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717-0398
The adsorption of Mussel Adhesive Protein (MAP) from the marine mussel Mytilus edulis has been investigated on polystyrene (PS) and poly (octadecyl methacrylate) (POMA) surfaces using angle dependent XPS and AFM. XPS analysis was performed at LN temperatures without dehydrating the samples and at room temperature following dehydration. The analyses indicate that adsorbed MAP is stabilized on the surface of the PS through specific interactions preventing the protein from losing lateral spatial distribution across the surface upon dehydration. The adsorbed MAP on the POMA surface is representative of a loosely bound protein layer that is adsorbed through non-specific types of interactions allowing the protein to lose much of its lateral distribution when dehydrated. These data demonstrate that the surface chemistry of the polymer films influences protein-protein and protein-surface interactions, and that hydration plays a significant role in structuring protein-surface interactions.
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