Nanocomposite Coatings - Applications and Properties
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NANOCOMPOSITE COATINGS – APPLICATIONS AND PROPERTIES Roger H. Cayton and R. W. Brotzman, Jr. Nanophase Technologies Corporation Romeoville, IL 60446, U.S.A. ABSTRACT Nanocomposite coatings were made by incorporating nano-sized and micron-sized alumina into aqueous and non-aqueous polymer systems. At approximately 50wt% nano-sized alumina a synergistic effect was observed in coating hardness with no degradation in optical properties. INTRODUCTION Nano-sized materials produced by gas phase condensation have novel characteristics including chemical reactivity, composition, morphology, and processing advantages. These materials are commercially available and are being engineered for nanocomposite coating applications. The structure of nanocomposites is important because often multiple physical properties are desired, i.e., electrical conductivity or abrasion resistance with transparency. In effect, the composite structure is selected for the desired physical property – from uniform surface distribution of nanoparticles for abrasion resistance to connected nanoparticle structures for electrical conductivity. Nanomaterial production Nanophase Technologies Corporation (NTC) produces nanocrystalline metal oxide powders by a patented Physical-Vapor Synthesis (PVS) process. The process involves vaporizing a metallic or metal oxide precursor in a plasma, followed by rapid quenching to induce condensation and formation of extremely small metal oxide crystallites. The size of the crystalline particles is controlled by the condensation rate and the particle concentration in the quench zone. The discrete metal oxide nanocrystalline particles form loose aggregates that are collected as a dry powder. The loose aggregates can be dispersed in solution to provide stable suspensions of the individual particles. The PVS process uses metal or metal oxide precursors and avoids product contamination that may result from solvent or solvated precursor materials. The resulting purity of the metal oxide nanoparticles, in both the bulk phase and on the surface, is maintained at a very high level. The PVS process has been scaled to provide production rates of tons/year. Examples of nanocrystalline oxides currently produced at bulk scale at NTC include alumina, ceria, titania, zinc oxide, iron oxide, antimony/tin oxide, and indium/tin oxide. Numerous other pure oxides and mixed metal oxides can be produced with the PVS process. Metal oxides prepared by the PVS process are crystalline, equiaxed, nonporous, discrete particles with mean diameters in the 10 – 50 nm range, and have surface areas of 15-90 m2/g.
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Particle surface treatment In most nanocomposite coating systems, the nanocrystalline metal oxide powders require surface treatment to enable dispersion into the matrix coating materials. NTC has developed proprietary surface treatment processes for metal oxide nanoparticles, each designed to provide one or more of the following properties: • dispersion into fluids (aqueous, alcohol, and hydrocarbons), • prevention of particle agglomera
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