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SELECTED APPLICATION AREAS. 96 material density and near-zero coefficient of thermal expansion plus the ability to form laminates by interdiffusion of the glass phase provides strong motivation for employment of PBZT-silica microcomposites for aerospace structural applications. CATALYSTS The application of new catalysts that replace current catalysts will be based primarily on performance criteria. Preparation techniques might be transferred from model catalyst systems, if favorable properties are identified and the preparation can be scaled up conveniently. New applications will be based on the potential for new product schemes and the economics for the entire process, of which the catalyst is just one part. The cost of the catalyst can be a factor if the preparation scheme is particularly complex, the raw materials are expensive, and the catalyst is used in very high volume, as for exhaust emission control catalysts. Broad classes of catalytic reactions that make use of submicron-sized catalytic particles include emission control catalysis, catalytic reforming, synthesis gas catalysis, Ziegler process for polyethylene, and oxidation catalysis. Other processes that similarly incorporate a catalytic component are photocatalysis and oxygen sensors. Possible future catalytic processes include catalytic activation of fuel for energy conversion. The performance of a catalyst is determined by measuring product yield. Catalysts are evaluated by monitoring their activity, selectivity, and durability under realistic conditions. Testing the activity of a catalyst for a particular reaction is the best way to choose a catalyst. Moreover, important discoveries are made in doing kinetic measurements, where serendipity can play a role. Catalyst characterization that is not related to performance is ancillary if the concern is economics. CERMETS Metal-ceramic (cermet) composites are routinely produced by conventional powder-metallurgy methods. A limitation to the approach has been the inability to obtain a microstructure in which the hard ceramic phase is less than 1 to 5 mm in cross section. Both the chemical-synthetic approach and the gas-condensation method provide the means for generating novel cermet materials with submicron-scale structures. Such ultrafine structures present the opportunity to synthesize a new class of cutting-tool materials, which will have the ability to form and maintain a very fine cutting edge that is resistant to chipping. For this reason, it is believed that nanophase composite cermets, such as Co-WC, will find great utility for such high-value-added applications as microtome blades and surgeon's scalpels. A number of
