Ceramic-metallic materials

Doyle C. 1990. Composite bioactive ceramic-metal materials. In Handbook of Bioactive Ceramics. T. Yamamuro, L.L. Hench, and J. Wilson (Eds.), pp. 195-208. CRC Press, Boca Raton, FL. 

In several cases, materials for combined erosive and corrosive conditions have been evaluated on the basis of separate erosion and corrosion studies and data, with the consequence that the synergistic effects are left out of the evaluation. Since one or the other of these effects may be large, the conclusions may be quite wrong. For materials fliat usually are passive due to a dense oxide film, such as stainless steels, Wc is by definition very low. But since sand erosion more or less destroys the passive film, the corrosion rate increases strongly and may reach very high values, i.e. the contribution of Wce may be particularly high for these materials. The other synergy effect, Wec, is most pronounced for ceramic-metallic materials in which the metallic phase has inferior corrosion resistance, e.g. for a cemented carbide with a metallic phase of cobalt (WC-Co). 

Somewhat higher ductility is obtained by combining ceramic particles with a metallic binder phase. Such ceramic-metallic materials (cermets) are excellent under erosive and abrasive conditions. A well-known material is WC Co. Better corrosion resistance is obtained by alloying Co with Cr or by using alloys of Ni, Cr and possibly Mo as the binding phase. 

Lower density than ceramic/metallic materials... 

NiAl or NiCr metals have been employed as MCFC anodes. These materials are used because Ni metal anodes are not stable enough under MCFC operating conditions as Ni creeps out [18,20]. Cermet (ceramic metal) materials avoid sintering, pore growth, and shrinkage of the Ni metal so that a loss of surface area does not occur. A low- cost process needs to be found, however, as these materials are still expensive to fabricate. 

Solution Combustion Synthesis (SCS) is becoming one of the most impoitnnt ways to produce a wide range of advanced porous ceramic, metallic materials and nanostmctuied catalysts, compared to the more conventional and expensive processes. SCS process is, in fact, characterized by exothermic, fast and self-sustaining reactions, formation of high purity products with a variety of size and shape, relatively easy procedures, use of relatively simple equipment and cheap reactants. Thanks to these main characteristics, SCS is easily tunable to complex systems to produce directly in situ stractured catalysts. 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

Microscopists in every technical field use the microscope to characterize, compare, and identify a wide variety of substances, eg, protozoa, bacteria, vimses, and plant and animal tissue, as well as minerals, building materials, ceramics, metals, abrasives, pigments, foods, dmgs, explosives, fibers, hairs, and even single atoms. In addition, microscopists help to solve production and process problems, control quaUty, and handle trouble-shooting problems and customer complaints. Microscopists also do basic research in instmmentation, new techniques, specimen preparation, and appHcations of microscopy. The areas of appHcation include forensic trace evidence, contamination analysis, art conservation and authentication, and asbestos control, among others. 

Description A tray or compartment diyer is an enclosed, insulated housing in which solids are placed upon tiers of trays in the case of particulate solids or stacked in piles or upon shelves in the case of large objects. Heat transfer may be direct from gas to sohds by circulation of large volumes of hot gas or indirect by use of heated shelves, radiator coils, or refractoiy walls inside the housing. In indirec t-heat units, excepting vacuum-shelf equipment, circulation of a small quantity of gas is usually necessary to sweep moisture vapor from the compartment and prevent gas saturation and condensation. Compartment units are employed for the heating and diying of lumber, ceramics, sheet materi s (supported on poles), painted and metal objects, and all forms of particulate solids. 

Metallic Versus Ceramic/Brittle Materials Recovery... 

The insulation around the central electrode is an example of a non-metallic material - in this case, alumina, a ceramic. This is chosen because of its electrical insulating properties and because it also has good thermal fatigue resistance and resistance to corrosion and oxidation (it is an oxide already). 

If the ore consists of separate grains containing the desired material, it can be separated from undesired minerals by physical methods such as flotation, sedimentation, or magnetic separation. For metals this step can lead to 80 to 95 percent concentration of the value of the ore. Ceramic raw materials such as sand and clay can often be found pure enough in nature so that no concentration is needed. 

Much of the early work on fretting was confined to mild steel or carbon steel. Although many of the same principles apply to the fretting of other metals such as gold , titanium and the superalloystheir reaction to the environment may be a more significant factor. In addition, non-metallic materials such as polymers composites and ceramics are becoming widely applied and the principles of contact here are very dififerent from the metallic case. 

Radiation In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of I010 and 10n erg per gram include... 

Non-metallic Materials Carbides, carbon, ceramic fiber, ceramic, cermet, composite, cork, elastomer, felt, fiber, glass, glycerin, non-metallic bearing material, rubber (natural), rubber (synthetic), silicone, wood, leather. 

New methods to produce large quantities of mono-sized particles of nearly any inorganic material desired (e g., metals, oxides, silicates, sulfides) are needed for the processing of ceramics, electronic materials, and other engineered materials. 

The investigations on boundary lubrication used to focus on the friction elements made of metallic materials, and of steel in particular. This is, of course, due to the fact that a great majority of machines are built from metal and steel, but it is also because the hydrocarbon-based oils have been proven to be an extraordinarily good lubricant for metal surfaces. Unfortunately, the conventional oils are not so effective to lubricate the components made of other materials, like ceramics, rubbers, silicon, etc., so that the study on new types of lubricants suitable for such materials has attracted great attention in recent years. 

Ring and saddle packings are available in a variety of materials ceramics, metals, plastics and carbon. Metal and plastics (polypropylene) rings are more efficient than ceramic rings, as it is possible to make the walls thinner. 

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