Other Oxide Ceramics

Pure sintered magnesium oxide ceramics have little importance compared with magnesium oxide-containing refractory products. They are used as high temperature materials. 

Nonporous spinel oxide ceramics of MgAl204 are notable for their very good high temperature corrosion resistance to alkaline media. Sintered yttrium oxide exhibits still better corrosion resistance at high temperatures (Y2O3 melting point ca. 2400°C), but its utilization possibilities are limited by its high price. 

In recent years sintered titanium(IV) oxide has been utilized in addition to aluminum oxide in the textile industry in which it is utilized as an abrasion-resistant material for thread guides. 

A new oxide ceramic solid electrolyte is so-called 3-aluminum oxide, a compound of AI2O3 with 5 to 10% Na20. Materials of this type are currently being evaluated in sodium-sulfur batteries. 

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Two approaches can be taken to utilize other oxide ceramic membranes for separations involving small molecules or ions. Either the pores of the membrane can be partially plugged by depositing insoluble materials therein (13,14) or membranes can be prepared using precursor sols which contain extremely small particles. The... 

Aluminum oxide, AljOj, commonly referred to as alumina, is by far the most common substrate material used in the microelectronics industry because it is superior to most other oxide ceramics in mechanical, thermal, and electrical properties. The raw materials are plentiful, low in cost, and amenable to fabrication by a wide variety of techniques into a wide variety of shapes. 

Besides the chemical industry, sihcon is used as a powder in the ceramics (qv) industry for the production of sihcon carbide and sihcon nitride parts (see Advanced ceramics). Sihcon powder is also used as an explosive for defense apphcations and in the refractory industry for plasma spraying with other oxide mixtures (see Refractory coatings). 

One final note is appropriate for this section. Dne to the fact that many oxide ceramics are used as insulating materials, the term thermal resistivity is often used instead of thermal conductivity. As will be the case with electrical properties in Chapter 6, resistivity and conductivity are merely inverses of one another, and the appropriateness of one or the other is determined by the context in which it is used. Similarly, thermal conductance is often used to describe the thermal conductivity of materials with standard thicknesses (e.g., building materials). Thermal condnctance is the thermal conductivity divided by the thickness (C = k/L), and thermal resistance is the inverse of the prodnct of thermal conductance and area R = 1/C A). 

Refractive index values vary from 1.0003 for air to over 2.7 for some solid oxide ceramics. Silicate glasses have a much narrower range of valnes, from abont 1.5 to 1.9. The refractive indices (or indexes) of other materials can be fonnd in Appendix 9. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

Ceramics Materials such as pottery made from inorganic chemicals by high-temperature processing. Other modern ceramics include zirconium oxide and silicon nitride. 

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