Boron carbide-transition metal diboride

Boron Carbide-Transition Metal Diboride Ceramics... 

Most borides are chemically inert in bulk form, which has led to industrial applications as engineering materials, principally at high temperature. The transition metal borides display a considerable resistance to oxidation in air. A few examples of applications are given here. Titanium and zirconium diborides, alone or in admixture with chromium diboride, can endure temperatures of 1500 to 1700 K without extensive attack. In this case, a surface layer of the parent oxides is formed at a relatively low temperature, which prevents further oxidation up to temperatures where the volatility of boron oxide becomes appreciable. In other cases the oxidation is retarded by the formation of some other type of protective layer, for instance, a chromium borate. This behavior is favorable and in contrast to that of the refractory carbides and nitrides, which form gaseous products (carbon oxides and nitrogen) in air at high temperatures. Boron carbide is less resistant to oxidation than the metallic borides. 

The electric refractory materials in this book are classified into metallic ceramics (i.e., transition metal carbides, nitrides, and diboride) and wide-gap semiconductors (i.e., diamond, SiC, GaN, BP, AIN, BN, and high-boron base semiconductors. 

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