Nonmetallic materials diamond

A number of nonmetallic materials are called high thermal conductivity materials. The most notable of these is diamond, with a thermal conductivity of 2000 Wm K. All of the others have a dia-mond-Uke stracture, and include boron nitride, BN, and aluminium nitride, AIN (Table 15.2). 

In the following sections, we look at several nonmetallic materials with applications in modem technology. We begin with a discussion of the different allotropes or forms of carbon—diamond, graphite, and the fullerenes—where research has produced some exciting discoveries (Section 13.4). The fullerenes are recently discovraed molecular forms of the element carbon, in which the carbon atoms form hollow balls and tubes that may make them important as catalysts or possibly as drug-delivay mataials. Diamond shows promise as a material that might supersede silicon in its role as a matmal for sohd-state electronics. Silicon and diamond can act as semiconductors, which we discuss in Section 13.5. We end the chapter with sections on silicon, silica, and silicates (Section 13.6), ceramics (Section 13.7), and finally composites (Section 13.8). 

Every nonmetallic material becomes opaqne at some wavelength, which depends on the magnitude of its E. For example, diamond, having a band gap of 5.6 eV, is opaque to radiation having wavelengths less than abont 0.22 p,m. 

Table 3 summarizes the properties of the so-called nonmetallic hard materials, including diamond and the diamondlike carbides B C, SiC, and Be2C. Also iacluded ia this category are comadum, AI2O2, cubic boroa nitride, BN, aluminum nitride, AIN, siUcon nitride, Si N, and siUcon boride, SiB (12). 

Defects that introduce extra electrons, or that give missing electrons or holes , have a large influence on electronic conduction in nonmetallic solids. Most semiconductor devices use doped or extrinsic semiconductors rather than the intrinsic semiconduction of the pure material. Doping Si with P replaces some tetrahedrally bonded Si atoms in the diamond lattice (see Topic D2) with P. Each replacement provides one extra valence electron, which requires only a small... 

Examples of materials falling into this class include salts such as sodium chloride, diamond, sapphire and other similar minerals, and solid nonmetallic elements such as krypton. The softer members of the class are generally found to obey Amonton s laws with frictional coefficients falling in the range of 0.5-1.0. The harder, more brittle substances such as sodium chloride tend to suffer extensive surface damage due to cracking but still hold more or less to normal behavior. 

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