BN Composites

Figure 7.38 Schematic diagram of experimental apparatus used to form SiC/BN composite particles by gas-phase synthesis on a substrate (a). From Carbide, Nitride, and Boride Materials Synthesis and Processing, A. W. Weimer, ed., p. 336. Copyright 1997 by Chapman Hall, London, with kind permission of Kluwer Academic Publishers.

SiC-BN composites show good thermal conductivity. The electrical resistivity depends on the BN content and can be adjusted from a few Q/cm to more than 1010 Q/cm. When the SiC content of the composites is high, the composites can be used as cutting tools [135]. BN additions reduce the friction coefficient. Thus these composites are used for sliding parts [136],... 

Effect of the h-BN content on the bending strength of Si3N4/h-BN composites. 

SEM micrographs of Si3N4/h-BN composites with different addition of h-BN, showing (a) Si3N4 (b) 5 vol% h-BN/Si3N4 ... 

Figure 2.35. Examples of indentation processes to determine surface hardness. Shown are (a) Vickers indentation on a SiC-BN composite, (b) atomic force microscope images of the nanoindentation of a silver nanowire, and (c) height profile and load-displacement curve for an indent on the nanowire. Reproduced with permission fromNanoLett. 2003, 3(11), 1495. Copyright 2003 American Chemical Society.

Hollow BN fibers are made by depositing a coating of BN on carbon fibers, heating in an oxidizing atmosphere to form CO or CO2, and leaving a BN coating. The reaction between BF3 and NH3 at 1200-1400°C may be used . Yarn and BN/BN composites can be made with similar techniques (see 17.3.5.6). 

FABRICATION AND PROPERTIES OF SijN4/BN COMPOSITE CERAMICS BY PRESSURELESS... 

Fabrication and Properties of Si3N4/BN Composite Ceramics by Pressureless Sintering... 

Figure 3. FESEM micrographs of Si3N4/BN composites with various amounts of Yb203 (a) 2wt%, (b) 4wt%, (c) 8wt%, and (d) 15wt%...

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