BN Alloy Composites

4 Boron Nitride as a Component of Alloys 4.1.1.10.4.1 a-BN Alloy Composites 

Ceramics consisting of BN and TiB2 or ZrB2 show electric conductivity and are used in the evaporation of aluminium and as refractory joint sections for continuous casting [15 to 20]. If used as cathode material in aluminium electrolysis, sodium penetration at the grain boundaries has been observed [21]. Titanium alloys containing a-BN may be used as composite materials for prosthetics [22]. 

NbN/BN granular films are sensitive, high-speed detectors for pulsed far infrared radiation. These films are deposited on sapphire or quartz substrates by reactive radiofrequency sputtering of a split Nb/BN target in an Ar/N2 atmosphere. These devices can also be operated in the superconducting or resistive region critical temperatures range between 1.6 to 15 K, 

The phase equilibria in the ternary systems Fe-B-N, Co-B-N, and Ni-B-N have been determined from X-ray powder diffraction data and isothermal sections at 900°C and 1 atm Ar have been constructed. In all three systems the binary transition metal borides form two-phase equilibria with a-BN [28]. The phase equilibria are depicted in Fig. 4-29 to 4-31. 

A critical review of published thermodynamic data on the nitride formation reactions in liquid iron alloys recommends log K = -10.000n + 4.64 as the most reliable value for the equilibrium constant for the reaction BN(s)- B-l-N in the Fe-B-N system [29]. 

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