Boride and Carbide Ceramics Containing a-BN

B4C/BN/Y2O3 refractories have been made by hot-pressing the material is stable toward molten metal chlorides, CI2, and molten aluminium [224, 308, 309]. Most preparative procedures for such ceramics originate from precursors that are formed from H3BO3 and glycerol (sintering in N2 above 1300°C) [225, 226] or from [(1,2-diaminoethane)-BioHi2]n or its A/-methyl-ated derivatives which are pyrolyzed in a stream of NH3 [227]. Boron nitride appears merely as an impurity or as a minor additive in other B4C composites [228 to 231]. 

TiB2 and ZrBg ceramics with admixed a-BN, besides their corrosion resistance toward molten Al, show electrical conductivity, and are primarily used in the (thermal) evaporation of aluminium and in the continuous casting of steel. Other materials contained in these composites include SiC, AIN, Si, B4C, and Y2O3 [232 to 241]. Sinters based on TiC and containing a-BN have high hardness and fracture toughness and low electrical resistivity [286]. 

The solubility of boron nitride in (3-SiC is small (0.5 to 1 mol%) under conventional hot-pressing conditions (35 MPa, below 2250°C) a-BN stabilizes 3-SiC and low hexagonality polytypes [242, 243]. The microstructure of BN-SiC composites as studied by transmission 

The different types of boron nitride composites cited can be reinforced with fibrous materials such as titanium alloy fibers [287], Si/Zr oxynitride fibers [288], SiOg/TiOg/ZrOg fibers [289], and carbon fibers [290 to 292, 313] (see also Section 4.1.1.10.1, p. 58). BN-containing oxide and carbide ceramics are used to protect graphite from being attacked in metallurgical processes [293 to 295]. Porous ceramics and ceramic foams which can be infiltrated either with metals or lubricants may contain a-BN or are produced in boron nitride ceramic molds [296 to 299]. 

(Japan. Kokai Tokkyo Koho 60-54978 [1985] from Koho 60-63157 [1985] from C.A. 103 [1985] 

---