Boron nitride ceramics

Renewed interest in borazine derivatives has resulted from their possible application as precursors to boron nitride ceramics. For example, the inorganic analogue of styrene, (H->C=CH)B3NjH5i has been polymerized and decomposed to produce BN.72... 

Fig. 9. Boron nitride ceramics. BN ceramics with SiC addition for break rings in continuous ferrous metals casting. Hot-pressed and HIPed BN crucibles and electrical insulators. (Courtesy of ESK-Kempten, a company of WACKER-Chemie)...

Kovar, D., Thouless, M.D., and Halloran, J.W. (1998), Crack deflection and propagation in layered silicon nitride/boron nitride ceramics , J. Am. Ceram. Soc., 81, 1004-1012. 

When the stabilization of the initial material requires high-pressure conditions, specific cells have been developed, in particular for the elaboration of diamond and cubic-boron-nitride ceramics. ... 

Chem. Descrip. Boron nitride, ceramic binder Uses Lubricant coating, mold release agent for many forging, exfrusion, and hot pressing operations... 

Ceral P. See Propylene glycol stearate Ceral PA. See Propylene glycol stearate SE Ceral TG] Ceral TN. See Glyceryl stearate SE Ceral TP. See Propylene glycol stearate SE Ceralan . See Lanolin alcohol Ceralold356. See Paraffin Ceramax. See Phospholipids Ceram Blanche. See Boron nitride Ceramic fiber. See Aluminum (III) silicate (2 1) Cera microcristallina. See Microcrystalline wax Ceramide H03 . See... 

Combustion Synthesis of Boron Nitride Ceramics Fundamentals and Applications... 

Modified polyborazylenes have better solubility properties than the parent polyborazylene. Also, these new versions of polyborazylenes are melt-spinnable and have been shown to afford boron nitride ceramic fibers on thermal treatment [33]. 

Triammine-decaborane and NH3 give an amorphous product containing both NH and BH groups when reacted between 300 to 450°C. Below 850°C, pure BN of low crystallinity is formed, which converts to crystalline a-BN above 1180°C [59]. Boron nitride ceramics are also formed by pyrolysis of other decaborane-amine adducts [60 to 62]. 

A method was developed for the examination of boron nitride ceramics by automated ultrasonic inspection [57]. A comparison of sliding and abrasive wear mechanisms in ceramics and cemented carbides shows that a-BN ceramics are quite susceptible to indentation fracture [58]. Many more additional applications are reported in Section 4.1.1.10.8, p. 129. 

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]. 

The dimers of type 47 and the B-N-bonded polymers 46 and 48 have been prepared from the corresponding B-chloroborazines and HN[Si(CH3)3]2 or H3CN[Si(CH3)3]2. They are useful as poly(borazinylamine) precursors for boron nitride ceramics [60, 61]. 

Other ceramic materials that find some use in vacuum devices include silicon carbide- (SiC-) based substances and boron nitride ceramics. 

Narula, C. K., Schaeffer, R., and Paine, R. T. (1987) Synthesis of Boron Nitride Ceramics from Poly(borazinylamine) Precursors, J. Amer. Chem. Soc. 109,5556-5557. 

Abstract - Studies of the syntheses, properties and ceramic conversion reactions of the new processable borazine-derived polymer systems, poly(vinylborazine), poly(vinylborazine/styrene) and poly(borazylene), along with selected applications of these polymer precursors for the formation of boron nitride ceramics are described. 

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