Nonoxide sintering

Y. Murata and R. Smoak in S. Somiya and S. Saito, eds., Proc. Int. Sjmp. of Factors in Densification and Sintering of Oxide and Nonoxide Ceramics, Gakujutsu Biinken Fukyu-Kai, Tokyo, 1979, p. 382. 

Tungsten carbide from tungsten chloride, methane, and hydrogen is another example of nonoxide ceramic powder preparation . The reaction of the vapors takes place in heated tubes, dc plasmas or rf plasmas. The preparation of fine particles for high sintering reactivity is important in these nonoxide ceramics, which are otherwise difficult to density. 

The resulting microstructure for each of these cases is shown in Figure 14.33. The process of LPS is also important in forming dense powder compacts of nonoxide ceramics such as the nitrides. In these ceramics, where the bonding is predominantly covalent, atomic mobility is limited and sintering to high density is difficult in the absence of a liquid phase or without the application of high pressure. 

Nonoxides can be formed from polymeric precursors that are already mixed in the right proportion on an atomic scale. The atoms in silicon carbide are bonded with covalent bonds and are not mobile. Similar to most other carbides and nitrides SiC is difficult to sinter and so has slow solid state reactions even at high temperatures. A good precursor for solid state formation of SiC is the polymer polycarbosilane, which is made at 450°C from polysilanes formed from dimethyl-dichlorosilane and sodium ... 

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