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Synthesis of Nanocrystalline Silicon Carbide Powder by Carbothermal Reduction.-A solution of sugar in silica sol is used as parent material for the manufacture of nanocrystalline SiC powders. The conversion is performed in two steps. First the sugar is converted to carbon particles and secondly the silica carbon mixture is heated up to the approved reaction temp. between 1550 and 1800 • C under an Ar pressure of 180 kPa. The oxygen content of the powder is ¡ 0.5 wt.% and the particles are ¡0.5 µm with crystallites ¡100 nm and specific surface areas in the range of 20-30 m 2 /g. -(MARTIN, H.-P.; ECKE, R.; MUELLER, E.; J.

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SubmicroStructure of Silicon Carbide Derived from Poly(methylchlorosilane).-Poly(methylchlorosilane) characterized by Si domains in the macromolecules is pyrolysed at 165 • C. SiC, Si, and C areas of nanoscale dimensions are detected by Raman spectroscopy at the resulting structure. The Si and C domains are extremely fine dispersed and property originated from the molecule structure of the polysilane. Furthermore the relation between molecular structure of the polysilane and SiC is described. The investigations show patterns corresponding to the β-SiC polytype. -(MARTIN, H.-P.; IRMER, G.; MUELLER, E.; J. Eur. Ceram. Soc. 18 (1998) 3, 193-199; Inst. Keram. Werkst.,

Crystallization Behavior and Polytype Transformation of Polymer-Derived Silicon Carbide.-The crystallization behavior of amorphous SiC material derived from polysilane precursors is studied by XRD, TEM, 29Si MAS NMR, and Raman spectroscopy. At 1200 • C crystallization of β-SiC crystallites starts and different polytypes are identified above 1400 . degree.C. A high density of stacking faults, which cover large areas in the crystallites, promotes the formation of α-polytypes which are finally reconverted into β-SiC. -(MARTIN, H.-P.; MUELLER, E.; IRMER, G.; BABONNEAU, F.; J. Eur.