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Turbostratic boron nitride (t-BN) powder prepared by mechanical grinding of hexagonal boron nitride (h-BN) under the nitrogen atmosphere with the oxygen concentration less than 1 ppm was consolidated by spark plasma sintering (SPS). The turbostratic structure was maintained after the consolidation, which was characterized by XRD, Raman and IR spectra. The t-BN consolidated without any additives at 1900°C for 10 min under applied pressure of 100 MPa showed a bulk density of 95%. The bending strength, Young's modulus and Shore hardness of the consolidated t-BN were 72 MPa, 259 GPa and 117 Hs, respectively. They were much higher than those of conventionally consolidated h-BN. On the other hand, the thermal conductivity was 3 W/mK and much lower than the compact of h-BN.

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Nanometric silicon carbide (SiC) powder (~5 nm) with a stacking-sequence disordered structure (SD-SiC), synthesized from elemental powders of Si and C, was investigated by microscopic and several spectroscopic methods. The structure of SD-SiC was characterized by transmission electron microscopy (TEM), 13 C, and 29 Si-NMR, and by infrared (IR), Raman, and X-ray photoelectron spectroscopy (XPS) methods. TEM characterizations showed relatively large deviations of the lattice parameters in the as-synthesized SiC, indicative of the presence of stacking-sequence disorder. IR analysis showed a weaker Si-C bond in the SD-SiC than in the 3C-SiC. XPS determinations showed that C and Si in SD-SiC are similar to those in 3C-SiC. Broader peaks of 29 Si and 13 C MAS-NMR also indicate that the structure of SD-SiC is different from that of 3C-SiC. Raman spectroscopy exhibited activities for the crystalline polytypes and the amorphous of SiC but lack of them for the SD-SiC. The inactivity of Raman spectroscopy for the SD-SiC along with large deviation of the lattice constant and the extremely broad X-ray diffraction peaks would indicate that SD-SiC is a possible intermediate state between conventional polytype SiC and amorphous SiC, that is, a possible new type of SiC.