Abstract
Chemically vapour-deposited (CVD) Si3N4-TiN composite (a plate with the maximum thickness of 1.9 mm) has been prepared on a graphite substrate using a mixture of SiCl4, TiCl4, NH3 and H2 gases. The CVD was carried out at deposition temperatures,T dep, in the range of 1050 to 1450 ° C, total gas pressures,P tot, from 1.33 to 10.7 kPa and gas flow rates of 136 (SiCl4), 18 (TiCl4), 120 (NH3) and 2720 (H2) cm3 min−1. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of Tin. The structure of the Si3N4 matrices varied from amorphous (initially) to theα- andβ-type, with increasingT dep. Most of theα- andβ-type deposits had a preferred orientation (001) parallel to the deposition surface. While the deposition surface of the amorphous deposits showed a pebble structure, the surfaces of theα- andβ-type deposits were composed of various kinds of facets. The heat-treating experiment suggested thatβ-Si3N4 obtained in the present work was formed directly via a vapour phase, and not from crystallization of amorphous Si3N4 or from transformation ofα-Si3N4.
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