Formation of Si₃N₄ coating on SiC substrate by gas transporting self‐propagating high‐temperature synthesis with the addition of NH₄Cl

Abstract

Under the urgent demand of high-performance silicon nitride substrate (Si 3 N 4 ), this paper reports a new gas transporting self-propagating high-temperature synthesis technology (GTST) to form Si 3 N 4 coating on silicon carbide (SiC) substrate with the addition of NH 4 Cl, which may partly be a candidate of high-performance Si 3 N 4 substrate. The effect of NH 4 Cl on the formation of the Si 3 N 4 coating is investigated, and the reaction mechanism with the participation of NH 4 Cl is discussed.The addition of the NH 4 Cl promotes the formation of the compact Si 3 N 4 coating with a thickness of 20-80 μm on both sides of SiC substrate. During the reaction, NH 4 Cl acts as a carrier to convert solid and liquid Si particles into gas phase SiCl 4 , and transport it to SiC substrate. Finally, SiCl 4 is nitride into Si 3 N 4 coating under the higher temperature generated by the combustion wave. Moreover, the research mechanism can provide a guide for other complex ceramic coatings by GTST.

Degradation mechanism of near stoichiometric SiC fibers after air and Ar–H2O–O2corrosion at 1000–1500°C

“…For example, HfC, 41 ZrC, 42 ZrB 2 , 43 and TiB 2 44 coatings with their insulating properties are established on the surface of SiC fibers. At present, these types of anti‐oxidation coatings have been widely used in carbon and silicon carbide matrix composites due to their excellent thermal matching performance with the matrix; In addition, Yb 2 O 3 , 45 Y 2 O 3 , 46 B 4 C, 47 Al 2 O 3 , 48 and Si 3 N 4 49 and other materials have a significant inhibitory effect on cristobalite. If appropriate processes can be taken to prepare them as coatings for SiC fibers or make their fibers surface modified and doped, it is believed that they can also inhibit the crystallization of the fiber oxide layer and improve the crystallization temperature and oxidation performance.…”