Abstract

Specific features of the synthesis of sialons (SiAlON) in the Si–Al–O–N system by firing at 1600–1700°C in a nitrogen atmosphere of mixtures of different initial compositions corresponding to the same composition of the final product Si₃Al₃O₃N₅ have been studied. β-Sialon was synthesized from reaction mixtures based on crystalline silicon and aluminum nitrides and amorphous highly dispersed hydrated oxides—(1) AlN + SiO₂(sol), (2) Si₃N₄ + Al₂O₃(sol), and (3) AlN + Si₃N₄ + Al₂O₃(sol)—obtained by applying sols based on silicon or aluminum alkoxides (based on the β-sialon stoichiometry) to the surface of nitride powders by the sol-gel method. It has been demonstrated that β-Si₃Al₃O₃N₅ can form in the reaction at 1600°C of highly dispersed mixed xerogels made of silicon and aluminum alkoxides—(4) (SiO₂ + Al₂O₃) (mixed sol)—with molecular nitrogen without the participation of the initial nitrides. The influence of the starting composition of xerogel mixtures and synthesis conditions on the phase composition and morphological features of sialons obtained in one stage of calcination in a nitrogen atmosphere has been studied by thermogravimetry, X-ray powder diffraction analysis, and electron microscopy. It has been shown that the proposed reactions of the formation of sialons involving crystalline nitrides, xerogels, and molecular nitrogen are related to reduction–nitridation reactions, in which the reducing agents are organic products of hydrolysis of silicon and aluminum alkoxides and their pyrolytic decomposition in a nitrogen atmosphere.