INVESTIGATION OF PHASE FORMATION PROCESSES IN COMPOSITE Al₂O₃-Si₃N₄ CERAMICS WITH VARIATIONS OF SINTERING TEMPERATURE

The purpose of this work is to establish regularities in the processes of phase formation in Al₂O₃-Si₃N₄ ceramics in the annealing temperature range from 800 to 1500 °C, as well as to determine the effect of the phase composition of ceramics on strength properties. Interest in this class of composite ceramics is due to the possibility of using them as materials for inert matrices of dispersed nuclear fuel. The evaluation of the phase composition as a result of thermal annealing of the samples was carried out using the method of X-ray phase analysis. In the course of the analysis, the following phase transformations were established: Si₃N₄/Al₂O₃ → Si₃N₄/Al₂O₃-M/Al₂O₃-R → Si₃N₄/Al₂O₃-R/Al₂SiO₅ → Al₂SiO₅/SiO₂, according to which a change in the annealing temperature leads to polymorphic transformations of aluminum oxide with an increase in the annealing temperature, as well as the formation of a complex oxide phase of the Al₂SiO₅ type. At the same time, at an annealing temperature above 1400 °C, a transformation of the Si₃N₄ → SiO₂ type is observed, associated with the processes of decomposition of silicon nitride and its transformation into silicon oxide upon interaction with air during annealing. It was found that the primary processes during annealing of ceramics are the processes of structural ordering of samples, without a significant change in the phase ratio.

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