Features of Production and High-Temperature Oxidation of SHS Ceramics Based on Zirconium Boride and Zirconium Silicide

Аннотация

This article is devoted to the investigation into the combustion kinetics and mechanism of reaction mixtures in Zr–Si–B and Zr–B systems formed according to the forced SHS-pressing of compact ceramic materials, as well as to studying their heat resistance. It is shown that dependences of the combustion temperature and rate on the initial temperature (T₀) for compositions in the Zr–Si–B system are linear; i.e., staging of chemical reactions of formation of zirconium diboride and disilicide remains invariable with an increase in T₀. The values of effective activation energy of SHS process, which evidence the leading role of the reaction interaction of zirconium with boron and silicon in the melt, are calculated. Staging of chemical transformations in the combustion wave of the Zr–Si–B system is investigated: initially the ZrB₂ phase is formed by crystallization from the melt, and then the ZrSi₂ phase appears with a delay of 0.5 s; unreacted Si crystallizes after 1 s. The phase composition of synthesis products, in which the main component is ZrB₂ diboride, and zirconium disilicide, Si, and ZrB₁₂ boride are contained depending on the composition of the reaction charge, is investigated. Compact samples having high hardness and low residual porosity are fabricated according to forced SHS-pressing technology. High-temperature oxidation of SHS samples results in the formation of SiO₂–ZrO₂–B2O₃ oxide films and ZrSiO₄ complex oxide on their surface depending on the composition, which serve the effective diffusion barrier and lower the oxidation rate.