Synthesis of aluminum oxynitride from MoO3/Al/AlN mixtures by SHS metallurgy

Abstract

This work investigates the regularities of autowave chemical transformation of MoO₃/Al/AlN mixture, gravity separation of its combustion products, and formation of composition and structure of end product (aluminum oxynitride). It is demonstrated that the mixtures of MoO₃, Al and AlN are capable of burning in wide ranges of reagent ratios. In the general case, this process is composed of three consecutive stages: stage 1—combustion and chemical transformation of MoO₃, Al, and AlN mixture into two-phase melt of end products (autowave synthesis); stage 2—gravity separation of combustion products (metallic and oxide phases), where two layers are generated: upper layer of “light” oxynitride (Al₂O₃–AlN) and bottom layer of “heavy” intermetallic compound (Mo–Al); stage 3—cooling and generation of phase composition and crystalline structure of metallic and oxide layers. It is established that variation of the aluminum content in the initial mixture at constant content of nitride additive significantly influences the combustion and autowave chemical transformation of the mixture and the phase composition and structure of the end product (aluminum oxynitride). Optimum compositions are determined for obtaining aluminum oxynitrides with high nitrogen content (up to 6–9 wt %) and impurity content (Al₇O₃N₅ and AlN) below 3 wt %. The obtained cast aluminum oxynitride and method of its production are promising for production of high-strength transparent ceramics.