Interaction of Nitrogen with Aluminum Oxide during Melt Growth of Corundum Crystals

Abstract

We examine possible interaction of molten aluminum oxide with a controlled (nitrogen) atmosphere in the pressure range 10⁴ to 10⁵ Pa at a temperature of 2400 K. Stochastic simulation is used to identify gas phase components and determine their concentration. We analyze the main chemical reactions that determine processes in the system. The results suggest that, even though neither molecular, nor atomic nitrogen directly interacts with molten aluminum oxide in the conditions under consideration, it is capable of entering into many chemical reactions in the form of its oxides or together with Al-containing dissociative melt vaporization products. We have calculated pressure ranges where the reactions under consideration and reverse reactions—aluminum oxide formation and precipitation in the melt—are possible on account of gas phase processes. Analysis of these processes makes it possible to optimize conditions for the use of nitrogen as a controlled atmosphere, the most important of which is to reduce the concentration of (atomic and molecular) oxygen and that of AlO₂ oxidizing oxide, which destroy the material of crystal growth system.