Dense γ-Alon Materials Derived from SHS Synthesized Powders

Abstract

Dense polycrystalline aluminium oxynitride with spinel structure, γ-alon, is noted for its excellent thermal properties, high-temperature mechanical properties, low dielectric constant, thermal expansion coefficients and intrinsic transparency extending from ultraviolet to mid-infrared wavelengths. The conventional way for synthesis of γ-alon powder is high-temperature reaction of aluminium nitride and corundum in pure nitrogen or a vacuum. The dense materials are made by reactive pressureless sintering or hot-pressing of a powder compact. This work is focused on preparation of γ-alon materials derived from SHS synthesized powders. The powders for sintering were synthesized from mixtures of aluminium and corundum powders of different proportions. The products of the SHS synthesis were composed mostly of γ-alon and aluminium nitride with small amount of non-reacted substrates. Ground powders were hot-pressed at 1750, 1850 and 1950°C for 1 h under 25 MPa in nitrogen flow. Such procedure allowed dense material composed of pure γ-alon with good mechanical properties to obtain.