Influence research of temperature heat treatment on the microstructure of alumina ceramics

Abstract

The JSC "URIR named after A. S. Berezhnoy" developed and introduced the technology of highly refractory alumina extra-dense ceramics. It is known that, the structure and properties of alumina ceramics in many cases depend on the temperature of its heat treatment, the holding time at the final temperature, the thermal unit, and a number of other factors. In order to study the processes of structure formation during of heat treatment the microstructure of alumina ceramic samples of two compositions (composition 1 with a moisture content of 30 %, as well as with dispersing and hardening additives, and composition 2 with a moisture content of 20 % only with dispersing additive) which were made by slip casting aqueous alumina slips based on reactive alumina α–from with Al2O3 content over 99 %, specific surface ~ 9 m2/g by electron microscopic analysis was studied. It was established that, after heat treatment at 1000 °C the beginning of sintering and recrystallization of corundum grains are observed, after heat treatment at 1200 °C take place packing of structure and recrystallization of α–Al2O3. After firing at 1400 °C the microstructure of samples composition 1 is represented to a large extent by crystals of tabular corundum with a particle size ~ 0.5—5.5 μm, predominant — ~ 2.5—3.0 μm. After firing at 1400 °C the microstructure of samples composition 2 is represented — by individual particles of a rounded and oval form with a size of ~ 0.5—3.5 μm, predominant — ~ 1.5—2.0 μm which are interconnected by intercrystalline layers. The microstructure of alumina ceramic samples of both compositions after firing at 1500 °C is similar and is composed of recrystallized corundum grains with a size of ~ 0.5—5.5 μm, predominant — ~ 1.5—2.0 μm, among which there are also larger α–Al2O3 grains, with a size of ~ 2—8 μm. After firing at 1580 °C the microstructure of samples is represented by a dense fine-grained structure of well-formed practically defect-free corundum grains, with a size of ~ 0.5—3.0 μm, among which grains of ~ 5—10 μm.