Ambient Gas Phase Research Articles

Effect of Composition of Kiln Atmosphere in the Firing of Refractory Oxides

The experimental results given in this paper show that (1) alumina lost oxygen when heated at 1400° to 1500°C. in water vapor but retained its weight unchanged when heated in air or in nitrogen and (2) kiln gases dissolved in a mullitic material at temperatures between 800° and 1200°C., and their solubility increased with temperature. These separate facts verify two theories that often have been suggested to explain the effect of the composition of the kiln atmosphere, viz., that (a) deviation from the stoichiometric composition occurs in stable ceramic oxides, such as Al2O3, at moderately elevated temperatures, even though the ambient gas phase does not affect the ceramic oxide in the ordinary chemical sense, and (b) lattice defects are caused by the solution of gases in the ceramic oxides. The frequency of lattice defects is assumed to depend on the surrounding gas phase.