Characterization of potassium aluminates in an α-Al2O3 matrix

Abstract

Potassium-rich aluminates have been observed along the grain boundaries of many commercial aluminas. The presence of alkali aluminates can seriously limit the operation lifetime of sodium vapor lamp tubing by increasing the rate of sodium leakage out of the tube. As part of an investigation into phase and interface structure within the K2O-Al2O3 system, high-purity α-Al2O3, seeded with small granules of potassium carbonate, was studied. In samples which were vacuum hot-pressed within a graphite die at 1400°C for 30min, the potassium (K) doping resulted in the precipitation of a spatially inhomogeneous array of K-rich aluminates. It has since been determined that the precipitation phenomenon was due to insufficient mixing of the starting powders. The potassium carbonate was therefore not originally distributed uniformly within the compacts and locally high K concentrations thus resulted.