Steam‐enhanced calcium segregation in dense alumina

Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) have been used to study surface segregation of calcium in dense alumina. Thin (∠1 mm) disks ?99% alumina were exposed to saturated steam at 5.3×106 Pa or 750 psia (266 °C) for periods ranging from 1 to 48 days. SEM examination of the surface after exposure revealed growth of calcium‐ and silicon‐rich structures at and near the surface. Auger depth profiles of the exposed specimens showed that the amount of calcium at the surface increased with increasing exposure time of up to 12 days. For longer exposures, the calcium‐rich area began to extend from the surface into the bulk.