Beryllium Oxide Whiskers and Platelets

Abstract

Beryllium oxide platelets and whiskers have been grown by heating beryllium metal in a silica furnace tube and boat with a hydrogen atmosphere for 16 hr at 1500°C. Three distinct types of whiskers formed: one type was parallel to the crystallographic c axis, another in the basal plane ([1̄010] direction), and the third in an intermediate direction (approximately the [3̄032] direction). The first type are called ``flagpole'' whiskers because they are topped by small balls of metallic appearance; they grew at the site of the original metal charge. These whiskers have pores along their axes, except in rare instances in which, instead of a pore, a whisker may have disconnected voids along its axis. Their axial growth rate was not observed directly, but was at least 0.02 μ/sec. The other two types have the more normal whisker appearance and grew at a distance of from 2 mm to 2 cm from the original metal charge. They have no pores or voids. Their growth rate was at least 0.2 μ/sec. The larger platelets, which grew in the vicinity of the normal whiskers, were long in [1̄010] direction and wide in the [0001] direction. Some of the very smallest platelets grew in the basal plane. A mechanism of growth for the flagpole whiskers is proposed. It is assumed that molten beryllium balls are splashed onto a BeO substrate, and then react with water vapor to form whiskers which push the balls away from the substrate. The normal whiskers and platelets grew at a distance from the beryllium metal, and therefore their growth involves a vapor transport mechanism.