Growth of Oxide Whiskers On Metals at High Temperature

Abstract

Growths of α-Fe 2 O 3 whiskers formed on pure iron in oxygen at 400∼850°C were studied by electron microscopy and diffraction using specimens cut off successively from a uniformly oxidized wire which was heated consecutively to avoid ill effect of contamination condensed during electron-microscopic observation. Whisker grows at the tip by surface diffusion of molecules from base to tip. Axial growth at a fixed temperature is approximately given by: l = k t 0.3 , where k , a constant, depends on temperature and has a maximum at 700∼750°C. Initial diameter corresponds to that which gives the minimum strength necessary to keep whisker shape at the growth temperature. A whisker has an axis parallel to hex , becoming thereafter blade-shaped crystal parallel to (001). Further growth at the tip of a blade-shaped crystal occurs at those sites which are in a plane parallel to (001), and similar growth happens on a fracture surface of a mechanically truncated crystal, too.