The high temperature (T~1000 K) oxidation of molybdenum

The oxidation of Mo was observed as a side effect of fundamental studies of high temp. oxidation of metals inside a hot stage environmental scanning electron microscope. The oxide grain on the rim of the Mo shield exhibited a complex oxide morphology composed of whiskers and oxide petals attached to the whisker tips. The whiskers were approx 0.4 mu m thick, 50 mu m long, and often exhibited secondary branches. Upon entry of the oxygen into the specimen chamber, MoO sub 3 whiskers grew very quickly and then the oxide petals grew and attached themselves to the whisker tips. After long periods, the petals grew to a size of approx 10 mu m and new petals appeared underneath the initial oxide to develop a stack of oriented oxide grains. Such oxide whiskers grow by a vapour--liquid--solid mechanism. The growth of oxide petals attached to the initial whiskers was then achieved by an evaporation--condensation mechanism. 9 ref.--J.L.B.