Formation of rare earth hydroxide nanotubes and whiskers as corrosion product of LaNi5-type alloys in aqueous KOH

Abstract
Mm(OH)3 (Mm = mischmetal) single crystalline needles with [001] growth axis form upon exposure of MmNi5-substituted alloys to aqueous KOH. Crystal structure, chemical composition and morphology of the needles are studied by means of scanning electron microscopy and quantitative transmission electron microscopy. The needles can be either solid (whiskers) or hollow (nanotubes). Their morphology and growth kinetics are studied as a function of immersion temperature, stirring rate of the aqueous KOH electrolyte and presence of tracer. Based on the observations, a model mechanism is developed for their growth.