Pt-induced formation of aluminium oxynitride whiskers during carbothermal reduction of alumina in nitrogen

Abstract

The effect of the addition of platinum on the carbothermal reduction of alumina in an argon–nitrogen gas mixture at 2000 K was studied by transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) methods. The presence of Pt (2 mass%) did not influence the major reaction product (hexagonal AIN) but it induced the formation of an additional minor phase, cubic γ-AION whiskers. The whiskers were 80–100 nm thick and a few pm long and always contained a Pt particle at one end. The Pt particles were single crystals with well developed faces oriented such that (111) Pt was parallel to (111)γ-AION. It is suggested that the γ-AION whiskers grew via gas-phase epitaxy on the Pt crystallites. The cubic (spinel) structure of the whiskers and the parallel (111) Pt–(111)γ-AION orientation is preferred due to a very low structure misfit (0.9%) at the interface.