Surface oxidation behavior of MgNd alloys

Abstract

The oxidation kinetics of MgNd alloys oxidized in pure O 2 at high temperatures has been investigated. The results revealed two stages of the reaction: A fast initial oxidation was followed by a slow oxide growth with a parabolic kinetics. For MgNd alloys (Nd = 25 wt.%), the oxidation rate increased with the enhancement of the oxidation temperature. A sudden ignition was found for this alloys oxidized at 873 K up to about 80 min. Moreover, the increase of the Nd content would harm the oxidation resistance of the MgNd alloys. By Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it was found that a triplex structure of oxide film formed. The outer layer was composed of MgO, Nd 2O 3 and Nd(OH) 3, the middle layer mainly consisted of MgO and Nd 2O 3, and the inner layer was the transitional layer made of MgO, Nd 2O 3 and the content of the substrate. The protective oxidation was associated with the formation of the dense Nd 2O 3/MgO layer during isothermal oxidation process. The oxidation mechanisms for the formation of oxide film are discussed.