NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

Abstract

The oxidation behaviour of the Nd2Fe14B phase is followed by nuclear magnetic resonance of Nd16Fe76B8 powders oxidized in ambient air at temperatures between 200 and 650 °C. It is shown that upon oxidation in the 200-400 °C temperature range, the destruction of the Nd2Fe14B phase leads to the formation of inhomogeneous or very small size α-Fe grains at the surface of the Nd2Fe14B grains, in agreement with previous investigations of the same powders. At 400 °C for long treatment times or at higher temperature, the α-Fe phase is oxidized and almost completely disappears at 500 °C. This validates the results of previous qualitative and quantitative Mössbauer studies of the oxidation of the Nd2Fe14B phase.