Oxidation sizing experiments on neodymium-iron-boron magnet powders

Abstract

Rare earth (NdFeB-based) permanent magnets can be manufactured by a powder processing route. Reliable methods for characterisation of the size and size distribution of the powders are thus required. Oxidation experiments on NdFeB powders showed that the rate of oxidation was dependent on powder size. Fine powders oxidised more quickly than coarse powders. The oxidation process was monitored by measurement of change in mass in a thermogravimetric analyser (TGA) and by X-ray diffraction experiments on oxidised and partially-oxidised powders. A theoretical expression for the change in mass during oxidation was developed to compare with experimental measurements.