Microstructure Observation of Oxidation of Nd-Magnet at High Temperatures

摘要

There is a growing interest in recycling/recovery of rare earth elements from permanent magnets. A number of processing techniques are currently being developed but highly sensitive to the oxidation state of rare earth in the magnetic waste. This study investigated the microstructural changes of thermal oxidation of an Nd-based magnet and the behaviour of its oxides under high temperature recycling/recovery process. XRD analyses were carried out on a powdered sample (～10 μm) heated to 1273 K. SEM-EDS analysis was conducted on the heated bulk samples to provide detailed metallographic information. Metallographic analysis revealed multiple oxidation zones where the outer scale did not effectively inhibit further diffusion of oxygen. The thickness of this scale was found to be grown quite rapidly at temperatures higher than 973 K. The results indicated that the micro-mechanism of oxidation at higher temperature are more complex than at temperature below 773 K.