Characterisation of oxidation products of modified Nd–Fe–B type magnets

Abstract

In order to study the influence of Co addition on oxidation behaviour, magnets with the compositions Nd 16Fe 76B 8, Nd 16Co 3Fe 73.3B 7.7, Nd 16Co 5Fe 71.5B 7.5, Nd 16Co 7Fe 69.6B 7.4, Nd 16Co 10Fe 66.9B 7.1, Nd 14Dy 3Co 9.7Fe 66.4B 6.9, Nd 13.9Dy 3Co 9.7Fe 66.2B 6.9Zr 0.3 and Nd 13.9Dy 3Co 9.7Fe 66.2B 6.9V 0.3 in powder and solid pellet forms were oxidised at 400 °C for 96 h. The resultant phases were identified using X-ray diffraction (XRD) and Mössbauer spectroscopy. α-Fe 2O 3 is the main final oxidation product of the iron content of these magnets, while Fe 3O 4 is the intermediate phase of this oxidation procedure. In addition the presence of several Nd oxides, as well as Dy oxides in the compositions with Dy additions was confirmed in all samples. B seems to prefer to react with Nd with the formation of oxide phases, while a minority Fe 2B phase is also detected in the powder samples. A delay of the oxidation process is found for the case of compact pelletised samples, and this is extended for those samples containing Dy in their structure.