Kinetic parameters of the dissociation of Nd2Fe14B during oxidation determined by Moessbauer spectrometry

Powdered Nd-Fe-B permanent magnets were sieved to different particle sizes and oxidized in an ambient air furnace in the 150-300 deg. C temperature range for different times. Transmission Moessbauer spectrometry was used to determine the dissociation kinetics of the Nd2Fe14B phase. The experimental curves were fitted according to the Ginstling-Brounshtein model, taking into account the real distribution of particle size. The kinetic parameters, namely the activation energy Ea and the diffusivity pre-exponential factor Do were determined to be 110 k J mol-1 and 2.4 mm2 s-1 respectively, It appeared that the kinetics parameters could be determined as well by considering a simple theoretical single-particle analysis model. The influence of the particle size was studied in the case of this simple model. (author)