KINETIC-PARAMETERS OF THE DISSOCIATION OF ND2FE14B DURING OXIDATION DETERMINED BY MOSSBAUER SPECTROMETRY

Powdered Nd-Fe-B permanent magnets were sieved to different particle s izes and oxidized in an ambient air furnace in the 150-300 degrees C t emperature range for different times. Transmission Mossbauer spectrome try was used to determine the dissociation kinetics of the Nd2Fe14B ph ase. The experimental curves were fitted according to the Ginstling-Br ounshtein model, taking into account the real distribution of particle size. The kinetic parameters, namely the activation energy E(a) and t he diffusivity pre-exponential factor D-0 were determined to be 1l0 kJ mol(-1) and 2.4 mm(2) s(-1) respectively, It appeared that the kineti cs parameters could be determined as well by considering ct simple the oretical single-particle analysis model. The influence of the particle size was studied in the case of this simple model.