Investigation of the influence of the annealing atmosphere on the structure of powders after recycling Nd-Fe-B magnets by solvothermal process

The effect of annealing under vacuum and argon atmospheres on the structure of a Nd-Fe-B powder recycled by a solvothermal treatment was investigated by means of X-ray diffraction and Mössbauer spectrometry. The results show that vacuum annealing at 300 °C is accompanied by the complete desorption of hydrogen from the magnetic Nd2Fe14BHx phase that was obtained after the solvothermal treatment. Vacuum annealing above 650 °C leads to the decomposition of Nd2Fe14B into iron and Fe2B. Annealing in argon atmosphere at 300 °C has almost no effect on the powder and the desorption of hydrogen from the Nd2Fe14BHx phase is partial. Argon annealing above 650 °C leads to the oxidation of the Nd2Fe14B phase.