The influence of decrepitation on the diffusion kinetics of hydrogen in Nd–Fe–B

The decrepitation process and related changes in the sample temperature are analysed to explain the experimentally observed weight gain curve of a Nd–Fe–B sample due to hydrogen uptake. It is shown that the expansion of the specific surface resulting from decrepitation of the sample is the most important parameter controlling the hydrogen diffusion process. As it follows from the presented analysis of the experimental weight gain curve and the theoretical one for a bulk sample, decrepitation accelerates the diffusion rate by five orders of magnitude. A one-dimensional model of decrepitation is presented to discuss in detail hydrogen diffusion into an Nd–Fe–B alloy. On the basis of this simple model the experimental weight gain curve and the particle size distribution of the decrepitation output are reproduced with a reasonable accuracy.