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 s pecific surface resulting from decrepitation of the sample is the most impo rtant parameter controlling the hydrogen diffusion process. As it follows f rom the presented analysis of the experimental weight gain curve and the th eoretical one for a hulk sample, decrepitation accelerates the diffusion ra te 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. O n 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. (C) 2000 Elsevier Science S.A. All rights reserved.