Hydrogen decrepitation

McGuiness, P. J., Harris, I. R., Rozendaal, E., Ormerod, J. Ward, M. (1986). The production of a NdFeB permanent magnet by hydrogen decrepitation/ attribution milling route. Journal of Materials Science, 21, 4107-10. 

H-H interaction due to the lattice expansion becomes important and the hydride phase (P phase) nucleates and grows. The hydrogen concentration in the hydride phase is often found to be H M = 1. The volume expansion between the coexisting a- and P-phases corresponds in many cases to 10-20% ofthe metal lattice. Therefore, at the phase boundary high stress is built up and often leads to decrepitation of brittle host metals such as intermetaiiic compounds. The final hydride is a powder with a typical particle size of 10-100 pm (Figure 5.24). 

Plateau Pressure/Temperature Plateau Slope Hysteresis Heat of Reaction Hydrogen Capacity Volume Change Rate of Decrepitation Ease of Activation Kinetics of Reaction Tolerance to Gaseous Impurities Chemical Stability (Disproportionation)... 

Decrepitation is the self-pulverization of alloy particles into smaller-size powder because of volume change upon hydrogenation and the brittle nature of hydriding... 

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