Second phase particles hydride

Second-phase particles, dispersed in the matrix of the intermetallic compounds, are able to promote as well as to retard activation (Sandrock, 1978). Second-phase particles richer in the hydrogen-attracting element than the main phase will usually promote activation since they form sites favourable to hydride nucleation. They may also serve as canals by means of which the hydrogen enters the bulk of the main phase. Furthermore, if the presence of the second-phase particles leads to an increase in the brittleness of the alloy, the major activation cracks will form more easily and activation can proceed much more rapidly. 

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