Detection of a-Phase Precipitates in Decomposing NiHß by Bitter Powder Pattern

In a preceeding paper [1] we proved that a variation of the well-known Bitter technique accord­ ing to Hutchinson [2] is appropriate to study trans­ formations in which a ferromagnetic component comes into existence. We were able to show the possibility how to apply this technique on the analysis of metal-hydrogen systems, especially of those with the ferromagnetic component nickel. In the case of the non-ferromagnetic nickel hydride [3] (NiH^, with atomic number ratio H/Ni between 0,7 and 1) the desorption of hydrogen gives rise to the ferromagnetic a-phase (with H/Ni between 0 and about 0,01), which has the spon­ taneous magnetization of pure nickel. This circum­ stance — i.e. the coexistence of magnetic and nonmagnetic regions — allows the application of the Bitter technique to recognize an arrangement of aand /?-phase areas in the surface or in layers next to it. The Bitter method was chosen because such a proof is hardly disturbed by surface rough­ ness; its modification according to Hutchinson furthermore is apt to produce a better contrast of areas. The Bitter method means that the surface of the sample is decorated with small ferromagnetic