| Popis: |
Extensive work has been carried out to obtain a stoichiometric manganese hydride using a high pressure hydrogen technique. Because of difficulties in obtaining the hydride at room temperature, the procedure previously applied to investigate the possibility of the formation of platinum, iron, and rhodium hydrides has been used. A series of NiMn alloys, starting from the pure nickel, which forms a hydride under well-defined thermodynamic conditions, has been investigated at 298 K with regard to the conditions of the alloy hydride formation. The miscibility gap in hydrogen-alloy systems at 298 K occurred only in alloys up to about 18 at.% manganese; at higher manganese contents the hydrogen was present only in the form of solid solution. The standard free energies of formation have clearly indicated the possibility of the formation of a pure manganese hydride under hydrogen pressures of 103−104 bar. A non-stoichiometric manganese hydride has been obtained at 577 K and under about 8 kbar: X-ray analysis indicated a h.c.p. arrangement of metal atoms in the hydride unit cell and with lattice parameters: a = 2.692 A ± 0.002, c = 4.361 A ± 0.002 . Mass-spectrometric analysis of hydrogen concentration gave a H/Mn atomic ratio of 0.82. |
