Ni-Re intermetallic oxygen getters

Two binary intermetallic compounds PrNi₅ and Nd₂Ni₁₇ have been tested as getters for reducing the oxygen content in a stream of pure argon. Both the intermetallics used are the Ni richest phase in the respective rare-earth (RE)-Ni phase diagrams. The gettering efficiency has been evaluated through the quantities MTGA and OPP_g. The former is the minimum temperature of the getter activity, i.e., the temperature at which the gettering action becomes detectable, and OPP_g is the oxygen partial pressure in the gas stream after reaction. The best MTGA values found are 242 and 287 °C for PrNi₅ and Nd₂Ni₁₇, respectively, with OPP_g minimum values equal to 1×10⁻¹⁶ and 1×10⁻¹⁵ Pa. Though these values are produced for a relatively short time, the average OPP_g values are satisfactory for practical purposes. It has been shown that the oxidation produces the rare-earth oxide (RE₂O₃) and Ni. The rate-determining step has been found to be the transport of oxygen in the gas phase and its transport constant has been also calculated.