Platinum Metals Review - Volume 32, Issue 1, 1988

Resistojets for space station auxiliary propulsion require both long life and multipropellant capability, and platinum dispersion strengthened with yttria and zirconia has been studied for possible use as a resistojet material. A series of propellant compatibility tests has been conducted, and the results are presented. Generally, on the basis of mass loss, there were no compatibility problems in any of the environments considered. Microscopy showed that the effect of the propellants on the surface of the platinum varied significantly; however material stability, as measured by grain growth, did not appear to be a major problem.

During the manufacture of nitric acid, rhodium-platinum gauzes are used to catalyse the oxidation of ammonia, an operation that results in a major reconstruction of the alloy surface. In this study, the effect of pretreatments, similar to those employed to prepare the catalysts for commercial use, have been examined to determine both the chemical and the physical effects on the surface. A successful pretreatment is shown to produce a generally clean, chemically receptive surface containing reactive crystal orientation sites. Additionally, the nature of the surface during catalyst operation has been investigated using a rapid quench facility in a miniature reactor. It has been established that, during catalyst operation, the surface of the catalyst is metallic, and not covered by an oxide layer as previously thought.

Certain unexpected effects observed during developments and reductions of pressures of hydrogen gas inside tubular membranes of palladium alloys now seem to be self-consistently interpretable in terms of lattice-strain-induced temporary “uphill” hydrogen diffusion processes.