Structure Reconstruction in Palladium Alloy Catchment Gauzes

Abstract

The changes of topography and structure in palladium-5 per cent nickel alloy catchment gauzes, which are used to capture the platinum lost from the catalyst gauzes employed in the ammonia oxidation reaction to produce nitric acid, have been studied by scanning electron microscopy, electron probe microarea analysis, X-ray diffraction and other techniques. The structure of the palladium-5per cent nickel alloy gauze is reconstructed by recrystallisation and this is controlled by vapour deposition (adsorption) and diffusion re-alloying. The initial solid solution of palladium (nickel) changed into palladium (platinum) solid solution, the nickel being gradually oxidised to nickel oxide until no nickel remained. The lattice constants of the palladium (platinum) solid solution increased with the ratio of platinum:palladium. Ladder-like (layered) growth was a main mechanism in the formation of new lattice planes and crystals, while screw-type growth played an important role in the formation of new crystals.