Deterioration of Platinum in a Hydrogen-Sodium Coexisting Environment

Abstract

It is known that heating platinum, which possesses excellent corrosion resistance, for several hours in a hydrogen atmosphere at a temperature of approximately 300°C causes the platinum to deteriorate to a sponge-like state. A study of the deterioration of platinum in a hydrogen and sodium atmosphere created in a laboratory yielded the following results:
(1) When sodium compounds are present in a reducing atmosphere, the platinum itself deteriorates even at low temperatures. When platinum was heated in an oxidizing atmosphere, no particular deterioration was observed.
(2) The following conditions supposes to be needed for platinum deterioration to occur:
a. Reducible sodium compounds are deposited and heated in the reducing atmosphere, becoming sodium, or
b. When the temperature is raised to a high temperature during pretreatment, the sodium changes temporarily to a gaseous state and then, when the temperature is lowered, the sodium becomes metallic sodium and is precipitated.
No platinum deterioration occurs when the platinum is simply exposed to an oxidizing atmosphere.
(3) Activation energy of 20kJ/mol is needed for platinum deterioration to occur. This value is equivalent to the energy needed for self-diffusion of liquid metal, liquid alloy and simple fused salt.