oa Platinum and the Refractory Oxides

Under normal atmospheric conditions platinum is exceedingly inert with respect to the more refractory oxides. Severe reactions can occur, however, when the oxidising potential of the surrounding atmosphere is reduced below a critical level. Alumina, zirconia and thoria dissociate, oxygen is evolved and platinum extracts the metal from the refractory to form dilute alloys and low melting point phases. Magnesia is very resistant to this type of decomposition, and appears to be an excellent refractory for use in contact with platinum. This article describes in general terms the reactions of platinum with alumina, zirconia, magnesia and thoria at temperatures up to 1700°C. Subsequent articles will discuss the effects of geometry and environment on such reactions, and finally their practical implications so far as the user of platinum is concerned.