Platinum Metals Review - Volume 25, Issue 3, 1981

Turbine blades in gas turbine engines operate at elevated temperatures and in highly oxidising atmospheres that can be contaminated with fuel residues and sea water salts. These components, which are expensive to produce, are subjected to high stresses during operation but must be totally reliable during their design life. An economic way to maintain blade properties is to coat the base metal superalloy with a protective layer capable of resisting both high temperature oxidation and hot corrosion. Conventional aluminide coatings are widely used for this purpose but platinum aluminides offer improved corrosion resistance. A collaborative exercise involving Rolls-Royce and Johnson Matthey has now resulted in the development of a platinum aluminide diffusion coating that offers some advantages over the commercial systems.

To extract the platinum group metals from the ore, and to refine them to the very high purity required for their many applications, requires a multitude of complex operations. At present the final refining stage that produces the individual platinum group metals is carried out by selective precipitation from a solution of mixed platinum group metals, but this is inefficient as far as the degree of separation is concerned. An improved process which makes use of liquid–liquid extraction has been developed to a pilot plant stage, and this paper highlights some of the chemical and process principles that underlie this method of separation.

The present knowledge of reactions between the alkali metals, lithium, sodium, potassium and rubidium with the platinum group metals, platinum, palladium, rhodium, iridium, osmium and ruthenium, their reaction products, and the relevant binary phase diagrams, is surveyed. Information is included on the magnetic and electrical behaviour of some alloys, especially those with the higher platinum contents.

The centenary of the death of Henri Sainte-Claire Deville, teacher, chemist and technologist, is a reminder of the quite exceptional part he played in laying the foundations of the modern platinum industry.