A study of the compatibility of thermionic converter materials with caesium

Abstract

The reasons for the current interest in thermionic energy conversion devices in the field of nuclear energy are briefly outlined. In a caesium thermionic device the problem of corrosion of the constructional materials by caesium is of prime importance. A method has been devised for carrying out compatibility tests in caesium vapour and investigations at temperatures up to 600° C are described. The materials studied include metals and ceramics likely to be employed in a thermionic converter device, and it is shown that in many cases severe corrosion can occur at temperatures as low as 300° C. Particular attention is paid to the behaviour of metal-ceramic seal assemblies where the choice of materials, particularly the metallising and brazing components, is of great importance. Most conventional commercially available seals are not entirely satisfactory and are unlikely to be suitable for prolonged use at temperatures in the region of 600° C. It is concluded that it may prove necessary to develop new methods of sealing high purity alumina to metals before the full potential of the thermionic converter can be realised.