Thermally stable mixed oxides containing tungsten or molybdenum

摘要

Mixed oxides of either molybdenum or tungsten trioxide with up to 3 mols. of the oxide of yttrium, lanthanium or a rare earth element having atomic number 59-71 inclusive, are prepared by firing in air a mixture containing the appropriate amounts of the oxides, or a slight excess, e.g. 5-10%, of MoO3 or WO3, at at least 1300 DEG C. Compounds claimed per se include WR6O12, having a rhombohedral crystalline structure, wherein R is yttrium or a rare earth metal from erbium to lutetium; MoR6O12, having a rhombohedral crystalline structure, wherein R is ythrium or a rare earth metal form holmium to lutetium; MO3(R2O3)1- 3 having a face-centred cubic crystalline structure, wherein M is Mo or W and R is a metal excluded in the first two formulae. The product is thermally stable and non-volatile at e.g. 1750 DEG C., and may be used as a protective coating for Mo or W, or, dispersed in a matrix of, e.g. stainless steel, in control rods for nuclear reactors (see Division G6).