Coprecipitation process for thermionic cathode type materials

A method for fabricating a thermionic cathode element comprising the steps of (A) dissolving a mixture of alkaline earth metal carbonates consisting essentially of about 2 to 10 weight percent calcium carbonate, 10 to 60 weight percent strontium carbonate, and the balance substantially all barium carbonate in trifluoroethanol to form a solvent mixture;

• (B) heating said solvent mixture for a period of time and at a temperature sufficient to evaporate said trifluoroethanol and form a uniform, homogeneous, ultra-fine particle sized co-precipitate of said alkaline earth metal carbonate mixture;
• (C) forming a slurry of said co-precipitate;
• (D) impregnating the porous surface of a suitable metal substrate selected from the group consisting of tungsten and nickel metal by dipping said substrate into said slurry;
• (E) heating said impregnated substrate to a temperature and for a period of time sufficient to effect the impregnation of said porous surface by said co-precipitate;
• (F) alternately repeating steps (D) and (E) a number of cycles sufficient to achieve a predetermined degree of impregnation of said porous substrate with a homogeneous, ultra-finely divided, uniformly sized, particulate mixture of said alkaline earth metal carbonates.