The Rocketdyne Division of Rockwell International has developed a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique.
In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination.
Bulk samples of thallium-based powder were prepared by spray calcination, collected, cold-pressed, and sintered. An optimized temperature schedule was developed to produce T12Ba2Ca2Cu3Ox. Samples were examined by X-ray diffraction and characterized by measurements of critical transition temperature, Tc. A complete transition to zero resistance at 112 K was measured.