Cryochemical method of preparing ultrafine particles of high-purity superconducting oxides

A method for producing particles of superconducting ceramic powders having a superconductivity transition temperature (T.sub.c) of about 77K or greater, which method comprises:

• (A) dissolving the compatible soluble salts of the cations selected from nitrates or acetates in an aqueous medium;
• (B) obtaining a solution having a pH between about 4 and 7;
• (C) spray atomizing the solution of step (B) onto liquid nitrogen at about -196.degree. C.;
• (D) removing the liquid nitrogen as a gas at about ambient temperature by evaporation without melting or coalescence of the ice-salt crystals;
• (E) removing the ice from the ice salt crystals by sublimation at reduced pressure without melting or coalescence of the ice-salt crystals into larger particles;
• (F) drying the salt crystals obtained in step (E) to about 40.degree.-60.degree. C. in a vacuum without melting or coalescence of the salt crystals;
• (G) calcining the solid residue of step (F) in sufficient oxygen or dry air at a temperature between about 200.degree. and 895.degree. C.;
• and
• (H) cooling slowly the solid of step (G) in an anhydrous atmosphere in sufficient oxygen or air to ambient temperature concurrently annealing the particles in sufficient oxygen or air at between about 200.degree. and 700.degree. C. for between about 2 and 30 hrs, and recovering the superconducting solid powder having an average diameter of between about 0.1 and 10 microns.

A method of preparing particles of superconducting ceramic powders, which method comprises:

• (a) dissolving the soluble salts of the cations in two or more separate aqueous media;
• (b) obtaining separate cation solutions having pH of about 4 and 7;
• (b') mixing the separate solutions of steps (a) and (b) intimately for about 60 seconds then immediately;
• (c) atomizing the solution of step (b') onto liquid nitrogen at about -196.degree. C.;
• (d) removing the liquid nitrogen by evaporation under conditions such that the ice-salt crystals do not coalesce into larger crystals;
• (e) removing the ice by sublimation at reduced pressure under reaction conditions such that the ice-salt crystals do not coalesce into larger particles;
• (f) heating the solid residue of crystals of step (e) to about 40.degree.-60.degree. C. at reduced pressure;
• (g) calcining the solid residue in sufficient oxygen or air at temperature of between about 200.degree. and 895.degree. C.;
• and
• (h) cooling the solid at a temperature of between about 900.degree. C. and ambient temperature in sufficient air or oxygen concurrently annealing of the particles in sufficient oxygen at between about 200.degree. and 500.degree. C. for between about 2 and 30 hrs and recovering the superconducting solid powder having an average diameter of between about 0.1 and 10 microns.