PREPARATION OF 1-2-3 SUPERCONDUCTORS FROM HYDROXIDE-CARBONATE COPRECIPITATION

A batch coprecipitation of 1-2-3 superconductor precursor powder was accomplished by adding an aqueous solution of mixed nitrates rapidly to a mixture of sodium or potassium hydroxide and carbonate. The blue hydrogel, an intimate mixture of Y(OH)3, BaCO3, and Cu(OH)2, was filtered and washed by decantation, using water sparged with CO2 to control the pH. After a second filtration, drying and calcination, the product was a homogeneous powder, with an average particle size of about 1-mu-m, free of alkali, and with excellent superconducting properties. The process is reproducible, inexpensive, and easy to scale to higher production rates. Important process parameters are the following: the time and temperature of precipitation; alkali ratios; volume, temperature, and pH of the wash water; and time of calcination.