MODIFIED COPRECIPITATION PROCESS OF SYNTHESIZING BI-SYSTEM SUPERCONDUCTOR PRECURSOR POWDER AND ITS STOICHIOMETRY

A modified coprecipitation process is presented based on the stoichiom etry study of oxalate coprecipitation process in water medium to synth esize Bi-Pb-Sr-Ca-Cu-O multi-component powder. Its characteristic is t hat the coprecipitation reaction takes place in a mixed solution mediu m composed of water and a kind of organic solvent (volume percentage > 90%). Thus, it overcomes the serious shortcoming of inability to maint ain stoichiometry in Bi-system superconductor powder synthesized by wa ter-medium coprecipitation. The effects of pH value, oxalic acid conce ntration and aging time on stoichiometry maintenance in precipitate ar e systematically studied. Bulk material made from the powder prepared by the new modified coprecipitation also shows the success of the new process.