Process for making 90.degree. K. superconductors by impregnating cellulosic article with precursor solution

An improved process for preparing a shaped article of a superconducting composition having the formula MBa.sub.2 Cu.sub.3 O.sub.x wherein

• M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu;
• x is from about 6.5 to about 7.0;
• said composition having a superconducting transition temperature of about 90 K.;
• said process consisting essentially of
• (a) forming in acetic acid a mixture of M(C.sub.2 H.sub.3 O.sub.2).sub.3, barium acetate and copper acetate in an atomic ratio of M:Ba:Cu of about 1:2:3;
• (b) heating the resulting mixture to boiling, and adding sufficient formic acid to dissolve any undissolved starting material while continuing to boil the solution;
• (c) contacting an article of cellulose material with the solution from step (b), thereby impregnating the article with the solution, said article having the shape desired;
• (d) removing excess solution from the resulting impregnated article of cellulose material and drying the impregnated article;
• (e) heating the impregnated article of cellulose material to a temperature from about 850.degree. C. to about 925.degree. C. in an oxygen-containing atmosphere for a time sufficient to form MBa.sub.2 Cu.sub.3 O.sub.y, where y is from about 6.0 to about 6.4, said heating effecting carbonization of the cellulose material and oxidization of carbon without ignition;
• and
• (f) maintaining the resulting article in an oxygen-containing atmosphere while cooling for a time sufficient to obtained the desired product.