Effect of controlled carbon impurities on Jc in Ag/Bi(2223) tapes

An extensive study of the detrimental effect of C on critical current densities (jc) of Ag sheathed Bi(2223) tapes has been carried out. High jc can only be obtained if the C content is kept to a minimum. Successive calcination steps at 820 C are effective in reducing the amount of C in the resulting powders. On the other hand, high energy milling increases the amount of C in the powder. Controlled quantities of C impurities were introduced into the powders performing the calcinations in a CO2 rich atmosphere. The jc measured on tapes obtained with C rich precursors are lower by a factor of 2 to 4 than the jc of tapes from powders calcined in air