Effect of ball milling materials and methods on powder processing of Bi2223 superconductors

Various milling systems consisting of agate and polypropylene grinding containers, agate and YSZ balls, and dry and wet milling were used in planetary ball-milling and YSZ balls and YSZ container were used in wet and dry attrition milling. The differently milled powders were then evaluated by measurements of particle size, surface area, porosity, size distribution and chemical analysis of the Si, Zr and C contents. The results show that dry milling is much more efficient for particle size reduction in planetary milling than wet milling, whereas wet milling and dry milling gave quite similar results in attrition milling. Meanwhile SiO2 contamination was found in powder milled with an agate container with agate balls. Some C contamination from the polypropylene container was detected after milling, but negligible Zr from YSZ balls and C from the grinding carrier (hexane). It was found that after 1 h milling in the planetary mill fracture mechanisms transform from the elastic to the plastic region. Therefore, further milling is not very effective. It was also shown that the Bi2212 phase decomposes into several non-superconducting oxides such as Ca2PbO4, (Sr, Ca)2CuO3, CuO and a main amorphous phase after extensive dry milling. (author)