Reprocessing of Sintered and Melt High Temperature Superconducting Materials

Abstract

AbstractIncreasing use of High Temperature Superconducting Ceramics (HTSC) in various applications and the cost of the new superconducting powder dictated the need for evaluating the potential of reusing the old HTSC material (yittrium-barium-copper oxide (YBCO); YBa2Cu3O7-x) with minimum reprocessing. This study examined various methods to reprocess two years old sintered and melt bulk YBCO ceramics. YBCO components were ground and processed with and without adding various amount of silver powder, organic binders and new YBCO powder. The reprocessed YBCO powder was also characterized at every step of processing using X-ray diffraction (XRD) and Differential Thermal Analysis (DTA) to identify impurities.The old YBCO components were first crushed and then ground using automatic grinder and a jet-mill. The ground powder was then mixed with additives and/or binders and compacted uniaxially to 45 ksi. The range of sintereing temperatures from 905 °C to 980 °C were selected based on the past history of sintering/melting temperatures. The reground powder was found to have impurity phases due to its exposure to carbon dioxide and humidity in the atmosphere. Addition of Ag powder resulted in higher relative densities at lower sintering temperatures. The need for re-calcination of used powders was also considered to improve the performance of reprocessed powders. The sintering temperature was selected based on achieving 85% relative density. The results show that the reprocessed powders have to be sintered at higher temperatures than their previous history. The sintered and melt-textured YBCO made from reprocessed powder had similar or better superconducting properties compared to the new powder.