Abstract
A metal acetate gel as a precursor of YBa2Cu3O7-y superconductor bloats in the range of 200°-300°C during heat treatment for conversion of the gel into a superconducting ceramic, becoming a porous and deformed product, when the heating rate is 5°C/min. In order to minimize the pore formation and deformation, the mechanism of bloating and the change of microstructure of the gel were investigated by thermal analysis, X-ray diffraction technique, infrared spectroscopy and mass spectroscopy of evolving gases. It was confirmed that the gel is composed of weak bonds between metal ions through acetate ions and that the sintering process includes elimination of water, thermal decomposition of metal acetates and reaction of precipitated intermediate species. It was also found that the bloating is caused mainly by abrupt thermal decomposition of acetate ions bonding with copper ions. Lower heating rates such as 0.0833-0.167°C/min(5-10°C/h) for the heat treatment of gel fibers were found to be effective in converting them into dense ceramic fibers by lowering the rate of thermal decomposition of acetate ions and by suppressing severe bloating.
