PREPARATION OF Y-BA-CU OXIDE PRECURSOR BY THE CITRATE GEL PROCESS

The citrate gel process was developed to prepare YBa2Cu3 oxide superconductor. A citrate-nitrate solution was dehydrated to yield the precursor gel. The thermal decomposition phenomena were studied using thermogravimetric, evolved gas, X-ray diffraction and infrared analyses. The gel was pulverized in air by thermal decomposition at around 200-degrees-C. At this stage, the weight loss was 52%. Gradually the loss reached 68% at around 500-degrees-C to yield mixed Y2O3, CuO and BaCO3 powders. It was proved that the heat process includes elimination of water, and thermal decomposition of metal carboxylate and other organic species. Violent reaction during pyrolysis at about 200-degrees-C was assumed to be mainly the result of an abrupt oxidation of carboxyl groups attached to copper and yttrium ions. Two-step decomposition, first in an inert gas and subsequently in an oxidizing gas atmosphere, has been proposed to depress the violent oxidation.