Up-scaling of superconductor powders by the acrylamide polymerization method

Abstract

Sol–gel methods allow the preparation of powders with high performance: very fine granularity with a low grain size dispersion and excellent chemical homogeneity. In addition, lower synthesis temperatures can be attained with respect to solid-state processes. From an industrial standpoint, some effort has to be made in the up-scaling of such techniques in order to bring laboratory operations to industrial practice in a cost-effective way. In this work, we attempt to scale-up the acrylamide (AA) process for obtaining large batches of superconductor powders and related compounds. This technique consists of polymerizing AA monomer in aqueous media containing cation derivatives in the presence of a reticulating agent. This process is the fastest way to perform monolithic and stable gels. Large quantities, around 1 kg, have been produced of the following superconducting compounds and related additives: Y123, Y211, (Bi,Pb)-2212 and (Bi,Pb)-2223. Phase evolution has been monitored by XRD and thermogravimetric analysis. The presence of carbonate phases, which is the main drawback in the sol–gel techniques, is checked by elemental analysis. Results show that the superconducting and additive powders can be prepared in a single thermal treatment step, except the (Bi,Pb)-2223 phase.