Improved Magnetic Refrigerators with Hi-Tc Superconducting Magnets.

: To produce pre-formed thick film Hi-T sub c superconducting magnets with improved critical current for magnetic refrigerators, the Hi-T sub c superconducting powder was coated with a thin film of beneficial metal(s) (Ag, Pb, Nb) before fabrication. It was anticipated that the metallic bonding between the Hi-T sub c superconducting grains would overcome the usual 'weak-links' that limit the superconducting current. This might be particularly effective with Lead and Niobium since these low temperature superconductors have long coherence lengths. After fabrication and heat treatment, the superconducting properties of the thick films were measured, particularly the critical current (Jc). Regarding improvements in Jc of Bi2Sr2CaCu2Ox thick Ag-coating gave improvements of +131%. However, for Bi1.8Pb.4Sr2Ca2Cu3Ox thick films, Ag-coating decreased Jc -29%, Nb-coating decreased Jc -48%, Ag+Nb-coating decreased Jc-52%, and Pb-coating chemically deteriorated the BiPb2223 superconductor.