Aging effect on copper stabilizers in second-generation high-temperature superconducting tapes

Abstract

Copper stabilizers play an essential role in second-generation high-temperature superconducting (2G-HTS) tapes. Corrosion or aging of the copper stabilizer is unavoidable and affects the tape performance. In this study, aging tests were performed on fresh copper-plated 2G-HTS tapes under steady-state damp heat conditions, in accordance with the IEC 60068–2-78:2012 regulations. To accelerate the aging, the conditions were set as 40 °C, a relative humidity of 93%, and test durations of up to 48 h. The surface contact resistivity (ρc) in liquid nitrogen was measured for fresh and aged specimens under normal pressure of up to 160 MPa. The results indicated that ρc increased with the test duration and tended to become saturated. After 48 h aging tests, the ρc of the specimens was three times higher that of the fresh 2G-HTS tapes. Moreover, the microstructure of the copper stabilizer was characterized. Height fluctuations were observed on all the specimen surfaces, which might be the reason for the ρc scattering. X-ray photoelectron spectroscopy elemental analysis revealed higher amounts of carbon and oxygen on the surfaces of the specimens after aging, which significantly reduced the purity of the copper stabilizer. It was also found that Cu2O was the main product on the tape surface during the reaction with oxygen and, water vapor and so on. This study provides a reference for the design of non-insulated coils and the preservation of 2G-HTS tapes.