Electrical properties of MgO-ZrO2 insulation coatings on Ag and AgMg/Bi-2212 tapes for magnet technology

High temperature MgO-ZrO2 insulation coatings were successfully fabricated on long-length Ag and Ag/AgMg sheathed Bi2Sr2Ca1Cu2Ox (Bi-2212) superconducting tapes and wires from solutions derived from alkoxide-based precursors using a reel-to-reel, continuous sol-gel technique for 3-5 T high field insert magnets. The insulation coatings were annealed at 850 degreesC for 20 h under O-2 flow. The surface morphology of coatings were characterized by scanning electron microscope (SEM). Dielectric constant and high voltage breakdown of insulation on tapes was measured by a multimeter and a standard high voltage breakdown power supply. SEM observations showed that MgO-ZrO2 insulation coatings possess homogenous and crack structures on AgMg/Bi-2212 tapes. It was found that dielectric constant and high breakdown voltage values of MgO-ZrO2 Coatings increased with increasing MgO content in ZrO2 and coating thickness. Also, it was measured that the dielectric constant values of coatings with and without epoxy were 33 and 47, respectively. The maximum high breakdown voltage value was determined to be 1100 V in sample with 24 mol% MgO-ZrO2 coating. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.