High temperature sol-gel insulation coatings for HTS magnets and their adhesion properties

This paper describes the adhesion properties of sol-gel insulation coatings with silver tape substrates using a mini-tensile-testing for HTS magnets. The sol-gel coatings were produced using solutions of Zr, Mg, Y, Ce, In and Sn based organometallic compounds. The growth mechanism of these coatings on Ag and AgMg sheathed Bi-2212 superconducting tapes was characterized by scanning electron microscopy, energy dispersive spectroscopy, differential thermal analysis and X-ray diffraction. The lap joints were fabricated by laying fresh sol-gel coated silver tape samples over each other and then heat treated. These joints with varying heat treatment conditions were pulled to failure by using a mini-tensile-tester. The results of bonding strength and microstructure of the failure surface are presented. Oxides were formed between temperatures of 450 °C and 550 °C. The results also indicated that the failure was in the form of a mixed type as interfacial/cohesive defect. The average adhesive strength of ZrO₂, MgO-ZrO₂, Y₂O₃-ZrO₂, CeO₂-ZrO₂, In₂O₃-ZrO₂ and SnO₂-ZrO₂ were found to be 0.763, 1.300, 2.400, 2.087, 1.650 and 1.580 MPa, respectively. Y₂O₃ and CeO₂ doped ZrO₂ showed the best adhesive properties.