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 l aying fresh sol-gel coated silver tape samples over each other and then hea t 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 degreesC and 550 degreesC. The results also in dicated that the failure was in the form of a mixed type as interfacial/coh esive defect. The average adhesive strength of ZrO2, MgO-ZrO2, Y2O3-ZrO2, C eO2-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. (C) 2000 Elsevier Science B.V. All rights reserv ed.