Sol-gel-Derived Al₂O₃- SiO₂ Composite Coating for Electrical Insulation in HTS Magnet Technology

Electrically insulating Al2O3-SiO2thin coatings have been deposited on long-length 316 stainless steel (SS) tape using a reel-to-reel continuous solgel dip coating process for cowinding insulation into YBCO pancake coils, a high-temperature superconductor magnet technology. Coatings with a thickness of ~ 5 μm are achieved after just two dips with a tape withdrawal speed of ~ 8 mm/s (0.5 m/min) and a calcination at 700 °C. The coatings are measured to have a room-temperature breakdown voltage of ~ 200 V, corresponding to a dc dielectric strength of about 40 MV/m. Consequently, this process has low cost and high throughput and produces a thin electrical insulation with excellent thermal, dielectric, and mechanical properties. A new technique has been developed in the coating process to mitigate Al2O3particulate aggregation and coating buildup along the edges of the SS tape.