Comparison of the Electrical Properties of Al₂O₃ Sprayed Coatings from Feedstock Powders and Aqueous Suspensions Available to Purchase

In this paper the characteristics (microstructure, phase compositions) and electrical insulating properties of thermally sprayed alumina coatings produced by suspension-HVOF (S-HVOF) process and conventional HVOF spray method are compared. The electrical resistance (electrical resistivity) and dielectric strength were investigated using DC-electrical resistance measurements, electrochemical impedance spectroscopy (EIS) and dielectric breakdown test. The electrical resistance was determined at room temperature at different relative air humidity (RH) levels, from 6% RH up to 97% RH. Differences in the electrical insulating properties due to the different coating characteristics are discussed. The suspension-sprayed Al₂O₃ coatings showed better electrical resistance stability at high humidity levels (> 75% RH), which could be explained by a specific microstructure and retention of a higher content of α-Al₂O₃. Nonetheless, the values of dielectric breakdown voltage and dielectric strength recorded for suspension sprayed coatings were lower than those of HVOF coatings.