Abstract

Thermally sprayed ceramic coatings can be used for wear protection as well as thermal and electrical insulation. When exposed to environments with high humidity; the water absorption of the ceramic coating has a tremendous impact on the electrical insulation. In thermally sprayed ceramic coatings; water can easily be absorbed by the porous microstructure of the coating. A general result of the water absorption is the reduction of the DC resistivity. However; in the high frequency regime of AC loads; contrary results were observed for sealed Al2O3-coatings on steel substrates. Specimens exposed to high air humidity have shown an increased AC resistance compared to dry specimens if frequencies above 1 MHz are considered. To analyse this phenomenon; a novel measurement technique was developed to investigate the influence of the water absorption of detached ceramic coatings on the AC resistivity at high frequencies. Moreover; the water absorption of the ceramic is measured gravimetrically. To ensure the results are also applicable to ceramic coatings on substrates; the morphology of the coating was analysed using electron microscopy and compared to reference specimen deposited on steel substrates from [1].

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