Comparative Study of the Electrical Properties and Characteristics of Thermally Sprayed Alumina and Spinel Coatings

Abstract

In this study, APS and HVOF processes have been used to prepare alumina (Al 2 O 3 ) and magnesium spinel (MgAl 2 O 4 ) coatings designed for insulating applications. The electrical characteristics, i.e., dielectric strength and electrical resistance (electrical resistivity) were investigated using different methods: dielectric breakdown test, direct current (DC) measurements, and electrochemical impedance spectroscopy (EIS). The electrical resistance was measured at room temperature at different relative humidity (RH) levels (from 6% RH to 95% RH) as well as at 200°C. The coating microstructure, phase composition, and water vapor sorption were studied. Differences in the electrical insulating properties due to the different coating system characteristics are discussed. Of the coatings and conditions investigated in this study, the HVOF spinel coatings showed superior dielectric breakdown strength and electrical resistance stability at high humidity levels.

Effects of Ambient Conditions on the Dielectric Properties of Thermally Sprayed Ceramic Coating

“…In addition, the measurement methods and conditions in previous studies are often not fully documented, and thus the evaluation and comparison of the properties of different coatings is difficult. Earlier studies of electrical properties of thermally sprayed coatings are mostly concentrated on the HVOF (high velocity oxygen fuel) and plasma sprayed alumina coatings [1,2,3,4]. Relative permittivity and dielectric loss behavior for plasma sprayed alumina (Al 2 O 3 ) coating has been studied in [1] but the results are not fully comparable to this study because of the different spraying technique.…”

“…Relative permittivity and dielectric loss behavior for plasma sprayed alumina (Al 2 O 3 ) coating has been studied in [1] but the results are not fully comparable to this study because of the different spraying technique. In [3], the DC resistance of HVOF alumina coatings was studied at room temperature (not exactly defined) with relative humidity of 30 % and 95 %, but the DC dielectric breakdown measurements were documented to be performed at room conditions. In [1,2], the DC resistivity and DC dielectric strength of plasma sprayed alumina coatings were studied at room temperature conditions.…”

“…In [1,2], the DC resistivity and DC dielectric strength of plasma sprayed alumina coatings were studied at room temperature conditions. The results of the papers [3,4] indicate that electrical properties of HVOF sprayed alumina coatings require to be examined more detailed and it has been already seen that especially the microstructure of a coating affects significantly the electrical properties. It has also been indicated that the environmental conditions affect also the electrical properties of thermally sprayed coatings.…”

Effect of Heat Treatment of the Alumina Powder on the Microstructure and Properties of Coatings

“…At the current stage of development of materials one of the most pressing tasks is to develop coatings with high hardness, wear resistance, heat resistance and insulating SURSHUWLHV 7KH Į -Al2O3 powder coatings obtained by the thermal methods of a raw material coatings are met all these requirements [1]. The cost of one kilogram of the powder EDVHG RQ Į -Al2O3 is rather high that eventually affect the final cost of the finished product.…”

“…A promising trend in the art is the use of an alumina powder in view of its low cost. The studies [1,2] show that the coatings obtained from the raw material based on alumina, in many respects the above coating lose as alumina powder consists of a number of metastable crystallographic modifications, which eventually leads to a high porosity and brittleness, and to a lack of durability of the resulting coatings. It has previously been shown that metastable alumina phase transition to a stable Į -Al2O3 by the heating [3].…”