This study assesses the influence of particle size and spray parameters on the structural, mechanical, and electrical insulation properties of alumina coatings deposited by atmospheric plasma spraying. It has been found that the combination of a relatively fine feedstock powder and high velocity plasma spraying promotes the formation of denser coatings with high dielectric strength. Correlations between dielectric strength and deposition efficiency, coating hardness, crystal structure, and surface roughness are also assessed.

In order to meet the increased requirements for power electronics in the automotive sector, an effective utilization of difficult installation spaces is necessary. A new production concept to realize this 3D integration of electronic circuit boards directly on components is the combination of thermal spraying and cold gas spraying to create multilayer-coating systems consisting of conducting and insulating coatings. In this study two- and tree-dimensional demonstrators were developed, showing the flexible use of thermal spraying in mechatronics and power electronics. In contrast to past studies on this construction concept, the main focus of this study was on the optimization of the ceramic insulting coatings and bond strength of the metallization. The ceramic coatings showed a dielectric strength and electrical resistance, which was suitable for most applications. Additional post treatment improved the electrical resistance in humid conditions. Already 150 µm thick electrical insulation layers showed a breakdown voltage of more than 5 kV AC and a specific electrical resistance of 5.1011 Ω.m.

This work investigates the properties of insulating coatings deposited by HVOF and atmospheric plasma spraying and the effects of various sealants. It is shown that adhesive tensile strength depends strongly on surface roughness and that the dielectric strength of a material is normally higher in the unsealed state. In the case of a new sealant, however, the dielectric strength of HVOF sprayed alumina coatings is shown to be higher in the sealed state, which potentially opens new applications in high-performance electronics.

Alumina and chromia coatings were deposited on steel substrates by detonation spraying in order to determine the effect of spray parameters on adhesion, hardness, porosity, and dielectric strength. Test results show that both coatings have low porosity, high hardness, and good adhesion strength and that both can be effective as wear-resistant electrically insulating layers on metal parts.

In this work, alumina coatings are produced by air plasma spraying (APS) using dense powders ranging in size from 3 to 36 µm and one porous powder with an average particle size of 33 µm. Two spray systems were used, one rated at 40 kW, the other at 100 kW. The powders were applied to grit-blasted Al 6061 and low-carbon steel substrates. Coatings applied to Al 6061 using the high-power sprayer and 3 µm powder peeled off, likely due to thermal shock and mismatch. For all other coatings, the microstructure was examined by cross-sectional SEM, porosity was estimated via optical microscopy, and dielectric strength and volume resistivity were measured. Coatings formed from 3 µm powder were found to be dense with a mostly γ-phase crystal structure. Surprisingly, however, their volume resistivity was lower than that of more porous coatings with high amounts of α-phase. The findings show that, in the case of resistivity, spray equipment has a bigger influence than particle size, but with coating density, the opposite is true.

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 Al 2 O 3 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-Al 2 O 3 . Nonetheless, the values of dielectric breakdown voltage and dielectric strength recorded for suspension sprayed coatings were lower than those of HVOF coatings.

In this investigation, titanium dioxide and hydroxyapatite (HA) suspensions are plasma sprayed onto stainless steel, titanium, and aluminum substrates and the structure and properties of the resulting layers are correlated with spraying conditions. The suspensions were formulated with fine TiO 2 pigment and HA milled from spray-dried powder or synthesized from calcium nitrate and ammonium phosphate. In some experiments, an atomizer was used to inject the suspensions into the plasma jet, and in others, the suspensions were fed into the jet using continuous stream injection. The deposits are characterized on the basis of morphology, chemical and phase composition, scratch hardness, and dielectric strength.

Ceramic oxides can be deposited by the High Frequency Pulse Detonation process leading to coatings with unique properties as result of simultaneous melting and high velocities of the sprayed particles. In this paper, several Al 2 O 3 based powders have been HFPD sprayed and the resulting coatings characterized. For this purpose, microstructural evaluation, XRD phase analysis and functional behavior (dielectric strength and wear resistance) have been tested.

This paper discusses the development of a metal-coated glass tube that produces ozone more economically than traditional methods. It describes the principle of ozone generation, provides information on ozonizer tubes, and presents the criteria for selecting thermal spray powders. It examines the properties of several multilayer coatings consisting of an oxide ceramic top layer, an Al/Si interlayer, and a borosilicate glass substrate. It was found that the porosity and surface roughness of the oxide layer have a significant impact on the dielectric strength of the composite and the efficiency of the ozone-producing tube.