Electromagnetic shielding can reduce electromagnetic or radio frequency interference, which can damage electronic components or disturb low-level signals. Such shielding is, for example, achieved by a metallic coating, often wire arc sprayed, on the inside surface of an instrumentation cabinet which is usually made of plastic or a composite material. In another application, conductive material coatings are cold sprayed on aluminum surfaces. Microwave integrated circuits (MIC) are made by plasma-sprayed Mg–Mn ferrite. Al, Ta, and Nb capacitor electrodes are sprayed in air. Unusual conductors such as aluminum titanate, barium titanate, molybdenum di-silicide, and other ceramic compounds are also sprayed.
Electrically resistive or insulating coatings: electrically insulating surfaces (mostly oxides and especially alumina) are used for dielectrics (for example, in ozonizers), high-temperature strain gages, oxygen sensors (ionic conduction of zirconia), and insulation of heating coils. Resistors are made of NiCr or super alloys doped with alumina particles to tailor their electrical conductivity.
Electrochemical active coatings including solid oxide fuel cells (SOFCs) and high-temperature electrolyser (HTE) are very efficient devices that electrochemically convert fuel energy into electricity and heat (SOFC) or electricity into hydrogen (HTE). SOFCs are well suited as cogeneration units for providing electricity and heat to buildings. They could greatly reduce the consumption of fuels, lowering greenhouse gas and pollutant emissions, but their development is hindered by high cost of manufacturing through wet-ceramic techniques (tape casting and screen printing). The HTE, working according to the reverse reaction of SOFC, produce hydrogen from water vapor. Plasma spray processes instead of wet-ceramic techniques could significantly reduce manufacturing costs and many works, with industrial applications, have been devoted to these techniques. – Heat transfer improvement is achieved with high-thermal conductivity coatings such as Cu or Al, or BeO for ceramics when electrical insulation is mandatory.
Medical coatings can be bioactive or biocompatible or bioinert. Bioactive coatings are made of hydroxyapatite, or tricalcium phosphate, that emulates the characteristics of bone material and induces the growth of new bone attached to the implant.
Dimensional restoration coatings are used for salvage of worn or over-machined parts. All spray processes are used for this salvage work and very often NiCr and NiAl materials are used. With plasma-transferred arc processes coating thicknesses can reach a few mm. Cold spray has been successfully used to impart surface protection and restore dimensional tolerances to magnesium alloy components.
– Free-standing shapes: parts are fabricated from hard-to-machine materials by building a coating on a removal form. This process is often less costly than conventional processing methods such as sintering or hot isostatic pressing. Ceramic membranes, ceramic tubes (1 m in diameter, 10 m long, and with wall thickness of a few mm), rocket nozzles, and ceramic or refractory material crucibles are manufactured this way.
Nuclear applications: in addition to the usual mechanical applications (however with short lifetime elements: no cobalt, for example) thermally sprayed coatings are used in Tokomak reactors and magnetic fusion devices.
Polymer coatings are used as protection against chemical attack, corrosion, or abrasion. Unlike inorganic coatings polymer coatings may have equal or better properties than their cast or molded counterpart.
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