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| Abstract No.: |
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Scheduled at:
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Thursday, May 22, 2014, Hall H2 9:20 AM
Ceramic Coatings 1
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| Title: |
Electrical properties and microstructure of plasma sprayed forsterite and alumina coatings
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| Authors: |
Jean-Michel Lamarre* / NRC-IMI, Canada
Cristian Victor Cojocaru/ National Research Council Canada, Canada
Jean-Gabriel Legoux/ National Research Council Canada, Canada
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| Abstract: |
Atmospheric plasma spray (APS) is an efficient technique for depositing high performance dielectric coatings at a low cost, with high deposition rate and on complex-shaped parts. Due to its availability, low price, ease to spray and good dielectric properties, alumina (Al2O3) is a very common choice of material for insulating applications. However, the coefficient of thermal expansion (CTE) of alumina does not represent the best match for the CTE of a metallic substrate hence alternative high CTE ceramic materials are of interest. We report on the microstructural and electrical properties of a dense high CTE forsterite (Mg2SiO4) coating deposited by APS. Forsterite coatings' microstructure, porosity level and high temperature degradation resistance are compared to that of alumina coatings. The ceramics electrical properties were evaluated by performing impedance measurements on as-sprayed and thermally exposed coatings at different temperatures. We show that both materials exhibit degradation after exposure to a threshold temperature. The coating electrical failure mechanisms are discussed. An equivalent electrical model is used to extract relevant coatings properties such of resistivity, dielectric constant and percentage (%) of absorbed water as a function of the microstructural evolution. The behavior of porous ceramic coatings under high level of humidity conditions is discussed.
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