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2933 |
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Thursday, September 29, 2011, Saal A 12:00 PM Young Professionals |
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Development of ceramic heating elements produced by thermal spray technology |
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Filofteia-Laura Toma / Fraunhofer IWS, Germany Stefan Scheitz / Fraunhofer Institute IWS, Germany Roberto Puschmann*/ Fraunhofer Institute IWS, Germany Lutz-Michael Berger/ Fraunhofer Institute IWS, Germany Viktar Sauchuk/ Fraunhofer Institute IKTS, Germany Mihails Kusnezoff/ Fraunhofer Institute IKTS, Germany |
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In this work, ceramic heating elements have been developed by the combination of conductive and insulating thermally sprayed coatings. These heating elements with a total thickness of less than 1 mm have been directly applied on metallic parts for different purposes. Al2O3 and Spinel (Al2O3-MgO) coatings obtained by atmospheric plasma spraying (APS) and high velocity oxy-fuel spraying (HVOF) starting from conventional feedstock powders were employed as insulators. The coating microstructures, phase composition and electrical properties (dielectric strength, electrical resistivity) were studied. Differences in the electrical insulating properties due to the different coating system characteristics are discussed. The HVOF spinel coatings showed superior dielectric breakdown strength and electrical resistance stability. For the development of electrical conductive coatings, commercial spray powders of the TiO2-Cr2O3 system and an experimental perowskite powder (LaCaMnO3) have been used. The microstructure, phase composition and oxidation stability at high temperature have been studied. The conductive properties of the coatings at room temperature and at 300°C and the electrical stability during long-term thermo-cycling (from RT to 300°C) which are of great importance for the functionality of the heating element have been investigated. Conductive coatings from the TiO2-Cr2O3 system can be successfully used for the producing of heaters for applications up to 300°C. Due to a better thermal stability, the perowskite coatings offer the possibility manufacturing ceramic heating elements providing significantly higher operating temperatures. |