Development of ceramic heating element produced by thermal spray technology

In this work, completely ceramic heating elements have been developed by the combination of conductive and insulating thermally sprayed oxide coatings. These heating elements with a total thickness of less than 1 mm have -been directly applied on metallic substrates. APS- and HVOF-sprayed Al2O3 and spinel (MgAl2O4) coatings were employed for insulation. A comparative anal. of the insulating properties (dielec. strength, elec. resistivity) of these coatings is presented. The HVOF-sprayed spinel coatings show better dielec. breakdown strength and higher elec. resistance stability. TiOx, TiO2-10%Cr2O3 and TiO2-20%Cr2O3 powders have been used to prep. the elec. conductive coatings. The thermal and oxidn. stabilities at high temp., as well the elec. properties have been investigated. Addn . of Cr2O3 reduced the oxidn. rate of titanium oxide and increased the operational temp. of the heating coating. A ceramic heater consisting of spinel coating as insulator and TiO2-20Cr2O3 as conductor was sprayed on a metallic roller and the elec. stability during the long-term (300h) thermo-cycling (from RT to 300°C) was successfully tested.