Development of ceramic heating elements produced by thermal spray technology

摘要

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 Al_2O_3 and spinel (MgAl_2O_4) coatings were employed for insulation. A comparative analysis of the insulating properties (dielectric strength, electrical resistivity) of these coatings is presented. The HVOF-sprayed spinel coatings show better dielectric breakdown strength and higher electrical resistance stability. TiO_x, TiO_2-10%Cr_2O_3 and TiO_2-20%Cr_2O_3 powders have been used to prepare the electrical conductive coatings. The thermal and oxidation stabilities at high temperature, as well the electrical properties have been investigated. Addition of Cr_2O_3 reduced the oxidation rate of titanium oxide and increased the operational temperature of the heating coating. A ceramic heater consisting of spinel coating as insulator and TiO_2 - 20Cr_2O_3 as conductor was sprayed on a metallic roller and the electrical stability during the long-term (300h) thermo-cycling (from RT to 300℃) was successfully tested.