Fe-cr-al Electrothermal Alloy Surface Insulation And Anti-oxidation Mechanism

Fe-Cr-Al alloys with high resistance and the low resistance temperature coefficient, high resistance of temperature oxidation, low price and so, is the most widely used metal heating element materials. But in some specific situations, you need to insulate the surface. In this paper, 0Cr25Al5 as the main object of study, were used to direct oxidation, molten salt immersion and anodic oxidation surface of insulating film was prepared. At the same time, the use of SEM, XRD, EDS and other means, test and analysis of the surface insulating film morphology, composition and formation mechanism. In direct oxidation process, the effects of time and temperature on the preparation of the surface insulating film are investigated. In preparation of liquid molten salt leaching process, the time on the preparation of molten salt surface insulation film were investigated. The effects of different current density on the preparation of the surface insulating film are investigated by constant current anodic oxidation.The results showed that: by direct oxidation at 1000℃for 72 hours under the conditions of preparation of the insulating oxide film surface compact and uniform, the resistance of not less than 2K?. Some surface spalling, crystal mainly columnar grains. Almost the entire oxygen insulation layer, aluminum elements, each element of the mass ratio increased with the temperature gradually stabilized. Surface insulation layer is part ofθ-Al₂O₃ andα-Al₂O₃. Flux method with immersion time at 450℃with different oxide, which oxide insulating film on the surface 72h to obtain the best effect, the electrical resistance of not less than 20K?. With the oxidation time, the surface grain alignment was tend to order from the chaos, tightly packed grains. Surface layer of aluminum oxide and chromium oxide based chromium oxide Cr₂O₃ and Cr8O21 mainly composed of aluminum oxide is mainlyα-Al₂O₃.Through constant current anodic oxidation ,which the surface film prepared by using a current density of 0.4A/dm² get the best insulation, the resistance of surface no less than 15K?, smoother surface, cracks and pores less. Surface insulation film is mainly from theθ-Al₂O₃ and Cr₃O₄ composition, also contains a small amount of chromite spinel andα-Al₂O₃. Above all, these three methods can be heating in the Fe-Cr-Al alloy prepared insulating film. Prepared by molten salt immersion resistance of the highest insulating film, the surface composition ofα-Al₂O₃ content of up to; anodic oxidation method followed by the insulation film resistors; insulating film which prepared by direct oxidation is the lowest surface resistance.