Study On Corrosion Behavior Of Several Materials In Chloride Thermal Storage Molten Salts

The thermal storage system which is the subsystem of the solar thermal power generation system is the core of the whole system.Nitrate molten salt is usually chosen as the heat storage medium in tower-solar thermal generation system which has been commercially used.However,the general using temperature of the nitrate is 300-500?,which leads efficiency of solar thermal power station is lower.Therefore,it is necessary to select another kind of molten salt which could be used in a higher temperature.Though chloride molten salt whose maximum operating temperature of thermal storage system can reach 900? presents good stability,it will cause serve corrosiveness for vessels and pipes at that high temperatures.Based on this corrosion problem of chloride molten salt in solar thermal power thermal storage system,we studied the corrosion behaviors of 316 stainless steel,Inconel 625 alloy and SiC ceramic by soaking method and electrochemical method in ternary chloride molten salt(52.9%ZnC12-33.7%KCl-13.4%NaCl)in different temperatures,and also studied the effect of the Ni-SiC composite coating with different SiC contents which was prepared by electrodeposition on the reduction of corrosion rate of chloride.The main results are as follows:(1)The quality loss of SiC ceramic was the least in 316 stainless steel,Inconel 625 alloy,SiC ceramic in the chloride molten salt.Thus,the SiC ceramic presented well corrosion resistance in chloride molten salt.Inconel 625 alloy had a smaller self-corrosion current and bigger charge transfer resistance than 316 stainless steel in 700? ternary chloride molten salt,so its corrosion resistance was superior to 316 stainless steel.(2)The oxide film growing on 316 stainless steel and Inconel 625 alloy after corrosion in the chloride molten salt would generate chlorine gas with salt.This chlorine gas would penetrate into the oxide film and then reach the interface between oxide scale and substrate.At the interface,the chlorine gas generated a metal chloride and then escaped outwards,reaching a higher oxygen pressure,where chlorine gas continued forming and it would go on infiltrating.(3)The hardness and wear resistance of the Ni-SiC composite coating prepared on the surface of 316 stainless steel was high,and the polarization curve in the chloride molten salt of which had obvious passivation characteristics,indicating that it had good corrsosion resistance properties in chloride molten salt.The corrosion resistance of the composite coatings whose SiC content was 40g/L,was the best.If further improving the density and the adhesion to the substrate of the coating,the Ni-SiC composite coating is expected to be applied as a corrosion protection coating in the field of solar thermal power generation of chloride molten salt.