| Enamel coating is a special alkali metal silicate glass.It can form a uniform and dense glass phase at low temperatures,with good chemical stability.Inorganic enamel coatings are low-cost,have a simple process,and can be mass-produced in large sizes,thus showing high application potential in the field of heat corrosion protection for salt evaporation tanks.Existing enamel coatings have stable chemical properties at room temperature,but poor heat corrosion resistance at higher temperatures,which limits their application in this field.Different SiO2 grindings of enamel coatings were prepared using a single dipping method.The study of the role mechanism of SiO2 in the bonding properties,oxidation resistance,and molten salt corrosion resistance of titanium alloy enamel coatings is of great significance for improving the protective performance of titanium alloy enamel coatings and expanding their application range.The main research contents of this paper are as follows:The phase composition,microstructure,and bonding properties of enamel coatings with SiO2 grinding amounts of 0%,2%,4%,6%,and 8 wt.%were studied.The results show that SiO2 can partially dissolve into the silicate network,participate in the formation and extension of the network,and partially undissolved SiO2 exists in the coating in the form of crystals.Grinding SiO2 in the coating can enhance the network polymerization degree,increasing the coating hardness.However,as the amount of SiO2 grinding increases,the difference in the expansion coefficient between the coating and the substrate increases,resulting in enhanced compressive stress in the coating.The increase in network polymerization can improve the bonding performance of the coating,but the increase in stress and crystal content will reduce the bonding performance.The bonding performance of the coating and the substrate decreases first and then increases with the increase of SiO2 grinding amount,and the 6%coating has the best bonding performance.The oxidation behavior of enamel coatings with different SiO2 grinding amounts at 550℃was studied.The results show that fine crystals are initially formed on the surface of the enamel coating during the initial stage of oxidation,and concentrated crystallization areas are formed locally in the later stage of oxidation,leading to the formation of large-scale loss areas on the coating surface.During oxidation,the Al2O3 formed by the interface reaction promotes the incorporation of SiO2 into the network structure,increasing the number of attachment sites outside the network and inhibiting the formation of crystals outside the network.Grinding SiO2 can effectively inhibit the precipitation of crystals during the oxidation process,and the inhibition ability increases with the increase of SiO2 grinding amount.However,grinding SiO2 will exacerbate the mismatch phenomenon of the thermal coating,resulting in enhanced compressive stress in the coating,increased crack expansion potential,and more prone to transverse cracks when precipitated crystals serve as crack nucleation sites,causing coating failure.Among them,the 6%coating has the best oxidation resistance.The thermal corrosion behavior of enamel coatings with different SiO2 grinding amounts in nitrate（50 wt.%NaNO3+50 wt.%KNO3）and mixed molten salts（6.5wt.%NaCl+34.5 wt.%KCl+59 wt.%Na2SO4）was studied.The results show that the damage of nitrate to the enamel coating is mainly reflected in the corrosion of nitrogen oxides and Na2O,K2O to the glass network.The fluidity of the corroded coating increases significantly,gas bubbles are formed during the corrosion process,and crystal precipitation in the coating causes crack expansion and failure.Grinding SiO2 can increase the Si-O bond content in the network,improve the network polymerization degree,and reduce the exchange rate between the coating and the corrosive medium.The increase in network polymerization can increase the viscosity of the glass network and reduce the crystallization rate in the coating.Among them,the 8%coating has the best nitrate molten salt corrosion resistance.The damage of mixed molten salts to the enamel coating is mainly manifested in the destruction of the silicate network by Na+and K+ions,and the decrease in the bonding performance of the enamel coating due to interface reactions,ultimately resulting in the formation of cracks and the failure of the enamel coating.Grinding SiO2 can improve the viscosity of the glass network,reduce the exchange rate between the coating and the corrosive medium,and the crystallization rate.However,as the SiO2 grinding amount increases,the thermal mismatch of the coating is exacerbated,making it easier to form crack expansion and accelerate the corrosion rate of the mixed molten salt to the coating.Among them,the 4%coating has the best mixed molten salt corrosion resistance. |
