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应用XRD、SEM和EDS等分析方法探讨了温度对表面喷涂二元碱金属硫酸盐的Super304H耐高温腐蚀特性的影响。结果表明:650℃时腐蚀过程以高温氧化为主,腐蚀动力学曲线遵循抛物线规律,基体表面形成相对致密且具有保护性作用的氧化层,腐蚀产物由较多的铁氧化物与部分Cr2O3以及少量的FeS组成,近基体处未见明显的微孔隙与裂纹。提高腐蚀温度至750℃,腐蚀动力学曲线遵循“钟型”规律变化;挥发性腐蚀产物形成,导致腐蚀动力学曲线呈现下降趋势;腐蚀产物以较多的铁氧化物与部分Cr2O3为主,伴生少量的(铁/镍)硫化物以及挥发性腐蚀产物硫酸铬酸钠Na4(CrO4)(SO4);氧化膜增厚且变得疏松多孔,近基体表面孔隙密度与裂纹深度增加,有内硫化发生。分析认为:上述现象的发生归因于低熔点共晶体Na2O·Na2SO4的产生以及Cr2O3在硫酸盐中的碱性熔融;提高温度加速了挥发性产物的形成以及腐蚀的深入发展。
The effects of temperature on the corrosion resistance of Super304H coated with binary alkali metal sulfate were investigated by XRD, SEM and EDS. The results show that the corrosion process is dominated by high temperature oxidation at 650 ℃ and the corrosion kinetic curve obeys the parabolic law. The oxide layer is formed on the surface of the substrate with relatively dense and protective effect. The corrosion products consist of more iron oxide and some Cr2O3, FeS composition, near the substrate at no obvious micro-pores and cracks. The corrosion kinetic curve follows the pattern of “bell-shaped” and the formation of volatile corrosion products leads to the declining trend of corrosion kinetic curve. The corrosion products mainly contain more iron oxide and some Cr2O3 (Iron / nickel) sulfides and volatile sodium sulfate Na4 (CrO4) (SO4), which are volatile corrosive products. The oxide film is thick and loose and porous, and the pore density and the crack depth on the surface of the near substrate are increased. Sulfuration occurs. It is concluded that the above phenomena are attributed to the formation of low-melting eutectic Na2O · Na2SO4 and the basic melting of Cr2O3 in sulphate. Increasing the temperature accelerates the formation of volatile products and further development of corrosion.