Molten nitrates or nitrate–nitrite mixtures have been used as heat transfer fluid as well as thermal energy storage medium in concentrated solar power plants and other industrial applications. However, containment materials in contact with these molten salts are subjected to molten salt corrosion, which has been a concern over the years. In this investigation, the corrosion behavior of pure Ni, Fe, Cr, and Fe-5Cr alloy (in weight percent) has been examined at 400°C in molten nitrates using electrochemical impedance spectroscopy and gravimetric tests. It is shown that Ni, Fe, and Fe-5Cr exhibit mass gain, with the best corrosion resistance for Ni followed by Fe-5Cr and Fe, while pure Cr goes through fast dissolution, forming hexavalent chromium product K₃Na(CrO₄)₂. The increase of salt basicity from Solar Salt to Hitec could accelerate the dissolution of Cr. Nevertheless, the formation of an inner Cr-containing scale could still offer the alloy good protection because the external insoluble Ni or Fe oxides can protect it from dissolution.

中文翻译：

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纯Ni、Fe、Cr和Fe-5Cr合金在熔融氮化物中腐蚀的电化学阻抗研究

熔融硝酸盐或硝酸盐-亚硝酸盐混合物已在聚光太阳能发电厂和其他工业应用中用作传热流体以及热能存储介质。然而，与这些熔盐接触的安全壳材料会遭受熔盐腐蚀，这多年来一直是一个令人担忧的问题。在这项研究中，使用电化学阻抗谱和重量测试在 400°C 的熔融硝酸盐中检查了纯 Ni、Fe、Cr 和 Fe-5Cr 合金（以重量百分比计）的腐蚀行为。结果表明，Ni、Fe和Fe-5Cr表现出增重，其中Ni的耐腐蚀性能最好，其次是Fe-5Cr和Fe，而纯Cr则快速溶解，形成六价铬产物K ₃ Na(CrO ₄ ) ₂ . 从太阳盐到Hitec盐碱度的增加可以加速Cr的溶解。尽管如此，内部含铬氧化皮的形成仍然可以为合金提供良好的保护，因为外部不溶性镍或铁氧化物可以保护合金不被溶解。