Sodium nitrate passivation has been developed as a new insulation technology for the production of FeSiAl soft magnetic composites (SMCs). In this work, the evolution of coating layers grown at different pH values is investigated involving analyses on their composition and microstructure. An insulation coating obtained using an acidic NaNO₃ solution is found to contain Fe₂O₃, SiO₂, Al₂O₃, and AlO(OH). The Fe₂O₃ transforms into Fe₃O₄ with weakened oxidizability of the NO₃^– at an elevated pH, whereas an alkaline NaNO₃ solution leads to the production of Al₂O₃, AlO(OH), and SiO₂. Such growth is explained from both thermodynamic and kinetic perspectives and is correlated to the soft magnetic properties of the FeSiAl SMCs. Under tuned passivation conditions, optimal performance with an effective permeability of 97.2 and a core loss of 296.4 mW∙cm⁻³ is achieved at 50 kHz and 100 mT.

硝酸钠钝化已发展成为一种用于生产 FeSiAl 软磁复合材料 (SMC) 的新型绝缘技术。在这项工作中，研究了在不同 pH 值下生长的涂层的演变，包括对其成分和微观结构的分析。_{发现使用酸性NaNO 3}溶液获得的绝缘涂层含有Fe ₂ O ₃、SiO ₂、Al ₂ O ₃和AlO(OH)。Fe ₂ O ₃转化为 Fe ₃ O _{4 ，NO 3}的氧化性减弱^——在升高的 pH 值下，而碱性 NaNO ₃溶液导致生成 Al ₂ O ₃、AlO(OH) 和 SiO ₂。这种生长可以从热力学和动力学的角度进行解释，并且与 FeSiAl SMC 的软磁性能相关。在调谐钝化条件下，在 50 kHz 和 100 mT 下实现了有效磁导率 97.2 和铁芯损耗 296.4 mW∙cm ^{−3的最佳性能。}