本研究发明了制备FeSiAl软磁复合材料（SMC）的硝酸钠钝化绝缘包覆新技术。结合成分组成和微观结构分析，研究了不同pH条件下包覆层的生成规律，发现酸性NaNO₃溶液钝化形成的绝缘包覆层由Fe₂O₃、SiO₂、Al₂O₃和AlO(OH)组成。随着pH值升高，由于NO₃⁻的氧化能力减弱，Fe₂O₃转化为Fe₃O₄，而碱性NaNO₃溶液钝化形成Al₂O₃、AlO(OH)和SiO₂。进一步地，从热力学和动力学角度揭示了包覆层生长机理及其与FeSiAl SMC软磁性能的内在关联。通过调整钝化条件，可实现在50 kHz和100 mT测试条件下，有效磁导率为97.2、损耗为296.4 mW·cm⁻³的最优性能。

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.