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| Effects of oxidation accelerator on phosphating of iron powders and soft magnetic properties of iron powder cores |
| LIU Xiangyang1, FU Jiaqian1, YU Yongliang2, LI Songlin1 |
1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China;
2. Shandong Luyin New Material Technology Co., Ltd., Laiwu 271105, China |
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Abstract The effects of oxidation accelerator Na2MoO4, NaNO2 and their compound addition on the phosphating reaction of iron powder in NaH2PO4 phosphating solution were investigated using reduced iron powder as matrix powder. The structure and properties of iron powder before and after phosphating and iron powder cores were characterized by scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectrometer, vibration sample magnetometer and soft magnetic AC measuring instrument. The results show that iron powder in 5% mass fraction of NaH2PO4 phosphating solution cannot form a complete and uniform coating with the rapid reaction speed. The soft magnetic loss of iron powder cores decreases, but the frequency stability of magnetic permeability is bad. The surface phosphating layer structure of iron powder phosphated by NaH2PO4 is mainly composed of Fe3(PO4)2 and FePO4. The addition of NaNO2 in NaH2PO4 phosphating solution promotes phosphate generation, but the coating isn’t uniform, and the coating layer is mainly composed of FePO4. Adding Na2MoO4 or Na2MoO4+NaNO2 composite oxidation accelerator to NaH2PO4 phosphating solution can generate uniform coating layer on the surface of iron powders and greatly reduce the eddy current loss of iron powder cores. The coating layer is mainly composed of FePO4 and Fe2(MoO4)3. The compound addition of Na2MoO4+NaNO2 compound addition has the best improvement effect on phosphating reaction. After heat treatment at 400 ℃, the resistivity of iron powder cores is 194.2 μΩ∙m, under the condition of Bm=50 mT, f =100 kHz, the magnetic permeability of iron cores is 92.5, and the soft magnetic loss is 142.0 W/kg.
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Received: 05 January 2022
Published: 19 July 2022
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2022, Vol. 27 
