Phosphoric acid addition effect on the microstructure and magnetic properties of iron-based soft magnetic composites

• Published in: Journal of magnetism and magnetic materials 2018-02, Vol.447, p.1-8
• Main Authors: Hsiang, Hsing-I, Fan, Liang-Fang, Hung, Jia-Jing
• Format: Article
• Language: English
• Subjects: Bias; Carbonyl iron powders; Carbonyl powders; Coating effects; Corrosion; Corrosion resistance; Domain walls; Insulation; Iron; Iron phosphate; Magnetic fields; Magnetic permeability; Magnetic properties; Magnetic resonance; Microstructure; Particulate composites; Phosphates; Phosphating; Phosphating (coating); Phosphoric acid; Precipitates; Protective coatings; Scanning electron microscopy; SMCs; Studies; Superposition (mathematics)
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2017.08.096

•H3PO4 concentration can adjust the iron phosphate shell thickness.•Iron phosphate shell is formed after phosphatizing treatment.•Temperature and corrosion resistance of SMCs were improved by phosphatizing.•DC-bias superposition characteristic was improved by phosphatizing. The phosphoric acid addition effect on phosphate insulation coating microstructure was investigated in this study. The relationships between the phosphate insulation coating microstructure and temperature resistance, corrosion resistance and magnetic properties of iron-based soft magnetic composites (SMCs) were studied by using SEM, TEM/EDS and FTIR. It was observed that an iron phosphate/carbonyl iron core/shell structure is formed with carbonyl iron powder after phosphatizing treatment. The iron phosphate phase was identified as amorphous and its thickness increased from 30nm to 60nm as the phosphoric acid concentration was increased from 1wt% to 2wt%. When the phosphoric acid concentration was further increased to 5wt%, the excess iron phosphate precipitates between the soft magnetic composite particles. The temperature and corrosion resistance and resistivity of the iron-based SMCs can be effectively improved using carbonyl iron powders after phosphatizing. The initial permeability of the iron-based SMCs decreased with increasing phosphoric acid concentration due to thicker insulation layer formation. However, the imaginary permeability below the domain wall displacement resonance frequency decreased with increasing phosphoric acid concentration. The DC-bias superposition characteristic can also be improved by increasing the phosphoric acid concentration. Iron-based SMCs with superior temperature and corrosion resistance, initial permeability, magnetic loss and DC-bias superposition characteristics can be obtained by controlling the phosphoric acid concentration during phosphatizing to adjust the iron phosphate precipitate thickness on the iron powder surface.