Manganese phosphate coated flaky FeSiAl powders with enhanced microwave absorbing properties and improved corrosion resistance

The electromagnetic wave absorption in X frequency band is every important for various applications. Except desired electromagnetic properties, excellent corrosion resistance is also required for the microwave absorbing materials used in harsh environments. Herein, the flaky FeSiAl (FSA) powders with large aspect ratios were coated with an insulation layer by manganese phosphating treatment. The electric insulating Mn3(PO4)2 coating reduces the eddy current between the particles. The heterointerface also improves the impedance matching of the absorbing materials and introduces additional loss mechanisms. By optimizing the thickness of the absorber, the composite consisting of 40 wt% FSA@Mn3(PO4)2 and 60 wt% paraffin wax with a thickness of 2.38 mm shows excellent microwave absorption properties with a minimum reflection loss of −62.86 dB at the frequency of 9.42 GHz and an optimized effective absorption bandwidth of 2.72 GHz. The anti-corrosion properties of the FSA@Mn3(PO4)2 and Teflon composites were also investigated. The corrosion rate of the optimally Mn3(PO4)2 coated FSA is 3 times slower than the naked FSA particles. The high stability of FSA@Mn3(PO4)2 composite in the corrosion environment results from the superior impermeability Mn3(PO4)2 coating. The present work provides a relatively low cost phosphating process for manufacturing anti-corrosion microwave absorbers working in the widely-used X frequency band.