Microwave absorption properties and complex permittivity of Fe/FeAl₂O₄ coatings deposited by reactive plasma spraying Al/Fe₂O₃ powders

In this study, spray dried Al/Fe₂O₃ composite powders were deposited for application as microwave absorbers by reactive plasma spraying (RPS). The morphology of the composite powders and cross-section of coatings were examined by scanning electron microscope (SEM). The main products were identified as hercynite (FeAl₂O₄) and iron (Fe) by X-ray diffraction. The effects of Al/Fe₂O₃ ratio on the complex permittivity and microwave absorption properties of the coatings were investigated in the frequency range from 8.2 to 12.4GHz. In addition, the mechanisms of polarization and microwave energy loss are discussed. The real part (ε') of the complex permittivity increases with increasing Al concentration, which is attributed to the more interfacial polarization and the imaginary part (ε') also increases which is ascribed to the increasing electrical conductivity of the coatings. By calculating the microwave absorption as a single-layer absorber, we find that the reflection loss varies with the changes of thickness and the amount of reduced Fe in coatings, due to the deviation of impedance matching condition.