Effects of Phosphating Treatment on the Growth of a Phosphate Layer and the Magnetic Properties of Fe-Based Amorphous Magnetic Powder Cores

In this work, amorphous soft magnetic powder cores (AMPCs) were prepared by inorganic-organic multiple-layer coating based on gas-atomized amorphous FeSiCrB powders. The influence of phosphating treatment on the performance of the AMPCs was studied. The results show that the powder coating with a low concentration of phosphoric acid-acetone solution leads to uneven coating, while increased phosphoric acid concentration causes peeling of the phosphate coating. However, by phosphoric acid-ethanol coating at relatively high temperature, the powder exhibits uniform and dense phosphate coating, resulting in significantly decreased eddy current loss of the AMPC. For the AMPCs coated with 0.6 wt.% phosphoric acid-ethanol solution in a 55 degrees C water bath, optimized magnetic properties were achieved, including good frequency stability of effective permeability mu(e) of 18.5 within 16 MHz and low core loss of 489.6 mW/cm(3) at 200 kHz under an applied magnetic field B-m = 0.03 T. These results indicate promising potential application of AMPCs for inductors working at high frequencies.