Preparation, chemical and mechanical properties of microcomposite materials based on Fe powder and phenol-formaldehyde resin

Preparation of microcomposite materials based on Fe powder and the modified phenol-formaldehyde resin (PFR) was investigated with the aim to design a new class of prospective soft magnetic materials. Undesirable evolution of water and other volatile by-products during curing process was eliminated by modification of resol prepolymer coating with two different inorganic additives – SiO2 and ZnSO4. The structure of synthesized PFR was confirmed by 13C-NMR spectroscopy. The effect of both additives on thermal degradation, structure and morphology was studied by employing TG, DSC, IR and SEM analysis. The addition of ZnSO4 into PFR caused a significant change in the polymer structure, which is constituted by nano-fibers linking Fe particles. The observed unusual structure of PFR–ZnSO4 coating on Fe particles results in a higher mechanical hardness and flexural strength compared to the Fe particles coated by the pure PFR or PFR–SiO2. It is shown that the microcomposites with a few percentages of PFR coatings exhibit a substantial increase of the specific resistivity and they still belong to soft magnetic materials with low enough coercivity.

► Core–shell microcomposite is prepared from Fe powder and phenol-formaldehyde resin.
► SiO2 and ZnSO4 additives prevent foaming and formation of microvoids.
► ZnSO4 additive provokes polymerization to fine fibers of nanometer size.
► SiO2 and ZnSO4 additives increase a hardness of prepared microcomposites.
► Electrical resistivity of microcomposites is much greater than that of Fe sample.