SMCs Fe/(0.4-2.0 wt.)SiO_2/Polymer Prepared by Vacuum/Pressure Impregnation

摘要

Fe/(0.4-2 wt.%) SiO_2/polymer composite materials based on irregularly and/or spherically shaped iron powder particles coated with sol-gel SiO_2 layer or with an addition of SiO_2 nano-powder were prepared in two ways. One method is based on a vacuum/pressure impregnation (VPI) of low-temperature sintered Fe/SiO_2 compacts with shellac dissolved in ethanol as well as with thermoplast SL450 and the second method is using a conventional procedure - by mixing the Fe/SiO_2 powder with shellac dissolved in ethanol. The influence of the iron particles shape, the way of adding SiO_2 and the effect of polymer type used on the properties of electro-insulating layer was microscopically evaluated and correlated with electrical resistivity and magnetic coercivity. It was found that the thickness and continuity of insulating phase is strongly controlled by the shape of iron particles. The use of the shellac polymer is more advantageous than the thermoset SL450. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles with smooth surface are well covered with insulating phase.