Preparation and Characterization of Fe/SiO_2 Powder Composites Using Impregnation Method

摘要

Fe/SiO_2 powder composite materials based on irregularly and/or spherically shaped iron powder particles with an addition of SiO_2 nanopowder were prepared in two ways, (ⅰ) by mixing the Fe/SiO_2 powder with 1.0 wt.% of Shellac dissolved in ethanol and (ⅱ) by vacuum/pressure impregnation of low-temperature sintered Fe/SiO_2 components with shellac dissolved in ethanol and with thermoplast SL450. SiO_2 was implemented either as nanopowder or by sol-gel coating. Vacuum/pressure impregnation (VPI) of pre-sintered samples was performed in a steel container. The influence of iron particle shape and processing conditions on the electro-insulating layer was microscopically evaluated and correlated with the values of the electrical resistivity and coercivity. It has been found that the continuity, distribution and thickness of insulating phase is strongly controlled by the shape of iron particles. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles are well covered with continuous evenly distributed insulating layer.