Synthesis of Al₂O₃-Fe₂O₃-FeAl₂O₄ Composites by Colloidal and Traditional Powder Routes of Nano-Al₂O₃-Fe₂O₃ Mixtures

Morphological and microstructural changes induced by colloidal and traditional powder synthesis routes of nano-Al₂O₃-Fe₂O₃ mixtures were analyzed. Al₂O₃ was progressively replaced by 1, 2.5, 5, 10, and 20 wt % Fe₂O₃ nanoparticles. The replacement effect on dense ceramic composites formed by 100 MPa uniaxial pressure and sintered at 1500 °C was evaluated by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. After sintering treatment, the solid solution hercynite spinel-FeAl₂O₄ is obtained through a colloidal and a solid-state route (in all compositions). The utilization of the colloidal processing route allowed a homogeneous distribution of the Fe₂O₃ nanoparticles into the alumina matrix. Fe₂O₃ nanoparticles diffused at the Al₂O₃ grain boundaries, promoting better densification via hercynite formation. Also, the presence of Fe₂O₃ nanoparticles at grain boundaries acts, to a certain extent, as a pining component, promoting grain refinement. The colloidal synthesis route is a suitable alternative to promote densification in Al₂O₃-Fe₂O₃ dense ceramic composites.