Effects of some extracted oxides on silica fume waste for mullite preparation: Physical, mechanical, optical, magnetic, and dielectric properties

Abstract

In this study, Ceramic pigments on the base waste silica-containing material were obtained. Extracted corundum from alum sludge is mixed with silica fume to prepare mullite. The ions of iron, in the form of hematite (α-Fe2O3), magnetite (Fe3O4), and maghemite (γ-Fe2O3), which were extracted from alum sludge are embedded, from 2 to 15 wt%, in the prepared mixtures. The samples are sintered at 1300, 1400, 1500, and 1550 °C to follow the phase compositions. The phase composition, microstructure, physical properties, mechanical properties, magnetic properties, and dielectric properties as well as UV–visible reflectance spectra are determined for the sintered samples. A decrease in apparent porosities (The minimum apparent porosity is about 2%) and an increase in the bulk density (maximum bulk density reaches 2.77 g/cm3) are observed with increasing iron ions and sintering. The strength of the resulting samples increases with an increase in iron ions that enhance the in situ mullite formations, which act as the reinforcement agent of the matrix and form enough liquid phase at 1550 °C. The compressive strength becomes 278 MPa for samples containing high iron ions. Thus, the liquid phase helps in holding a crystalline mass together. The highest saturation magnetization is 2.26 emu/g after sintering at 1500 °C, obtained for the sample containing high amount of iron ions. The presence of high amount of iron oxide enhances the formation of the glassy phase that facilitates the mobile ions to find an easy path to move, thus, increasing the dielectric constant to 16. The pale browns to dark brown pigments are obtained to be recommended for ceramic paints and colored glazes for building materials.