Novel ceramic materials based on industrial wastes within the CaO–MgO–Al2O3–SiO2 system

Abstract

The use of solid waste and raw materials such as ceramic sludge, klin rollers, magnesite, and limestone to produce low cost refractory ceramics after sintering at 1300 °C for 2 h was studied. Sample D30 with a composition of, 30 % diopside and 70 % mullite, was selected to be treated at 1200 °C for 2 h to investigate the effect of temperature on phase evolution. Microstructure, morphology and physical properties were also studied. Several techniques including XRF, XRD, SEM, EDX, flexural strength, and dielectric properties were used for samples characterisation. Densification parameters, morphology and microstructure were studied in order to evaluate the influence of the formed phases on the properties of produced ceramic materials. The study showed that the bulk density increased with the formation of corundum and mullite phases and decreased with the formation of anorthite and spinel phases. Bulk density also increased at higher firing temperatures. In contrast, porosity and water absorption showed the opposite trend to density. The main phases developed after firing at 1300 °C for 2 h were corundum, spinel, mullite, and anorthite. Flexural strength values were increased by increasing the precipitation pecent of corundum and mullite phases, as well as with bulk density. But it decreased with increasing porosity and both anorthite and spinel contents; ranging between 8.00 and 11.00 MPa. Bulk density increased with increasing of mullite content and temperature, ranging from 1.72 to 2.00 g/cm³, while porosity and water absorption ratio decreased from 32.59 to 22.10 and from 19.66 to 10.98, respectively. The microstructure morphology was converted from coarse-grained to fine-grained with increasing anorthite and spinel phases by increasing the temperature. To investigate the effect of the phases precipitated from the diopside-mullite system on their dielectric properties, parameters such as permeability (ε’), dielectric loss (ε′′), alternating current conductivity (σac) and Modulus'' were measured at the frequency range from 10⁻¹ Hz–10⁶ Hz. There is no noticeable effect on any of the dielectric parameters by increasing the concentration of diopside (CaMgSi₂O₆). In addition, the conductivity indicated that all the samples are insulators (σ_dc ≈ 10 pS/cm at f = 0.1 Hz) without any noticeable effect of composition.