Development of the properties of magnesia alumina spinel-based refractory composites with modifying oxides
Aleksandra Bąk, Bartosz Surówka, Ryszard Prorok, Dominika Madej
Quarterly No. 3, 2025 pages 166-180
DOI: https://doi.org/10.62753/ctp.2025.01.3.3
keywords: spinel-based high-temperature ceramics, refractories, sintering, additives, composites
abstract The present study investigates the synthesis of MgAl2O4 spinel via one-step sintering, producing a reference sample without additives and four additional samples containing 5 wt% ZrO2, Fe2O3, SiO2, or TiO2, respectively. The MA sample along with the four types of modified spinel-based composites [MA_5T, MA_5Z, MA_5F, MA_5S] were characterized in terms of their phase composition, microstructure, bulk and true densities, as well as open and true porosities of the sintered materials. High-temperature microscopy was employed to evaluate dimensional changes of the samples during their heat treatment process. The presence of phases and the firing behavior of the resulting composite materials were evaluated using thermodynamic simulation (FactSage 8.3). The study demonstrated that the incorporation of specific oxide additives significantly influences the synthesis and properties of MgAl₂O₄ spinel. Iron (Fe³⁺) and titanium (Ti⁴⁺) ions were found to induce structural modifications within the spinel lattice, suggesting partial substitution or incorporation into the crystal framework. XRD analysis showed that the addition of the SiO₂ modifier leads to the formation of Mg₂SiO₄, which can partially dissolve into the spinel phase, while ZrO₂ promoted the extraction of Al³⁺ ions from the spinel structure, as corroborated by the thermochemical simulations using FactSage. The highest microstructural densification was achieved in the samples with TiO₂ and SiO₂, indicating their positive role in enhancing sintering efficiency. Conversely, the addition of Fe₂O₃ did not significantly affect the densification behavior, despite the formation of an Fe-rich spinel phase.