Porous acicular mullite was fabricated at 1300 °C starting from Al₂O₃ and mixture of SiO₂ and MoO₃ obtained by previous oxidation of waste MoSi₂. It was found that the presence of MoO₃ favors formation of acicular (prism-like) mullite grains with sharp edges. The effect of addition of Fe₂O₃ (4–12 wt.%) on phase composition, compressive strength, thermal conductivity and microstructure was studied. The addition of Fe₂O₃ improved the compressive strength from approximately 25 MPa in pure mullite to about 76 MPa in samples containing 12 wt.% Fe₂O₃, while the open porosity decreased from 55.4% to 51.8%. The presence of Fe₂O₃ caused a decrease in mullite formation temperature owing to the formation of liquid phase and accelerated diffusion. The solubility of iron oxide in mullite lattice was between 8 and 12 wt.% Fe₂O₃. The incorporated iron ions also promoted the rounding of sharp edges in prismatic mullite grains, leading to a reduced specific surface area of 0.55 m²/g in the sample with 12 wt.% Fe₂O₃. The thermal conductivity of mullite increased with addition of 12 wt.% Fe₂O₃ reaching value of 1.17 W/m·K.

A promising approach for the removal of Cs⁺ ions from aqueous solutions and their long-term immobilization was investigated, as the safe containment of radioactive cesium is essential due to its long half-life and environmental hazards. The approach involves ion exchange using zeolite, geopolymerization, and subsequent heat treatment of the geopolymer/zeolite composite. Cs⁺ ions were removed from water by ion exchange using Na-13X zeolite, in which Cs⁺ ions replaced Na⁺ ions within the zeolite framework. The resulting Cs-13X zeolite was subsequently combined with kaolinite to prepare geopolymer/Cs-13X zeolite composites containing 10–50 wt% Cs-13X zeolite. During geopolymerization, a portion of the Cs was released from Cs-13X zeolite and incorporated into the geopolymer matrix, while the remaining Cs remained immobilized within the zeolite structure. Heat treatment of the geopolymer/Cs-13X zeolite composites at 950 °C induced crystallization of two stable Cs-bearing phases. The Cs incorporated into the geopolymer matrix crystallized as the CAS phase, whereas the Cs retained in the Cs-13X zeolite crystallized as pollucite. The crystalline phase content in the heat-treated composite samples increased with Cs-13X zeolite loading, resulting in improved density and compressive strength. The highest values of crystallinity (72%), bulk density (2.42 g/cm³), and compressive strength (~53 MPa) were measured for samples containing 50 wt% Cs-13X zeolite. This level of compressive strength is sufficient to ensure safe handling and long-term containment of the immobilized Cs⁺ ions.

Dense Ce,Pr-doped YAG transparent ceramics (YAG:Ce,Pr) with enhanced red emission were fabricated by pressureless sintering in air at 1600 °C. Fine YAG powders containing 0.2 mol% Ce and varying amounts of Pr (0.04–0.32 mol%) were synthesized using a glycine–nitrate combustion method. The emission and excitation spectra were analyzed to investigate the influence of Pr doping on red emission. The results indicate that YAG: Ce,Pr ceramics are a promising candidate for blue-to-yellow light conversion. The strongest red emission component was measured in samples containing 0.16 mol% Pr. It was confirmed that electron transfer from Ce to Pr enhances the red emission component (609 nm), primarily by increasing the population of electrons relaxing from the ¹D₂ excited state to the ³H₄ ground state. Further increasing the Pr concentration beyond 0.16 mol% resulted in a reduction in the red emission intensity due to concentration quenching. Microstructural analysis of YAG:Ce,Pr revealed a dense and homogeneous microstructure composed of equiaxed grains.