The compactability and sinterability of alumina granules prepared by spray freeze granulation drying (SFGD) and spray drying (SD) were compared. The strengths of the granules made by SFGD and SD, densities of the green bodies and sintered bodies, pore size distributions of the green bodies, internal structures and strengths of sintered bodies made from SFGD and SD granules were evaluated. The strength of SFGD granules was lower than that of SD granules. The lower granule strength of the SFGD granules was advantageous to form a uniform structure without inter-granular pores in the green body, resulted in higher density and strength of the sintered body.

Al₄SiC₄–SiC composite carbides are expected as a high-temperature structural material because Al₄SiC₄ and SiC have high melting points. Synthesis, its densification and its oxidation behavior of Al₄SiC₄–SiC composite carbides have been investigated in this paper. Al₄SiC₄–SiC composite carbides were synthesized from the mixtures of Al₄C₃, C and kaolin powder by carbothermal reduction heating at 1550 °C for 12 h in vacuum. The dense sintered Al₄SiC₄–SiC composite carbide with above 97.6 % relative density is obtained by heating at 1700 °C for 1 h under 50 MPa by hot-pressing (HP). Oxidation of the sintered Al₄SiC₄–SiC composite carbides doesn’t almost progress even at 1500 °C, because of the formation of an oxide protective layer near the surface.

MgO, Mg₂SiO₄, and MgO/Mg₂SiO₄ nanostructures were synthesized, and their luminescence properties were investigated. The morphological and structural properties of the MgO nanostructures were also characterized. Sponge-like MgO particles with layered nanosheet structures were synthesized by thermally annealing MgCl₂ in air. The MgO nanostructures exhibited a cathodoluminescence emission peak at 5.2 eV with a small peak at 2.4 eV. The Mg₂SiO₄ and MgO/Mg₂SiO₄ nanostructures were also synthesized by annealing MgCl₂ with CaSi₂. Mg₂SiO₄ domains were formed on the surface of the MgO particles. Two main emission peaks were observed for the MgO/Mg₂SiO₄ nanostructures—one at approximately 5.2 eV and another in the range of 2.4–3.4 eV. Compared to MgO, the photoluminescence characteristics of the MgO/Mg₂SiO₄ nanostructures were modified, and the emission peaks were shifted. The formation of Mg₂SiO₄ with MgO expanded the visible–ultraviolet emission regions from 2.4 to 3.4 eV under cathode-ray excitation, followed by a shift from 2.1 to 2.0 eV under photo excitation.

The effects of HCl additives (HCl/Si molar ratio = 0.1) on the crystallization behavior, chemical microstructure, and surface morphology of gel-derived lithium disilicate (Li₂Si₂O₅, LD) powders were investigated using sol–gel and heat treatment processes. With HCl additives, the lithium metasilicate (Li₂SiO₃, LM) phase preferentially crystallized even at 200 °C for post-heat treated gel-derived LD powders. Moreover, several Li⁺ ions might not be attached to the [SiO₄] network but could be located in the residual pores and surfaces in the form of Li(H₂O)_n⁺ ions for pre-heat treated gel-derived LD powders. Meanwhile, Cl⁻ ions could occupy residual pores and surfaces, and be located in the [SiO₄] network by forming Si–Cl bonds. In contrast, without HCl additives, only simultaneous crystallization of LM and LD phases appeared at 600 °C. Correspondingly, fewer Li(H₂O)_n⁺ ions were estimated to be located in the residual pores and surfaces, and more Li⁺ ions were located in the [SiO₄] network. With HCl additives, the surface morphology of pre-heat treated gel-derived LD powders was characterized by larger particles and smaller voids, in contrast to those without HCl additives, which comprised smaller particles and larger voids. The unique crystallization behavior might be caused by the interactions that occurred between Li(H₂O)_n⁺ ions and Si–OH groups, as well as Cl⁻ ions and Si–Cl bonds in the chemical microstructure of pre-heat treated gel-derived LD powders. These results indicate that HCl additives could effectively modify crystallization behaviors, chemical microstructure, and surface morphologies of gel-derived LD powders, by reacting with LiOH·H₂O precursors during the sol–gel process.

This present study focuses on the synthesis and characterization of orthorhombic niobate compounds, including TbNbTiO₆ and DyNbTiO₆, as well as their solid solutions. These solid solutions were synthesized by substituting Dy³⁺ for Tb³⁺ in a high-temperature solid-state reaction, while maintaining a stoichiometric atomic ratio. The study has identified the solid solution range as well. X-ray diffraction (XRD) analyses of all synthesized compounds revealed that their crystal structures exhibit an orthorhombic system within the Pbcn space group. Additionally, scanning electron microscopy (SEM) was employed for surface morphology assessments, and UV–visible diffused reflectance spectroscopy (DRS) was used for band gap assessments. Furthermore, electronic properties, such as the band structure and density of states, were computationally elucidated. The study also delved into the photocatalytic properties of the materials.

Fly ash is a chemically promising material composed of several metal oxides, including SiO₂, Al₂O₃, MgO, and Fe₂O₃. However, its chemical properties have not been successfully exploited in catalysis applications. One of the reasons for this is that the effective surface area of fly ash is extremely small because vitrification proceeds through combustion in a furnace under high-temperature conditions. In this study, a pozzolanic reaction was applied to increase the surface area of fly ash and improve its performance as a solid base catalyst. Microcrystals of calcite (CaCO₃) and tobermorite (Ca₅Si₆O₁₈H₂·4H₂O) were formed on the surface by reacting fly ash with calcium hydroxide in water at 40 °C. After 11 days of the reaction, the surface area of the fly ash (22 m² g⁻¹) increased to almost 11 times that of the raw fly ash (2 m² g⁻¹). The fly ash–based catalyst was applied as a solid base catalyst to the Knoevenagel condensation reaction of malonic acid with benzaldehyde. Although the catalytic activity of the raw fly ash for the Knoevenagel condensation reaction was considered acceptable, the catalytic activity of the fly ash–based catalyst increased by approximately fivefold after 11 days of reaction with calcium hydroxide. The changes in the physical and chemical properties of fly ash induced by the reaction with calcium hydroxide were discussed.

This study demonstrates the inverse prediction of the discrete-element method (DEM) input friction coefficient from the DEM output powder properties such as the outflow rate, aerated bulk density, and repose angle. Support vector (SV) regression can reasonably reproduce the friction coefficient from the DEM output powder properties. Among the powder properties considered in this study, the outflow rate is found to be the most effective for predicting the friction coefficient. Other powder properties also contribute to improving the prediction accuracy. The accuracy of the SV model depends on the number of cases used for the inverse regression of the friction coefficient, and models with practical accuracy can be obtained for 100–200 cases. These results will lead to further use of machine learning in DEM simulations.

A colloidal solution dispersing Ag nanoparticles (AgNPs) of ∼5–30 nm in diameter was prepared using a silane coupling agent 3-mercaptopropyltrimethoxysilane. The AgNPs were immobilized on glass fiber cloth and Ti plates by forming, most likely, Si–O–Si and Si–O–Ti bonds, respectively, by simply applying and drying the solution. The resultant AgNPs-immobilized glass fiber cloth and Ti plates exhibited excellent bactericidal behavior, even after sonication in water for 30 min.