Synthesis and Sintering

Crystallinity control in covalent triazine frameworks: Synthetic approaches and mechanistic insights

2026-08-09T16:45:19-03:00

An important class of emerging porous organic materials is covalent triazine frameworks (CTFs), which have attracted much attention in wastewater treatment, energy conversion, and gas absorption due to their chemical and thermal properties and high nitrogen content. The synthesis of CTFs faces several challenges, including the reversibility of the reactions, which leads to structural defects and poor crystallinity. As a result, achieving high crystallinity is a major goal in the research and development of CTFs. This brief review focuses on the latest advances in the synthesis and control of crystallinity of these nitrogen-rich materials. The paper proceeds in order to review the principles governing crystal formation, the synthesis methods and factors affecting the reactions, and the final operations to prepare the product to enhance crystallinity. In addition, common crystallinity assessment techniques, including powder X-ray diffraction, Fourier transform infrared spectroscopy and advanced analysis, are reviewed. The effect of framework crystal structure on performance optimization is also discussed. Finally, challenges and future prospects in the development of synthesis techniques for the technological advancement of CTFs are presented.

Design and finite element analysis of a bio-inspired cellular airfoil for selective laser melting

2026-08-09T16:36:40-03:00

The development of lightweight aerospace structures with high structural efficiency has increased interest in bio-inspired cellular architectures and additive manufacturing. In this study, a bio-inspired cellular airfoil developed as a candidate architecture for future fabrication by selective laser melting (SLM) is proposed and systematically investigated using finite element analysis. The internal architecture, inspired by the hierarchical structural characteristics of banana stems and spiral shells, was generated through a parametric methodology and integrated into NACA0010 and NACA2412 airfoil profiles. Eighteen configurations were created by varying the position factor (K₁) and scaling factor (K₂), and their mechanical responses were evaluated under bending using an elastic–perfectly plastic material model. The effects of the geometric parameters on load–displacement response, bending stiffness, von Mises stress distribution, and first-yield load were examined. The NACA2412 configurations exhibited bending stiffness values of 84.0–99.9 kN/mm, approximately twice those of the NACA0010 designs (41.2–48.0 kN/mm). The highest stiffness of 99.9 kN/mm was obtained for the NACA2412 configuration with K₁=0.5 and K₂=0.5; however, this design developed a maximum von Mises stress of 360 MPa and an estimated first-yield load of 16.0 kN. In contrast, the NACA2412 configuration with K₁=0.75 and K₂=0.5 achieved a bending stiffness of 90.6 kN/mm, a lower peak stress of 276.7 MPa, and the highest estimated first-yield load of 18.8 kN. These results demonstrate that maximizing structural stiffness alone does not necessarily provide the optimum cellular architecture and that the combined control of cellular size and internal member positioning is essential for balancing global stiffness and local stress concentration. The proposed parametric design framework provides a practical approach for developing structurally efficient bio-inspired cellular airfoils suitable for SLM-based aerospace applications.

Influence of K2O/(CaO+ZnO) ratio on crystallization behavior, phase formation, and properties of transparent borosilicate glazes

2026-08-10T04:52:39-03:00

The crystallization behavior of transparent borosilicate glass–ceramic glazes is strongly influenced by the composition of network-modifying oxides, which governs phase evolution and the resulting functional properties. In this study, the effect of the K₂O/(CaO+ZnO) ratio on the thermal behavior, structural evolution, phase formation, microstructure, optical properties, and mechanical performance of transparent borosilicate glazes was systematically investigated. Glass frits with different K₂O/(CaO+ZnO) ratios were prepared using the conventional melt-quenching method, applied onto ceramic substrates, and fired under identical conditions. The resulting glazes were characterized by differential thermal analysis (DTA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), optical measurements, and Vickers microhardness testing. The results showed that decreasing the K₂O/(CaO+ZnO) ratio significantly increased the glass transition temperature, indicating improved thermal stability of the parent glass, while only slightly affecting the crystallization peak temperature. Structural modifications of the borosilicate network promoted systematic changes in the crystalline phase assemblage, leading to the formation of anorthite, willemite, and calcium silicate phases with distinct crystal morphologies. Increased crystallization at lower K₂O/(CaO+ZnO) ratios reduced the gloss of the fired glazes because of enhanced light scattering, whereas the formation of harder crystalline phases improved the microhardness of the glass–ceramic coatings. These findings demonstrate that the K₂O/(CaO+ZnO) ratio is an effective compositional parameter for controlling the structure–property relationships of transparent borosilicate glazes and provides a practical strategy for optimizing their crystallization behavior and overall performance.

Microstructural transformation and recovery of rare earth elements during hydrochloric acid leaching of apatite concentrate

2026-08-09T16:30:58-03:00

Hydrochloric acid concentration plays a pivotal role in governing the dissolution behavior of apatite and the recovery of rare earth elements (REEs) during hydrometallurgical processing. In this study, the influence of hydrochloric acid concentration on the leaching of cerium (Ce), lanthanum (La), and neodymium (Nd) from an apatite concentrate derived from iron ore processing waste was comprehensively investigated by correlating microstructural evolution with leaching performance. Response surface methodology (RSM) coupled with central composite design (CCD) was employed to evaluate the combined effects of hydrochloric acid concentration and leaching temperature on the recovery of cerium, lanthanum, and neodymium. Throughout the optimization study, the solid-to-liquid ratio (1:9) and leaching time (60 min) were maintained constant to isolate the influence of the selected variables and improve the reliability of the statistical model. Under the optimum conditions of 37 wt% HCl, a solid-to-liquid ratio of 1:9, a leaching time of 60 min, and a temperature of 65 °C, the recoveries of Ce, La, and Nd reached 94.19%, 86.33%, and 76.34%, respectively. SEM analysis of the leaching residues revealed a progressive transition from relatively smooth, well-preserved crystalline particles at low acid concentrations to severely corroded, fragmented, and porous structures at higher acid concentrations. These microstructural transformations provide direct evidence of enhanced apatite decomposition and increased REE liberation, explaining the substantial improvement in extraction efficiency. The strong correlation between acid-induced microstructural evolution and REE recovery demonstrates that hydrochloric acid concentration is the primary driving force governing leaching performance. This study provides new mechanistic insight into acid-assisted apatite dissolution and establishes an optimized, economically attractive strategy for the efficient recovery of valuable REEs from apatite-rich iron ore tailings.