This review presents an advanced methodology for producing silicon nitride (Si₃N₄) ceramics with tailored microstructures and distinctive engineering characteristics. Si₃N₄ ceramics are typically composed of highly complex microstructures, including elongated grains dispersed amidst fine grains and grain boundaries, resulting in excellent mechanical, thermal, and electrical properties. Owing to these unique morphologies, Si₃N₄ with enhanced thermal conductivity and mechanical strength has potential practical industrial applications, particularly in insulated heat-dissipating substrates for power modules. In this review, first, the nitridation parameters for the sintered reaction-bonded Si₃N₄ method, which can be utilized to prepare high-performance Si₃N₄ ceramics, are discussed. Second, details of the dielectric breakdown in Si₃N₄ are introduced, and possible defects are suggested based on the results. Finally, artificial intelligence (AI)-based determination technologies utilizing microstructural images via convolutional neural network models are proposed, demonstrating a relatively high accuracy in the AI evaluation of the bending strength and fracture toughness.

Glass with a chemical composition of 69.7SiO₂–7.9CaO–5.5Na₂O–3.5K₂O–1.4Al₂O₃–12CaF₂ (mol %) was crystallized via a simple heat treatment. CaF₂ and xonotlite precipitated above the glass transition temperature, followed by the precipitation of α-cristobalite above 900 °C. Thermal expansion curve of the glass–ceramics containing α-cristobalite exhibited a steep increase around 270 °C due to α–β phase transition of cristobalite. Ball indentation test on the glass–ceramics resulted in a clear circular dent in the glass–ceramics with precipitated cristobalite but only ring cracks in the glass–ceramics without cristobalite. X-ray computed tomography using synchrotron radiation revealed the formation of microcracks around cristobalite, with a greater number of microcracks observed after ball indentation. Therefore, it was concluded that the stress caused by a large volume change during the α–β phase transition of cristobalite induced the generation of microcracks in the glass–ceramics during cooling, eventually leading to ductile behavior. The glass–ceramics also exhibited ductile behavior in the bending test that was used to measure fracture toughness. The obtained findings offer valuable insights into the fabrication of a new type of glass–ceramics with ductile behavior, which is expected to expand the application scope of glass–ceramics.

Porosity plays an essential role in the performance of ceramics. In this study, the effects of clay composition and firing temperature on the pore size distribution of ceramics were evaluated by small-angle neutron scattering (SANS) measurements. Compared with quartz-rich pure Kasama clay, a mullite-rich Kasama clay blend had smaller pores after heat treatment. SANS measurements of D₂O-absorbed samples revealed that open pores with sizes ranging from tens of nanometers to about a micrometer contributed to the absorption of water. The closed and open pores coarsened and the total porosity decreased with increasing firing temperature.

Optical properties, shrinkage, and crack formation up to 800 °C were studied on TiO₂ and SiO₂ sol–gel films for application to thermal radiation control. Using precursor sols comprising hydrolyzed alkoxides and polymers, high-transparency films were obtained for TiO₂ and SiO₂. However, after heating at high temperatures, TiO₂ films exhibited a slight degradation in transmittance due to light scattering by rutile grains. For both materials film thickness decreased by nearly half by increasing the heating temperature from 130 to 800 °C, giving rise to a much smaller critical cracking thickness than that obtained at low temperatures. Within the maximum thickness of the crack-free films, we fabricated TiO₂/SiO₂ alternating stacks as very near-infrared optical filters that allowed the control of the radiation spectra from a plate heater. The emissivity spectra measured on the film/heater system at 750 °C indicated fair agreement with the designed optical transmittance of the stacks, proving the feasibility of applying sol–gel films to thermal radiation control.

It is crucial to develop calcium phosphate cements with high bone regeneration abilities. This study demonstrates synthesis of porous calcium phosphate cements that are set by precipitating octacalcium phosphate (OCP) using α-tricalcium phosphate (α-TCP) and calcium hydrogen phosphate dihydrate (DCPD). Porous spherical granules composed of α-TCP were mixed with either a DCPD powder or α-TCP/DCPD powder mixture as a binder. Next, an appropriate amount of water was added, and the mixture was kneaded. Notably, employing the α-TCP/DCPD powder mixture reduced the setting time of the cement to about 30 min. Porous cements with macropores and micropores were obtained upon precipitation of OCP. Dissolution rate of the obtained cement was higher than that of cements comprising Ca-deficient hydroxyapatite and hydroxyapatite porous ceramics. Our results suggest that this cement may exhibit excellent bone regeneration ability.

Relaxation analysis has been carried out on charge–discharge cycled SiO-graphite composite anode to evaluate the effect of the cycle process on the relaxation behavior after lithium insertion. From the stage change in Li-GIC during the relaxation period, we measured the migrated amount of Li-ion from Li-GIC into SiO and discussed the contribution of charge/discharge cycles. The amount of Li-ion migration is decreased with the cycle number due to the degradation of SiO, which results in the increased rate constant of Li-ion migration.

Slip-casting is a shaping technique for producing fine ceramic green bodies by mixing a raw powder with water and a dispersant to form a slurry, which is then poured into a gypsum mold to create a solid shape. Coarse-grained raw powders are less expensive but present challenges in slip-casting owing to faster sedimentation and reduced water retention, prompting the need for thickening agents to improve the process. In this study, cellulose nanofibers (CNFs) are added to a slurry to actualize the slip-casting of coarse-grained alumina (∼3.6 µm) with a sintering additive, and their effect on the castability of the slurry is investigated. The slurry without CNFs consolidates immediately after being poured into a gypsum mold. Thus, it can be concluded that slip-casting is difficult for slurries without CNFs. In contrast, the addition of CNFs to the slurry suppresses rapid water absorption and produces a healthy slip-casted green body. A suitable slurry for slip-casting is investigated by adjusting the volume fraction of alumina powder and the amount of CNFs added to the slurry. Shape forming by slip-casting becomes possible by using the optimized slurry. Moreover, a dense sintered body is produced using the slurry via slip-casting and sintering.