Expectations for the sensing of very small amounts of gases and odors are increasing in many fields such as medicine, healthcare, and mobility. In recent years, nanomaterials with various forms such as needle-like, belt-like, sheet-like, and dendrite-like have been developed. These nanomaterials have been used to detect very small amounts of gas with a semiconductor gas sensor. In addition, detection of various gases and odor molecules has been realized using these gas sensors. In particular, in the field of ceramics, which requires high-temperature firing at several hundred degrees Celsius, the realization of “cold crystallization”, which has been a long-standing issue, has had a great impact. Nanomaterials with high surface area, unique shape, metastable crystal facets, etc. have been developed with cold crystallization of ceramics. These nanomaterials have improved the low-concentration gas detection characteristics of gas sensors and odor sensors. In this review, I would like to introduce the fabrication of new SnO₂ nanomaterials and the development of gas and odor sensors using the SnO₂ nanomaterials.

It is important to control and characterize the particles dispersion and aggregation state in a slurry for ceramics wet forming processes. In these processes the particle concentration of the slurry must be high, thus, it is desired to directly evaluate the particles dispersion state for dense slurries without dilution. In this paper, we discuss the relationship between the density of green body fabricated in tape casting process and the slurry characteristics measured without dilution, such as apparent viscosity (relative viscosity) and the packing fraction of sediment. It was demonstrated that the slurry with the highest packing fraction of sediment yields the green sheet with the highest density, while the slurry with the lowest apparent viscosity (relative viscosity) does not necessarily yield the green sheet with the highest density. It was indicated that the key of slurry characterization for controlling the density of green sheet should be considering the change of the particles dispersion and aggregation state due to thickening and dehydrating of the slurry in tape casting process.

This review focuses on our results on the fabrication of large-area patterning of tin oxide suspensions by the “micromolding in capillary” (MIMIC) method, one of the soft lithography techniques. Usually, suspensions with high solid loadings have been experimented, but since the filling mechanism of the MIMIC method is capillary action, the viscosity increases during the process, resulting in a smaller patterning area. We have confirmed that a low solids ethanol suspension of tin oxide nanoparticle can be used to achieve large-area patterning, forming a stripe pattern with a thickness of almost 1/3 the depth of the mold channel, resulting in a dense structure. Confirming the patterning mechanism, we found that controlling solvent evaporation during the process was very effective. It is expected that this MIMIC process for low solids loading suspensions of nanoparticles will be widely deployed for other types of ceramic suspensions.

Grinding is a unit operation to reduce particle size by milling, and recently the demands for such operations have been increasing more and more. Computer simulation is effective in optimizing the grinding process and designing equipment, and the number of studies is increasing. To predict grinding results quickly with a low calculation load, it is useful to output the impact energy obtained from ball-only calculations as an indicator of grinding. We introduce how simulation can be used in grinding process analysis, including examples of reproducing ball behavior, predicting grinding results such as particle size distribution, and analyzing mechanochemical effects.

Among the many methods, the use of solar photocatalytic water splitting to produce hydrogen is the most promising one. The water splitting process mainly includes the following three steps: solar energy capture, transfer and separation of photogenerated charges, and catalytic protons to generate hydrogen. At present, a high number of studies mainly focus on the first and second steps, and there are relatively few studies garding the third step. The introduction of a co-catalyst can effectively improve the photocatalytic activity and increase the hydrogen production rate. Co-catalysts mainly include noble metal catalysts and non-noble metal catalysts. Although noble metal catalysts provide a better performance, their high price limits their wide application. Therefore, it is particularly important to develop efficient and inexpensive non-precious metal catalysts. This paper briefly summarizes the use of non-noble metal catalysts based on TiO₂ photocatalytic hydrogen evolution. The action mechanism and related synthesis methods of the co-catalysts are discussed, and the development direction of non-noble metal cocatalysts is briefly described.