Haruhisa Shiomi

Preparation of SnO2 Monolithic Gel by Sol-Gel Method

The effects of aging of a wet gel at room temperature and a use of a drying control chemical additive (DCCA) were investigated on the prevention of cracking of the gel during drying. N,N-Dimethylformamide (DMF) having low surface tension was used as a DCCA in this study. Before drying, the aged wet gel was immersed in DMF for several days to replace the pore liquid in the wet gel with DMF.The longer the aging and DMF immersing times became, a fewer cracks generated during drying. Especially, the immersion in DMF for over 8 days made it possible to obtain the SnO2 gel monolith without cracking from the wet gel aged for short time (1 day). However, the wet gel aged for long time without immersing in DMF could not be dried without cracking. Therefore, the replacement of the pore liquid in the wet gel with DMF having low surface tension is thought to be more effective on avoiding a crack generation than aging. From a pore size distribution measurement by N2 gas adsorption, it was found that the pore size and the breadth of the pore size distribution of the dried gel became larger and narrower respectively with increasing DMF immersing time. DMF is thought to be capable of forming strong hydrogen bonding to hydroxyl groups remaining on the surface of the wet gel and providing a shielding cage around the reactants (Sn–OH), thus further condensation reaction is probably suppressed. Consequently, a large pore distribution is developed in the gel, which reduces the magnitude of capillary stress induced during drying.

Preparation of Inorganic Consolidated Body Using Aluminium Hydroxide Mechanically Activated by Dry Milling

Aluminium hydroxide (Al(OH)3) was mechanically activated by dry milling. In order to develop an inorganic consolidated material, the structure and reactivity of milled Al(OH)3 were investigated and consolidated bodies were prepared using the reaction between activated Al(OH)3 and a potassium silicate solution. Milling up to 1 h apparently reduced the grain size and promoted amorphization, although milling longer than 2 h did not give a significant physical change. Milled Al(OH)3 directly transformed to χ-Al2O3 around 270°C. The transformation temperature decreased with increasing milling time. The remarkable enhancement of the reactivity was attained. The reactivity of Al(OH)3 milled for 2 h improved 1000 times more than that of as-received Al(OH)3. The preforming paste, prepared with as-received Al(OH)3, could not consolidate at room temperature without drying. On the other hand, for Al(OH)3 milled for 2 h, the preforming paste consolidated in 10 min and the consolidated material showed much better resistance against water than that prepared with as-received Al(OH)3. The possibility of a new inorganic consolidated material was suggested using the reaction between mechanically activated Al(OH)3 and the potassium silicate solution.

Effect of addition of Ag on the microstructures and electrical properties of sol-gel derived SnO2 glass composites

The effect of addition of Ag on the microstructure and electrical properties of sol-gel derived SnO2-glass composites was examined. Comparisons of the microstructures and electrical properties were carried out between glass composites prepared by a sol-gel method and a conventional one using glass frit. The glass composite gels and the SnO2-glass powder mixtures containing AgNO3 were calcined at 500 °C in order to decompose AgNO3 into Ag and then fired at 900 °C. In the sol-gel derived glass composites, the grain growth of Ag was suppressed and Ag particles connected mutually at the boundaries of aggregated gel particles to form three-dimensional networks. Thus, the glass composite derived by the sol-gel method showed a high electrical conductivity and a positive temperature coefficient of resistance (TCR). The highly electrical conductive paths of Ag in the glass composite were effectively formed when powder compacts were formed at a higher pressure. On the other hand, in the glass composites prepared using SnO2-glass powder mixtures, coarse-grained Ag particles were isolated in closed pores regardless of the forming pressure, and therefore did not contribute to electrical conduction in the glass composite.

Effect of pH and aging temperature on the phosphorus removal properties of layered hydroxide synthesized from zinc acetate

ABSTRACT Zinc hydroxide acetate (ZHA) is a promising material for anion exchange applications because it has a layered structure with intercalating CH3COO− and H2O. ZHA can be synthesized through a direct precipitation method by adding sodium hydroxide solution to a Zn(OCOCH3)2 solution. In this study, ZHAs were synthesized under various conditions and tested as phosphorous removal agents. The ZHA precipitates were obtained at pH 6, 7, and 9. They were then aged at 25°C, 60°C, 90°C, and 120°C under hydrothermal conditions. At pH 6, nearly pure single-phase ZHAs were obtained regardless of the aging temperature. On the other hand, most of the ZHAs that were prepared at higher pH and aged at higher temperature were transformed to ZnO. For the phosphorous removal experiments, the single-phase ZHA precipitates removed approximately 99% of the phosphate ions in a 100 mg L−1 phosphorous solution, and the phosphorus removal efficiency decreased with increasing amounts of ZnO. Therefore, ZHAs that were prepared at lower pH and aged at lower temperatures contained little to no ZnO, thereby showing high phosphorous removal capabilities.

Synthesis of SnO2 Microcapsule Containing Cu by Colloidal Process and Its Application to Semiconductive Glass Composite.

SnO2 microcapsules containing Cu were synthesized by an interfacial reaction method using W/O type emulsion with dispersing phases including Cu spherical particles. The microcapsules with different SnO2/Cu ratios were prepared and used as electrical conductive components of semiconductive glass composites. The effect of the SnO2/Cu ratio on the electrical properties of the glass composite was investigated by comparing with glass composites fabricated with Cu and SnO2 powders. The SnO2 microcapsule with average particle size of 2.73μm was obtained. The wall of the microcapsule had about 0.65μm thickness and consisted of about 15 particle layers of fine SnO2 particles of 0.05μm. The electrical properties of the glass composites with the SnO2 microcapsules had small dependence on the SnO2/Cu ratio. The glass composite with relatively small temperature dependence of electrical resistance was obtained because a good compensating effect between SnO2 and Cu on the electrical properties of the glass composites would appear by the use of the microcapsules. On the other hand, the glass composites using SnO2 and Cu powders had large compositional dependence of the electrical properties, and showed metallic properties at about 25vol% Cu.

Microstructure and electrical properties of the SnO2 glass composite containing Cu particles precipitated by reducing copper oxides – Effect of particle size of reducing agent

An attempt was made to improve the electrical properties of SnO2 glass composites by dispersing metal particles having low resistivity and positive temperature coefficient of resistance (TCR) in the glass matrix. Cu metal particles were precipitated by reducing Cu2O by adding LaB6O as a reducing agent. The effects of LaB6O content and particle size on the microstructure and electrical properties of the SnO2 glass composites were monitored. When coarse LaB6O particles were used, the amount of the precipitated metal particles was large because SnO2 was also reduced as well as Cu2O during firing. However, in this case, the glass composite showed a porous microstructure including large pores because of the simultaneous evaporation of SnO formed as an intermediate product by reduction of SnO2. On the other hand, the glass composite prepared using fine LaB6O particles showed a dense microstructure uniformly dispersed with small pores. The porosity of the glass composite decreased by increasing the LaB6O content at first and then increased by further addition of LaB6O. The minimum of the porosity occurred at 2 wt % and 3 wt % LaB6O for the samples containing coarsest (4.81 μm) and finest (0.15 μm) LaB6O, respectively. Electrical conductivity (σ) and TCR of the glass composites containing LaB6O were higher and closer to zero, respectively, than those of a LaB6O free sample. The samples containing 2–3 wt % LaB6O showed 5–7 times higher σ and 50–70% smaller TCR in comparison with the sample without LaB6O. However, at high LaB6O content above 3–4 wt %, σ decreased and TCR moved in the negative direction with increase in LaB6O content. Especially, when coarse LaB6O was used, the declines σ and TCR at high LaB6O contents were remarkable. This was due to the decrease in the continuity of conductive paths related to the increase in number of the large pores caused by the evaporation of SnO.