The effects of Li₂CO₃ additions on the densification and microwave dielectric properties of CaSiO₃–1 wt % Al₂O₃ ceramics were investigated. With Li₂CO₃ addition, the densification temperature of CaSiO₃–1 wt % Al₂O₃ ceramics could be effectively reduced from 1250 to 925°C. During the sintering process, Li₂CO₃ existed as a liquid phase and assisted the densification of CaSiO₃–1 wt %Al₂O₃ ceramics, and then reacted with CaSiO₃ to form Li₂Ca₃Si₆O₁₆ and Li₂Ca₄Si₄O₁₃ second phases. However, the Li₂CO₃ addition deteriorated the microwave dielectric properties because of the lower quality values of Li₂Ca₃Si₆O₁₆ and Li₂Ca₄Si₄O₁₃ phases. The proper Li₂CO₃ addition was found to be 2 wt %. Under this addition, microwave dielectric properties of ε_r = 7.33, Q×f = 21,904 GHz and τ_f = −34 ppm/°C were obtained for the CaSiO₃–1 wt % Al₂O₃ ceramic sintered at 975°C for 2 h.

View full abstract

To improve the light resistance of the organic–inorganic composite for optical use, barium titanate (BTO) dispersion was prepared instead of titanate (TiO₂) dispersion by a high pressure reaction between titanium oxide (TiO₂) dispersions treated with silane-coupling reagent and barium hydroxide [Ba(OH)₂]. The obtained BTO was observed by transmission electron microscope (TEM) and its diameter was less than 10 nm. This seemed the result from the treatment of the TiO₂ before the reaction. In addition, X-ray diffraction analysis (XRD) indicated TiO₂ crystals didn’t remain in the BTO. Transparent composites composed of 2-hydroxy-butylacrylate as the organic matrix and the BTO or the TiO₂ as the inorganic filler were prepared. The composite including the BTO showed much longer decomposition time than that of TiO₂ in the light (405 nm) resistance test. This indicates that the BTO has lower photocatalytic activity than the TiO₂.

View full abstract

Sol–gel methods is a commonly used methods for encapsulation of enzyme and drug, but this method has two disadvantages of using acid or base as a catalyst and being difficult to control pore size of silica material. Even though synthesis under mild condition or silica with controlled pore size in the mesopore region have been reported, it is still difficult to achieve these two characteristics simultaneously. In this work, we chose 10-mer peptides of lysine (K), histidine (H), and block and alternate K and aspartic acid (D) as catalysts for silica mineralization, and silica gels were prepared using the synthetic peptides and a “leave to stand” synthesis method. The resulting silica hydrogels were lyophilized, and their surface areas and morphologies were characterized using the Brunauer–Emmett–Teller (BET) method and field-emission scanning electron microscopy (FE-SEM), respectively. Silica gels prepared by the “leave to stand” method with K₁₀ and H₁₀ exhibited a mesoporous structure with high surface area (576 and 451 m² g⁻¹, respectively) and pore volume (0.35 and 0.30 cm³ g⁻¹, respectively). SEM images confirmed the mesoporous structure of these gels. We encapsulated fluorescein sodium salt as a model drug within silica hydrogels using K₁₀ and H₁₀ as a catalyst. The silica hydrogel prepared using H₁₀ exhibited faster release of the drug (approximately 2.5-fold) than gels prepared using K₁₀. These results demonstrate that by changing isoelectric point binding between the peptide and pore structure, the synthesized silica hydrogel-peptide composites can be designed to control the release rate of an encapsulated drug.

View full abstract

The present paper demonstrates that inorganic ceria (CeO₂) nanoparticles effectively inhibit anomalous oxidative damage of DNA induced by ultraviolet (UV) light irradiation. To utilize the CeO₂ nanoparticles for the protection test of DNA, a colloidal solution of monodispersed and crystallized CeO₂ nanoparticles is synthesized through a photochemical reaction of Ce(NO₃)₃ solution, followed by dialysis to remove unreacted electrolytes. Subsequently, the UV light induced oxidative damage of DNA in the presence or absence of CeO₂ nanoparticles is evaluated by a quantitative analysis of 8-hydroxy-2′-deoxyguanosine (8-OHdG) which is an oxidation product of guanine in base sequences. The 8-OHdG concentration in DNA is increased by the exposure to UV light. On the other hand, the co-presence of CeO₂ nanoparticles diminish the formation rate of 8-OHdG. Such favorable effect of CeO₂ nanoparticles is due to an excellent annihilation activity of reactive oxygen species (ROS) accounting for the DNA oxidation as well as a UV light absorption ability based on semiconducting nature.

View full abstract

Single-crystalline YFeO₃ particles with the perovskite structure have been fabricated through a facile KCl-assisted solution combustion synthesis (SSCS) method, using alanine as a fuel and corresponding nitrates as oxidants. The effects of the fuel-to-nitrate ion (F/N) and the KCl-to-metal ratios (KCl/M) on the phase and microstructure of the products are studied in detail by X-ray diffraction analysis, scanning electron microscopy, low temperature N₂ adsorption, UV–visible diffuse reflection spectroscopy. It is remarkable that the introduction of KCl into the solution combustion synthesis (SCS) process results in a dramatic increase in surface of the obtained YFeO₃, i.e. a more than sixth-fold increase from 2.9 to 19.6 m²/g when F/N = 0.30 and forty-fourth-fold increase from 0.5 to 24.2 m²/g in the case of F/N = 0.33. Results show that both of YFeO₃ nanoparticles prepared by SCS and SSCS exhibit excellent photocatalytic activity for the photodegradation of rhodamine B in the presence of H₂O₂. The photo-generated holes (h⁺) and •OH were the main active species of YFeO₃ for RhB degradation under visible light irradiation.

View full abstract

The samples from A-type zeolite and ground soda-lime glass powders were solidifed by calcinations at 600 to 800°C in air atmosphere. These hybrid zeolite/glass samples at 700°C were in part insufficiently densified and hybrid samples were fully densified at 800°C, although the densification was not generated at 600°C. A-zeolites were still stable in glass melt at 800°C for hybrid zeolite/glass samples. These hybrid zeolite/glass samples had the ion exchange ability of 20% against Sr²⁺ and the high ability over 80% against Cs⁺ as well as A-zeolite. Microstructures of obtained hybrid zeolite/glass samples were evaluated.

View full abstract

In this study, we succeeded, for the first time, in changing the particle morphology of a transition metal nitride using ammonothermal post-treatment with a mineralizer. Tantalum (V) nitride (Ta₃N₅) was post-treated using NaI as a mineralizer under ammonothermal conditions with an ammonia pressure of 100 MPa at 673–973 K for 24 h. Post-treatment above 873 K changed the particle morphology of Ta₃N₅ markedly; the particle size was reduced, the crystallite size was increased, and the specific surface area was decreased compared to the as-prepared Ta₃N₅, suggesting the dissolution of particle surface during post-treatment. In addition, all treated Ta₃N₅ samples showed enhanced photocatalytic activity for hydrogen evolution from an aqueous methanol solution under visible light irradiation compared to untreated Ta₃N₅. However, the hydrogen evolution activity for the samples post-treated above 873 K was less than that of the samples post-treated at lower temperatures due to the increase in lattice defects in Ta₃N₅ resulting from thermal decomposition.

View full abstract

This study reports on the effect of soda-lime-silica (SLS) glass on the physical properties of the ceramic material obtained from white rice husk ash (WRHA). The crystallisation behaviour of samples was investigated by XRD analysis after different heat treatments. The bulk density and linear shrinkage (LS) of the samples were determined using Archimedes’ method and direct geometric measurement, respectively. The residual pore contents of the specimens were determined using SEM micrographs. The results show that the bulk density and LS of the samples increased and the porosity decreased as the sintering temperature increased. The XRD analysis results show the formation of cristobalite to be a major phase and some tridymite phase was detected in the specimens.

View full abstract

La₂O₃ and Nb₂O₅ doped Al₂O₃ ceramics [5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃, x = 2.5–15.0, volume percent] were prepared by microwave sintering processes. The effects of La₂O₃ content and sintering temperature on densification, phase composition, microstructure and mechanical properties of 5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃ composite ceramics were investigated. The results show that all investigated specimens consisted of α-Al₂O₃, LaNbO₄ and LaAl₁₁O₁₈. The sintering temperature of La₂O₃/Nb₂O₅ doped Al₂O₃ ceramic was at least 150°C lower than that of Al₂O₃ ceramic. The specimens sintered at 1500°C exhibited relative density higher than 92.0%, revealing good sinterability. During the sintering period, LaNbO₄ and plate-like LaAl₁₁O₁₈ were formed in-situ. The fracture toughness of 5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃ composite ceramics was above 70% higher than that of Al₂O₃ ceramic. 5Nb₂O₅/7.5La₂O₃–82.5Al₂O₃ composite ceramic presented excellent mechanical properties: HV = 12.6 GPa, K_IC = 6.3 MPa·m^1/2 (1500°C).

View full abstract

Large silicon nitride blocks were joined without using any insert material; further the microstructure of the joint region, and joining strength and its Weibull distribution of the joined block were investigated. Commercially available silicon nitride blocks sintered with Y₂O₃ and Al₂O₃ were used as the parent material; and the blocks were joined at 1800°C for 4 h under a nitrogen gas pressure of 0.9 MPa and a mechanical pressure of 11 MPa. The equiaxed and/or elongated silicon nitride grains of the parent silicon nitrides seemed to directly bond to each other; moreover, the joint interface was not clearly distinguishable from the parent silicon nitride region. The joined silicon nitride block had a room-temperature flexural strength of 622 MPa. The high-temperature strength of this block at 1000°C was decreased to 426 MPa, in spite of the absence of a joint layer. Further, the joined silicon nitride block had a Weibull modulus comparable to that of the parent silicon nitride.

View full abstract

Ti-doped and undoped CaFe₂O₄ powders were prepared from a malic acid complex and their properties were evaluated using analytical instruments. According to an XRD measurement, there were no traces of impurity phases in 5 mol % Ti-doped CaFe₂O₄ powder, while impurity phases such as α-Fe₂O₃ and CaTiO₃ were observed for 10 mol % Ti-doped CaFe₂O₄. When Ti was added to CaFe₂O₄, the crystallite growth of CaFe₂O₄ was suppressed and the BET surface area increased. SEM observation revealed that the addition of Ti atoms to CaFe₂O₄ causes interconnected CaFe₂O₄ particles to separate. From the results of an XRF measurement, it is suggested that Fe atoms are substituted with Ti atoms. The optical band gap of CaFe₂O₄ hardly changed as a result of doping with Ti.

View full abstract