We report our recent results on the photoinduced transient optical absorption measurements of amorphous (a-) As2Se3 and a-As2S3, after the illumination of nanosecond pulsed laser. From the measurements, we have observed a photodarkening in the nanosecond and microsecond domains for the first time. Since the fast photodarkening was also observed in the liquid state, the structural origin of the photodarkening should be different from the conventional metastable photodarkening, which is observed only below the glass transition temperature. We have also examined accumulated photoinduced changes for the stronger repeated pulsed laser illumination. From the measurements, we have found for As2S3 that there exists an accumulated photoinduced absorption in the supercooled liquid state. On the basis of the detailed results of the transient optical absorption measurements, structural origin of the photodarkening is discussed.
For the recovery of nuclear materials from the spent nuclear fuel, the sulfide process which consists of voloxidation of spent fuel and selective sulfurization of fission products has been proposed. In this paper, cerium was used as a stand-in of plutonium as well as one of rare-earth elements of fission products. Sulfurization behavior of cerium dioxide by CS2 was studied by thermogravimetry (TG) and X-ray diffraction (XRD) methods. From the TG results, it was found that the sulfurization reaction begun at temperatures higher than 450°C forming tetravalent cerium oxydisulfide. Then the reduction of cerium from tetravalent to trivalent of occurred forming intermediate oxysulfides such as Ce4O4S3, Ce2O2S and Ce10S14O which were identified by XRD. Finally, Ce2S3 was found to be formed at higher temperatures up to 1000°C. The experimental results were in good agreement with those of thermodynamic consideration.
A new series of chalcogenide glasses in the Cu2S-Sb2S3 system was prepared by a conventional melt-quenching method. The glassy nature of prepared compositions was proved using X-ray diffraction analysis. The homogeneity and microstructure were evaluated using FE-SEM. Physical properties such as glass transition temperature, crystallization temperature, density, optical transmission and electrical resistivity were measured. The results show that the Cu-Sb-S glasses form in the composition region of 21.5 and 24.5 mol% Cu2S. The glass transition temperature is 185°C and the optical transmission window is lying between 0.9 and 15 μm for the representative 22.5Cu2S - 77.5Sb2S3 glass sample. The result of electric resistivity indicates that the change of electric resistivity is about 3 orders by the crystallization of glass.
The pulsed laser deposition of titanium sulfide films was investigated in order to develop new thermoelectric materials. The rutile-type TiO2 powder was first sulfurized with carbon disulfide (CS2) gas. After the sulfurization at 1023 K for 14 h, the resultant powder consisted entirely of the CdI2-type TiS2 phase. The TiS2 target was fabricated by pressing the TiS2 powder under a uniaxial pressure of 20 MPa. The films were prepared on fused quartz substrates by the pulsed laser deposition from the TiS2 target under CS2 pressure. The effects of the CS2 pressure and substrate temperature on the microstructure and composition were investigated. When the film was prepared at room temperature under CS2 pressure of 1.33 Pa, the composition of the film was found to be close to the target composition. The room-temperature electrical resistivity and Seebeck coefficient of this film are 63 μΩ•m and -42 μV/K, respectively.
A sulfur-doped titanium dioxide thin film was prepared by pulsed laser deposition in the atmosphere controlled in carbon disulfide partial pressure. Optical and spectroscopic analyses demonstrated that the doped sulfur atom successfully triggered visible light sensitization by substituting with the lattice oxygen of titanium dioxide, which can absorb ultraviolet light only. As a result, photocatalytic hydrogen evolution activity of sulfur-doped titanium dioxide thin film was remarkably increased, compared with un-doped one. Moreover, an investigation on increase of the substrate temperature during laser ablation revealed that stabilization of sulfur atom in titanium dioxide was attained, resulting in high photocatalytic activity.
Koji UOTANI, Shigeru UEDA, Katsunori YAMAGUCHI, Takashi OKURA
Most of waste plaster board, which contains gypsum has been buried in the landfill. However, this treatment of waste gypsum board is becoming a serious problem due to lack of landfill capacity, and secondary pollution by toxic substance. In this study, we focused a recycle of calcium resources as CaO or CaS from the waste gypsum, and developed a reduction process of the gypsum using plastics at high temperature. Reduction behavior of CaSO4 by Polyethylene at temperature from 1273 to 1573K was studied with gravimetry and X-ray diffraction analysis. From the experimental results, we found that increasing CaSO4-CH2 gas interface tend to advance the reduction of CaSO4. Furthermore, direct formation of CaS from CaSO4 was observed only at temperature of 1273K without an intermediate compounds stage, and the reduction sequence was CaSO4→CaO→CaS at temperatures higher than 1373K. Finally, the sequence of reduction process for CaSO4 was discussed on the potential diagram of the Ca-S2-O2 system.