Nobuya Iwamoto

Photocatalytic decomposition of NO under visible light irradiation on the Cr-ion-implanted TiO2 thin film photocatalyst

Transparent TiO2 thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by the ionized cluster beam (ICB) method. In order to improve the photocatalytic performance of these thin films under visible light irradiation, transition metal ions such as Cr and V were implanted into the deep bulk inside of the films using an advanced metal‐ion‐implantation technique. The UV‐vis absorption spectra of these metal‐ion‐implanted TiO2 thin films were found to shift smoothly toward visible light regions, its extent depending on the amount and kinds of metal ions implanted. Using these metal‐ion‐implanted TiO2 thin films as photocatalysts, the photocatalytic decomposition of NOx into N2 and O2 was successfully carried out under visible light (λ 450 nm) irradiation at 275 K.

Analysis of CaOSiO2 and CaOSiO2CaF2 glasses by Raman spectroscopy

Abstract Raman spectra of CaOSiO2 and CaOSiO2CaF2 glasses were measured to analyze three states of oxygen, i.e. bridging, non-bridging and free oxygen, in a similar way to the previous work on PbOSiO2 glasses. The stretching vibrational modes of the SiO bond in CaOSiO2 and CaOSiO2CaF2 glasses corresponded to the bands at 880, 920, 975 and 1050 cm−1. It is suggested from the comparison of the Raman spectra of the glasses with the Raman and infrared absorption spectra of crystalline silicates that these bands would arise from the SiO4 tetrahedron with four, three, two and one non-bridging oxygens, respectively. The fractions of bridging, non-bridging and free oxygens were calculated from the intensities of the four Raman bands and the composition of the glasses. They were in agreement with those obtained from the thermodynamical model for the CaOSiO2 glasses. When the content of CaF2 was smaller than 15–20 mol.% and the CaO SiO 2 ratio was smaller than unity, CaF2 contributed to the breakage of some SiO bonds.

Preparation of efficient titanium oxide photocatalysts by an ionized cluster beam (ICB) method and their photocatalytic reactivities for the purification of water

Abstract Using an ionized cluster beam (ICB) method, titanium oxide photocatalysts were prepared on porous Vycor silica glass (PVG) and activated carbon fibers (ACF), and their photocatalytic reactivities for the degradation of 2-propanol diluted in water was investigated. Characterizations of these catalysts by means of SEM, XAFS, XRD, XPS and UV–Vis absorption techniques showed that the titanium oxide in transparent thin films could be formed on PVG and titanium oxide clusters could be deposited on the ACF. UV irradiation of these catalysts in a diluted aqueous solution of 2-propanol or 1,2-dichloroethane led to the efficient decomposition of these reactants into CO 2 , H 2 O and HCl. The titanium oxide catalysts prepared on these porous materials exhibited higher photocatalytic reactivities than TiO 2 powder and titanium oxide catalysts prepared by a conventional impregnation method. The present results have clearly shown that the ICB method is useful in the preparation of titanium oxide photocatalysts combined with porous supports such as PVG and ACF.

Photocatalytic decomposition of NO on titanium oxide thin film photocatalysts prepared by an ionized cluster beam technique

Transparent TiO2 thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by an ionized cluster beam (ICB) method. The UV‐VIS absorption spectra of these films show specific interference fringes, indicating that uniform and transparent TiO2 thin films are formed. The results of XRD measurements indicate that these TiO2 thin films consist of both anatase and rutile structures. UV light (λ > 270 nm) irradiation of these TiO2 thin films in the presence of NO led to the photocatalytic decomposition of NO into N2, O2 and N2O. The reactivity of these TiO2 thin films for the photocatalytic decomposition of NO is strongly dependent on the film thickness, i.e., the thinner the TiO2 thin films, the higher the reactivity.

The mechanical properties and microstructure of Ti-Si-N nanocomposite films by ion plating

Abstract The hardness and microstructure of Ti–Si–N films were investigated. The hardness of the films increased with increasing Si content of the films, and the maximum hardness, more than Hk4500 was obtained within the range of 0.3–0.5 of Si/(Si+Ti) ratio. The X-ray diffraction (XRD) data showed only TiN peaks and no Si–N peaks. The XRD peaks of TiN of the Ti–Si–N films became broad with Si content of the films. The TiN crystallite sizes calculated from the FWHM values of TiN diffraction peaks decreased with the increment of Si content of the films. It became clear that when the Si/(Si+Ti) ratio of the films was more than 0.1, TiN crystallite sizes decreased to less than 7 nm. The thin amorphous grain boundaries of Si–N and the TiN crystallites in size of approximately 5 nm were observed by high resolution transmission electron microscopy. It was assumed that the high hardness of the Ti–Si–N nanocomposite films was due to a halt of propagation of dislocations by an amorphous phase on TiN grain boundaries in addition to nano-scale size of TiN crystallites brought by inhibition of crystal growth of TiN through an amorphous Si–N phase.

Electrical conductivity of plasma-sprayed titanium oxide (rutile) coatings

Abstract Plasma spraying has been used to prepare n-type polycrystalline TiO2 coatings on SUS304 steel substrates. The influence of plasma spray process on the phases (corundum type Ti2O3, monoclinic Ti3O5, triclinic magneli phases, and tetragonal rutile) formed and the relation between deoxidation and the electrical conductivity of plasma-sprayed TiO2 coatings have been studied. The amount of oxygen loss in the plasma-sprayed TiO2 coatings is influenced greatly by the addition of hydrogen in the plasma gas. Accordingly, the electrical conductivity of TiO2 coatings increases with decreasing oxygen during plasma spraying. The amount of reduced TiO2 coating increases with a drop in pressure of the plasma spray atmosphere and an increase in the quantity of hydrogen. The amounte of Ti2O3 and Ti3O5 phases formed by plasma spraying increase with the deoxidation of TiO2 coatings.

Investigation of calcium-iron-silicate glasses by the Mössbauer method

Abstract The oxidation-reduction and coordination of iron atoms in calciumsilicate glasses has been studied as functions of the basic oxide content and partial oxygen pressure on the basis of Mossbauer spectra. It was found that the equilibrium concentration ratio NFe3+/NFe2+ increased as the CaO content or partial oxygen pressure increased. The coordination behavior of iron atoms was complicated. In the glasses containing a large amount of Fe2O3, the Fe2+ ion was always present in the octahedral site, while the Fe3+ ion showed amphoteric behaviour. The ratio in number of tetrahedrally coordinated to octahedrally coordinated ferric ions did not exhibit any remarkable variation for larger partial oxygen pressures (1 and 0.21 atm), but increased slightly with the CaO/SiO2 ratio for the small oxygen pressure (3 × 10−7 atm). In the glasses containing a small amount of Fe2O3, the Fe2+ ion was present in both tetrahedral and octahedral sites. However, the coordination state of the Fe3+ ion was not sufficiently clear in such glasses.

Characterization of plasma-sprayed zirconia coatings by X-ray diffraction and Raman spectroscopy

Three zirconia ceramics, ZrO2−4.5mol.%Y2O3, ZrO2−12mol.%Y2O3 and ZrO2−8mol.%MgO, were investigated using X-ray diffraction before and after plasma spraying. The amounts of monoclinic, tetragonal and cubic phases existing in the three zirconia ceramics were determined from the integrated intensity ratios in the {400} and {111} regions of the X-ray diffraction patterns. The tetragonal-to-monoclinic transformation in the plasma-sprayed coatings caused by indentation, fracture and/or heat treatment with a laser beam was examined using Raman spectroscopy. As a result, this spectroscopic technique is shown to be a powerful tool for the observation of this transformation.

A structural study of rapidly quenched glasses in the system Li2OSiO2

Abstract Raman spectra of 4 glasses in the system Li2O SiO2 (41.3 ≦ Li2O ≦ 61.3 mol%) prepared by rapid quenching were measured. The proportions of SiO4 units with 1, 2, 3 and 4 non-bridging oxygens per Si were determined for these glasses from the quantitative analysis of their Raman spectra. X-ray structural analysis of the Li2O SiO2 glasses showed that the average atomic distance of Si O pair was elongated with increasing Li2O content due to the weakening of the Si O bond.

Joining of zirconia using zirconium-based alloys

The contact angles of Zr-Ni, Zr-Cu and Zr-Co alloys against PSZ were measured by the sessile drop method. Each alloy wetted PSZ very well. Zr-Co alloys showed a different behaviour. Joints of PSZ plates were obtained using Zr-17Ni alloy. At the joint interface, internal oxidation of zirconium occurred. The fracture shear strength of this joint was 55 MPa.