Naoto Azuma

Chlorine gas recovery from polyvinyl chloride

Abstract Hydrogen chloride, evolved from polyvinyl chloride by heating at 533 K, was fixed by metal oxides at 533–673 K to form the corresponding metal chlorides. The metal chlorides thus formed were calcined at 623–723 K under an oxygen flow in order to recover chlorine gas and to regenerate the metal oxides. Among the metal oxides employed, cobalt oxide was the most effective both for the fixation and release of chloride ions. With the iterative use of cobalt oxide for HCl fixation at 573 K and subsequent Cl2 release at 673 K, the amount of chloride ions fixed by cobalt oxide powder decreased to one-fifth of those fixed by the fresh cobalt oxide. This is due to the decrease in the BET surface area of cobalt oxide caused by the iterative use.

Effects of Catalyst Heating Rates Upon the Activity of Silica-Supported Silicomolybdic Acid Catalysts for Methane Partial Oxidation

Silica-supported silicomolybdic acid (SMA) catalysts showed a very high activity for partial oxidation of methane into formaldehyde at 873 K in the presence of an excess amount of water vapor in feed. However, the high activity was observed only when the catalysts were heated to 873 K with very high heating rates such as 100 K min-1. In this article, the reason why these high heating rates are necessary to exhibit the higher catalytic activity into formaldehyde will be discussed based on the structural changes in SMA during heating the catalysts to 873 K.

Study on the structural transformation process from ZnS epitaxial film grown on Si substrate to ZnO epitaxial film by oxidation

ZnO epitaxial thin film was successfully obtained by oxidation of ZnS epitaxial thin film with the orientation of (0002),[1120]ZnO∥(111),[110]Si. The ZnS film was completely oxidized at 800°C for 1 h in O 2 flow. An interface layer was formed between the ZnO layer and the Si substrate by excess annealing. The ZnO layer showed near ultraviolet emission due to exciton in addition to visible emission, and by annealing for 5 h, strong exciton emission without the visible emission.

Correlation of surface acidity with electrical conductivity of silica-supported heteropoly compounds studied by the complex-impedance method

A.c. electrical measurements and impedance analysis have been carried out to characterize silica-supported heteropoly compounds (HPC), viz. 12-molybdophosphoric acid (H3PMo12O40), 12-tungstophosphoric acid (H3PW12O40) and their sodium, potassium, and caesium salts under various conditions of humidity. The absorption of water was found to enhance the electrical conductivity of silica-supported HPC. In H3PMo12O40 and its salts supported on silica, complex-impedance plots showed one semicircular arc due to adsorbed water. For H3PW12O40 and its salts supported on silica, the plots showed two arcs; these are ascribed to fast and slow relaxation processes of orientation polarization for conductive species, supposedly protons in occuluded and adsorbed water, respectively. As the relative humidity was increased, the conductivity increased logarithmically, showing humidity-sensing characteristics. The conduction behaviour was affected by the loaded amount of HPC and the substitution of cations in HPC. The activation energy for electrical conduction of low-loaded heteropoly acid (HPA) on silica was lower than that for bulk HPA. It changed both with the amount of loaded HPA and with the substitution for hydrogen ions in the loaded HPA.The acidity function, H0, of the silica-supported HPC has been examined also in connection with their electrical behaviour. The electrical conductivity increased with increasing acidity. A linear relationship was found between the electrical conductivity and the acidity function.

Porous silicon annealed under mixed hydrogen and argon atmosphere

Abstract Light emitting properties of porous silicon annealed under mixed H2 and Ar gas flowing at various temperatures has been examined. Photoluminescence of the porous silicon annealed at 950°C gives a peak at 470 nm with the full-width-at-half-maximum of 50 nm.

Preparation of titanium dioxide thin films by means of a hot wall technique

Titanium oxide films were prepared on a Si(100) surface by means of a hot wall technique using titanium iso-propoxide as a source material. It was found that the films could be deposited onto a Si(100) substrate in the temperature range 30-150°C. The growth rate was between 0.03-0.045 A s -1 depending on the substrate temperature. Although the as-deposited film prepared at a substrate temperature of 150°C has a stoichiometry close to TiO 2 , it was implied from the XPS spectra that the film is an oxide precursor. Polycrystalline oxide films with anatase were obtained after annealing the as-deposited films at 500°C in air. Capacitance vs. voltage characteristics of the films are also discussed.

ZnSe epitaxial growth on Si(100) and Ge(100) by H-radical assisted MOCVD

Epitaxial ZnSe is a polar material grown on non-polar substrates such as Si(100) and Ge(100) by metal organic chemical vapor deposition methods. Epitaxial growth of ZnSe on non-polar materials is more difficult than on polar materials, for example, on GaAs. For the growth of ZnSe on non-polar substrates, a polarization of substrate surface at the initial step is of importance. The FWHM of XRD peak obtained for ZnSe(100) grown on Ge is wider than that obtained for ZnSe(100) grown on GaAs, in spite of both Ge and GaAs having nearly the same lattice constant. Further, the surface morphology of ZnSe films grown on Ge and GaAs substrates is observed to be different. It is considered that the surface polarization of Ge substrate at the initial stage is not uniform. This results in a lower number of growth sites on Ge substrate compared with that on GaAs substrate.