Satoru Inoue

Sol-Gel Transition in the Hydrolysis of Silicon Methoxide

Abstract The sol-gel transition in the hydrolysis of silicon methoxide in acidic, basic and neutral pH media has been investigated by means of gas chromatography and small angle X-ray scattering measurements to elucidate the effect of a catalyst on gelling time and the properties of the obtained gel. In an acidic medium, the evolution of methanol immediately after the addition of water was remarkable, and only a trace of silicon methoxide could be detected after 30 min, although the gelling time was as long as 150 h. In an ammonia catalyzed basic medium, the rates of the polycondensation reaction and the coagulation of particles were very large and the gelling occurred after several hours. But about half of the silicon methoxide remained unreacted in the sol sampled after two thirds of the gelling time. In a neutral pH medium, both the hydrolysis and polycondensation reactions proceeded at the intermediate rates of those in the acidic and the basic media.

Preparation of gels to obtain glasses of high homogeneity by low temperature synthesis

Abstract The conditions for the preparation of gels in order to obtain oxide glasses of high homogeneity by low temperature synthesis are discussed with reference to the system TiO2SiO4. Three kinds of titanium alkoxides, ethoxide, iso-propoxide and ter-amyloxide, were mixed with silicon methoxide or ethoxide by various methods and were hydrolysed to form gels. Titanium ethoxide was added to an ethanol solution of partially hydrolysed silicon ethoxide. The mixture of titanium iso-propoxide and silicon ethoxide was hydrolysed very slowly by adding distilled water. Titanium ter-amyloxide, the rate of hydrolysis of which is supposed to be much lower than those of ethoxide and methoxide, was mixed with silicon methoxide to be hydrolysed with ammonia water of pH = 11.2 ∼ 11.3. The uniformity of composition in the gels so formed was investigated by measuring the homogeneity of the glasses obtained by melting the mixtures of gels and sodium nitrate for a very short time, i.e., until immediately after the melt became batch free. The gel obtained from titanium ter-amyloxide and silicon methoxide was the most homogeneous, indicating that the employment of alkoxides with a close rate of hydrolysis is essential for the preparation of glass of high homogeneity by the low temperature process.

REFRACTIVE-INDEX PATTERNING OF TELLURITE GLASS SURFACES BY LASER SPOT HEATING

A dot pattern of a refractive-index change was formed by spot heating with laser-beam irradiation on sodium tellurite glasses. The 15Na2O.85TeO2 (mol. %) glass doped with 2 mol. % of CoO was irradiated by a green light-beam spot (532 nm) approximately 800 microm in diameter from the second-harmonic generator of a Q-switched pulsed YAG laser. The map of the refractive index of the glass was determined with an He-Ne laser beam by a scanning ellipsometric technique at a resolution of 100 microm x 50 microm, indicating that the spots possessing a refractive index lower by approximately 0.05 were formed at the region irradiated by the laser beam.

Mechanism of photochromism in oxide glasses containing a large amount of CdO or ZnO

Abstract UV-induced optical and ESR absorptions of borosilicate glasses containing a large amount (⪯ 50 mol%) of CdO or ZnO were measured at room temperature and 77 K while changing the wavelength of the illuminating light. The induced optical absorption was one order of magnitude stronger at 77 k than at room temperature, and the most intense absorption was observed for 340 nm irradiation. At 77 K peak wavelengths of the induced band changed with changing illuminating wavelength; from 420 nm on 300 nm irradiation to 600 nm on 360 nm irradiation. Tailing of the bands to the near-infrared region was pronounced. The induced optical absorptions were photo-bleached at 77 K by illumination with light whose wavelength is in the induced absorption bands. The lineshape of the bleaching spectra, a difference between the spectra before and after illumination, changed with changing illumination wavelength. Three types of ESR signals, signals (a), (b) and (c), were induced simultaneously with the optical absorptions. The dependencies of intensities of the ESR absorptions on the illuminating temperature and wavelength were found to be similar to those of the induced optical absorptions. From the observed g-tensors of the ESR signals, signal (a) was assigned to a trapped hole on a nonbridging oxygen neighboring on Si, signal (b) was assigned to a trapped hole on oxygen(s) surrounded by several Cd ions and having no direct bonding to Si or B, and signal (c) was assigned to a trapped electron delocalized over several Cd ions. It was found that the hole centers give rise to the optical absorption in the visible region and the electron center absorptions were in the visible and near-infrafed regions.

Precursor to paramagnetic centers induced in gamma-irradiated doped silica glasses

We prepared silica glasses having various concentrations of chlorine, fluorine, hydrogen (SiO2−x), and oxygen (SiO2+x) to examine the precursors of paramagnetic centers induced by γ rays. In the case of glasses sintered under chlorine and hydrogen ambients, the concentration of the E’ center induced by γ‐ray irradiation scaled with the partial pressure of chlorine and hydrogen. In contrast, the E’ center was suppressed in glasses doped with fluorine. Stress in the glasses was also found to enhance formation of the E’ center. Planar ring structures in the glass are influenced by stress and are proposed as precursors to the E’ center.

IR transparency of the glass of ZnCl2-KBr-PbBr2 system

IR transparency and some properties of halide glass of composition 48ZnCl2-48KBr-4PbBr2 (mol%) have been investigated as the basic study on the development of IR glass fiber for CO2 gas laser. The glass transition temperature Tg, crystallization temperature Tc, softning temperature Ts, and linear thermal expansion coefficient α of the glass were found to be 45–46°C, 100°C, 54°C, and 570×10−7 / °C, respectively. The refractive index of the glass for He-Ne laser emission (632.8 nm) was about 1.63. The amount of impurity which decreases the transmissibility for CO2 laser beam due to the absorption in the wavelength region 10–11 μm could be reduced by preparing the glass from a batch containing NH4 Cl under reactive atmosphere of CCl4 or CBr4 in a glove box filled with He gas of dew point −62∼ −45°C. The minimum value of absorption loss of the glass for CO2 gas laser measured by laser calorimetry was about 20 dB/m.

Photochromic property of glass in the AgIAgBrPbBr2CsBrCdBr2 system

Abstract Photolytic darkening of glass in the AgIAgBrPbBr2CsBrCdBr2 system has been investigated. The glass containing a small amount of PbS darkened after irradiation with a photographic bulb and remained unchanged while it stored in the dark. The dark color could be bleached optically by flashing with light whose wavelength was longer than 560 nm. Irradiation with UV light from a mercury-arc lamp was also effective in darkening the glass. The color obtained in this case, however, was irreversible and could not be bleached.

Estimation of the infrared absorption of ZnCl 2 –KBr glass by molecular dynamics

Molecular dynamic calculations have been made on glasses in the ZnCl 2 –KBr system in order to estimate the infrared (IR) absorption of these glasses. Oxygen-free glass was estimated to be transparent up to 25 μm. Glasses containing oxygen impurities were estimated to be transparent only up to 16 μm, with a weak absorption band around 10.4 μm. This agrees with experimental results of glasses in the ZnCl 2 –KBr–PbBr 2 system.