Iwao Matsuyama

Diffusion of gases in porous silica gel

Abstract Gas diffusion in porous silica gels prepared by the sol-gel process is studied at room temperature. It is shown from the measurement of helium or oxygen gas diffusion in the gels that the gas diffusion is limited by the average pore diameter of the gel, R a ; that is, the mean free path of gas in a porous gel can be regarded as equal to R a . The results also indicate that the gas diffusing length is about three times larger than the geometrical thickness of the sample gel. Some adsorption of oxygen gas appears to take place on the silica surface of the gel at room temperature.

Sol-gel-derived binary silica glasses with high refractive index

Doped silica glasses, SiO 2 MO n/m (M = Ga, Gd, Nb, Sb, Sn, Ta, Ti and Zr), were prepared by the sol-gel method and evaluated. Refractive index and X-ray diffraction measurements showed that SiO 2 Sb 2 O 3 , SiO 2 Ta 2 O 5 , SiO 2 TiO 2 and SiO 2 ZrO 2 glasses are potentially suitable for optical components. Experimentally observed refractive indices are in good agreement with the calculated values using Appens empirical law.

Reduction of chlorine content in sol-gel derived silica glass

Abstract The undesirable influence of chlorine gas in the production of hydroxyl-free and bubble-free silica glass by the sol-gel method was minimized by introducing a dechlorination treatment of the gel during a sintering process. The dechlorination treatment can be effectively carried out in an oxygen atmosphere at 1000 to 1100°C after the gel is chlorinated at 800°C to remove the hydroxyl. The dechlorination reaction seems to be rate-determined by a diffusion process which is probably governed by the adsorption and desorption of chlorine atoms. The reduction of the specific surface area by a pre-sintering process is useful for the reduction of both the hydroxyl and chlorine content in the densified silica glass. The behaviors of adsorbed chlorine and hydroxyl groups are discussed in relation to the densification mechanism.

Sol-gel derived Ge-doped silica glass for optical fiber application. II, Excess optical loss

Abstract Optical fibers of sol-gel derived germanium-doped silica core glasses are fabricated by the rod-in-tube method. Typical losses of the fibers are 20 to 30 dB/km at a wavelength in the 0.63–0.83 μm region. Contributions of absorption and scattering losses to the total loss of the fibers are examined. An excess absorption loss that increases with increasing germanium content is found in the optical fibers. The origin of the excess loss can be attributed to the transition metal impurities, the valence state of which is influenced by the divalent germanium ions in the fibers.

Raman and GC-MS study of the initial stage of the hydrolysis of tetramethoxysilane in acid and base catalyzed sol-gel processes

Abstract Raman spectroscopy and GC-MS analysis have been employed to examine the role of HCl and NH4 OH as a catalyst at the initial stage of the hydrolysis of Si(OCH3)4. Under the condition that the hydrolysis proceeded under the presence of amount of water less than theoretically required for the complete hydrolysis of Si(OCH3)4, H2O/Si(OCH3)4

Sol–gel preparation and optical properties of SiO2–Ta2O5 glass

Abstract Tantalum-doped silica glass was fabricated by the sol–gel process in order to obtain a glass with a high refractive index for optical use. A crack-free, clear glass rod was successfully prepared from a low-density gel and used as the core material for fabricating optical fibers. Transmission loss in the fabricated fibers was high, in the range of 10 3 –10 4 dB/km, which may be caused by coloration due to the multivalency of tantalum; however, the loss was reduced by nearly one order of magnitude by heat treatment at 800 °C, that is, to 75 dB/km at a wavelength of 0.8 μm.

Effects of the lapped surface layers on the dielectric properties of ferroelectric ceramics

The effects of lapped surface layers on the dielectric properties of Ba‐ and Sr‐modified lead titanate and lead zirconate ferroelectric ceramics are examined. Specimens with lapped surfaces show anomalous dielectric behaviors, namely, smaller dielectric constant, higher Curie temperature, smaller dielectric loss (below Curie point), and smaller remanent polarization than those of specimens whose surface layers are removed by chemical etching. This may be ascribed to the existence of a lapped surface layer, which seems to be a (0.1–2)‐μm‐thick nonferroelectric layer of small dielectric constant with a two‐dimensional tensile stress of 5–15 kbars. The thinness of the layer results in a large capacitance on the order of 0.5 μF/cm2. The above model for lapped surface layer, especially involving the two‐dimensional tensile stress, explains well the anomalous dielectric behaviors measured in this paper.

Optical properties of sol–gel derived Sb-doped silica glass

Abstract The sol–gel preparation of Sb-doped silica glass with high refractive index was investigated. A base-catalyzed low density gel rod with dopant content up to 15 mol% was prepared. Sintering resulted in an OH-free Sb-doped silica glass rod with a maximum specific refractive index of 3.17% with reference to pure silica. Above 5 mol% the refractive index was radially graded with a maximum at the center. Optical fiber fabricated from the 5 mol% Sb-doped silica as a core exhibited optical loss of about 700 dB/km at 0.6 μm. The loss may be attributed to coloration due to multivalent Sb.

Chlorination reduction in sol—gel-derived porous silica gels

Abstract Chlorine dehydroxylation in plate-like silica gels prepared by hydrolysis of Si(OCH3)4 was investigated for gels treated in chlorine at 800°C. The infrared absorption spectrum of OH on the open pore surface of the gel was measured. The exchange reaction between OH and Cl was found to decrease linearly with the square root of treatment time and with reciprocal gel thickness. The dependence of the dehydroxylation rate on gel thickness indicated that the exchange between OH and Cl is limited by Cl2 diffusion into the gel.

Method for magnetic orientation of magnetic recording medium using Meissner effect of high Tc superconductor

A method for magnetic orientation of a magnetic recording medium using Meissner effect of a superconductor and a system therefor and a magnetic recording medium produced thereby. The magnetic particles of plate hexagonal barium ferrite in the magnetic coating are allowed to orient in the longitudinal direction thereof so that a magnetic recording medium having a magnetic orientation in such direction with the magnetic particles can be obtained.