Edson H. Sekiya

Effect of Chlorine on Rayleigh Scattering Reduction in Silica Glass

The Rayleigh-scattered light intensities of silica glasses containing chlorine with concentrations from 0 to 1.8 mol% were measured. The scattered intensity was found to change linearly to the fictive temperature but was independent of chlorine concentration within experimental error. The result indicates that chlorine dopant influences neither density nor concentration fluctuation. From the present result, how much the Rayleigh scattering can be reduced by heat treatment and doping of chlorine was estimated, and chlorine was found to be an effective dopant for achieving the reduction.

Crystalline and amorphous phases of GeO2 in VAD silica–germania soot preform

In germanium doped optical fiber, produced by vapor-phase axial deposition (VAD) technique, the refractive index profile is controlled by the radial distribution profile of germanium. At the porous soot state, GeO2 may be deposited as amorphous and/or crystalline phases in a SiO2‐GeO2 system. To correlate the quantitative deposition between amorphous and crystalline phases of GeO2, several silica‐germania soot preforms were prepared under diAerent deposition conditions and their X-ray diAraction (XRD) patterns and X-ray fluorescence spectra were analyzed. The presence of GeO2 crystalline (hexagonal) phase was detected in all soot samples, and its concentration was aAected by deposition conditions, mainly the soot surface temperature and H2/O2 ratio in the flame. The concentration of the crystalline phase is minimum at the center of the silica‐germania soot preform and increases along the radial direction. The greater concentrations at the outer diameter of the silica‐germania soot preform are due to the lower deposition temperature ( 850∞C). The GeO2 is eliminated at the center of preform in reductive atmosphereOH2=O2 > 2U and higher temperature (T 1000∞C), independently of SiCl4/GeCl4 ratio. These results are important to understand the main parameters of the doping process, to produce high quality materials with a given germanium concentration profile. ” 2000 Elsevier Science B.V. All rights reserved.

Effect of H2/O2 ratio on the GeO2 concentration profile in SiO2:GeO2 glass preforms prepared by vapor-phase axial deposition

GeO 2 radial concentration in silica glass preforms, prepared by vapor-phase axial deposition (VAD) method, was analyzed by X-ray fluorescence (XRF) measurements. The results were used to evaluate the effect of the H 2 /O 2 ratio used during the deposition process in the formation of the GeO 2 concentration profile. Considering four different H 2 /O 2 ratios, GeO 2 distribution was observed to decrease monotonically with the increasing radius for H 2 /O 2 ≤1.5, and the acute shape around the core center of the GeO 2 concentration profile, decreased with increasing H 2 /O 2 ratio. When the ratio H 2 /O 2 =2.5, the central doping of GeO 2 was minimal, and a constant distribution was obtained along glass preform radii. The results seem to indicate that the control of spatial distribution in the concentration of GeO 2 deposited is favorable for the ratio H 2 /O 2 ≤1.5.

Facile catalytic combustion of rice husk and burning temperature dependence of the ashes.

In this work, it was discovered and demonstrated that the combustion of rice husk is a catalytic process by the thermoanalytical technique. The catalyst involves the oxides of such transition metals as Mn, Fe, and Cu, which are mainly formed in the initial stage of rice husk combustion and remain in the rice husk ash as an impurity. Mn(2+) ions of various concentrations were reloaded into the HCl-washed husk for cocombustion. As a result, the complete combustion temperature of the husk was decreased exponentially depending on the Mn(2+) concentration. By the facile Mn loading technique using a 0.5 M solution, the combustion temperature can be decreased by approximately 100 degrees C, and the resulting ashes themselves can be a good catalyst in the complete combustion of many other organic compounds. The physicochemical properties and amorphous structure of the ashes from both the raw and HCl-washed husks were found to be strongly dependent on the burning temperature. A decreased complete rice husk combustion temperature can be beneficial in preparing porous amorphous silica with high surface area, high densification, and small Si-O-Si band angles.

Effect of Heat Treatment on the High-Purity Silica Glass Prepared from Amorphous and Crystalline Powders by Small Angle X-Ray Scattering

High-purity silica glass prepared from high-purity amorphous and crystalline powders by flame fusion and sintering at high temperatures in vacuum, was heat-treated at 1250°C for several periods of time and its structure was studied using the small-angle X-ray scattering technique. As a result, the structure of silica glass was dependent on its thermal history. The structure of as-fused silica glass samples prepared by flame fusion appeared to be quite similar, even though raw materials with different degrees of homogeneity were used. However, the structure of silica glass behaved differently after heat treatment. This different response of the structure of silica glass to heat treatment was analyzed in terms of impurity content and viscosity.

DEPENDENCE OF FLAME CHARACTERISTICS ON THE BUBBLE GENERATION AND HYDROXYL CONTENT IN SILICA GLASS

Abstract High quality silica glass was prepared by flame fusion Verneuil technique using two types of silica powders: purified natural quartz and synthetic sol-gel silica. Two different types of flames, GC2/O2 and LPG/O2, with various conditions of mixture ratios were used. Bubble generation and hydroxyl incorporation were analyzed in these as-fused materials. Silica glass prepared with purified natural quartz powder showed large concentration of bubbles in the most recently fused region. The bubbles were generated from the fluid and depending on the fusion condition it was possible to obtain bubble-free silica glass. A strong dependence of hydroxyl concentration on the flame mixture ratio was also observed.

Small-angle X-ray scattering of heat-treated flame-fused silica glass from amorphous and crystalline powders

High-quality as-fused silica glass, heat treated at 1523 K and prepared by the flame-fusion process using natural crystalline quartz and high-purity amorphous silica glass powders, was investigated by small-angle X-ray scattering (SAXS). The X-ray scattering intensity amplitude from the amorphous structure after heat treatment was analysed in terms of viscosity, density and metallic impurity content. It is shown that SAXS scattering of the amorphous sample is sensitive to the structural change induced by annealing.