Papers by Keyword: Silica Glass

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Authors: Peter A. van Nijnatten
Abstract: Spectral behaviour of the real and imaginary parts of the optical constants of glass has been widely investigated to obtain band structural parameters of optically induced transitions. Curve fitting procedures for obtaining a classical oscillator fit to reflectance and/or transmittance data play an important role in this application. The present form of the dispersion model that is widely used to describe disordered media like glass uses a convolution of the Lorentzian oscillator function and the Gaussian Probability Density Function. This model is capable of describing symmetrical band shapes only. In this paper a convolution model is proposed based on using the Beta function as PDF. The maximum of the PDF, which corresponds to the frequency with the highest probability, corresponds to the central frequency of the particular oscillator species in the convolution model. For a certain value of the parameter that describes the degree of asymmetry, the new model is equivalent with the present convolution model and the remaining parameters have an identical meaning yielding practically identical values. The new model also solves a problem related to the infinite integration intervals of the Gaussian PDF based convolution model.
Authors: Janina Setina, V. Akishins, L. Petersone
Abstract: The new generation of high silica materials with high thermal resistance was created by leaching of chopped glass fibre. These materials with low thermal conductivity are inert to the majority of chemical reagents, resistant to organic and mineral acids, weak alkali, water and highpressure steam. High silica chopped strand mats are non-woven fabrics designed for using in a wide range of insulation and protection applications at temperature till 11000C. The technology and quality of leaching process of initial Si-Al-Na glass widely depends on quality of fibre surface characteristics, i.e., roughness of surface of glass filaments. The surface roughness of the fibre before leaching is a function of chemical durability, therefore it depend on content of Al2O3. The thermal conductivity (within 20…10000C) of chopped strand mats directly depends on the surface roughness. The morphology and compositional profiles of surface of glass fibre before and after leaching were investigated using AFM, SEM, X-ray microanalysis and X-ray powder diffractometer. The different defects for fibre with content of Al2O3 <2.5% and high roughness namely cracking and crystalline deposits of Na2SO4 on top and into pores of fiber after leaching have been identified. The presence of sodium ions on surface of fibre decreases the heat insulation properties of mats. The structure of glass filaments surface was investigated in order to clarify the influence of surface characteristics on thermal conductivity of high silica glass fibre non-woven fabrics.
Authors: Paulo S. Pizani, M.R. Joya, F.M. Pontes, L.P.S. Santos, M. Godinho Jr, E.R. Leite, Elson Longo
Abstract: Visible photoluminescence was generated in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The broad emission band maximum shows a linear dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. The photoluminescence was attributed to defect generation related to unsatisfied chemical bonds due to the high surface area. Raman scattering and ultraviolet-visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that the powder is composed by nanocrystallites with about 10-20 nanometers immersed in an amorphous media.
Authors: Gabriella Zsoldos, István Kocserha, András Szegedi
Abstract: High energy explosions and irradiation may cause that the minerals and mineraloids form glassy phase on the earth surface. We would like to determine the mechanical properties of these glassy materials. To achieve this and manufacture samples we need to measure the main technological property, the viscosity.
Authors: O. Dersch, A. Zouine, F. Rauch, Eisuke Arai
Authors: J.S. Santos, E. Ono, Carlos Kenichi Suzuki
Abstract: This research reports the development of high homogeneity silica glass for photonic components synthesized by the VAD (Vapor-phase Axial Deposition) method. Structural radial homogeneity of silica soot were characterized by scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS). It was established a relationship with the refractive index homogeneity, n, and the birefringence of consolidated boules characterized through interferometry, optical spectrometry, and polarization spectrophotometry. By controlling the silica soot nanostructure during the deposition stage, a material with high radial homogeneity of refractive index of 1 ppm and birefringence of 2 nm/cm can be synthesized.
Authors: Yuan Cheng Sun, Xue Fu Song, Xiu Rong Du, Xiao Qiang Zhang, Hui Wang, Xiao Hui Yang
Abstract: Type IV silica glass is the key material in inertial navigation and optical field due to its high purity and unbroken structural network. Structural homogeneity of type IV silica glass, which is mainly affected by producing process, is one of the most important properties and determines its usability. The influence of ionizing gas flow of plasma was studied in this paper. Flow rate of working gas and protecting gas was changed and the depositing temperature field was measured. Structural homogeneity of deposited silica glass was discussed by optical homogeneity, fictive temperature and stress birefringence. Results show that more uniform temperature field can be obtained with higher working gas flow and lower protecting gas flow, and the structural homogeneity of type IV silica glass is better. But the proportion of working gas and protecting gas should not be larger than 2. When the working gas and protecting gas are 5 m3/h and 2.5 m3/h respectively, the structural homogeneity of type IV silica glass is the best.
Authors: Markus Eberstein, Guido Mann, Jens Vogel, M. Zoheidi, Jörg Krüger
Abstract: High-power optical multimode fibers are essential components for materials processing and surgery and can limit the reliability of expensive systems due to breakdown at the end faces. The breakdown threshold of fibers is determined by intrinsic materials properties and parameters of the technology applied. The aim of this paper is the identification of technological parameters that are crucial for the fiber quality. Fibers were drawn from preforms of Heraeus SWU with core material F300 and a low amount of OH-. Both, the cladding (fluorine doped SiO2) to core diameter ratio (CCDR) and the drawing speed were varied. CCDR values between 1.05 and 1.4 were used. Afterwards, the laser-induced damage thresholds (LIDT) of the fibers were determined. For comparison, also samples from preforms, which underwent different thermal treatments above the transition temperature, were tested with respect to their damage resistivity. Single and multi pulse LIDT measurements were done in accordance with the relevant ISO standards. Nd:YAG laser pulses with durations of 15 ns (1064 nm wavelength) and 8.5 ns (532 nm) at a repetition rate of 10 Hz were utilized. For the fibers, LIDT values (1-on-1, 1064 nm and 532 nm) increased with growing CCDR and with decreasing drawing velocities.
Authors: Edson Haruhico Sekiya, Kazuya Saito
Abstract: Emission spectra of Sn, Sb, Pb and Bi doped silica glasses co-doped with Al and P prepared by modified chemical vapor-phase deposition (MCVD) using solution doping technique are presented. Bi doped silica glasses present emission/excitation (Em/Ex) bands around 470/(330, 220nm) 600/(470, 350, 270nm), 730 and 830/(820, 420, 380, 250nm), with the intensity ratio of these bands depends on the composition, indicating that different emission sources (valence states or defects) are present together. The Em/Ex of Sb doped silica glasses also depend on composition, and are similar of Bi doped silica glasses. The lifetime at 830 and 1400 in Bi or Sb doped silica glasses are similar and around 60 and 850μs, respectively. The lifetime around 600nm was 3.2 and 11μs, respectively to Bi and Sb doped silica glasses. The Sn doped silica glass present Em/Ex bands around 305/265nm, 400/(270, 340nm) and 430/280nm. The Pb doped silica glass present Em/Ex around 370/290nm and 540/320nm. No significant change in the emission bands in the visible range are observed when the Sn or Pb doped silica glass are co-doped with Al or P. The present results of Em/Ex suggest that Bi and Sb can be candidate for fiber lasing in visible range (around 600nm) using the available LD pumping (ex: 405nm). Despite Sn and Pb doping shows strong emission around 400nm, unfortunately until now there is no LD that can be used as pumping source.
Authors: Y.T. Dai, Gang Xu, Wei Lai Li
Abstract: Owing to the large photo energy, 157nm laser is considered as one of promising micro-fabrication tools. In this paper, a micromachining system based on the 157nm laser is introduced. 2D laser direct-writing and 3D micro-structuring experiments are carried out for silica glasses, fibers and diamond. For natural diamond, the ablation threshold by 157nm laser is about 2.0J/cm2. Material removal is dominantly due to photon-chemical effect for 157nm laser ablation. Effectiveness of using 157nm laser for 3D micromachining is clearly demonstrated.
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