Papers by Keyword: Fused Silica

Abstract: Boron Oxide (B₂O₃) was doped in fused silica using slip casting technique. Effects of addition of B₂O₃ on mechanical as well as dielectric properties along with microstructure were studied. It was observed that B₂O₃ acts as devitrification inhibitor by reducing the formation of cristobalite content during sintering of fused silica. Mechanical properties were improved by addition of B₂O₃. Density and flexural strength with (3% by weight) addition of B₂O₃ was 1.89 g/cc and 52MPa respectively.

Abstract: For the key-optical material, the laser induced damage character of fused silica is crucial for the application among the optical laser fitting. As the defect of each point of the silica sample is diverse, and the lasers focus point by point, we divided the sample block into three-dimensional structure for each laser-point to discuss the relationship between the LIDT of each points and the OH-content. The result shows that the LIDT of the center of the sample block is up to 10-11J/cm² which is consistent after the treatment while the LIDT of border pieces is 9-10 J/cm². The different temperature and the aggradation during the fusing process and the machine process caused the different OH content of different location of the sample.

Abstract: Because of its excellent optical performance, photo-physical properties, thermal stability, the fused silica is widely used in laser and aerospace industry. Fused silica can be made to the large-aperture lens for high power laser facilities or the windows for detecting devices. In order to meet the applications, the surface shape of the fused silica must be polished to better than 1/3λ(P-V). If the result of stress-birefringence is big, it is hard to control the surface shape. The permanent stress of a large-aperture fused silica was measured with digital stressmeter and analyzed from manufacturing process stand point.The forming reason and the removing way of different types of stresses were also analyzed in this article. The structure stress is the permanent one in all the types, which also affects the result and the morphology of optical homogeneity.

Abstract: To relax the surface residual stress of fused silica lens or windows irradiated by CO₂ laser, it was proposed to treat it at high temperature above glass strain temperature in the traditional annealing process. However it is a time and energy consuming process, and a distortion will be introduced during the heat treatment. To deal with these problems, annealing temperatures lower than glass strain temperature were applied to the annealing process and a new scheme was designed in this paper. An numerical model was built to simulate the laser induced residual stress and optimize the stress variation in the annealing process. The surface stress of fused silica can be relaxed and deformation induced by heat treating can be ignored.

Abstract: The process of dimensional fused silica etching was offered. The production process of molycoat by magnetron sputtering of molybdenum target in inert gas (Argon) on vacuum distillation unit (NIKA-2012 TN) was examined. The coat quality (delamination, discontinuity) was analyzed; the influence of the first kind internal strains on the type of the observed defects was determined. The research was conducted by means of microscopic and X-ray diffraction analysis. It has been established that the internal strain value in the coat depends on the sputtering gas (Argon) flow rate, and, consequently, its pressure in the magnetron system for molybdenum sputtering. Zero stresses are registered under Argon's flow rate, which is 7.5 L/h. Influence of internal stresses level in the barrier coating on the quality of etching dimple.

Abstract: In this study, cristobalite was used as the addition to prepare silica based ceramic cores, and then the effect of cristobalite content on the mechanical and chemical properties was investigated. The increasing of pre-added cristobalite content resulted in more crystallized cristobalite in the sintered samples and the variation of the linear shrinkage and mechanical properties. When pre-added cristobalite content was 6.0 wt%, the shrinkage of ceramic core was 0.42%, the creep at 1540°C for 30 min was 0.10 mm, and the flexural strength at room temperature and at 1550°C were 25.2 MPa and 28.7 MPa, respectively, which meets the need of ceramic cores of hollow turbine blades.

Abstract: To grind fused silica in ductile mode, it was proposed to repair surface and subsurface micro cracks of fused silica by CO₂ laser irradiation. However, excessive residual stress remains on the surface because the melt fused silica on the surface quenches in air. It causes the critical depth of cut for ductile grinding fused silica to be smaller than 0.2μm. To investigate the distribution of the residual stress and look for an optimal manner of irradiation to control residual tensile stress, a numerical model of was built for simulating the dynamic behavior of fused silica when irradiated by CO₂ laser. Laser energy absorption, heat transmission, viscoelastic behavior of fused silica and thermally induced stress were considered in the numerical simulation. The results show how the residual stress is formed and distributed. We found that an appropriate control of the temperature field as a function of time and position in the laser process is the key to reduce the residual stress. Therefore, three kinds of processes were proposed to reduce residual tensile stress on the surface of fused silica introduced by laser irradiation. The residual stress distributions of these three processes were compared by numerical analysis to decide a better method of laser irradiation.

Abstract: Residual stresses in fused silica induced by two machining methods, diamond blade saw cutting and GC grinding wheel grinding, are studied in this study. Photoelastic method would be applied as measuring tool analyzing the gradient of residual stresses caused by different machining condition. This sentence is strange with analyzing the chips of grinding and observation of surface defects, it is assumed that the stresses gradient differs probably cause by the different material removal mechanism.

Abstract: Silicone rubber composites filled with fused silica were prepared through sigma mixing followed by hot pressing. Filling fraction of fused silica in the silicone rubber matrix was varied from 0-0.51 volume fraction (V_f) and its effects on dielectric properties at different frequencies, thermal properties and moisture absorption were investigated. The results indicate that with the increase of filler volume fraction the relative permittivity increases and dielectric loss decreases. The coefficient of thermal expansion decreased and the moisture absorption increased marginallyas the filler loading increased.

Abstract: Nickel alloys have wide-spread applications in mechanical, tribological and corrosion components such as clutches, cylinder liners, pistons in the automotive industry and marine components in sea water owing to its relative corrosion resistant & good thermal conductivity. The presence of silicon results in reduction of the co-efficient of thermal expansion of nickel & produces an alloy with good casting machining & corrosion characteristics. Further it is reported that addition of silica, improves the mechanical properties which in turn has profound influence on the mechanical properties and corrosion behavior of Nickel-SiO2 alloys. Therefore an investigation in the present research will be made to fabricate and evaluate the microstructure, corrosion of chilled composites consisting of nickel matrix and fused SiO2 particles as the reinforcement (size 40-150 µm) in the matrix. The reinforcement being added ranges from 3 to 12 wt. % in steps of 3%. The resulting composites cast in moulds containing metallic and non metallic chill block (MS, SiC & Cu) were tested for their microstructure and corrosion behaviors. The main objective of the present research is to obtain fine grain Ni/SiO2 chilled sound composite having very good mechanical and corrosion properties.