Papers by Keyword: Fused Silica

Abstract: High volume fraction Aluminum/alumina-fused silica hybrid metal matrix composites containing alumina with 0, 10, 30 and 50 wt% fused silica were produced by melt squeezing casting method. Microstructure of hybrid composite was investigated by optical microscope and scanning electron microscopy (SEM). The SEM images showed uniform distribution of fused silica particles in composite microstructure. Also compressive strength of the composites changed (310-110 MPa) with amount of fused silica.

Abstract: Formation of depletion region and the charge distribution are analyzed using multi-charges’ migration under a polling field in fused silica. The internal fields induced are calculated based on a junction model. The field distributions and their intensities within the whole depletion inside the silica are calculated. The maximum field is on the order of 109 V/m in a abrupt junction, and the optical nonlinearities generated by this internal field are consistent with the experimental results published, which proves the junction model is reasonable and feasible to calculate optical nonlinearity in air by thermal polling.

Abstract: Fused silica particles and zirconyl chloride were used as main raw material. Meanwhile, ammonia was used as precipitator and polyethylene glycol as dispersant. Firstly, the composite powders were prepared by wet chemical synthesis. Then, fused silica/zirconia ceramic composites containing zirconia with different contents (5%, 15%, 25%, 35% and 45%) were fabricated in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1 h. The thermal expansion ratios and XRD of samples were examined. The analysis of XRD indicated that the cristobalite peaks intensity of sample with more zirconia is lower at the same sintering temperature, and the intensity of cristobalite was higher while sintered at higher temperature. Zircons were found in all samples’ XRD patterns. The results of thermal expansion ratios showed the ratios of samples with more zirconia were lower, especially at higher sintering temperature. So, existence of zirconia can inhibit crystallization of fused silica/zirconia ceramic composites effectively.

Abstract: The synthesis process of the fused silica glass uses chemical vapor deposition (CVD) method in a furnace. The synthesis process involves complicated physical-chemical phenomena such as turbulence, combustion, radiation, two-phase flow, and so on. A CFD simulation has been carried out for an industrial furnace and process. The simulation result including temperature and major species concentration then is input to CHEMKIN to calculate the radical equilibrium concentration on the fused silica surface. The trend of the simulated fused silica surface temperature is consistent with the measured refraction index showing that the surface temperature is one of the most important parameters influencing the refractive index uniformity of the fused silica product.

Abstract: Ultrasonic vibration assisted processing is well known for the improvement in machined surface quality and processing efficiency due to the reduced forces and tribology-generated heating when grinding hard-brittle materials. We transplanted this philosophy to chemo-mechanical fixed abrasive polishing of optical glass, namely fused silica, in an attempt to improve surface roughness and/or material removal rate. Experiments were conducted to elucidate the fundamental characteristics of chemo-mechanical fixed abrasive polishing of fused silica in the presence and absence of ultrasonic vibration on a setup with an in-house built gadget. The experimental results show that ultrasonic vibration assisted chemo-mechanical fixed abrasive polishing can yield increased material removal rate while maintaining the surface roughness of manufactured optics compared to conventional fixed abrasive polishing without ultrasonic vibration. The mechanism of material removal in fixed abrasive polishing was also delved. We found that the glass material is removed through the synergic effects of chemical and mechanical actions between abrasives and glass and the resultant grinding swarf contains ample Si element as well as Ce element, standing in stark contrast to the polisher that contains abundant Ce element and minor Si element.

Abstract: A rough ground fused silica surface can be ground in a ductile mode by ultra-precision grinding after repairing the surface and subsurface micro cracks (SSMC) by CO2 laser irradiation. In this paper, 2D finite element thermal analysis of unidirectional multi-pass laser irradiation on fused silica was conducted, and the simulation results were compared with the thermal analysis and experiments results of single pass laser irradiation. Thermal analysis results show that the SSMC on the ground fused silica can be repaired and surface roughness can be decreased simultaneously by unidirectinal laser raster scan with a power of 10.5 W, a scan velocity of 0.2 m/s and a scan spacing of 40 μm.

Abstract: Removal of gold particles (40 nm and 100 nm) from fused silica and thermal oxide surfaces in dilute ammonium hydroxide solutions has been investigated. The particle removal efficiency (PRE) from fused silica surface has been found to be a strong function of ammonium hydroxide concentration and bath temperature. PRE increases from 0 to 85 % with increase in bath temperature from 30 to 80 °C for ammonium hydroxide concentration of 1 %. Addition of megasonic energy to the ammonium hydroxide bath at 30 °C has also shown to improve the PRE significantly. In the case of thermal oxide, the removal of gold particles is much easier compared to that from fused silica. Even for cleaning at 30 °C, the PRE for oxide surface increases from 10 to 90 % with increase in ammonium hydroxide concentration from 0 % to 4 %. Atomic force microscopy measurements reveal that an adhesion force of 10 mN/m exists between fused silica and gold particles in 4 % ammonium hydroxide solution as opposed to only repulsive force in the case of thermal oxide.

Abstract: High efficiency and high surface integrity grinding of fused silica lens used in the ultraviolet (UV) laser transmission equipments is highly demanded. It is necessary to decrease the undeformed chip thickness for producing better surface integrity. We conducted creep feed grinding (CFG) and conventional shallow cut grinding (SCG) experiments of fused silica with a resin bond diamond wheel. Experiment results shows that owing to thinner undeformed chip thickness, the normal grinding force, radial wheel wear and P-V value of surface roughness of CFG are smaller than those of SCG at the same MRR. At the same table speed, surface roughness decreased with the increase of MRR in both CFG and SCG as a result of decreased undeformed chip thickness which is attributed to the elasticity of resin bond.

Abstract: Fused silica micro-powders with D₅₀ of 1.8μm were firstly prepared by ball milling. Effects of milling time on particle size distribution and microstructures of the powders were discussed. Then, the green compacts with volume density of 1.86g/cm³ was obtained by slip casting with lactic acid as dispersant. Effects of lactic acid content on apparent viscosity of the slurry, thickness and density of the green compacts were investigated. Finally, fused silica ceramics with thermal expansion coefficient of 0.56∙10^-6/°C, bending strength of 64MPa and volume density of 1.94g/cm³ were prepared.

Abstract: To grind fused silica in ductile mode, surface and subsurface micro cracks (SSMC) on ground fused silica should be repaired by CO2 laser irradiation before ultra-precision grinding. In this paper, 2D thermal analysis of single pass laser irradiation of fused silica was conducted, and the simulation results were discussed by comparing with the experiment results. To repair SSMC and decrease the surface roughness of ground fused silica simultaneously, the maximum temperature on the surface during laser irradiation should be controlled higher than 3280 K and lower than 3550 K.