Transparent Silica Glass Research Articles

Fabrication of transparent silica glass and evaluation of silica particle dispersibility in silica slurries based on the solubility parameters of the slurry components

Silica particles were dispersed in 11 acrylic monomers at various concentrations. The dispersibility of the silica particles was evaluated based on the viscosity of the slurry. Furthermore, the relationship between the viscosity of the slurry and the solubility parameters (SPs) of the silica particles and acrylic monomers was investigated. When the SPs of the silica particles and acrylic monomers were close, the viscosity of the silica slurry decreased and high concentrations of the silica particles could be dispersed in the acrylic monomers. Therefore, SP can be used for predicting the dispersibility of silica particles. The prepared slurry was then used to fabricate sintered silica glass. Silica slurry was cured through photopolymerization to obtain a green body, which was then heat-treated at 850°C in air atmosphere and sintered at 1710°C under vacuum to obtain sintered silica glass. Transparent sintered silica glass with no cracks was obtained using 4-hydroxybutyl acrylate, which has a similar SP to that of silica particles, as a solvent. The obtained sintered silica glass exhibited a transmittance of 92% at a wavelength of 400 nm. In the ultraviolet region, light absorption originated from two-coordinated Si in the glass. The absorption spectrum in the infrared region showed an extremely low peak of the SiOH group, indicating that low-OH silica glass was obtained. Thus, this study provides a new method for fabricating silica glass and provides a method of selecting solvents for the slurries used in powder sintering.

Research on additive manufacturing technology of high solid loading silica glass slurry

In this work, digital light processing (DLP) 3D printing technology was used to fabricate transparent silica glass with complex structures. The effects of different particle sizes and mixing ratios of silica powders on the viscosity of the prepared slurries were investigated. The results showed that when 100–200 nm and 800 nm silica powders were mixed in a 1:4 vol ratio, the slurry exhibited the lowest viscosity. The highest solid loading of the slurry prepared with this mixed silica powder reached 75 wt%, with a viscosity of only 1245 mPa·s. The high solid loading slurry was subjected to 3D printing, debinding, and sintering treatment, and the transparent silica glass samples with complex structures was obtained.

Two-photon polymerization of silica glass diffractive micro-optics with minimal lateral shrinkage.

Three-dimensional printing enables the fabrication of silica glass optics with complex structures. However, shrinkage remains a significant obstacle to high-precision 3D printing of glass optics. Here we 3D-printed Dammann gratings (DGs) with low lateral shrinkage (<4%) using a two-photon polymerization (2PP) technique. The process consists of two steps: patterning two-photon polymerizable glass slurry with a 515 nm femtosecond laser to form desired structures and debinding/sintering the structures into transparent and dense silica glass. The sintered structures exhibited distinct shrinkage rates in the lateral against longitudinal directions. As the aspect ratio of the structures increased, the lateral shrinkage decreased, while the longitudinal shrinkage increased. Specifically, the structure with an aspect ratio of approximately 60 achieved a minimal lateral shrinkage of 1.1%, the corresponding longitudinal shrinkage was 61.7%. The printed DGs with a surface roughness below 20 nm demonstrated good beam-shaping performance. The presented technique opens up possibilities for rapid prototyping of silica diffractive optical elements.

Low-temperature 3D printing of transparent silica glass microstructures.

Transparent silica glass is one of the most essential materials used in society and industry, owing to its exceptional optical, thermal, and chemical properties. However, glass is extremely difficult to shape, especially into complex and miniaturized structures. Recent advances in three-dimensional (3D) printing have allowed for the creation of glass structures, but these methods involve time-consuming and high-temperature processes. Here, we report a photochemistry-based strategy for making glass structures of micrometer size under mild conditions. Our technique uses a photocurable polydimethylsiloxane resin that is 3D printed into complex structures and converted to silica glass via deep ultraviolet (DUV) irradiation in an ozone environment. The unique DUV-ozone conversion process for silica microstructures is low temperature (~220°C) and fast (<5 hours). The printed silica glass is highly transparent with smooth surface, comparable to commercial fused silica glass. This work enables the creation of arbitrary structures in silica glass through photochemistry and opens opportunities in unexplored territories for glass processing techniques.

Fabrication of Glass Microchannels Using Plant Roots and Nematodes

Microchannels have been studied actively in recent years. Various types of materials are used for fabricating microchannels in different types of applications including polymers, and ceramics. Since glass materials have appealing properties such as hardness, transparency, thermal resistance, and chemical resistance, they are used in biomedical devices and microfluidic application. Glass microchannel fabrication methods include chemical etching, imprinting, and 3D printing. This paper proposes unprecedented methods to fabricate glass microchannels using plant roots growth and nematodes migration. The microchannels fabricated by these methods have a complex three-dimensional structure, and the smallest channels have a diameter of several tens of micrometers in the glass. Although glass is attractive material, it is challenging to sinter the green body to fully dense and transparent solid structure. Hence, experiments were also conducted to establish a fabrication technique for transparent silica glass.

Hybrid additive manufacturing for the fabrication of freeform transparent silica glass components

Additive manufacturing of ceramic and glass materials has been developed extensively over the past years, revealing strengths and limitations of the various technologies. In this work, a hybrid extrusion-photopolymerization process is developed to exploit the benefits of both approaches. Their combination allows for more complex geometries with less rheological constraints and no influence of scattering and/or absorption. With this method, transparent silica glass 3D honeycomb-like structures are fabricated starting from a suspension that combines silica particles and a silicon alkoxide. The rheological behavior and reactivity of the ink are tailored with an appropriate blend of acrylates as well as with the alkoxide addition. The latter also contributes to the final ceramic yield, allowing for faster thermal treatments despite a low particle loading. The final components closely match the shape provided by the CAD model; their physical properties confirm the formation of a fully dense silica glass after the heat treatment.

Rapid Manufacturing of Complex-Structured Transparent Silica Glass Materials through a Hybridized Approach of Photo-Curing and Machining from Interparticle Photo-Cross-Linkable Suspensions.

The rapid manufacturing of transparent SiO2 glass components via a hybridized 3D structuring approach for photo-curing and green machining, followed by a fast debinding/sintering process (at a heating rate of 20 °C min-1), is reported to be based on the design of a new series of interparticle photo-cross-linkable suspensions. In these suspensions, small amounts of multifunctional acrylates and silane alkoxides with acryloyl groups (A-Si) are co-photo-polymerized and further reacted with SiO2 particles modified using functionalized polyethyleneimine to form hybridized interparticle networks. The addition of A-Si increases the interparticle cross-linking densities, leading to an improvement in the mechanical properties and green machinability of the photo-cured bodies. Furthermore, the A-Si component in the cross-links forms siloxane-based networks among SiO2 particles in situ during the debinding/sintering process, which increases the mechanical strength of the debinded bodies and successfully prevents structural collapses under rapid heating conditions. The study demonstrates that the photo-cured body from the newly designed suspensions can be green-machined into pillars, microfluids, and assembling blocks and can be sintered into highly transparent SiO2 glass components. Overall, this work provides new options for the time- and energy-effective processing of SiO2 glass materials with tailor-made 3D structures.

Fabrication of Transparent Silica Glass by Powder Sintering Method Aiming Desired Shape Molding

Fabrication of Transparent Silica Glass by Powder Sintering Method Aiming Desired Shape Molding

Obtaining transparent silica glass from nano-silica hydrosol

Transparent silica glass is widely used in various fields. However, a simple and economical method of synthesis remains to be developed for high-precision device manufacturing. In this study, transparent silica glass is fabricated from low-cost commercial nano-silica hydrosol. To obtain transparent glass, the crystallization temperature of bulk materials must be higher than their densification temperature. Based on XRD analysis, impurity ions such as Na+ have a strong influence on the crystallization characteristics of sintered samples. Purification can be performed by soaking preheated samples in boiling water for a given duration. Transparent silica glass was obtained for purified samples from acidic silica hydrosol sintered at 900–950 °C. The optical characteristics of the samples were investigated for the presence of silica glass, and the transparency was enhanced for samples sintered in vacuum. The mechanical and dielectric properties of the sintered samples were also characterized.

How fluorine minimizes density fluctuations of silica glass: Molecular dynamics study with machine-learning assisted force-matching potential

Transparent silica glass is an indispensable material for today's information technology society as an ultra-low loss optical fiber. Recently, further low-loss optical fibers are demanded due to rapidly expanding information. A small amount of fluorine doping is known to reduce the Rayleigh scattering further by reducing the density fluctuations of silica glass, even though the fluorine is an impurity for the pristine silica glass. This study devoted to answer the riddle of F-doping and an accurate force-matching potential optimized by machine-learning enables us to understand how fluorine remedies the disorders in silica glass. It was found that fluorine mainly replaces an oxygen in tetrahedral SiO4 unit, but also forms five-fold Si, such as SiO4F and SiO3F2 units. The former disrupts silica network, while the latter attenuates the network rigidity by loosening the five Si-O(F) bonds. Since the two local effects of fluorine spreads through the glass network, F-doping prompts silica glass to relax further even at temperature lower than the glass transition (fictive) temperature. Consequently, fluorine minimizes the density fluctuation (thus, Rayleigh scattering) of silica glass at around 1 wt%, although fluorine itself is an impurity for silica glass.

Luminescence Behavior of GdVO4: Tb Nanocrystals in Silica Glass-Ceramics

Glass ceramics with GdVO4: Tb nanocrystals impregnated in the highly transparent silica glass were prepared by the porous glass and sintering process and confirmed by XRD, Raman spectrum, and TEM. Spectral analysis shows that there are multifarious energy transfer processes in GdVO4: Tb nanocrystals, such as VO43− → Tb3+, Gd3+ → VO43−, Gd3+ → VO43− → Tb3+, and Gd3+ → Tb3+, and the main one is VO43− → Tb3+. In this process, 3T1,2 → 1A1 transition of VO43− transfers the energy to Tb3+ and generates 5D3 → 7F6,5,4,3,2 and 5D4 → 7F5 transitions of Tb3+. The energy transfer efficiency is 29.5%, and the excitation wavelength range of Tb3+ ions can be shifted from 230–260 nm to 280–365 nm. This shows that GdVO4 can effectively change the excitation wavelength of Tb3+, which is conducive to the application of Tb3+ ions excited by LED light sources.

Broadband enhancement of devices and microsystems for light harvesting and photocatalysis

Plasmonic materials, stochastically roughened, can provide localized field enhancement under optical irradiation (light trapping). The use of plasmonic materials in semiconductor photocatalists also leads to drastic enhancement of their photoreactivity. Plasmonic enhancement can be seen in an extension of the useful range of solar spectrum, and in a high increase of the amount of collected light energy. The structures we propose here not only can be utilized for a vast majority of photocatalytic systems (including those microreactor-based,) but also for the enhancement of light harvesting devices of any kind, including all types of solar cells, as well as for ultrasensitive chemical sensing. Here we consider a structure with a roughened metallic film on the bottom and a roughened transparent conductive oxide (TCO) or silica glass layer on the top, separated by a thin dielectric layer. We fabricated experimental structures and simulated their electromagnetic properties by the finite element method. Thus we verified that the combined influence of two rough films significantly improves light trapping within the dielectric layer between them, while plasmonic effects lead to concentration of electromagnetic field into subwavelength volumes. Consequently, the radiation intensities are vastly increased within the dielectric layer, even for several orders of magnitude, compared to the incident beam. Another interesting property observed is that while both TCO and silica glass structures act as diffractive light traps well into the UV range, the TCO structure simultaneously acts as a plasmonic superabsorber for IR light, turning the increase of TCO opaqueness with wavelength into a benefit since it significantly expands the useful spectral range. Tuning of dopant levels in TCO or using alternative plasmonic materials, together with varying coarseness of the films can further be used to tailor the electromagnetic response.

Preparation and characterization of sol-gel derived highly transparent aluminosilicate glass thin films with ultrahigh doping level of Yb3+ ions

A series of highly transparent aluminosilicate glass films with ultrahigh doping level of Yb3+ ions have been prepared by Sol-Gel method and deposited on transparent silica glass substrates with thickness ranging from 0.901 μm to 1.314 μm and doping level of Yb3+ ions up to 30 mol%. Each film exhibits a characteristic photoluminsecence spectrum of Yb3+ ions with a maximum at 975 nm and high transmission in VIS-NIR region. The refractive index for the film has been measured by spectroscopic ellipsometry. AFM images and EPMA cross-sectional images have presented the formation of film surface and cross section respectively and a uniform film formation has been achieved with the composition of 10YbO1.5-15AlO1.5-75SiO2 and 20YbO1.5-12AlO1.5-58SiO2. It has been verified that multilayer films get a major improvement in photoluminescence intensity still with high transmission in VIS-NIR region.

Lubrication Analysis of Micro-Dimple Textured Die Surface by Direct Observation of Contact Interface in Sheet Metal Forming

To investigate the underlying mechanism of the effects of surface texturing on lubricated sliding friction in the metal forming operation, an in-situ observation system using transparent silica glass dies and a high speed recording camera was newly developed. To correlate the dimensional parameters of micro-dimple textured structures and tribological properties in the metal forming operation, the in-situ observation was performed during bending with the ironing process of the stainless steel sheet with a thickness of 0.1 mm. The lubrication behavior were compared between the different lubricant viscosities and the micro-dimple textures with different diameters of 10 µm, 50 µm, 100 µm fabricated by using femto-/pico-second laser processing. As a result, the textured die with dimple diameters of 10 µm and 50 µm showed the lubricant flow transferred from one to the other dimples owing to the lubricant reservoir effect, while that of 100 µm indicated the less supply of the lubricant. However, the textured die with a dimple diameter of 10 µm demonstrated higher ironing force than that of 50 µm, due to the severe adhesion of work materials inside the dimple structures. Based on these experimental findings, the dimple size dependencies on lubricant reservoirs effects and the generation of the hydrodynamic pressure were discussed by correlating with the in-situ observation results, a fluid-flow analysis and a laminar two-phase flow analysis using the finite element method.

Sintered silica bodies with persistent luminescence

Strong persistent luminescence (PeL) from silica bodies was obtained, for the first time, by sintering silica powder mixed with PeL SrAl2O4:Eu2+,Dy3+ microparticles (MPs). We show that it is not possible to prepare transparent PeL silica glass due to the decomposition of the MPs, which occurs already at 1450 °C. The MPs decomposition was associated with the precipitation of Sr3Al10SiO20 phase when sintering up to 1650 °C and of SrAl2Si2O8 when sintering between 1650 and 1750 °C. Cristobalite was found to also precipitate when sintering for 10 min but has no impact on the PeL of the bodies.

The devitrification kinetics of transparent silica glass prepared by gel-casting method

The kinetics of the crystallization of cristobalite in the amorphous silica glass were studied for samples prepared by gel-casting and sintering in air. Avrami and rate equations were used to calculate the rate constants and the activation energy. The results showed that the crystallization obeys the first order and occurs mainly on the surface with activation energy of 543-546kJ/mol. The fewer amounts of OH-groups and the high amount of oxygen vacancies are expected to stand behind the increase in the activation energy as compared with that reported in literatures. Keywords: Devitrification, Gel-Casting, Silica Glass, Cristobalite, Crystallization.

Characterisation of silicon fibre Bragg grating in near‐infrared band for strain and temperature sensing

Fibre Bragg grating inscription in the crystalline silicon (Si)-core fibre is described using visible light femtosecond laser pulses. The femtosecond pulses at 517 nm propagate through the transparent silica glass cladding and are fully absorbed by the Si core generating locally high temperatures and stress fields in forming the grating periods. The Si FBGs were characterised in reflection, calibrated for a first time as strain and temperature sensors and compared with that of FBGs inscribed in standard silica fibres.

Additive Manufacturing of Transparent Silica Glass from Solutions.

A sol, aqueous solution-based ink is presented for fabrication of 3D transparent silica glass objects with complex geometries, by a simple 3D printing process conducted at room temperature. The ink combines a hybrid ceramic precursor that can undergo both the photopolymerization reaction and a sol-gel process, both in the solution form, without any particles. The printing is conducted by localized photopolymerization with the use of a low-cost 3D printer. Following printing, upon aging and densifying, the resulting objects convert from a gel to a xerogel and then to a fused silica. The printed objects, which are composed of fused silica, are transparent and have tunable density and refractive indices.

Visualization investigation on flowing condensation in horizontal small channels with liquid separator

A simultaneous visualization and measurement experiment was carried out to investigate condensation flow patterns and condensing heat transfer characteristics of refrigerant R141b in parallel horizontal multi-channels with liquid-vapor separator. The hydraulic diameter of each channel was 1.5 mm and the channel length was 100 mm. The refrigerant vapor flowing in the small channels was cooled by cooling water. The parallel horizontal multi- channels were covered with a transparent silica glass for visualization of flow patterns. Experiments were performed at different inlet superheat temperatures (ranging from 3°C to 7°C). Mass velocity was in the range of 82.37 kg m-2s-1 to 35.56 kg m-2s-1. It was found that there were three different flow patterns through the multi- channels with the increase of mass velocity. The flow patterns in each channel pass almost tended to be same and all of them were annular flows. The efficiency of the liquid-vapor separator with U-type was related to vapor mass velocity and the pressure in the small channels. It was also found that the heat transfer coefficient increased with the increase of the mass velocity while the cooling water mass flow rate increased. It increased to a top point and then decreased. It increased with the increase of superheat in the low superheat temperature region.

In-situ observation of lubricant flow on laser textured die surface in sheet metal forming

Abstract In the present study, to observe the contact interface during sheet metal forming process, in-situ observation system using transparent silica glass dies and high speed recording camera was developed. To correlate the dimensional parameters of micro-textured structures and tribological properties during the forming operation, in-situ observation during ironing process of stainless steel sheet with a thickness of 0.1 mm was performed. Tribological behavior was compared between the different dimple structures under different contact state. Dimple structure arrays with diameters of 10, 50, 100 µm were achieved by using femto-/pico-second laser processing. As results, the textured die with dimple diameters of 10 and 50 µm showed the lubricant flow transferred from one to the other dimple structures, in which hydrodynamic pressure seems to generate inside the dimples, while that of 100 µm indicated the less supply of lubricant. However, for the textured die with a dimple diameter of 10 µm demonstrated higher ironing force than that of 50 µm, due to the coverage of dimple structures by generated wear debris during the forming process. Based on these experimental findings between different contact states, the principle in generation of hydrodynamic pressure, the function of micro-trap for wear debris and the micro-reservoirs effect for lubricant retention depending on the size of dimple structures were discussed by correlating with the in-situ observation results.