International Journal of Applied Glass Science最新文献

Due to its extremely high optical uniformity and excellent hot stability, glass–ceramic serves as a key material for ultraprecision imaging of lithography lens, and low-deformation machining is of significance for achieving high-quality surface. Aiming at controllable processing, the annealing of different nanoscratches on glass–ceramic was investigated for revealing the mechanism of material removal and damage repair. The volume change of the single-pass nanoscratch under various normal loads and sliding velocities before and after the annealing was calculated for quantifying the contribution of shear flow, densification, and residual stress to the material removal, respectively. It is found that ductile removal under high normal load or low sliding velocity is dominated by shear flow, thereby improving removal efficiency and reducing machining deformation and defects caused by densification and residual stress. The changes of microstructures beneath the scratches before and after annealing further reveal that the excess processing energy will be absorbed in glass–crystal interface and form micro-cracks on crystal surface. For comparison, brittle removal under variable cycles was simulated by multi-pass nanoscratches, and it reveals that the shear flow ratio raises gradually with the increase of cycle number. These findings provide theoretical guidance for ultraprecision processing of glass–ceramic surfaces.

The glass transition temperature (T_g) is a parameter used in many glass melt viscosity models as it denotes a temperature around which liquid-glass transition occurs. In this work, T_g values were measured for a series of low-activity waste (LAW) glasses using differential scanning calorimetry. These data were combined with T_g data of other waste glasses available from literature. The combined dataset, consisting of 137 data points, was used for the development of several models to estimate T_g from glass composition. When testing the number of influential components and different supervised learning methods, we demonstrated that using more than 10 components or using non-linear methods brought marginal improvement to the model accuracy. The best model predicts T_g of both LAW and high-level waste glasses with reasonable accuracy.

During the forming process of a vial by tubing glass, temperatures of up to 1200°C are applied to adjust the glass viscosity. This process causes the release of volatile components such as alkali borates. Consequently, the percentage of sodium and boron measured on the inner surface of the vial can be higher than that measured on the corresponding glass tube. This study aimed to characterize the inner surface of two different borosilicate glass tubes of type I before and after the vial forming process at the nanoscale level. Quantitative elemental analysis of the surface along the vertical axis of glass tubes and vials was performed by X-ray photoelectron spectroscopy, whereas the topographical investigation was carried out by scanning electron microscopy (SEM). In the near-bottom region of a vial, which is usually the area most prone to corrosion, the SEM micrographs showed the appearance of bulges on the surface. The latter were then analyzed by time-of-flight secondary ion mass spectrometry to characterize their molecular composition. The purpose of this work is to identify possible new strategies for faster identification of factors that eventually influence chemical resistance of pharmaceutical glasses and to provide useful information needed to improve industrial processes.

Binary alkali silicate glasses were synthesized as beads by aerodynamic levitation coupled to laser heating to test the applicability of the method to this compositional range. While bubble-free lithium disilicate beads could be easily obtained, sodium and potassium silicates proved more challenging to melt without significant alkali evaporation: the final samples contained bubbles and exhibited compositional drifts compared to the starting stoichiometry, especially at high SiO₂ content. The risk of volatilization from the melts was evaluated empirically: the volatility of each oxide component scaled to the ratio between its melting temperature T_m and the T_m of the target composition (r_evap), while the difference between such ratios (Δ_evap) provided a qualitative estimation of the risk of differential evaporation. The formulated approach enables to evaluate the suitability of aerodynamic levitation synthesis for a given target glass composition: while low melting temperature and low liquidus viscosity (η < 10⁰ Pa s) represent the primary optimal conditions, more viscous materials can still be prepared without major compositional drifts using a more careful melting procedure, especially if r_evap and Δ_evap are minimized.

Thermal paints have been used for decades by the gas turbine engine community to map surface temperature with low resolution. A novel thermal paint based on the sintering of a lead-silicate glass powder was developed that can map maximum temperature with high resolution (±5°C) over a 60°C range beginning at the glass transition temperature ($�T_g$). The paint exhibited excellent adhesion to nickel-based superalloy components due to similar coefficients of thermal expansion between the superalloy and glassy ceramic coating. An optical transition was qualitatively and quantitatively observed using scanning electron microscopy, ultraviolet-visible (UV-VIS) reflectance spectroscopy, and visual inspection. UV-VIS reflectance spectroscopy was used to confirm the optical transition observed by the naked eye and quantitatively assess the transition of the thermal paint with high resolution. This technique for obtaining high resolution experimental temperature maps can aid the performance, efficiency, and reliability of gas turbine engines.

The high temperature synthesis of glasses in the system (100-x)(0.16Na₂O/0.10CaO/0.74SiO₂)/xFe₂O₃, x = 5 ÷ 20 mol% is reported. For Fe₂O₃ concentrations ≤15 mol%, glasses are formed while the sample with 20 mol% crystallizes during cooling the melt. X-ray diffraction shows the crystallization of magnetite. The microstructure of the glass-crystalline sample is investigated by optical microscopy and scanning electron microscopy and two types of iron-rich crystals corresponding to magnetite and hematite are detected. The refractive indices as determined by the Becke line method are in the 1.567 - 1.639 range and. increase with increasing Fe₂O₃ concentration. The structure is characterized using Infra-red spectroscopy. The presence of symmetric stretching, asymmetric stretching and bending vibrations of Si-O-Si is detected and attributed to the occurrence of SiO₄ tetrahedral units with varying numbers of nonbridging oxygens. Also, the increasing Fe₂O₃ concentration results in occurrence of Fe-O-Si bonds indicating the glass network depolymerization due to Fe₂O₃ addition. In all samples, the presence of Fe³⁺ and Fe²⁺ and the existence of iron ions in tetrahedral and octahedral coordination, as well as a very small amount of Fe⁰ and the precipitation of hematite and magnetite in the glass-crystalline sample is revealed by Mössbauer spectroscopy.

Microlens arrays will suffer from filling defects due to trapped gas when molded in a nitrogen atmosphere by precision glass molding (PGM). In this paper, a multistep molding method is proposed to avoid gas trapping and improve the accuracy of a microlens array. The defect formation mechanism of the microlens array caused by the trapped gas is investigated, and the effect of the molding pressure on the defect formation is analyzed. A numerical model of the mold-nitrogen-glass interface at high temperature is established to evaluate the defect evolution, and the minimum number of PGM steps required to greatly reduce defects caused by the trapped gas is predicted. The numerical model is validated by a multistep PGM experiment of D-K59 glass material. The results show that a three-step PGM process significantly reduced the height of the defect. The difference between the height of the microlens unit and the depth of the mold is less than 0.4%. The molded microlens array has a peak-to-valley value of 0.38 μm and a surface roughness Ra of 3.5 nm. This work is instructive for the fabrication of high-precision glass microlens arrays.

Recently developed methods for high resolution birefringence measurement have been applied to distinguish between the surface and interior birefringence of silica glass fibers as a function of drawing temperature and initial surface condition for two types of silica glass with different water contents. Fibers were drawn in a water-free argon environment using graphite heating elements. It was found that fibers drawn at lower temperatures resulted in greater, interior birefringence, in agreement with previous reports. Additionally, it was found that in the case of low-water silica glass, flame polishing via oxygen–hydrogen mixture and drawn into fibers at lower temperature resulted in significant surface compressive stress upon drawing. This compressive stress may be the result of surface stress relaxation in silica glass that occurs in the presence of water during fiber drawing. In silica glass that contains greater internal hydroxyl impurity concentrations, the interior birefringence as well as the surface stress relaxation was significantly reduced under the same fiber drawing conditions. Characterization of such stress responses provides insight into the effects of common processing techniques as well as impresses the significance of preform processing for consistent fiber production.

Some polymers and oxide glasses exhibit unusual diffusion of liquid or gas, with the depth of diffusion exhibiting a linear increase with time, instead of normal square root of time dependence. There have been many models, but very few experimental data that can help clarify the cause of the phenomenon's existence in glass. Residual stress in sodium trisilicate glass (Na₂O–3SiO₂) samples was characterized following Case II water diffusion at 80°C in a saturated water vapor environment. The surface-swelled layer of the glass was removed by dissolving it in water, and birefringence of the newly revealed surface layer was measured. The presence of a constant negative tensile stress gradient was revealed by indicating that Case II diffusion in sodium trisilicate glass originates from this stress gradient, which overwhelms the more typical Fick's law concentration-dependent flux.