International Journal of Applied Glass Science最新文献

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.

Lead-containing alkali/alkaline-earth borate and barium lead phosphate glasses were prepared by melt-quenching for a detailed investigation of the Pb²⁺ ions’ optical properties. UV–Vis absorption and photoluminescence spectroscopy reveal variations in the s–p transition of Pb²⁺, which are shown to correlate with the optical basicity of the host glass in both borates and phosphates. Pb²⁺ emission differs significantly for borate and phosphate glasses, as the nature of the charged sites available to accommodate Pb²⁺ cations vary. Optical basicity values were determined from the composition (Λ_th) and the measured refractive index (Λ_n). The UV-cutoff shifts toward higher wavelengths with increasing optical basicity and lead content. In borate glasses, the frequency of the stretching modes due to nonbridging oxygen atoms of trigonal metaborate species is identified to be inversely proportional to the excitation wavelength (directly proportional to the excitation energy) of Pb²⁺. Lead-containing alkali and alkaline-earth borate glasses show additional correlations between the Pb²⁺ emission wavelength and the weighted average of the field strength of the modifier(s). Complementary to the investigation of optical properties, radiation and neutron shielding parameters were calculated, suggesting the potential utility of some of the studied compositions for radiation shielding applications.

In this study, glasses in composition 70WO₃–(30 − х)P₂O₅–хB₂O₃ (0 ≤ х ≤ 20 mol%) were prepared by melt quenching method. The glass formation, structure, and thermal and electrical properties are discussed. Homogeneous glasses were obtained at x = 0–10 mol% B₂O₃, whereas glasses with x = 15 and 20 contain microinclusions of WO₃. The glass transition temperature decreases from 709 to 531.6°C with increasing B₂O₃ content, as well as the crystallization temperature and the thermal stability. The structure of the glasses was studied by Raman spectroscopy and infrared spectroscopy. The Raman spectra are characterized by a band near 995 cm⁻¹, a broad band at 788–800 cm⁻¹, and a band near 675 cm⁻¹ ascribed to vibrations of W–O–P, W–O–W, and P–O–B bonds, respectively. The Fourier-transform infrared spectra show vibrational bands due to characteristic phosphate and borate groups. Tetrahedral BO₄ units prevail in the structural network. The electrical conductivity of the glasses decreased with x content due to the growth of WO₃-deficient regions.

In the study of deep geological disposal of high-level radioactive waste (HLW), beta decay has been widely studied, whereas the nuclear transmutation effects due to beta decay on vitrification are generally neglected. In this work, a series of sodium borosilicate glasses doped with cesium was fabricated. The nuclear transmutation due to beta decay evolving with the deposited time was simulated by substituting for cesium with barium. The macroscopic properties of the glasses, including density, hardness, and Young's modulus, were measured using the Archimedes (buoyancy) method and nanoindentation, respectively. The microscopic structures of the glasses were characterized by grazing incident X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and Raman spectroscopy. The nuclear transmutation effects were significant. With the substitution of barium for cesium, the density, hardness, and modulus of the glasses increased and eventually tended to saturation. A decrease of [BO₃] units and an increase of [BO₄] units were observed in the infrared spectra and NMR spectra. In addition, the results were systematically compared to previous strontium-doping work in order to evaluate nuclear transmutation effects due to beta decay on vitrification in HLW comprehensively. The comparison demonstrated that the nuclear transmutation effect of cesium is completely opposite to that of strontium. The research is expected to contribute to a deeper understanding on the nuclear transmutation effects due to beta decay in HLW on vitrification.