On the possibility of devitrification of ancient glass

The question whether some crystallization will take place in old glass during long-time storage (up to 1000 years) at low temperatures well below T_g is considered theoretically. Evaluations for the systems Na₂O · SiO₂ and Li₂O · 2SiO₂ are carried out using the model of homogeneous and heterogeneous nucleation theory. For these systems a barely observable crystallized volume fraction will be reached at 300 K only after storage for astronomical periods (10⁶ ? 10¹³ years), depending on the number of heterogeneities and the contact angle of heterogeneity. If the observed strong influence of H₂O content in glass on crystallization is also taken into account, crystallization will not take place for at least 1000 years of storage at 300 K. This limiting value is close to archaeological periods and will therefore merit careful attention in further investigations.     

A mössbauer study of hematite dissolution and devitrification in float glass

The effect of 5% hematite on the devitrification behaviour of float glass has been measured as functions of time and temperature by Mössbauer spectroscopy and X-ray diffraction (XRD). The devitrification products are devitrite (Na₂O·3CaO·6SiO₂), cristobalite, quartz and an iron-rich pyroxene, aegirine ((Na Ca)(Fe, Mg) Si₂O₆) for which XRD data are tabulated. The Mössbauer parameters for glassy and crystalline materials are interpreted in terms ofthe aegirine structure, whose site assignment is discussed in terms of next-nearest neighbour effecs. The bulk dissolution data obtained by Mössbauer and XRD are used to generate diffusion coefficients for Fe³⁺ in the glass melt, using a moving boundary model for diffusion controlled dissolution. The diffusion coefficients at 800°C are D_{Fe³⁺ (XRD)} = 3.52 × 10^?15 cm²/s and D_{Fe³⁺ (MS)} = 1.27 × 10^?15 cm²/s.     

Elasticity of ion stuffing in chemically strengthened glass

The chemical strengthening of glass involves the stuffing of large ions into network sites previously occupied by smaller ions. Typically this involves an exchange of Li⁺ or Na⁺ ions in the glass for larger K⁺ ions from a molten salt bath. This swapping of ions creates compressive stress in the surface of the glass, significantly increasing the strength of the final glass product. The magnitude of this compressive stress is governed by the linear network dilation coefficient (LNDC), which defines the amount of linear strain per unit of ion substitution. However, the amount of strain attainable through ion exchange is much smaller compared to what is expected from as-melted versions of the same final glass composition. This effect, which we have termed the “network dilation anomaly,” is a result of the different local environment around the invading ion species in as-melted versus ion-exchanged glasses. A remaining question concerns the nature of the network strain due to ion stuffing. Using molecular dynamics simulations, we show that the strain induced by ion stuffing is entirely elastic. In other words, when a reverse ion exchange is performed to swap the original ions back into the glass, the initial volume of the as-melted glasses is entirely recovered. Moreover, we show that the local structural environment around the alkali ions is restored to the as-melted conditions. The elastic nature of ion stuffing demonstrates that the network dilation anomaly is not a result of plasticity, but rather a failure to achieve the full amount of expected elastic strain during ion exchange. The elasticity itself consists of both instantaneous and delayed contributions.     

Micro-photoluminescence study on defects induced by ion microbeam in silica glass

We have evaluated the irradiation effects by ion microbeam on silica glass for various ion species by means of a micro-photoluminescence technique. Defect generation and refractive index change were observed for silica at the area of 10 μm × 50 μm scanned by ion microbeam of H⁺, He⁺, N⁴⁺, C⁴⁺, O⁴⁺, and Si⁵⁺ with energy from 1.7 to 18 MeV. The μ-PL spectroscopy measurements were performed along the side surface perpendicular to the microbeam irradiated surface. Based on the comparison with a result of SRIM (stopping and range of ions in matter) simulation, the defect generation mechanism was discussed in terms of the energy deposition processes due to electronic and nuclear stopping powers. We conclude that the electronic stopping power is responsible for the defect generation at the track of ions. The effect of the nuclear stopping power is also not negligibly small at the end of range.     

Planar waveguides by ion exchange in Er-doped tellurite glass

This work reports the preparation of planar waveguides by Ag⁺ → Na⁺ ion exchange in Er³⁺-doped tellurite glass with a composition of 75TeO₂-2GeO₂-10Na₂O-12ZnO-1Er₂O₃ (mol%). The metric, of T_x − T_g, indicates that the glass has good thermal stability. Measurments of refractive index, absorption spectrum, luminescence and lifetime were made. The glass was chemically stable during the ion exchange process. Monomode and multimode planar waveguides in the tellurite glasses have been prepared. We determined the depth of the guides, effective diffusion coefficient and the activation energy. The depths of the waveguides could be controlled by varying ion exchange temperatures and times (250-280 °C, and 3-12 h were used).     

Gallium colloid formation during ion implantation of glass

Data are reported on the size and depth distribution of gallium colloids formed by gallium ion implantation at energies of 50 and 60 keV, and nominal doses up to 1.1 × 10¹⁷ ions/cm² into coverlip glass, float glass and white crown glass. Measurement techniques used to reveal colloid-induced changes include the wavelength dependence of optical reflectivity, transmission electron microscopy (TEM) and Rutherford backscattering (RBS). The reflectivity can be controlled by variations in ion dose, implant temperature and ion beam energy. The highest reflectivity is found after implants near 50°C and the level is extremely sensitive to the implant temperature. For controlled beam conditions, the reflectivity data are reproducible, despite there being variations in the colloid size and depth distributions as seen by TEM and RBS. The TEM data reveal that the depth distribution develops in two distinct regions, which at high concentration can precipitate into two layers of large colloids. Subsidiary experiments are reported to attempt to separate the effects of variations in the implant temperature and surface charging which influence the reflectivity, RBS and colloid formation.     

The effect of ion exchange on glass surface morphology and composition

The surface morphology and K⁺, Na⁺ concentration distributions of plate glass were investigated by atomic force microscope (AFM) and electron probe microanalyzer (EPMA) before and after ion exchange. The AFM images indicate that the surface microcrack of chemical strengthened glass can be closed to a certain extent and the surface smoothness can be improved. The EPMA results indicate that the relationship between the weight gain and time, temperature follows Fick’s law, which are same as that of the thickness of ion exchanged layer, the total exchanged amount. Consequently, a simple and accurate weighing method was first proposed to estimate the ion exchange state.     

Effect of stirring on striae in glass melts

Chemical striae have often negative effect on the glass properties, and hence, elimination of striae has been a key issue in glass science and technology. To produce highly homogeneous glasses, it is necessary to stir melts during the melting process. To explore the physical origin of the stria elimination during stirring, and to optimise the homogenisation process, both simulations of striation and homogenisation experiments are performed. The results show that stirring broadens the stria size distribution in the melt through conversion of larger striae into smaller ones. Only the striae with a size below half the diffusion length in the melt can be eliminated during the melting process. Stirring itself does not homogenise the melt, but enhances the stria elimination rate by generating small striae.     

Influence of relaxation on migration of ions during ion exchange by electrolysis in glass

After the first electrolysis of an ordinary sheet glass causing Na⁺ → K⁺ ion exchange below its strain point, the glass was subjected to the second electrolysis under the reverse electric field. In the second electrolysis, some of the potassium ions were removed from the previously ion-exchanged layer, while potassium ions were simultaneously introduced into the opposite surface (the anode side). The initial resistivity and the slope of the straight line expressing the relation of resistivity to the quantity of electricity passed through at the second electrolysis were determined numerically. These observations agreed fairly well with theoretical values obtained by taking stress relaxation into account.     

Effect of fragility on relaxation of density fluctuations in glass

Density fluctuations play a crucial role in governing the optical, mechanical, thermodynamic, and kinetic properties of glass. The relaxation of density fluctuations displays an inherently nonmonotonic behavior, yielding a minimum in fluctuations following a quench and isothermal hold. Here we investigate the impact of liquid fragility on the relaxation of density fluctuations in the nonequilibrium glassy state. While fragility has a direct impact on the kinetics of the relaxation process, the minimum level of density fluctuations is unaffected by changes in fragility alone. The magnitude of density fluctuations can be minimized by tailoring the thermal history of the glass.     

The devitrification kinetics of silica powder heat-treated in different conditions

In the present paper, the devitrification kinetics of silica powder heat-treated in air and in nitrogen were investigated. The heat-treated powders were confirmed to partially crystallize into cristobalite by X-ray diffraction analysis. The devitrification kinetics data of silica powder fitted the Avrami equation very well. The measured value of n was ascertained to be 1.63 and 1.60 when the silica powder was heat-treated in air and in nitrogen, respectively, corresponding to activation energies of 408 kJ/mol and 529 kJ/mol, respectively. The effect of phenolic resin-derived carbon on crystallization of silica powder was also studied. By adding phenolic resin into silica powder, the devitrification of silica powder was fully restrained up to 1500 °C in flowing nitrogen. High concentrations of oxygen vacancies may retard the nucleation of cristobalite on the surface of silica powder. Phenolic resin-derived pyrolysis carbon restrained the nucleation of cristobalite, because it prevented the reactions of oxygen vacancies with H₂O and O₂ molecules.     

Mechanical strength improvement of glass by ion exchange in the solid state

Ion exchange of glasses in the solid state has been studied. Two salt systems have been chosen: KCl---ZnCl₂ and KCl---KNO₃. Mechanical strength has been measured after heat treatment. It has been shown that with the KCl---KNO₃ system one can get better results than with the KCl---ZnCl₂ system.     

Fabrication of a high lithium ion conducting lithium borosilicate glass

A lithium ion conducting glass, Li₂O-B₂O₃-SiO₂, is fabricated by the conventional melt and quenching technique from a mixture of Li₂CO₃, B₂O₃ and SiO₂ powders. It appears that B₂O₃ decreases the crystallization tendency of the Li₂O-SiO₂ binary glass, resulting in an expanded glass forming region in the Li₂O-B₂O₃-SiO₂ ternary glass. The maximum conductivity is 2 × 10^− 6 S cm^− 1 at 25 °C for the 50Li₂O-38B₂O₃-12SiO₂ glass sample. The observed high conductivity is due to the mixed former effect. The conductivity strongly depends on the Li₂O content, but not on K (SiO₂/B₂O₃) in the Li₂O-B₂O₃-SiO₂ ternary glass.     

Effect of additives in the salt bath on glass strengthening

In this paper, we mainly study the effects of anion or anion group additives (such as the monovalent anions OH⁻, Cl⁻ or NO₃⁻, the divalent anion SO₄⁻, and the trivalent anion PO₄³⁻, respectively) in a salt bath of KNO₃ on glass strengthening. The Na₂O---Al₂O₃---SiO₂ system is selected to be the base glass.     

Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass

We investigated optical spectroscopic properties of silica glass doped with ytterbium (Yb³⁺) ions to assess their lasing performance in diode-laser pumped systems. The Yb-doped silica glass preforms were fabricated by solution doping technique using the MCVD process. The stimulated emission cross-section and laser performance parameters were determined from the measured absorption spectra using the method of reciprocity. Fluorescence decay characteristics were observed to be deviated from exponential behavior as the Yb³⁺ ions doping level increases and there exists a lifetime quenching behavior related to the cluster effect of Yb³⁺ ions into silica glass. Nevertheless, lasing parameters indicated that clustering of Yb³⁺ ions does not significantly affect the spectral properties relevant to the predicted lasing performance when concentration is low, but becomes predominant at higher concentration.     

Nano-composite soda lime silicate glass prepared using silver ion exchange

Commercial soda lime silicate glasses have been subjected to ion exchange at different temperatures ranging from 320 to 500 °C in a molten mixture of AgNO₃ and NaNO₃ with molar ratio of 10:90, 02:98 and 50:50 for different time periods ranging from 40 to 180 min. Optical and structural properties of the ion exchanged glass are measured using UV–Vis–NIR absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). Signature of silver nanoparticle formation is obtained from the UV–Vis–NIR spectra, which shows a peak at 425 nm due to surface plasmon resonance (SPR). Replacement of Na⁺ ions by Ag⁺ ions is inferred from FTIR spectra. Fluorescence spectra reveal the formation of Ag⁰ atoms from Ag⁺ ions at higher temperatures. TEM image shows the silver nanoparticles of average size 3.75 nm. At exchange temperature of 500 °C Ag nanoparticles are formed without post-exchange annealing treatment.     

Field-assisted ion exchange between molten alloys and soda lime glass

Using molten alloys, the electrolysis of soda lime glass has been studied. Ions from a molten anode can be driven into soda lime glass by applying a modest electric potential. The anode current densities have been measured. The temperature and potential dependences have also been measured. The current-time behavior depends on the ion exchange. In a molten alloy the most easily oxidized metal is suited for exchange.