Ion-exchange strengthening of borosilicate glass: Influence of salt impurities and treatment temperature (original) (raw)
Related papers
Strengthening of Soda-Borosilicate Glasses by Ion Exchange Processes
2017
Flexible electronics and displays rely on strong thin borosilicate glasses. Furthermore, borosilicate glass play a vital role in pharmaceutical packaging, particularly for the container of liquid medicine in the auto-injectors. Because of the risk of failure due to the fracture of the glass ampule the costumers need to purchase several units of auto-injector; also, the injector price increases dramatically. This renewed the interest in the strengthening of soda-borosilicate glass. Moreover, the applications of strong thin borosilicate glasses in flexible electronics attracted attention. Chemical strengthening is a practical means of improving the mechanical performance of soda borosilicate glasses. The chemical strengthening process involves the immersion of an alkali-silicate glass in a molten nitrate salt containing potassium ions at temperatures below the glass-transition temperature where the replacement of small alkali ions in the glass with larger potassium ions from the molte...
ION CONCENTRATION AND STRESS PROFILE MODIFICATIONS OF ION EXCHANGED GLASS AFTER THERMAL TREATMENTS
Ion exchanged soda lime (SLS) glass has been exposed to ion exchange and the effect of a subsequent thermal treatment has been evaluated. Ion exchange has been performed at temperatures below transformation range. Thermal treatment temperature is, in general, different from the ion exchange temperature even though below transformation range. Effects on ion concentration and stress profile have been evaluated. A mathematical model have been proposed for the calculation of both concentration and stress profile after ion exchange and subsequent thermal treatment at different temperature. Strength has been evaluated after ion exchange and after ion exchange and thermal treatment. Results are discussed in view of structural application of chemically strengthened glass. Introduction Strengthening of silicate glasses by alkali ion exchange performed below the transformation temperature range is a well known technology [1] since the sixties [2]. Recently, some excellent reviews [3,4] have been published where the process has been extensively described. There are still some issues to be fully clarified [5,6] in order to have a well defined and consistent theory of ion-exchange and stress build-up. Nevertheless first approximation models can be presented [1,7,8] to predict ion concentration and stress profile as a result of ion-exchange. Based on first approximation models of ion exchange and knowing the original glass strength, even final strength prediction, based on fracture mechanics concepts, can be performed [1,9]. Modification and tailoring of stress profile have been proposed [10,11] by multiple ion-exchange processes. Modifications of ion concentration and stress profile can be achieved also by thermal treatments after ion exchange [12]. In [12] it has been extensively investigated the effect of thermal treatment to ion concentration and stress profile for lithium aluminosilicate glass, when both ion-exchange and subsequent thermal treatment are performed at the same temperature. In the appendix of [12] a solution for the concentration profile is presented for thermal treatment temperature different from ion exchange one. In the following a first approximation mono dimensional model is presented for both ion exchange and subsequent thermal treatment performed at any temperature. At the moment relaxation effects [1,8] to stress profile are not taken into account. This approximation is justified by the short time of both ion exchange (less or equal to 24 hours) and thermal treatment (less or equal to 4 hours), even though temperature may be an issue because of viscoelastic effects in glass at both ion exchange and thermal treatment temperatures. Another future investigation subject can be both thermal treatments before and after ion exchange. Temperature treatments before ion exchange performed at temperatures close or even exceeding the transformation range (example is glass bending) may result in modification of the glass fictive temperature. The resulting structural modifications have an impact on both strengthening effect (residual compression levels) and ions inter diffusion in the glass structure. These effects may alter ion concentration and residual stress profile and finally may alter glass strength. This last type of processes (thermal treatments before ion exchange) will be not treated in this paper.
Non Crystalline Solids, 2018
In this study, an attempt was made to investigate the influence of immersion temperature and time of ion-exchange on the microstructure and mechanical properties of chemically toughened soda-lime glass (CTG). Glass samples of 120 × 50 × 40 mm were immersed in potassium nitrate (KNO 3) salt placed inside a salt bath and subjected to heating at temperatures of 450 °C and 500 °C with the immersion time varied for 4 h and 5 h for each temperature inside a muffle furnace. Scanning Electron Microscopy (SEM) was used to evaluate the micro-structure of the chemically toughened glasses while tests such as hardness, flexural strength and impact strength were used to assess the mechanical properties of the chemically toughened glasses. The results obtained show that hardness value decreased as temperature and time increases with maximum hardness of 26.35 BHN for CTG 1 (450 °C for 4 h). The impact strength increased as temperature and time increases with maximum impact strength of 36.72 J for CTG 4 (500°C for 5 h). However, the maximum flexural strength of 95.87 MPa was obtained for CTG 2 (450 °C for 5 h).
Thermal and mechanical characterization of borosilicate glass
Physics Procedia, 2009
The aim of this work is to characterize thermally (dilatometric analysis) and mechanically a Pyrex type borosilicate glass. The mechanical tests (Vickers indentations, mechanical strength and fracture toughness) were made on the glass in an annealed state and after a chemical strengthening treatment by ionic exchange. The indentations imprints morphologies and details were observed by optical and scanning electron microscopy. The dilatometric analysis shows that the thermal expansion variation with temperature is essentially non linear, increasing rapidly up to 200°C and slowing down beyond. The optimal glass chemical strengthening was obtained for a bath duration of 15 hours. This corresponds to a relatively moderate increase of the mechanical strength (~70%). The fracture toughness measured by indentation was appreciably improved by the chemical treatment. It seems also to increase with the applied indentation load.
Can annealing improve the chemical strengthening of thin borosilicate glass?
Journal of Non-Crystalline Solids, 2017
In this work, we try to point out the influence of annealing prior to chemical strengthening on the mechanical strength of thin ion exchangeable alkali borosilicate glass. The effect of annealing at 425°C on density, hardness and cracking behaviour were investigated. Then, as-received and annealed samples were subjected to ion exchange in a molten potassium nitrate bath at the same temperature for 4 h and the generation of compressive stress in glass was analyzed as well as the bending strength. Annealing makes the glass denser, improves hardness and enhances the compressive stress build-up. However, bending strength of as-received and annealed glass after ion-exchange is substantially the same, this being probably attributed to the limited case depth if compared to surface flaws. Annealing before ion exchange does not appear to be a crucial factor in improving chemical strengthening efficiency in thin borosilicate glass.
Electric Field-Assisted Ion Exchange of Borosilicate Glass Tubes
Ion Exchange - Studies and Applications, 2015
In this work, DC electric field-assisted ion exchange was carried out to enhance the sodium-potassium inter-diffusion and improve the mechanical performance of borosilicate glass. Electric fields with intensity varying between 100 V cm-1 and 3000 V cm-1 were applied in both direct and inverted polarizations. Four point bending test and the Vickers indentation method were used to characterize the mechanical properties. Energy dispersion x-ray spectroscopy was carried out to determine the potassium concentration within the surface layers of the samples. The analysis of the potassium concentration profile near the surface shows that the external electric field governs the ion exchange process and it is possible to send potassium ions down to a depth of 45 µm in only 5 min. By plotting the electrical current versus time, it is revealed that the process stops after a certain saturation time. Vickers indentation measurements show that the compressive residual stress in the samples treated under electrical field is 3 times higher than that obtained by conventional chemical tempering. The bending strength of samples prepared by reversing the field direction is higher than that measured in specimens treated only on one side due to the symmetrical distribution of the stress on both sides.
Frontiers in Materials, 2016
Glasses can be chemically strengthened through the ion exchange process, wherein smaller ions in the glass (e.g., Na +) are replaced by larger ions from a salt bath (e.g., K +). This develops a compressive stress (CS) on the glass surface, which, in turn, improves the damage resistance of the glass. The magnitude and depth of the generated CS depend on the thermal and pressure histories of the glass prior to ion exchange. In this study, we investigate the ion exchange-related properties (mutual diffusivity, CS, and hardness) of a sodium aluminosilicate glass, which has been densified through annealing below the initial fictive temperature of the glass or through pressure quenching from the glass transition temperature at 1 GPa prior to ion exchange. We show that the rate of alkali interdiffusivity depends only on the density of the glass, rather than on the applied densification method. However, we also demonstrate that for a given density, the increase in CS and increase in hardness induced by ion exchange strongly depend on the densification method. Specifically, at constant density, the CS and hardness values achieved through thermal annealing are larger than those achieved through pressure quenching. These results are discussed in relation to the structural changes in the environment of the network modifiers and the overall network densification.
Influence of salt bath calcium contamination on soda lime silicate glass chemical strengthening
Journal of Non-Crystalline Solids, 2017
Soda lime silicate float glass was ion exchanged in potassium nitrate baths systematically contaminated with calcium nitrate up to 0.01 mol%. The results show that surface compression and flexural strength are dramatically depressed if the treatment is carried out in salt containing calcium nitrate in excess of 0.0015 mol%, this being related to more limited sodium-potassium exchange on the surface. The presence of calcium in the salt accounts for a "blocking" effect of the conventional Na-K exchange which is shown to be thermodynamically less favoured than Na-Ca one, especially at higher temperature.
Development of empirical potentials for sodium borosilicate glass systems
Journal of Non-Crystalline Solids, 2011
New parameter values are proposed for the empirical potentials used to describe SiO 2 -B 2 O 3 -Na 2 O alkali borosilicate glass systems. They are based on Buckingham potentials, but include dependence between the fitting parameters and the glass chemical composition to improve the representation of the complex environment around the boron atoms. In particular, the boron anomaly (observed when the [Na 2 O]/[B 2 O 3 ] ratio varies) is correctly reproduced. The structural and mechanical properties of a wide range of glass compositions and of reedmergnerite crystals are correctly simulated: bond distances, mean angles, densities, elastic moduli. The deviations from the experimental values are small.
Journal of the Australian Ceramic Society, 2019
The aim of this study is to determine the mechanical properties differences in between the air and tin surfaces of thin soda-lime silicate float glasses that subjected to ion exchange using KNO 3 salt bath. The ion exchange process was carried out at different times and temperatures. Chemically tempered glasses were investigated by means of compressive stress (CS), microhardness measurements, cracking probability, fractographic analysis, and flexural strength. The relationship among these properties was also discussed. The Weibull distributions of the samples were determined for a better understanding of the strength results. The AFM was used to determine the surface roughness. The weight of glass samples was increased gradually with increasing ion exchange time and temperature due to the inter-diffusion of K +-Na + ions. The fracture load of chemically strengthened glass with ion exchange at 435°C-8 h showed an increase of~4.4 times that of untreated glass (raw glass), and it was selected as the optimum process conditions. The number of broken pieces was increased by increasing flexural strength, and smaller pieces were obtained with a great deal of branching. The air side always has greater compressive stress than the tin side. The maximum hardness value was reached with ion exchange at 435°C for 12 h on a tin surface was 8.25 GPa with an increase of~18% with respect to the raw glass. The crack resistance of chemically tempered glasses showed an increase in the range of 410-1290% and 241-1895% for air and tin surfaces, respectively. According to the AFM analysis, surface roughness of the samples after ion exchange did not change dramatically. SEM-EDS analysis revealed that the surface potassium concentration and diffusion depth increase with temperature.