Influence of Al2O3 Addition on Structure and Mechanical Properties of Borosilicate Glasses (original) (raw)
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Journal of Non-Crystalline Solids, 2015
We provide a comprehensive description of the defect tolerance of sodium-borosilicate glasses upon sharp contact loading. This is motivated by the key role which is taken by this particular glass system in a wide variety of applications, ranging from electronic substrates, display covers and substrates for biomedical imaging and sensing to, e.g., radioactive waste vitrification. The present report covers the mechanical properties of glasses in the Na 2 O-B 2 O 3 -SiO 2 ternary over the broad range of compositions from pure SiO 2 to binary sodium-borates, and crossing the regions of various commercially relevant specialty borosilicate glasses, such as the multi-component Duran-, Pyrex-and BK7-type compositions and typical soda-lime silicate glasses, which are also included in this study. In terms of structure, the considered glasses may be separated into two groups, that is, one series which contains only bridging oxygen atoms, and another series which is designed with an increasing number of nonbridging oxygen ions. Elastic moduli, Poisson ratio, hardness as well as creep and crack resistance were evaluated, as well as the contribution of densification to the overall amount of indentation deformation. Correlations between the mechanical properties and structural characteristics of near-and mid-range order are discussed, from which we obtain a mechanistic view at the molecular reactions which govern the overall deformation reaction and, ultimately, contact cracking.
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.
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.
Journal of Non-crystalline Solids, 2015
Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examined during indentation with a three-sided pyramidal indenter. Compositions of 74.0SiO 2-10.0B 2 O 3-16.0Na 2 O (NBS1), and 74.0SiO 2-20.7B 2 O 3-4.3Na 2 O-1.0Al 2 O 3 (NBS2) (mol%) were investigated. The effect of thermal history was additionally considered for the NBS2 composition, which lies near the boron anomaly line. Hardness, elastic modulus, and fracture toughness were estimated with instrumented indentation techniques. Atomic force microscopy (AFM), Raman micro-spectroscopy, and post-indent annealing experiments were used to analyze surface topographies, densification, and recovery of deformed material. The results indicate that NBS1 exhibits a greater hardness and elastic modulus, and undergoes less densification than the NBS2 glasses. Different casting conditions influenced the plastic deformation and onset of crack initiation in NBS2. Interpretation of fracture toughness measured by indentation is complicated by residual stresses, densification during contact, and model assumptions. However, distinct differences in elastic modulus, plastic deformation and cracking between the glasses were noticeable. Such results and observations are discussed in terms of structural changes in the glass.
The influence of a changing glass topology on local mechanical properties was studied in a multitechnique nanomechanical approach. The glass response against sharp contacts can result in structural densification, plastic flow, or crack initiation. By using instrumented indentation testing, the mechanical response was studied in different strain rate regimes for a sodium borosilicate glass (NBS) exhibiting altering structures due to varying processing conditions. Comparison with data from former studies and with literature data on other glass structures helped to elucidate the role of the borate and silicate subnetworks and to understand the overall mechanical properties of the mixed glass systems. A peculiarity of some of the NBS glasses tested in this study is the fact that the connectivity of the borate and silicate entities depends on the sample's thermal history. Although the influence on macroscopic material properties such as E and H is minor, the onset of cracking indeed is influenced by those structural changes within the glass. Rapidly quenched glass shows an improved crack resistance, which is even more pronounced at high strain rates. Studies on various processing conditions further indicate that this transition is closely related to the cooling rate around Tg. The strain rate dependence of cracking is discussed in terms of the occurrence of shear deformation and densification.
Mechanical properties and structure of a nanoporous sodium borosilicate glass
Glass Physics and Chemistry, 2007
The nanohardness (H) and microhardness (H M) of sodium borosilicate glasses with and without nanopores were studied. From nanoindentation measurements, along with the hardness H , the Young's modulus E was derived. While both H and H M varied between ~10 GPa and ~7 GPa for the bulk glass, the values for nanoporous specimens were one order of magnitude lower at about 0.5 GPa. The Young's moduli were found to be ~82 GPa and ~5 GPa for bulk and porous glasses, respectively. Cracks and pileups were observed, respectively, arising from microindents and nanoindents in the bulk glass, whereas none of them could be detected in the nanoporous material. The molecular structures of both glasses studied by X-ray diffraction are similar.
Journal of the American Ceramic Society, 2002
Fatigue behavior of borosilicate glasses was studied using the analysis of subcritical propagation of Vickers indentation cracks. Glasses containing various amounts of glass-network modifiers, mainly soda, were considered. Cone and median/ radial crack systems were observed, depending on glass composition, indenter geometry, and test environment. Indentation tests were performed in water, holding the maximum load for durations ranging from 15 s to 6 d. The analysis of the crack length as a function of dwell time allowed evaluation of the subcritical growth parameters and fatigue limit at crack arrest. The influence of composition on fatigue parameters and fatigue limit was discussed in terms of fourfold-coordinated boron atoms fraction compared with the content of glassnetwork modifier ions. tests. 13-16 An alternative technique based on subcritical growth of indentation cracks has been recently proposed by Sglavo and Green 17-19 and successfully applied to soda-lime-silica, sodaalumina-silica, 20 and silica glasses. 21 In the present work, the indentation method suggested by Sglavo and Green has been used to analyze the influence of composition on fatigue behavior and K th for borosilicate glass. Glasses containing various amounts of network modifier oxide, mainly soda, have been considered. II. Experimental Procedure (1) Glass Production and Characterization Three borosilicate glasses were considered in the present work. One of them was a commercial borosilicate float glass (Boro-float™, Schott Glas, Jena, Germany) characterized by high chemical resistance and supplied in sheets of 1150 mm ϫ 850 mm ϫ 3.3 mm dimensions. The other two glasses, labeled as BS 75-10-15 and BS 80-10-10, were produced in the laboratory. The nominal composition of these glasses, whose main difference is the amount of network-modifier alkali oxide, is shown in Table I. Silica quartz, anhydrous sodium carbonate (commercial grade, Cookson Matthey Ceramics, Segrate, Italy) and boric acid (pure reaction grade, Analytical Carlo Erba Reagenti, Milano, Italy) powders were used as raw materials. Batches were prepared mixing together the dried components using a slow-speed mixer to obtain a good homogeneity before heating. The mix, ϳ200 g for each batch, was poured into a platinum crucible † and heated at 1500°-1550°C for 14 h to completely melt and homogenize the glass. The melt was then cast in rectangular stainless-steel molds, previously sprayed using a Teflon ® film to make the removal of the glass after cooling easier. After ϳ20 s, the glass ingots were removed from the molds, placed in a furnace at 600°C for 2 h to avoid cracking due to thermal shock, and then cooled slowly by switching off the power of the oven. An average cooling rate of ϳ2°C/min was therefore applied. Chemical analysis was performed on the examined glasses to verify the actual composition. To this purpose, powders were prepared by manually grinding glass in an agate mortar. After the powders were sieved to 100 m, ϳ500 mg samples were analyzed. ‡ Solid-state 11 B nuclear magnetic resonance (NMR) analysis was performed § to estimate the fraction of fourfold-coordinated boron atoms, B(IV), in the glasses. Experiments were performed using a spectrometer (Model MSL-400, Bruker, Canada) at 128.29 MHz, using a 5 mm probe (Model CP-MAS, Doty). The samples were spun between 9 and 10 kHz. The spectra were recorded using a single-pulse excitation of 1 s and a 1 s recycle delay. Simulations of the spectra were performed using the Bruker-Winfit software, using a Gaussian line shape for the B(IV) signal and a second-order quadrupolar line shape for the B(III) signal. S. Wiederhorn-contributing editor Manuscript No. 187327.
Role of aluminium oxide in the structure of heavy metal oxide borosilicate glasses
physica status solidi (a), 2012
ABSTRACT Lead borosilicate and bismuth borosilicate glasses with and without aluminium oxide of varying compositions were prepared by conventional melt-quench method. Raman spectroscopy was used to analyze the influence of Al 2O 3 incorporation in the heavy metal oxide borosilicate glass network. The compositions of glasses were chosen in a way that Al 2O 3 is added at expenses of PbO and Bi 2O 3 in lead borosilicate and bismuth borosilicate glasses, respectively. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim