Structure Of Borosilicate Glasses Research Articles

Effect of lithium concentration on the network connectivity of nuclear waste glasses

Structure of borosilicate glasses with varying Li2O contents were investigated using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), employing 6Li, 11B, 23Na, 27Al and 29Si nuclei. 11B MAS NMR revealed that increasing Li2O contents result in formation of [BO4]− sites at the expense of BO3. 11B{6Li} and 27Al{6Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed Li as a charge compensator for anionic tetrahedral sites with increased Li. 11B{6Li} J-coupling mediated HMQC NMR suggested the possible association of Li with non-bridging oxygens on Q2 and Q3 sites, indicating its dual role in the glass network. 29Si and 23Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased Li. NMR results are supported by Raman spectroscopy and thermal analysis that indicate depolymerisation of the silicate network and a reduction in glass transition temperature at higher Li content.

Enhanced photoluminescence properties and stability of CsPbBr3 quantum dots borosilicate glasses modified by ZnO

Halide perovskite quantum dots (QDs) glass has attracted much attention in the field of optoelectronics, but its photoluminescence (PL) properties and water stability still need further improvement. In this work, the melt-quenching method is used to successfully precipitate CsPbBr3 QDs in borosilicate glass. By increasing the concentration of ZnO, the photoluminescence quantum yield (PLQY) of CsPbBr3 QDs glass is enhanced up to 30 times from 1.91 % to 65.87 %. The results demonstrate that the introduction of ZnO loosens the glass network structure, which contributes to the QDs to precipitate. In addition, it can be found that the PL intensity maintains 91.68 % of the initial PL intensity after 30 days of immersion, which is attributed to ZnO delays the corrosion of borosilicate glass by water. The effect of ZnO-modified borosilicate glass structure on PL and stability provides a certain reference value for further research on QDs glass, and the good PLQY and water stability make ZnO-modified CsPbBr3 QDs glass a potential material in the field of WLEDs.

Effects of Fe2O3-[BOx] reaction on sodium borosilicate glass structure doping with nano to macro sized α-Fe2O3 particles

Fe3+ is readily reacted with structural units to modify various properties of the borosilicate glasses and glass ceramics. However, there exists some controversies on Fe2O3 containing borosilicate glasses: (1) whether the Fe2O3 turned into the nanometer-sized polycrystalline structure or reacted with the glass matrix to form a new substance and (2) whether the role of Fe2O3 was depended on its concentration in the network of glass. Theoretical extinction spectra of α-Fe2O3 particles ranging from 1 to 180 nm in borosilicate glass align with UV–vis absorption spectra. Based on the Na2O-B2O3-Fe2O3 phase diagram, xFe2O3·(100-x) [41.6B2O3–20.7Na2O-19.2CaO-9.7Al2O3–7.0SiO2–0.6ZnO] (x=1.20∼1.95 mol%) were prepared for this study, analyzing from exterior characteristics to interior structure. Molecular vibrational spectroscopy and component structure measurement were applied to study the effect of doping α-Fe2O3 powders (particle sizes of 30 nm, 1 μm, 75 μm) on the sodium borosilicate glasses. Combination of experimental characterization and numerical simulation were also utilized to investigate the effects of iron oxide particle size on the color of dispersion systems. We discovered that (i) doping with either nanometer-sized or micron-sized particles of α-Fe2O3 can result in both the substitution for B3+ in tetra-coordination [BO4] and the bonding with [BO3] units within the amorphous network of sodium borosilicate glasses; (ii) Even at lower concentrations, α-Fe2O3 can still act as a network intermediate, combining both its former role and modifying properties. Based on these outcomes, for the reactive process, we formulated a constitutive model which offers valuable insights into understanding the behavior of iron oxide in sodium borosilicate glass. These findings are crucial for comprehending the processes involved in matrix preparation and are pivotal for progressing to the subsequent stage where designing and fabricating nanocomposite materials based on these matrices with spatial separation.

Development of mesoporous borosilicate bioactive glass nanoparticles containing Mg2+ and Zn2+: biocompatibility, bioactivity and antibacterial activity

In this study a microemulsion assisted sol-gel method was used to synthesise mesoporous bioactive glass nanoparticles (MBGNs) in the SiO2-B2O3-CaO-MgO-ZnO system, followed by calcination at 600̊C/3 h. The obtained MBGNs showed a typical borosilicate glass structure with similar spherical shape and nanometric dimension. Also, they exhibited high specific surfaces and interconnected networks of slit-shape mesopores. In vitro tests proved that all MBGNs had good bioactivity and biocompatibility. Thus, when MBGNs were immersed in simulated body fluid, a uniform layer of calcium phosphates covered the surface of all samples. However, the presence of ZnO led not only to a lower degree of crystallinity of the newly formed layer, but also to different morphologies of the phosphates. The cytotoxicity assays revealed an increase of the cell viability for the samples containing MgO without inducing intracellular oxidative stress. On the other hand, MBGNs with ZnO had a higher antibacterial activity against Escherichia coli.

Correlating Sulfur Solubility with Short-to-Intermediate Range Ordering in the Structure of Borosilicate Glasses

The present study focuses on understanding the structural dependence of sulfur (as SO3) solubility in Na2O–B2O3–SiO2 glasses over a broad composition space exhibiting a rich variety of structural associations. The focus is on probing the impact of the (1) structural role of Na+, (2) degree of polymerization, and (3) network former connectivity (formation of Si–O–B and B–O–B linkages) on sulfur solubility in borosilicate glasses. By employing a suite of state-of-the-art characterization techniques, including inductively coupled plasma-optical emission spectroscopy (ICP-OES), magic-angle spinning (MAS) NMR spectroscopy, and Raman spectroscopy, an inverse correlation has been established between the sulfur solubility and the degree of network polymerization in the glasses across the investigated composition space. While the modification of SO3 leading to the formation of SO42– can successfully compete with the network depolymerization mechanisms (i.e., creation of nonbridging oxygens) and induce repolymerization in the glass network, the BO3 → BO4 conversion facilitated by the charge compensation by alkali cations takes precedence. The results from this study, when extended to more complex borosilicate-based glass compositions, will not only add to our understanding of the fundamental science controlling the sulfur solubility in borosilicate-based real-world nuclear waste glasses but will also form a basis for the development of nonempirical quantitative structure–property relationship (QSPR)-based predictive models.

Nanoscopic structure of borosilicate glass with additives for nuclear waste vitrification

We investigated the nanoscopic structure of borosilicate glasses as a host for high-level radioactive liquid waste (HLLW) in the presence of the additives Na2O and CaO/ZnO with and without Li2O. These additives have been used to lower the glass melting point, suppress the macroscopic phase separation, and increase the chemical durability of glasses. Small-angle neutron scattering was used to elucidate the effect of the additives on the nanoscopic structure along with macro- and atomic-scale observations obtained using neutron imaging and X-ray diffraction, respectively. The borosilicate glass made without Na2O formed a microphase-separated structure of SiO2- and B2O3-rich domains approximately 100 nm in size, and the material was homogeneous at length scales up to millimeters. With the addition of increasing amounts of Na2O, the domain spacing decreased. Introducing CaO/ZnO additives induced inhomogeneities in the glass, such as void structures several nanometers in size, although the inhomogeneity was suppressed by the coaddition of Li2O. These results provide insights into the performance of host glasses for HLLW vitrification. Incorporating HLLW into glasses is likely to cause changes in the nanoscopic structure of host glasses similar to those revealed here.

Effect of irradiation on the atomic structure of borosilicate glasses

AbstractBorosilicate glasses incorporating high‐level nuclear waste are exposed to high‐energy radiations during their storage in the deep geological repositories. However, the effect of radiation on the atomic structure of borosilicate glasses remains poorly understood. Herein, using molecular dynamics simulations, we study the irradiation‐induced structural changes of a series of calcium‐sodium borosilicate glasses with varying Si/B molar ratios—ranging from pure silicate to pure borate glasses. We observe that irradiation leads to an increase in disorder, both in the short‐ and medium‐range, as evidenced by the enthalpy, coordination number, and ring distribution. In particular, the impact of the change in the atomic structure (due to radiation) on the glass volume is investigated. Interestingly, we observe a composition‐dependent transition in the volumetric response of borosilicate glasses under irradiation—wherein borate‐rich compositions tend to swell, whereas silica‐rich glasses tend to densify. Through a detailed analysis of the structure, we demonstrate two competing mechanisms contributing to the volume change, i.e., a decrease in the coordination number of boron atoms and a reduction in the average silicon inter‐polytope angle. We also show that the increase in the disorder in the medium‐range order may play a major role in governing the volumetric changes in the irradiated structure in a non‐trivial fashion. Altogether, the present study highlights that irradiation has a non‐trivial effect on borosilicate glasses, which, in turn, could impact their corrosion kinetics.

Mixed alkali effect on borosilicate glass structure with vanadyl ion as spin probe

Mixed alkali borosilicate glasses doped with 2% vanadium oxide were synthesized by conventional melt-quench method. The Micro structure of the materials was analysed using XRD, SEM and EDX spectrum. Optical nature of glasses was studied by computing optical bandgaps with absorption spectral data. Covalent nature of glasses was estimated correlating optical bandgap energy with EPR spectral data. The metallization criterion of glasses was evaluated from the physical parameters. FTIR and Raman spectral techniques were used to identify the structural groups of the borates and silicates that are formed with addition of modifiers. Emission spectra were recorded at excitation wavelength of 350 nm and their thermal nature was also studied using TGA/DTA techniques.

Vitrified Municipal Waste for the Immobilization of Radioactive Waste: Preparation and Characterization of Borosilicate Glasses Modified with Metal Oxides

Municipal solid waste is used as a raw material for the production of borosilicate glasses by melting annealing technique. Many chemical and physical measurements are studied to test their possibility in the immobilization of radioactive wastes. The results show good behaviors against gamma radiation doses such as suitable density and microhardness values, stable behaviors towards low and high doses of gamma radiation indicated by IR and EPR techniques. As well as good chemical durability in H2O and NaOH leaching solutions. The network structure of borosilicate glasses consists of tetrahedral silicate units SiO4 and the triangle BO3 or tetrahedral BO4 groups which strengthen the structure of glasses and enhance their desired properties for achieving the goal of immobilizing nuclear wastes.

Simulation of borosilicate glasses with non-constant force field molecular dynamics

In this study the simulation of microscopical behavior of borosilicate glasses was conducted with non-constant force field molecular dynamics. The suggested model consists of classical pair potentials in the Buckingham form, long range Coulomb interaction, intramolecular bonded interactions and possibility of bond breaking and formation. The latter effects are accompanied by changes in the types of the bond-forming particles. The simulated system corresponds to the structure of borosilicate glasses with predominantly four-coordinated boron atoms. Different structure groups are formed due to the dissociation / formation of intramolecular bonds, and the processes of the glass network rearrangement intensifies with temperature increasing.

Silicon carbide fiber oxidation behavior in the presence of boron nitride

AbstractThe oxidation behavior of Sylramic SiC fibers without a boron nitride surface layer was compared to Sylramic iBN SiC fibers with a boron nitride surface layer by conducting thermogravimetric analysis in dry O2 at temperatures ranging from 800 to 1300°C for times up to 100 hours. Sylramic fibers followed the Deal and Grove oxidation kinetic model. A transient period of accelerated oxidation kinetics was observed with Sylramic iBN fibers. Raman spectroscopic analysis of oxidized fibers provided evidence for a borosilicate glass structure. The boron concentrations in the oxides, quantified by inductively coupled plasma‐optical emission spectrometry, were correlated with the weight change behavior, oxide thickness, and fiber recession of the oxidized fibers. Oxides formed from Sylramic iBN fibers were typically higher in boron concentration, which led to initial rapid oxidation rates that were 3‐10 times faster than observed for pure SiC. Slower oxidation rates followed as the oxide surface became increasingly enriched with SiO2 due to boria volatilization, thus limiting boria effects on SiC fiber oxidation kinetics. The accelerated high‐temperature oxidation of SiC fibers due to the presence of BN are discussed in terms of the borosilicate glass structure and composition.

Structure of Ca–Sr–Ba Sodium–Borosilicate Glasses according to 11B and 29Si NMR Spectroscopy

The structure of borosilicate glasses is studied with 11B and 29Si NMR spectroscopy in order to investigate the influence of replacement of Na2O by oxides of alkali earth metals on their local structure. The quantitative data are analyzed with respect to their correspondence to the criterion of the average charge of the structural unit. The reasons for the deviation between the experimental results and this criterion are considered. It is shown that, in the case of glass devoid of borate structural units with nonbridging oxygen atoms, the corrected contents of these units are consistent with the predictions of thermodynamic modeling of the structure and properties of oxide glasses.

Relaxation oscillation of borosilicate glasses in supercooled liquid region

Most supercooled non-polymeric glass-forming melts exhibit a shear thinning phenomenon, i.e., viscosity decreases with increasing the strain rate. On compressing borosilicate glasses at high temperature, however, we discovered an interesting oscillatory viscous flow and identified it as a typical relaxation oscillation caused by the peculiar structure of borosilicate glass. Specifically, the micro-structure of borosilicate glass can be divided into borate network and silicate network. Under loading, deformation is mainly localized in the borate network via a transformation from the three coordinated planar boron to trigonal boron that could serve as a precursor for the subsequent formation of a BO4 tetrahedron, while the surrounding silicate network is acting as a stabilization/relaxation agent. The formation of stress oscillation was further described and explained by a new physics-based constitutive model.

Relaxation Oscillation in the Viscous Flow of Borosilicate Glass

Relaxation oscillation is a nonlinear dynamic phenomenon, commonly observed in viscous-plastic deformation of materials. However, it is the first time that we observed this phenomenon in the viscous flow of borosilicate glass in its super-cooled liquid region. Our investigation identified that the oscillation is caused by the particular microstructure of borosilicate glass. Specifically, the structure of borosilicate glass consists of borate-rich and silicate-rich networks. During the viscous flow, the fast deformation in borate network tends to be localized. However, the network mixing reaction between the borate-rich and silicate-rich networks can slowly relax the fast localized deformation. These two processes occur simultaneously and as a result bring about the relaxation oscillation. Based on this mechanism, the study established a physical constitutive model to predict the relaxation oscillation during the compression of borosilicate glass.

Investigation of gamma radiation induced changes in local structure of borosilicate glass by TDPAC and EXAFS

Gamma radiation induced changes in local structure around the probe atom (Hafnium) were investigated in sodium barium borosilicate (NBS) glass, used for immobilization of high level liquid waste generated from the reprocessing plant at Trombay, Mumbai. The (NBS) glass was doped with 181Hf as a probe for time differential perturbed angular correlation (TDPAC) spectroscopy studies, while for studies using extended X-ray absorption fine structure (EXAFS) spectroscopy, the same was doped with 0.5 and 2 % (mole %) hafnium oxide. The irradiated as well as un-irradiated glass samples were studied by TDPAC and EXAFS techniques to obtain information about the changes (if any) around the probe atom due to gamma irradiation. TDPAC spectra of unirradiated and irradiated glasses were similar and reminescent of amorphous materials, indicating negligible effect of gamma radiation on the microstructure around Hafnium probe atom, though the quaqdrupole interaction frequency (ω Q) and asymmetry parameter (η) did show a marginal decrease in the irradiated glass compared to that in the unirradiated glass. EXAFS measurements showed a slight decrease in the Hf-O bond distance upon gamma irradiation of Hf doped NBS glass indicating densification of the glass matrix, while the cordination number around hafnium remains unchanged.

Electrochemical Reduction of Borosilicate Glass in Molten CaCl2

1. Introduction In spite of the potential to mitigate the global warming and replace the current fossil fuel power generation, nuclear power generation has a problem on the geological disposal of radioactive wastes from the viewpoint of long-term safety. Thus, a new disposal process is proposed in Japan that the long-lived fission products (LLFPs) such as 135Cs, 79Se, 93Zr, and 107Pd whose half-lifes are around million years are separated and converted into short-lived or stable nuclides by nuclear transmutation [1]. According to the conventional scenario of geological disposal, huge amount of vitrified wastes have been produced. Since LLFPs are immobilized in a three-dimensional (3-D) network structure of glass in the vitrified wastes, it is necessary to develop a new method to recover LLFPs from the vitrified wastes. As a first-step of the recovery method, we propose the electrochemical reduction in molten CaCl2 to break the 3-D network structure of borosilicate glass in the vitrified wastes. In the present study, as an initial consideration, we investigated the electrochemical reduction behavior of borosilicate glass without LLFPs in molten CaCl2. 2. Experimental The experiments were conducted in molten CaCl2 in a dry Ar atmosphere at 1123 K. As a working electrode, a glass-seal electrode which was prepared by sealing a tungsten rod (diameter: 2.0 mm) into an alkali borosilicate glass tube (Pyrex®, SiO2 81.1 wt%, B2O3 12.6 wt%, Al2O3 2.3 wt%, Na2O/K2O 4.0 wt%, o.d. 8 mm) was used. The counter and reference electrodes were a graphite rod and an Ag+/Ag electrode, respectively. After potentiostatic electrolysis at 0.9 V vs. Ca2+/Ca for 30 minutes, the glass-seal electrodes were rinsed by distilled water, and then characterized by SEM/EDX and XRD. For XPS measurement, the samples were consecutively rinsed by distilled water, 8 % HCl aqueous solution, and 10 % NaOH aqueous solution. 3. Results and Discussion 3-1. Thermodynamic Analysis & Cyclic Voltammetr y According to the Gibbs energies of formation for the oxides composing borosilicate glass (MO x , M = Si, B, Al, Na, K), K2O, Na2O, and B2O3 are less stable than SiO2 at the experimental temperature of 1123 K. On the other hand, the reduction of Al2O3 occurs at more negative potentials than the reduction of SiO2. From the Gibbs energies of formation for the related oxides and chlorides (MO x and MCl x , M = Ca, Si, B, Al, Na, K), the following reactions of the oxides with molten CaCl2 are thermodynamically favorable. Na2O (s) + CaCl2 (l) = CaO (s) + 2 NaCl (l) ΔGº(1123K) = −246.5 kJ mol-1 K2O (s) + CaCl2 (l) = CaO (s) + 2 KCl (l) ΔGº(1123K) = −347.7 kJ mol-1 Namely, the dissolutions of Na2O and K2O from borosilicate glass are highly expected only by immersion in molten CaCl2. In the cyclic voltammogram for a borosilicate glass-seal electrode, cathodic current was observed at more positive potential than that for silica glass [2]. Based on the thermodynamic calculations, the reduction of B2O3 was suggested to occur in this potential region. 3-2. Characterization of Products Prepared by Potentiostatic Electrolysis An XRD pattern of the reduced borosilicate glass confirmed the reduction of SiO2 and the formation of crystalline silicon. From XPS spectra for B 1s before and after the reduction, the weakened B–O peak and strengthened B–B or B–Si peak were clearly observed. The existence of the reduced state of boron confirms the reduction of B2O3. The reduction of SiO2 was also confirmed by XPS Si 2p spectra. As shown in the SEM image in Fig. 1, granules with a diameter of 1~10 μm were produced in the reduction product. From the EDX mapping results, the oxide portions in the sample always contain all of Al, Ca, and Cl. This indicates that aluminum oxide is not reduced at 0.9 V, and that calcium aluminate is formed by reacting with CaO in the molten salt. The existence of chlorine is explained by the formation of complex compounds consisting of calcium aluminate and CaCl2. The dissolution of Na2O into molten CaCl2 was also confirmed from EDX analysis. Acknowledgement This work was partly funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

Nuclear Magnetic Resonance and FTIR Structural Studies on Borosilicate Glasses Containing Iron Oxide

The structure of borosilicate glasses of composition 30Na2O-2Al2O3-25SiO2-xFe2O3 (43-x) B2O3 has been investigated in the composition range of 0.5 20 mol% Fe2O3. 27Al, 11B, 29 Si MAS NMR and FTIR spectroscopies have been used to measure the fraction of different structural species in the glasses. It is evidenced from NMR data that both sodium and Fe2O3 (in low region up to 7 mol%) are the main glass modifier. Structural determination for borosilicate glasses with a high content of (Fe2O3) was carried out by FTIR spectroscopy, where both 11B and 29Si MAS NMR are impossible because of the high quantities of paramagnetic iron (III) species present. NMR analysis was performed on borosilicate glasses containing up to 7 mol% Fe2O3 and the N4 values obtained by FTIR spectroscopy agree within error with the 11B NMR results of the same glass samples. Fe2O3 is a main glass modifier in the low-Fe2O3-content region (≤6 mol%). On other hand, it plays the role of glass former at higher content of Fe2O3. Increasing both N4 of boron tetrahedral units and chemical shift of silicon nuclei to reach maxima at 5 mol% Fe2O3 confirms the role of Fe2O3 as a glass modifier in the low composition region. On the other hand, fast decrease in N4 with further increasing Fe2O3 contents ≥6 mol%) is an evidence for iron oxide to inter the glass network as a network former.

Influence of lanthanum on borosilicate glass structure: A multinuclear MAS and MQMAS NMR investigation

The physical and chemical properties of silicate glasses containing rare-earth elements (REEs), either as dopants or at higher concentrations, are sensitive to the REE structural and chemical environment. An unambiguous role of REEs in the glass structure still remains difficult to define because many configurations may exist and are strongly composition-dependent. The structural configuration of lanthanum and its interactions with sodium and calcium are examined here in borosilicate glasses. The impact of lanthanum and calcium substituted for sodium on the boron speciation is investigated by 11B MAS NMR. The resulting 29Si MAS NMR spectra and their interpretations are discussed. A quantitative approach of 17O MQMAS NMR data with the reconstruction of 17O NMR parameter distributions provides an overview of lanthanum distribution and its interactions with the other cations in the vitreous network. No clustering of lanthanum atoms is observed; they are uniformly distributed in the glass structure, surrounded by about 6 non-bridging oxygen atoms and mixed with sodium and calcium atoms to the detriment of the number of BO4 groups. These data provide a better understanding of the addition of rare earths in the glass and of the conditions favorable to their uniform distribution in soda-lime borosilicate glass matrices.

Effect of the ratio R = [Na2O]/[B2O3] on the structure of glass in the Na2O-B2O3-SiO2 system

Sodium borosilicate glass, with the ratio R = [Na2O]/[B2O3] varied from 0.31 to 1, were studied by IR spectroscopy and Raman scattering techniques. The dependence of the structure of borosilicate glasses on their composition was studied also for the section with a constant value R = 1. The main borate and silicate groups in the system, and especially changes in the structure of glasses depending on the ratio R were identified.

Effect of temperature and thermal history on borosilicate glass structure

The influence of the temperature and quenching rate on the structure of a borosilicate glass was studied by high-resolution solid-state ${}^{11}$B, ${}^{23}$Na, ${}^{29}$Si nuclear magnetic resonance (NMR) and high-temperature Raman spectroscopy. Data were obtained for glass in the solid state after annealing and quenching at cooling rates covering four orders of magnitude as well as in the liquid state from Raman experiments and from calorimetry and rheological data. Nuclear magnetic resonance measurements were used to calibrate the Raman spectra in order to quantify the change in boron coordination with temperature. This result can then be used to determine the fictive temperature of the glass directly from the boron coordination. The fictive temperature, heat capacity, and configurational entropy are extracted from calorimetry and viscosity measurements. Changes in the boron coordination account for only 25$%$ of the configurational heat capacity of the liquid. The structural parameters capable of accounting for the remaining quantity are discussed on the basis of structural data, both local (inhomogeneity of the sodium distribution) and medium-range (from NMR parameter distribution). It has thus been shown that, although the B-O-B angular distributions of the boroxol rings (and probably the Si-O-Si distributions) are not affected by temperature, a structural disorder is identified through the angular distributions of the bonds linking borate and silicate groups.