Binary Sodium Silicate Research Articles

Accurate and Transferable Machine Learning Potential for Molecular Dynamics Simulation of Sodium Silicate Glasses.

An accurate and transferable machine learning (ML) potential for the simulation of binary sodium silicate glasses over a wide range of compositions (from 0 to 50% Na2O) was developed. The potential energy surface is approximated by the sum of atomic energy contributions mapped by a neural network algorithm from the local geometry comprising information on atomic distances and angles with neighboring atoms using the DeePMD code [Wang, H. Comput. Phys. Commun. 2018, 228, 178-184]. Our model was trained on a large data set of total energies and atomic forces computed at the density functional theory level on structures extracted from classical molecular dynamics (MD) simulations performed at several temperatures from 300 to 3000 K. This allows for the generation of a robust and transferable ML potential applicable over the full compositional range of glass formability at different temperatures that outperforms the empirical potentials available in the literature in reproducing structures and properties such as bond angle distribution, total distribution functions, and vibrational density of state. The generality of the approach enables the future training of a potential with other or more elements allowing for simulations of structures, properties, and behavior of ternary and multicomponent oxide glasses with nearly ab initio accuracy at a fraction of the computational cost.

Raman spectroscopy study of glass corrosion

Binary sodium silicate and potassium silicate glasses with different alkali content were exposed to the corrosion environment of 35 % hydrochloric acid (HCl). Glass samples were measured by Raman spectroscopy and the spectra were compared with Raman spectra of original pristine glasses in order to observe structural changes induced by corrosion within the surface layer. The usage of confocal Raman spectroscope enabled the measurement of Raman spectra from the depths of few micrometres to document the range of structural changes. The results suggest the depolymerisation of silicate structure due to the growth of the corrosion layer on the surface. The decrease of D2 peak points at the decomposition of three-membered rings. In addition, it is assumed that the Si-O-Si angle changes within the surface layer.

Compression creep and dynamic viscoelastic studies of binary sodium and lithium silicate glasses around deformation temperature

Compression creep and dynamic viscoelastic studies of binary sodium and lithium silicate glasses around deformation temperature

Spectroscopic Inquiry of the Fe2O3-role in Binary Sodium Borate, Sodium Silicate and Sodium Phosphate Glasses and Effects of Gamma Irradiation

Optical absorption spectral investigations have been carried out on Fe3+ ions doped sodium borate, sodium silicate and sodium phosphate glasses before and after gamma irradiation. The UV-visible absorption spectrum exhibits bands characteristic of Fe3+ ions coordination in each system. Interesting aspects of FT-IR spectra were found, and this gives information about the structure changes in the constituent units of these glass systems as a function of Fe2O3 concentration. All glasses reveal characteristic absorption bands due to the addition of different ratios of iron which explain the state of iron in each system in terms of its valence and coordination number. Results indicate that iron favors a higher oxidation state (tetrahedral coordination) in the case of sodium silicate glasses. The doping with progressive Fe2O3 additions (0.5−7.5 %) has some effect on the number and position of the characteristic bands due to formation of FeO4 groups. The IR absorption spectra after irradiation reveal limited changes in the intensity which can be correlated with minor changes in bond angles and /or bond lengths within the structural units by irradiation.

Using the two-point bend technique to determine failure stress of pristine glass fibers

Two-point bending (2pb) is the simplest technique for the measurement of failure strains of glass fibers under a variety of experimental conditions. There is little chance of damage to fibers even when testing in liquid nitrogen, leading to reproducible and precise measurements of failure strain with Weibull moduli of greater than 100 measured routinely. However, a limitation of 2pb is that it measures failure strain not failure stress, and thus the Young's modulus of the sample must be known at the failure strain in order to evaluate the failure stress.In this paper the failure strains, under both inert and ambient conditions, for a number of conventional glasses (commercial silica, soda-lime silicate, and E-glass), as well as a number of simple glasses, including a nepheline glass and a range of binary sodium and potassium silicate glasses are presented. These strain values are converted to failure stresses using known or estimated non-linear modulus parameters and compared with strength values found in the literature. For silica optical fibers, the failure stresses calculated from 2pb failure strains vary from 12.1±0.2 to 14.4±0.3GPa in inert (liquid nitrogen, 77K) conditions and 7.0 to 7.3±0.1GPa in ambient conditions (room temperature, 50% RH), compared to reports of 11–14GPa for liquid nitrogen and 4–5GPa ambient tensile strength measurements. For a commercial E-glass, the calculated failure stress from 2pb, is 5.1 to 5.2±0.1GPa in inert conditions and 3.7 to 3.8±0.1GPa in ambient conditions, compared to reported tensile strengths of 5.3GPa and 3.0–3.8GPa, respectively. The failure stresses for binary alkali silicate glasses calculated from 2pb failure strains are 2–3 times greater than those reported in the literature.

Sodium Silicate and Phosphate as Corrosion Inhibitors for Mild Steel in Simulated Cooling Water System

Two inorganic inhibitors were used to protect mild steel in cooling water system (single and binary sodium silicate and phosphate). Four different concentrations of silicate and phosphate ions were used (1 × 10−3, 5 × 10−3, 1 × 10−2 and 0.2M) and (1 × 10−3,5 × 10−3, 1 × 10−2 and 0.1M), respectively, in addition to two mixtures of \({{\rm SiO}_{3}^{2-}}\) and \({{\rm PO}_{4}^{3-}}\). Corrosion parameters were measured by electrochemical method using potentiostat such as corrosion potentials, corrosion current densities and Tafel slopes to calculate polarization resistance. Protection efficiencies P% were calculated to know the best concentration of inhibitors; these results indicate that the best concentration of \({{\rm SiO}_{3}^{2-}}\) and \({{\rm PO}_{4}^{3-}}\) is 1 × 10−2M that gave P% 74.088 and 95.494, respectively, while \({{\rm PO}_{4}^{3-}}\) gave better protection than \({{\rm SiO}_{3}^{2-}}\) and its mixtures. The adsorption of \({{\rm SiO}_{3}^{2-}}\) and \({{\rm PO}_{4}^{3-}}\) on the steel surface in simulated cooling water obeys the Langmuir adsorption isotherm model.

Effects of the degree of polymerization on the structure of sodium silicate and aluminosilicate glasses and melts: An 17O NMR study

Revealing the atomic structure and disorder in oxide glasses, including sodium silicates and aluminosilicates, with varying degrees of polymerization, is a challenging problem in high-temperature geochemistry as well as glass science. Here, we report 17O MAS and 3QMAS NMR spectra for binary sodium silicate and ternary sodium aluminosilicate glasses with varying degrees of polymerization (Na 2O/SiO 2 ratio and Na 2O/Al 2O 3 ratio), revealing in detail the extent of disorder (network connectivity and topological disorder) and variations of NMR parameters with the glass composition. In binary sodium silicate glasses [Na 2O- k(SiO 2)], the fraction of non-bridging oxygens (NBOs, Na–O–Si) increases with the Na 2O/SiO 2 ratio ( k), as predicted from the composition. The 17O isotropic chemical shifts ( 17O δ iso) for both bridging oxygen (BO) and NBO increase by about 10–15 ppm with the SiO 2 content (for k = 1–3). The quadrupolar coupling products of BOs and NBOs also increase with the SiO 2 content. These trends suggest that both NBOs and BOs strongly interact with Na; therefore, the Na distributions around BOs and NBOs are likely to be relatively homogenous for the glass compositions studied here, placing some qualitative limits on the extent of segregation of alkali channels from silica-enriched regions as suggested by modified random-network models. The peak width (in the isotropic dimension) and thus bond angle and length distributions of Si–O–Si and Na–O–Si increase with the SiO 2 content, indicating an increase in the topological disorder with the degree of polymerization. In the ternary aluminosilicate glasses [Na 2O] x [Al 2O 3] 1− x SiO 2, the NBO fraction decreases while the Al–O–Si and Al–O–Al fractions apparently increase with increasing Al 2O 3 content. The variation of oxygen cluster populations suggests that deviation from “Al avoidance” is more apparent near the charge-balanced join (Na/Al = 1). The Si–O–Si fraction, which is closely related to the activity coefficient of silica, would decrease with increasing Al 2O 3 content at a constant mole fraction of SiO 2. Therefore, the activity of silica may decrease from depolymerized binary silicates to fully polymerized sodium aluminosilicate glasses at a constant mole fraction of SiO 2.

Na-relaxation and intermediate range structure in sodium–potassium silicate melts

We report on the investigation of fast alkali-ion transport and its relation to microscopic structure for mixed Na–K silicate melts. Na 2O K 2O 4SiO 2, Na 2O K 2O 6SiO 2, and K 2O 3SiO 2 are studied by means of quasielastic neutron scattering and the results are discussed in the context of results on Na 2O 2SiO 2, Na 2O 3SiO 2, and K 2O 2SiO 2. The height and position of the prepeak in the elastic structure factor scales with the Na 2O:K 2O ratio between the binary alkali silicates. The addition of K 2O to a binary sodium silicate melt appears to have no influence on the time scales of the Na self-relaxation. The data suggest the presence of two different subnetworks of percolation channels in the static structure for the two different alkali species Na and K.

Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in sodium silicate glasses

Experimental ionic conductivity σ and activation energy E A data in the binary sodium silicate system are reviewed. Analysis and brief discussion based on 48 glasses in a wide compositional range (between 4 and 45 Na2O mol%) are presented. Emphasis is placed on the application of the Anderson–Stuart model to describe the variation of activation energy E A with sodium concentration. In this analysis were considered experimental parameters such as shear modulus G and relative dielectric permittivity e, also in wide compositional range. A ‘universal’ finding is obtained using log10σ vs. E A/k B T in 47 of the 48 glasses investigated, where E A is the activation energy for conduction, k B is the Boltzmann constant and T is the absolute temperature. Using conductivity and molar volume from density data, both measured at 20 °C in the same glasses, it was found a remarkable common cubic scaling relation between conductivity enhancement of the free volume due to increase in alkali content. The drastic drop in conductivity by 16 orders of magnitude for so many ion-conducting binary sodium silicate glasses is then caused by structure and ion content. The effects of shear modulus, relative dielectric permittivity and free volume are taken into account, as also the problem of phase separation. In particular, it is suggested that the glass network expansion, which is related to the available free volume, is a parameter that could partially explain the increase in ionic conductivity for this binary system.

Test of Anderson-Stuart model in sodium silicate glasses and the general Arrhenian conductivity rule in wide composition range

We collected and analyzed literature data on ionic conductivity sigma and activation energy E A in the binary sodium silicate system in a wide composition range. The Anderson and Stuart model has been considered to describe the decreasing tendency of activation energy E A with alkali concentration in this system. In this analysis were considered experimental parameters, such as shear modulus G and relative dielectric permittivity epsilon. A general conductivity rule is found in 194 of 205 glasses, when one plots log sigma vs. E A/kB T, where kB is the Boltzmann constant and T is the absolute temperature. This fact means that the arrhenian relation has universal uniqueness of form sigma = sigma (E A,T) in wide Na2O composition range. The results also show that there is strong correlation by more than 19 orders of magnitude on conductivity with E A/kBT. An explanation for this behavior links ionic conductivity and microscopic structure. The problem of phase separation in this system is also considered.

Quantum chemistry study on superstructure and Raman spectra of binary sodium silicates

Raman spectra of binary sodium silicates in various components were calculated by the self-consistent field molecular orbital ab initio calculation quantum chemical (QC) method with several polysilicon–oxygen tetrahedral model clusters with both 6–31G and 6–31G(d) basis sets being applied. Relevant pure anion clusters were also be calculated in order to determine the cation effect by comparison with the available sodium series. High and intermediate Raman-active wavenumber ranges were especially considered. The symmetric stretching vibrational wavenumber of non-bridging oxygen (NBO) in the high-wavenumber range and its Raman scattering cross-section were deduced and analyzed. Several synthesized binary sodium silicate crystals were measured for comparison. The correlation between the vibrational Raman shift and the microscopic environment of the silicon–oxygen tetrahedron (SiOT) was found based on interior stress of configuration or superstructure, which depends on the connecting topology of adjacent SiOTs. A newly established empirical stress index of a tetrahedron (SIT) was introduced to elucidate the above relationship. A new notation of SiOT accompanied by superstructure information was proposed and used to describe the practical and delicate types of SiOT in various states of binary sodium silicates. The Raman scattering cross-section of the symmetric stretching vibration of NBO shows a roughly decreasing relationship with SIT or the Raman shift in the high-wavenumber range only under the circumstance of equivalent linkage between SiOTs, and Raman optical activity (ROA) enhancement of Q3 species occurs with Q4 species as its nearest neighbor, which indicates the electronic coupling between them. It was also demonstrated that the SiObSi bending vibrational Raman shift in the intermediate wavenumber range shows a monotonic decreasing relationship with the value of the SiObSi angle while other minor impacting factors remains unknown. This work offers basic information on the superstructure of binary sodium silicates and its relationship with characteristic vibrational Raman spectra, which can be widely applied in qualitative and quantitative studies of the microstructure of silicates. Copyright © 2004 John Wiley & Sons, Ltd.

The distribution of sodium ions in aluminosilicate glasses: a high-field Na-23 MAS and 3Q MAS NMR study

The local configurations around sodium ions in silicate glasses and melts and their distributions have strong implications for the dynamic and static properties of melts and thus may play important roles in magmatic processes. The quantification of distributions among charge-balancing cations, including Na + in aluminosilicate glasses and melts, however, remains a difficult problem that is relevant to high-temperature geochemistry as well as glass science. Here, we explore the local environment around Na + in charge-balanced aluminosilicate glasses (the NaAlO 2-SiO 2 join) and its distribution using 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at varying magnetic fields of 9.4, 14.1, and 18.8 T, as well as triple-quantum (3Q)MAS NMR spectroscopy at 9.4 T, to achieve better understanding of the extent of disorder around this cation. We quantify the extent of this disorder in terms of changes in Na-O distance ( d[Na-O]) distributions with composition and present a structural model favoring a somewhat ordered Na distribution, called a “perturbed” Na distribution model. The peak position in 23Na MAS spectra of aluminosilicate glasses moves toward lower frequencies with increasing Si/Al ratios, implying that the average d(Na-O) increases with increasing R. The peak width is significantly reduced at higher fields (14.1 and 18.8 T) because of the reduced effect of second-order quadrupolar interaction, and 23Na MAS NMR spectra thus provide relatively directly the Na chemical shift distribution and changes in atomic environment with composition. Chemical shift distributions obtained from 23Na 3Q MAS spectra are consistent with MAS NMR data, in which deshielding decreases with R. The average distances between Na and the three types of bridging oxygens (BOs) (Na-{Al-O-Al}, Na-{Si-O-Al}, and Na-{Si-O-Si}) were obtained from the correlation between d(Na-O) and isotropic chemical shift. The calculated d(Na-{Al-O-Al}) of 2.52 Å is shorter than the d(Na-{Si-O-Si}) of 2.81 Å, and d(Na-{Al-O-Al}) shows a much narrower distribution than the other types of BOs. 23Na chemical shifts in binary (Al-free) sodium silicate glasses are more deshielded and have ranges distinct from those of aluminosilicate glasses, implying that d(Na-NBO) (nonbridging oxygen) is shorter than d(Na-BO) and that d(Na-{Si-O-Si}) in binary silicates can be shorter than that in aluminosilicate glasses. The results given here demonstrate that high-field 23Na NMR is an effective probe of the Na + environment, providing not only average structural information but also chemically and topologically distinct chemical shift ranges (distributions) and their variation with composition and their effects on static and dynamic properties.

Chemical durability of commercial silicate glasses. I. Material characterization

Six commercial silicate glasses; silica, sodalime silicate, two fiberglass compositions and two Bioglass ® compositions were subjected to three solutions: distilled water, Dulbecco's phosphate buffered saline solution and Ham's F-12 1x cell culture media under the exact experimental conditions that would be encountered during a cell culture study. For companion, a binary sodium silicate glass was also exposed. Weight loss, diffuse reflectance infrared spectroscopy (DRIFTS) and potentiometric titration were used to determine the chemical evolution of the substrates during a typical period for cell culturing. The silica, sodalime silicate and high-silica fiberglass material showed only small changes in all cases except for differences in OH active site concentration. The bioglass compositions and the low-silica fiberglass exhibited solution-dependent dynamic surface chemistry. The sodium silicate was too dynamic for even the most aggressive buffering system. The purpose of this study was to elucidate cell behavior to be reported in a later paper.

Crack Growth in the High Crack Velocity Region for Binary Sodium Silicate Glasses.

The crack growth behavior in the high crack velocity region (region III) for binary sodium silicate glasses was investigated by using a DCDC (double cleavage drilled compression) specimen under compressive stress. For 15mol% Na2O glass, despite the anomalous characteristic of the bulk modulus, subcritical crack growth in region III was detected. The slope of stress intensity factor (KI)-crack velocity (v) curve for silicate glass depended on the number of non-bridging oxygen per SiO4 tetrahedron rather than on the alkali content in the glass. This compositional dependence of the slope of KI-v curve for silicate glasses could not be explained in terms of thermally activated crack growth process where the crack-tip shape would vary with the pressure derivative of bulk modulus. The smaller KI-v slope and the higher KIC value of 35mol% Na2O glass may be related to the structural change from a three-dimensional network to a two-dimensional network because of the introduction of many non-bridging oxygens into the silica network.

Experimental studies investigating the structure of soda-lime glasses after silver-sodium ion exchange

Structural rearrangements as a result of silver-sodium ion exchange have been investigated systematically on commercial soda-lime glasses by EXAFS experiments, X-ray diffraction, Fourier transform infrared spectroscopy, and density measurements. It was found that the atomic structure of the base glass is closely related to binary sodium silicates and that the addition of calcium causes a CaO bond length of ≌ 0.25 nm. Silver has been incorporated in an extended range of concentration (0.7 to 11 mol% Ag 2O) well below the glass transformation temperature. Nevertheless, the typical silver environment consisting of two oxygens at an average distance of 0.215 nm was found. The second sphere around silver is dominated by an AgAg correlation at an approximately 0.298 nm spacing. Additionally, AgO and AgSi correlations have to be considered. The determined AgAg bond length indicates a d 10-d 10 interaction between silver ions. The so formed silver pairs or clusters should be precursory of the precipitation of crystalline silver particles at elevated temperatures. The interpretation of the difference function of diffraction data yields a pair correlation at 0.342 nm that can be ascribed to AgSi bond lengths. Comparing the EXAFS data at the Na and Ag K-edge structural relaxation is observed around the silver ions during low-temperature ion exchange although the glass volume remains constant in a wide range of composition. This relaxation entails essential consequences with respect to diffusion and conductivity behavior. Thus, it yields the structural basis of the mixed mobile effect in ion-exchanged glasses. The suggested memory effect means the inability of sodium to re-convert ‘silver-like’ sites below T g which leads to local electric fields.

In situ electrochemical investigation of copper in binary sodium silicate melts at 1000 °C

The influence of the melt composition on the redox ratio of copper in binary sodium silicates at 1000 °C was determined by means of in situ electrochemical methods. The redox ratio was calculated from the currents measured by Repetitive Multi-Pulse Chronoamperometry. It appears that the redox ratio does not depend on the total copper concentration over the range 0,25 to 1 wt% Cu. However, the proportion of copper(II) was found to increase with increasing basicity, ie with increasing the sodium oxide content. We deduced from a model based on the formation of pure ionic oxocomplexes that the coordination number of the Cu(II) oxocomplex is greater than that of the Cu(I) oxocomplex. The difference between the coordination numbers, which is calculated from the experimental results is equal to 0.56. The fractional number is quite far from the integer that would indicate the occurrence of well defined oxocomplexes of copper.

Anodic polarization in molten silicates

The anodic polarization in binary sodium silicates containing 22–40 mol% Na 2O equilibrated with air was studied at 1000° C by means of voltammetry and double-step chronoamperometry. The electrochemical oxidation of the oxide ions produced by condensation reactions of silicate species is a two-electron process kinetically controlled by mass transport of O 2− to the anode. The oxygen atoms generated by the oxidation rapidly dimerize to produce dissolved oxygen which is further transformed into gaseous oxygen in the saturated bulk liquid. In basic liquids, the voltammetric peak corresponding to oxygen evolution is preceded by a prewave which has been explained by the formation of chemisorbed peroxide ions via an electrochemical reaction which involves dissolved and adsorbed oxide ions.

Oxidation States of Chromium Dissolved in Glass Determined by X‐ray Photoelectron Spectroscopy

The oxidation states of chromium dissolved in binary sodium silicate glasses were analyzed by X‐ray photoelectron spectroscopy (XPS). The measured “equilibrium” Cr6+ fractions in glasses with varying Na2O contents are shown to be in good agreement with results obtained by other techniques reported in the literature. XPS was then used to analyze the interface of a sodium silicate glass/chromium alloy (Inconel 718) seal. It is shown that Cr2+ and Cr3+ were the major chromium species dissolved in the glass interfacial region.

On the na + self-diffusion and electrical conductivity of Na 2O-B 2O 3-SiO 2 glasses derived from the Na 2O·2SiO 2 glass

Five borosilicate glasses, whose composition is deduced from that of the disilicate glass (Na2O·2SiO2). are investigated for hydrolytic durability and for Na+ transport properties. The motion of the Na+ ions is studied by measurements of the 22Na tracer-diffusion coefficients D* and of the electrical conductivity σ in dependence on temperature. The deduced activation parameters (EA.D, D0: EA.σ, σ0) and the Haven ratio HR = D*/Dn are discussed in relation to Na+ concentration and to structural features of the glasses. The results are compared with the behaviour of binary sodium silicate glasses with related Na+ concentrations.

Acidity and ionic structure of molten alkali silicates

An attempt has been made to identify the structural elements in binary lithium, sodium, potassium and cesium silicate melts by voltammetry. In the lithium melts g-SiO 2 or quartz-like clusters are proposed, although other interpretations are possible. Further, a second voltammetric wave may be an indication of peroxo bonds in lithium melts. In sodium melts, anions derived from cristobalite have been confirmed by comparison with information from Raman spectra, as have the tridymite derivatives in potassium melts. The structural elements in cesium silicate melts resemble those of potassium. The influence of the alkali ion on the acidity of the melt is calculated and is found to increase in the order Cs < K < Na < Li.