Sodium Silicate Glasses Research Articles

Atomic properties of sodium silicate glasses obtained from the building-block method

Atomistic simulations of $({\mathrm{Na}}_{2}\mathrm{O}{)}_{x}({\mathrm{SiO}}_{2}{)}_{1\ensuremath{-}x}$ glasses are carried out using the building-block method that uses copies of low-energy units, ``building blocks,'' to build large realistic structural models. The calculated pair-correlation functions show that the local structure of these glasses is in good agreement with diffraction experiments. The electronic density of states for the doped models reveals defects in the band gap close to the conduction tail that are localized around undercoordinated Na atoms. Thermal properties for the systems, including the thermal expansion coefficient, are studied within the quasiharmonic approximation, and compare favorably with experiment. The elastic properties of the glasses are studied by calculating bulk and shear modulus.

Repercussions of yttrium oxides on radiation shielding capacity of sodium-silicate glass system: experimental and Monte Carlo simulation study

Five glass samples with composition 37.5 Na2O + (61.1 − x) SiO2 + xY2O3, x = 1, 2, 5, 5.7 and 6 mol% were synthesized using the melting methods at temperatures varying between 1400 and 1500 °C, depending on the Y2O3 insertion ratio. The synthesized glasses density was measured using the Archimedes method. Moreover, the linear attenuation coefficient was measured experimentally using the gamma-ray transmission method with NaI (Tl) crystal and radio-isotopes C-137 and Co-60. The mass attenuation coefficient was calculated based on the experimental linear attenuation coefficient and confirmed using the Monte Carlo simulation MCNP-5 code and XCOM program. The gamma-ray shielding capacity was enhanced with the replacement of SiO2 by Y2O3. The LAC at energy 0.662 MeV varied in the range between 0.201 and 0.232 cm−1, increasing the Y2O3 insertion ratio between 1 and 6 mol%, respectively. The fast neutron effective removal cross section ∑R (cm2/g) was also evaluated theoretically for the fabricated glass samples. The computed ∑R values decreased linearly with the Y2O3 content.

Three-dimensional nano-hydroxyapatite sodium silicate glass composite scaffold for bone tissue engineering - A new fabrication process at a near-room temperature

Hydroxyapatite nanoparticles (n-HAp) due to their structural similarity to the mineral part of human bone is one of the most promising materials for the preparation of highly biocompatible and osteoconductive scaffolds to be used in bone tissue regeneration. Yet, the conversion of n-HAp powder into a 3D scaffold is usually occurring by sintering at high temperatures for several hours. Such a high temperature process, strongly affects the physicochemical and biological properties of n-HAp and therefore losing their similarity to the human bone tissue. In the present study, sodium silicate solution is applied, for the first time, as a mineral binder for consolidation of n-HAp through a dehydration-drying process at a near-room temperature (37 °C). The new consolidation process preserves the low crystallinity, non-stoichiometry, and nanosize of the precursor n-HAp, so important to mimic bone tissue. Furthermore, the consolidated 3D composite scaffold presents an adequate porosity and mechanical profile required for bone-healing applications. The in vitro cytotoxicity tests proved the non-hazardous and inductive nature of the fabricated 3D composite over the MG-63 osteoblast-like cell line. In fact, the results show significantly enhanced cell proliferation. Overall, this new consolidation process can deliver a porous 3D composite scaffold with high potential for bone tissue engineering applications.

Atomistic modeling approach to the thermodynamics of sodium silicate glasses

AbstractA good description of the vibration modes of silicate glasses is necessary for the accurate determination of their thermodynamical properties. While the properties of amorphous SiO2 are well‐known, those of more complex silicate glasses remain poorly described. In this work, the atomic‐scale models have been used to investigate the vibration modes and thermodynamical properties of amorphous sodium silicate (Na2O)x(SiO2)1−x. Several empirical potentials have been considered, and their predictions have been compared to available experimental data. Different Na2O concentrations have also been simulated, highlighting the effect of sodium network modifiers on vibration spectra and thermodynamical properties. Statistical effects related to the simulation box size have been investigated, which helps interpreting quantitative results from simulations based on small systems, for example, electronic structure calculations. The potentials used can describe different oxides besides SiO2 and Na2O. The results presented here pave the way for future use of these potentials to study more complex glasses with different types of network formers and modifiers.

ВЛИЯНИЕ ГРУБОДИСПЕРСНЫХ КОМПОНЕНТОВ НА СВОЙСТВА КЕРАМИЧЕСКОГО МАТЕРИАЛА

In modern conditions, clay raw materials of fine-grained structure are used for the production of building ceramics. The task of using coarse non-traditional non-plastic components in the compositions of ceramic masses and the choice of rational sizes of their grains is relevant. The exclusion of pre-grinding determines the reduction of energy costs and, as a result, the cost of finished products. The paper offers an optiom of using diopside concentrate of various grain sizes in compositions with minor additions of clay and sodium silicate solution. The problems of stress development at the interface of grain and ligament contact, which in case of a negative outcome do not make it possible to obtain a strong structure of a ceramic shard, are solved. The presence of an insignificant voltage formed as a result of the relationship between the diopside and the forming glass phase is revealed, this does not prevent the consideration of the probability of obtaining a ceramic material. The study of the behavior of ceramic samples containing diopside of different granulometric composition when adding a solution of sodium-silicate glass after molding and firing shows the effectiveness of using diopside concentrate in 100-150 microns. Contacts of this size of diopside are wrapped in liquid glass during molding. A glass phase is formed when fired. In this case, the diopside is partially melted, but it is preserved and exists as an independent unit. A smaller grain size during sintering requires more glass phase, which leads to structural stresses, and with a larger size, not enough glass phase is formed and the strength of the material is significantly reduced. When studying the influence of grain size on the properties of the sample, the results of water absorption indicators of 7 %, mechanical compressive strength – 36 MPa, bending strength-17 MPa are obtained. It is found that the dispersion of diopside in 100–150 microns allows to develop a technology for the use of coarse-grained raw materials in the ceramic mass

Structure and vibrational properties of sodium silicate glass surfaces.

Using molecular dynamics simulations, we investigate how the structural and vibrational properties of the surfaces of sodo-silicate glasses depend on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered: A melt-formed surface (MS) in which a liquid with a free surface has been cooled down into the glass phase and a fracture surface (FS) obtained by tensile loading of a glass sample. We find that the MS is more abundant in Na and non-bridging oxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural defects such as two-membered rings and under-coordinated Si than the MS. We associate these structural differences to the production histories of the glasses and the mobility of the Na ions. It is also found that for Na-poor systems, the fluctuations in composition and local atomic charge density decay with a power-law as a function of distance from the surface, while Na-rich systems show an exponential decay with a typical decay length of ≈2.3 Å. The vibrational density of states shows that the presence of the surfaces leads to a decrease in the characteristic frequencies in the system. The two-membered rings give rise to a pronounce band at ≈880 cm-1, which is in good agreement with experimental observations.

КЕРАМИЧЕСКИЕ СТРОИТЕЛЬНЫЕ МАТЕРИАЛЫ С ИСПОЛЬЗОВАНИЕМ НЕТРАДИЦИОННОГО ВИДА СЫРЬЯ

the paper raises questions about the search for the possibility of obtaining a construction ceramic material using a special type of raw material component. Diopside concentrate was chosen as the basis for the ceram-ic masses due to its positive parameters necessary to improve the strength properties of the material and to support local deposits of raw materials in the East Siberian region. To reduce the optimal firing temperature, an aqueous-alkaline solution of sodium silicate was used in small quantities. The chemical composition of the diopside rock showed mainly the presence of silicon oxides. X-ray diffraction analysis revealed the presence of diopside, quartz and calcite. Sodium-silicate glass is characterized by a full content of silica and a modulus of 3. Using the state diagram of three-component systems, the temperature limits necessary for sintering ceramic masses are established. The fusibility curves show that at a temperature of 1040oC, the values of the primary melt for various compositions are 4-14%, and the total melt content is observed at 1475oC. The parameters of physical and mechanical properties of the ceramic material were determined, where at the firing temperature of 1000-1100oC the value of fire shrinkage was no more than 1%, water ab-sorption up to 10%, and compressive strength up to 31 MPa. Moreover, with an increase in the amount of diopside to 90% by weight, the strength increases, and shrinkage decreases. X-ray phase analysis of the compositions determined mainly analytical lines of diopside, which begin to decrease by 1000oC, which de-termines the relationship with the liquid glass. The DTA and TG curves of the thermogram showed endo-thermic and exothermic effects due to the release of adsorbed water and crystallization of glass. The possi-bility of obtaining high-strength low-shrink ceramics using diopside raw materials as the basis of ceramic masses when adding sodium-silicate glass in the form of a melt is established.

Insights into the tribochemistry of sliding iron oxide surfaces lubricated by sodium silicate glasses: An ab initio molecular dynamics study

Binary alkali silicate glasses are new promising lubricants for harsh working conditions, such as high pressure, elevated temperature, and high sliding speed. In the present work, the tribochemical reaction of sodium silicate under sliding contact with iron oxide substrates was investigated using First Principle Molecular Dynamics. The result indicates that the silicate is chemically active against the iron oxide surface at high temperature. Non-bridging oxygen (NBO) in glass lubricant and iron from the substrate forms the covalent bonds (NBO-Fe), which play a crucial role in the tribological performance. Interestingly, NBO in the glass can change continuously its covalent bond with different Fe atom of the substrate as a consequence of the shearing. Positively charged sodium atoms in the silicate network have an extremely high mobility, which allows them to diffuse towards the substrates, due to the electrostatic interaction with the negatively charged oxygen atoms of iron oxide substrates. These results explain the formation mechanism of a sodium-rich layer on iron oxide substrates. Reducing the sodium content in the glass lubricant will limit the formation of the sodium-rich tribofilm layer and increase the connectivity of the silicate network, which significantly reduce the friction and antiwear properties of the glass lubricant.

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.

Dynamic and stress signatures of the rigid intermediate phase in glass-forming liquids.

We study the evolution of enthalpic changes across the glass transition of model sodium silicate glasses (Na2O)x(SiO2)100-x, focusing on the detection of a flexible-rigid transition and a possible reversibility window in relationship with dynamic properties. We show that the hysteresis resulting from enthalpic relaxation during a numerical cooling-heating cycle is minimized for 12% ≤ x ≤ 20% Na2O, which echoes with the experimental observation. The key result is the identification of the physical features driving this anomalous behavior. The intermediate-flexible boundary is associated with a dynamic onset with increasing depolymerization that enhances the growing atomic motion with a reduced internal stress, whereas the intermediate-stressed rigid boundary exhibits a substantial increase in the temperature at which the relaxation is maximum. These results suggest an essentially dynamic origin for the intermediate phase observed in network glass-forming liquids.

Anionic speciation in sodium and potassium silicate glasses near the metasilicate ([Na,K]2SiO3) composition: 29Si, 17O, and 23Na MAS NMR

Abstract Alkali silicate glasses near to the metasilicate composition provide sensitive tests of anionic speciation. However, reports on 29Si NMR data vary considerably in their derived proportions of silicate species. In some cases, an apparent deficit in the content of non-bridging oxygen has been attributed to up to 5 to 10% “free” oxide ions. Here we provide new NMR data on a series of sodium silicate glasses ranging from 56 to 45 mol% silica with accurately analyzed compositions. High signal-to-noise data for a 29Si-enriched glass provide improved constraints on fitting models for spectra, and suggests a slight asymmetry in the main Q2 component. Data are consistent with conventional models in which “free” oxide contents are below detection limits of about 0.5 to 1%. Spectra for an 17O-enriched K-silicate glass with about 53% silica confirm that there is no obvious direct signature for “free” oxide species in this compositional range.

Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

AbstractRecent development of reactive force fields have enabled molecular dynamics simulations of interactions between silicate glasses and water at the atomistic scale. While multicomponent silicate glasses encompass a wide variety of compositions and properties, one common structural feature in these glasses is the combination of the network structure that is made up of silica tetrahedra linked through corner sharing interspersed with network modifiers like alkali and alkaline‐earth ions that break up the Si–O–Si linkages by forming nonbridging oxygen. In reactions with water, ion exchange between alkali ions in the glass and proton or hydronium in the solution, as well as hydrolysis reaction of the Si–O–Si linkages and subsequent silanol formation, is observed and well documented. We have used a set of recently developed reactive force field to investigate the reactions between water and the surfaces of silica and sodium silicate glasses of different compositions for reactions up to 8 nanoseconds. Our results indicate sodium leaching into water and diffusion of water molecules up to 25 Å into the glass surface. We examined the structural and compositional changes inside the glass and around the diffused ions and use these to explain the rates of silanol formation at the surface. We also observed proton transport in the glass which has an indirect influence on the silanol formation rates. While the surface of the glass was rough to start with, it undergoes further modification into a hydrated gel‐like structure in the glass for up to 5 Å in the higher alkali containing glasses. It was found that the leached sodium ions remain close to the interface and that fragments of silicate network from the surface is capable of dislodging from the bulk glass and enter the aqueous solution. These simulations thus provide insights into the formation and structure of an alteration layers commonly observed in multicomponent silicate glasses corroded in aqueous solutions.

New insights into the structure of sodium silicate glasses by force-enhanced atomic refinement

Atomistic simulations can offer direct access to the atomic structure of glasses, which is otherwise invisible from conventional experiments. However, molecular dynamics (MD) simulations of glasses based on the melt-quenching technique remain plagued by the use of high cooling rates, while reverse Monte Carlo (RMC) modeling can yield non-unique solutions. Here, we adopt the force-enhanced atomic refinement (FEAR) method to overcome these limitations and decipher the atomic structure of a sodium silicate glass. We show that FEAR offers an unprecedented description of the atomic structure of sodium silicate, wherein the simulated configuration simultaneously exhibits enhanced agreement with experimental diffraction data and higher energetic stability as compared to those generated by MD or RMC. This result allows us to reveal new insights into the atomic structure of sodium silicate glasses. Specifically, we show that sodium silicate glasses exhibit a more ordered medium-range order structure than previously suggested by MD simulations. These results pave the way toward an increased ability to accurately describe the atomic structure of glasses.

MAS-NMR studies of carbonate retention in a very wide range of Na2O-SiO2 glasses

Glasses that contain carbon are of geological interest, and the form of that carbon can be probed by Magic-Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. Previous studies of the Na2O-SiO2 glass system could only reach 56 mol% Na2O. Here we reproduce and extend those studies to cover a very wide compositional range, from 20 to 70 mol% Na2O, by using a combination of conventional melt-quench and twin roller quenching technologies on natural and 99% 13C-enriched sodium silicate glasses. 13C MAS-NMR reveals that measurable levels of carbon retention occur above at least 40 mol% Na2O, and takes the form of CO32− ions incorporated in the glass structure. These CO32− anions are surrounded by Na+ cations, forming nanoscale domains in a sodium silicate glass network. 23Na MAS-NMR showed a linear decrease in mean Na—O bond length with increasing Na2O content, up to 60 mol% Na2O, above which the mean Na—O bond length increased. Elemental analysis detected significant (>5%) carbon dioxide by mass in the 65 and 70 mol% Na2O glasses. For the 70 mol% Na2O glass, 13C and 23Na MAS-NMR detected ordered nanoscale domains composed of only Na2O and CO2. These results have shown the quantity and nature of carbon retention in the archetypal sodium silicate glass system, which will better inform structural models and carbonate solubility limits.

Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

AbstractInfrared (IR) and Raman spectroscopic features of silicate glasses are often interpreted based on the analogy with those of smaller molecules, molecular clusters, or crystalline counterparts; this study tests the accuracy and validity of these widely cited peak assignment schemes by comparing vibrational spectral features with bond parameters of the glass network created by molecular dynamics (MD) simulations. A series of sodium silicate glasses with compositions of [Na2O]x[Al2O3]2[SiO2]98−x with x = 7, 12, 17, and 22 were synthesized and analyzed with IR and Raman. A silica glass substrate and a crystalline quartz were also analyzed for comparison. Glass structures with the same compositions were generated with MD simulations using three types of potentials: fixed partial charge pairwise (Teter), partial diffuse charge potential (MGFF), and bond order‐based charge transfer potential (ReaxFF). The comparison of simulated and experimental IR spectra showed that, among these three potentials tested, ReaxFF reproduces the concentration dependence of spectral features closest to the experimentally observed trend. Thus, the bond length and angle distributions as well as Si–Qn species and ring size distributions of silica and sodium silicate glasses were obtained from ReaxFF‐MD simulations and further compared with the peak assignment or deconvolution schemes—which have been widely used since 1970s and 1980s—(a) correlation between the IR peak position in the Si–O stretch region (1050‐1120 cm−1) and the Si–O–Si bond angle; (b) deconvolution of the Raman bands in the Si–O stretch region with the Qn speciation; and (c) assignment of the Raman bands in the 420‐600 cm−1 region to the bending modes of (SiO)n rings with different sizes (typically, n = 3‐6). The comparisons showed that none of these widely used methods is congruent with the bond parameters or structures of silicate glass networks produced via ReaxFF‐MD simulations. This finding invokes that the adequacy of these spectral interpretation methods must be questioned. Alternative interpretations are proposed, which are to be tested independently in future studies.

Ab Initio Molecular Dynamics of CdSe Quantum-Dot-Doped Glasses.

We have probed the local atomic structure of the interface between a CdSe quantum dot (QD) and a sodium silicate glass matrix. Using ab initio molecular dynamics simulations, we determined the structural properties and bond lengths, in excellent agreement with previous experimental observations. On the basis of an analysis of radial distribution functions, coordination environment, and ring structures, we demonstrate that an important structural reconstruction occurs at the interface between the CdSe QD and the glass matrix. The incorporation of the CdSe QD disrupts the Na-O bonds, while stronger SiO4 tetrahedra are reformed. The existence of the glass matrix breaks the stable 4-membered (4MR) and 6-membered (6MR) Cd-Se rings, and we observe a disassociated Cd atom migrated in the glass matrix. Besides, the formation of Se-Na and Cd-O linkages is observed at the CdSe QD/glass interface. These results significantly extend our understanding of the interfacial structure ofCdSe QD-doped glasses and provide physical and chemical insight into the possible defect structure origin of CdSe QD, of interest to the fabrication of the highly luminescent CdSe QD-doped glasses.

The critical role of the interaction potential and simulation protocol for the structural and mechanical properties of sodosilicate glasses

We compare the ability of various interaction potentials to predict the structural and mechanical properties of silica and sodium silicate glasses. While most structural quantities show a relatively mild dependence on the potential used, the mechanical properties such as the failure stress and strain as well as the elastic moduli depend very strongly on the potential, once finite size effects have been taken into account. We find that to avoid such finite size effects, samples of at least 75,000 atoms for silica and 300,000 atoms for the sodosilicate are needed. Finally we probe how the simulation ensemble influences the fracture properties of the glasses and conclude that fracture simulations should be carried out in the constant pressure ensemble.

Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

AbstractUnderstanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear‐induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF‐MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF‐MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Sisubstrate–O–Sicounter_surface bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water‐producing hydroxyl groups and their key role in the hydrolysis reaction is discussed.

Predicting Ionic Diffusion in Glass from Its Relaxation Behavior.

In low-viscosity liquids, diffusion is inversely related to viscosity via the Stokes-Einstein relation. However, the Stokes-Einstein relation breaks down near the glass transition as the supercooled liquid transitions into the non-ergodic glassy state. The nonequilibrium viscosity of glass is governed by the liquid-state viscous properties, namely, the glass transition temperature and the fragility. Here, a model is derived to predict the ionic diffusivity of a glass from its nonequilibrium viscosity, accounting for the compositional dependence of the glass. The free energy activation barrier for diffusion is related to the activation enthalpy for viscous flow using the Mauro-Allan-Potuzak model of nonequilibrium viscosity [Mauro, J. C.; Allan, D. C.; Potuzak, M. Nonequilibrium Viscosity of Glass. Phys. Rev. B 2009, 80, 094204]. These insights allow for accurate prediction of activation barriers for diffusion of alkali ions. The model is supported by experimental results and nudged-elastic band calculations applied to sodium silicate and borate glasses.

ТЕОРЕТИЧНІ ПЕРЕДУМОВИ ЕКСПЛУАТАЦІЇ КОНСТРУКЦІЙ З МЕТАЛ-СКЛЯНИМИ ЗАХИСНИМИ ПОКРИТТЯМИ В УМОВАХ СУДНОВИХ ВІБРАЦІЙ

The article is devoted to looking for a solution for the scientific and technical issue of reducing vibrations on vessels. It is considered to be achieved with the application of the vibration-absorbing composite coatings. The purpose of the work is to theoretically substantiate the possibility of operation of structures with metal-glass coatings taking into consideration the vibration environment of a vessel. The formulation of the research includes the discovery of the solution for the micromechanics issue set up on the model of a two-layer plate St3 ‒ metal-glass coatings, taking into account their structural features, and experimental tensile tests. The influence of the polydisperse structure of coatings on the mechanisms of absorption of elastic-plastic waves of dynamic oscillations has been analyzed with the help of the analytical description of microdisplacement deformations. The influence of morphology and volume content of glass fillers, specifically hollow glass microspheres, powders of sodium silicate and lead-containing glass on the vibration coefficient, strength limit and yield strength has been investigated. Calculations have shown the feasibility of using metal-glass coatings in conditions of vessel vibration, which is due to the absorption of energy by glass inclusions of spherical and angular shape. It has been experimentally proven that coated plates are slightly inferior in tensile strength to samples with St3; the destruction of coatings occurs between glass inclusions. The obtained results have scientific and practical significance for the design of ship structures using composite materials and coatings.