Structure Of Silicate Glasses Research Articles

Thirty-year quest for structure–nucleation relationships in oxide glasses

Over the past three decades, researchers have investigated the existence of possible relationships between crystal nucleation kinetics and the atomic-scale structure of silicate glasses. The main driving force for this quest was the fact that while the vast majority of glass-forming substances only undergo surface (heterogeneous) nucleation when sufficiently heated, a few systems also show the thermodynamically less favourable case of internal (homogeneous) nucleation on laboratory time/length scales. For such glass systems, various macroscopic properties, such as densities, configurational entropies and frozen-in birefringence, have suggested that the structure in the glassy state shows a closer resemblance to the structure of the phase formed upon crystallisation than in the case of glass systems only undergoing heterogeneous nucleation. However, the specific structural features and their length scales have remained uncertain. In this article, we review and discuss the research investigating relationships between the occurrence of internal nucleation and structural parameters related to various different length scales. The latter include (1) short-range order, concerning both network modifier cation-oxygen distances and coordination numbers as well as network former Qn distributions, (2) intermediate range order describing network former connectivities, network former/network modifier correlations, and network modifier distance distributions, and (3) medium range order as reflected by silicate tetrahedral ring-size statistics. Inspection of this data for several stoichiometric oxide glasses and their respective isochemical crystals suggests a positive correlation between homogeneous nucleation ability and structural similarity at the level of short- and intermediate-range order of the network modifier cations. In contrast, no correlation can be found with regard to any structural parameters describing the local structures of the network former species (Qn distributions). Based on the limited set of data available, we develop concrete recommendations for future experiments to test this hypothesis.

ChemInform Abstract: A Review of the Structures of Oxide Glasses by Raman Spectroscopy

AbstractReview: 253 refs.

The effect of structural and energy parameters of glassy melts on the protective performance of coatings made of these glassy melts

We have designed a procedure for calculating strength criterion Kn as a parameter determining the mean strength of structure of silicate glasses and melts. The infrared spectra of silicate glasses used as coatings to protect low-alloy and low-carbon steels against high-temperature gas-phase corrosion in process heating are studied. Aluminum cations in the glasses under study are four-coordinate, while boron ions may be both fourand three-coordinated. The latter fact has a significant effect on the Kn values. The Kn values are calculated at operating temperatures of the studied glassy coatings. The correlation ratio between protective effect Δg of the glassy coatings and their Kn is analyzed. For glassy coatings with an operating temperature that lies within their vitrification range, there exists a nonlinear correlation between Δg and Kn; the correlation ratio between these parameters increases with temperature. Regression equations (significance level p = 0.05) describing the relationship between Δg and Kn are obtained for temperatures of 900 and 1000°C.

Diluted Fe3+ in silicate glasses: Structural effects of Fe-redox state and matrix composition. An optical absorption and X-band/Q-band EPR study

Sodium-alkaline earth-silicate glasses, of nominal molar composition 16Na2O–10RO–74SiO2 (R=Ca, (Ca,Mg) and Mg) doped with 0.5wt.% of Fe2O3, were studied by UV–Visible–NIR absorption spectroscopy and electron paramagnetic resonance (EPR) at X- and Q-band to understand the structural control of Fe3+ optical absorption properties as a function of iron redox and glass composition. By comparing with a set of [4]Fe3+, [5]Fe3+ and [6]Fe3+ crystalline references, optical absorption spectra indicate the presence of 5-fold Fe3+ in addition to a majority of tetrahedral Fe3+. The combination of Q- and X-band EPR data shows Fe3+ partition among isolated, distributed sites and Fe-rich clusters, providing unique insight into the distortion of isolated Fe3+ sites. It demonstrates also the peculiar character of the residual Fe3+ sites that exist in reduced glasses. Changing Ca to Mg increases the amount of tetrahedral Fe3+ sites and decreases their distortion. The presence of Mg also reduces the amount of isolated rhombic Fe3+ sites and promotes the formation of clusters. These clusters confirm the non-homogeneous structure of silicate glasses, as well as the preference of Fe3+ for a more calcic than magnesian environment in sodic (Ca,Mg) glasses.

<i>x</i>Na<sub>2</sub>O-(1−<i>x</i>) SiO<sub>2</sub> ガラスに適用する原子間相互作用の考察

The interatomic potential for a wide composition range of sodium silicate glasses was proposed by first-principles calculation. Point charge was set for each glass composition on the basis of population analysis of the alkali silicate crystals by using the density functional theory. The potential parameters were obtained from the energy surface of the SiO2+ model by using the molecular orbital method. The molecular dynamics simulation using the new interatomic potential showed improved structures of sodium silicate glasses.

Structure and topology of soda-lime silicate glasses: implications for window glass.

The structural and topological properties of soda-lime silicate glasses of the form (1-2x)SiO2-xNa2O-xCaO are studied from classical molecular dynamics using a Buckingham type potential. Focus is made on three compositions (x = 6%, 12%, and 18%) which are either silica-rich or modifier-rich. We compare the results to available experimental measurements on structural properties and find that the simulated pair correlation function and total structure factor agree very well with available experimental measurements from neutron diffraction. The detail of the structural analysis shows that the Na and Ca coordination numbers tend to evolve with composition, and with increasing modifier content, changing from 5.0 to 5.6 and from 4.0 to 5.0 for Ca and Na, respectively. The analysis from topological constraints shows that the picture derived on a heuristic basis using classical valence rules remains partially valid. Ultimately, typical elastic phases are identified from the application of rigidity theory, and results indicate that the 6% system is stressed-rigid, whereas the modifier-rich composition (18%) is flexible. These results receive support from a full analysis of the vibrational density of states showing the low-energy bands at E < 20 meV increase as the system becomes flexible, providing another indirect signature of the presence of rigid to flexible transitions in this archetypal glass. Consequences for window glass are discussed under this perspective.

Structural study of sodium silicate glasses and melts

We report an X-ray diffraction study and modeling of the structure of sodium silicate glasses and melts that are used as binders in the production of the latest generation of ceramic welding fluxes. Experimental data and reverse Monte Carlo (RMC) simulations results are analyzed in comparison with results for a sodium silicate monolith and the water glass prepared from it. The RMC results agree well with structure factor and radial distribution function analysis data. The sodium silicate glasses and melts are shown to have a number of structural features, which have much in common with their crystalline counterparts. The high capacity of the silicate glasses and melts for water is due to the presence of nanopores formed (largely) by six-membered rings of silicon-oxygen tetrahedra and partially by sodium-oxygen octahedra.

Iron modified structural and optical spectral properties of bismuth silicate glasses

Iron bismuth silicate glasses have been successfully synthesized by melt quenching technique. The amorphous nature of the glass samples is ascertained by the XRD patterns. The values of density, molar volume and crystalline volume have been measured and are found to decrease with increase in iron content. The glass transition temperature measured using Differential Scanning Calorimetry (DSC) also varies with increase in Fe2O3 content. The Raman and FTIR spectra of the studied glass system taken at room temperature suggests that Fe2O3 modifies the structure of bismuth silicate glasses and it acts as both network modifier as well as network former. Bismuth also plays the role of both network modifier (BiO6 octahedra) as well as network former (BiO3 pyramids) and SiO2 exists in SiO4 tetrahedral structural units with two non-bridging oxygens. The Hydrogenic excitonic model is found to be applicable to the studied glass compositions. The variation in Urbach energy value observed for the studied glass samples suggests the possibility of increase in the number of glass defects. The metallization criterion for the synthesized glass samples is determined and found to be in the range 0.30–0.38.

Structural investigations of silicate–phosphate glasses containing MoO3 by FTIR, Raman and 31P MAS NMR spectroscopies

Molybdenum is a transition metal (refers to the “d” block of the periodic table) whose atom has an incomplete d sub-shell. It is known that in silicate glasses molybdenum may exist under four oxidation states: Mo6+, Mo5+, Mo4+ and Mo3+, simultaneously molybdenum cations, depending on their content in the glass network, may either be a glass forming component, or act as a modifier. The contemporary literature data show studies conducted mostly on the structure of silicate, phosphate, borate and borosilicate glasses containing molybdenum ions, but not silicate–phosphate glasses. Therefore, the author has undertaken detailed studies using FTIR, Raman and 31P MAS NMR techniques in order to examine the effect of MoO3 addition into the structure of silicate–phosphate glasses from SiO2P2O5K2OCaOMgO system. On the basis of obtained results it was concluded that molybdenum ions in the analysed glasses act as a modifier, which follows from the gradual breakage of oxygen bridges, i.e. POP, SiOSi, and SiOP, and the following formation of connections such as Mo[MoO4]OSi and/or Mo[MoO4]OP. In summary, it is concluded that the increase of MoO3 content (up to 4.4mol.%) in the structure of glasses of SiO2P2O5K2OMgOCaO system results in weakening of the structure and gradual increase of the degree of silico-oxygen and phosphor-oxygen frameworks depolymerisation.

Evolution of the heterogeneous structure of model sodium silicate glasses during binodal decomposition: X-ray small-angle scattering investigation

The kinetics of binodal decomposition in model glasses of the Na2O-SiO2 system from the initial stage to the stage of the Ostwald ripening inclusive has been investigated in situ. It has been found that the spatial-temporal evolution of the heterogeneous structure during binodal decomposition has a multistage character. The characteristic size of the phase regions at each stage of the binodal decomposition varies with time according to the power law L ∼ tβ. The values of exponents β for different stages of the binodal decomposition are as follows: 1/20 (fluctuation stage), 1/2 (growth stage), 0 (transient stage), and 1/3 (Ostwald ripening stage). The particle size distributions for all stages of the binodal decomposition have been presented.

Effects of doping CeO2/TiO2 on structure and properties of silicate glass

In order to elucidate the effects of doping CeO2/TiO2 on the structure and physical properties of silicate glass, glasses with composition 72SiO2–3Al2O3–10Na2O–10K2O–5CaO doped with varied ratios of CeO2/TiO2 were synthesized by melt-quenching method and were characterized by X-ray diffraction, infrared and Raman spectrometry, UV–Visible spectrophotometry and micro-indentations. X-ray diffraction conforms the amorphous state of doped glasses. The spectroscopic analysis reveals that doping CeO2 alone results in depolymerization of glass network and narrowed distribution of Qn (Si–O tetrahedral with n bridging oxygen atoms), while doping TiO2 singly or combined with CeO2 favors the enhanced polymerization of network and regains a broader Qn distribution relative to doping CeO2 alone. It is proposed that doped cerium and titanium in glass exists in multivalent state and the former in presence of trivalent state preferentially acts as modifier inducing network depolymerization, whilst the latter in form of tetrahedral tends to interconnect network units as intermediate. Doped cerium in trivalent state contributes mainly to the red-shift of absorption edge while titanium suppresses such change of absorption band. Either adding cerium alone or co-doping with titanium will result in decreased optical band gap due to the structural modifications. The relatively loosened structure due to depolymerization induced by cerium is responsible for the decline in hardness and E-modulus but rising in fracture toughness, whereas network compactness by virtue of interconnectivity of titanium and structural densification may account for the increase of hardness and E-modulus at the cost of slight loss of fracture toughness. For silicate glasses co-doped cerium and titanium, the mechanical properties should be the synergy of the two opposite mechanism.

Analysis of the surface structure of soda lime silicate glass after chemical strengthening in different KNO3 salt baths

This paper deals with the physico-chemical and mechanical properties of soda lime silicate float glass treated in KNO3 baths with different purity levels. The potassium concentration profile in the surface layers was measured by EDXS and correlated with the residual stress frozen in the material, which was determined by a procedure based on the measurement of the strengthened sample curvature deriving from progressively etching one of its surfaces. This allowed pointing out a significant influence of the used salt. In order to better understand the phenomena and mechanisms underlying the surface equilibrium conditions, micro-Raman measurements were also performed on the glass surface in the aim to investigate the variation of the glass microstructure after ion-exchange in the different salt baths.

Structure and viscosity of soda lime silicate glasses with varying Gd2O3 content

In order to reveal the influence of variation of Gd2O3 amounts (0.00, 0.25, 0.50, 0.75, 1.00mol%) on the viscosity at high temperature and melting temperature of soda lime silicate glass, the structure of soda lime silicate glasses doped with different content of Gd2O3 were investigated with Fourier transform infrared spectrometer using the KBr disc method and INVIA confocal microRaman spectrometer. The effect of variation of Gd2O3 content on the structure of soda–lime–silicate glass was characterized by the shift of peak position and change of the full width at half maximum in 950–1200cm−1 of FTIR absorption curve, and conversion of the [SiO4] tetrahedron structural unit Qn, fraction of non-bridging oxygen and the average number of bridging corners per tetrahedron in Raman spectra. The effect of doping different content of Gd2O3 into glass on the viscosity and melting temperature was interpreted by changing in structure of soda–lime–silicate glasses.

Visible light activated photo-catalytic effect and local structure of iron silicate glass prepared by sol-gel method

A relationship between methylene blue (MB) decomposition ability under visible light and local structure of xFe2O3·(100-x)SiO2 glass abbreviated as xFS prepared by sol-gel method was investigated by 57Fe-Mossbauer spectroscopy, X-ray diffractometry (XRD) and ultraviolet-visible light absorption spectroscopy (UV-Vis). Mossbauer spectra of xFS glass with x of 10, 30 and 50 annealed at 1000 °C for 3 h were mainly composed of a paramagnetic doublet due to fayalite (Fe2SiO4), and magnetic sextets due to magnetite (Fe3O4) or hematite (α-Fe2O3). The absorption area (A) of α-Fe2O3 gradually increased from 0.0 to 10.3 and 100 % with the increasing Fe2O3 content (x) of annealed xFS glass. A leaching test performed by 20 mL of MB aqueous solution and 40 mg of annealed 50FS glass showed that MB concentration decreased from 16.2 to 4.7 μmol L−1 after 2 h with the first order rate constant of 1.8 × 10−4 s−1. These results prove that annealed iron silicate glass containing α-Fe2O3 can decompose MB effectively under visible light irradiation.

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ~10(3) atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application in different fields. In addition, as a first application of the present findings, the fully converged structure of the 45S5 glass was further analyzed to shed new light on several dissolution-related features whose interpretation has been rather controversial in the past.

Free volume and structure of Gd2O3 and Y2O3 co-doped silicate glasses

Viscosity and melting temperature of soda lime silicate glasses co-doped with Gd2O3 and Y2O3 measured using the rotating crucible viscometer, and derived on the basis of the Arrhenius Equation have been reported in our previous paper. To reveal the effect of substituting Y2O3 for Gd2O3 on the performance of soda lime silicate glass at high temperature, the free volume fraction and structure of soda lime silicate glass co-doped with Y2O3 and Gd2O3 were investigated. The results show that a small amount of Gd2O3 decrease the fraction of free volume of soda lime silicate melt, and then increase when the content above 0.5 mol%, while Y2O3 addition decrease the fraction of free volume. For FTIR spectra, doping of Gd2O3 and Y2O3 into glass causes the peak position of bands assigned to Si–O–Si asymmetric and symmetric stretching vibration move to lower wavenumber, and broadens the distribution of structural units. Raman spectra results show that Gd2O3 and Y2O3 result in the structural units with more bridging oxygen depolymerize to species with more non-bridging oxygen, consequently provide with more non-bridging oxygen and decrease the rigidity of glass structure. The behavior of soda lime silicate glasses doped with Gd2O3 and Y2O3 at high temperature can be elucidated by the change of the free volume and structure.

Structural modifications of binary lithium silicate glasses upon femtosecond laser pulse irradiation probed by micro-Raman spectroscopy

The effects of single femtosecond laser pulse irradiation (130 fs pulse duration, 800 nm center wavelength) on the structure of binary lithium silicate glasses of varying chemical compositions were investigated by micro-Raman spectroscopy. Permanent modifications were generated at the surface of the glass samples with varying laser fluences in the ablative regime and evaluated for changes in the corresponding Raman band positions and bandwidths. For increasing laser fluences, the position of certain Raman bands changed, indicating an increase in the mass density of the glass inside the irradiated area. Simultaneously, the widths of all investigated bands increased, indicating a higher degree of disorder in the glass structure with respect to bond-angle and bond-length variations.

New approach to modeling of a local structure of silicate glasses and melts

Structural model of silicate melts and glasses obtained by rapid cooling of the melt is far from complete at present. Modern models suggest the existence of the five different types of silicon-oxygen tetrahedra which are distinguish by the ratio of bridging and terminal oxygen atoms per silicon atom (the so-called basic structural blocks or units) in the structure of silicate glasses and melts and also assume that the several types of such units can exist in the glass and melt structures simultaneously. The knowledge of the concentrations of these units depending on the composition and temperature (the so-called Qn distribution) is a necessary element for the development of an adequate model of silicate systems and to explaining their physical and chemical properties. Three-parameter statistical method to modeling of Qn distribution in silicate melts and glasses is present in this paper. This method allows calculating the concentration of structural units in a wide composition range at different temperatures. The method is based on a destruction of a preassigned network as a model of depolymerization of the silicon-oxygen framework in the process its interaction with the modifier oxides. Qn distribution, distribution of silicon-oxygen tetrahedra according to their next-nearest neighbours, and distribution of bridging bonds in alkali-silicate glasses and melts were obtained in frame of the developed approach.

Evidence of Nanometric-Sized Phosphate Clusters in Bioactive Glasses As Revealed by Solid-State 31P NMR

Bioactive glasses are able to form strong bonds to bone. This property, crucial for medical applications, depends on the glass composition and structure. Dissolution of phosphates in melt-quenched silicate glasses raises the question of chemical homogeneity and possible formation of clusters. A detailed structural characterization of the bioactive glasses is thus highly desirable. In this work, the nature of the distribution of phosphate units in a melt-quenched bioactive glass is elucidated for the first time using 31P spin-counting solid-state NMR experiments. The structure of a dense bioactive calcium silicate glass with 2.6 mol % of phosphorus oxide is shown to exhibit nanometric-sized chemical and structural heterogeneities. Clear experimental evidence of the presence of phosphate clusters of five and six PO4 tetrahedral units embedded in the disordered polymeric silicate network is given.

Water cleaning ability and local structure of iron-containing soda-lime silicate glass

A relationship between waste-water cleaning ability and local structure of iron-containing soda-lime silicate glass, 15Na2O·15CaO·xFe2O3·(70-x)SiO2 (x = 10–50 in mass%), abbreviated as NCFSx glass, was investigated by means of 57Fe-Mossbauer spectroscopy, redox titration with KMnO4 for the determination of chemical oxygen demand (COD) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Mossbauer spectra of NCFSx glass with “x” of 10 and 30 were composed of two doublets: one due to FeIIIO4 tetrahedra (Td) with isomer shift (δ) of 0.23–0.26 mm s − 1 and quadrupole splitting (Δ) 1.01–1.04 mm s − 1, and the other due to FeIIO6 octahedra (Oh) with δ of 1.00–1.03 mm s − 1 and Δ of 2.03–2.05 mm s − 1. Absorption area for FeII(Td) was decreased from 9.7 to 6.5 and 0.0 % when “x” was increased from 10 to 30 and 50. A leaching test performed with 500 mL of artificial waste water and 2.0 g of NCFS50 revealed waste-water cleaning ability of soda-lime glass, e.g., COD was reduced from 280 to 55.2 mg L − 1 after 10 day-leaching. After 10 day-leaching, it proved that iron was dissolved into waste water to a level of 5.3\(_{7} \times 10^{-1}\) mg L − 1. These results prove that organic matter could be effectively decomposed with iron-containing soda-lime silicate glass.