Structure Of Silicate Glasses Research Articles

The structure of sodium silicate glass

Atomistic scale computer simulations can provide a more detailed understanding of the structure of glasses. Our results on sodium silicate glasses show that sodium ions are associated with nonbridging oxygens and that the sodium ions and nonbridging oxygens tend to aggregate to form silica rich regions and alkali rich regions. Interatomic distances of our simulated glasses are in good agreement with experimental results. O–Si–O bond angles are centered around 109° with narrow distributions. Si–O–Si bond angles are broadly distributed from 120° to 180° with an average of about 153°.

Application of infrared spectroscopy to studies of silicate glass structure: Examples from the melilite glasses and the systems Na2O-SiO2 and Na2O-Al2O3-SiO2

Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (<15 Å) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200–800 cm−1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from ‘cage-like’ motions of cations in their oxygen co-ordination polyhedra. In aluminosilicates these bands can provide information on the structural environment of Al that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 cm−1 is indicative of network-substituted AlO4 polyhedra in glasses with Al/(Al+Si)>0·25 and a band at 520–620cm−1 is shown to be associated with AlO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of Al, Si tetrahedral site ordering. An important conclusion is that differences in Al, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity.

High-field 29Si NMR studies of alkali silicate glasses

Previous work has demonstrated the utility of high-field magic-angle sample spinning (MASS) NMR spectroscopy in determining the structure of alkali silicate glasses. In addition, results from static spectra at high field are highly informative and in many cases yield results that are not easily obtainable from MASS spectra. Here a comparison of static and MASS spectra of alkali silicates is reported. Computer simulations of the data determine the relative contributions of the different Q n sites to the spectral intensities, and the values for the components of the chemical shift tensor for each site.

Effects of temperature and composition on silicate glass structure and dynamics: SI-29 NMR results

The distribution of bridging and non-bridging oxygens is a fundamental aspect of the intermediate range order of silicate glasses and liquids. Disorder in this distribution can be characterized by the relative abundances of Qn species, which can be quantified by 29Si NMR on both spinning and static samples. We emphasize the latter here, and show that increasing the field strength of the network modifying cation and increasing temperature have similar randomizing effects on this distribution. These changes have a major influence on thermodynamic activities. In the liquid, exchange between sites is rapid, but the exchange rate may become slow enough with decreasing temperature to actually define Tg. In silicate liquids, some kind of high energy, low abundance, defects probably are present to allow this structural change to occur, to account for the bulk of the configurational heat capacity, and to explain the observed spin-lattice relaxation times.

The structure of dense-packed metallic and oxide glasses

Despite obvious differences, the structures of silicate glasses and amorphous binary alloys display some remarkable similarities. In particular, it can be argued by analogy with the amorphous transition metal-metalloid alloys, that the structure in the dense-packed regions of alkali and alkaline earth silicates exerts a significant influence on the overall structure of the glass. Preliminary results are presented of an investigation of the environment of typical ‘network-modifying’ cations in silicate glasses by neutron scattering with isotopic substitution of Ca and Li. The immediate neighbourhood of each cation appears to be ordered with a suggestion that organisation extends to second-neighbours, at least.

Identification of multiple structural species in silicate glasses by 29Si NMR.

Knowledge of the structure of silicate glasses is one key to understanding their chemical and physical properties, as well as those of the high-temperature liquids from which they form. Because first-neighbour ordering into SiO4 tetrahedra is well known, much of the recent discussion about glass structure has concerned intermediate-range order. One of the most fundamental questions that can be posed is the distribution of silicate tetrahedra with n bridging oxygens (shared between two tetrahedra), labelled as 'Qn' (0 less than or equal to n less than or equal to 4). This distribution is probably important in determining the properties of melts and glasses, but considerable controversy exists concerning the identification and quantification of such species. Here I present new evidence from 29Si NMR (nuclear magnetic resonance) spectroscopy that clearly resolves one significant part of this dispute: at least in sodium silicate glasses, a variety of species is present that is greater than that required by composition alone.

Speciation and local structure in alkali and alkaline earth silicate glasses: Constraints from 29Si NMR spectroscopy

29Si NMR spectroscopy provides important contributions to the understanding of silicate glass structure, as the resonance frequency is sensitive to several aspects of the local chemical environment (including intertetrahedral bond angles, bond distances, and number of bridging oxygens per silicon atom). New data on a series of binary alkali and alkaline earth glasses are presented which highlight the effects of composition, as well as the complications that can arise in the interpretation of spectra. In binary alkali silicate glasses, two partially resolved peaks may be observed, which are attributable to Si in sites with different numbers of bridging oxygens. These are present even in glasses which are almost certainly single, homogeneous phases. In alkaline earth and in aluminosilicate glasses, single, broad, often asymmetric resonances are found, whose linewidths span the frequency ranges of three or more structural species. Using a combination of slow sample spinning and non-spinning techniques, NMR spectra also provide data on local electronic symmetry, and indicate that silicon sites in glasses can be more symmetrical than those in crystalline materials.

Spectroscopic Analysis of the Structure of Silicate Glasses along the Joint xMAlO2‐(1–x)SiO2(M = Li, Na, K, Rb, Cs)

Infrared spectroscopic studies of charge‐coupled substitution in silicate glasses and crystals along the joints xMAlO2(1 –x)SiO2 (M = Li, Na, K, Rb, and Cs; 0.10 ≤x≤ 0.60) were carried out in the range 2000 to 200 cm−1 Three major absorption bands appeared in the 1100‐, 800‐, and 500‐cm−1 regions. For a specific value of x, the observed changes in frequency, intensity, and bandwidth decreased in the order Li &gt; Na &gt; K &gt; Rb &gt; Cs and the apparent disorder in the glass structure caused by the substituted aluminum increased in the direction K &lt; Na &lt; Li. The 800‐cm−1 band splits at SiO2≃ 0.75 mol, which has been interpreted in terms of the number of AlO4 tetrahedra in the structure. Most of the substituted aluminum in the glasses and the crystals was found to be in the fourfold coordination.

Effect of Small Concentrations of Gallium Oxide on the Structure of Sodium Silicate Glasses

The glass transformation temperatures and de electrical conductivities of sodium silicate glasses with low‐level gallia additions have been measured. The composition/property relationships observed in these glasses are different from those observed with larger gallia additions. These trends are discussed in terms of structural models proposed for these glasses.

The structure of binary alkali silicate glasses

The role of alkali metal cations in determining the structure of binary silicate glasses has been studied by magic angle spinning NMR of 29Si and 133Cs in Rb 2OSiO 2 and Cs 2OSiO 2. Glasses with up to ≈ to mol% alkali metal oxide have been investigated and the results compared with those for Li 2OSiO 2 and Na 2OSiO 2. At high concentrations of Rb 2O or Cs 2O there is a deviation from the formation of solely Q n and Q n−1 species which was found for Na 2OSiO 2. We suggest that the structure of binary silicates is determined by a balance between the repulsion of non-bridging oxygens on different Q species and the mutual attraction or repulsion of the alkali metal cations.

Structure of Glasses and Melts in the Na&lt;sub&gt;2&lt;/sub&gt;O-SiO&lt;sub&gt;2&lt;/sub&gt;-TiO&lt;sub&gt;2&lt;/sub&gt; System

In order to elucidate the influence of TiO2 on the structure of sodium silicate glasses and melts, a MD (molecular dynamics) simulation using the ionic pair potential function, Born-Mayer-Huggins form, has been performed for 0.25Na2O⋅0.47SiO2⋅0.28TiO2 glass and the corresponding melt. The calculation pair correlation functions were in good agreement with a RDF (radial distribution function) curve obtained from the previous structural analysis by TOF (time-of-flight) pulsed neutron scattering. The computer-simulated configuration for the glass indicated that most of Ti ions were in 4-fold coordination, whilst the remainder were 6-fold coordination. The frequency spectrum of the glass obtained from MD simulation was in good agreement with the Raman spectra measured on glasses in the Na2O-SiO2-TiO2 system. As a result, the weak Raman band near 700cm-1 can be assigned to Ti ion in 6-fold coordination, and the strong Raman band near 900cm-1 reflects a Ti-O stretching band, which is characteristic of TiO4 tetrahedra corner-linked with SiO4 tetrahedra. The Raman spectra for glasses and melts in Na2O-SiO2-TiO2 system were measured by the high temperature Raman spectroscopic technique. A slight difference in the obtained Raman spectra was observed between the glasses and the corresponding melts, implying that the structure of glass should be similar to that of the corresponding melt.

Structure of Alkali‐Zinc Silicate Glasses by Raman Spectroscopy

Raman spectra were measured for a series of Na2O·xZnO·ySiO2 glasses where x=O to 2 and y = 1,2, or 3. The spectra exhibit bands characteristic of sheet‐like and chain‐like strucrural units. Frequency and intensity shifts with ZnO content suggest that Zn2+ is a simple network modifier over this composition range.

New methods of determining the real structure parameters of special gels and silicate glasses

This paper is concerned with the application of new x-ray diffraction methods for studying the structure of gels and silicate glasses. Low- and wide-angle x-ray diffraction methods were applied. The summarized, differential and differentiated by subtraction radial distribution functions were analyzed. Basic structural parameters (interatomic distances, distances between groups of atoms and coordination numbers and zones) internal ordering degree and concentrations of inhomogeneous zones were determined. Structural models approximating the real structure of special gels (SiO 2·xH 2O and SiO 2·xH 2O + R 2O 3) and models of local ordering in silicate glasses (SiO 2, SiO 2 + Na 2O 3 + CaO + MgO + R 2O 3/FeO, Fe 2O 3) are also described. The theory of the structural analysis applied to the materials studied is presented, including a detailed description of the new methods used to determine the parameters of the real structure of the substances studied. The usefulness of the measuring and analysis methods is described also. A comparison is made between data obtained in my laboratory and that available in the literature. The structural models constructed from the structural parameters obtained by the radial function method are considered as to their accuracy and probability to be found. The accuracy of the measurements, both apparatus and numerical calculations, is evaluated. The structural diffraction measurements are supplemented with the analyses of surface layers made by other methods including x-ray spectrometry and microspectrometry, emission electron microscopy, and local microhardness and microplasticity.

Raman spectroscopic studies of silicate and related glass structure : a review

La spectrométrie Raman a été largement utilisée afin d'étudier la structure moléculaire des verres silicatés. Une grande partie de ces travaux ont eu pour but d'élaborer des modèles structuraux susceptibles d'être appliqués aux liquides silicatés à intérêt géologique. Cet article procède au recensement de ces études afin de faciliter l'accès à la littérature pertinente, et présente quelques travaux des auteurs non publiés à ce jour. Les interprétations des diverses études sont commentées, et les modèles qui en résultent pour les structures des verres et liquides silicatés sont considérés afin de faire ressortir les domaines d'accord général, et ceux qui, sujet à controverse, nécessitent une étude approfondie.

Raman spectroscopic investigation of the structure of silicate glasses. III. Raman intensities and structural units in sodium silicate glasses

The Raman scattering intensity of the 1100 cm−1 polarized band, which appears on the addition of Na2O to SiO2 glass, reaches a maximum at the disilicate composition. The intensity of the polarized band at 950 cm−1 increases sharply as the Na2O concentration increases above 30 mole %. These data were interpreted by normal mode calculations and by IR and Raman intensity calculations for the silicate anion structural units: SiO4 isolated tetrahedra, Si2O7 dimers, Si2O6 chain links, Si2O5 sheet units, and Si2O4 framework units. According to these simplified models, the polarized high frequency band is due to symmetric stretching of Si–O− nonbridging bonds and the frequency increases with degree of polymerization of the tetrahedra. The previous assignments of the 1100 cm−1 band to the symmetric stretch of tetrahedra containing one nonbridging oxygen and of the 950 cm−1 band to the symmetric stretch of tetrahedra containing two nonbridging oxygens were confirmed. The other main feature of the alkali silicate glasses, an intense polarized band in the range of 400–600 cm−1, was shown to be a mixed stretching bending mode of the Si–O–Si bridging bond. The model also accounts for the loss of intensity of the high frequency band with increasing degree of silica polymerization.

Local structure of silicate glasses

Extended X-ray absorption fine structure is used to study local order in silicate glasses around sodium and silicon atoms. It is demonstrated that modifying cations like sodium have well-defined short range order that is complementary rather than incidental to the glass forming silicate network.

Infrared absorption spectra and structure of fluorine-containing alkali silicate glasses

Infrared absorption spectra were studied in the 800-700 cm −1 range for fluorine containing alkali silicate glasses. Only one absorption maximum appeared in that range for SiO 2, R 2OSiO 2 (RLi,Na,K,Rb or Cs) and RFSiO 2 (RLi or Na) glasses. In the case of RFSiO (RK,Rb or Cs) glasses, two maxima appeared. The higher and lower frequency peaks were tentatively interpreted as corresponding to symmetric stretching vibrations of SiO 2 and SiO 4− α F α ( α<4) tetrahedra, respectively. Owing to more extensive formation of SiO 4−αF α tetrahedra in the KFSiO 2, RbFSiO 2 and CsFSiO 2 glass system, these could be prepared with larger amounts of fluoride than the LiFSiO 2 and NaFSiO 2 glasses.

A Gas‐Probe Analysis of Structure in Silicate Glasses

An analysis of helium and neon transport in vitreous silica is consistent with a statistically distributed structure of the random network. The jump distance, d, for diffusion in common borosilicate glass is greater than in vitreous silica due to the additional modifier ions, Na+. The addition of Na+ or K+ to a silicate structure produces an increase in d. The vibrational frequencies for a gas atom in a “doorway” (v*) and in a solubility site (v) indicate structural trends such as phase separation.

Raman spectroscopic investigation of the structure and crystallization of binary alkali germanate glasses

Raman spectra have been measured on bulk GeO2 glass and the alkali germanate glasses of composition M2OxGeO2 where M=K, Na, Li, and x varies from 19 to 1, as well as on crystallized glasses. The low alkali content glasses (x≥3) retain a completely polymerized structure of germania polyhedra. Addition of small amounts of alkali oxide to GeO2 glass does not break the Ge-O-Ge bridging bonds and creates higher co-ordination of germanium atoms. Further addition of alkali oxide eventually breaks up some of the Ge-O-Ge bonds to create Ge-O− non-bridging oxygens. In the K- and Na-glasses a small number of non-bridging oxygens already exist at x=4.5, while in the Li-glasses they do not exist even at x=4. The structures of the low alkali content glasses start to disappear at x between 4 and 3 and they disappear almost completely at x=2. At x between 2 and 1, glass structures become analogous to the silicate glass structures. At x=2, the glass consists of disordered (Ge2O5)n sheet-like structures and at x=1 disordered (GeO3)n chain structures.

A molecular dynamic calculation of the structure of sodium silicate glasses

Molecular dynamic calculations of the structure of a series of sodium silicate glasses, a common soda–lime glass, a sodium borosilicate glass and a sodium–potassium silicate glass were made. Calculated radial distribution functions are in good agreement with existing x-ray diffraction data and a previous MD calculation on silica glass. During the dynamical runs alkali and alkaline earth cations cluster around nonbridging oxygen atoms. In the borosilicate glass studied, the boron atoms enter the silica network and are tetrahedrally coordinated by oxygen. Other features of the simulated glasses include the coordination number of cations, the degree of inhomogeneity, the distribution of bridging and nonbridging oxygen atoms, the Si–O–Si bond angles, the ring structure, etc. Some preliminary diffusion studies will be presented.