Increasing Na2O Content Research Articles

The short-range structure of sodium ultraphosphate glasses

Anhydrous sodium ultraphosphate glasses were prepared with Na2O contents between 0 and 50 mol% and were characterized by several structurally sensitive spectroscopic probes to determine the nature of the phosphate tetrahedra that constitute the short-range glass structure. Solid state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy reveals that Na2O depolymerizes the branched (Q3) P-O network of P2O5 to form metaphosphate (Q2) sites, in quantitative agreement with Van Wazer's ‘chemically simple’ model. X-ray photoelectron spectroscopy reveals that the concomitant increase in non-bridging oxygen with increasing Na2O content is also in quantitative agreement with this structural model. Raman spectroscopic analyses of glasses with approximately 40 mol% Na2O suggest that some intermediate-range order, perhaps associated with strained rings, also exists within the glass network. Strained sites are eliminated when the solid glass is heated to melt temperatures.

Molecular Dynamics Study of Na‐Si‐O‐N Oxynitride Glasses

The structure and properties of Na‐Si‐O‐N oxynitride glasses have been studied by molecular dynamics calculations using a pair potential of the Busing approximation of the Born‐Mayer‐Huggins type. Nitrogen atoms bonded to one, two, and three silicon atoms coexist in the glass structure. The mean of the number of silicon atoms bonded to a nitrogen atom ranges from 2.4 to 2.1, decreasing with increasing Na2O content from 15 to 30 mol%. It has been assumed that nitrogen atoms bonded to two or fewer silicon atoms are formed when nitrogen atoms substitute for non‐bridging atoms. The bond angle ∠Si‐N‐Si exhibits a bimodal distribution around 105–135° and 140–170°, roughly corresponding to the nitrogen atoms bonded to three and two silicon atoms, respectively. The dependences of the density, the bulk thermal expansion, and the bulk modulus on the nitrogen content are consistent with those observed in real systems.

Structural Analysis of Na2O-B2O3 Melts by Pulsed Neutron Total Scattering Method and Molecular Dynamics Simulation.

In order to obtain direct information on the structure of sodium borate melts which are of use in metallurgical processes, pulsed neutron total scattering measurements have been carried out on 10mol%Na2O- and 30mol%Na2O-B2O3 melts at 1073 K, in addition to the previous measurement on pure B2O3 melt. Molecular dynamics (MD) calculations have also been made on pure B2O3 and 30mol%Na2O-B2O3 melts at 1073 K.With increase in Na2O content, the first peak of RDF(r), representing B-O correlation, spread asymmetrically to larger r side, and the coordination number of O atoms around a reference B atom nB-O increased from 3.0 to 3.5, showing variation of B-O correlation. This increase in nB-O could be explained by the simple assumption that two BO3 triangle structure units are converted to two BO4 tetrahedron structure units with the addition of one Na2O molecule in the same way as in Na2O-B2O3 glasses. These nB-O values also agreed well with those obtained by MD calculations, which showed the clear evidence of the appearance of BO4 units that the distribution of O-B-O bond angle spread from 120° to smaller angle side for 30mol%Na2O-B2O3.From these results, it is safely concluded that a part of BO3 triangle structure units converted to BO4 tetrahedron structure units with the addition of Na2O up to 30 mol% to B2O3 melt in the same way as in Na2O-B2O3 glasses.

Transformation-Range Viscosity and Thermal Property of Sodium Silicate Glasses

The viscosity and thermal properties of glasses in the system Na2O-SiO2 were measured near the transformation temperature. The parameters of fragility, ΔCp and Eη/Tg, increased with an increase in Na2O content. Results of these measurements showed a good correlation between ΔCp and Eη/Tg.

Gel Formation and Drying Characteristics in the Na<sub>2</sub>O-ZrO<sub>2</sub>-SiO<sub>2</sub> System

Gel formation and drying characteristics in the system aNa2O-bZrO2-(100-a-b) SiO2 (a=0, 7, 13, 18, b=3, 6, 10mol%) were investigated. Gelling time decreased with increasing Na2O content, perhaps due to the catalytic reaction of NaOH released from NaOC2H5. The release of NaOH was confirmed from pH measurements of sol mixtures with or without water. The weight loss-time curve indicated that the falling rate period decreased with increasing Na2O content, which corresponds to a gel structure with large pore size at high Na2O cocentrations. This was confirmed by measurement of pore size distribution on dried gels. The linear shrinkage of Na2O-containing gels was smaller than that of Na2O free compositions. The tendency of crack formation in gels increased with increasing Na2O content, but decreased with increasing ZrO2 content. It was inferred that this was due to an easy deformable gel structure made up of linear molecules in Na2O-free gels, or to a rigid gel structure made up of particle molecules in Na2O-containing gels.

Formation and Chemical Durability of Na-Si-O-N and Na-Al-Si-O-N Oxynitride Glasses

Using oxide glasses of compositions xNa2O⋅(100-x)SiO2 (x=20-50 in mol) and 40Na2O⋅(60-y)SiO2⋅yAl2O3 (y=5, 10 in mol) as base glass, Na-Si-O-N and Na-Al-Si-O-N oxynitride glasses were prepared by melting powder mixture of oxide glass and Si3N4 or AlN, and the effects of the base oxide glass composition on the glass forming ability, the amount of incorporated nitrogen and the chemical durability of oxynitride glasses were studied. It was found in Na-Si-O-N glasses that the lower Na2O content is favorable for the formation of nitrided glass, giving larger glass forming regions. Retained nitrogen content decreased with increasing Na2O content in Na-Si-O-N glasses and with increasing Al2O3 content in Na-Al-Si-O-N glasses. Chemical durabilily of Na-Si-O-N glass increased with increasing of nitrogen content for any Na2O content of the base glass. For Na-Al-Si-O-N system, however, nitrogen incorporation increased or decreased chemical durability, depending on the Al2O3 content and nitrogen content in the glasses or had no appreciable effect.

Structure of R<sub>2</sub>O-Ga<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> (R=Na, K, Cs) Glasses Studied by Raman Spectroscopy

Raman spectra of R2O-Ga2O3-TiO2 glasses, where R is Na, K, or Cs, have been measured and the structure of the glasses has been discussed on the basis of Raman spectroscopy and the X-ray radial distribution analysis on the binary R2O-Ga2O3 and R2O-TiO2 glasses reported previously. It has been confirmed that both Ga3+ and Ti4+ ions are four-coordinated by oxygens as in the respective binary glasses. It was found that the strength of the bridged Ga-O bonds decreases and nonbridging oxygens are formed with increasing R2O and TiO2 content. The Ti-O bond strength has been found to be higher for the glasses containing larger alkali ions. It was also found that in Na2O-containing glasses the Ti-O bond becomes strong with increasing Na2O content, whereas in Cs2O-containing glasses the Ti-O bond becomes weak with increasing Cs2O content.

Structural Study of Na2O–TeO2 Glasses by Mössbauer Spectroscopy and Differential Thermal Analysis

Abstract A Mössbauer spectrum of xNa2O·(95−x)TeO2·5Fe2O3 glasses (0≤x≤35) consists of a paramagnetic quadrupole doublet peak with an isomer shift of 0.39±0.01 mm s−1 with respect to metallic iron. Quadrupole splitting of the doublet peak changes gradually from 0.76 to 0.60 mm s−1 when Na2O content is changed from 0 to 35 mol% at 5 mol% intervals. These results suggest that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids. Each of the distorted TeO4 trigonal bipyramids has an oxygen vacancy and a lone electron pair at one of the equatorial sites. Decreased quadrupole splitting is ascribed to an increased symmetry of FeO4 (and also TeO4) trigonal bipyramids, due to a formation of nonbridging oxygen atoms followed by a gradual change of the glass matrix from a two-(β-TeO2) or three-(α-TeO2) dimensional network structure to a lower dimensional network structure. These structural changes are also deduced from a composition dependency of glass transition temperatures (Tg), which decrease continuously from 318 to 232 °C with increasing Na2O content.

ChemInform Abstract: Conductivity Activation Energy Relations in High‐Sodium‐Content Borate and Aluminoborate Glasses.

AbstractIt is found that the conductivity activation energy of borate and aluminoborate glasses decreases with increasing Na2O content below 50 mol% Na2O, which is attributed to a decreasing cation jump distance.

Molecular dynamics calculations for boron oxide and sodium borate glasses

Molecular dynamics (MD) calculations were carried out for boron oxide and sodium borate glasses using the interionic potentials derived by the MD calculations of crystals. It is shown that the calculated composition dependence of the fraction of the boron ions having tetrahedral coordination is in good agreement with the results measured by NMR. The pair distributions and bond angle distributions around 3- and 4-fold coordinated boron ions showed remarkable differences from each other and gave the particular local structures. It is concluded that the network is developed at first with an increase of Na 2O content and the maximum development is shown near 33 mol% Na 2O. Above 33 mol% Na 2O, the network of the sodium borate glass starts to disintegrate and a significant increase of the non-bridging oxygen ion is found.

Raman Spectra and Structure of Glasses in the System Na<sub>2</sub>O-Ga<sub>2</sub>O<sub>3</sub>-B<sub>2</sub>O<sub>3</sub>

The glass-forming region was determined by the water quenching method in the system Na2O-Ga2O3-B2O3. Raman spectra were measured for glasses in the composition range 10-40mol% Na2O, 0-30mol% Ga2O3 and 30-90mol% B2O3. The Raman spectroscopic study revealed that, at a given Ga2O3 concentration, an increase in Na2O content causes changes in boron coordination in the sequence BO3→BO4→BO3, while for a given Na2O concentration an increase in Ga2O3 content reduces the BO4 concentration in the Na2O-Ga2O3-B2O3 glass. Change in coordination number of gallium from 6 to 4 was deduced from the Raman spactra. The compositional dependence of density and refractive index consistent with the deduced structural changes in glass.

The low-temperature thermal expansion and specific heat of glassy B2O3and two glassy sodium borates

The results of thermal expansion measurements using a three-terminal capacitance dilatometer for pure glassy B2O3 (B2O3)0.99(Na2O)0.01 and (B2O3)0.90(Na2O)0.10 are reported in the temperature range 2010K. The isothermal compressibility has also been measured at room temperature. The linear term in the thermal expansion, attributed to the effect of two-level systems, is analyzed in comparison with that for other borate glasses-(B2O3)1-x(Na2O)x for x=0.06, 0.16 and 0.25-studied previously. The authors arrive at the conclusion that a negative cubic term in the thermal expansion gives rise to a negative expansivity in all borate glasses at the lowest temperatures (around 3K) and that the linear term characteristic of disordered systems is positive and grows with increasing Na2O content. They argue that this is due to the change in short-range coordination produced in B2O3 glass by addition of Na2O. The first measurements of the specific heat of sodium boron oxide glass are reported at low temperatures.

A mössbauer investigation of non-bridging oxygens in Na2O-Fe2O3-B2O3 glasses

Mossbauer measurements of sodium borate glasses 4 Fe2O3· x Na2O· (96-x) B2O3 (x=6, 10, 15, 20, 25, 30) have been carried out. It was found that Fe3+ is present in both octahedral and tetrahedral sites, whereby the tetrahedral sites are preferred. In the range of Na2O contents higher than about 15 mol%, the isomer shifts and quadrupole splittings for Fe3+ decrease continuously with increasing Na2O concentration. These changes could be attributed to the formation of non-bridging oxygens (NBO) in the neighborhood of ferric ions. Increasing Na2O content thus gives rise to more NBO increasing the symmetry of the iron polyhedra.

Crystallization behavior of coal gasification ash

Large-scale commercialization of coal gasification would result in large volumes of ash or slag requiring disposal. Burial of ash or slag raises environmental concerns because of the possible leachability of harmful trace elements into groundwater. In this study, Hygas ash was melted as a means of reducing the volume for disposal. The crystallization behavior of melted ash (slag) and other slags modified to lower the melting temperatures was determined. The principal constituents of Hygas ash were Al 2O 3, SiO 2, and Fe 2 O, with low alkali and alkaline earth content and small concentrations of other elements. This material melted at 1400 °C and recrystallized by rejection of iron oxides from a silicate glass. Increasing the Na 2O content to 37 wt% resulted in a totally glassy structure and a lowering of the melting temperature to about 850 °C. Limited leaching tests indicated that the leachability of melted Hygas ash and modified slags increased substantially with increasing Na 2O content.

The structure of soda-silica glasses: A mas NMR study

“Magic-angle spinning” NMR of sodium silicate glasses has shown that the introduction of Na 2O into the SiO 2 structure causes the progressive replacement of [SiO 4] tetrahedra containing four bridging oxygens by [SiO 4] tetrahedra with three bridging and one non-bridging oxygens. At 33.3 mol.% Na 2O all [SiO 4] are of the latter type and on further increase of Na 2O content they are progressively replaced by [SiO 4] with two non-bridging oxygens until complete replacement is achieved at 50 mol/% Na 2O. The chemical shifts of both [ 29SiO 4] types and also 23Na vary continuously with composition, i.e. there is no evidence for clustering of either species. The spectra of glasses of the disilicate and metasilicate compositions have been compared with those of the corresponding crystal phases and differences are observed between the sodium sites in both compositions and also for the silicon sites in the disilicate. This indicates that there are no “crystal-like” areas in the glass structure. In fact the increase in the 29Si resonance halfwidth on approaching a “crystal” composition suggests an increased range of SiOSi bond angles at these compositions.

Photoelectron spectra of alkali phosphate glasses.

X-ray photoelectron measurements were made on the P2O5 glass and the alkali phospate glasses. From these measurements, the following facts were confirmed quantitatively:(1) The oxygen ion in the P2O5 glass can be divided into the bridging and the double bond states.(2) The discrimination between bridging and non-bridging oxygen atom in the alkali phosphate glasses is possible.(3) The cation effect of Li, Na and K in the alkali phosphate glasses is almost same.(4) The O 1s chemical shift of the bridging oxygen atoms in sodium phosphate glasses increases with increasing Na2O content.

EPR and optical absorption of Cr3+ in binary Na2O-B2O3 glasses

The optical absorption and EPR spectra of Cr3+ in binary sodium borate glasses have been studied as functions of chromium concentration and Na2O/B2O3 ratio in the glass; the ligand field and EPR parameters have been calculated and were found to be independent of Cr3+ concentration in any particular glass. In low-alkali borate glasses (Na2O = ∼ 11 or ∼ 14 mol %) a single symmetrical EPR line was observed with g ¦=g⊥ =1.984±0.001 corresponding to perfect octahedral symmetry of the Cr3+ ion in these glasses. With increasing Na2O content of the glass, the EPR line becomes more asymmetric (characteristic two-peaked pattern); this has been explained as being due to axial elongation of the six co-ordinated Cr3+-complex in these glasses.

Optical and esr spectra of vanadium (IV) in different simple germanate, phosphate and borate glasses

The optical and esr spectra of some Na2O-GeO2, Na2O-P2O5, Na2O-CaO-P2O5 and Na2O-Al2O3-B2O3 glasses containing vanadium(IV) have been studied; these spectra have been analyzed by assuming that vanadium(IV) is present as the vanadyl ion in a ligand field of C4V symmetry. It has been found that in Na2O-GeO2 and Na2O-P2O5 glasses the covalency in the in-plane V-O δ-bonds increases, and the degree ofπ-bonding with the vanadyl oxygen decreases, with increasing Na2O content of the glass; the rate of change being greatest in the region 15 to 20 mol % Na2O for the Na2O-GeO2 series and around 50 mol % in the Na2O-P2O5 series. In the Na2O-CaO-P2O5 glasses the covalency in the in-plane V-O δ-bond decreases andπ-bonding with vanadyl oxygen increases on substitution of CaO for Na2O in the glass. Gradual addition of Al2O3 in three different Na2O-B2O3 glasses did not cause any significant change in covalency either in the δ or in theπ-bonding. These changes have been discussed in terms of possible structural units in these glasses.

A Study of Na2O-TiO2-SiO2 Glasses by Infrared Spectroscopy

The infrared absorption spectra of six Na2O-TiO2-SiO2 glasses in the frequency range of 1600 to 200 cm−1 are reported. These glasses, having a SiO2/Na2O molar ratio of 1.07 to 3.54, and containing 20 or 25 mole % TiO2, demonstrate two main absorptions at ∼950 cm−1 and at ∼450 cm−1. A weak absorption at ∼790 cm−1 becomes progressively weaker in intensity, and a weak shoulder at 1050 cm−1 appears with increasing Na2O content. The frequency of the absorption band at ∼950 cm−1 is found to decrease markedly and systematically with a decrease in the SiO2/Na2O molar ratio, whereas the frequency of the band at ∼450cm−1 shows a slight increase. The infrared results may be interpreted in terms of a lowering of symmetry occurring for the SiO4 units. The effect of TiO2 content on the relationship between vibrational frequency is discussed. The frequency composition curves for glasses containing 20 and 25 mole % of TiO2 intersect at SiO2/Na2O ratio ∼2. A reversal in the frequency vs SiO2/Na2O ratio relation was also found at SiO2/Na2O ∼2 for the sodium silicate glasses.

Effect of Alkali Oxides on the Diffusion of Helium in a Simple Borosilicate Glass

Helium permeation rates, diffusivities, and solubilities in a simple borosilicate glass containing alkali oxides were measured. The major effect of increasing Na2O content from 2 to 13 mol% is a systematic decrease in permeation rate and diffusivity, indicating that the Na+ ion is essentially filling space in the glass network. At 7 mol% alkali oxide, as the alkali‐ion size is increased, the changes in diffusivity and activation energy indicate that from Li+ to Na+ to K+, the larger ion more effectively plugs the network interstices. The size distribution of interstices in the base‐glass network is such that ions larger than K+ are too large to simply fill the network and consequently tend to spread the network as well.