Na2O-SiO2 System Research Articles

Energy Relations in Alkali Silicates by Solution Calorimetry

The energy relations in some alkali silicate glasses and crystals of the same composition at 25°C are reported. The data have been obtained by solution calorimetry in 5% HF aqueous solution and, for Na2O-SiO2 system, also in distilled water.The results of these experiments in 5% HF aqueous solution are summarized as follows. Heats of solution per SiO2 obtained for both crystals and glasses in the systems Li2O-SiO2, Na2O-SiO2 and K2O-SiO2 generally show the linear relationship with mole% alkali oxide in the region above 33.3mole% alkali oxide, and show the departure from linearity in the region below 33.3mole% alkali oxide. Heats of solution decrease in the order Rb>K>Na>Li in all compositions. The values of intersecting points obtained by extrapolating the straight line to the ordinate correspond to the heat of solution of Si-O-Si network of the alkali silicates. These points gather at the value ca. 11kcal/SiO2 in crystals and in Na2O-SiO2 and K2O-SiO2 glasses; this value is ca. 1/3 of the heat of solution of quartz. The enthalpy differences between these glasses and crystals of the same composition decrease in the order Li>Na>K.From the results of experiments of solution calorimetry in distilled water in the system Na2O-SiO2, it has been found that the sodium component is dissolved and weak-points in Si-O-Si bonds are broken to form poly-silicic acids. The average number of Si contained in a poly-silicic acid discrete anion formed by the dissolution of crystals are 2 to 6, slightly larger than the case formed by the dissolution of glasses. These results will be useful to elucidate the nature of bonds in glassy state.

O-R Bond Energy in Alkali Silicates (R<sub>2</sub>O-SiO<sub>2</sub>)

In order to obtain the knowledge of the bond energy relations in alkali silicate glasses and crystals, a series of thermochemical calculations was carried out.The experimental data used for the calculation were the previously reported values of the heat of solution of silicates in high alkali region and the present values in low alkali region. From the reexamination of the data the previous discussion on the Si-O-Si bond strength was partly amended. On the basis of the present results the heats of formation of the glasses and crystals were calculated, and the equations for calculating the O-R bond energy were derived from the heats of formation and other thermochemical data.The calculated values of O-R bond energy of glasses and crystals in the systems Li2O-SiO2, Na2O-SiO2 and K2O-SiO2 were listed and discussed in comparison with the coulombic energies. The Si-O-R and Si-O bond energies were also calculated from the total energy and the O-R bond energy by applying the thermochemical cycle. It was shown that the differences between the bond energies of Si-O-Si and of Si-O were generally small.

Effective cross section for ?-ray-induced displacement of atoms in some two-component glasses

The article describes a calculation of the theoretical effective cross sections for the formation of defects resulting from the 1.25- MeV γ-ray-induced displacement of atoms which are constituents of the glass systems Na2O-SiO2, K2O-SiO2, Na2O-TeO2, Cs2O-TeO2, V2O5-TeO2, and WO3-TeO2.

Solubility Dependence of Ruthenium Volatilisation from Glass

Solubility dependence of ruthenium volatilisation from glass at glass forming temperature and the effect of time and temperature on the rate of volatilisation were investigated. Simple glasses in the system Na2O-SiO2 were considered for the study. Volatilisation runs were carried out at different temperatures in an air flow of 118 cm/min and the surface of glass subjected to evaporation was 2.73 sq. cm.The plot of ruthenium volatilisation loss vs solubility at 1100°C showed a direct relation between them upto 38 mole percent Na2O content and the curve was a straight line passing through the origin with a slope of 1.64 X 10-2 mg/ppm. For the glasses, with more Na2O, volatilisation was believed to depend on solubility as well as on oxygen diffusion. Volatilisation at different temperatures showed that it followed the Arrhenius law and the calculated activation energy for evaporation was 18.65 K Cal/mole. Rate of ruthenium volatilisation decreased with time and attained a constant value as soon as ruthenium lost due to evaporation was made up by more ruthenium entering into solution.It was suggested that ruthenium volatilisation might be minimised by rendering the ruthenium insoluble in glass either by the selection of suitable glass composition or by the use of some reducing agents.

Na2CO3-SiO2 Reaction

The reaction in a solid state of mixture of powdered sodium carbonate and silica systems in various mole ratios was followed by thermogravimetric analysis (TGA), X-ray diffraction and RI-tracer technique. The powders consisting of coarse particles of silica in a fine grained matrix of sodium carbonate were used.The isothaml TGA shows that the reaction does not exactly follow simple diffusion mechanism at the temperature range 750∼835°C. The rate data are best described by the Crank equation which is given to the reaction which is controlled both by the diffusion of one of the reactant through a product layer on the surface of the second spherical reactant and by the rate of phase boundary reaction at their reactant interface:α=Mt/M∞=1-Σ∞n=16L2e-βn2Dt/a2βn2(βn2+L(L-1))where Mt/M∞ is the fraction of reaction, D is the diffusion coefficient, βn are the positive root of the equation, βn·cotβn+L-1=0, L=a·k/D, a is the radius of the particle, k is the rate constant of the phase boundary reaction.The diffusion coefficient calculated from penetration of 22Na into the fused silica is 5, 0.10-11cm2/sec and well agrees with the diffusion coefficient calculated by the Crank equation from the present data. Since the self-diffusion coefficients of sodium ions in the glass Na2O-SiO2 system are in the order of 10-7-10-8cm2/sec at the temperature range 300∼450°C and their activation energies are about 15kcal/mole, it is found that the diffusion of sodium ions does not control this reaction.In atmosphere, meta-silicate is the primary reaction product but this disappears somewhat later. In vacuum, meta-silicate is scarcely detectable, and the rate of its reaction is much smaller than in air, and their behavior are similar to the reaction of Li2CO3-SiO2 system.The reaction scheme in air will be represented as follow:Na2CO3 2Na2O·SiO2 Na2O·SiO2 SiO2Diffusion 2Na++O2- 2Na++O2-Phase boundary Na2CO3 Na2O·SiO2 SiO2reactions -CO2 +Na2O + Na2O=Na2O =2Na2O·SiO2 =Na2O·SiO2It is inferable, therefore, that the diffusion of oxygen ions through the product layer of silicate and the phase boundary reaction control the whole reaction.

Infrared spectra up to 25? of crystalline and glassy silicates from the Na2O-SiO2 system

Infrared spectra up to 25? of crystalline and glassy silicates from the Na2O-SiO2 system

Viscosity and the structure of molten silicates

A mgnetically controlled null-point modification of the rotating crucible viscometer has been devised which enables measurements of the viscosity of liquids to be made at maximum temperatures of 1850° C. The instrument has been applied to measure the viscosity of the system CaO -SiO 2 over the composition range 30 to 58 mole % CaO. The flow is Newtonian . The viscosity isotherms are smooth functions of composition and donot exhibit the inflexion found in previous work carried out in (attackable) graphite crucibles. Up to 1700° C the energy of activation is constant for all systems. For compositions containing more than 38-8 mole % CaO, the energy of activation falls at temperatures 1700° C. The energy of activation is small compared with that for flow in liquid silica. Over the composition range studied it falls little (45 to 35 kcal mole -1 ) with increase of CaO content. The energy of activation observed is inconsistent in magnitude and variation with composition with the current theory of the structure of liquid silicates and glasses due to Endell & Hellbriigge. In liquid SiO 2 and systems containing less than about 12 mole % metal oxide the flow unit is SiO 2 . At about this composition a fundamental change occurs in the structure of the melt. For systems with a metal oxide content of more than about 12 mole % the flow unit is a discrete silicate anion, the size of which increases regularly with increasing concentration of SiO 2 . The simplest discrete silicate anions compatible with valency, stereochemical and electro-neutrality considerations are deduced for various compositions of the liquid. The structure thus suggested is consistent with observations on the viscosity of silica and of the system Na 2 O-SiO 2 ; and with results on the temperature of maximum density in silica, X-ray diffraction in glasses, the solubility of CaF 2 in silicates, and the partial molar volume results for simple alkali metal glasses.

Reactions of vitreous silicates and aluminosilicates with aqueous solutions Communication I. Reactions of vitreous sodium silicates with water and with hydrochloric acid solutions

1. A study has been made of the action of water and hydrochloric acid sol~utions on vitreous, sodium silicates having compositions correspondlng to the invariant points on the phase diagram of the system Na2O-SiO2, to intermediate points, and also to points representing high silica contents. 2. The process of interaction of sodium silicates with water can be broken down into two stages: exchange of sodium ions of the glass for hydrogen ions of the solution, resulting in the formation of a residual layer of silica acid, which together with the silica of the original glass comprises a protective film on the surface; and reaction of the protective layer with the alkaline solution that has been formed, resulting in removal of silicic acid from the surface by dissolution 3. In the case of sodium silicates having a low silica content, a kinetic equilibriumi s established between the primary and secondary reactions, so that dissolution of the glass appears to take place. In the case of sodium silicates of high silica content, the main process is the leaching of Na2O from the glass. 4. When sodium silicates are treated with hydrochloric acid solutions, transfer to the solution of SiO2 lags behind that of Na2O to a greater extent than in the case of water treatments. In the case of glasses having a silica content greater than that of disilicate, no SiO2 could be detected in the solution. 5. The relation between the logarithms of the amounts of components passing into solution and the molecular percentage of silica the glass is represented over the range of compositions examined by smooth curves or (in the case of acid treatment) by straight lines, without appreciable deviations at compositions corresponding to invariant points on the phase diagram of Na2O-SiO2. 6. With rise in temperature the amounts of the components passing into solution increase considerably, and at the same time the boundary of the region of soluble silicates moves in the direction of glasses of higher original silica content.

The Role of Titania in Silica Glasses

A series of glasses in the system Na2O–SiO2–TiO2 were melted. Density measurements and refractive indices were determined. Molar refractions of the various glasses were calculated using the Lorentz‐Lorenz relationship. The partial molar refraction of TiO2, as determined in glass, corresponds closely with the values obtained from crystalline compounds and indicates that the Ti4+ ion exists in sixfold coordination. Interionic distances were calculated using the Kordes equation, the calculated Si–O distance being 1.60 a.u. and the Ti–O distance, equal to 2.01 a.u.

二元系溶融スラツグの電氣傳導度

In order to study the properties of molten slags, it is one of the most important problems to measure their electrical conductivity, which shows most probably that they consist of several ions, This paper deals with the electrical conductivity of the systems Na2O-SiO2, CaO-SiO2 and MnO-SiO2 in molten state.The specific conductivities (κ) of these systems are of the order of 0.1-1 Ω-1 cm-1, and increase with temperature. The conductivity of the system MnO-SiO2 suddenly decreases in the neighbourhood of the solidifying temperature. At constant temperature the conductivity rises with inrrease of basic oxides. Further logκ is linear, being plotted against 1/T (T: absolute temperature).Additionally we attempted the electrolysis in the system CaO-SiO2. The concentration of CaO is larger at positions near the cathode than near the anode. The result indicates that Ca++ migrates to the cathode.The conduction mechanism is ionic, and refering to the specific conductivity of fused salts, it has heen established that molten slags are highly dissociated into ions.The mechanism of viscosity and electrical conductivity are described on the basis of the model of quasi-crystal. The linear relationship between logκ and 1/T can be shown theoretically. The activation energy of viscosity is greater than of electrical conductivity. This fact indicates that viscosity is mainly controlled by the large silicate ions, while perhaps the conduction by the cations.The fact that electrical conductivity rises with increase of basic oxides is partly due to the increase of the numher of cations. Further it is also controlled by the mobility of ions.In the system CaO-SiO2 the rate of the increase of the conductivity with CaO % decreases at high CaO contents. This may be due to the fact that the strong bonds are formed between Ca++ and SiO44-.

The A Review of the System Na2O—SiO2—H2O.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe A Review of the System Na2O—SiO2—H2O.J. H. WillsCite this: J. Phys. Chem. 1950, 54, 3, 304–310Publication Date (Print):March 1, 1950Publication History Published online1 May 2002Published inissue 1 March 1950https://doi.org/10.1021/j150477a002RIGHTS & PERMISSIONSArticle Views150Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (330 KB) Get e-Alerts

SOME PROPERTIES OF SODA‐SILICA GLASSES AT HIGH TEMPERATURES*

AbstractA study is made of density, expansion, surface tension, parachor, and viscosity data for glasses in the system Na2O‐SiO2 within the temperature range 900° to 1400°C. The best values have been selected and correlated with composition.

Equilibria in the Systems Na2O–SiO2–H2O and Na2O–Al2O3–H2O at 25°C.

Equilibria in the Systems Na₂O–SiO₂–H₂O and Na₂O–Al₂O₃–H₂O at 25°C.