Optimal Strategy Searching for a Component Composition of Synthetic Sodium Silicates Used in the Production of Microspheres

The results of synthesis of a sodium silicate batch for microspheres in an aqueous medium using sol-gel technology are described. It is demonstrated that crystalline phases marked on the Krachek diagram have been formed without high-temperature treatment. A nomogram has been developed, which is recommended for designing glasses to model a phase composition based on a preset silica modulus and a structure cohesion factor taking into account the effect of Na₂O and SiO₂ on glass properties, to determine the range of probable glass formation, and to optimize the technological process.     

Understanding the structural origin of intermediate glasses

Intermediate glasses show nearly constant elastic moduli with temperature and/or pressure. These glasses would prove useful in designing a-thermal optical fibers for enhanced telecommunication, fiber sensing applications, and in designing glass products for applications where a broad range of thermal and mechanical stimulation is expected. In this study, intermediate glasses belonging to the Na₂O–SiO₂, Na₂O–Al₂O₃–SiO₂, and Na₂O–TiO₂–SiO₂ glass systems were identified from in situ high-temperature Brillouin light scattering (BLS) experiments. Glasses important for engineering applications like the international simple glass (ISG) and the less brittle glass (LBG) were also found to exhibit intermediate behaviors. In situ Raman spectroscopy was used to investigate their structural evolution from room temperature to temperatures beyond T_g. Raman spectra along with molecular dynamics simulations revealed common structural signatures that intermediate glasses with different compositions possess. Our study showed that the intermediate elastic behaviors come from a delicate balance between the stiffening effect associated with conformation changes in the medium-range flexible rings and the softening effect due to the weakening of short-range chemical bonds with temperature.     

REPRESENTATION OF DENSITY AND OPTICAL PROPERTIES OF TERNARY SILICATE GLASS SYSTEMS

A general procedure is outlined for the preparation of contour maps representing such properties as density, refractive index, and Abbe value for ternary glass systems in which one component is silica, using previously published equations and constants. The procedure is illustrated by application to the Na₂O–MgO–SiO₂ and Na₂O–CaO–SiO₂ systems.     

Generalized Universal Calculation of SiO2 Diffusion Coefficients in Melts of the Na2O – SiO2 System

Experimental data are summarized, and a generalized formula for the calculation of SiO₂ diffusion coefficients in melts of the Na₂O – SiO₂ system is obtained. The formula is recommended for the practical calculations of the process of melting impure sodium disilicate.     

Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m³ and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na₂O·mSiO₂·nH₂O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na₃(CO₃)(HCO₃)·2H₂O, formed during interaction between unbound NaOH and CO₂ and H₂O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.     

Synthesis of a mesoporous material from two natural sources

Mesoporous materials were obtained from two natural silica sources, diatomite and pumicite, under hydrothermal conditions, autogenic pressure and in presence of the surfactant cetyltrimethylammonium bromide (CTAB) as the template. Using diatomite, a temperature of 383 K and the following molar ratios in the initial reaction gel: SiO₂/Al₂O₃ = 8.86; CTAB/SiO₂ = 0.1; Na₂O/SiO₂ = 0.10–0.25 and H₂O/Na₂O = 250–300, the mesoporous material MCM‐41 was obtained in a reaction time of 48 h. When pumicite was used, a mesoporous material was obtained in a reaction time of 96 h, a reaction temperature of 423 K and an initial reaction gel with the following molar ratios: SiO₂/Al₂O₃ = 8.86; CTAB/SiO₂ = 0.1; Na₂O/SiO₂ = 0.25 and H₂O/Na₂O = 330. Copyright © 2006 Society of Chemical Industry     

THE EFFECTS OF SODA,BARIUM, AND ZINC ON THE ELASTICITY AND THERMAL EXPANSION COEFFICIENTS OF GLASS1

An investigation is made of the effect, on the elasticity and expansion behavior of a base glass containing 60%, SiO₂ and 40% Na₂O, of replacing Na₂O in this glass by ZnO and BaO, respectively. The elasticity and expansion factors of the two oxides, ZnO and BaO, are determined and compared with published results. Elasticity factors of 80 for ZnO, 35 for Na₂O, and 55 for BaO are proposed. Cubical coefficient of expansion factors of 12.5 Na₂O, 5.7 for BaO, and 1.85 for ZnO are also proposed. Neither the factors of Winkelmann and Schott nor those of English and Turner fit very well the results reported in this paper.     

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li₂O–K₂O–Na₂O–CaO–MgO–ZrO₂–Al₂O₃–P₂O₅–SiO₂ glass system has been reported here. Increased amount of MgO enhanced the participation of Al₂O₃ as a glass network former along with [SiO₄] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (～10 GPa) and elastic modulus (～127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.     

Glass-forming region and enhanced Bi NIR emission in sodium tantalum silicate laser glass

Bismuth (Bi)-doped glasses and fibers are of current interest as promising active media for new fiber lasers and amplifiers due to their 800-1700 nm near-infrared (NIR) emission. However, the optically active Bi centers in silica are easily volatilized during high-temperature fiber drawing, which results in low Bi doping concentration and low gain NIR luminescence. Here, we explored the glass-forming region in a model glass system of sodium tantalum silicate (Na₂O-Ta₂O₅-SiO₂) glass and attained suitable glass host for enhancing Bi NIR emission, right followed by detailed analysis on optical and structural characterization. Glass-forming region roughly lies in where Ta₂O₅ ≤ 30 mol%, SiO₂ ≥ 40 mol%, and Na₂O ≤ 40 mol%. Not only is glass-forming ability improved but also Bi NIR emission is enhanced (~60 times) by the introduction of Ta into glass network. Dissociated Na cations are restricted beside Ta, the high-field-strength element, so that the negative impacts of Na cations on glass formation and Bi NIR emission are weakened, which is responsible for the highly enhanced Bi NIR emission. This work helps us understand the glass-forming of tantalum silicate glass systems and luminescent behaviors of Bi. Hopefully, it could contribute to designing the Bi-doped laser glasses and high gain fibers with stable luminescent properties in future.     

Induction plasma synthesis of nanometric spheroidized glass powder for use in cementitious materials

Because of its high throughput, Inductively-Coupled Plasma (ICP) torch can commercially provide an added value to waste glass (WG). It vaporizes WG into nanometric spheroidized glass powder (SGP) that could be used as a cementitious material. Changing the plasma gas (N₂ vs O₂), quench flow rate, pressure and WG feed rate induce variations on the particle size distribution and chemical composition. Using Field Emission Gun Scanning Electron Microscopy (FEGSEM), Brunauer, Emmet and Teller (BET) method, nano phase separation and Inductively-Coupled Plasma-Mass Spectrometry (ICP-MS), low quench gas, pressure and WG feed rate increase the nanometric content and specific surface of SGP. The use of O₂ increases silica (SiO₂) and decreases the sodium oxide (Na₂O) content of SGP. The use of N₂ rather demonstrates enrichment of SGP in Na₂O in the cold reactor zones. This study shows that the nucleation theory of a crystalline material can be applied to an amorphous material.     

The effect of alkali metal oxide on the properties of borosilicate fireproof glass: Structure,thermal properties,viscosity, chemical stability

The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R₂O–CaO–B₂O₃–SiO₂) systematically. Because the glass would emulsify when Li₂O was added to the glass batch, this article did not discuss Li₂O. The results showed that when the amount of Na₂O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na₂O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased.     

On the Glass Formation in the Na2O–SiO2–H2O System

The glass formation in the Na₂O–SiO₂–H₂O system is considered in the framework of the free volume theory of glasses. The boundaries of the glass transition range in the given system are determined from the dependences of the specific volume and the degree of connectivity on the water content in the system. The differences in the structure of hydrated glasses prepared by different methods are revealed. It is demonstrated that the molecular packing coefficients of the structures formed by drying of sodium silicate solutions are smaller than those of glasses prepared by hydration of anhydrous glasses. The densities are determined and the molar volumes are calculated for hydrated glasses in the Na₂O–SiO₂–H₂O system with a water content of 12–23 wt % (33–51 mol %) at a constant molar ratio SiO₂ : Na₂O = 2.8. The correlation relationship for the partial molar volume of water as a component of hydrated glasses is proposed as a function of the water content in the system. The use of this dependence allows one to calculate the molar volumes (densities) of hydrated glasses with different water contents.     

Inorganic binders for graphite-containing crucibles

Some technological features of obtaining acid silica sol from slags of ferroalloy production are considered. A new binder (Vanal analog) was synthesized on the basis of the V₂O₃−Al₂O₃−TiO₂−SiO₂−Na₂O system. Advantages of using slag binders in the fabrication of graphite-containing crucibles are demonstrated. Articles using these binders exhibit lower open porosity, gas permeability, specific volume, and permeable-pore size. The thermal stability of crucibles for casting black silumin, fabricated using the silica sol binder, was 3.8 times that of crucibles with the usual binder. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 27–30, March, 1997.     

EFFECT OF BARIUM OXIDE AND ZINC OXIDE ON PROPERTIES OF SODA-DOLOMITE LIME-SILICA GLASS*

To a base glass containing 14% of sodium oxide, 12% of dolomite lime, and 74% of silica, barium oxide and zinc oxide, respectively, were systematically substituted for (a) Na₂O, (b) CaO.MgO, and (c) SiO₂ in amounts of 1, 3, and 5%. The effects of these substitutions on such physical properties as liquidus temperature, viscosity, deformation temperature, density, fiber softening point, coefficient of expansion, and the resistance of the glasses to dilute acid and distilled water are presented.     

Vibrational spectra and dissociation of aqueous Na2SiO3 solutions

To facilitate molecular spectroscopic observation of the mysterious transition of dissolved sodium silicate molecules into nanoparticles of desired silica gel and zeolite structures, the IR and Raman spectra of Na₂H₂SiO₄ monomers are studied here in details. It is demonstrated that the 3–0.2 mol/L aqueous solutions of Na₂SiO₃ and Na₂SiO₃ × 9H₂O contain mostly Na₂H₂SiO₄ monomers dissociated about 30%–80%, respectively. In contrast to the common belief the Si–O vibrations of these monomers depend on their dissociation level generating FTIR and Raman bands which are frequently associated with polymer silica structures in the current literature. To stay consistent with the molweight and dissociation measurements, these vibrational assignments are revised in this paper. Some unique and unexpected effects of D₂O used instead of H₂O as solvent are also reported.     

Crystallization of zeolite L from Na2O-K2O-Al2O3-SiO2-H2O system

Zeolite L powder was prepared from the substrate mixture of Na₂O-K₂O-Al₂O₃-SiO₂-H₂O system at temperatures of 373-443 K. In order to investigate the factors which influence the synthesis outcome, a reference system which yields zeolite L in a reproducible manner was chosen and subjected to controlled changes in synthesis parameters. The crystalline zeolite L samples obtained were characterized by elemental chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). It was established that phase purity, morphology, and the size of crystals of crystalline product were affected by molar ratios of the substrate, such as SiO₂/Al₂O₃, (K₂O+Na₂O)/SiO₂, Na₂O/(K₂O+Na₂O), and H₂O/(K₂O+Na₂O). Amorphous silica powder (Zeosil) was the preferred silica source, and the crystallization rate was promoted by introducing gel aging, seeding, and rapid heating rate.     

Certain Physical Properties of Binary Glasses Depending on Their Structural Specifics

The concept of structural elements, whose interaction determines glass properties, is used to interpret the regularities of the dependence of the refractive index in binary glass on glass composition, certain results of the mass-spectrometric analysis of the glasses vapor in the Rb₂O - B₂O₃ system, and the data on small angle x-ray scattering for glasses in the Na₂O - SiO₂ and Li₂O - SiO₂ system. Methods for estimating the refractive index of binary glasses depending on their composition and structure are proposed and examples of such calculations for alkali-silicate glasses are given.__________Translated from Steklo i Keramika, No. 1, pp. 8 – 11, January, 2005.     

Effect of BaO ratio on the structure of glass–ceramic composite materials from the SiO2–Al2O3–Na2O–K2O–CaO system

This article focused on effect of the content of barium oxide on microstructure of the glass–ceramic materials based on the system SiO₂–Al₂O₃–Na₂O–K₂O–CaO. The following characterisation techniques have been used: X-ray diffraction (XRD), scanning electron microscopy with micro-analyser (SEM–EDS), mid-infrared analysis (MIR), far-infrared analysis (FIR) and Raman Spectroscopy. Significant differences were observed in microstructure of silica–alumina network of glassy phase and phase composition related to changes in the amount of the barium oxide additive. Discussed results are part of a larger project implemented under the PBS Applied Research Programme, in order to determine the compositions of glass–ceramic materials with potential application as a chemically resistant hard coatings or/and resistant to thermal shock or as construction materials.     

THE DEVITRIFICATION OF SODA-LIME-SILICA GLASSES1

The isotherms and boundary curves in that portion of the ternary system Na₂O-SiO₂–CaO.SiO₂–SiO₂ of direct application to glass technology, namely, from 64 to 78% SiO₂, 0 to 20% CaO, including the whole of the field of the compound Na₂O.3CaO.6SiO₂, and portions of the adjoining fields of Na₂O.2SiO₂, Na₂O.2CaO.3SiO₂, CaO.SiO₂, tridymite, and quartz, have been determined with greater precision than in a previous study² by greatly increasing the number of mixtures studied, and thereby decreasing the interpolation necessary in the interpretation. An extended discussion is given of the devitrification of glass, in which it is shown that the liquidus temperature is the only datum point which is solely a function of glass composition, and is unaffected by the past history of the glass or by fortuitous circumstances at the time devitrification is taking place. At the liquidus the first trace of crystalline phase is in equilibrium with the glass; above the liquidus the glass will dissolve any such crystals which may have been formed at some previous time, but new crystals cannot form; while only below the liquidus is there a tendency for crystals to separate. The driving force causing this reaction is derived from the difference in free energy between the unstable glass and the stable aggregation of crystalline phases, and this force is opposed by a resistance of the nature of a viscosity. The dissociation in the liquid phase of the compounds which separate on devitrification diminishes the rate at which the devitrification equilibrium is reached, and increasing the complexity of the glass will have a similar effect. The excess in surface energy at the interface glass-crystal may have an influence at the instant of formation of the first infinitesimal crystal, hut after the crystal has grown to a dimension appreciably greater than the sphere of molecular action the excess energy at this interface ceases to be of importance. The only surface tension measurements which have been made on glass refer to the interface glass-air, and the excess energy at this interface has no necessary correlation with the devitrification process.