The effect of composition on spinel crystals equilibrium in low-silica high-level waste glasses

The liquidus temperature (T_L) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO₂) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al₂O₃, B₂O₃, Cr₂O₃, Fe₂O₃, Li₂O, MnO, Na₂O, NiO, SiO₂, and ZrO₂. In the low-silica region, Cr₂O₃ increased the T_L substantially less, and Li₂O and Na₂O decreased the T_L significantly less than in the region with 42-56 mass% SiO₂. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25-64 °C below the T_L.     

Effect of composition on ionic transport in SiO2–B2O3–Na2O glasses

Ionic diffusion was investigated in the SiO₂–B₂O₃–Na₂O glass system over a wide composition range by impedance spectroscopy measurements. The Na⁺ cation transport mechanism was described by an interstitial pair migration model based on Frenkel defects in ionic crystals. The activation energy of the static electrical conductivity is shown to be correlated with the boron coordination number in these glasses. Published ¹¹B NMR results were used to calculate the activation energies of sodium cations acting as charge compensators for the [BO_4/2]⁻ tetrahedron and of sodium cations bonded to non-bridging oxygen atoms. These values are in agreement with the activation energies of the Na₂O–B₂O₃ and Na₂O–SiO₂ binary systems, respectively.     

X-ray diffraction studies of glasses in the systems Na2OMeOSiO2 (MeMg,Zn, Ca,Ba)

X-ray diffraction studies of glasses in the following ternary systems have been made: Na₂OMgOSiO₂, Na₂OZnOSiO₂, Na₂OCaOSiO₂ and Na₂OBaOSiO₂. The following heavy atom substitutions have been used: Ag for Na and Ge for Si. The changes in the electron radial distribution curves resulting from AgNa replacement can be explained as amplifications of relatively well-defined NaSi distances, which are nearly the same in all the glasses investigated. The GeSi substitution causes changes which can be explained on the basis of isostructural GeSi substitutions.     

A kinetic treatment of glass formation. VIII: Critical cooling rates for Na2OSiO2 and K2OSiO2 glasses

The critical cooling rates required to form glass have been measured for Na₂OSiO₂ compositions containing 15.4, 20.6, 29.9 and 34.0 wt% Na₂O and for K₂OSiO₂ compositions containing 15.3, 21.7, 34.3, 41.8 and 43.9 wt% K₂O. Pronounced minima in critical cooling rate are observed in the ranges about 25 wt% Na₂O and 33 wt% K₂O. The locations of these minima correlate with regions of low liquidus temperatures (near eutectics) in the phase diagrams.Calculations of critical cooling rates have been carried out using the analysis of crystallization statistics and the simplified model of glass formation. In both cases, the models predict well the measured critical cooling rates and their variation with composition.     

Single Crystal Growth and Pyroelectric,Dielectric, Piezoelectric,Elastic, and Thermoelastic Properties of Orthorhombic Li2SiO3, Li2GeO3, and Na2GeO3

Single crystals of optical quality of isotypic Li₂SiO₃, Li₂GeO₃, and Na₂GeO₃, space group Ccm2₁, with diameters of ca 16 mm and lengths of ca 20 mm (Li₂SiO₃) and ca 60 mm (Li₂GeO₃ and Na₂GeO₃) have been grown from the melt using the Czochralski technique. On Li₂SiO₃, Li₂GeO₃, and Na₂GeO₃ pyroelectric coefficients and complete dielectric, piezoelectric, elastic, and thermoelastic tensor properties have been determined; the latter from the temperature dependence of resonance frequencies. All crystals investigated exhibited only a small amount of 180° twins. They all possess large pyroelectric coefficients about-five times that of tourmaline. The longitudinal piezoelectric constant d₃₃₃ is about five times larger than d₁₁₁ of alpha quartz. Qualitative measurements on Na₂SiO₃ revealed similar values of pyroelectric and piezoelectric effects. The technical application of these crystals encounters some difficulties: Li₂SiO₃ is excellently cleavable parallel (010). This face contains the polar direction [001]. Na₂GeO₃ suffers from chemical decomposition in humid atmosphere and is well cleavable too. Both happens to a much less extent in Li₂GeO₃. Na₂SiO₃ proved to be hardly suitable for any application of its polar properties due to its bad chemical stability against humid air and its excellent cleavage.     

Hydrothermal Synthesis and Characterization of VSZ-3 Zeolite Crystals

Zeolite crystals (named here VSZ-3) synthesized at 350°C by hydrothermal method are illustrated and described. These crystals are shown to be analcime type zeolites. It is established that their size is the largest among the zeolite crystals ever reported, and are stable upto 1000°C. The VSZ-3 crystals are prismatic pyramidal and needle-like. They are characterized by X-rays, SEM, TGA, DTA and IR. Their chemical composition is shown to be 5.95 SiO₂ ṁ Al₂O₃ ṁ 0.91 Na₂O ṁ 0.17 H₂O. Mechanism of growth of these crystals is explained.     

Infrared and Raman spectroscopy of mullite‐type Bi2Ga4O9

Mullite‐type Bi₂Ga₄O₉ single‐crystals were grown by the top‐seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro‐Raman spectra were acquired at room temperature. Powder IR spectra of sol‐gel‐derived samples were also recorded. Using model calculations and comparison to other mullite‐type compounds, bands at ∼ 850 – 400 cm^‐1 could be assigned to stretching and bending vibrations of the structural GaO₄ and GaO₆ units. Low‐energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi₂Ga₄O₉ display close similarities to those of the mullite‐type alkali gallates (9Ga₂O₃ · Rb₂O), while their differences to those of mullite sensu stricto (3Al₂O₃ · 2SiO₂ and 2Al₂O₃ · SiO₂, repectively) are assigned to Si‐O stretching vibrations of the corresponding tetrahedral units. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of xNa2O − (1 − x)SiO2 gels for the gel-glass process II. The gel-glass conversion

SiO₂ gels containing from 3.7 to 40 mol.% Na₂O have been synthesized by the hydrolysis and polycondensation of metal organic precursors. The effect of Na₂O content on thermal processing variables includes: evacuation of residual organic residues, decomposition of carbonates (T_ce), beginning of densification (T_db) and initiation of crystallization (T_ci). Thermal control of the gel-glass conversion is shown to be a function of Na₂O content and ΔT_v = T_ci ? T_db. At high Na₂O content (> 33 mol.%) ΔT_v is very small whereas at the Na₂OSiO₂ eutectic compositio it is nearly 200°C. By using this method Na₂OSiO₂ glasses are obtained in the range of 440–640°C.     

Growth,Morphology, Structure and Properties of Na3BaCl5 2H2O Crystals

Single crystals of Na₃BaCl₅ 2H₂O were obtained from saturated aqueous solutions at two different temperatures (27° C and 32° C). The crystal size increases with increasing temperature. The crystals obtained were subjected to a systematic morphological, X-ray and thermal analyses. The study of as-grown crystal morphology and surface morphology of Na₃BaCl₅ 2H₂O crystals clearly indicate the requirement of a slow rate of evaporation at temperatures 27 to 28° C, moderate supersaturation in order to obtain high quality single crystals of Na₃BaCl₅ 2H₂O. The X-ray diffraction studies give the following cell parameters for the title compound: monoclinic, P21/n, a = 8.5773(9), b = 9.5502(4), c = 5.2873(3) A, β =92.069°, V = 432.8 A³, Z = 2. The study of TGA curves indicate the occurrence of dehydration process at around 200° C and not the decomposition of the compound. Similarly, the low temperature DSC study indicates a thermal anomaly at 267 K, and the high temperature DSC study (323 K to 873 K) indicates the transition from dihydrate to monohydrate and in turn anhydrous state at 454.6 K for Na₃BaCl₅ 2H₂O crystals. Thus both the TGA and DSC curves conclude that the Na₃BaCl₅ 2H₂O crystals contain two molecules of water of crystallization and its molecular formula is Na₃BaCl₅ 2H₂O.     

NMR studies on rapidly solidified SiO2Al2O3 and SiO2Al2O3Na2O-glasses

²⁷Al and ²⁹Si MAS NMR studies were performed on roller-quenched SiO₂Al₂O₃-glasses with Al₂O₃ contents ranging from 10 to 60 mol% and on SiO₂Al₂O₃Na₂O glasses containing 10 mol% Al₂O₃ and 2.5 to 10 mol% Na₂O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO₂Al₂O₃Na₂O the 30 ppm peak decreases to zero as the Na₂O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al₂O₃ over Na₂O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na₂O.     

Medium range order in sodium silicate glasses: role of the network modifier

The effect of different concentrations of the network modifier Na₂O on the position of the Boson peak, observed in the low frequency Raman scattering experiments, is analyzed. Glasses containing 25% Na₂O (Na₂O · 4SiO₂) and 33% Na₂O (Na₂O · 2SiO₂) are compared with pure SiO₂ glass. The observed shift of the Boson peak is interpreted in terms of a change of a correlation length, ℓ, corresponding to some medium range order. This length, ℓ, decreases when the amount of sodium oxide increases.     

Synthesis and characterization of ZSM-8-type zeolite crystals

Procedure for hydrothermal synthesis of ZSM-8-type zeolite crystals, using TEA—OH as a template, in the system having molar composition 16.2 (Na₂O) — Al₂O₃ — 117 (SiO₂) — 4.8 (TEA)₂O — 3887 H₂O at 170 °C is described. Results of characterization of these crystals by XRD, IR, EDAX, SEM, TGA, and adsorption studies are described and discussed. X-ray diffraction studies establish that the crystals are ZSM-8-type with structure similar to that of ZSM-5-type crystals. Crystals have prismatic bipyramidal morphology with average size 18–25 microns. Degased calcined samples adsorb xylenes in the order p > m > 0. Pore length per unit cell, estimated from n-hexane adsorption studies, is 46 Å.     

Application of D‐optimal experimental design in nano‐sized ZSM‐5 synthesis for obtaining higher crystallinity

D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, SiO₂/Na₂O and TPABr/TPAOH ratio parameters was used to optimize the experimental parameters by the analysis of variance (ANOVA). The effects of above mentioned ratios in the initial synthetic mixture on the crystallinity of the ZSM‐5 zeolite were studied. The synthesized samples were characterized by XRD, FE‐SEM, and TEM analysis. Fischer test results showed that SiO₂/Al₂O₃ and H₂O/SiO₂ molar ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variable was that of template/SiO₂ and Na₂O/SiO₂ molar ratios. The optimum composition of the gel compound to achieve relative maximum crystallinity is SiO₂/Al₂O₃ = 99.96, template/SiO₂ = 0.16, H₂O/SiO₂ = 34.68, Na₂O/SiO₂ = 0.02 and TPABr/TPAOH = 1.44.     

Effect of Al2O3 on the viscosity and structure of calcium silicate-based melts containing Na2O and CaF2

The effect of Al₂O₃ on viscosity in the calcium silicate melt-based system containing Na₂O and CaF₂ was investigated and correlated with the melt structure using FTIR (Fourier transform infrared) spectroscopy, XPS (X-ray photoelectron spectroscopy), and Raman spectroscopy. Substituting SiO₂ with Al₂O₃ modified the dominant silicate network into a highly structured alumino-silicate structure with the aluminate structure being particularly prevalent at 20 mass% of Al₂O₃ and higher. As the melts become increasingly polymerized with higher Al₂O₃ content, the fraction of symmetric Al–O⁰ stretching vibrations significantly increased and the viscosity increased. XPS showed a decrease in the amount of non-bridged oxygen (O^?) but an increase in bridged oxygen (O⁰) and free oxygen (O^2?) with higher Al₂O₃. Although changes in the structure and viscosity with higher CaO/(SiO₂ + Al₂O₃) were not significant, the symmetric Al–O⁰ stretching in the [AlO₄]^5?-tetrahedral units decreased. The apparent activation energy for viscous flow varied from 118 to 190 kJ/mol.     

The Effect of Different Inorganic Salts on the Growth Rate of NaCl Crystallized from Sea Water

A comprehensive experimental study on the effect of fourteen different inorganic salts on the growth rate of NaCl single crystals is presented. The fourteen different inorganic salts are chosen as they are present in Chinese sea water. The impurity content of each salt has been varied according to its presence in the natural sea water. The impurities are differentiated in groups related to their effect on the growth rate of NaCl. The examined impurities are: MgCl₂ · 6 H₂O, KCl, SrCl₂, NaBr, Nal, NaF, Na₂SO₄, NaBO₂ · 4 H₂O, Na₂CO₃, Na₂SiO₃ · 9 H₂O, ZnSO₄, CuSO₄ · 5 H₂O, PbCl₂, and K₄Fe(CN)₆.     

Mechanical properties of single crystalline and glassy lithium triborate

Mechanical properties of LiB₃O₅ single crystal plates with different orientation as well as of glass with the same composition have been investigated. The nano‐ (H) and microhardness (H_M), the reduced Young's modulus (E_r) and the crack behaviour of the samples were studied. Both hardness and Young's modulus of glass appeared smaller in comparison to corresponding single crystal data (H ∼ 7 – 8 GPa, H_M ∼ 6 GPa, E_r ∼ 70 – 80 GPa for glass and H ∼ 10 – 15 GPa, H_M ∼ 6 –11 GPa, E_r ∼ 93 – 155 GPa for single crystal). H, E_r, and the plane of crack propagation proved orientation‐dependent. Cracks in the glass sample were not observed up to 0.49 N microindentation load, whereas for the single crystal the cracks appeared already at 0.098N. In single crystals the observed cleavage planes {211} and/or {412} are oriented nearly parallel to planes of B‐O rings. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of phase separation on crystallization behavior

The effects of phase separation on the kinetics of crystal growth have been investigated for three compositions in the Na₂OSiO₂ system, containing about 1.5, 10 and 15 mol% Na₂O. In the two cases for which reliable data could be obtained over the full range of temperature (10 and 15% Na₂O), the measured growth rates are independent of time, for crystallization temperatures within as well as outside the miscibility gap. In both cases, the growth rate versus temperature relations are continuous through the region of the immiscible boundary. These results are related to previous data on the effects of phase separation on viscosity in the Na₂OSiO₂ system and on nucleation and crystallization in the Li₂OSiO₂ system. It is suggested that transport at the crystal-liquid interface in a phase-separating system involves different types of atomic rearrangements than those involved in viscous flow.     

A discussion about the structural model of “nuclear magnetic resonance studies of glasses in the system Na2OB2O3SiO2”

The structural model for the system Na₂OB₂O₃SiO₂ suggested by Yun, Feller and Bray is discussed. A different structural model is suggested in this paper the results of which are in better agreement with experiment.     

Fracture toughness-composition relationship in some binary and ternary glass systems

Measurements of the critical stress intensity factor K_Ic are reported for glasses in the Na₂OSiO₂, PbOSiO₂, ZnOB₂O₃, PbOB₂O₃, Na₂OGeO₂ and 20Na₂O?(80 ? x) B₂O₃ ? xSiO₂ systems. The variations of K_Ic with composition are not directly related to the simultaneous variations of Young's modulus. A tentative interpretation is given.     

Chemical durability of Na2OCaOSiO2 glasses in acid solutions

The resistance of Na₂OCaOSiO₂ glasses to acid solutions has been studied. The compositions studied were Na₂O · 4SiO₂, Na₂O · x CaO · (4?x) SiO₂ and a common electrode glass containing 22.63Na₂O and 5.58 CaO, mol%. The reaction was made at 40°C for about 3 h in 1N solutions of HCl, HNO₃ and H₂SO₄. Powdered glass samples were used and the reaction was followed by analyzing the solution for soda, lime and silica.The extraction rates of each constituent were measured. The effect of acid concentration was also studied for each glass using 10^?3–10N solutions of the three acids for a fixed time. The quantity of calcium extracted increased slowly at first with increasing calcium content in the glass, but rapidly when the lime content exceeded ≈10 mol%. Above this concentration, both calcium and sodium appears to pass into solution in the same proportion in which they are present in the glass. The extraction rate was found to depend on the type and concentration of the acid used, being least in H₂SO₄ and much higher and almost equal in both HCl and HNO₃.An attempt was made to correlate the results of decomposition of the soda-lime-silica glasses to their membrane potentials in acidic solutions.