Thermal stability of Li2O–SiO2–TiO2 gels evaluated by the induction period of crystallization

To evaluate the thermal stability of materials, various criteria have been used. Not only the simple parameters, as characteristic temperatures, but also the combined criteria E/RT _p , k _f (T) and criterion based on the length of induction period of crystallization have been taken into account. Four gels with the composition Li₂O–2SiO₂–nTiO₂ (n = 0.00, 0.03, 0.062, and 0.1) were prepared and the validity of the criteria was tested by applying them to these gels. The results indicate that thermal stability of the studied gels decrease with amount of TiO₂.     

Determination of the Activity Coefficients of NaCl in the System NaCl–NH4Cl–H2O

Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl–NH₄Cl–H₂O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH₄Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH₄⁺ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg^-1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.     

Prediction and experimental verification of the salt effect on the vapour–liquid equilibrium of water–ethanol–2-propanol mixture

Experimental vapour–liquid equilibria of water–ethanol–2-propanol saturated with NaNO₃, NaCl, KCl and containing 0.05 mol CH₃COOK/mol total solvent compared well with those predicted by Tan–Wilson and Tan–non-random two liquid (NRTL) models for multicomponent solvent–solute mixture using a set of solvent–solvent interaction parameters obtained from the regression of the vapour–liquid equilibrium of the solvent mixture without the dissolved solute and a set of solute–solvent interaction parameters calculated from the bubble points of the individual solvent components saturated or containing the same molar ratio of solute/total solvents as the mixture. The results also showed that a solvent component i is salted-in or out of the liquid phase relatively more than solvent component j would depend on whether A_sj/A_si (Tan–Wilson model) or exp(τ_is−τ_js) (Tan–NRTL model) is less or greater than 1. This is consistent with earlier publications on the effect of dissolved solutes (electrolytes and non-electrolytes) on the binary solvents mixtures. These findings confirmed that Tan–Wilson and Tan–NRTL models for multicomponent solvent–solute system can provide an accurate and rapid screening of electrolytes and non-electrolytes for their suitability in facilitating solvent separation by salt distillation of ternary solvent mixtures simply by determining the relative ratios of the solute–solvent interaction parameters from the respective bubble points of the solvent components containing the dissolved solute. The results also suggest that this may also be extended to other multicomponent solvent mixtures.     

Phases in the subsolidus area of the system CuO–V2O5–Fe2O3

The phase equilibria in the solid state in the system FeVO₄?CCu₃V₂O₈ and FeVO₄?CCuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO?CV₂O₅?CFe₂O₃ has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite- and lyonsite-type structure have been investigated by DTA, IR, and SEM methods.     

Thermodynamic performance of the NaNO3–NaCl–NaNO2 ternary system

Calculations of phase diagram for additive ternary molten salt system are carried out by the conformal ionic solution theory. The liquidus temperatures of the system NaNO₃–NaCl–NaNO₂ are determined according to different types of solid–liquid equilibrium and different values of the binary interaction coefficients. For the system NaNO₃–NaCl–NaNO₂, the calculated and experimental temperatures differ are very small below 673 K, but the oxidation and decomposition of the mixed salts are found when the temperature is higher than 673 K. Meanwhile, the eutectic point is obtained from calculated phase diagram and the eutectic temperature is 507 K. Thermal stability of this eutectic mixture is investigated by thermo-gravimetric analysis device. Experimental results show this kind of molten salt has a lower melting point (501.28 K), similar to solar salt (493 K). It is thermally stable at temperatures up to 819 K, and may be used up to 827 K for short periods.     

New approach to simplify the equation for the excess Gibbs free energy of aqueous solutions of electrolytes applied to the modelling of the NH3–CO2–H2O vapour–liquid equilibria

A new, simple, empirical equation for G^E (excess Gibbs free energy) of electrolyte solutions is proposed in which, contrary to the commonly used Pitzer equation, binary and ternary interaction parameters relate to the interactions of electrolytes in a solution rather than to the interactions of real species in a solution (i.e., anions, cations and nondissociated molecules). Such an approach radically reduces the number of parameters in the new equation for G^E as compared with the Pitzer equation and consequently significantly simplifies their calculation. The efficiency of the new approach is demonstrated on the example of modelling the vapour–liquid equilibria of the industrially important and widely investigated NH₃–CO₂–H₂O system.     

Synthesis of the novel CuAl2O4–Al2O3–SiO2 nanocomposites for the removal of pollutant dye and antibacterial applications

Research on Chemical Intermediates - CuAl2O4–Al2O3–SiO2 nanocomposites with different amounts of CuAl2O4 (40, 50, 60 and 70 wt. %) were synthesized by the sol–gel method and...     

Influence of SrO content on microstructure and crystallization of glazes in the SiO2–Al2O3–CaO–MgO–K2O system

The effect of the SrO addition on the microstructure and structure of the glazes from the SiO₂–Al₂O₃–CaO–MgO–K₂O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range.

     

Thermal Studies of the Hardening of the Systems Calcium Silicates–Electrolyte–Water

Thermal studies, sometimes together with X-ray analysis, were applied to investigate the process of hydration in the systems calcium silicates (tricalcium silicate or dicalcium silicate) - water - electrolyte. Alkali metal or alkaline-earth metal salts were used as electrolytes. Results and conclusions are presented concerning the action of electrolytes upon the kinetics of hardening of the calcium silicates and the composition and phase transformation of calcium hydrosilicate in the presence of low proportions of electrolytes (0.5, 2 and 5 mass%), these effects being due to ionic substitution. A higher proportion of electrolyte (above 2%) in the systems calcium silicate-water can determine the formation of a complex salt, e.g. calcium hydroxysalts or double hydrosilicates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rheological Properties of the Hydrated Al2O3–TiO2System

The rheology of mixtures of hydrated aluminum oxide and hydrated titanium dioxide sols was investigated. It was shown that flow curves depend on the mixture composition, the age of initial sols, the contact time of components, and the temperature. At low deformation rates, particles are aligned with the flow; this effect is partially reversible. At high shear rates, a discontinuity appears in the system; the effect depends on the age of initial sols.     

Structural studies of copper-containing multicomponent glasses from the SiO2–P2O5–K2O–CaO–MgO system

Multicomponent glasses from the SiO₂–P₂O₅–K₂O–MgO–CaO–CuO system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of CuO and P₂O₅ addition on the structure of glasses was evaluated by FTIR, Raman, ³¹P, and ²⁹Si MAS NMR spectroscopies. The studies showed that the Cu²⁺ ions displacing Ca²⁺ ions and Mg²⁺ ions in the structure of glass prefer to associate with the phosphorus Q¹ species, forming the Q⁰ species with chemically stable POCu bonds. This is accompanied by the reduction of the degree of polymerization of the phospho-oxygen sub-network, with a simultaneous increased degree of polymerization of the silico-oxygen sub-network of the silicate–phosphate glasses.     

Experimental study and thermodynamic modeling of the MgO–NiO–SiO2 system

The MgO–NiO–SiO₂ system has been studied by a combination of thermodynamic modeling and experimental measurements of phase equilibria. A complete literature review, critical evaluation and thermodynamic modeling of phase diagrams and thermodynamic properties of all oxide phases in the MgO–NiO–SiO₂ system at 1 atm total pressure are presented. To resolve the contradictions in the literature data, a new experimental investigation has been carried out over the temperature range from (1400 to 1650) °C using an equilibration and quenching technique followed by electron probe X-ray microanalysis (EPMA). Tie-lines between olivine and monoxide, olivine and proto-pyroxene, liquid and olivine and liquid and cristobalite have been measured. The whole set of experimental data, including the new experimental results and previously published data, has been taken into consideration in thermodynamic modeling of oxide phases in the MgO–NiO–SiO₂ system. The Modified Quasichemical Model has been used for the liquid phase. A simple random mixing model with a polynomial expansion of the excess Gibbs energy has been used for the monoxide solid solution. The models for olivine and proto-pyroxene were developed within the framework of the Compound Energy Formalism. The optimized model parameters reproduce all available thermodynamic and phase diagram data within experimental error limits.     

Kinetic analysis of the crystallization processes in the glasses of the Bi–As–S system

Kinetic analysis of the crystallization process in Bi₄(As₂S₃)₉₆ and Bi₆(As₂S₃)₉₄ glasses was performed based on DSC curves recorded under non-isothermal measurement conditions. Samples were thermally treated at different heating rates in the temperature range 300?C770?K. The activation energy of crystallization E and the pre-exponential factor K ₀ are determined by the Kissinger method and the characteristic crystallization parameters m and n of investigated glasses by the Matusita method. For both crystallization processes the glass with 4 at.% of Bi is characterized by the mechanism of volume nucleation, which is manifested in the form of two-dimensional growth at the first crystallization process, and as three-dimensional at the second one. On the other hand, in the sample with 6 at.% Bi, the average value of the parameter m is close to one, which indicates one-dimensional crystal growth. Compatibility of the values of the parameters m and n suggests that this sample has a large number of crystallization centers, which do not increase significantly during the thermal treatment.     

Influence of the Length of the Alanine Spacer on the Acidic–Basic Properties of the Ac–Lys–(Ala) n –Lys–NH2 Peptides (n?=?0, 1, 2, …, 5)

By using the potentiometric titration method, we have determined the pK _a values of the two terminal lysine groups in six alanine-based peptides differing in the length of the alanine chain: Ac?CLys?CLys?CNH₂ (KK), Ac?CLys?CAla?CLys?CNH₂ (KAK), Ac?CLys?CAla?CAla?CLys?CNH₂ (KAK2), Ac?CLys?CAla?CAla?CAla?CLys?CNH₂ (KAK3), Ac?CLys?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK4), and Ac?CLys?CAla?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK5) in aqueous solution. For each compound, the model of two stepwise acid?Cbase equilibria was fitted to the potentiometric-titration data. As expected, the pK _a values of the lysine groups increase with increasing length of the alanine spacer, which means that the influence of the electrostatic field between one charged group on the other decreases with increasing length of the alanine spacer. However, for KAK3, the pK _a1 value (8.20) is unusually small and pK _a2 (11.41) is remarkably greater than pK _a1, suggesting that the two groups are close to each other and, in turn, that a chain-reversal conformation is present for this peptide. Starting with KAK3, the differences between pK _a1 and pK _a2 decrease; however, for the longest peptide (KAK5), the values of pK _a1 and pK _a2 still differ by about 1 unit, i.e., by more than the value of log₁₀ (4)?=?0.60 that is a limiting value for the pK _a difference of dicarboxylic acids with increasing methylene-spacer length. Consequently, some interactions between the two charged groups are present and, in turn, a bent shape occurs even for the longest of the peptides studied.     

The influence of the temperature on the liquid–liquid equilibrium of the ternary system 1-pentanol–ethanol–water

Liquid–liquid equilibrium data for the ternary system 1-pentanol–ethanol–water have been determined experimentally at 25, 50, 85 and 95°C. These results have been correlated simultaneously by the uniquac method obtaining two sets of interaction parameters: one of them independent of the temperature and the other with a linear dependence. Both sets of parameters fit the experimental results well.     

Measurements of the Solid–Liquid Equilibria in the Quaternary System NaCl–NaBr–Na2SO4–H2O at 323 K

Phase equilibria of the quaternary NaCl–NaBr–Na₂SO₄–H₂O system at 323 K were studied by the isothermal dissolution equilibrium method. The solubilities of salts and densities of saturated solutions were determined. Solid solutions [Na(Cl, Br)] were found in the experiments. The phase diagram of the quaternary system has no invariant point, but has one univariant curve at the boundary of Na(Cl, Br) and Na₂SO₄ crystallization fields. The experimental results show that an increase of the NaBr concentration is accompanied by an obvious increase of the solution density and the decrease of the solubilities of NaCl and Na₂SO₄.     

One-pot co-precipitation of copper–manganese–zinc oxide catalysts for the oxidation of CO and SO2 in the presence of ultrasonic irradiation

Research on Chemical Intermediates - This paper studies the effect of addition of Zn and ultrasound-assisted co-precipitation on Cu-Mn oxide catalysts for the oxidation of CO. Cu-Mn-Zn oxide...