Solubility prediction for the HCl–MgCl2–H2O system at 40 C and solubility equilibrium constant calculation for HCl ⋅ MgCl2 ⋅ 7H2O at 40 C

The component solubilities of the HCl–MgCl₂–H₂O system at 40 ^°C were calculated by using Pitzer’s ion-interaction model and the solubility equilibrium constant of HCl⋅MgCl₂⋅7H₂O at 40 ^°C was evaluated according to the solubility data for the HCl–MgCl₂–H₂O system at −19.8, 0, 20, 25 and 50 ^°C. This study can provide the parameters necessary for solubility prediction for the HCl–LiCl–MgCl₂–H₂O system at 40 ^°C and supply a theoretical basis for the manufacturing process which was proposed by Gao and employed to extract MgCl₂⋅6H₂O from salt lake brine.     

Solubility prediction in the ternary systems NaCl–RbCl–H2O, KCl–CsCl–H2O and KBr–CsBr–H2O at 25 C using the ion-interaction model

The component solubilities in NaCl–RbCl–H₂O, KCl–CsCl–H₂O and KBr–CsBr–H₂O systems at 25 C were calculated by using the Pitzer ion interaction model and its extended HW models. Excellent agreement with experimental solubilities indicated that the models can be successfully used to calculate the component solubilities. This study affords the necessary parameters for solubility predictions of complicated systems containing rubidium and caesium and establishes a theoretical basis for the separation of these valuable metals from salt lake brine.     

Liquid–solid equilibria in quinary system Na,Mg/Cl,SO4,NO3–H2O at 298.15 K

In order to develop the nitrate deposits found close to Lop Nur in the Xinjiang region in China, the solubilities of the system Na⁺,Mg²⁺/Cl⁻,SO₄²⁻, NO₃⁻–H₂O and its subsystems, the quaternary systems Na⁺,Mg²⁺/SO₄²⁻,NO₃⁻–H₂O and Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O, were studied at 298.15 K. The phase diagrams were plotted according to the solubilities achieved. In the equilibrium phase diagram of Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O, there are two invariant points, five univariant curves and four regions of crystallization: Mg(NO₃)₂6H₂O,MgCl₂6H₂O,MgSO₄7H₂O and MgSO₄(1–6)H₂O. In the equilibrium phase diagram of Na⁺,Mg²⁺/SO₄²⁻, NO₃⁻–H₂O, there are five invariant points, eleven univariant curves and seven regions of crystallization: Na₂SO₄,Na₂SO₄10H₂O,NaNO₃,MgSO₄Na₂SO₄4H₂O,NaNO₃Na₂SO₄2H₂O,Mg(NO₃)₂6H₂O and MgSO₄7H₂O. In the equilibrium phase diagram of the Na⁺, Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O system, there are six invariant points, and ten regions of crystallization: NaCl, NaNO₃,Na₂SO₄,Na₂SO₄10H₂O,MgSO₄Na₂SO₄4H₂O, NaNO₃Na₂SO₄2H₂O,MgCl₂6H₂O,Mg(NO₃)₂6H₂O, MgSO₄(1–6)H₂O and MgSO₄7H₂O.     

Determination of water activities and osmotic and activity coefficients of the system NaCl–BaCl2–H2O at 298.15 K

The water activities of the mixed aqueous electrolyte NaCl–BaCl₂(aq) are measured at total molalities from 0.25 mol kg⁻¹ to about saturation for different ionic strength fractions (y) of NaCl with y=0.33,0.50,0.67. The results allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii, Stokes, and Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LSII), Reilly, Wood, and Robinson (RWR), and Pitzer models. From these measurements, the Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The excess Gibbs energy is also determined.     

Water activities, osmotic and activity coefficients of the system (NH4)2SO4–K2SO4–H2O at the temperature 298.15 K

The mixed aqueous electrolyte system consisting of ammonium and potassium sulfates has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total ionic strength values ranging from 0.60 to 8.25 mol kg⁻¹ for different ionic strength fractions (y) of (NH₄)₂SO₄ with y=0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood and Robinson (RWR) and Pitzer models. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture.     

A new equation of state and Fortran 77 program to calculate vapor–liquid phase equilibria of CH4–H2O system at low temperatures

A new equation of state (EOS) and the corresponding computer program package VLEWM are developed to calculate vapor–liquid phase equilibria and volumetric properties of CH₄–H₂O system at low temperatures. The EOS can predict vapor–liquid equilibria and volumetric properties of CH₄–H₂O system accurately at temperatures 273–383 K, and at pressures 0–1000 bar. The program package VLEWM is written in FORTRAN 77. It provides two main functions: (1) to calculate the composition in vapor phase and liquid phase of CH₄–H₂O system at equilibrium and (2) to judge the phase and to calculate molar volume of CH₄–H₂O mixture.     

Solubility prediction for the nonelectrolyte urea–hydrogen peroxide–water system and thermodynamic solubility product calculation for CO(NH2)2 ⋅ H2O2 using the modified Pitzer model

The Pitzer interaction model, which has been applied successfully to the thermodynamic simulation of electrolyte solutions and electrolyte–nonelectrolyte solutions, was extended to nonelectrolyte–nonelectrolyte solution system. In the present work, the modified Pitzer model was used for calculation and correlation of the ternary CO(NH₂)₂–H₂O₂–H₂O system at 283.15 K. The value of the Pitzer interaction parameters for the ternary system and the thermodynamic solubility product of CO(NH₂)₂⋅H₂O₂ were determined using a least-square optimization procedure with coupling activity coefficient and solubility data. The predicted isothermal solubilities agree well with the result obtained from the experiment. The results indicated that the modified Pitzer model could be successfully used to predict the component solubility of the nonelectrolyte–nonelectrolyte system.     

Experimental study and thermodynamic modelling of the ZrO2–LaO1.5 system

Phase relations in the ZrO₂–LaO_1.5 system were studied experimentally in the temperature range from 1673 to 1973 K. X-ray diffraction and scanning electron microscopy were employed to obtain the structural information and the compositions of the tetragonal and pyrochlore (La₂Zr₂O₇) phases. The solubility of LaO_1.5 in the tetragonal phase was determined to be very small. The homogeneity range of the pyrochlore phase is estimated to be less than 2 mol% at 1973 K, and less than 1 mol% at 1673 K according to the present work. Based on the experimental results obtained in this work, as well as the available phase diagram and thermodynamic data in literature, a self-consistent thermodynamic assessment was carried out by using the ionic sublattice solution model.     

Measurements and calculations of solid–liquid equilibria in the quaternary system NaBr–KBr–CaBr2–H2O at 298 K

The solubilities and densities of the quaternary system NaBr–KBr–CaBr₂–H₂O were investigated by the method of isothermal solution saturation at 298 K. On the basis of the experimental data, the phase diagram, water content diagram and the density-composition diagram were plotted, respectively. In the phase diagram of quaternary system NaBr–KBr–CaBr₂–H₂O at 298 K, no complex salt or solid solution was found. There are two invariant points, five univariant curves, and four crystallization fields corresponding to NaBr, NaBr·2H₂O, KBr and CaBr₂·6H₂O. Pitzer's equations based model has been applied to calculate bromide minerals solubilities in the quaternary system NaBr–KBr–CaBr₂–H₂O at 298 K. All binary and mixing ion interaction parameters and solubility products of bromide solids are taken from previously published T-variation model for the system under study, adapted to 298 K. The predicted and experimental solubilities are in a very good agreement up to a very high total concentration of the quaternary system.     

Modeling of the influence of H2O on metal oxide sensor responses to CO

In this work a model able to predict the dynamic response of conductimetric SnO₂ sensors in presence of humid mixtures of a reducing gas and oxygen is presented. Sensors consisting of large-grained porous films are taken into account. For these sensors the conduction is given by the surface charge carriers, whose density is exponentially related to the height of the potential barrier that establishes at the surface of the grains. The barrier is due to the presence of some localized charge, trapped both on surface intrinsic defects and on chemisorbed species. In this perspective the complete dynamic model of sensor response is obtained by combining a set of differential equations describing the kinetics of surface species adsorption and ionization, the relationship between the density of the charge trapped at the surface and the potential barrier magnitude, and, finally, the relationship between film conductance and the potential barrier height.The presented work is a development of some previous studies that led to the development of a model of the sensor behavior in dry mixtures of oxygen and CO. In the present study the influence of water on sensor response, in the same operating conditions previously considered, is treated, and a simple model of its effect is proposed. Water is accounted for as a further adsorbant interacting with the other two chemical species. A dissociative adsorption is considered, where adsorbed OH⁻ groups, by loosing their electrons, behave as donors and inject a non-negligible (significant) amount of free electrons in the conduction band. The experimental results obtained with a set of 8 Taguchi sensors prove that the proposed model can predict the most important characteristics of the sensor behavior.     

Correlation of solubilities for the system with the Pitzer model at 15, 25, 50, and

Solubility data of the NaCl+LiCl+H₂O system have been measured at 15 C. These data along with others recorded in the literature, at 25, 50, and 100 C, have been correlated using the Pitzer model and the extended Debye–Hückel model. The latter was used to determine the activity and osmotic coefficients of the binary systems NaCl+H₂O and LiCl+H₂O. The results obtained in this work show that the calculated solubility values are in good agreement with the experimental ones.     

Measurement and correlation of vapor–liquid equilibria of the poly(vinylpyrrolidone)+NaH2PO4+H2O system at different temperatures

Vapor–liquid equilibrium data for the poly(vinylpyrrolidone) (PV P)+NaH₂PO₄+H₂O system have been determined experimentally using the improved isopiestic method at 298.15, 308.15 and 318.15 K. The effect of temperature on the vapor–liquid equilibrium has been studied and compared with that on the liquid–liquid equilibrium of the aqueous PV P+NaH₂PO₄ two-phase system. It was found that the slope of constant water activity lines and tie-lines increased with increasing the temperature. The results have been discussed on the basis of the effect of temperature on the hydrophobicity of the polymer. Furthermore, the segment-based local composition Wilson model has been used for the correlation of the experimental water activity data. The agreement between the correlation and the experimental data is good.     

Experimental determination of the liquidus in the high basicity region in the Al2O3(30 mass%) - CaO - MgO - SiO2 system

The liquidus in the high basicity region in the Al₂O₃(30 mass%)-CaO-MgO-SiO₂ system were determined experimentally at 1773 and 1873 K using the quench technique followed by EPMA analysis. Based on the experimental data, a phase diagram of the Al₂O₃(30 mass%)-CaO-MgO-SiO₂(<20 mass%) section was constructed for 1773 and 1873 K. The solubilities of 2CaO.SiO₂ and 3CaO.SiO₂ at 1773 K were found to be considerably higher in comparison with the existing phase diagram. Even the solubility of MgO at 1873 K was found to be somewhat higher. In addition, the activities of MgO, CaO and Al₂O₃ at 1773 K were estimated using the phase diagram information.     

pH sensor based on the crown heteropolyanion K28Li5H7P8W48O184·92H2O immobilized using a layer by layer assembly process

A new sensitive pH sensor based on immobilization of the crown heteropolyanion K₂₈Li₅H₇P₈W₄₈O₁₈₄·92H₂O (P₈W₄₈) on a electrode surface through a layer by layer assembly process is described. The immobilization is based on the electrostatic adsorption of the complex in layers of charged polyelectrolyte poly(allylamine hydrochloride) (PAH). The deposited P₈W₄₈/LBL film was investigated by cyclic voltammetry, potentiometry and electrochemical impedance spectroscopy. Compared to the electrochemical behavior of dissolved P₈W₄₈, a slight shift in the redox peak towards negative potentials is observed, which have been attributed to a slight decrease in the acidity of the interior of the P₈W₄₈/LBL film compared to the testing buffer solution. The relationship between the peak currents of the deposited P₈W₄₈/LBL film and the number of layers is shown to be linear, which demonstrates that equal amounts of P₈W₄₈ are adsorbed in each deposition layer. The P₈W₄₈/LBL modified electrode showed high sensitivities toward pH. Therefore, such electrodes were tested as pH sensors using the titration method. The resulting pH sensor has a detection range of pH 1–13, a sensitivity of 69 ± 2 mV/pH, high repeatability (<3 mV), fast response time (<7 s), low sensitivity toward change in ionic strength and nature of the supporting electrolyte, low internal resistance and a working life time of at least 3 months. Moreover, the sensor is easy to manufacture and can be easily miniaturized for measurements in micro- and nano-systems.     

Thermodynamic properties of aqueous mixed ternaries { y NH4Cl+(1−y) BaCl2 } (aq) and { y NH4Cl+(1−y) CaCl2 } (aq) at 298.15 K

Hygrometric measurements of the water activity are reported for the thermodynamic properties of the mixed aqueous electrolyte systems of ammonium–calcium chloride and ammonium–barium chloride at 298.15 K. The measurements were made at a large number of total molalities, varying from 0.4 mol kg⁻¹ to saturation at three ionic-strength fractions (y$y$) of NH₄Cl for the systems NH₄Cl–CaCl₂ (aq) and NH₄Cl–BaCl₂ (aq) with y=0.20,0.50$y=0.20,0.50$ and 0.80. The experimental data are reported as water activities and osmotic coefficients at various molalities, along with derived values of the activity coefficients of both solutes. The ranges of water activities _aw$a_w$ are 0.800–0.989 for ammonium–barium chlorides and _aw=0.560–0.989$a_w=0.560\text{–}0.989$ for ammonium–calcium chlorides. The activity coefficients were calculated by means of a thermodynamic model based on a variant of the Pitzer ion-interaction equations with extended binary parameters. However, the results were also compared for the precision of the presentation of the osmotic coefficients using an extended model with the calculations of the Zdanovskii–Stokes–Robinson, Kusik and Meissner, Robinson and Stokes, Lietzke and Stoughton, Reilly, Wood and Robinson, and Pitzer models.     

Comment on “Thermodynamic modelling of an Al2O3-MnO system using the ionic model” by A.B. Farina and F.B. Neto

The MnO-Al₂O₃ system is very important for the non-metallic inclusion controls in steelmaking and the slag chemistry for high Mn alloy production. Farina and Neto presented their recent thermodynamic assessment on the MnO-Al₂O₃ system using a two-sublattice ionic liquid model for liquid oxide phase and the Compound Energy Formalism for solid phases. However, we found several doubts and mistakes in their assessment in particular related to the Gibbs energy of MnAl₂O₄ spinel phase.