This is the first study of solubility in the NaCl-NH4Cl-KCl-H2O four-component water-salt system at 25, 50, and 75°C. Phase fields of individual salts and potassium and ammonium chloride
solid solutions were demarcated. Experimental data were used to develop a mathematical model of the K+, Na+, NH4+/Cl−, Cr2O72−-H2O five-component reciprocal system, which includes the title four-component system. 相似文献
A complete, critical evaluation of all phase diagram and thermodynamic data was performed for all phases of the (Na2SO4 + K2SO4 + Na2S2O7 + K2S2O7) system and optimized model parameters were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range ordering, where the cations (Na+ and K+) are assumed to mix on a cationic sublattice, while anions were assumed to mix on an anionic sublattice. The Compound Energy Formalism was used for modelling the solid solutions of (Na,K)2SO4 and (Na,K)2S2O7. The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature were reproduced within experimental error limits. 相似文献
Samples in the system Lu2−xYxSi2O7 (0?x?2) have been synthesized following the sol-gel method and calcined to 1300 °C, a temperature at which the β-polymorph is known to be the stable phase for the end-members Lu2Si2O7 and Y2Si2O7. The XRD patterns of all the compositions studied are compatible with the structure of the β-polymorph. Unit cell parameters are calculated as a function of composition from XRD patterns. They show a linear change with increasing Y content, which indicates a solid solubility of β-Y2Si2O7 in β-Lu2Si2O7 at 1300 °C. 29Si MAS NMR spectra of the different members of the system agree with the XRD results, showing a linear decrease of the 29Si chemical shift with increasing Y content. Finally, a correlation reported in the literature to predict 29Si chemical shifts in silicates is applied here to obtain the theoretical variation in 29Si chemical shift values in the system Lu2Si2O7-Y2Si2O7 and the results compare favorably with the values obtained experimentally. 相似文献
Solubility in the Na2Cr2O7-(NH4)2Cr2O7-K2Cr2O7-H2O four-component water-salt system at 25, 50, and 75°C was studied for the first time. Phase field boundaries for individual
salts and potassium and ammonium dichromate solid solutions, monovariant lines, and invariant points were determined. Experimental
data were used to optimize the looped isohydric process of potassium dichromate preparation involving additional salts. 相似文献
The activity of NiAl2O4 in NiAl2O4MgAl2O4 solid solutions has been measured by using a solid oxide galvanic cell of the type, Pt, Ni + NiAl2O4 + Al2O3(α)/CaOZrO2/Ni + NixMg1?xAl2O4 + Al2O3(α). Pt, in the temperature range 750–1150°C. The activities in the spinel solid solutions show negative deviations from Raoult's law. The cation distribution in the solid solutions has been calculated using site preference energies independent of composition for Ni2+, Mg2+, and Al3+ ions obtained from crystal field theory and measured cation disorder in pure NiAl2O4 and MgAl2O4, and assumi g ideal mixing of cations on the tetrahedral and octahedral positions. The calculated values correctly predict the decrease in the fraction, α, of Ni2+ ions on tetrahedral sites for 1>x>0.25, observed by Porta et al. [J. Solid State Chem.11, 135 (1974)] but do not support their tentative evidence for an increase in α for x < 0.25. The measured excess free energy of mixing can be completely accounted for by using either the calculated or the measured cation distributions. This suggests that the Madelung energy is approximately a linear function of composition in the solid solutions. The composition of NiOMgO solid solutions in equilibrium with NiAl2O4MgAl2O4 solid solutions has been calculated from the results and information available in literature. 相似文献
The solubility in the water-salt quaternary reciprocal system Na2Cr2O7 + 2NH4Cl ⇆ (NH4)2Cr2O7 + 2NaCl-H2O has been investigated for the first time at 25, 50, and 75°C. Using a formal analytical model, the boundaries of the phase
fields have been determined, and the univariant lines and invariant points have been calculated. The experimental data have
been used to calculate the temperature and concentration parameters of the circular isohydric process of potassium dichromate
preparation with the participation of ammonium salts as intermediates. 相似文献
CoAl2O4, CoGa2O4, and their solid solution Co(GazAl1−z)2O4 have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B2O3 at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing. 相似文献
For studying the sulfation of Al2O3, CaO, CdO and ZnO with (NH4)2SO4, free energy values have been calculated for possible reactions utilising the available thermodynamic data. Further differential thermal analysis has been carried out to find out the exact reaction. The ΔH0 values calculated theoretically and that from DTA peak are very close in case of CaO and ZnO, whereas in the other two cases there is no proper match. The mismatch may be due to some uncertainty in thermodynamic values and the possibility of some side reactions. 相似文献
This paper examines the structural changes with temperature and composition in the Sc2Si2O7-Y2Si2O7 system; members of this system are expected to form in the intergranular region of Si3N4 and SiC structural ceramics when sintered with the aid of Y2O3 and Sc2O3 mixtures. A set of different compositions have been synthesized using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1750 °C during different times. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the β-RE2Si2O7 polymorph, with γ-RE2Si2O7 and δ-RE2Si2O7 showing very reduced stability fields. Isotherms at 1300 and 1600 °C have been analysed in detail to evaluate the solid solubility of the components. Although, the XRD data show a complete solid solubility of β-Sc2Si2O7 in β-Y2Si2O7 at 1300 °C, the 29Si MAS-NMR spectra indicate a local structural change at x ca. 1.15 (Sc2−xYxSi2O7) related to the configuration of the Si tetrahedron, which does not affect the long-range order of the β-RE2Si2O7 structure. Finally, it is interesting to note that, although Sc2Si2O7 shows a unique stable polymorph (β), Sc3+ is able to replace Y3+ in γ-Y2Si2O7 in the compositional range 1.86?x?2 (where x is Sc2−xYxSi2O7) as well as in δ-Y2Si2O7 for compositions much closer to the pure Y2Si2O7. 相似文献
Activities of water in the K2SO4+Rb2SO4+H2O system at 25°C have been measured isopiestically. On the basis of the experimental activities of water ternary parameters of the Pitzer equations have been calculated. According to our data and experimental solubility data from the literature, continous solid solutions between K2SO4 and Rb2SO4 are formed in this system. With the use of the Guggenheim polynomial for simulating excess functions of solid solutions on the basis of the original and literature solubility data, excess Gibbs energies of solid solution formation as well as a solubility diagram have been calculated. Results of the solubility calculation are in good agreement with experimental data. 相似文献
An attempt has been made to calculate the free energy values for possible reactions utilising the available thermodynamic data in order to study the sulfation of CuO, Fe2O3, MnO2 and NiO with (NH4SO4, and further trials have been made to determine the exact reaction through differential thermal analysis. There is no real correlation between the theoretical value of ΔH° and that calculated from the DTA peak, which may be due to some uncertainty in the thermodynamic values and the possibility of some side reactions. 相似文献
The standard free energies of formation of zinc aluminate and chromite were determined by measuring the oxygen potential over a solid CuZn alloy, containing 10 at.?% Zn, in equilibrium with ZnO, ZnAl2O4+Al2O3(χ) and ZnCr2O4+Cr2O3, in the temperature range 700–900°C. The oxygen potential was monitored by means of a solid oxide galvanic cell in which a Y2O3ThO2 pellet was sandwiched between a CaOZrO2 crucible and tube. The temperature dependence of the free energies of formation of the interoxidic compounds can be represented by the equations, The heat of formation of the spinels calculated from the measurements by the “Second Law method” is found to be in good agreement with calorimetrically determined values. Using an empirical correlation for the entropy of formation of cubic spinel phases from oxides with rock-salt and corundum structures and the measured high temperature cation distribution in ZnAl2O4, the entropy of transformation of ZnO from wurtzite to rock-salt structure is evaluated. 相似文献
The objectives of this study were to address uncertainties in the solubility product of (UO2)3(PO4)2⋅4H2O(c) and in the phosphate complexes of U(VI), and more importantly to develop needed thermodynamic data for the Pu(VI)-phosphate system in order to ascertain the extent to which U(VI) and Pu(VI) behave in an analogous fashion. Thus studies were conducted on (UO2)3(PO4)2⋅4H2O(c) and (PuO2)3(PO4)2⋅4H2O(am) solubilities for long-equilibration periods (up to 870 days) in a wide range of pH values (2.5 to 10.5) at fixed phosphate concentrations of 0.001 and 0.01 M, and in a range of phosphate concentrations (0.0001–1.0 M) at fixed pH values of about 3.5. A combination of techniques (XRD, DTA/TG, XAS, and thermodynamic analyses) was used to characterize the reaction products. The U(VI)-phosphate data for the most part agree closely with thermodynamic data presented in Guillaumont et al.,(1) although we cannot verify the existence of several U(VI) hydrolyses and phosphate species and we find the reported value for formation constant of UO2PO−4 is in error by more than two orders of magnitude. A comprehensive thermodynamic model for (PuO2)3(PO4)2⋅4H2O(am) solubility in the H+-Na+-OH−-Cl−-H2PO−4-HPO2−4-PO3−4-H2O system, previously unavailable, is presented and the data shows that the U(VI)-phosphate system is an excellent analog for the Pu(VI)-phosphate system. 相似文献
Gadolinium aluminates, GdAlO3, Gd3Al5O12 and Gd4Al2O9 were synthesized by the solution combustion method. Very fine particles in the nanoparticle range of ∼10-20 nm could be prepared by this method as evidenced by surface area measurement by multipoint BET method. Thermal studies on these compounds were carried out using high-temperature X-ray diffraction (HT-XRD) and differential scanning calorimetry (DSC) methods. The thermal expansion coefficients of GdAlO3, Gd3Al5O12 and Gd4Al2O9 were calculated from the lattice parameter data and specific heats were calculated from DSC data. The lattice parameters of GdAlO3 and Gd3Al5O12 were found to increase linearly with temperature whereas Gd4Al2O9 did not show a linear trend. The specific heats of these compounds show an increasing trend with increase in aluminum atom fraction. Based on the thermodynamic data available in the literature and the specific heat data obtained in this study, oxygen potential diagram was constructed at 1000 K. 相似文献
Atomistic computer simulation techniques are used to investigate the effects of lithium insertion into YBa2Cu3O7. Attention is focused on various possible lattice sites occupied by the inserted lithium ions and pathways for their migration. The square-planar position in the Cu(2) layer is calculated to be the most energetically favorable. This is supported by the structural modeling of the ordered lithiated phase Li0.33YBa2Cu3O7. The calculated activation energies derived from migration profiles are in accord with experimental values and suggest fairly mobile lithium ions. 相似文献