Studies On Phase Equilibria And Thermodynamic Properties Of The Quinary System Na⁺?K⁺?//Cl^-,Br^-,SO₄^2-,B₄O₇^2--H₂O And Its Subsystems At Multi–temp

Phase equilibria and thermodynamic properties of the quinary system Na⁺(K⁺)//Cl^–,Br^–,SO₄^2–,B₄O₇^2––H₂O and its subsystems at multi–temperature were studied.Isothermal dissolution method was used to study phase equilibria of the following system:quinary system Na⁺//Cl^–,Br^–,SO₄^2–,B₄O₇^2––H₂O,its three quaternarysubsystemsNa⁺//Cl^–,Br^–,SO₄^2––H₂O,Na⁺//Cl^–,Br^–,B₄O₇^2––H₂O,Na⁺//Br^–,SO₄^2–,B₄O₇^2––H₂O,andonereciprocalquaternarysystems Na⁺,K⁺//Br^–,B₄O₇^2––H₂Oat373K;onesimplequaternarysystem K⁺//Br^–,SO₄^2–,B₄O₇^2––H₂O at 348 K.The solubilities and densities of these systems were mensurated at corresponding temperature.the isothermal phase diagrams,water content diagrams and density–composition diagrams of the relevant systems were drew.Potential difference measurement was used to study thermodynamic properties of these two ternary systems K⁺//Cl^–,B₄O₇^2––H₂O and Na⁺//Cl^–,B₄O₇^2––H₂O at 308.15K.The mean activity coefficients of the component were calculated by the electromotive force.Pitzer parameters obtained using the linear regression method.Moreover,the osmotic coefficients,water activity,the excess Gibbs energy of the systems were calculated.The experimental results showed that the isothermal phase diagram of reciprocal quaternary systemNa⁺,K⁺//Br^–,B₄O₇^2––H₂O at 373 K was a simple common saturation and without complex salt as wellas solid solution.The phase diagramcomprises two invariant points,five univariant curves and four fields of crystallization.The equibrium solid phases of the four fields of crystallization were Na₂B₄O₇·5H₂O?K₂B₄O₇·4H₂O?KBr and NaBr.Theisothermalphasediagramofthequaternarysystem Na⁺//Br^–,SO₄^2–,B₄O₇^2––H₂O at 373 K was a simple common saturation and without complex salt as well as solid solution.The phase diagram consists of one invariant points,three univariant curves and three fields of crystallization.The equibrium solid phases of crystallization were NaBr?Na₂SO₄ and Na₂B₄O₇·5H₂O.The quaternary system Na⁺//Cl^–,Br^–,B₄O₇^2––H₂O at 373 K contained solid solution,the solid solution was Na?Cl,Br?,and there was no complex salt formed in the process of experiment.The isothermal phase diagram consists of one univariant curve,two fields of crystallization and without any invariant point of quaternary system.The equilibrium solid phases of the two crystallization fields were Na?Cl,Br?and Na₂B₄O₇·5H₂O.The quaternary system Na⁺//Cl^–,Br^–,SO₄^2––H₂O at 373 K contained solid solution,the solid solution was Na?Cl,Br?,and there was no complex salt formed in the process of experiment.The isothermal phase diagram consists of one univariant curve,two fields of crystallization and without any invariant point of quaternary system.The equilibrium solid phases of the two crystallization fields were Na?Cl,Br?and Na₂SO₄.The quinary system Na⁺//Cl^–,Br^–,SO₄^2–,B₄O₇^2––H₂O contained solid solution,the solid solution was Na?Cl,Br?,and there was no complex salt formed in the process of experiment.The isothermal phase diagram?saturated with Na₂SO₄?consists of one univariant curve,two fields of crystallization and without any invariant point of quinary system.The equilibrium solid phases of the two crystallization fields were Na?Cl,Br?and Na₂B₄O₇·5H₂O.Theisothermalphasediagramofthequaternarysystem K⁺//Br^–,SO₄^2–,B₄O₇^2––H₂O at 348 K was a simple common saturation and without complex salt as well as solid solution.The phase diagram consists of one invariant points,three univariant curves and three fields of crystallization.The equibrium solid phases of crystallization were KBr?K₂SO₄ and K₂B₄O₇·4H₂O.The mean activity coefficients of KCl in the K⁺//Cl^–,B₄O₇^2––H₂O ternary system were experimentally determined at 308.15 K over the total ionic strength from?0.0100 to 1.0000?mol·kg^–1.K⁺–ISE and Cl^––ISE presented a good Nernst effect,which implied that this method could be used to measure the activity coefficients of the above system.The experimental results show that the activity coefficients decreased with the increase of the ionic strength.The mean activity coefficients of NaCl in the Na⁺//Cl^–,B₄O₇^2––H₂O ternary system were experimentally determined at 308.15 K over the total ionic strength from?0.0100 to 0.5000?mol·kg^–1.Na⁺–ISE and Cl^––ISE presented a good Nernst effect,which implied that this method could be used to measure the activity coefficients of the above system.The experimental results show that the activity coefficients decreased with the increase of the ionic strength.