Study On Metastable Equilibria In Quinary System Mg²⁺, K⁺, Na⁺, Li⁺//B₄O₇^2--H₂O At 288K

Metastable phase equilibria of the quinary system of Mg²⁺,K⁺,Na⁺,Li⁺//B4O₇^2- -H₂O and its subsystems(three ternary systems and four quaternary systems ) at 288K. were studied by the method of isothermal evaporation. Solubilities and densities in the solution of these systems were determined. According to the experimental data, metastable phase diagrams and density-composition diagrams of ternary systems were plotted; Metastable phase diagrams, corresponding water content diagrams and density-composition diagrams of quaternary systems were also plotted; Metastable phase diagram, corresponding water content diagram and density-composition diagrams of the quinary system at 288K(saturated with Na₂B₄O₇·10H₂O) were also constructed.The results show that two univariant curves ,one invariant point, and two equilibrium phase Solids(MgB₄O₇·9H₂O,K₂B₄O₇·4H₂O) were found in the metastable phase diagram of the ternary system of Mg²⁺,K⁺//B₄O₇^2--H₂O at 288K, The composition of the metastable equilibrium solution of MgB₄O₇ and K₂B₄O₇ at the invariant point in the ternary system of Mg²⁺,K⁺//B₄O₇^2--H₂O at 288K increased significantly compared with the invariant point in the system of Mg²⁺,K⁺//B₄O₇^2--H₂O at 25℃; There were two univariant curves, one invariant point, and two equilibrium phase Solids(MgB₄O₇·9H₂O,LiBO₂·8H₂O) in the metastable phase diagram of the ternary system of Mg²⁺,Li⁺//B₄O₇^2--H₂O at 288K; There were two univariant curves, one invariant point, and two equilibrium phase Solids(MgB₄O₇·9H₂O,Na₂B₄O₇·10H₂O) in the metastable phase diagram of the ternary system of Mg²⁺,Na⁺//B₄O₇^2--H₂O at 288K. The solubility of MgB₄O₇ increased obviously in the ternary system of Mg²⁺,Na⁺//B₄O₇^2--H₂O at 288K, Na₂B₄O₇ had salting-in effect on MgB₄O₇. Three univariant curves, one invariant point and three crystallization fields (MgB₄O7·9H₂O,K₂B₄O₇·4H₂O,LiBO₂·8H₂O) were found in the metastable phase diagram of the quaternary system of Mg²⁺, K⁺, Li⁺//B₄O₇^2--H₂O at 288K, K₂B₄O₇ had salting-out effect on Li₂B₄O₇ in this ternary system. The salt K₂B₄O₇·4H₂O has the smallest crystallization field, the salt LiBO₂·8H₂O has the largest crystallization field; Three univariant curves, one invariant point and three crystallization fields (MgB₄O₇·9H₂O,Na₂B₄O₇·10H₂O,LiBO₂·8H₂O) were found in the metastable phase diagram of the quaternary system of Mg²⁺,Na⁺,Li⁺//B₄O₇^2--H₂O at 288K. The salt Na₂B₄O₇·10H₂O has the smallest crystallization field, the salt LiBO₂·8H₂O has the largest crystallization field; Three univariant curves, one invariant point and three crystallization fields (MgB₄O₇·9H₂O,K₂B₄O₇·4H₂O,Na₂B₄O₇·10H₂O) were found in the metastable phase diagram of the quaternary system of Mg²⁺,K⁺,Na⁺//B₄O₇^2--H₂O at 288K. The salt K₂B₄O₇·4H₂O has the smallest crystallization field, the salt MgB₄O₇·9H₂O has the largest crystallization field.There were three univariant curves, one invariant point and three crystallization fields(MgB₄O₇·9H₂O,Na₂B₄O₇·10H₂O,LiBO₂·8H₂O) in the metastable phase diagram of the quinary system of Mg²⁺,K⁺,Na⁺,Li⁺//B₄O₇^2--H₂O which was saturated with Na₂B₄O7·10H₂O at 288K.These Metastable phase equilibria of the quinary system and its subsystems(three ternary systems and four quaternary systems ) at 288K above all were of simple eutectic type and no double salt or solid solution.