Phase diagram of thermodynamic non-equilibrium state of MgO-B_2O_3-18%MgCl_2-H_2O system at 0 deg C

摘要

The supersaturated solutions of MgO-B_2O_3-18%MgCl_2-H_2O with different mole ratios of MgO:B_2O_3 have been prepared and kept at 0+-0.1 deg C. The crystallization paths of boric acid, Mg-borates and Mg-oxychloride from the solutions have been determined by chemical analysis of the solution samples taken at a given time interval during crystallization, and then the liquid-solid phase diagram of thermodynamic non-equilibrium state of MgO-B_2O_3-18%MgCl_2-H_2O system at 0 deg C has been constructed. In this phase diagram, five crystallization fields appear, boric acid (H_3BO_3), mcallisterite (MgO(centre dot)3B_2O_3(centre dot)7.5H_2O), hungtsaite (MgO(centre dot)2B_2O_3(centre dot)9H_2O), inderite (2MgO(centre dot)3B_2O_3(centre dot)15H_2O) and magnesium oxychloride (5Mg(OH)_2(centre dot)MgCl_2 (centre dot)8H_2O).