Ion-exchange characteristics of 12CaO·7Al2O3 for halide and hydroxyl ions

Substitution characteristics of the halide ions F− Cl− for the OH− ions in the crystal lattice of 12CaO·7Al2O3 solid solution were investigated. Single phases of composition 11CaO·7Al2O3·CaF2 and 11CaO·7Al2O3·CaCl2 were formed at 900 °C or above. The OH− ions in 12CaO·7Al2O3 solid solution, i.e. 11CaO·7Al2O3·Ca(OH)2, could be replaced wholly or partially by F− or Cl− ions from the corresponding calcium halide, forming 11CaO·7Al2O3·Ca(OH,F)2 and 11CaO·7Al2O3·Ca(OH,Cl)2 solid solutions above 500 °C and above 700 °C, respectively. Lattice constants of 12CaO·7Al2O3 solid solution changed continuously with the proportion of F− ions or Cl− ions. The F− ions in 11CaO·7Al2O3·CaF2 could be wholly or partially substituted by Cl− ions from CaCl2 at 900 °C or more, forming the solid solution 11CaO·7Al2O3·Ca(F,Cl)2. The Cl− ions in 11CaO·7Al2O3·CaCl2 could be partially replaced F− ions from CaF2 at 1000 °C or above, apparently due to slow chloride loss by evaporation.