Cements containing the phases C[sub(12)]A[sub(7)] or C[sub(11)]A[sub(7)].CaF[sub(2)]

The phases dodecacalcium heptaaluminate (12CaO.7Al2O3 or Cai2Al14O33, abbreviation C12A7) and calcium fluoroaluminate (HCaO.7Al2O3.CaF2 or Ca12AlMO32F2, abbreviation CnA7.CaF2 or CnA7F) are closely related. The crystal structure of the former consists of an incomplete framework of corner-sharing (A1O4) tetrahedra with the empirical composition A17O16"~ and Ca2+ ions. One additional O2 ion per formula unit is distributed statistically between 12 sites. Upon heating in air of normal humidity the material tends to take up water to an amount corresponding to the formula C,2A7H. Under these conditions the O2~ ions that statistically occupy one of 12 possible sites in a formula unit are replaced by two OH ions.