Substitution of Sodium and Silicon in Tricalcium Aluminate

Abstract

Four types of tricalcium aluminate solid solutions with different concentrations of Na 2 O and SiO 2 were prepared and examined using an electron probe microanalyzer. The atomic ratios, including those determined in a previous study, were derived from the oxide compositions and provided excellent correlations between Ca and Na + Si (i.e., Ca = 3.003 − 0.48[Na + Si]), and Al and Si (Al = 1.997 − 1.02Si). Because the replacement reactions, Ca 2+ ↔ 2Na + and Ca 2+ + 2Al 3+ ↔ 2Si 4+ , independently occur within the same crystal, these reactions have been simply combined together to generate a new formula, Na 2 x Ca 3− x − y (Al 1− y Si y ) 2 O 6 , where x is the amount of Ca substituted by Na, and y is the amount of Al substituted by Si. This formula leads to the equations Ca = 3 − 0.5[Na + Si] and Al = 2 − Si, which nicely account for the constrained chemical variation of the actual solid solutions with 0 ≤ x < 0.049 and 0 ≤ y < 0.073.