Thermodynamic Analysis of Hydration Processes of Calcium Aluminoferrites

Abstract

The processes of hydration and hydrate phase formation of calcium aluminoferrites are insufficiently covered in the technical literature. Thermodynamic analysis of the hydration processes of calcium aluminoferrite of 4CaO·Al2O3·Fe2O3 is difficult due to the unreliability of the initial data for hydration products. The question of the basicity of calcium hydroferrites requires clarification. There is insufficient data on the justification of the method of calculating the thermodynamic properties of hydroferrite -∆G0298, - ∆H0298 and c(T), verification of their results, the mechanism of formation of the complex anion Fe(OH)4- and its stability in the liquid phase of hydrating C4AF.
 The hydration of 4CaO·Al2O3·Fe2O3 with the formation of 2CaO·Al2O3·8H2O as hydrate phases is considered. The energy of hydrogen bonds between the layers of Ca(OH)2, Al2(OH)3 and Fe(OH)3, from which the hexagonal layers of these complex calcium, aluminum and iron hydroxides are composed, is compared. It is shown that the values of ∆G0298 and ∆H0298 2CaO·Fe2O3·8H2O, which are equal to -937.2 and -1082.3 kcal/mol, respectively, are not consistent with experimental data on the solubility of C2FH8 and the specific heat release during C4AF hydration (100-115 kcal/g). Values for C2FH8, ∆G0298= -933, ∆H0298 = -1072 kcal/mol are recommended. It is shown that the formation of Fe(OH)3 hydroxide in the amorphous state, rather than the Fe(OH)4 ion, is preferable as an intermediate product of C4AF hydration.