Estimation of the solubility limit of iron in tricalcium aluminate using different techniques

Tricalcium aluminate (C3A) is one of the four main phases found in portland cement clinker. For this study Fe2O3 was added to C3A in two ways. In the first, it was added to previously synthesized C3A by firing it at 1350°C for 3 h with intermediate grinding in air after each hour then quenching it in air. In the second mixture Fe2O3 was added to the starting materials (CaCO3 and Al2O3) and fired at 1350°C for 15 h with intermediate grinding in air at 3 h intervals during firing then finally quenching it in air. The percentages of the Fe2O3 added were 3, 4, 6, 8, 12, 16 and 20 wt.%. The extent of iron in solid solution was measured using an X-ray diffractometer, Mِssbauer spectrometer, d.c. conductivity meter and magnetic susceptibility tests. It was found that the solubility limit of iron oxide (Fe2O3) in C3A is about 4 wt.%. Mِssbauer spectroscopy and magnetic susceptibility can be considered useful tools to estimate the solubility limit of iron in C3A. The sequence of adding iron to the C3A (either before or after firing) is found to affect the structural positions of the iron ions in the C3A structure.