Transition of Friedel phase to chromate-AFm phase

The transition of the Friedel phase to the chromate-AFm phase in chromate solution and the thermal stability of the products was investigated using thermal analysis combined with mass spectrometry, X-ray diffraction and Fourier transform infrared spectrometer. The results indicated that easily substituted for Cl in the Friedel phase forming chromate-AFm. The chemical formula of chromate-AFm was characterised as 3CaO·Al2O3·CaCrO4·12H2O. Chromate-AFm gave two steps of dehydration, two steps of dehydroxylation and one step of redox reaction of Cr(VI) in the whole heating process from 40 to 1000°C. The Fourier transform infrared spectra showed different OH-metal binding ways for the Freidel phase and chromate-AFm.