Ettringite dependace in thaumasite formation

Thaumasite has been synthetized with and without ettringite in the reaction medium. The compositions of solids have been analyzed over time by means of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM-EDX) in order to check the relation between ettringite and thaumasite. The results indicate that in the synthesis in absence of ettringite, the thaumasite appears at 6 months. By contrast, in the synthesis with presence of ettringite, at 7 days much of the ettringite has become thaumasite and at 2 months ettringite has disappeared and only thaumasite is detected. The results obtained at the end of two years experience, using the Rietveld method, show that thaumasite forms from ettringite by substitution of aluminum with silicon.