Mineralogical characteristics of Ettringites synthesized from solutions and suspensions

Due to the wide technical importance of Ettringite (3CaO·Al2O3·3CaSO4·32H2O) in hydrated cement based systems, four different synthesis methods were applied to get a better overview on how and under what favoring conditions Ettringite can be formed. In the first step different precipitation methods resulting in Ettringite were established. For all methods Al3+ was supplied by aqueous CO2-free solution of Al2(SO4)3·18H2O. As a source of CaO-supply a clear solution and otherwise a Ca(OH)2-suspension was utilized. Four synthesis routes with and without sucrose were employed.Variation of reaction parameter like temperature, time of reaction, pH-value of synthesis solution and influence of additional Gypsum were investigated. The qualitative phase analysis was performed by X-ray diffraction method (XRD). Morphological aspects of some synthesis products were studied by scanning electron microscopy (SEM). Finally lattice and structural parameter of the Ettringites were determined by refinement of XRD-pattern using the Rietveld-Method.