Characterisation of iron inclusion during the formation of calcium sulfoaluminate phase

The iron distribution among the sulfoaluminate clinker phases and its ability to enter the calcium sulfoaluminate lattice in solid solution can have a significant influence on manufacturing process and reactivity of calcium sulfoaluminate (CSA) cements. X-ray diffraction (XRD) analysis, Mossbauer spectroscopy, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis system (EDAX) and infrared spectroscopy were used to identify the mineralogical conditions of iron inclusion during the formation of calcium sulfoaluminate (C(4)A(3)S) phase from different mixtures in the CaO-Al(2)O(3)-Fe(2)O(3)-SO(3) system. The mixtures, heated in a laboratory electric oven, contained stoichiometric amounts of reagent grade CaCO(3), Al(2)O(3), Fe(2)O(3) and CaSO(4)center dot 2H(2)O for the synthesis of Ca(4)Al((6 - 2x))Fe(2x)SO(16), where x, comprised between 0 and 3, is the mole number of Al(2)O(3) substituted by Fe(2)O(3). With x increasing from 0 to 1.5, both the iron content of C(4)A(3)S phase and the amounts of side components such as C(2)F and CS increased. For x values included in the range of 1.5-3.0, at temperatures higher than 1200 degrees C, melting phenomena were observed and, instead of the C(4)A(3)S solid solution, ferritic phases and anhydrite were formed. (C) 2010 Elsevier Ltd. All rights reserved.