The superstructure of C3S from synchrotron and neutron powder diffraction and its role in quantitative phase analyses

We have synthesised the room temperature MIII form of alite stabilised by doping with Mg and Al. The complex disordered superstructure of this tricalcium silicate [Ca3SiO5 (C3S)] sample has been studied by a joint Rietveld refinement of ultra-high-resolution synchrotron X-ray powder diffraction data, medium-resolution neutron powder diffraction data and soft constraints of interatomic distances. Alite crystallises in a monoclinic cell with dimensions a = 33.1078(6) Angstrom, b = 7.0355(1) Angstrom, c = 18.5211(4) Angstrom, beta = 94.137(1)degrees and V = 4302.9(2) Angstrom(3). The final R factors were R-WP = 8.76% and R-F(C3S) = 3.45% for the synchrotron data and R-WP = 6.09% and R-F(C3S) = 5.10% for the neutron data. The reported superstructure is simpler than those previously reported, and it fits properly to a variety of Portland clinker and cement patterns. The Rietveld analyses of four clinkers with variable Mg contents have shown that the refinements are good. The Bogue approach gave quite poor results when compared to these state-of-the-art powder diffraction analyses. Bogue method slightly underestimates the C3S + C2S content, overestimates the C(3)A fraction and underestimates the C(4)AF content. Similar analyses of Portland cements with nine crystalline phases are shown to be feasible. (C) 2002 Elsevier Science Ltd. All rights reserved.