Synchrotron Powder Diffraction Quantitative Phase Analysis of Ordinary Portland Cements

Miguel A. G. Aranda, Ángeles G. de la Torre, Aurelio Cabeza, Enrique R. Losilla,

Departamento Química Inorgánica, Universidad de Málaga, 29071 Málaga, Spain (g_aranda@uma.es)

There is a great interest in the Quantitative Phase Analysis (QPA) of Ordinary Portland Cements (OPC) as their final performances depend on the mineralogical composition. Rietveld analysis of Laboratory X-ray Powder Diffraction (LXRPD) is the most powerful technique for obtaining QPA. However, LXRPD data contain systematic errors such as strong preferred orientation, optical aberrations which change with 2Q, microabsorption and strong peak overlapping of the different phases. Furthermore, the small mean penetration depth (~ 25 mm for Cu K_a) may lead to poor particle statistic.

High-Resolution Synchrotron X-ray Powder Diffraction (HRSXRPD) overcomes these drawbacks. Rotating capillary geometry (transmission) avoids preferred orientation. High energy X-rays minimise microabsorption and a large amount of sample is tested leading to good particle statistic. High resolution data minimize the overlapping and parallel synchrotron X-rays geometry, with an analyser crystal, do not show optical aberrations. Hence, we have used HRSXRPD to get good QPA of commercial OPC [1] and to show that accurate Rietveld QPA for cements can be obtained [2].

Here, we will report several QPA of OPC by using HRSXRPD. We will report data for white Portland clinkers, grey Portland clinkers and reference NIST 8488 clinker. The direct evidence of the co-existence of two alite phases in some patterns is highlighted. The alite phase(s) crystallise in the monoclinic MIII superstructure. The Figure shows a selected white OPC with a single alite (bottom) and a selected grey OPC clinker with two alites (top). The reference NIST 8488 clinker (intermediate) has also been analysed and it has two different alites. Furthermore, a-Al₂O₃ has been added to determine the non-diffracting contents of the studied samples. Full QPA of several OPC and the relevance of these results for the LXRPD analyses will be discussed. We will show the differences in the QPA of some cements with two alites by using medium resolution CuKa_1,2 laboratory data and high-resolution strictly monochromatic CuKa₁ laboratory X-ray powder diffraction data.

Figure 1. Selected region of HRSXRPD patterns (l=0.400Å) with peaks labelled in cement jargon. Bottom: a selected commercial white OPC; intermediate: NIST-8848; top: a selected commercial grey OPC clinker.

[1] A.G. de la Torre, A. Cabeza, A. Calvente, S. Bruque, M.A.G. Aranda “Full Phase Analysis of Portland Clinker by Penetrating Synchrotron X-rays” Analytical Chemistry 73, 151 (2001)

[2] A.G. de la Torre and M.A.G. Aranda “Accuracy in Rietveld Quantitative Phase Analysis of Portland Cements” Journal of Applied Crystallography 36, 1169 (2003)