Quantitative X-ray diffraction of free, not chemically bound water with the PONKCS method

Abstract

The free water in calcined phyllosilicate–water mixtures exhibits a distinctly different behaviour in its X‐ray amorphous scattering contribution as opposed to fly ash– or limestone powder–water mixtures. While fly ash and limestone powder yield a continuous increase in the scattering contribution when water is added, the scattering contribution stagnates for calcined phyllosilicates over a wide range of water addition. There is a direct correlation between the consistency of the sample and the X‐ray amorphous scattering contribution caused by the water. The same correlation can also be found in in situ X‐ray diffraction measurements of hydrating systems. As long as the sample has a pasty consistency, the scattering contribution of the water decreases with progressive reaction. After the transition from fresh paste to final set, there is no further reduction of the X‐ray amorphous scattering contribution caused by the free water, which means that the free water cannot be quantified correctly from this point in time.

Reactivity of Metakaolin in Alkaline Environment: Correlation of Results from Dissolution Experiments with XRD Quantifications

“…The chemical composition was determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) and the mineralogical composition by quantitative powder X-ray diffraction (QPXRD) with 20 wt.% ZnO as an internal standard to determine the X-ray amorphous content (Table 1). The data have already been published by the authors in [38,44]. For the experiments, 5 g MK was shaken in 400 mL solution for 24 h on a vibrating unit.…”

“…The sample was prepared with a back-loading tool and covered with a Kapton film (DuPont, Wilmington, DE, USA). The use of the Kapton film allows to summarize the instrumental background and the background caused by the Kapton film and ensures a stable refinement [38]. The quantifications were performed combining external standard [47,48] and PONKCS method [35,49].…”

“…The calibrations for quantitative analysis of the hkl-phases were performed with ZnO as internal standard. The procedure for creating the hkl-phases, their calibration, as well as the refinement parameters, are described in detail in [38].…”

“…Quantifications of the degree of reaction of metakaolin in cementitious systems with the PONKCS method [28] also confirm this assumption. An accurate modelling and calibration of the X-ray amorphous content as well as a precise description of the background [38] seems to be more important for a reliable quantification with the PONKCS method.…”

“…The quantification of X-ray amorphous SCM with the partial or no known crystal structure (PONKCS) method [35] is a powerful tool to determine the SCM content in blended cements [36,37]. Quantification of SCM in hydrating systems is a challenging task due to strong overlap of the broad SCM peaks with X-ray amorphous hydrates and the free, not chemically bound, water [36,38]. The latest research confirms the possibility of quantifying the reacted SCM during in situ XRD measurements of hydrating systems [28].…”