Application of combined multivariate techniques for the description of time-resolved powder X-ray diffraction data

Abstract

In this work, multivariate statistical techniques are employed to determine patterns and conversion curves from time-resolved X-ray powder diffraction data. For these purposes, time-window statistical total correlation spectroscopy is introduced for the pattern matching of the crystalline phase and is shown to be effective even in the case of overlapping peaks. When combined with evolving factor analysis and multivariate curve resolution-alternating least squares, this technique allows a definite estimation of patterns and conversion curves. The procedure is applied to in situ synchrotron powder diffraction patterns to monitor the setting reaction of magnesium potassium phosphate ceramic (MKP) from magnesia (MgO) and potassium dihydrogen phosphate. It is shown that the phases involved in the reaction are clearly distinguished and their evolution is correctly described. The conversion curves estimated with the proposed procedure are compared with the ones determined with the peak integration method, leading to an excellent agreement (Pearson's correlation coefficient equal to 0.9995 and 0.9998 for MgO and MKP, respectively). The approach also allows for the detection and description of the evolution of amorphous phases that cannot be described through conventional analysis of powder diffraction data

3D microstructure of magnesium potassium phosphate ceramics from X-ray tomography: new insights into the reaction mechanisms

“…It is well known that the microstructure of MPCs develops very quickly. Reaction rates slow down after the first hour; by this time, a compact solid has already formed [50,57]. Recent works pointed to amorphous gel-like phases as first reaction products [13,14,18,57,58], in agreement with previous models of ceramic formation [59,60].…”

“…Reaction rates slow down after the first hour; by this time, a compact solid has already formed [50,57]. Recent works pointed to amorphous gel-like phases as first reaction products [13,14,18,57,58], in agreement with previous models of ceramic formation [59,60]. It has been proposed that the amorphous fraction forms thanks to the high degree of supersaturation established in solution in proximity of the MgO grains [50,61].…”

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed byin situtotal scattering

“…Using MCR-ALS analysis, a complex system with multiple evolving components is reduced to the least number of components that can describe the initial dataset. This makes MCR-ALS especially suitable for the analysis of large datasets generated during in situ and/or operando experiments, e.g., IR, 54 Raman, 55 XAS, 56 XRD, 57 or PDF. 58,59 MCR-ALS provides the characteristic profiles of the individual components and the evolution of these components with time (time-concentration profiles).…”

Microstructural evolution and texture analysis of magnesium phosphate cement

“…Despite a solid mass is obtained few minutes after mixing, most of the strength development is delayed and occurs over a long time scale (several days) . Such behavior has been attributed to the formation of an amorphous/paracrystalline intermediate reaction product, precursor of K‐struvite . Correlation of mechanical performance with amount of K‐struvite, indicated in the progressive development of a pervasive network of tabular/elongated K‐struvite crystals the main toughening mechanism in MPCs …”

“…to the formation of an amorphous/paracrystalline intermediate reaction product, precursor of K-struvite. 12,15 Correlation of mechanical performance with amount of K-struvite, 8,14 indicated in the progressive development of a pervasive network of tabular/elongated K-struvite crystals the main toughening mechanism in MPCs. 8,16 As recently probed for MPC formulations in a range of water-to-solid weight ratios using Synchrotron X-ray microComputed Tomography (mCT), 17 the amorphousto-crystalline transformation, which is always incomplete, plays a central role in dictating the development of the microstructure and, ultimately, the performance of the cement, establishing the link between reaction mechanisms and properties.…”