Atomic-scale characterisation of sodium aluminosilicate hydrates (N-A-S-H) and Mg-substituted N(-M)-A-S-H using XANES

Xinyuan Ke, Jiaqi Li, Vahiddin Baki, Alexander Large, Georg Held

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2 Citations (SciVal)

Abstract

The chemical structures of aluminosilicate hydrates presented in alkali-activated geopolymer materials underpin their performances. Mg-substituted sodium aluminosilicate hydrates (N(-M)-A-S-H) are likely to be present in alkali-activated geopolymer materials prepared using MgO-containing precursors, however, their atomic-level structures remain unclear. The lack of such knowledge made it challenging to identify and distinguish N(-M)-A-S-H from complex alkali-activated geopolymer systems (i.e., alkali-activated slag, alkali-activated Mg-rich minerals), and therefore brought challenges in understanding and predicting their durability. This study characterised for the first time the atomic structures of the synthetic N(-M)-A-S-H gels, prepared through ion-exchange or co-synthesis, using X-ray absorption near-edge spectroscopy (XANES) at Si, Al and Mg K-edge. The results suggest that the substitution of Mg in the extra-framework locations of the alkali aluminosilicate hydrates (N-A-S-H) leads to negligible changes in the coordination environments of the aluminosilicate framework. However, the Mg coordination environment is distinguishably different from other Mg-containing phases in the systems, e.g., hydrotalcite. The Mg K-edge XANES of N(-M)-A-S-H shows a 0.8–1.2 eV shift compared with hydrotalcite. The results presented in this study can be used as the fingerprint to probe the presence of N(-M)-A-S-H in alkali-activated geopolymer materials containing Mg element.
Original languageEnglish
Article number105515
JournalApplied Geochemistry
Volume147
Early online date12 Nov 2022
DOIs
Publication statusPublished - 31 Dec 2022

Bibliographical note

EPSRC
EP/W010828/1
Diamond Light Source Ltd
Proposal SI28470
University of Bath
Prize Fellowship
Lawrence Livermore National Laboratory
21ERD050

Funding Information:
This work was carried out with the support of Diamond Light Source, instrument B07 (proposal SI28470). This research was partially funded by the UK Engineering and Physical Sciences Research Council (EPSRC) through Grant EP/W010828/1. The participation of XK was partially funded by the University of Bath Prize Fellowship (2018–2021). The participation of JL was under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (contract No. DE-AC52-07NA27344), with LLNL IM release number LLNL-JRNL-833223. The authors would also like to thank Imerys (UK) for supplying metakaolin materials for this study. The authors would also like to acknowledge Dr Daniel Geddes, The University of Sheffield, for assisting the collection of 29Si solid-state MAS NMR data (included in Supplementary data).

Funding Information:
This work was carried out with the support of Diamond Light Source , instrument B07 (proposal SI28470 ). This research was partially funded by the UK Engineering and Physical Sciences Research Council (EPSRC) through Grant EP/W010828/1 . The participation of XK was partially funded by the University of Bath Prize Fellowship (2018–2021). The participation of JL was under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (contract No. DE-AC52-07NA27344), with LLNL IM release number LLNL-JRNL-833223. The authors would also like to thank Imerys (UK) for supplying metakaolin materials for this study. The authors would also like to acknowledge Dr Daniel Geddes, The University of Sheffield, for assisting the collection of 29 Si solid-state MAS NMR data (included in Supplementary data).

Keywords

  • Alkali-activated geopolymer materials
  • Amorphous material
  • Atomic-level characterization
  • X-ray absorption spectroscopy

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Geochemistry and Petrology

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