Bernal Lopez, SA

Brown, A

Freeman, H

Hodson, ME

Leadley, V

Marsh, ATM

Mills, R

Neumann, A

Pendlowski, H

Stennett, MC

Walkley, B

Wright, A

White Rose Research Online

This is a repository copy of Investigating aluminium co-ordination in a thermally activated iron rich kaolinitic clay by STEM-EELS.White Rose Research Online URL for this paper:https://eprints.whiterose.ac.uk/191679/Version: Accepted VersionConference or Workshop Item:Marsh, ATM orcid.org/0000-0002-5603-4643, Brown, A orcid.org/0000-0001-9692-2154, Freeman, H orcid.org/0000-0001-8242-9561 et al. (9 more authors) (2022) Investigating aluminium co-ordination in a thermally activated iron rich kaolinitic clay by STEM-EELS. In:Calcined Clays for Sustainable Concrete 2022, 05-07 Jul 2022, Lausanne, Switzerland. This is an author produced version of a conference abstract presented at Calcined Clays for Sustainable Concrete 2022.eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. INVESTIGATING ALUMINIUM CO-ORDINATION IN A THERMALLY ACTIVATED IRON RICH KAOLINITIC CLAY BY STEM-EELS Alastair T.M. Marsh1; Andy Brown2; Helen Freeman3, Mark E. Hodson4, Vicky Leadley5, Rob Mills6, Anke Neumann7, Helen Pendlowski8, Martin C. Stennett9, Brant Walkley10, Amy Wright11, Susan A. Bernal12 1School of Civil Engineering, University of Leeds; a.marsh@leeds.ac.uk 2School of Chemical and Process Engineering, University of Leeds; a.p.brown@leeds.ac.uk  3School of Civil Engineering, University of Leeds; h.m.freeman@leeds.ac.uk  4Department of Environment and Geography, University of York; mark.hodson@york.ac.uk  5Department of Chemistry, University of York; vicky.leadley@york.ac.uk  6Department of Environment and Geography, University of York; robert.mills@york.ac.uk  7School of Engineering, Newcastle University; anke.neumann@newcastle.ac.uk  8James Hutton Institute; helen.pendlowski@hutton.ac.uk 9Department of Materials Science and Engineering, University of Sheffield; m.c.stennett@sheffield.ac.uk  10Department of Chemical and Biological Engineering, University of Sheffield; b.walkley@sheffield.ac.uk  11Department of Environment and Geography, University of York; aw1503@york.ac.uk  12School of Civil Engineering, University of Leeds; s.a.bernallopez@leeds.ac.uk   Introduction Iron-rich kaolinitic clay deposits provide opportunities for supplementary cementitious material production due to their widespread occurrence in several regions, but they also provide challenges around characterisation. In particular, high iron contents preclude the use of solid state nuclear magnetic resonance (NMR) spectroscopy to assess changes in Al coordination state after calcination. Chemical treatments to remove crystalline Fe compounds from clays [1] cannot be guaranteed to have no effect on the clay minerals themselves, and so there is value in exploring alternative techniques to measure Al coordination which are compatible with high Fe contents. Electron energy loss spectroscopy (EELS) is a microscope-based analytical technique that has been widely used to measure coordination states for a range of minerals [2]. In this study an iron-rich clay was thermally activated, and subjected to a range of conventional/bulk solid-state characterisation techniques, and then results were augmented with Scanning Transmission Electron Microscopy (STEM) with Energy Dispersive X-ray Spectroscopy (EDX) and EELS. Materials and Methods A pre-ground iron-rich lithomarge from the interbasaltic formation in Country Antrim, UK, was thermally activated by calcination for 1 hour at 750°C in a laboratory static furnace. Quantitative powder X-ray Diffraction (XRD) analysis was carried out via the full pattern reference intensity ratio method [3]. TEM samples were prepared by diluting suspensions of the clays in ethanol and drop casting onto holey amorphous carbon Cu grids. A FEI Titan3 Themis G2 S/TEM operating at 300 kV was used with an FEI Super-X energy dispersive X-ray (EDX) system, a monochromator with an energy spread of ca. 0.4 eV, a Gatan Quantum 965 ER energy filter for dual EELS and a Gatan OneView CCD. Spectra were acquired by continuously scanning the  focussed probe over a 30 mrad collection angle, at < 180k times to ensure minimal damage per pixel dwell occurred at the kaolinite plates (as per the method described in Freeman et al. [4]. Collected spectra were energy calibrated and background subtracted (power law) in ‘Gatan Microscopy Suite’ software (version 3.0.1).   Results and Discussion XRD results showed that thermal treatment resulted in the complete dehydroxylation of kaolinite to form metakaolinite, alongside transformation of goethite surface particles to hematite (Table 1).   Table 1: Quantitative breakdown of phases, in wt.%. Mineral abbreviations: Qz = Quartz; Ant = Anatase; Gth = Goethite; Hem = Hematite; Mag = Magnetite; Gbs = Gibbsite; Kln = Kaolinite.  Sample ID Qz Ant Gth Hem Mag Gbs Kln Amorphous-I TOTAL Raw 1.1 0.3 29 2.7 2.6 1.6 62.7 0 100 Calcined 1.6 1.1 1.1 24.2 0 0 0 72 100  In the uncalcined clay, TEM images show regularly spaced kaolinite sheets with nanoscale particles of goethite adsorbed to their surfaces (Figure 1a,b). After calcination, there is some evidence of delamination of the metakaolin plates, along with transformation of goethite to larger, hematite particles on the clay plates’ surface (see arrow, Figure 1c). In the uncalcined clay, STEM-EEL spectra of kaolinite plates’ Al K-edge suggests 100% AlVI co-ordination [5] (Figure 2a). After calcination, the Al K-edge profile suggests a transformation to AlIV co-ordination, associated with metakaolin formation [5, 6] (Figure 2b).  a  b  c  Figure 1: Bright field TEM images of kaolinite plates pre-calcination (a) with Fe-rich surface nanoparticles shown by STEM-EDX elemental maps from the yellow boxed inset (b; Al – green; Si- red; Fe blue), and post-calcination (c).  a  b  Figure 2: EEL Al K-edge spectra pre-calcination (a) and post-calcination (b).   Conclusions STEM-EELS shows potential for assessing Al co-ordination in kaolinite and metakaolin particles present in a mixed phase clay, in a spatially resolved manner not achievable with NMR. There is further potential to investigate the changes in iron hydroxide/oxide minerals adsorbed on clay minerals both pre- and post-calcination, and their role in affecting reactivity and early age hydration in blended cementitious systems. STEM-EELS will not be a routine characterisation technique, but does offer potential insight to the local degree of kaolinite transformation. The sensitivity to Al coordination changes will be quantified by fitting of experimental data by reference spectra from pre- and post-calcined china clay standards.  Acknowledgements Funding is gratefully acknowledged from White Rose Collaboration Fund and EPSRC (EP/R001642/1). Keywords: Transmission electron microscopy; electron energy loss spectroscopy; metakaolin.  References 1. Mehra, O.P. and M.L. Jackson, Iron Oxide Removal from Soils and Clays by a Dithionite-Citrate System Buffered with Sodium Bicarbonate. Clays and Clay Minerals, 1958. 7(1): p. 317-327. 10.1346/CCMN.1958.0070122 2. Lee, M.R., Transmission electron microscopy (TEM) of Earth and planetary materials: A review. Mineralogical Magazine, 2010. 74(1): p. 1-27. 10.1180/minmag.2010.074.1.1 3. Butler, B.M. and S. Hillier, Automated full-pattern summation of x-ray powder diffraction data for high-throughput quantification of clay-bearing mixtures. Clays and Clay Minerals, 2021. 69(1): p. 38-51. 10.1007/s42860-020-00105-6 4. Freeman, H.M., et al., Beam-induced oxidation of mixed-valent Fe (oxyhydr)oxides (green rust) monitored by STEM-EELS. Micron, 2019. 122: p. 46-52. 10.1016/j.micron.2019.02.002 5. Ildefonse, P., et al., Aluminium X-ray absorption Near Edge Structure in model compounds and Earth’s surface minerals. Physics and Chemistry of Minerals, 1998. 25(2): p. 112-121. 10.1007/s002690050093 6. Li, D., et al., Al K-edge XANES spectra of aluminosilicate minerals. American Mineralogist, 1995. 80(5-6): p. 432-440. 10.2138/am-1995-5-602   

Investigating aluminium co-ordination in a thermally activated iron rich kaolinitic clay by STEM-EELS

https://eprints.whiterose.ac.uk/191679/1/Investigating%20aluminium%20co-ordination%20in%20a%20thermally%20activated%20iron%20rich%20kaolinitic%20clay%20by%20STEM-EELS.pdf

Investigating aluminium co-ordination in a thermally activated iron rich kaolinitic clay by STEM-EELS

Abstract

Similar works

Full text

Available Versions

White Rose Research Online