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Open AccessArticle

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution

Department of Civil Engineering, Kyonggi University, Suwon 16227, Korea
School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Korea
School of Environmental and Life Sciences, Kean University, Union, NJ 07083, USA
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
Author to whom correspondence should be addressed.
Academic Editor: Jorge de Brito
Materials 2016, 9(5), 401;
Received: 4 May 2016 / Revised: 16 May 2016 / Accepted: 16 May 2016 / Published: 21 May 2016
(This article belongs to the Section Advanced Composites)
Monosulfoaluminate (Ca4Al2(SO4)(OH)12∙6H2O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO42− and OH) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formed ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel’s salt or Friedel’s salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed. View Full-Text
Keywords: cement chemistry; STXM; XANES; chloride; Kuzel’s salt; Friedel’s salt; monosulfate cement chemistry; STXM; XANES; chloride; Kuzel’s salt; Friedel’s salt; monosulfate
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Yoon, S.; Ha, J.; Chae, S.R.; Kilcoyne, D.A.; Jun, Y.; Oh, J.E.; Monteiro, P.J. Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution. Materials 2016, 9, 401.

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