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A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate

The conversion of CaSO(4)·0.5H(2)O to CaSO(4)·2H(2)O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in...

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Autores principales: Gurgul, Sebastian J., Seng, Gabriel, Williams, Gareth R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: International Union of Crystallography 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510200/
https://www.ncbi.nlm.nih.gov/pubmed/31074442
http://dx.doi.org/10.1107/S1600577519001929
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author Gurgul, Sebastian J.
Seng, Gabriel
Williams, Gareth R.
author_facet Gurgul, Sebastian J.
Seng, Gabriel
Williams, Gareth R.
author_sort Gurgul, Sebastian J.
collection PubMed
description The conversion of CaSO(4)·0.5H(2)O to CaSO(4)·2H(2)O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in this work. The CaSO(4)·2H(2)O product is very similar regardless of whether the α- or β-form of CaSO(4)·0.5H(2)O is used as the starting material, but the reaction process is very different. The induction time is usually shorter for α-CaSO(4)·0.5H(2)O than β-CaSO(4)·0.5H(2)O, and a greater conversion percentage is observed with the former (although in neither case does the reaction proceed to 100% completion). The temperature of the system, widely used in industry as an indirect measure of the extent of the hydration process, is found to be a poor pr­oxy for this, with the maximum temperature reached well before the reaction is complete. The Avrami–Erofe’ev and Gualtieri models could both be fitted to the experimental data, with the fits being substantially closer in the case of α-CaSO(4)·0.5H(2)O. The rate of reaction in the Avrami model tends to increase with the amount of gypsum seeds added to accelerate the process, and the importance of nucleation declines. The Gualtieri analysis suggested that the rate of nucleation increases substantially with the amount of seeds added, while there are less distinct changes in the rate of crystal growth. At low seed concentrations (<0.5% w/w) the rate of crystal growth is greater than the rate of nucleation, but at concentrations above 0.5% w/w nucleation is faster. These findings represent the first synchrotron study of the conversion of CaSO(4)·0.5H(2)O to CaSO(4)·2H(2)O, and will be of importance to gypsum producers globally.
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spelling pubmed-65102002019-06-03 A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate Gurgul, Sebastian J. Seng, Gabriel Williams, Gareth R. J Synchrotron Radiat Research Papers The conversion of CaSO(4)·0.5H(2)O to CaSO(4)·2H(2)O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in this work. The CaSO(4)·2H(2)O product is very similar regardless of whether the α- or β-form of CaSO(4)·0.5H(2)O is used as the starting material, but the reaction process is very different. The induction time is usually shorter for α-CaSO(4)·0.5H(2)O than β-CaSO(4)·0.5H(2)O, and a greater conversion percentage is observed with the former (although in neither case does the reaction proceed to 100% completion). The temperature of the system, widely used in industry as an indirect measure of the extent of the hydration process, is found to be a poor pr­oxy for this, with the maximum temperature reached well before the reaction is complete. The Avrami–Erofe’ev and Gualtieri models could both be fitted to the experimental data, with the fits being substantially closer in the case of α-CaSO(4)·0.5H(2)O. The rate of reaction in the Avrami model tends to increase with the amount of gypsum seeds added to accelerate the process, and the importance of nucleation declines. The Gualtieri analysis suggested that the rate of nucleation increases substantially with the amount of seeds added, while there are less distinct changes in the rate of crystal growth. At low seed concentrations (<0.5% w/w) the rate of crystal growth is greater than the rate of nucleation, but at concentrations above 0.5% w/w nucleation is faster. These findings represent the first synchrotron study of the conversion of CaSO(4)·0.5H(2)O to CaSO(4)·2H(2)O, and will be of importance to gypsum producers globally. International Union of Crystallography 2019-04-05 /pmc/articles/PMC6510200/ /pubmed/31074442 http://dx.doi.org/10.1107/S1600577519001929 Text en © Sebastian J. Gurgul et al. 2019 http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.http://creativecommons.org/licenses/by/4.0/
spellingShingle Research Papers
Gurgul, Sebastian J.
Seng, Gabriel
Williams, Gareth R.
A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title_full A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title_fullStr A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title_full_unstemmed A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title_short A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
title_sort kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
topic Research Papers
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510200/
https://www.ncbi.nlm.nih.gov/pubmed/31074442
http://dx.doi.org/10.1107/S1600577519001929
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