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Phase relations of portlandite, Ca(OH)_2 and brucite, Mg(OH)_2 to 33 kilobars

Irving, A. J. and Huang, W.-L. and Wyllie, P. J. (1977) Phase relations of portlandite, Ca(OH)_2 and brucite, Mg(OH)_2 to 33 kilobars. American Journal of Science, 277 (3). pp. 313-321. ISSN 0002-9599. doi:10.2475/ajs.277.3.313.

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Using piston-cylinder apparatus, we have extended to 33 kb the dissociation curve for brucite by the quench method and the fusion curves for portlandite dry and with excess water vapor by differential thermal analysis. Experimental brackets for the fusion of portlandite are 800° to 809°C al 10 kb, 796° to 800°C at 20 kb, and 781° to 786°C at 30 kb, and for the fusion of portlandite with excess vapor 715° to 719°C at 10 kb, 675° to 682°C at 20 kb, 643° to 649°C at 30 kb. Experimental brackets for the brucite dehydration are 920° to 940°C at 17 kb, 1050°C at 27 kb, and 1080° to 1100°C at 33 kb; the 33 kb bracket was reversed; one DTA run at 27 kb gave 1055° ± 7°C, overlapping the definitive quench run. We find no evidence for the previously reported temperature maximum on the brucite dehydration curve at 32 kb. From the experimental data for the brucite reaction, values calculated for the Gibbs free energy function, G*, of water arc -15.325 kcal mole^(-1) at 17 kb, 930°C; -6.647 kcal mole^(-1) at 27 kb, 1050°C; and -2.997 kcal mole^(-1) at 33 kb, 1090°C.

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Alternate Title:Phase relations of portlandite, Ca(OH)2 and brucite, Mg(OH)2 to 33 kilobars
Additional Information:© 1977 American Journal of Science. This research was supported by the Earth Sciences Section, National Science Foundation, NSF Grant GA-41730. We would like to acknowledge also the general support of the Materials Research Laboratory by the National Science Foundation. We thank John Holloway for supplying unpublished thermodynamic data and for helpful discussion.
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Official Citation:A. J. Irving, W.-L. Huang, and P. J. Wyllie Phase relations of portlandite, Ca(OH) 2 and brucite, Mg(OH) 2 to 33 kilobars Am J Sci March 1, 1977 277:313-321; doi:10.2475/ajs.277.3.313
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64069
Deposited By: Tony Diaz
Deposited On:28 Jan 2016 23:48
Last Modified:10 Nov 2021 23:25

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