Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation
Single crystals and polycrystalline samples of transparent calcite (Iceland spar) were used to investigate the effects of pressure (p), temperature (T), pressure beyond an accepted equilibrium value (Δp), and grain size (D) on the kinetics of the calcite–aragonite transformation. Transformed mass fr...
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crcansciencepubl:10.1139/e79-125 2024-03-03T08:45:48+00:00 Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation Brar, N. S. Schloessin, H. H. 1979 http://dx.doi.org/10.1139/e79-125 http://www.nrcresearchpress.com/doi/pdf/10.1139/e79-125 en eng Canadian Science Publishing http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining Canadian Journal of Earth Sciences volume 16, issue 7, page 1402-1418 ISSN 0008-4077 1480-3313 General Earth and Planetary Sciences journal-article 1979 crcansciencepubl https://doi.org/10.1139/e79-125 2024-02-07T10:53:40Z Single crystals and polycrystalline samples of transparent calcite (Iceland spar) were used to investigate the effects of pressure (p), temperature (T), pressure beyond an accepted equilibrium value (Δp), and grain size (D) on the kinetics of the calcite–aragonite transformation. Transformed mass fractions x(t), produced after different times of exposure to constant pressure ranging from 14 to 25 kbar (1.4 to 2.5 GPa) and constant temperature from 300 to 600 °C, were determined from integrated X-ray peak intensities of the (012), (021), and (111) reflections of aragonite. Values for the rale constant K and the exponent n characterizing the transformation were computed from the x(t) data using Cahn's nucleation and growth model for solid–solid transformations. At 17 kbar(1.7 GPa), K(s −1 ) increases from 2.00 × 10 −5 at 300 °C to 1.39 × 10 −3 at 600 °C. The exponent n, of the order of 1, mostly <1, indicates that the nucleation stage is terminated rapidly by site saturation and that most of the transformation takes place thereafter by growth as expected from theory. For single crystals the relationship between x(t) and Δp, for a period of 1 hour is almost linear. At 600 °C the relative increase of x(t) amounts to 0.1 kbar −1 (1 × 10 7 Pa −1 ). For a given time, x increases nearly exponentially with T. The apparent activation energy for the transformation, at 17 kbar (1.7 GPa), is 16 kcal mol −1 . For polycrystals x(t) decreases as [Formula: see text]. This somewhat surprising result may be related to deviatoric stresses and stress concentration by the already transformed volume fractions, which act as misfitting, ellipsoidal, inclusions. Article in Journal/Newspaper Iceland Canadian Science Publishing Canadian Journal of Earth Sciences 16 7 1402 1418 |
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Canadian Science Publishing |
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English |
topic |
General Earth and Planetary Sciences |
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General Earth and Planetary Sciences Brar, N. S. Schloessin, H. H. Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
topic_facet |
General Earth and Planetary Sciences |
description |
Single crystals and polycrystalline samples of transparent calcite (Iceland spar) were used to investigate the effects of pressure (p), temperature (T), pressure beyond an accepted equilibrium value (Δp), and grain size (D) on the kinetics of the calcite–aragonite transformation. Transformed mass fractions x(t), produced after different times of exposure to constant pressure ranging from 14 to 25 kbar (1.4 to 2.5 GPa) and constant temperature from 300 to 600 °C, were determined from integrated X-ray peak intensities of the (012), (021), and (111) reflections of aragonite. Values for the rale constant K and the exponent n characterizing the transformation were computed from the x(t) data using Cahn's nucleation and growth model for solid–solid transformations. At 17 kbar(1.7 GPa), K(s −1 ) increases from 2.00 × 10 −5 at 300 °C to 1.39 × 10 −3 at 600 °C. The exponent n, of the order of 1, mostly <1, indicates that the nucleation stage is terminated rapidly by site saturation and that most of the transformation takes place thereafter by growth as expected from theory. For single crystals the relationship between x(t) and Δp, for a period of 1 hour is almost linear. At 600 °C the relative increase of x(t) amounts to 0.1 kbar −1 (1 × 10 7 Pa −1 ). For a given time, x increases nearly exponentially with T. The apparent activation energy for the transformation, at 17 kbar (1.7 GPa), is 16 kcal mol −1 . For polycrystals x(t) decreases as [Formula: see text]. This somewhat surprising result may be related to deviatoric stresses and stress concentration by the already transformed volume fractions, which act as misfitting, ellipsoidal, inclusions. |
format |
Article in Journal/Newspaper |
author |
Brar, N. S. Schloessin, H. H. |
author_facet |
Brar, N. S. Schloessin, H. H. |
author_sort |
Brar, N. S. |
title |
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
title_short |
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
title_full |
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
title_fullStr |
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
title_full_unstemmed |
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
title_sort |
effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation |
publisher |
Canadian Science Publishing |
publishDate |
1979 |
url |
http://dx.doi.org/10.1139/e79-125 http://www.nrcresearchpress.com/doi/pdf/10.1139/e79-125 |
genre |
Iceland |
genre_facet |
Iceland |
op_source |
Canadian Journal of Earth Sciences volume 16, issue 7, page 1402-1418 ISSN 0008-4077 1480-3313 |
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http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining |
op_doi |
https://doi.org/10.1139/e79-125 |
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Canadian Journal of Earth Sciences |
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16 |
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7 |
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1402 |
op_container_end_page |
1418 |
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1792501448797323264 |