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@ARTICLE{Gasc:311029,
      author       = {Gasc, Julien and Brunet, Fabrice and Brantut, Nicolas and
                      Corvisier, Jérôme and Findling, Nathaniel and Verlaguet,
                      Anne and Lathe, Christian},
      title        = {{E}ffect of {W}ater {A}ctivity on {R}eaction {K}inetics and
                      {I}ntergranular {T}ransport: {I}nsights from the
                      $\mathrm{{C}a({OH})_{2}  + {M}g{CO}_{3} \to {C}a{CO}_{3}
                       + {M}g({OH})_{2}}$ {R}eaction at 1·8 {GP}a},
      journal      = {Journal of petrology},
      volume       = {57},
      number       = {7},
      issn         = {1460-2415},
      address      = {Oxford},
      publisher    = {Oxford Univ. Press},
      reportid     = {PUBDB-2016-04578},
      pages        = {1389 - 1408},
      year         = {2016},
      note         = {(c) The Author. Published by Oxford University Press},
      abstract     = {The kinetics of the irreversible reaction Ca(OH) 2
                       + MgCO 3 → CaCO 3  + Mg(OH) 2 were investigated
                      at high pressures and temperatures relevant to metamorphic
                      petrology, using both in situ synchrotron X-ray diffraction
                      and post-mortem analysis of reaction rim growth on recovered
                      samples. Reaction kinetics are found to strongly depend on
                      water content; comparable bulk-reaction kinetics are
                      obtained under water-saturated (excess water, c. 10 wt
                      $\%)$ and under intermediate (0·1–1 wt $\%$ water)
                      conditions when temperature is increased by c. 300 K. In
                      contrast, similar reaction kinetics were observed at
                      ∼673 K and 823 K between intermediate and dry
                      experiments, respectively, where dry refers to a set of
                      experiments with water activity below 1·0 (no free water),
                      as buffered by the CaO–Ca(OH) 2 assemblage. Given the
                      activation energies at play, this gap—corresponding to the
                      loss of no more than 1 wt $\%$ of water by the
                      assemblage—leads to a difference of several orders of
                      magnitude in reaction kinetics at a given temperature.
                      Further analysis, at the microscopic scale, of the
                      intermediate and dry condition samples, shows that
                      intergranular transport of calcium controls the reaction
                      progress. Grain boundary diffusivities could be retrieved
                      from the classic treatment of reaction rim growth rate. In
                      turn, once modeled, this rate was used to fit the bulk
                      kinetic data derived from X-ray powder diffraction, offering
                      an alternative means to derive calcium diffusivity data.
                      Based on a comparison with effective grain boundary data for
                      Ca and Mg from the literature, it is inferred that both dry
                      and intermediate datasets are consistent with a
                      water-saturated intergranular medium with different levels
                      of connectivity. The very high diffusivity of Ca in the CaCO
                      3  + Mg(OH) 2 rims, in comparison with that of Mg in
                      enstatite rims found by earlier workers, emphasizes the
                      prominent role of the interactions between diffusing species
                      and mineral surfaces in diffusion kinetics. Furthermore, we
                      show that the addition of water is likely to change the
                      relative diffusivity of Mg and Ca in carbonate aggregates.
                      From a qualitative point of view, we confirm, in a
                      carbonate-bearing system, that small water content
                      variations within the 0–1 wt $\%$ range have tremendous
                      effects on both intergranular transport mechanisms and
                      kinetics. We also propose that the water content dependent
                      diffusivity of major species (Mg, Ca) in low-porosity
                      metamorphic rocks is strongly dependent on the interaction
                      between diffusing species and mineral surfaces. This
                      parameter, which will vary from one rock-type to another,
                      needs also to considered when extrapolating ( P , T , t , x
                      H 2 O) laboratory diffusion data to metamorphic processes.},
      cin          = {DOOR},
      ddc          = {550},
      cid          = {I:(DE-H253)HAS-User-20120731},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      experiment   = {EXP:(DE-H253)D-F2.1-20150101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000383734100006},
      doi          = {10.1093/petrology/egw044},
      url          = {https://bib-pubdb1.desy.de/record/311029},
}