Hydration of periclase at 350 ∘ C to 620 ∘ C and 200 MPa: experimental calibration of reaction rate
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The hydration of periclase to brucite was investigated experimentally. Single crystals of periclase machined to millimeter sized cubes with (100) surfaces were reacted with distilled water at temperatures of 350 to 620 ∘C and a pressure of 200 MPa for run durations of 5 to 40 minutes. Hydration produced a layer of brucite covering the surface of periclase. While the shrinking periclase largely retained its cube shape a surface roughness developed on the μm scale and eventually outward pointing spikes bounded by (111) faces emerged on the retreating faces of the periclase due to kinetic selection of less reactive (111) and (110) surfaces. The periclase to brucite conversion followed a linear rate law, where the reaction rate increased from 350 to 530 ∘C and then decreased towards higher temperature and finally vanished at about 630 ∘C, where periclase, brucite, and water are in equilibrium at 200 MPa. The overall kinetics of the hydration reaction is conveniently described in terms of a phenomenological interface mobility. Measuring the velocity of the hydration front relative to the lattice of the reactant periclase, the temperature dependence of its mobility is described by an Arrhenius relation with pre-exponential factor 1.7.10−12 m 4/s.J and activation energy of E A =55 kJ/mol.
KeywordsPericlase Hydration experiment Reaction kinetics Interface reaction control
Financial support by the Austrian Science Foundation project I-474 N19 in the framework of the FWF-DFG DACH research group FOR 741 and by University of Vienna in the framework of the doctoral school IK 053 on “Deformation of geological materials: mechanical-chemical feedback and the coupling across scales” is gratefully acknowledged. The authors are indebted to Ralf Milke for efficient handling of and constructive comments on the manuscript.
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