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.
- Blaha J (1995) Kinetics of hydration of MgO in aqueous suspension. Ceram Silik 39(2):41–80Google Scholar
- Brady JB (1983) Intergranular diffusion in metamorphic rocks. Am J Sci 283-A:181–200Google Scholar
- Bugajski J, Gamsjger H (1983) Osterr Chem Z 9:214Google Scholar
- Heidberg B, Bredow T, Littmann K, Jug K (2005) The structure and reaction of water layers on magnesium oxide. A cylic cluster study. Mater Sci Pol 23:501–508Google Scholar
- Ostapenko G (1976) Excess pressure on the solid phases generated by hydration(according to experimental data on hydration of periclase). Geokhimiya 6:824–844Google Scholar
- Robie R, Hemingway B, Fisher J (1979) Thermodynamic properties of minerals and related substances at 298.15k and 1 bar (105 pascals) pressure and at higher temperatures. Geological Survey Bulletin, 1452Google Scholar
- Smith JM (1981) Chemical engineering kinetics, 3rd edition. McGraw-Hill, New YorkGoogle Scholar
- Snedecor G, Cochran W (1980) Statistical methods, 7th edition. Iowa State University Press, Ames, p 342Google Scholar
- Zhou S (2004) Hydration mechanisms of magnesia-based refactory bricks. PhD thesisGoogle Scholar