Thermodynamics and kinetics of H[sub 2]O(v) chemisorption and solubility in nanometric and single-crystal MgO particles during sintering
- Univ. of Genoa (Italy)
- Lawrence Berkeley Lab., CA (United States)
Equilibrium chemisorption of H[sub 2]O at 613 Pa on nanometric and micrometric MgO particles was measured at 549-1053 K. Degrees of coverage are calculated on the assumptions that only [100] surfaces of MgO were exposed and that each surface O[sup 2[minus]] ion reacted with H[sub 2]O to form 2OH[sup [minus]] ions. When the thermal entropy of adsorption is assumed to be equal to the correspondent value for the reaction of H[sub 2]O(v) with MgO to form Mg(OH)[sub 2], the data fit a regular solution model. The enthalpy of adsorption is calculated to be [minus]189 kJ mol[sup [minus]1] at low coverage and [minus]113 kJ mol[sup [minus]1] at 70% coverage. At temperature of 898 K and above water dissolved rapidly enough in the nanometric MgO particles to permit the equilibrium concentration to be measured. From the temperature dependence of solubility, the heat of solution is calculated to be [minus]84 kJ mol[sup [minus]1]. It is shown that if the water dissolved by reacting with O[sup 2[minus]] ions to form OH[sup [minus]] ion sites, the observed catalysis of MgO sintering by water vapor can be qualitatively explained. 22 refs., 4 figs., 1 tab.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5652106
- Journal Information:
- Journal of Physical Chemistry; (United States), Vol. 97:36; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
MAGNESIUM OXIDES
SINTERING
SURFACE PROPERTIES
WATER VAPOR
CHEMISORPTION
SOLUBILITY
CATALYSTS
CHEMICAL REACTION KINETICS
ENTHALPY
ENTROPY
EQUILIBRIUM
MATHEMATICAL MODELS
MONOCRYSTALS
THERMODYNAMICS
ALKALINE EARTH METAL COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTALS
FABRICATION
FLUIDS
GASES
KINETICS
MAGNESIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
SEPARATION PROCESSES
SORPTION
THERMODYNAMIC PROPERTIES
VAPORS
400201* - Chemical & Physicochemical Properties
360200 - Ceramics
Cermets
& Refractories