KINETICS OF THE REACTION MGO + AL2O3 → MGAL2O4 AND AL-MG INTERDIFFUSION IN SPINEL AT 1200 TO 2000°C AND 1.0 TO 4.0 GPA
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dc.contributor.author | Watson E.Bruce | |
dc.contributor.author | Price J.D. | |
dc.date.accessioned | 2021-09-24T09:06:30Z | |
dc.date.available | 2021-09-24T09:06:30Z | |
dc.date.issued | 2002 | |
dc.identifier | https://elibrary.ru/item.asp?id=13779263 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2002, 66, 12, 2123-2138 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/30541 | |
dc.description.abstract | The rate of spinel (MgAl2O4) growth at the interface between MgO and Al2O3 was investigated systematically at temperatures of 1200° to ∼2000°C and pressures between 1.0 and 4.0 GPa with a solid-media, piston-cylinder apparatus. As reported in previous 1-atm studies, the thickness (ΔX) of the spinel layer increases linearly with the square root of time for experiments differing only in duration, irrespective of pressure–temperature (P-T) conditions. The reaction rate constant (k = ΔX2/2t) is log-linear in 1/T and also in pressure. The apparent activation energy of 410 kJ/mol is independent of pressure; the apparent activation volume increases systematically with increasing temperature. Electron microprobe traverses across the spinel layer reveal a significant Al excess and charge-compensating Mg deficit near the spinel/corundum interface. This nonstoichiometry is promoted by high temperatures (>1500°C), suppressed by high pressures and varies linearly across the spinel to a near-stoichiometric composition at the interface with periclase. The Al and Mg composition gradients can be used to extract interdiffusion coefficients for Al ↔ Mg exchange through the spinel, which are described by D̃=2.5×10−6 exp(−28200/T) m2sThese diffusivities differ substantially from the reaction rate constant k, reflecting the fact that k is a combination of the diffusivity and the reaction potential as indicated by the difference in spinel composition across the spinel layer (i.e., coexisting with corundum vs. coexisting with periclase). A simple model can be used to separate the two effects and show that the reaction potential (i.e., the MgO-Al2O3 phase diagram) is sensitive to changes in both temperature and pressure, whereas the governing diffusivity depends only on temperature. | |
dc.title | KINETICS OF THE REACTION MGO + AL2O3 → MGAL2O4 AND AL-MG INTERDIFFUSION IN SPINEL AT 1200 TO 2000°C AND 1.0 TO 4.0 GPA | |
dc.type | Статья |
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