Kinetic rate laws derived from order parameter theory IV: Kinetics of Al,Si disordering in Na-feldspars

Autor: Ekhard K. H. Salje, B. Wruck, Ann Graeme-Barber
Rok vydání: 1991
Předmět:
Zdroj: Physics and Chemistry of Minerals. 17
ISSN: 1432-2021
0342-1791
DOI: 10.1007/bf00202240
Popis: The kinetic rate laws of Al-Si disordering under dry conditions (T = 1353K, 1253 K, 1223 K, 1183 K) and in the presence of water (p = 1 kbar, T = 1023 K, 1073 K, 1103 K) were studied both experimentally and theoretically. A gradual change of the degree of order was found under dry conditions. For intermediate degrees of order broad distributions of the order parameter Qod occur. The variations of Qod are correlated with structural modulations as observed in the transmission electron microscope. The time evolution of the mean value of Qod can be well described by the rate law: $$\frac{{dQ_{od} }}{{dt}} = - \frac{\gamma }{{RT}}\exp \sum\limits_{i = 1}^n {X_i^2 } \left[ {\frac{{ - (G_a^0 + \varepsilon (\Delta Q_{od} )^2 )}}{{RT}}} \right]\frac{{dG}}{{dQ_{od} }}$$ with the excess Gibbs energy G and Ga0= 433.8 kJ/mol, ɛ= -27.4 kJ/mol, γ = 1.687 · 1014 h −1.
Databáze: OpenAIRE
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