Compositional dependence of alkali diffusivity in silicate melts: Mixed alkali effect and pseudo-alkali effect
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Huaiwei Ni
Abstract
Compositional dependence of alkali diffusivities in silicate melts is modeled by explicitly considering mixed alkali and “pseudo-alkali” effects. The well-known mixed alkali effect describes that the presence of light alkalis (Li, Na) retards diffusion of heavy alkalis (K, Rb, Cs) and vice versa, which can be attributed to stronger interaction between dissimilar alkalis and reduction of favorable sites for the alkali in question. Due to the same reasons, Ca, which has similar ionic radius as Li and Na but carries more charge and greater field strength, also impedes the migration of light alkalis. In this regard Ca behaves as a “pseudo-alkali,” and I refer to the influence caused by Ca on Li and Na diffusion as the “pseudo-alkali effect,” which belongs to the category of mixed cation effects in glass literature. Pseudo-alkali effect is expected to exist also between other size-matching divalent cations and alkali cations, such as Ba blocking K diffusion. Mixed alkali and pseudo-alkali effects are manifested mainly by an increase in the activation energy for diffusion. Sodium diffusivities for melt compositions ranging between albite, orthoclase, and anorthite reveal that the amplitude of the pseudo-alkali effect is much larger than that of the mixed alkali effect. Furthermore, the activation energy increases more rapidly as more Ca substitutes for Na, but the mixed alkali effect approaches saturation as K substitutes for sodium. A general model based on mixed alkali effect and pseudo-alkali effect, together with a special treatment relating Cs diffusion to melt polymerization, successfully characterizes existing experimental data on alkali diffusion in silicate melts. Enthalpies of mixing between end-member melts (e.g., Ab-Or melts and Ab-An melts) inferred from the model agree well with previous experimental investigations.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements
- Mejillonesite, a new acid sodium, magnesium phosphate mineral, from Mejillones, Antofagasta, Chile
- Silician magnetite from the Dales Gorge Member of the Brockman Iron Formation, Hamersley Group, Western Australia
- The mechanism of thermal decomposition of dolomite: New insights from 2D-XRD and TEM analyses
- A revised diamond-graphite transition curve
- Insights into the crystal and aggregate structure of Fe3+ oxide/silica co-precipitates
- Compositional dependence of alkali diffusivity in silicate melts: Mixed alkali effect and pseudo-alkali effect
- Kinetics of evaporation of forsterite in vacuum
- X-ray absorption near edge structure (XANES) study of the speciation of uranium and thorium in Al-rich CaSiO3 perovskite
- Rehydration of dehydrated-dehydroxylated smectite in a low water vapor environment
- Effect of high pressure on the crystal structure and electronic properties of magnetite below 25 GPa
- OH group behavior and pressure-induced amorphization of antigorite examined under high pressure and temperature using synchrotron infrared spectroscopy
- Single-crystal Raman spectroscopy of natural paulmooreite Pb2As2O5 in comparison with the synthesized analog
- The dissolution of laumontite in acidic aqueous solutions: A controlled-temperature in situ atomic force microscopy study
- Crystal structure of CaRhO3 polymorph: High-pressure intermediate phase between perovskite and post-perovskite
- Oxide melt solution calorimetry of Fe2+-bearing oxides and application to the magnetite–maghemite (Fe3O4–Fe8/3O4) system
- Static compression of (Mg0.83,Fe0.17)O and (Mg0.75,Fe0.25)O ferropericlase up to 58 GPa at 300, 700, and 1100 K
- Implications of ferrous and ferric iron in antigorite
- Markascherite, Cu3(MoO4)(OH)4, a new mineral species polymorphic with szenicsite, from Copper Creek, Pinal County, Arizona, U.S.A.
- Natural hydrous amorphous silica: Quantitation of network speciation and hydroxyl content by 29Si MAS NMR and vibrational spectroscopy
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: VII. Chromschieffelinite, Pb10Te6O20(OH)14(CrO4)(H2O)5, the chromate analog of schieffelinite
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- Thermodynamic model for growth of reaction rims with lamellar microstructure
- The high-pressure behavior of micas: Vibrational spectra of muscovite, biotite, and phlogopite to 30 GPa
- Critical evaluation of the revised akdalaite model for ferrihydrite—Discussion
- Critical evaluation of the revised akdalaite model for ferrihydrite—Reply
