Diffusion in silicate melts: II. Multicomponent diffusion in CaO-Al{sub 2}O{sub 3}-SiO{sub 2} at 1500{degrees}C and 1 GPa

Journal Article · Sun Dec 01 04:00:00 EST 1996 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(96)00352-3· OSTI ID:569828

Liang, Yan ^[1]; Richter, F M ^[1]; Watson, E B ^[2]

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1. Univ. of Chicago, IL (United States)
2. Rensselaer Polytechnic Institute, Troy, NY (United States)

Chemical diffusion profiles in molten CaO-Al{sub 2}O{sub 3}-SiO{sub 2} have been measured over a large range of compositions at 1500{degrees}C and 1 GPa. The diffusion profiles have been inverted for effective binary diffusion coefficients (EBDCs) and for the chemical diffusion matrix. The EBDCs are shown to depend strongly on both composition and direction of diffusion in composition space. The dependence of EBDCs on direction in composition space, which for the system studied here can be as large as a factor of seven. severely limits the applicability of EBDCs to interdiffusion in any direction other than the one used to derive the EBDCs. The chemical diffusion matrix for molten CaO-Al{sub 2}O{sub 3}-SiO{sub 2} was determined using diffusion profiles from two or three mutually orthogonal diffusion couples in the ternary composition space. All features of the diffusion profiles shown in this work can be reproduced by representing the chemical fluxes in the three-component system as a linear combination of concentration gradients via a 2 X 2 diffusion matrix. Chemical diffusion in molten CaO-Al{sub 2}O{sub 3}-SiO{sub 2} shows clear evidence of strong diffusive coupling among the components. This can be seen in the uphill diffusion profiles of components that were initially uniform, in the fact that the apparent rate of diffusion of some components is a strong function of direction in composition space, and most quantitatively in the magnitude of off-diagonal elements of the diffusion matrix relative to the magnitude of the diagonal elements. SiO{sub 2} for example. is found to be strongly coupled with CaO in relatively silicic melts, whereas Al{sub 2}O{sub 3} is strongly coupled with CaO in less silicic melts. Furthermore, the coupling of CaO with either Al{sub 2}O{sub 3} or SiO, reverses sign between more and less polymerized compositions. 64 refs., 7 figs., 5 tabs.

• DOE Contract Number: FG02-94ER14478
• OSTI ID: 569828
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 24 Vol. 60; ISSN 0016-7037; ISSN GCACAK
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
CHEMICAL REACTIONS
DIFFUSION
GEOCHEMISTRY
MAGMA
SILICATES