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Title: Isotope fractionation by diffusion in molten oxides

Abstract

Laboratory diffusion experiments specifically designed to resolve small differences in the relative mobility of isotopes were used to measure the mobility of {sup 76}Ge vs. {sup 70}Ge in molten GeO{sub 2} (1,400 C, 0.5 GPa) and {sup 48}Ca vs. {sup 40}Ca in molten CaO-SiO{sub 2}-Al{sub 2}O{sub 3} (1,500 C, 1.0 GPa). When the mass (m) dependence of the diffusion coefficient (D) of isotopes 1,2 is written in the form (D{sub 1}/D{sub 2}) = (m{sub 2}/m{sub 1}){sup {beta}}, the authors find {beta} {le} 0.025 for Ge isotopes and {beta} = 0.05 to 0.1 for Ca isotopes. The degree of isotope fractionation by diffusion between melts of the same initial isotopic composition but different elemental abundance depends not only on {beta} but also on the ratio of the elemental concentrations in the two melts. Given their measured value of {beta} for Ca isotopes, the authors predict that diffusion between melts with a factor of 5 to 10 difference in Ca content will produce variations in {sup 44}Ca/{sup 40}Ca ratio of 2 to 5%. To the extent that Ge is a good analogue for Si, the authors would not expect significant fractionation of Si isotopes. But even if the value of {beta} formore » Si isotopes were as large as that for Ca, they would still not expect measurable diffusive isotopic fractionations of Si because the contrast in Si content between most natural melts is less than a factor of 2.« less

Authors:
; ;
Publication Date:
Research Org.:
Univ. of Chicago, IL (US)
Sponsoring Org.:
USDOE; National Aeronautics and Space Administration
OSTI Identifier:
20000938
DOE Contract Number:  
FG02-94ER14478; FG02-97ER14773
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 63; Journal Issue: 18; Other Information: PBD: Sep 1999; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GERMANIUM ISOTOPES; DIFFUSION; GERMANIUM OXIDES; CALCIUM ISOTOPES; CALCIUM OXIDES; SILICON OXIDES; ALUMINIUM OXIDES; MOLTEN SALTS; ISOTOPE RATIO; GEOCHEMISTRY

Citation Formats

Richter, F.M., Liang, Y., and Davis, A.M. Isotope fractionation by diffusion in molten oxides. United States: N. p., 1999. Web. doi:10.1016/S0016-7037(99)00164-7.
Richter, F.M., Liang, Y., & Davis, A.M. Isotope fractionation by diffusion in molten oxides. United States. doi:10.1016/S0016-7037(99)00164-7.
Richter, F.M., Liang, Y., and Davis, A.M. Wed . "Isotope fractionation by diffusion in molten oxides". United States. doi:10.1016/S0016-7037(99)00164-7.
@article{osti_20000938,
title = {Isotope fractionation by diffusion in molten oxides},
author = {Richter, F.M. and Liang, Y. and Davis, A.M.},
abstractNote = {Laboratory diffusion experiments specifically designed to resolve small differences in the relative mobility of isotopes were used to measure the mobility of {sup 76}Ge vs. {sup 70}Ge in molten GeO{sub 2} (1,400 C, 0.5 GPa) and {sup 48}Ca vs. {sup 40}Ca in molten CaO-SiO{sub 2}-Al{sub 2}O{sub 3} (1,500 C, 1.0 GPa). When the mass (m) dependence of the diffusion coefficient (D) of isotopes 1,2 is written in the form (D{sub 1}/D{sub 2}) = (m{sub 2}/m{sub 1}){sup {beta}}, the authors find {beta} {le} 0.025 for Ge isotopes and {beta} = 0.05 to 0.1 for Ca isotopes. The degree of isotope fractionation by diffusion between melts of the same initial isotopic composition but different elemental abundance depends not only on {beta} but also on the ratio of the elemental concentrations in the two melts. Given their measured value of {beta} for Ca isotopes, the authors predict that diffusion between melts with a factor of 5 to 10 difference in Ca content will produce variations in {sup 44}Ca/{sup 40}Ca ratio of 2 to 5%. To the extent that Ge is a good analogue for Si, the authors would not expect significant fractionation of Si isotopes. But even if the value of {beta} for Si isotopes were as large as that for Ca, they would still not expect measurable diffusive isotopic fractionations of Si because the contrast in Si content between most natural melts is less than a factor of 2.},
doi = {10.1016/S0016-7037(99)00164-7},
journal = {Geochimica et Cosmochimica Acta},
issn = {0016-7037},
number = 18,
volume = 63,
place = {United States},
year = {1999},
month = {9}
}