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Pressure dependence of Si diffusion in gamma -Fe

Noriyoshi Tsujino, Andreea Marza and Daisuke Yamazaki
Pressure dependence of Si diffusion in gamma -Fe
American Mineralogist (March 2020) 105 (3): 319-324


The pressure dependence of Si diffusion in gamma -Fe was investigated at pressures of 5-15 GPa and temperatures of 1473-1673 K using the Kawai-type multi-anvil apparatus to estimate the rate of mass transportation for the chemical homogenization of the Earth's inner core and those of small terrestrial planets and large satellites. The obtained diffusion coefficients D were fitted to the equation D=D (sub 0) exp[-(E*+PV*)/(RT)], where D (sub 0) is a constant, E* is the activation energy, P is the pressure, V* is the activation volume, R is the gas constant, and T is the absolute temperature. The least-squares analysis yielded D (sub 0) =10 (super -1.17+ or -0.54) m (super 2) /s, E*=336+ or -16 kJ/mol, and V*=4.3+ or -0.2 cm (super 3) /mol. Moreover, the pressure and temperature dependences of diffusion coefficients of Si in gamma -Fe can also be expressed well using homologous temperature scaling, which is expressed as D=D (sub 0) exp{-g[Tm(P)]/T}, where g is a constant, Tm(P) is the melting temperature at pressure P, and D (sub 0) and g are 10 (super -1.0+ or -0.3) m (super 2) /s and 22.0+ or -0.7, respectively. The present study indicates that even for 1 billion years, the maximum diffusion length of Si under conditions in planetary and satellite cores is less than approximately 1.2 km. Additionally, the estimated strain of plastic deformation in the Earth's inner core, caused by the Harper-Dorn creep, reaches more than 103 at a stress level of 103-104 Pa, although the inner core might be slightly deformed by other mechanisms. The chemical heterogeneity of the inner core can be reduced only via plastic deformation by the Harper-Dorn creep.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 105
Serial Issue: 3
Title: Pressure dependence of Si diffusion in gamma -Fe
Affiliation: Okayama University, Institute for Planetary Materials, Tottori, Japan
Pages: 319-324
Published: 202003
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 37
Accession Number: 2020-034454
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: University of Bucharest, ROM, Romania
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2020
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