start-ver=1.4
cd-journal=joma
no-vol=105
cd-vols=
no-issue=3
article-no=
start-page=319
end-page=324
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2020
dt-pub=20200501
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=Pressure dependence of Si diffusion in gamma-Fe
kn-title=Pressure dependence of Si diffusion in γ-Fe
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=The pressure dependence of Si diffusion in γ-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 = D0 exp[−(E* + PV*)/(RT)], where D0 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 D0 = 10-1.17±0.54 m2/s, E* = 336 ± 16 kJ/mol, and V* = 4.3 ± 0.2 cm3/mol. Moreover, the pressure and temperature dependences of diffusion coefficients of Si in γ-Fe can also be expressed well using homologous temperature scaling, which is expressed as D = D0exp{–g[Tm(P)]/T}, where g is a constant, Tm(P) is the melting temperature at pressure P, and D0 and g are 10-1.0±0.3 m2/s and 22.0 ± 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 ∼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.
en-copyright=
kn-copyright=

en-aut-name=TsujinoNoriyoshi
en-aut-sei=Tsujino
en-aut-mei=Noriyoshi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=MârzaAndreea
en-aut-sei=Mârza
en-aut-mei=Andreea
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=YamazakiDaisuke
en-aut-sei=Yamazaki
en-aut-mei=Daisuke
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Institute for Planetary Materials, Okayama University
kn-affil=

affil-num=2
en-affil=Faculty of Geology and Geophysics, University of Bucharest
kn-affil=

affil-num=3
en-affil=Institute for Planetary Materials, Okayama University
kn-affil=
en-keyword=γ-Fe
kn-keyword=γ-Fe
en-keyword=silicon diffusion
kn-keyword=silicon diffusion
en-keyword=high pressure
kn-keyword=high pressure
en-keyword=planetary core
kn-keyword=planetary core
END

start-ver=1.4
cd-journal=joma
no-vol=103
cd-vols=
no-issue=8
article-no=
start-page=1271
end-page=1281
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2018
dt-pub=20180801
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=The effects of ferromagnetism and interstitial hydrogen on the equation of states of hcp and dhcp FeHx: Implications for the Earth's inner core age
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract= Hydrogen has been considered as an important candidate of light elements in the Earth's core. Because iron hydrides are unquenchable, hydrogen content is usually estimated from in situ X-ray diffraction measurements that assume the following linear relation: x = (V-FeHx - V-Fe)/Delta V-H, where x is the hydrogen content, Delta V-H is the volume expansion caused by unit concentration of hydrogen, and V-FeHx and V-Fe are volumes of FeHx and pure iron, respectively. To verify the linear relationship, we computed the equation of states of hexagonal iron with interstitial hydrogen by using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). The results indicate a discontinuous volume change at the magnetic transition and almost no compositional (x) dependence in the ferromagnetic phase at 20 GPa, whereas the linearity is confirmed in the non-magnetic phase. In addition to their effect on the density-composition relationship in the Fe-FeHx system, which is important for estimating the hydrogen incorporation in planetary cores, the magnetism and interstitial hydrogen also affect the electrical resistivity of FeHx. The thermal conductivity can be calculated from the electrical resistivity by using the Wiedemann-Franz law, which is a critical parameter for modeling the thermal evolution of the Earth. Assuming an Fe1-ySiyHx ternary outer core model (0.0 <= x <= 0.7), we calculated the thermal conductivity and the age of the inner core. The resultant thermal conductivity is similar to 100 W/m/K and the maximum inner core age ranges from 0.49 to 0.86 Gyr.
en-copyright=
kn-copyright=

en-aut-name=GomiHitoshi
en-aut-sei=Gomi
en-aut-mei=Hitoshi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=FeiYingwei
en-aut-sei=Fei
en-aut-mei=Yingwei
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=YoshinoTakashi
en-aut-sei=Yoshino
en-aut-mei=Takashi
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=Institute for Planetary Materials, Okayama University
kn-affil=

affil-num=2
en-affil=Geophysical Laboratory, Carnegie Institution of Washington
kn-affil=

affil-num=3
en-affil=Institute for Planetary Materials, Okayama University
kn-affil=
en-keyword=FeHx
kn-keyword=FeHx
en-keyword=ferromagnetism
kn-keyword=ferromagnetism
en-keyword=chemical disorder
kn-keyword=chemical disorder
en-keyword=equation of states
kn-keyword=equation of states
en-keyword=KKR-CPA
kn-keyword=KKR-CPA
END