### Abstract

Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200–1500 K by means of in-situ X-ray diffraction observation to be G^{n}−G_{0}^{n}=kt, where G (m) is the grain size at time t (s), G_{0} (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k=k_{0}exp(−H^{⁎}/RT) with log k_{0}(m^{n}/s)=−5.8(±2.4) and activation enthalpy H^{⁎}=221(±61) kJ/mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper–Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core.

Original language | English |
---|---|

Pages (from-to) | 238-243 |

Number of pages | 6 |

Journal | Earth and Planetary Science Letters |

Volume | 459 |

DOIs | |

Publication status | Published - Feb 1 2017 |

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### Keywords

- grain growth
- inner core
- ε-iron

### ASJC Scopus subject areas

- Geophysics
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science

### Cite this

*Earth and Planetary Science Letters*,

*459*, 238-243. https://doi.org/10.1016/j.epsl.2016.11.049

**Grain growth of ε-iron : Implications to grain size and its evolution in the Earth's inner core.** / Yamazaki, Daisuke; Tsujino, Noriyoshi; Yoneda, Akira; Ito, Eiji; Yoshino, Takashi; Tange, Yoshinori; Higo, Yuji.

Research output: Contribution to journal › Article

*Earth and Planetary Science Letters*, vol. 459, pp. 238-243. https://doi.org/10.1016/j.epsl.2016.11.049

}

TY - JOUR

T1 - Grain growth of ε-iron

T2 - Implications to grain size and its evolution in the Earth's inner core

AU - Yamazaki, Daisuke

AU - Tsujino, Noriyoshi

AU - Yoneda, Akira

AU - Ito, Eiji

AU - Yoshino, Takashi

AU - Tange, Yoshinori

AU - Higo, Yuji

PY - 2017/2/1

Y1 - 2017/2/1

N2 - Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200–1500 K by means of in-situ X-ray diffraction observation to be Gn−G0n=kt, where G (m) is the grain size at time t (s), G0 (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k=k0exp(−H⁎/RT) with log k0(mn/s)=−5.8(±2.4) and activation enthalpy H⁎=221(±61) kJ/mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper–Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core.

AB - Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200–1500 K by means of in-situ X-ray diffraction observation to be Gn−G0n=kt, where G (m) is the grain size at time t (s), G0 (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k=k0exp(−H⁎/RT) with log k0(mn/s)=−5.8(±2.4) and activation enthalpy H⁎=221(±61) kJ/mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper–Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core.

KW - grain growth

KW - inner core

KW - ε-iron

UR - http://www.scopus.com/inward/record.url?scp=85006298142&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85006298142&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2016.11.049

DO - 10.1016/j.epsl.2016.11.049

M3 - Article

AN - SCOPUS:85006298142

VL - 459

SP - 238

EP - 243

JO - Earth and Planetary Sciences Letters

JF - Earth and Planetary Sciences Letters

SN - 0012-821X

ER -