Compositional effects in the liquid Fe–Ni–C system at high pressure

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY
Esther S. Posner, Gerd Steinle-Neumann
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Abstract

We performed molecular dynamics simulations based on density functional theory to systematically investigate the Fe–Ni–C system including (1) pure Fe and Ni; (2) binary Fe–Ni, Fe–C, and Ni–C; and (3) ternary Fe–Ni–C liquid compositions at 3000 K and three simulation volumes corresponding to pressure (P) up to 83 GPa. Liquid structural properties, including coordination numbers, are analyzed using partial radial distribution functions. Self-diffusion coefficients are determined based on the atomic trajectories and the asymptotic slope of the time-dependent mean-square displacement. The results indicate that the average interatomic distance between two Fe atoms (rFe–Fe) decreases with P and is sensitive to Ni (XNi) and C (XC) concentration, although the effects are opposite: rFe–Fe decreases with increasing XNi, but increases with increasing XC. Average rFe–C and rNi–C values also decrease with increasing XNi and generally remain constant between the two lowest P points, corresponding to a coordination change of carbon from ~ 6.8 to ~ 8.0, and then decrease with additional P once the coordination change is complete. Carbon clustering occurs in both binary (especially Ni–C) and ternary compositions with short-range rC-C values (~ 1.29 to ~ 1.57 Å), typical for rC-C in diamond and graphite. The self-diffusion results are generally consistent with high-P diffusion data extrapolated from experiments conducted at lower temperature (T). A subset of additional simulations was conducted at 1675 and 2350 K to estimate the effect of T on diffusion, yielding an activation enthalpy of ~ 53 kJ/mol and activation volume of ~ 0.5 cm3/mol.

Abstract Image

高压下液态Fe-Ni-C体系的成分效应
本文基于密度泛函理论进行了分子动力学模拟,系统地研究了Fe - Ni - c体系,包括:(1)纯Fe和Ni;(2)二元Fe-Ni、Fe-C和Ni-C;(3) 3000 K下的Fe-Ni-C三元液体组成和对应压力(P)高达83 GPa的三个模拟体积。利用部分径向分布函数分析了液体的结构特性,包括配位数。自扩散系数是根据原子轨迹和随时间变化的均方位移的渐近斜率确定的。结果表明:两个铁原子之间的平均原子间距离(rFe-Fe)随P的增加而减小,对Ni (XNi)和C (XC)浓度敏感,但影响相反:rFe-Fe随XNi的增加而减小,而随XC的增加而增大。平均rFe-C和rNi-C值也随着XNi的增加而降低,在两个最低P点之间基本保持不变,对应于碳从~ 6.8到~ 8.0的配位变化,配位完成后随P的增加而降低。碳聚簇发生在二元(尤其是Ni-C)和三元(rC-C值范围为~ 1.29 ~ ~ 1.57 Å)的组合物中,这是金刚石和石墨中典型的rC-C。自扩散结果与在较低温度(T)下进行的实验推断出的高p扩散数据基本一致。在1675和2350 K下进行了额外的模拟,以估计T对扩散的影响,得到活化焓为~ 53 kJ/mol,活化体积为~ 0.5 cm3/mol。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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