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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Anisotropy of oxygen diffusion in diopside
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Anisotropy of oxygen diffusion in diopside

机译：透辉石中氧扩散的各向异性

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摘要

~(18)O diffusion coefficients have been measured by nuclear reaction analysis (NRA) in Fe-free synthetic diopside single crystals along the three crystallographic directions and in Fe-bearing natural diopside single crystals along the c direction at room pressure in the range 1050-1370 ℃ and under controlled oxygen partial pressure (10~(-1)-10~(-12) atm). Diffusion along a and c crystallographic directions is one order of magnitude faster than along b direction. Diffusion along c in natural diopside is about two times faster than in the synthetic sample. The activation energy along b is 323 ± 27 kJ mol~(-1) and diffusion is insensitive to oxygen fugacity. For a and c directions activation energies are around 250 kJ mol~(-1) and the diffusion coefficients are slightly dependent on fO_2 (≈fO_2~(0.04)). We suggest that the observed diffusion anisotropy is related to the oxygen diffusion paths within the crystallographic structure that prefer the underbonded O2 oxygen sites. We propose a single law to describe diffusion along the two fast crystallographic directions a and c in diopside for natural conditions close to the QFM buffer: log D_(a,c) (m~2 s~(-1)) = -10.0 ± 0.6 - (259 ± 15 kJ mol~(-1))/2.303 RT, and D_b D_(a,c).
机译：通过核反应分析（NRA）在室温下在1050范围内在三个晶体学方向上的无铁合成透辉石单晶和在c方向上的含铁天然透辉石单晶的〜（18）O扩散系数进行了测量-1370℃，氧分压受控（10〜（-1）-10〜（-12）atm）。沿a和c结晶方向的扩散比沿b方向的扩散快一个数量级。天然透辉石中沿c的扩散比合成样品中快约两倍。沿b的活化能为323±27 kJ mol〜（-1），扩散对氧逸度不敏感。对于a和c方向，活化能大约为250 kJ mol〜（-1），扩散系数略微取决于fO_2（≈fO_2〜（0.04））。我们建议，观察到的扩散各向异性与晶体结构内的氧扩散路径有关，该结构优选欠键合的O2氧位。对于接近QFM缓冲区的自然条件，我们提出了一条定律描述透辉石沿两个快速晶体学方向a和c的扩散：log D_（a，c）（m〜2 s〜（-1））= -10.0± 0.6-（259±15 kJ mol〜（-1））/ 2.303 RT，且D_b D_（a，c）。

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