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首页> 外文期刊>Contributions to Mineralogy and Petrology >Silicon and oxygen self diffusion in enstatite polycrystals: the Milke et al. (2001) rim growth experiments revisited
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Silicon and oxygen self diffusion in enstatite polycrystals: the Milke et al. (2001) rim growth experiments revisited

机译：硅和氧在顽辉石多晶体中的自扩散：米尔克等人。 （2001）重新研究轮辋生长实验

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Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) studied the diffusion of Si, Mg and O in synthetic polycrystalline enstatite reaction rims. The reaction rims were grown at 1,000°C and 1 GPa at the contacts between forsterite grains with normal isotopic compositions and a quartz matrix extremely enriched in 18O and 29Si. The enstatite reaction rim grew from the original quartz-forsterite interface in both directions producing an inner portion, which replaced forsterite and an outer portion, which replaced quartz. Here we present new support for this statement, as the two portions of the rim are clearly distinguished based on crystal orientation mapping using electron backscatter diffraction (EBSD). Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) used the formalism of LeClaire (J Appl Phys 14:351–356, 1963) to derive the coefficient of silicon grain boundary diffusion from stable isotope profiles across the reaction rims. LeClaire’s formalism is designed for grain boundary tracer diffusion into an infinite half space with fixed geometry. A fixed geometry is an undesired limitation in the context of rim growth. We suggest an alternative model, which accounts for simultaneous layer growth and superimposed silicon and oxygen self diffusion. The effective silicon bulk diffusivity obtained from our model is approximately equal within both portions of the enstatite reaction rim: D Si,En eff =1.0–4.3×10−16 m2 s−1. The effective oxygen diffusion is relatively slow in the inner portion of the reaction rim, D O,En eff =0.8–1.4×10−16 m2 s−1, and comparatively fast, D O,En eff =5.9–11.6×10−16 m2 s−1, in its outer portion. Microstructural evidence suggests that transient porosity and small amounts of fluid were concentrated at the quartz-enstatite interface during rim growth. This leads us to suspect that the presence of an aqueous fluid accelerated oxygen diffusion in the outer portion of the reaction rim. In contrast, silica diffusion does not appear to have been affected by the spatial variation in the availability of an aqueous fluid.
机译：米尔克等。 （Contrib Mineral Petrol 142：15–26，2001）研究了Si，Mg和O在合成多晶顽辉石反应边缘中的扩散。反应边缘在具有正常同位素组成的镁橄榄石晶粒与极富18 O和29 Si的石英基体之间的接触点处于1,000°C和1 GPa下生长。顽辉石反应边缘从原始的石英-镁橄榄石界面沿两个方向生长，产生了一个内部，代替了镁橄榄石和一个外部，取代了石英。在此，我们为这一说法提供了新的支持，因为根据使用电子背散射衍射（EBSD）的晶体取向映射，可以清楚地区分轮辋的两个部分。米尔克等。 （Contrib Mineral Petrol 142：15–26，2001）使用LeClaire的形式主义（J Appl Phys 14：351–356，1963）从整个反应边沿的稳定同位素分布中得出硅晶界扩散系数。 LeClaire的形式主义旨在将晶界示踪剂扩散到具有固定几何形状的无限半空间中。在轮辋生长的情况下，固定的几何形状是不希望的限制。我们建议使用替代模型，该模型考虑了同时层生长以及硅和氧的自扩散叠加。从我们的模型获得的有效硅体积扩散率在顽辉石反应边缘的两个部分内大致相等：D Si，En eff = 1.0–4.3×10-16 m2 s-1 。在反应边缘内部，有效氧扩散相对缓慢，DO，En eff = 0.8–1.4×10−16 m2 s-1 ，并且速度相对较快，在外部，DO，En eff = 5.9–11.6×10−16 m2 s-1 。微观结构证据表明，在边缘生长过程中，瞬时孔隙和少量流体集中在石英-顽辉石界面。这使我们怀疑水性液体的存在会加速反应边缘外部的氧扩散。相反，二氧化硅扩散似乎不受水性流体可用性的空间变化的影响。

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