Dissolution rates of porous crystalline materials reflect the superposition of transport and surface control, mainly via the parameters saturation of the ambient fluid and distribution of surface energy. As a result, reacting surfaces evolve over time showing a heterogeneous distribution of surface rates. The spatiotemporal heterogeneity of surface reaction rates is analyzed using the rate map and rate spectra concept. Here, we quantify the dissolution rate variability covering the nm- to mm-scale of dissolving single-crystal and polycrystalline calcite samples, using a combined approach of X-ray micro-computed tomography (μ-CT) and vertical scanning interferometry (VSI). The dissolution experiments cover reaction periods from 15 minutes up to 54 days. The observed rate ranges are remarkably consistent over the entire reaction period but include a variability of about two orders of magnitude (10−9 − 3 × 10−7 mol m−2 s−1). The rate map data underscore the concurrent and superimposing impact of surface- vs. fluid flow controlled rate portions. The impact of fluid flow on reactivity at the mm-scale in the transport-controlled system is confirmed by 2-D reactive transport modeling. The sub-mm spatial heterogeneity of low vs. high reactivity surface portions of polycrystalline calcite is clearly below the mean crystal size. This suggests the dominant impact of highly reactive surface portions irrespective of the orientation of larger crystals on the overall surface reactivity. Correspondingly, the overall range of intrinsic reactivity heterogeneity as observed using singly crystal material is not further expanded for polycrystalline material. As a general conclusion, numerical reactive transport concepts would benefit from the implementation of a reactivity term resembling the experimentally observed existence of multiple rate components.

中文翻译：

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使用 X 射线显微计算机断层扫描和垂直扫描干涉测量法相结合的方法进行晶体表面反应性分析

多孔晶体材料的溶解速率反映了输运和表面控制的叠加，主要通过环境流体的饱和和表面能分布参数。结果，反应表面随时间演变，显示表面速率的不均匀分布。使用速率图和速率谱概念分析表面反应速率的时空异质性。在这里，我们使用 X 射线显微计算机断层扫描 (μ-CT) 和垂直扫描干涉测量法 (VSI) 的组合方法，量化了涵盖溶解单晶和多晶方解石样品的纳米到毫米尺度的溶解速率变异性. 溶解实验涵盖了从 15 分钟到 54 天的反应期。在整个反应期间观察到的速率范围非常一致，但包括大约两个数量级的可变性（10-9 - 3 × 10-7 mol m-2 s-1）。速率图数据强调了表面与流体流量控制速率部分的并发和叠加影响。2-D 反应性输运模型证实了流体流动对输运控制系统中毫米尺度反应性的影响。多晶方解石的低与高反应性表面部分的亚毫米空间异质性明显低于平均晶体尺寸。这表明高反应性表面部分的主要影响与较大晶体的取向对整体表面反应性无关。相应地，对于多晶材料，使用单晶材料观察到的内在反应异质性的总体范围没有进一步扩大。作为一般结论，数值反应输运概念将受益于反应性术语的实施，类似于实验观察到的多个速率分量的存在。