Effect of surface orientation on dissolution rates and topography of CaF2
Effect of surface orientation on dissolution rates and topography of CaF2
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DOI：
10.1016/j.gca.2012.02.032
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发表时间：
2012-06-01
影响因子：
5
通讯作者：
Evins, L. Z.
中科院分区：
文献类型：
--
作者：
Godinho, J. R. A.;Piazolo, S.;Evins, L. Z.
本文报道了在溶解过程中，表面化学差异如何影响具有类似于二氧化铀乏核燃料微观结构的氟化钙芯块的形貌演变。三维共聚焦轮廓术和原子力显微镜被用来量化撤退率，并分析不同方向的表面上的形貌变化，作为溶解进行到468小时。使用pH值为3.6的NaClO 4（0.05 M）溶液，该溶液相对于CaF 2远离平衡。{111}是最稳定的平面，溶解速率为（1.2 +/- 0.8）× 10（-9）mol m（-2）s（-1），{112}是最不稳定的平面，溶解速率比{111}快33倍。在同一平面上暴露Ca和F原子的表面溶解得更快。溶解速率被发现是相关的表面取向，其特征在于由一个特定的表面化学，因此与表面能。提出了每个表面由三个参考面{111}、{100}和{110}的相对比例以及它们相交处的高能位来表征，并根据所观察到的不同溶解速率提出了一个溶解模型来解释溶解过程中的形貌变化。具有较慢溶解速率和推断的较低表面能的表面倾向于形成，而溶解进行导致粗糙度和表面积增加。表面的这种调整表明，溶解早期阶段的溶解速率与后期阶段不同。在预测长期溶出速率时，需要考虑该动态系统的时间依赖性。(C)2012爱思唯尔有限公司保留所有权利。
This paper reports how during dissolution differences in surface chemistry affect the evolution of topography of CaF2 pellets with a microstructure similar to UO2 spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 h. A NaClO4 (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF2 was used.Measured dissolution rates depend directly on the orientation of the exposed planes. The {111} is the most stable plane with a dissolution rate of (1.2 +/- 0.8) x 10(-9) mol m(-2) s(-1), and {112} the least stable plane with a dissolution rate 33 times faster that {111}. Surfaces that expose both Ca and F atoms in the same plane dissolve faster. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It is proposed that every surface is characterized by the relative proportions of the three reference planes {111}, {100} and {110}, and by the high energy sites at their interceptions.Based on the different dissolution rates observed we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form while dissolution proceeds leading to an increase of roughness and surface area. This adjustment of the surface suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration when predicting long-term dissolution rates. (C) 2012 Elsevier Ltd. All rights reserved.