Atom-Probe Tomography, TEM and ToF-SIMS study of borosilicate glass alteration rim: A multiscale approach to investigating rate-limiting mechanisms
Atom-Probe Tomography, TEM and ToF-SIMS study of borosilicate glass alteration rim: A multiscale approach to investigating rate-limiting mechanisms
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DOI：
10.1016/j.gca.2016.12.029
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发表时间：
2017-04-01
影响因子：
5
通讯作者：
Dupuy, L.
中科院分区：
文献类型：
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作者：
Gin, S.;Jollivet, P.;Dupuy, L.
在了解硅酸盐玻璃和矿物的溶解方面已经做出了重大的努力，但关于形成过程和表面层的性质仍然存在争议。在这里，我们研究了ISG玻璃-一种核感兴趣的6氧化物硼硅酸盐玻璃-在接近饱和的条件下在90 c - 1微米下改变的玻璃券，持续时间从1到875天。涂改后的玻璃片从原子到宏观层面进行了表征，以更好地了解表层是如何起保护作用的。通过这种方法，我们发现了一个粗糙的界面，其物理特征已经建模，在几天内形成，然后以生长蚀变层内水的反应性输运控制的速率传播到原始物质中。在蚀变层的其余部分，B、Na和Ca界面的刚性剖面和阻尼剖面等观测结果与经典的扩散模型或界面溶解-沉淀模型不一致。提出了一种新的范式来解释这些特征。相互扩散，一个基于水进入玻璃和离子交换的过程，可能只能解释玻璃腐蚀早期粗糙界面的形成。这个过程形成了一层薄薄的变色玻璃，随着层的增长，水进入反应界面的速度受到限制。结果，只有最容易接近的物种被溶解。其他的则未溶解在蚀变层中，可能固定在高度耐水解的簇中。当钝化层覆盖时，水在玻璃中的扩散系数由B和H剖面之间的位移确定，为10(-23)m(2)。S(-1)，即比原始物质中的水扩散率低约3个数量级。总的来说，在缺少可以消耗蚀变层主要成分（Si, Al）的二次晶相的情况下，可以假设玻璃的溶解速率由于输运限制蚀变层的增长而不断降低，这与文献中报道的该玻璃的残留速率很好地一致。根据我们的结果，可以预期新的动力学模型应该从纳米孔蚀变层中精确的随时间变化的水预算中出现。(C) 2016 Elsevier Ltd.版权所有。
Significant efforts have been made into understanding the dissolution of silicate glasses and minerals, but there is still debate about the formation processes and the properties of surface layers. Here, we investigate glass coupons of ISG glass - a 6 oxide borosilicate glass of nuclear interest - altered at 90 C-omicron in conditions close to saturation and for durations ranging from 1 to 875 days. Altered glass coupons were characterized from atomic to macroscopic levels to better understand how surface layers become protective. With this approach, it was shown that a rough interface, whose physical characteristics have been modeled, formed in a few days and then propagated into the pristine material at a rate controlled by the reactive transport of water within the growing alteration layer. Several observations such as stiff interfacial B, Na, and Ca profiles and damped profiles within the rest of the alteration layer are not consistent with the classical inter-diffusion model, or with the interfacial dissolution-precipitation model. A new paradigm is proposed to explain these features. Inter-diffusion, a process based on water ingress into the glass and ion-exchange, may only explain the formation of the rough interface in the early stage of glass corrosion. A thin layer of altered glass is formed by this process, and as the layer grows, the accessibility of water to the reactive interface becomes rate-limiting. As a consequence, only the most easily accessible species are dissolved. The others remain undissolved in the alteration layer, probably fixed in highly hydrolysis resistant clusters. A new estimation of water diffusivity in the glass when covered by the passivating layer was determined from the shift between B and H profiles, and was 10(-23) m(2). s(-1), i.e. approximately 3 orders of magnitude lower than water diffusivity in the pristine material. Overall, in the absence of secondary crystalline phases that could consume the major components of the alteration layer (Si, Al), it is assumed that the glass dissolution rate continuously decreases due to the growth of the transport limiting alteration layer, in good agreement with residual rates reported in the literature for this glass. According to our results it can be expected that new kinetic models should emerge from an accurate time dependent budget of water within the nanoporous alteration layer. (C) 2016 Elsevier Ltd. All rights reserved.