Department of Chemistry and Bioscience, Aalborg University , Fredrik Bajers Vej 7H, Aalborg 9220, Denmark.
Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.
J Phys Chem B. 2017 Feb 9;121(5):1139-1147. doi: 10.1021/acs.jpcb.6b11371. Epub 2017 Jan 27.
Glasses gradually dissolve and corrode when they are exposed to aqueous solutions, and for many applications it is necessary to understand and predict the kinetics of the glass dissolution. Despite the recent progress in understanding the impact of chemical composition on the dissolution rate, a detailed understanding of the structural and topological origin of chemical durability in solutions of different pH is still largely lacking. Such knowledge would enable the tailoring of glass dissolution kinetics as a function of chemical composition. In a recent study focusing on silicate minerals and glasses, a direct relation was demonstrated between the dissolution rate at high pH and the number of chemical topological constraints per atom (n) acting within the molecular network [Pignatelli, I.; Kumar, A.; Bauchy, M.; Sant, G. Langmuir 2016, 32, 4434-4439]. Here, we extend this work by studying the bulk dissolution rate (D) of a wider range of oxide glasses in various acidic, neutral, and basic solutions. The glass compositions have been selected to obtain a wide range of chemistries and values of n, from flexible phosphate glasses to stressed-rigid aluminosilicate glasses. We show that, in flexible glasses, the internal modes of deformation facilitate the hydration of the network, whereas, in stressed-rigid glasses, the high number of constraints largely inhibits hydration in basic, neutral, and acidic solutions. Our study of chemical dissolution also allows establishing the kinetic mechanisms, which is controlled through an effective activation energy and depends on pH and glass topology. The energy barrier that needs to be overcome to break a unit atomic constraint is approximately constant for pH > 2, but then decreases at lower pH, indicating a change in dissolution mechanism from hydrolysis to ion exchange at low pH. Thus, with this research and existing topological models, the atomistic design of new oxide glasses with a specific chemical durability for a determined pH could become possible.
当玻璃暴露于水溶液中时，会逐渐溶解和腐蚀，对于许多应用，有必要了解和预测玻璃溶解的动力学。尽管最近在理解化学成分对溶解速率的影响方面取得了进展，但对于不同 pH 值溶液中化学耐久性的结构和拓扑起源，仍然缺乏详细的了解。这种知识将使玻璃溶解动力学能够根据化学成分进行定制。在最近一项针对硅酸盐矿物和玻璃的研究中，人们证明了在高 pH 值下的溶解速率与每个原子（n）作用于分子网络中的化学拓扑约束数之间存在直接关系[Pignatelli, I.; Kumar, A.; Bauchy, M.; Sant, G. Langmuir 2016, 32, 4434-4439]。在这里，我们通过研究各种酸性、中性和碱性溶液中更广泛的氧化物玻璃的体相溶解速率（D）来扩展这项工作。选择玻璃组成以获得广泛的化学性质和 n 值，从柔性磷酸盐玻璃到受应力的刚性铝硅酸盐玻璃。我们表明，在柔性玻璃中，内部变形模式促进了网络的水合作用，而在受应力的刚性玻璃中，大量的约束极大地抑制了碱性、中性和酸性溶液中的水合作用。我们对化学溶解的研究还允许建立动力学机制，该机制通过有效活化能控制，并取决于 pH 值和玻璃拓扑结构。打破单位原子约束所需克服的能量势垒对于 pH > 2 基本保持不变，但在较低 pH 值下会降低，这表明在低 pH 值下溶解机制从水解变为离子交换。因此，通过这项研究和现有的拓扑模型，有可能为特定 pH 值设计具有特定化学耐久性的新型氧化物玻璃。
