Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), Hermann-von-Helmholtz-Platz 1, Building 330, 76344, Eggenstein-Leopoldshafen, Germany.
Chemistry. 2018 Jun 18;24(34):8603-8608. doi: 10.1002/chem.201705974. Epub 2018 May 24.
Concrete is the most important construction material used by mankind and, at the same time, one of the most complex substances known in materials science. Since this mineral compound is highly porous, a better understanding of its surface chemistry, and in particular the reaction with water, is urgently required to understand and avoid corrosion of infrastructure like buildings and bridges. We have gained insight into proton transfer from concrete upon contact with water by applying the so-called Surface Science approach to a well-defined mineral, Wollastonite. Data from IR (infrared) spectroscopy reveal that exposure of this calcium-silicate (CS) substrate to H O leads to dissociation and the formation of OH-species. This proton transfer is a chemical reaction of key importance, since on the one hand it triggers the conversion of cement into concrete (a calcium-silicate-hydrate phase), but on the other hand also governs the corrosion of concrete. Interestingly, we find that no proton transfer takes place when the same surface is exposed to methanol. In order to understand this unexpected difference, the analysis of the spectroscopic data obtained was aided by a detailed, first-principles computational study employing density functional theory (DFT). The combined experimental and theoretical effort allows derivation of a consistent picture of proton transfer reactions occurring in CS and CSH phases. Implications for strategies to protect this backbone of urban infrastructure from corrosion in harsh, aqueous environments will be discussed.
混凝土是人类使用的最重要的建筑材料，同时也是材料科学中已知的最复杂的物质之一。由于这种矿物化合物具有很高的多孔性，因此迫切需要更好地了解其表面化学性质，特别是与水的反应，以便理解和避免建筑物和桥梁等基础设施的腐蚀。我们通过将所谓的表面科学方法应用于一种定义明确的矿物质——硅灰石，深入了解了混凝土与水接触时质子的转移。来自红外（IR）光谱的数据表明，暴露于 H2O 会导致这种钙硅酸盐（CS）基质的解离和 OH 物种的形成。这种质子转移是一种至关重要的化学反应，因为一方面它引发了水泥向混凝土（硅酸钙水合物相）的转化，但另一方面也控制着混凝土的腐蚀。有趣的是，当相同的表面暴露于甲醇时，我们发现没有质子转移发生。为了理解这种出乎意料的差异，对获得的光谱数据的分析得到了详细的、基于第一性原理的计算研究（密度泛函理论，DFT）的辅助。实验和理论的综合研究使我们能够对 CS 和 CSH 相中的质子转移反应得出一致的认识。将讨论保护这种城市基础设施骨架免受恶劣水介质腐蚀的策略的影响。
