Department of Mineralogy and Petrology, University of Granada , Fuentenueva s/n, 18002 Granada, Spain.
Langmuir. 2013 Sep 10;29(36):11457-70. doi: 10.1021/la4017728. Epub 2013 Aug 26.
Alcohol dispersions of Ca(OH)2 nanoparticles, the so-called nanolimes, are emerging as an effective conservation material for the consolidation of stone, mortars, and plasters present in old masonry and/or mural paintings. To better understand how this treatment operates, to optimize its performance and broaden its applications, here we study the nano and microstructural characteristics, carbonation behavior, and consolidation efficacy of colloidal alcohol dispersions of Ca(OH)2 nanoparticles produced by both homogeneous (commercial nanolime) and heterogeneous phase synthesis (aged slaked lime and carbide lime putties). We observe that the alcohol not only provides a high colloidal stability to Ca(OH)2 particles, but also affects the kinetics of carbonation and CaCO3 polymorph selection. This is due to the pseudomorphic replacement of Ca(OH)2 particles by calcium alkoxides upon reaction with ethanol or 2-propanol. The extent of this replacement reaction depends on Ca(OH)2 size and time. Hydrolysis of alkoxides speeds up the carbonation process and increases the CaCO3 yield. The higher degree of transformation into calcium alkoxide of both the commercial nanolime and the carbide lime fosters metastable vaterite formation, while calcite precipitation is promoted upon carbonation of the aged slaked lime due its lower reactivity, which limits calcium alkoxide formation. A higher consolidation efficacy in terms of strength gain of treated porous stone is achieved in the latter case, despite the fact that the carbonation is much faster and reaches a higher yield in the former ones. Formation of alkoxides, which has been neglected in previous studies, needs to be considered when applying nanolime treatments. These results show that the use Ca(OH)2 nanoparticle dispersions prepared with either aged slaked lime or carbide lime putties is an economical and effective conservation alternative to commercial nanolimes produced by homogeneous phase synthesis. Ultimately, this study contributes to show that nanotechnology can help saving the built and sculptural heritage.
氢氧化钙纳米颗粒的酒精分散体，即所谓的纳米石灰，作为一种有效的保护材料，正在用于加固旧砌体和/或壁画中的石材、灰浆和石膏。为了更好地理解这种处理方法的作用，优化其性能并拓宽其应用范围，我们研究了由均相（商业纳米石灰）和多相合成（陈化熟石灰和电石石灰腻子）制备的胶体酒精分散体的纳米和微观结构特性、碳化行为和固结效果。我们观察到，酒精不仅为 Ca(OH)2 颗粒提供了高胶体稳定性，而且还影响了碳化动力学和 CaCO3 多晶型选择。这是由于 Ca(OH)2 颗粒与乙醇或 2-丙醇反应时，被钙烷氧基取代。这种取代反应的程度取决于 Ca(OH)2 的尺寸和时间。烷氧基的水解加速了碳化过程并增加了 CaCO3 的产率。商业纳米石灰和电石石灰的水解反应更快，且碳化产物中的 CaCO3 产率更高，这进一步促进了亚稳的方解石的形成，而对于陈化熟石灰，由于其反应性较低，促进了方解石的沉淀，从而限制了钙烷氧基的形成。尽管在前者中碳化更快且达到更高的产率，但在后者中，以强度增益为衡量标准，处理后的多孔石材的固结效果更高。在以前的研究中被忽视的烷氧基的形成，在应用纳米石灰处理时需要考虑。这些结果表明，使用由陈化熟石灰或电石石灰腻子制备的 Ca(OH)2 纳米颗粒分散体是一种经济有效的保护替代方案，可替代由均相合成制备的商业纳米石灰。最终，本研究有助于表明纳米技术可以帮助保护建筑和雕塑遗产。
