Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA.
Acc Chem Res. 2010 Jun 15;43(6):897-905. doi: 10.1021/ar9002224.
The single most important cause of the deterioration of monuments in the Mediterranean basin, and elsewhere around the world, is the crystallization of salt within the pores of the stone. Considerable advances have been made in recent years in elucidating the fundamental mechanisms responsible for salt damage. As a result, new methods of treatment are being proposed that offer the possibility of attacking the cause of the problem, rather than simply treating the symptoms. In this Account, we review the thermodynamics and kinetics of crystallization, then examine how a range of technological innovations have been applied experimentally to further the current understanding of in-pore crystallization. We close with a discussion of how computer modeling now provides particularly valuable insight, including quantitative estimates of both the interaction forces between the mineral and the crystal and the stresses induced in the material. Analyzing the kinetics and thermodynamics of crystal growth within the pores of a stone requires sensitive tools used in combination. For example, calorimetry quantifies the amount of salt that precipitates in the pores of a stone during cooling, and dilatometric measurements on a companion sample reveal the stress exerted by the salt. Synchrotron X-rays can penetrate the stone and identify the metastable phases that often appear in the first stages of crystallization. Atomic force microscopy and environmental scanning electron microscopy permit study of the nanometric liquid film that typically lies between salt and stone; this film controls the magnitude of the pressure exerted and the kinetics of relaxation of the stress. These experimental advances provide validation for increasingly advanced simulations, using continuum models of reactive transport on a macroscopic scale and molecular dynamics on the atomic scale. Because of the fundamental understanding of the damage mechanisms that is beginning to emerge, it is possible to devise methods for protecting monuments and sculptures. For example, chemical modification of the stone can alter the repulsive forces that stabilize the liquid film between the salt and mineral surfaces, thereby reducing the stress that the salt can generate. Alternatively, molecules can be introduced into the pores of the stone that inhibit the nucleation or growth of salt crystals. Many challenges remain, however, particularly in understanding the complex interactions between salts, the role of metastable phases, the mechanism of crack initiation and growth, and the role of biofilms.
导致地中海盆地及世界其他地区古迹恶化的最主要因素是盐在石头孔隙中的结晶。近年来，在阐明导致盐损害的基本机制方面取得了相当大的进展。因此，正在提出新的处理方法，这些方法有可能针对问题的根源，而不仅仅是治疗症状。在本报告中，我们回顾了结晶的热力学和动力学，然后研究了一系列技术创新如何在实验中得到应用，以进一步了解孔隙内结晶。最后，我们讨论了计算机建模如何提供特别有价值的见解，包括矿物与晶体之间相互作用力和材料中诱导的应力的定量估计。分析晶体在石头孔隙内生长的动力学和热力学需要使用敏感工具进行组合分析。例如，量热法可定量确定冷却过程中盐在石头孔隙中沉淀的量，而对伴生样品的膨胀测量可揭示盐施加的应力。同步加速器 X 射线可以穿透石头并识别出结晶初期经常出现的亚稳相。原子力显微镜和环境扫描电子显微镜允许研究通常位于盐和石头之间的纳米级液体膜；该薄膜控制施加的压力的大小和应力的弛豫动力学。这些实验进展为越来越先进的模拟提供了验证，这些模拟使用宏观尺度上的反应性传输连续体模型和原子尺度上的分子动力学。由于开始出现对损坏机制的基本理解，因此有可能设计出保护古迹和雕塑的方法。例如，对石头进行化学改性可以改变稳定盐和矿物表面之间液体膜的排斥力，从而降低盐可能产生的应力。或者，可以将分子引入石头的孔隙中，以抑制盐晶体的成核或生长。然而，仍然存在许多挑战，特别是在理解盐之间的复杂相互作用、亚稳相的作用、裂纹起始和生长的机制以及生物膜的作用方面。
