Department of Mineralogy and Petrology, University of Granada, Fuentenueva s/n, 18002 Granada, Spain.
Phys Rev Lett. 2012 Dec 28;109(26):265503. doi: 10.1103/PhysRevLett.109.265503. Epub 2012 Dec 26.
Pressure exerted by crystallization of salts within porous materials contributes to damage in historic and modern construction. By unequivocally identifying the precipitating phase(s) while simultaneously determining solution supersaturation and associated crystallization pressure in subsurface pores, we show that the formation of a thermodynamically metastable salt phase (heptahydrate; Na2SO4·7H2O) and the resulting transition to a less soluble stable phase (mirabilite; Na2SO4·10H2O) is largely responsible for the high supersaturation and crystallization pressure developed during evaporative crystallization of sodium sulfate, the most damaging salt known. These results help to explain why salts with various (stable and metastable) hydrated phases are the most damaging. We also show that damage associated with metastable-stable phase transitions can be suppressed by the use of crystallization promoters. These results open new ways for the prevention of salt damage to building materials.
盐类在多孔材料中结晶所产生的压力会导致历史建筑和现代建筑的损坏。通过明确鉴定沉淀相，同时测定亚表层孔隙中溶液过饱和度和相关结晶压力，我们发现热力学亚稳盐相（七水合硫酸钠；Na2SO4·7H2O）的形成以及向溶解度更低的稳定相（芒硝；Na2SO4·10H2O）的转变，是硫酸钠蒸发结晶过程中过饱和度和结晶压力升高的主要原因，而硫酸钠是已知最具破坏性的盐。这些结果有助于解释为什么具有各种（稳定和亚稳）水合相的盐是最具破坏性的。我们还表明，通过使用结晶促进剂，可以抑制与亚稳-稳定相转变相关的损坏。这些结果为防止建筑材料受到盐类损坏开辟了新的途径。
