西安城墙古砖表面风化病害及腐蚀机理研究

Studies on the Mechanisms of the Surface Weathering Disease and Erosion of the Bricks of the Xi’an City Wall

西安城墙古砖在露天环境下经历了上百年的侵蚀,表面形成了不同程度的风化产物。为了揭示城墙表面风化病害成因与腐蚀机理,利用环境扫描电子显微镜、X射线衍射仪、红外光谱仪、热分析系统和多功能成像光电子能谱仪对盐析、剥离和泥化样品进行了检测分析。结果显示腐蚀性盐类是导致古砖腐蚀的重要因素,盐析样品的主要物质组成为碳酸钙、石英、硫酸钠和硫酸钙,剥离与泥化样品有着相似的物质组成,均与氯化钠、硫酸钠和硝酸盐的作用有关;风化主导因素为Na2SO4转化为Na2SO4·10H2O产生的结晶应力,以及CaSO4水合结晶压力,其中CaCO3与CaSO4的转化是关键,在此基础上提出了保护性建议。

The bricks of the walls of the Xi'an City have been exposed to weathering in the open air for centuries,and weathering products have been formed on their surfaces.To reveal the mechanisms of the surface weathering disease and erosion of the city wall bricks,the salt precipitation,peeling off and argillization samples gathered from them are tested and analyzed by environmental SEM,XRD,infrared spectrometer,thermal analysis system and multifunctional photoelectron spectroscopy.The results show that corrosive salts are important factors for the erosion of the ancient bricks;the main components of the salt precipitation samples are calcium carbonate,quartz,sodium sulfate and calcium sulfate;the compositions of the peeling off and argillization samples are similar,which are all related to the effects of sodium chloride,sodium sulfate and nitrates;the main factors causing weathering are crystallization stresses brought about by Na2SO4 changing into Na2SO4·10H2O,and the pressure of the crystalline hydrate of CaSO4;the keys of them are the changes of CaCO3 and CaSO4,based on which this paper puts forward protective suggestions.