茂陵石刻表面污染物和可溶盐的分析研究

Analytical study of contaminants and soluble salts on the surface of stone sculptures at Mao Mausoleum,Shaanxi

为了厘清造成茂陵石刻文物劣化的原因和机理,对石刻表面的污染物和析出可溶盐进行了分析研究,以找出石刻文物劣化和污染物、可溶盐之间的关系,为制定科学有效的保护措施提供科学依据。采用X射线衍射仪(XRD)、扫描电镜-能谱仪(SEM-EDS)、傅里叶变换显微红外光谱仪(FTIR)等仪器对采集的茂陵石刻文物表面污染物和可溶盐进行了表征,用离子色谱(IC)分析了可溶盐的离子种类和含量。结果表明,“马踏匈奴”石刻雕像表面污染物的主要成分是CaSO4·2H2O,其形成原因是石材与空气污染物经长期化学反应形成的钙质结壳,或者是地下水中可溶盐的毛细运移造成的;“怪兽吃羊”石刻雕像表面析出的可溶盐有Na2SO4、NaNO3和CaSO4·2H2O,主要是由于地下水中可溶盐从砖石基座迁移到石刻文物本体,随温湿度变化反复结晶溶解所造成。可溶盐会引起石质文物表面酥粉、片状剥落、内部结构破坏等侵蚀,是茂陵石刻文物的主要病害之一。

In order to study the reasons for and mechanisms of deterioration of stone sculptures at Mao Mausoleum,we characterized the contaminants and soluble salts collected from the sculpture surfaces using X-ray diffraction(XRD),scanning electron microscopy-energy dispersive spectrometry(SEM-EDS)and Fourier transform infrared spectrometry(FTIR),and also determined the ions of soluble salts and quantified their distribution using ion chromatography(IC).The results show that 1)gypsum crusts(CaSO4·2H2O)on“Horse Stepping on a Hun Soldier”was formed either by chemical reactions occurring on the sculpture surface due to deposition of atmospheric pollutants,or by capillary migration of soluble salts from underground water;2)soluble salts containing Na2SO4,NaNO3 and CaSO4·2H2O on the surface of“Monster Preying on a Sheep”,were mainly caused by capillary migration of soluble salts of underground water through the brick base to the stone matrix,resulting in repeated crystallization and dissolution on the sculpture surface according to environmental cycles of temperature and humidity.Soluble salts are known to cause stone deterioration in the form of lifting spalls,detaching scales and breakage of the internal material structure of stone sculptures.These are also the main diseases seen on the stone sculptures at the Mao Mausoleum.