硫酸盐与氯化物对壁画的破坏性对比研究--硫酸钠超强的穿透、迁移及结晶破坏力证据

Comparative study of salt damage caused by sulfates and chlorides to mural paintings——evidence of superpenetration,migration and crystallization destruction resulting from sodium sulfate

莫高窟壁画酥碱病变的可溶盐主要为NaCl和Na2SO4,其中Na2SO4是破坏性最严重的盐。为此,以莫高窟壁画典型盐害为模拟对象进行仿真试验研究,重点研究Na2SO4盐在温度交变、干湿循环作用下对砂砾岩、地帐层的剥蚀破坏和强度的影响。结果表明,Na2SO4具有超强的穿透、迁移能力及结晶破坏能力,其结晶行为机理及壁画损害表现形式与氯化钠有很大不同。Na2SO4引起的试块膨胀和剥蚀破坏随着Na2SO4浓度和干湿循环次数的增加明显增大。气象条件中,32.4℃以下的温度区间的温度变化及40%以上的干湿度循环交变,是造成病害加剧的主要因素。盐涨试块强度测试表明,盐的结晶对壁画基体材质砂砾岩的强度损害是非常大,常见不可逆的粉末状酥碱及粒状剥离。研究结果可为正确保护壁画作理论探索时参考。

The soluble salts that cause damage to mural paintings in the Mogao grottoes are usually sodium chloride（ Na Cl） and sodium sulfate（ Na2SO4）. Of the destructive forces,the crystallization of sodium sulfate is the worst.This article focuses on how sodium sulfate damages the glutenite and ground layers under different temperature conditions and multiple wet-dry cycles. Sodium sulfate has a great ability to penetrate,migrate and crystallize,causing serious damage. The crystallization mechanism of sodium sulfate and the appearance of damage caused by it are quite different from those of sodium chloride. Expansion and erosion are accelerated by increased sodium sulfate concentrations and certain wet-dry cycle times. Among various meteorological conditions,a dry-wet cycle above40% humidity and the temperature changes below 32. 4 ℃ accelerated the damage. Salt expansion test block strength tests show that the intensity of damage caused by salt crystallization is very large. Typical damage characteristics are formation of powders and granular peeling. The work aimed to explore theories aimed at murals protection.