화학공학소재연구정보센터
Journal of Crystal Growth, Vol.519, 25-34, 2019
Transport and crystallization of NaCl solution in porous silicate materials
Salt damage is the most common and severe type of damage to silicate cultural relics. The transport and distribution of NaCl solution in porous SiO2 and porous silicate materials as well as its crystallization and destructive effects on the silicate samples were analyzed using low-field nuclear magnetic resonance (NMR), X-ray micro-computed tomography (micro-CT), three-dimensional digital microscopy with a large depth-of-field, and polarized light microscopy. The migration of solution was more active in the capillary pores smaller than 4.5 mm, and the interconnected pores transport the solution directly from the interior to the surface via capillary action. Salt crystals first grow and accumulate in the corner pores, which have a large surface area and exert an adsorption effect on the surrounding solution. This results in transport of the surrounding solution to the crystallization region on the edges, contributing to the growth of large crystals. Movement and turning of the particles occurred during the transitions of the porous silicate particles or Al2O3 particles caused by crystallization of the soluble salts. This was likely associated with the expansion effect caused by the growth of small-sized crystals within particles in the crystalline region, the layer-by-layer accumulative growth effects of large-sized crystals formed on the interface between the solid phase and the liquid phase in the capillary pores, and the attraction and contraction forces in the dehydration stage. These effects accelerated the destruction of the bonds between the silicate particles. The crystallization of salt solution on the interior morphology and displacement of porous materials were observed directly, which provides a scientific rationale for discussing the change of the main forces in the destruction of silicate particles.