Dispersions of Surface Modified Calcium Hydroxide Nanoparticles with Enhanced Kinetic Stability: Properties and Applications to Desalination and Consolidation of the Yungang Grottoes

Calcium hydroxide (Ca(OH) 2 ) is one of the most interesting materials used to consolidate stone sculptures, monuments, mortars or wall paintings. In this study, we reported on the synthesis and characterization of surface modified Ca(OH) 2 nanoparticles as a dispersion with enhanced kinetic stability and the applications for the conservation of sandstone monuments. Uniform hexagonal Ca(OH) 2 nanoparticles (∼35nm) were obtained by mixing NaOH and NaCl aqueous solutions at 100∼175 o C using homogeneous-phase reactions. It was further demonstrated that 3-(Methacryloyloxypropane oxygen) trimethoxysilane surfactant agent can significantly reduce agglomeration and simultaneously improve specific surface area of as-synthesized Ca(OH) 2 nanoparticles. Brunauer-Emmett-Teller (BET) measurement showed that specific surface area of modified Ca(OH) 2 nanoparticles reaches up to ∼48.78m 2 /g, about 2.5 and 3.4 times higher than that of unmodified and commercial ones, respectively. The kinetic stability of Ca(OH) 2 despersion can be further enhanced and its viscosity can be decreased by optimizing the ratio of ethanol and n-propanol. Especially, a technique, which combined the Ferroni-Dini method and dispersion of Ca(OH) 2 nanoparticles with enhanced kinetic stability, was proposed to effectively desalinate and consolidate the decayed stone, as evidenced by significant decreases of the porosity and concentration of detrimental Cl - and SO 4 2- ions in the severely decayed sandstone samples from the Yungang grottoes.