Effects of addition of colloidal silica particles on TEOS-based stone protection using n-octylamine as a catalyst

Protective agents based on tetraethoxysilane (TEOS) have been widely used for the protection of stone heritages. However, TEOS-based protective agents suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developed capillary force, which is typical for TEOS-based protective agents. In this paper, we have prepared new TEOS-based protective agent containing flexible hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and colloidal silica particles (167   nm) using n-octylamine as a catalyst in order to reduce capillary force development and increase hydrophobicity, and have characterized them for the application of stone protective agent. The extent of surface hydrophobization depends on concentration of colloidal silica particles and reaches a maximum value of 123° at 0.2% (w/v) of colloidal silica particles for the case of treated with the modified composition. The presence of n-octylamine is a key factor which promotes the increase of the gel pore size. The protective performances were also evaluated by its ability to resist acid corrosion. The results reveal that the protective effects are satisfying.