TEOS/PDMS-OH hybrid material for the consolidation of damaged pottery

The use of organic–inorganic hybrid compounds containing tetraethoxysilane (TEOS) and hydroxyl-terminated polydimethylsiloxane (PDMS-OH) is one of the most promising approaches for using alkoxysilane-based formulations to improve the effectiveness of the consolidation of traditional silicate artifacts, such as ancient stone. Based on analysis of existing damaged potteries influenced by the crystallization of NaCl salt, the hybrid we prepared in this study provided a crack-free and homogeneous gel on the premise of appropriate PDMS-OH content. The consolidants were applied to samples prepared following procedures that simulate old pottery and the effect of the protective products was evaluated by characterizing the surface morphology, the determination of the consolidant uptake, color changes, water vapour permeability and several wet-dry cycles with salt. The best formulation found for the hybrid in the present work was made up of 10% PDMS-OH with TEOS, which showed a significant increase in compressive strength, with a value of 3.50 MPa at 3 mm depth of consolidation, similar to the sample treated with Primal SF(the commercial protective agents used for comparison purposes), which had 3.20 MPa in compressive strength at 2 mm depth of consolidation. Except for small color changes and excellent water vapor permeability, there was still no significant change, and the destructive effects from NaCl crystallization for the hydrophobic surface of the sample treated with hybrid material was different to what happened for the hydrophilic case in the original. Thus, this study has revealed, for the first time, the addition of an appropriate amount of PDMS-OH to TEOS helps to improve the mechanical properties, hydrophobic behavior and salt resistance of damaged pottery effloresced by the NaCl crystals; in addition small color changes and excellent water vapor permeability should also be taken into consideration.