Surfactant-template sol-gel protective coatings for cast iron corrosion: Effect of the surfactant type and concentration

Abstract

Different surfactants-template tetraethylorthosilicate-3-mercaptopropyl-trimethoxysilane (TEOS-MPTMS) sol–gel materials are prepared by the hydrolysis of silane precursors, in presence of the surfactant. Three surfactants are used, cationic cetyltrimethylammonium bromide (CTAB), non-ionic TritonTM X-100, and anionic sodium dodecyl sulfate (SDS). Prepared sol–gel materials are applied as protective coatings for cast iron corrosion in 0.5 mol.L-1 HCl. The protection efficiency is estimated by electrochemical measurements. Structural and surface properties of the prepared sol–gel materials are examined by FTIR and scanning electron microscope (SEM) and are affected by the surfactant species and concentration. Surfactant-template sol–gel materials acquire higher porosity than the free material. However, the presence of the surfactant stabilizes the silane network formation, and facilitates the protection performance, especially at lower and intermediates surfactant amounts. The presence of TritonTM X-100 and CTAB enhance the protection performance of the sol–gel coatings, average efficiencies are 95 and 86 %, respectively. On the other hand, SDS-template sol–gel coatings offer lower efficiency and can not be used as protective coatings at high SDS concentrations due to the repulsion between SDS and negatively charged silanolate groups, which results in a highly unstabilized sol–gel structure with a distorted morphology. The proposed surfactant-template sol–gel coatings show excellent operational stability in the corrosive medium for a long time.