Electrodeposition of hybrid sol-gel glass coatings on 304 stainless steel for corrosion protection

Melting gels are a class of materials which are capable of protecting 304 stainless steel against corrosion. These are organically modified silica gels that are rigid at room temperature and begin to soften when heated to 110°C. They are consolidated at temperatures above 120°C where they are transformed into hybrid glasses, which are excellent anticorrosive barriers. The primary goal of this study was to produce anticorrosive hybrid glass coatings on 304 stainless steel using melting gels prepared using ethyltriethoxysilane (EtTES) and diethyldiethoxysilane (DEtDES). Gels were prepared over a wide range of compositions between 100mol%EtDES-0mol%DEtDES and 50mol%EtDES-50mol%DEtDES. Processable melting gels were obtained for those compositions below 80mol% EtTES. It was found that the temperature of consolidation increased from 122°C to 153°C. The thermal stability of the gels was studied using thermogravimetric-differential thermal analysis and differential scanning calorimetry. The hybrid glass coatings were deposited by pouring or by electrodeposition, followed by a thermal treatment at the consolidation temperatures. The hybrid glass coatings were characterized to compare the poured and electrodeposited coatings. The hydrophobicity was estimated using contact angle measurements. For coatings obtained by pouring, an average contact angle of 95° was measured. For the electrodeposited coatings, the highest contact angle (96 ^o ) was achieved for the hybrid glasses with composition of 70mol%EtDES-30mol%DEtDES. Protection against corrosion was evaluated by corrosion tests. These results show a good resistance against the corrosion for coatings obtained by pouring.