Electrochemical deposition of silica sol-gel films on stainless steel: preliminary analysis of key variables

The sol-gel electrodeposition of coatings on conductive substrates has been presented the first time in 1999, and since then, a significant number of papers have been published, mainly devoted to explore the possibilities of application. However, a clear and complete picture of the fundamental aspects and of the role of the many parameters involved is still lacking. In this work, which is intended to be a preliminary approach to a systematic study, the effect of potential and time on the coating thickness was studied, trying to analyze the different factors that make experimentation difficult, looking for possible solutions and putting the basis for a more complete and analytic investigation. Simple tetraethyl orthosilicate-based acidic solutions were used to coat planar stainless steel samples. Different starting solutions were tested, varying the amount of precursor, water and hydrochloric acid. The role of working temperature, oxygen concentration and the presence of potassium nitrate until saturation was tested. Morphology, thickness, cyclic voltammetry and chronoamperometry were used to characterize the coatings and to monitor the current in function of potential and time. The thickness was found to increase with both the concentration of the solution and the HCl/TEOS ratio. Temperature was found to be an important factor, but also the amount of oxygen and electrolyte (KNO3) in solution seems to influence the thickness of coatings.