Multivariable analysis of electrodeposited silane based superhydrophobic coatings for corrosion protection of carbon steel

• Published in: Journal of sol-gel science and technology 2020-06, Vol.94 (3), p.695-707
• Main Authors: Batalha Leoni, Gabriel, de Freitas, Denise S., Ponciano Gomes, José A. C., Brasil, Simone L. D. C.
• Format: Article
• Language: English
• Subjects: Carbon steel; Carbon steels; Ceramics; Chemistry and Materials Science; Coated electrodes; Composites; Contact angle; Controllability; Corrosion; Corrosion prevention; Film thickness; Glass; Hydrophobic surfaces; Hydrophobicity; Impedance; Independent variables; Inorganic Chemistry; Materials Science; Moisture content; Nanotechnology; Natural Materials; Optical and Electronic Materials; Original Paper: Sol–gel and hybrid materials with surface modification for applications; Precursors; Process variables; Protective coatings; Sol-gel processes; Submerging; Surface energy; Tetraethyl orthosilicate; Toxicity
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-020-05225-y

Superhydrophobic coatings are a field of great interest due to its many applications, including corrosion protection. Such films have been increasingly produced by coupling sol–gel processing with electrodeposition of silane precursors for the sake of its simplicity, controllability, variety of precursors, low toxicity, and low cost. However, despite of the method’s sensitivity to process variables, current literature mostly reports univariate analysis, failing to provide their combined effect and relative importance on response variables. In order to fill this knowledge gap, this paper presents a screening design considering 11 independent variables, followed by a surface response design, to assess the water contact angle (WCA), film thickness, and impedance modulus of silane films electrodeposited onto carbon steel, under several conditions. Here, octyltriethoxysilane (OTES) was selected as one of the sol–gel precursors, since it presents a non-hydrolysable alkyl chain capable of providing low surface energy and consequently water repellence. Results pointed out pH and the ratio between the number of mols of OTES and tetraethoxysilane (TEOS) as key factors for achieving higher WCAs, while pH and the volumetric percentage of water in the deposition solution were the most relevant variables for film thickness. Improved deposition conditions led to WCAs and film thicknesses above 157° and 70 µm, respectively, while monitored impedance modulus at 0.01 Hz in NaCl 3.5 wt% solution were superior to 10 6  Ohm cm 2 , even after 48 h of immersion. Highlights Production of electrodeposited sol–gel coating using TEOS and OTES as precursors. Plackett–Burman design helped to estimate and rank the effects of 11 variables. Central composite design maximized water contact angle and film thickness. Hydrolysis under low pH and low amount of water provide higher angles. Superhydrophobic films present corrosion protection even after prolonged immersion.