Corrosion Evaluation of Copper with Polystyrene-Block-Poly(ethylene-ran-butylene)-Block-Polystyrene Triblock (SEBS) Copolymer Coating in 3?% NaCl Solution by Using Response Surface Methodology

The present research work undertakes the investigation of preparation of the polystyrene-block-poly (ethylene-ran-butylene)-block-polystyrene triblock (SEBS) copolymer coating on a copper surface (Cu-SEBS) following a well-defined immersion protocol. The SEBS ratio, drying temperature (Temp), and drying time (time) are the factors for the determination of the immersion protocol of the Cu-SEBS electrode's preparation. To evaluate the effects of these factors on the anticorrosive behaviour of copper in NaCl 3 % solution and to determine the best conditions to produce a protective SEBS film on the copper surface (low corrosion rate), we used the experimental design and the central composite design (CCD). The response surface methodology (RSM) was used in this study as an optimization method and the Statgraphics software was used to treat experimental design data. The corrosion rate of Cu-SEBS at the different runs of the experimental matrix was measured by voltammetry around the open circuit potential (OCP) (& UDelta;E=& PLUSMN;50 mV vs SCE). The analysis of variance, the Pareto graph and the figure of the main and combined effect of the experimental factors show that the SEBS rate is the most significant factor. The linear effect of time and Temp, the quadratic effect of SEBS ratio, and the interaction between SEBS ratio and the drying temperature is, even though important, less significant. The optimized parameters were determined to obtain the lower corrosion rate, which was a 3.059 % of SEBS ratio, 70.18 & DEG;C of drying temperature, and 21 min of drying time. Then, to confirm the model, an electrochemical investigation of SEBS-coated copper at optimal conditions of immersion protocol (Cu-SEBS-Opt-Cond) was successfully applied in a 3 wt % NaCl aqueous solution. The corrosion rate of Cu-SEBS-Opt-Cond was obtained by voltammetry around the open circuit potential (OCP) equal 0.00023 mm year-1 which is close to that found by the experimental design. The measures of voltammetry around OCP, cyclic voltammetric (CV), and electrochemical impedance spectroscopy (EIS) showed that the Cu-SEBS-Opt-Cond electrode exhibited more stability and a much higher corrosion resistance than that observed for bare copper. In this paper, the use of experimental design and response surface methodology to assess the impacts of the basic operating parameters (SEBS ratio, drying temperature, and drying time) in the process of the treatment of the SEBS-coated copper (Cu-SEBS) on the response factor (corrosion rate) was investigated. The results demonstrated that the SEBS ratio is the most significant parameter that influenced the corrosion rate of SEBS coated copper. Besides, even though the drying time, drying temperature, the quadratic effect of the SEBS ratio, and the interaction SEBS ratio - drying temperature are important, they are less significant. The fit of the experimental design indicated that the optimum protocol for the formation of SEBS film by dip-coating the surface to obtain a lower corrosion rate could be found at the SEBS ratio of around 3.059 %, the temperature around 70.18 & DEG;C, and the time around 21 min. The optimal operating conditions found (Cu-SEBS-Opt Cond) were tested on a real protocol, leading to 0.00023 mm year-1 of the corrosion rate. This value is near the value found by the experimental design. In addition, the potentiodynamic polarization studies substantiate that the SEBS coating act as cathodic-type corrosion inhibitor.image