No abstract

The Box-Behnken Design (BBD) is used to model the sacrificial Cathodic Protection System (SCPS) to find the factors effectiveness behaviour. For protection potential assessment the BBD receives (resistivity of environment, sacrificial anode alloy, distance between anode and cathode and surface area for the structure to be protected) as input and gives the protection potential as output. By applying BBD with their analysis tools we get many results. The important results which are the factors individual effectiveness on the sacrificial cathodic protection (SCP) process are the resistivity which has the greatest effect on the potential protection (rank=1) followed by sacrificial anode alloy type (rank=2), surface area for structure protected required (rank=3) and distance between anode and cathode (rank=4). The interaction of sacrificial anode alloy and cathode area (χ 2 χ 4 ) has significant effect on CP process with the limits which are used in this work while the other factors interaction (χ 1 χ 2 , χ 1 χ 3 , χ 1 χ 4 ,χ 2 χ 3 , χ 3 χ 4 ) has insignificant effect on the limits which used in this work.

Potential natural and environment-friendly substances are often used as substitutes for inhibitors to protect steel against corrosion in a sustainable way. Here, three biodegradable N-acyl sarcosine derivatives are evaluated for corrosion protection by polarisation, weight loss, electrochemical impedance, optical and scanning electron microscopy (SEM) spectroscopy including energy dispersive spectroscopy (EDS) to find the best possible application interval of concentration and dip-coating time. The substances present vary in their carbon chain length on the sarcosine-amino acid and are tested in 0.1 M NaCl as protective barrier for low-carbon steel CR4. Corrosion protection improved with increasing sarcosine concentration in the dip-coating stock solutions (25, 50, 75, and 100 mmol/L). Best efficiencies were found in polarisation for the highest studied concentrations of Oleoylsarcosine (O) with 97% followed by Myristoylsarcosine (M) with 82%. The lowest overall performance showed the shorter Lauroylsarcosine (L) with 51%. The best immersion time for dip-coating on CR4 for present compounds turned out to be 10 min. Surface analysis results with SEM and EDS revealed a significant higher C content caused by increased film-forming adsorption of sarcosines on the metal surface.

To investigate the corrosion protection behavior of naturally derived cocoyl sarcosine in combination with N-b-hydroxyethyl oleyl imidazole for steel CR4 in 0.1 M NaCl, different evaluation systems (weight loss, electrochemical measurements, and spray corrosion tests) were used. Both compounds were tested in different concentrations (25–100 mmol/L) and with variable dip coating times (1–30 min), first individually and then in combination, to check any synergistic effects for surface protection. Both showed only an insignificant corrosion inhibiting effect with less than 50% efficiency at all concentrations and dip coating times if used alone. In contrast, compound combinations revealed an improved corrosion inhibition correlated with higher concentrations. Across all methods, the compound combination concentration of 100 mmol/L resulted in improved efficiency of up to 83% for gravimetric tests, up to 84% for the impedance measure and more than 91% for potentiodynamic polarization. Dip coating variations proved 10 min to be the best option for all compounds with a maximum efficiency of up to 86% for the compound combination.

Optimization and statistical methods are used to minimize the number of experiments required to complete a study, especially in corrosion testing. Here, a statistical Box–Behnken design (BBD) was implemented to investigate the effects of four independent variables (inhibitor concentration [I], immersion time t, temperature ϑ, and NaCl content [NaCl]) based on the variation of three levels (lower, middle, and upper) on the corrosion protection efficiency of the green inhibitor oleoylsarcosine for low-carbon steel type CR4 in salt water. The effects of the selected variables were optimized using the response surface methodology (RSM) supported by the Minitab17 program. Depending on the BBD analytical tools, the largest effects were found for ϑ, followed by [I]. The effect of interactions between these variables was in the following order: [I] and ϑ > t and ϑ > [I] and [NaCl]. The second-order model used here for optimization showed that the upper level (+1) with 75 mmol/L for [I], 30 min for t, and 0.2 mol/L [NaCl] provided an optimal protective effect for each of these factors, while the lower level (−1) was 25 °C for ϑ. The theoretical efficiency predicted by the RSM model was 99.4%, while the efficiency during the experimental test procedure with the best-evaluated variables was 97.2%.