Concentration and coating time effects of N-acyl sarcosine derivatives for corrosion protection of low-carbon steel CR4 in salt water – defining the window of application

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.