THE INHIBITIVE EFFECT OF THYMUS SERPYLLUM EXTRACT ON CORROSION OF STEEL

The study examined the inhibitive effect of thyme extract as a green inhibitor on the corrosion of two steel types, steel 1 - DC01 and steel 2 - X5 CrNi 18-10, in a 3% NaCl solution. Four test solutions were used: 1) blank 3% NaCl, 2) 3% NaCl + 0.5 g/L thyme extract, 3) 3% NaCl + 1.0 g/L thyme extract, and 4) 3% NaCl + 1.5 g/L thyme extract. Steel samples (3x3x0.2 cm) underwent chemical treatment before being exposed to the non-inhibited and inhibited solutions. Weight loss and electrochemical techniques, i.e. electrochemical impedance spectroscopy, were employed to investigate the corrosion rate and the inhibitive effect of thyme extract. All experiments were obtained on room temperature. After chemical treatment samples were immersed in blank and inhibited solutions for 2h, 4h, 6h, 8h, 24h, 48h и 168h. Based on the weight loss in steel samples for the time spent in prepared solutions, negative mass index of corrosion, Km - (g/m2h), depth corrosion indicator, π (mm/year), and degree of efficiency, protection factor, z (%), were calculated. The results of the gravimetric and electrochemical measurements showed that thyme extract had an inhibitive effect on the corrosion of the tested steels, but not sufficient to be recommended for commercial application. The average corrosion inhibition efficiency of thyme extract was below 60% for both steel types. For steel 1, the protection factor was above 80% only in solution 4 after 48h and 168h, while for steel 2, the protection factor was greater than 80% for all three inhibited solutions only after 168h. These findings suggest a very slow adsorption of phytochemicals from thyme extract on the surface of the tested steels.