NATURE-DERIVED CORROSION INHIBITION OF CARBON STEEL IN HCL BY BLACK PINE ESSENTIAL OIL AND ITS ACTIVE COMPOUNDS

This study investigates the potential of black pine essential oil and its phytochemicals as eco-friendly corrosion inhibitors for carbon steel in a 1 M HCl solution. The chemical composition of the oil was analyzed using GC/MS and FTIR, revealing the presence of active phytochemicals, including α-pinene, β-pinene, and caryophyllene. To compare the efficiency of the essential oil and its phytochemicals, impedance and polarization methods were employed. All tested inhibitors exhibited mixed-type inhibition, with predominant cathodic control. The inhibition efficiency of all compounds increased with time. After 4 hours, the efficiency of the inhibitors at the same concentration of 80 ppm increased in the following order: β-pinene < α-pinene < black pine essential oil < caryophyllene. Additionally, the active compounds were tested at concentrations similar to their natural occurrence in 100 ppm of essential oil. α-pinene demonstrated the highest efficiency compared to β-pinene and caryophyllene, though it was slightly less effective than 100 ppm of the essential oil. Surface morphology analysis using SEM revealed significant changes in the steel surface, further supporting the corrosion inhibition properties of the oil. XPS analysis confirmed the formation of a protective film composed of Fe oxides/hydroxides and phytochemicals. These results highlight the potential of black pine essential oil as a sustainable, green corrosion inhibitor, contributing to the growing shift toward environmentally friendly industrial practices.