Synergistic effect of essential oil distillates on the corrosion protection of GX4CrNiMo16-5-1 stainless in acid-chloride electrolyte

The inhibition capability of admixed rosemary oil with cinnamon cassia oil (RC), and grapefruit oil with lemongrass oil (GL) on GX4CrNiMo16-5-1 martensitic stainless steel (GX4ST) corrosion was studied in 6 M H2SO4/3.5% NaCl electrolyte by potentiodynamic polarization and optical microscopy characterization. Results show both admixed distillates performed effectively on GX4ST. The corrosion rate of GX4ST without the distillates at 2.82 mm/y significantly decreased to average value of 0.04 mm/y and 0.05 mm/y analogous to average inhibition efficiency of 98.64%and 98.23%for RC and GL compound. The oil distillates exhibit consistent anodic corrosion inhibition behavior at all concentrations studied. Corrosion thermodynamic calculations showed the distillates chemisorbed on the martensitic steel with Gibbs free energy values greater than -46.01 Kjmol-1with respect to Langmuir isothermequation which indicates negligible of lateral interaction effect among inhibitor molecules and surface coverage protection mechanism. Optical image representations of GX4ST after corrosion without the distillates showed severe surface degradation of general and localized corrosion. This contrast the images of the inhibited steel surface which were closely similar to the steel image before corrosion