Protection Effect of Admixed Melaleuca alternifolia and Citrus paradisi Macf. Oil Extracts on High Carbon and 3310 Low Grade Alloy Steels in HCl Solution

Protection performance of admixed Melaleuca alternifolia and Citrus paradisi Macf. oil extracts (MACP) on high carbon steel (HCS) and 3310 low-grade alloy steel (AS33) were studied in 0.5 M HCl solution. Potentiodynamic polarization technique, weight loss analysis, open circuit potential measurement, optical microscopy, X-ray diffractometry, and ATR–FTIR spectroscopy were employed to assess their effectiveness. Results from weight loss analysis and potentiodynamic polarization showed MACP performed very poorly at low concentrations (0.5% and 1% MACP concentration for HCS, and 0.5–2% MACP concentration for AS33). However, at higher concentrations, effective protection of the alloys was obtained with peak performance values of 92.45% and 86.32% for HCS, and 73.25% and 78.01% for AS33 from weight loss and polarization techniques. The protection performance of MACP increased with an increase in its concentration with cathodic-type inhibition effect on HCS and mixed-type on AS33. MACP induced passivation characteristics on the anodic portion of the polarization plot compared to the extended cathodic slope. X-ray diffractometry revealed the presence of Fe 2 O 3 as the dominant phase compound on HCS and AS33 after corrosion in HCl. FeS 2 , Fe(ZnS 2 ), SiO 2 , and ZnCO 3 were the dominant compounds on HCS and AS33 after corrosion in the presence of MACP indicating the formation of complex pseudo-corrosion-resistant precipitates on both alloys. ATR–FTIR spectroscopy identified the active groups (alkyl halides, aromatics, primary, secondary amines, aliphatic amines, alcohols, carboxylic acids, nitro compounds, etc.) and bonds responsible for corrosion inhibition of the alloys. Optical images of the corroded HCS indicate severe general corrosion compared to localized corrosion on the AS33 surface. These images significantly differed from MACP inhibited HCS and AS33 surfaces where corrosion oxidation was suppressed.