Synergistic Corrosion Inhibition of Mild Steel by Palmityltrimethylammonium Bromide and Methyl Protocatechualdehyde in Acidic Media: Experimental and Statistical Modeling Approaches

This study investigates the corrosion inhibition performance of a synergistic inhibitor system comprising palmityltrimethylammonium bromide and methyl protocatechualdehyde (PMB+MPA) on mild steel (MS) in 0.5 M H2SO4 and 0.5 M HCl solutions. The inhibition efficiency was assessed over 480 hours using seven concentrations ranging from 4.8 × 106 M to 2.9 × 105 M. Corrosion rates and inhibition efficiencies were determined through gravimetric analysis, and the effects of concentration and exposure time were statistically evaluated using ANOVA. Results show that inhibition efficiency increases with both exposure time and inhibitor concentration, reaching a plateau in H2SO4 (~95–97%) beyond 288 h due to surface saturation. In HCl, however, efficiency peaks earlier (~120–144 h) and declines significantly at lower concentrations due to Cl~ ion aggression. A second-order polynomial model was proposed to describe inhibition efficiency as a function of time and concentration. Overall, PMB+MPA demonstrated superior long-term stability in H2SO4, with notable concentration-dependent sensitivity in HCl, suggesting its suitability as an eco-friendly inhibitor in less aggressive environments.