The corrosion protection properties of the intermixed of l-leucine and vanillin (LLVL) on P4 mold steel within 1.5 M H2SO4 and HCl media was studied by weight loss analysis. Calculated data revealed the inhibition effect of the intermixed compound performed poorly at low H2SO4 concentrations due to inability of the combined inhibitor molecules to aggregate and effectively hinder the dispersion of the destructive anions to the steel surface. The inhibition efficiency decreased significantly with time to values below effective inhibitor performance. However, from mid to optimum concentration, inhibition efficiency of the compound was generally stable with time with values generally above 85%. In HCl media, the inhibition efficiency of the intermixture was generally above 80% at all concentrations with respect to the inspection time. The inhibitor compound exhibited greater stability in HCl compared to H2SO4 solution. Calculated values of standard deviation in H2SO4 were broadly greater than the outputs received in HCl due to the degree of variation between LLVL inhibition efficiency values. The margin of error at 95% confidence shows 65% of LLVL inhibition efficiency values obtained in H2SO4 solution have values above 70% inhibition efficiency with margin of error at +12.07% while in HCl solution, 100% of the LLVL inhibition efficiency data obtained is above 70% with margin of error of +1%. Analysis of variance showed the statistical relevance of inhibition efficiency in H2SO4 and HCl solution is significantly higher the corresponding relevance for inspection time with values of 70.45% and 71.18%.

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AbstractStudy of the synergistic inhibition properties of the combined admixture of 4-methyl-norvalin and 2-methoxy-4-formylphenol (non-toxic organic compounds) on the corrosion of P4 low carbon mold steel in 1.5 M H2SO4 and HCl solution was performed with weight loss measurement, potentiodynamic polarization and optical microscopy analysis. Results obtained showed the inhibition efficiency of the admixed compound performed above the value for effective corrosion inhibition at very low concentrations in H2SO4 solution. However, from mid concentration to the highest concentration studied, the inhibition efficiency of the compound was above 85% from electrochemical tests. In HCl solution the inhibition efficiency of the compound was well above 80% and 90% for weight loss and polarization tests at all concentration studied. Anodic corrosion inhibition mechanism was determined for the compound in H2SO4 according to Freundlich and Frumkin adsorption isotherms due to weak Van der Waals attraction between the inhibitor molecules and the steel’s surface. The mechanism of corrosion inhibition in HCl was calculated to be cathodic type according to Langmuir isotherm model.Morphological images of inhibited and non-inhibited steel surfaces significantly contrast each other though the extent of deterioration was much severe for the steel from H2SO4 solution.