The leaf extract of Combretum micranthum (CM) was tested as green corrosion inhibitor for Al-Si-Mg alloy in 3.5wt% NaCl solution using gravimetric and linear polarization methods at 30 0 C, 50 0 C and 70 0 C, from 1, 2, 3, 4, 5 hours of exposure time with concentration of the extract 0, 0.2, 0.4, 0.6, 0.8 and 1.0 v/v respectively. The result obtained indicate that the leaf extract of CM is a good corrosion inhibitor in the simulated sea water medium. The inhibition efficiency of the extract increased with an increase in concentration of the CM extract and decreased with increase in temperature. On the other hand, inhibition efficiency (IE%) synergistically decreased on addition of surfactant (Monoethylamine). The adsorption of the inhibitor on Al-Si-Mg surface is exothermic, Spontaneous and is best described by Langmuir, Freundlick and El-Awady adsorption models. The calculated values of activation energy, enthalpy of activation entropy of activation, free energy of process is by physical adsorption. Equally, methanol extract CM is a good adsorption inhibitor for the corrosion of Al-Si-Mg in 3.5wt% NaCl solution. Tafel polarization analysis indicates that the studied plant extract is a mixed type inhibitor.
A study on the inhibition of Al-Cu-Ni alloy in simulated sea-water environment was investigated using Sodium Chromate as inhibitor. The inhibitor concentration was varied as control, 0.25, 0.5, 1.0, 1.5 and 2.0 Molar. Al-Cu-Ni alloy was sand cast into cylindrical bars of 20 mm x 300 mm dimension. The corrosion of the sand-cast and treated alloys in 3.5wt% sodium chloride solution at temperatures 30oC, 50oC and 70oC over 1-5 hrs was evaluated using the weight loss method. It was observed that the corrosion rate of the treated alloys decreases with increase in inhibitor concentration. The decrease in corrosion rate on addition of the inhibitor can be attributed to the adsorption of the inhibitor onto the surface of the alloy. The attachment is by physical adsorption as the values of heat of adsorption were less than -10 kJ/mol. The plots obtained were linear meaning that they obey the Langmuir and Temkin adsorption isotherms. The inhibition efficiency increases generally with increase in temperature and inhibitor concentration.KEYWORDS: inhibition, simulated sea-water, corrosion, alloy, concentration, adsorption
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