The inhibition of the corrosion of mild steel in 2M hydrochloric acid solutions by Pyridoxol hydrochloride (PXO) has been studied using weight loss and hydrogen evolution techniques. The inhibitor (PXO) exhibited highest inhibition efficiency of 71.93% at the highest inhibitor concentration of 1.0 x 10-2 M investigated and a temperature of 303K from weight loss result. Also, inhibition was found to increase with increasing concentration of the inhibitor and decreasing temperature. A first order type of mechanism has been deduced from the kinetic treatment of the weight loss results and the process of inhibition attributed to physical adsorption. The results obtained from the two techniques show that pyridoxol hydrochloride could serve as an effective inhibitor of the corrosion of mild steel in HCl acid solution. The compound obeys the Langmuir adsorption isotherm equation.
The anticorrosion effect of 5-hydroxytryptophan (5-HTP) on mild steel (MS) was investigated by gravimetric and electrochemical techniques. Two different concentrations (1 M and 15%) of hydrochloric acid were used to simulate well-acidizing fluid. The results show that 10 × 10 −5 M 5-HTP is 96.1% efficient in 1 M HCl and 78.1% efficient in 15% HCl at 30 • C. The efficiency decreases as the temperature increases, reaching 66.9% and 39.8% in 1 M and 15% HCl, respectively, at 90 • C. When 5-HTP is blended with potassium iodide and glutathione, the efficiency increases to above 88% and 78% in 1 M and 15% HCl, respectively, at 90 • C. Increasing the 5-HTP concentration decreases the double-layer capacitance and increases the charge-transfer resistance. 5-HTP behaves as a mixed-type corrosion inhibitor with anodic predominance and is spontaneously adsorbed on the steel surface. Physisorption of 5-HTP is best described by the Langmuir adsorption model and is also exothermic with a resultant decrease in the entropy of the bulk solution. The results of SEM/EDAX, FTIR and UV-VIS studies support the hypothesis that a protective film of 5-HTP forms on MS facilitated by O, N and C C functionalities.
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