Application of aqueous extracts of coffee senna for control of mild steel corrosion in acidic environments

Chris O Akalezi,Conrad K Enenebaku,Emeka E Oguzie

doi:10.1186/2228-5547-3-13

Abstract

Abstract Background The inhibitive effect of the aqueous extract of Coffee senna (CS) on the corrosion of mild steel in 1 M HCl and 0.5 M H2SO4 solutions was investigated by weight loss measurement as well as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. Result The extract was found to efficiently inhibit the corrosion process in both environments and inhibition efficiency increased with extract concentration as well as rise in temperature. Data from electrochemical measurements suggest that the extract functioned by adsorption of the organic matter on the metal/corrodent interface, inhibiting both the anodic and cathodic half reactions of the corrosion process. Adsorption of the extract organic matter was approximated by the Langmuir isotherm. The adsorption behavior of selected organic constituents of the extract on the metal surface was assessed at the molecular level, in the framework of the density functional theory. Conclusion This study clearly shows the potentials of CS extract for control of mild steel corrosion in acidic environment.

Highlights

Premature deterioration of concrete structures mainly occurs due to the ingress of chloride ions and carbon dioxide [1]
Some authors argue that those compounds which are used to protect concrete reinforcement are not effective [10] when the concrete is kept immersed in NaCl solution, whereas others report that some compounds are effective in reducing corrosion rate of steel rebar in concrete contaminated with chlorides [22, 23]
It is understandable from the polarization data that at very low concentration (50 ppm), sodium nitrite acted as a corrosion antagonist, i.e., the corrosion rate of steel rebar treated with nitrite was greater than that of the rebar immersed in concrete pore solution (CPS) without nitrite

Summary

Introduction

Premature deterioration of concrete structures mainly occurs due to the ingress of chloride ions and carbon dioxide [1]. Some authors argue that those compounds which are used to protect concrete reinforcement are not effective [10] when the concrete is kept immersed in NaCl solution, whereas others report that some compounds are effective in reducing corrosion rate of steel rebar in concrete contaminated with chlorides [22, 23]. The present investigation aims to explain the behaviour of these chemical species on steel rebar in contaminated concrete pore solution. Chemicals such as trisodium citrate (98%), sodium chloride (> 99.9%), NaNO2 (EMSURE®) and zinc acetate (> 99%) were purchased from Merck Millipore. To investigate the surface morphological changes on the steel rod dipped in simulated concrete pore solution [46, 47], microscopic studies were performed using Leica Stereo Microscope (S8ACO)

Results and discussion

NaNO2 50ppm

Conclusions