Experimental and computational chemistry studies on the inhibition of aluminium and mild steel in 0.1 M HCl by 3-nitrobenzoic acid

Nnabuk Okon Eddy,Paul Ocheje Ameh,Nsikak Bassey Essien

doi:10.1080/16583655.2018.1500514

Abstract

ABSTRACTThe effectiveness of 3-nitrobenzoic acid towards the inhibition of the corrosion of mild steel and aluminium in solution of HCl was investigated using theoretical and experimental methods (weight loss, thermometric, polarization, FTIR and SEM techniques). Inhibition efficiency of 3-nitrobenzoic acid, evaluated from weight loss technique ranged from 71% to 90% and from 71% to 82% for mild steel and aluminium, respectively. Results from linear polarization and potentiodynamic studies were comparable to weight loss results. Calculated kinetic (activation energy), thermodynamic (changes in entropy and enthalpy) and adsorption parameters indicated that the adsorption of the inhibitor on the surface of the respective metal is accompanied by molecular association and is endothermic, spontaneous and favoured the mechanism of physical adsorption. Best-fitted adsorption isotherms were Langmuir and Frumkin models, which gave evidences for the existence of interaction, characterized by attractive behaviour of the inhibitor on both mild steel and aluminium surfaces. Scanning electron micrographs of the metal before and after inhibition clearly revealed that the inhibitor prevented crevice and pitting corrosion by forming adsorbed protective layer on the respective metal surface. FTIR spectra of the inhibitor and the corrosion products indicated the formation of new bond, existence of interaction between the inhibitor molecules and the involvement of some functional groups in the adsorption and inhibition processes. Quantum chemical study revealed that the inhibitor is adsorbed on the metal surface through the nitro functional group in the ring. Calculated semi empirical parameters were comparable to those reported for excellent corrosion inhibitors.

Highlights

Efforts in tackling degradation of metals and their alloys through extension of lifespan have shown that it is difficult to produce or design metallic structures that are completely resistant to corrosion attack
Some organic compounds have been investigated as possible green corrosion inhibitors for the corrosion of metals and the outstanding characteristics that favour their corrosion inhibition efficiency are the possession of hetero atom (i.e. N, S, O or P) in their aromatic or long carbon chain, availability of π -electron and suitable functional groups, among others [7]
Patterns obtained for the variation of weight loss with time at different temperatures for the corrosion of mild steel and aluminium in 0.1 M HCl are shown graphically in Figures 1 and 2

Summary

Introduction

Efforts in tackling degradation of metals and their alloys through extension of lifespan have shown that it is difficult to produce or design metallic structures that are completely resistant to corrosion attack. Corrosion is an electrochemical process that returns metals to their natural state. Corrosion cannot be terminated, anodic/cathodic protection, galvanizing, painting, oiling and the use of corrosion inhibitors are some measures that have proven to be successful in retarding the rate of corrosion of metals [1,2,3,4]. Of significant interest is the use of corrosion inhibitors, which are compounds that retard the rate of corrosion, when added in minute concentration [5]. Some organic compounds have been investigated as possible green corrosion inhibitors for the corrosion of metals and the outstanding characteristics that favour their corrosion inhibition efficiency are the possession of hetero atom (i.e. N, S, O or P) in their aromatic or long carbon chain, availability of π -electron and suitable functional groups, among others [7]

Methods

Results

Conclusion