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The inhibition of corrosion of steel in 1 M HCl solution by newly synthesised pyrazole derivatives has been studied by weight loss and polarisation techniques at 308°K. Its inhibitory power is compared to N,N′‐bis(3,5‐dimethylpyrazol‐1‐yl‐methyl)‐pentanolamine (Bipyr). The results obtained reveal that tripyrazole exhibits a good protection. Inhibition is found to increase with increase in inhibitor concentration. The inhibition behaviour of the compound has been explained on the basis of molecule size and charge density of adsorption active centres. The adsorption phenomenon obeys the Langmuir adsorption isotherm model.

The purpose of this study is to perform quantum chemical calculations based on the DFT method on four bipyrazoles used as corrosion inhibitors for the plain carbon (“mild”) steel in acid media to determine the relationship between inhibition efficiency and the molecular structure of inhibitors.

Several quantum chemical parameters, such as the charge distribution, energy and distribution of highest occupied molecular orbital and lowest unoccupied molecular orbital, the absolute electronegativity (χ) values and the fraction of electrons (△N) transferring from inhibitors to the steel surface, were calculated and correlated with inhibition efficiencies.

The results showed that the inhibition efficiency of bipyrazole increased with the increasing in EHOMO, and the areas containing N atoms were the most probable sites to donate electrons for adsorbing the inhibitor molecules onto the metal surface.

It is a useful method to investigate the mechanisms of reaction by calculating the structure and electronic parameters, which can be obtained by means of theoretical quantum theory. Thus, the behavior and mechanism of the organic inhibitors can be obtained. Quantum chemical method can also be used to guide the selection and molecular design of inhibitors.

The purpose of this paper is to evaluate the corrosion inhibition potential of Calotropis procera in sulphuric acid medium on mild steel with a view to developing green corrosion inhibitors.

Extract of the C. procera was studied for its corrosion inhibitive effect by weight loss, electrochemical, SEM and UV methods. Using weight loss measurement data, mechanism of inhibitive action is probed by fitting in adsorption isotherm.

C. procera has been found to show significant corrosion inhibitive effect in sulphuric acid medium on mild steel. Inhibition is through adsorption of the phytoconstituents on mild steel following Tempkin adsorption isotherm. The results of ac impedance and polarization studies correlate well with the weight loss studies.

The plant has been investigated for the first time for its corrosion inhibitive effect. The effect has been studied by proven methods. This green inhibitor can find use in the inhibition of corrosion in industries where mild steel is used as a material of choice for the fabrication of machinery.

This paper aims to investigate the corrosion inhibition effects of indole-3-carbaldehyde and 2-methylindole on mild steel in 1 M HCl solution.

Indole-3-carbaldehyde and 2-methylindole as corrosion inhibitors of mild steel in 1 M HCl solution were investigated by polarisation and electrochemical impedance spectroscopy (EIS). Adsorption isotherm and mechanism were calculated. Quantum chemical calculations were used to find out a correlation between electronic structure of inhibitors and inhibition efficiency. Changes in the properties of metal surface in HCl solution in the presence of inhibitors were studied by contact angle measurements.

Polarisation results revealed inhibitors could reduce cathodic and anodic reactions rates on metal surface. EIS analysis showed that inhibition efficiency of indoles increases by increasing the inhibitors’ concentration; maximum inhibition efficiency was 95 and 94 per cent in solutions containing 1 mM indole-3-carbaldehyde and 2-methylindole, respectively. Inhibitors’ adsorptions on metal surface were confirmed by analysing the exposed metals’ surface through contact angles measurements. The adsorption of inhibitors was found to follow Langmuir isotherm. Quantum chemical calculations showed that a more positively charged benzene ring in the structure of two indole-based inhibitors would lead to higher adsorption to metal.

This research was carried out to understand the effects of two different functional groups (-C=O, -CH3) with different induction effects on the indole structure and on inhibition efficiency of corrosion inhibitors with the purpose of using these components in industrial application as acid wash solutions to etch and remove rusts from metal surfaces.

To evaluate the effect of synthesised calixarenes as new inhibitors on the corrosion of steel in HCl media at various temperatures.

Calixarenes have been synthesised and tested as corrosion inhibitors. Gravimetric technique and potentiodynamic polarisation and impedance spectroscopy methods were used.

Calixarenes exhibited a good inhibition. Their efficiency decreases slightly with temperature.

It was found that the inhibition efficiency increases with the concentration of inhibitors to reach 92 per cent at 10⁻⁴M.

The efficiency of calixarene derivatives increases with the concentration and falls slowly with temperature to attain 84 per cent at 353 K range. Calixarenes can be used in chemical cleaning and pickling processes.

The originality of this work is to find an inhibitor to give protection close to 100 per cent.

The purpose of this paper is to make people aware of organic corrosion inhibitors.

As it is a literature review paper, no specific method is used.

It has been found that plant extracts and oils show inhibition efficiency up to 98 percent, so it is certain that plant extracts and oils are effective corrosion inhibitors and can be successfully used at the industrial level.

Plant extracts and oils are also found to be non‐toxic, highly efficient, renewable and cheap. But less effort has been given towards the identification of which compound is active in the extract.

The paper shows detailed account of the inhibitors obtained from plants, which are used as natural corrosion inhibitors.