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To investigate the inhibitive effect of Congo red dye (CR) for aluminium corrosion in strong alkaline solutions and evaluate the synergistic effect of halide ions on the inhibition efficiency.

Corrosion rates of aluminium test coupons were determined by gravimetric technique at 30 and 60°C. Inhibition efficiencies of the additives (0.01‐5.0 mM CR and 5.0 mM CR+0.5 mM halides) were evaluated by comparing corrosion rates of the test coupons in 2 M KOH solution in the absence and presence of the additives.

CR inhibited aluminium corrosion in 2 M KOH by physical adsorption of the dye molecules on the corroding metal surface. Maximum efficiency at 30 and 60°C was 31.72 and 19.32 per cent, respectively. Dye adsorption was enhanced in the presence of halides in the order KCl < KBr < KI, with KI increasing efficiency up to 48.63 and 41.70 per cent at 30 and 60°C, respectively.

Further studies to involve variation of dye and halide concentrations for CR+halide systems to determine the best combination for optimum inhibition synergism.

This paper forms part of an extensive database on the inhibition characteristics of organic dyes for corrosion of different metals in various aggressive environments. This is to serve as a guide to possible applications in metal‐surface anodizing and as additives in surface coatings for service in different environments.

To appraise the inhibiting effect of Ocimum basilicum extract on aluminium corrosion in 2 M HCl and 2 M KOH solutions, respectively, at 30 and 60°C.

Corrosion rates were determined using the gas‐volumetric technique and the values obtained in absence and presence of extract was used in calculation of the inhibition efficiency. The mechanism of inhibition was estimated from the trend of inhibition efficiency with temperature.

Ocimum basilicum extract was found to inhibit aluminium corrosion in the acidic and alkaline environments. Inhibition efficiency increased with extract concentration but decreased with rise in temperature, suggesting physical adsorption of the organic matter on the metal surface. These results were corroborated by kinetic and activation parameters for corrosion and adsorption processes evaluated from the experimental data at the temperatures studied. Halide additives synergistically improved the inhibition efficiency of the extract.

This paper provides new information on the possible application of Ocimum basilicum extract as an environmentally friendly corrosion inhibitor. The mixed extract – iodide formulation provides an effective means for retarding aluminium corrosion even in highly aggressive alkaline environments.

The purpose of this paper is to study methyl green dye (MG) as a corrosion inhibitor for low carbon steel (LCS) in hydrochloric acid (1 M) and sulphuric acid (0.5 M) and to assess the effect of temperature variation and halide additives on the inhibition efficiency.

Corrosion rates are monitored using the gravimetric technique. Inhibition efficiency is determined by comparing the corrosion rates in the absence and presence of additives. Attempts are also made to elucidate the inhibition mechanism from the trend of inhibition efficiency with change in temperature and type of acid anion.

MG reduces the corrosion rate of the LCS specimens in both acid media within the investigated temperature range by adsorption at the metal/solution interface. Inhibition efficiency increases with MG concentration but decreases with rise in temperature. Maximum values of 67 and 73 per cent are obtained in 1 M HCl and 0.5 M H₂SO₄, respectively, at [MG]=0.001 mol dm⁻³. Halide additives increase the inhibition efficiency mainly in the sulphuric acid medium.

The inhibiting effect of MG is studied within a fixed concentration range, which can be expanded for further studies. The same applies to the effect of halide additives. Also, the dye structure can be modified by introducing different functional groups, and the effect on inhibition efficiency is investigated.

The research findings can find practical application for corrosion control in aqueous acidic environments.

This paper provides new information on the application of MG for corrosion inhibiting purposes. The experimental results form part of an extensive database on the corrosion inhibiting characteristics of organic dyes.

This paper aims to appraise the effectiveness of Gongronema latifolium extract as an environmentally friendly corrosion inhibitor for aluminium in strong acid (2 M HCl) and alkaline (2 M KOH) environments.

Corrosion rates were determined using the gas‐volumetric technique. The efficiency of inhibition was estimated by comparing corrosion rates in absence and presence of the additive, while the mechanism of inhibition was assessed by considering temperature effects on corrosion and inhibition processes.

The results show that the extract was well adsorbed on the metal surface and significantly repressed aluminium corrosion in both environments. Inhibition efficiency generally increased with concentration up to maximum values of 97.54 and 90.82 per cent in 2 M HCl and 2 M KOH, respectively. Temperature dependence studies revealed that the extract was chemically adsorbed on the aluminium surface at all concentrations in 2 M HCl and physically adsorbed in 2 M KOH, with likely tendency to become chemisorbed at higher concentration.

Gongronema latifolium has been studied for the first time as an inhibitor of aluminium corrosion and the results suggest that the extract could find practical application in corrosion control in aqueous acidic and alkaline environments. The findings are particularly useful, considering the scarcity of reports on the effective inhibition of aluminium corrosion in strong alkaline solutions.

To assess the protective effect and adsorption behaviour of Azadirachta indica extract in controlling mild steel corrosion in 1 M H₂SO₄ and 2 M HCl.

The inhibitive effect of the plant extract was monitored using the gas‐volumetric technique. The inhibition mechanism was inferred by curve fitting of the experimental data to known adsorption isotherms and the trend of inhibition efficiency with temperature.

Azadirachta indica extract effectively inhibited steel corrosion in the acid media studied by virtue of adsorption. The inhibitor adsorption characteristics were approximated by Langmuir isotherm. The extract functioned as a mixed inhibitor, depending on its concentration. The prime effect at lower concentration was mitigation of the cathodic reaction by physical adsorption of protonated species in the extract and at higher concentration the anodic reaction was inhibited by chemisorption of molecular species.

This paper provides novel information on the effectiveness of Azadirachta indica extract as a green corrosion inhibitor for steel in highly acidic environments as well as possible mechanisms of the inhibitive action.

This paper aims to investigate the inhibitive effect of ethanol extracts of Garcinia kola (EXG) for the corrosion of mild steel in H₂SO₄ solutions. The study is another trial to find a cheap and environmentally safe inhibitor for mild steel corrosion.

The inhibition efficiency has been evaluated using the hydrogen evolution technique at 30‐60°C. The mechanism of adsorption inhibition and type of adsorption isotherm were proposed based on the trend of inhibition efficiency and kinetic data.

The results obtained indicate that EXG inhibits the corrosion of mild steel in acidic medium and that the inhibition efficiency increases with an increase in the concentration of ethanol extracts and decreasing temperature. The inhibition efficiency increased on addition of potassium iodide to EXG, indicating synergism. The experimental data obeyed the Langmuir adsorption isotherm as well as the El‐Awady et al. thermodynamic‐kinetic model. The activation energy of inhibition of 6.8508 KJ/mol calculated for the corrosion process suggests that the EXG molecules are physically adsorbed on the metal surface.

Further investigations involving electrochemical studies such as polarization method will provide further enlightenment on the mechanistic aspect of the corrosion inhibition.

This paper provides new information on the possible application of EXG as an environmentally friendly corrosion inhibitor under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coatings.

To investigate the efficacy of Telfaria occidentalis extract as a corrosion inhibitor for mild steel in 2 M HCl and 1 M H₂SO₄ solutions, respectively, and to assess the effect of temperature and halide additives on the inhibition efficiency.

Corrosion rate was monitored by careful volumetric measurement of the evolved hydrogen gas at fixed time intervals. Inhibition efficiency was determined by comparing the corrosion rates in the absence and presence of additive. Attempts were made to elucidate the inhibition mechanism from the trend of inhibition efficiency with temperature. The adsorption mode of inhibiting species in the extract was assessed by considering the influence of both acid and halide ions on inhibition efficiency.

Telfaria occidentalis extract inhibited mild steel corrosion in 2 M HCl and 1 M H₂SO₄ solutions. Inhibition efficiency increased with extract concentration but decreased with rise in temperature. Synergistic effects increased the efficiency of the extract in the presence of halide additives in the order KCl<KBr<KI. Protonated species in the extract composition played a vital role in the inhibiting action.

This paper provides new information on the inhibiting characteristics of Telfaria occidentalis extract under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodising and surface coatings.

To investigate the efficacy of Congo red dye (CR) as an inhibitor of the acid corrosion of mild steel and aluminium alloy (AA 1060) and to assess the influence of halide ions on the inhibition efficiency.

Corrosion rates were estimated by monitoring the weight losses of the metal specimen as a function of time at different temperatures. Inhibition efficiency was determined by comparing the corrosion rates in the acid medium in the absence and presence of the additive.

CR dye reduced the corrosion rates of mild steel and aluminium in the acidic environment. Better inhibition was observed with the mild steel specimen. Protection efficiency was sensitive to inhibitor concentration as well as temperature and generally increased with an increase in CR dye concentration. The halide additives improved the inhibition efficiency in the order KCl < KBr < KI.

The inhibiting effect of CR dye was studied within a fixed concentration range, which could be expanded for further studies. The same applies to the CR+halide systems. Also, the dye structure could be modified by introducing different functional groups, and the effect on inhibition efficiency investigated.

The research findings could find practical application in corrosion control in aqueous acidic environments.

This paper provides new information on the inhibiting characteristics of CR dye under the specified conditions, as a guide to possible applications in metal surface anodizing and surface coatings.

This paper aims to investigate the influence of temperature and lignin concentration on the inhibition of carbon steel corrosion in 1 M HCl.

Weight loss corrosion tests were performed at different temperatures in the range of 30-70°C (303-343 K).

It was found that the corrosion inhibition efficiency (IE) of lignin on the carbon steel decreased when the temperature was increased from 60 to 70°C. However, at lower temperatures ranging from 30 to 50°C, the IE improved, due to occurrence of lignin adsorption on the surface of metal specimens. The IE was higher with increasing lignin concentration, thus reducing the weight loss of the carbon steel. The adsorption phenomenon involved exothermic processes because the value of enthalpy of adsorption (ΔH°_ads) < 0 and Gibbs free energy of adsorption (ΔG°_ads) were less negative with increase in temperature. The entropy of adsorption (ΔS°_ads) had negative values, representing the decrease in disorder of adsorption. The adsorption of lignin on the carbon steel surface in 1 M HCl was comprehensive, as deduced from kinetic and thermodynamic parameters. However, physisorption was the major contributor in the inhibition mechanism. The inhibitive features of carbon steel surfaces showed less damage once the steel was treated in lignin, as evident from macroscopy images.

The use of lignin as an acid corrosion inhibitor at high temperature is practical in metal surface treatment process.

The use of organic compounds gives an advantage to the environment, universal health and save cost, as the compounds can be found in nature.

Lignin can act as a flexible corrosion inhibitor within the temperature range of 30-70°C in 1 M HCl because it exhibits comprehensive adsorption (i.e. a combination of both physisorption and chemisorption) at specific concentrations.

To investigate the inhibitive effect of Delonix regia extracts to reduce the corrosion rate of aluminium in acidic media. The study was a trial to find a low cost and environmentally safe inhibitor to reduce the corrosion rate of aluminium.

The inhibition efficiency was evaluated using the hydrogen evolution technique at 30°C. The mechanism of adsorption inhibition and type of adsorption isotherm was characterised from trends of inhibition efficiency and kinetic data.

Delonix regia extracts inhibited the corrosion of aluminium in hydrochloric acid solutions. The inhibition efficiency increased with increasing concentration of the inhibitor but decreased with increase in exposure time. The acid extracts (hydrochloric acid seeds extract (HSE) and hydrochloric acid leaf extract (HLE)) were found to be more effective than the ethanolic extracts (ethanol seeds extract (ASE) and ethanol leaves extract (ALE)) and the inhibition followed the order: HSE (93.6 per cent) > HLE (83.5 per cent) > ASE (63.9 per cent) > ALE (60.4 per cent). The low negative values of ΔG_ad: −20.14 kJ mol⁻¹ for HSE, −18.08 kJ mol⁻¹ for HLE, −15.96 kJ mol⁻¹ for ASE and −15.12 kJ mol⁻¹ for ALE, as calculated from the Langmuir isotherm, indicated that the inhibitor molecules adsorbed onto aluminium by a physiosorption‐based mechanism. A first‐order type of reaction mechanism was obtained from the kinetic treatment of the H₂ gas evolution data.

Further investigations involving electrochemical studies such as polarization method should shed further light on the mechanistic aspects of the corrosion inhibition.

This paper provides new information on the possible application of Delonix regia as an environmentally friendly corrosion inhibitor under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coatings.