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Purpose -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. Design/methodology/approach -The inhibition efficiency was evaluated using the hydrogen evolution technique at 308C. The mechanism of adsorption inhibition and type of adsorption isotherm was characterised from trends of inhibition efficiency and kinetic data. Findings -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 DG ad : 2 20.14 kJ mol 2 1 for HSE, 218.08 kJ mol 2 1 for HLE, 2 15.96 kJ mol 2 1 for ASE and 215.12 kJ mol 2 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 H 2 gas evolution data. Research limitations/implications -Further investigations involving electrochemical studies such as polarization method should shed further light on the mechanistic aspects of the corrosion inhibition. Originality/value -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.

ABSTRACT:The corrosion inhibition of aluminum in H 2 SO 4 in the presence of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) and the effect of addition of halides (KCl, KBr, KI) was studied using the hydrogen evolution technique at 30 and 40°C. Inhibition efficiency (%I) increases with concentration of PVA and PEG--but with PEG having higher %I. The %I decrease with increase in temperature from 30 to 40°C in the absence and presence of inhibitor and halides. PVA and PEG were found to obey Freundlish adsorption isotherm. Phenomenon of physical adsorption is proposed from the obtained E a , ⌬G ads , and Q ads values obtained. The synergism parameters (S I ) obtained were found to be greater than unity for both PVA and PEG, which indicates that the enhanced inhibition efficiency caused by the addition of halides is only due to synergism.

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 corrosion inhibition of zinc in hydrochloric acid by extract of Nypa Fruticans Wurmb was studied using weight loss techniques. Maximum inhibition efficiency (and surface coverage) was obtained at an optimum concentration. However increase in temperature decreased the inhibition efficiency at the temperature range studied. The inhibition action of Nypa Fruticans Wurmb extract compared closely to that of 1, 5 Diphenyl Carbazone (DPC). Optimum inhibition efficiency for zinc in the presence of Nypa Fruticans Wurmb extract was 36.43% and 40.70% with DPC. The phenomenon of physical adsorption has been proposed from the activation energy values (19.33 kJ mol -1 and 21.11 kJ mol -1 ) with Nypa Fruticans Wurmb extract and DPC respectively. A first order kinetics has been deduced from the kinetic treatment of the results. The heat of adsorption, Q ad range from (-33.63 to -58.52 kJ mo l -1 ) for both additives studied. Mean ∆G o ads values (-7.82 to 8.68 kJ mol -1 ) are negative and suggestive of adsorption on metal surface. The data obtained from this study fits well into the Langmuir isotherm. Evidence is hereby provided to show that Nypa Fruticans Wurmb extract and DPC inhibits the corrosion of zinc comparatively @ JASEM