The corrosion inhibition of Al and its alloys is the subject of tremendous technological importance due to the increased industrial applications of these materials. This study reports the corrosion inhibition of AA8011 aluminium alloy in acidic solutions using Newbouldia leavis leaf extract by way of gravimetric measurements. It was shown that the presence of Newbouldia leavis leaf extract inhibited the corrosion of aluminium in the test solutions and the inhibition efficiency depended on the concentration of the plant extract as well as on the time of exposure of the aluminium samples in H 2 SO 4 solutions containing the extract. The experimental data complied to the Langmuir adsorption isotherm and the value and sign of the Gibb's free energy of adsorption obtained suggested that inhibitor molecules have been spontaneously adsorbed onto the aluminium surface through a physical adsorption mechanism.

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The effect of Euphorbia hirta and Dialum guineense leave extracts on the corrosion of aluminium in 0.25M NaOH was investigated using gravimetric technique. It was shown that the presence of Euphorbia hirta and Dialum guineense leave extracts inhibited the corrosion of aluminium in the test solutions and that the inhibition efficiency depended on the concentration of the plant extract as well as on the time of exposure of the aluminium samples in 0.25M NaOH solutions containing the extracts. Dialum guineense extract shows the best inhibition capability for aluminium corrosion in sodium hydroxide, probably, this is due to the planer orientation of the adsorbed extract molecules. Inhibition efficiency of the inhibitors tested increases with decreasing sodium hydroxide concentrations. The experimental data complied to both Langmuir and Temkin adsorption isotherms and the value and sign of the apparent activation energy of adsorption obtained suggests that inhibitor molecules have mixed inhibition mechanism.

The corrosion inhibition evaluation of aluminium alloy AA7075-T7351 in 1.0 M HCl environment, by biologically active and water soluble luteolin 7-glucoside and phenolic polymeric compounds in Newbouldia laevis (NBL) extracts-as organic corrosion inhibitors of aluminium-have been investigated using gravimetric, electrochemical and thermodynamic techniques respectively, at room temperature (25 ± 1 °C), and at elevated temperatures of 40, 50, 60 and 65 °C. Gravimetric results showed that optimal inhibition efficiency ( ), at room temperature (298 ± 1 K) and 338 K are 86.1% and 67.5% respectively for the maximum concentration of 0.6 g/L. This suggests that NBL extract was affected by temperature and accomplished the inhibiting episode through an electrostatic pull of the polymeric components of the NBL extract onto AA7075-T7351 coupons or physical adsorption, that obeyed Langmuir, Freundlich and Temkin adsorption isotherms, in increasing order; Temkin, Freundlich and Langmuir. Adsorption coefficient, K ads , and Gibb's free energy of adsorption, ΔG 0 ads , values obtained from Temkin isotherms were high and proved that adsorption of NBL on AA7075-T7351 surfaces were strong and spontaneous. Potentiodynamic polarization and electrochemical impedance spectroscopy results showed that NBL is a mixed-type corrosion inhibitor of AA7075-T7351 in 1 M HCl environment, which was achieved through the blockage/obstruction/reduction of charge flow by the polymeric barrier on the aluminium alloy's surface. Increases in the linear part of the Bode plot slopes with increase in NBL concentrations further indicated the existence of a protective layer on the AA7075-T7351 surface.

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Complexes of Ba(II), Sr(II) and Zn(II) with 1-phenyl-3-methyl-4-(p-nitrobenzoyl) pyrazolone-5(HNPz) have been synthesized and characterized. The HNPz was prepared from high grade p-nitrobenzoyl chloride and 1-phenyl-3-methyl-5-pyrazolone. The process involved benzoylation of 17.60 g (0.10 M) 1-phenyl-3-methyl-5-pyrazolone (HPMP) with 14.55 g (0.103 M) nitrobenzoylchloride. The complexes of Ba (II), Sr (II) and Zn (II) were prepared by dissolving 5 mmol of BaCl 2 .2H 2 O,SrCl 2 .6H 2 O and ZnSO 4 .7H 2 O respectively in 10 mmol of HNPz. The complexing agent and the metal complexes were characterized by elemental analysis, UV-visible and infrared spectroscopies. The results show the complexes to be dihydrated bischelates conforming to a general molecular formula, MLn.2H 2 O, where L is the 4-acylpyrazolonato ion and n is the ligand number or oxidation state of metal,M (Ba, Sr, Zn). The study also indicates the formation of octahedral complexes which are presumed to have been formed through the enolic and carbonyl oxygen atoms of the coordination reagent; in which water molecules complete the expected coordination numbers of Ba(II), Sr(II) and Zn(II).