Available online at www.scholarsresearchlibrary.com Scholars Research Library Archives of Applied Science Research, 2012, 4 (1):207-217 (http://scholarsresearchlibrary.com/archive.html) ISSN 0975-508X CODEN (USA) AASRC9 207 Scholars Research Library Inhibition by Newbouldia leavis Leaf Extract of the Corrosion of Aluminium in HCl and H 2 SO 4 Solutions L. A. Nnanna 1* , V. U. Obasi 1 , O. C. Nwadiuko 1 , K. I. Mejeh 2 , N. D. Ekekwe 3 , S. C. Udensi 4 1 Department of Physics/Electronics, Abia State Polytechnic, P. M. B. 7166, Aba, Nigeria 2 Department of Mechanical Engineering, Abia State Polytechnic, P. M. B. 7166, Aba, Nigeria 3 Department of Chemistry, Abia State Polytechnic, P. M. B. 7166, Aba, Nigeria 4 Department of Physics, Federal University of Technology, P. M. B. 1526, Owerri, Nigeria ______________________________________________________________________________ ABSTRACT The inhibition effect of Newbouldia leavis leaves extract on the corrosion of aluminium in 0.2- 1.0 M HCl and 0.1–1.0 M H 2 SO 4 solutions was investigated by the gravimetric technique. The results show that Newbouldia leavis is a good inhibitor, and exhibits more efficient in 1.0 M HCl than 0.5 M H 2 SO 4 . 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. The adsorption of Newbouldia leavis on aluminium surface obeys Langmuir adsorption isotherm. Keywords: Corrosion inhibition, aluminium, adsorption mechanism, Newbouldia leavis, free energy of adsorption. ______________________________________________________________________________ INTRODUCTION The use of inhibitors is one of the most practical methods for protection against corrosion, especially in acidic media [1]. Among numerous inhibitors that have been tested and applied industrially as corrosion inhibitors, those that are non-toxic or low-toxic are now far more strategic than in the recent past. In the 21st century, the research in the field of ‘‘green’’ or ‘‘eco- friendly’’ corrosion inhibitors has been addressed toward the goal of using cheap, effective compounds at low or ‘‘zero’’ environmental impact.