The inhibiting effect of Baphia nitida (BN) leaves extract on the corrosion of mild steel in 1？M H2SO4 and 2？M HCl was studied at different temperatures using gasometric and weight loss techniques. The results showed that the leaves extract is a good inhibitor for mild steel corrosion in both acid media and better performances were obtained in 2？M HCl solutions. Inhibition efficiency was found to increase with increasing inhibitor concentration and decreasing temperature. The addition of halides to the extract enhanced the inhibition efficiency due to synergistic effect which improved adsorption of cationic species present in the extract and was in the order KCl < KBr < KI suggesting possible role of radii of the halide ions. Thermodynamic parameters determined showed that the adsorption of BN on the metal surface is an exothermic and spontaneous process and that the adsorption was via a physisorption mechanism. 1. Introduction One of the most practical methods of preventing electrochemical corrosion is to isolate the metal surface from corrosive agents [1]. Of the many methods available, the use of corrosion inhibitors is usually the most appropriate method to achieve this objective [2–9]. These inhibitors could be in the form of organic, inorganic, precipitating, passivating, or volatile species. Generally, corrosion inhibitors may be divided into three broad classes, namely, oxidizing, precipitating, and adsorption inhibitors [10]. Adsorption inhibitors are usually organic substances containing heteroatoms with high electron density such as nitrogen, sulfur, and oxygen [11, 12] and the presence of unsaturated bonds or aromatic rings in the molecular structure of the inhibitor favors adsorption on corroding metal surface [13]. The adsorption is influenced by the nature and the surface charge of the metal, the type of corrosion media, and the molecular structure of the inhibitor [4]. Some corrosion inhibitors used in different media and for different metals and alloys decrease considerably the oxidation states of the corroding metals. In acid corrosion, inhibitor adsorption may lead to structural changes in the double layer, which could reduce the rates of either the anodic metal dissolution and the cathodic hydrogen ion reduction or both. It is known that some corrosion inhibitors and their derivatives are toxic and pollute the environment [14]. There is therefore the need to explore new nontoxic, environmental friendly, ecologically acceptable and inexpensive corrosion inhibitor substitutes. Among the alternative corrosion inhibitors, natural
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