Effect of the addition of oxo-anions on the corrosion and passivation of tin in synthetic industrial water E.H. Ait Addi a , L. Bazzi a , M. Elhilali a , R. Salghi b , B. Hammouti c, * , M. Mihit b a Equipe de Chimie mole ´culaire & Corrosion, Faculte ´ des Sciences, B.P. 8106/S, Cite ´, Agadir, Morocco b Equipe d’Analyse Agroalimentaire, Ecole Supe ´rieure de Technologie d’Agadir, B.P. 33/S, Agadir, Morocco c Laboratoire de Chimie des Eaux & Corrosion, Faculte ´ des Sciences, B.P. 717, Oujda, Morocco Received 24 October 2005; received in revised form 15 December 2005; accepted 15 December 2005 Available online 26 January 2006 Abstract Effect of the addition of oxo-anions MoO 4 2 , SiO 4 2 , HPO 4 2 and HCO 3  on the corrosion and passivation of tin in a synthetic medium similar to industrial water has been studied by using electrochemical techniques. The results show that tin manifests a passivation phenomenon with breakdown of passivity. Addition of oxo-anions leads to retard a breakdown of passivation and the inhibition of pitting process of tin. The more marked inhibiting effect is obtained in the presence of MoO 4 2 and SiO 4 2 . The detailed study of the influence of the MoO 4 2 shows that the pitting sensitivity of tin decreases when the molybdate concentration increases in solution. Then, these ions offer a good efficiency even at high temperature and for a chloride concentration up to 0.5 M. # 2006 Elsevier B.V. All rights reserved. Keywords: Corrosion; Passivation; Inhibition; Oxo-anions; Tin; Industrial water 1. Introduction Due to its important applications in the food and electronic fields, tin receives considerable attention despite its moderate corrosion resistant. Moreover, tin is widely used as a protective coating material for iron in contact with aggressive solutions. Numerous works focused on the electrochemical behaviour of tin in aqueous solution [1–4]. Several authors report that the pitting corrosion occurs when passivity breaks down at local points of the surfaces exposed to corrosive solutions that contain aggressive anions such as halides or other anions such as sulphate, perchlorate and nitrite [4–7]. Among the methods used to avoid corrosion problems, we cite the use of corrosion inhibitors. The study of addition of inorganic anions (NO 3  , CrO 4 2 , Cr 2 O 7 2 , MoO 4 2 , NO 2  , ClO 4  , SO 4 2 ) to the solutions showed that some of these ions inhibit corrosion of tin while others accelerate it [6,7]. In one part of our program, the effect of some inorganic ions like CrO 4 2 , MoO 4 2 , WO 4 2 and HPO 4 2 on the corrosion behaviour of 6063 and 3003 aluminium alloy in bicarbonate– chloride medium has been investigated [8–11]. It was found that the addition of chromate ions leads to the inhibition of general and pitting corrosion of this alloy. The study of the effect of inorganic anions (CrO 4 2 , MoO 4 2 , NO 3  , NO 2  ) on the corrosion of tin in citric acid solution showed that both CrO 4 2 and MoO 4 2 inhibit the corrosion of tin and the extent of inhibition enhances with their concentrations [12]. Refaey et al. [13] studied the effect of CrO 4 2 , Cr 2 O 7 2 , MoO 4 2 , NO 3  and NO 2  on the pitting corrosion of tin in alkaline and near neutral media. They found that the effectiveness of inhibitors increases in the order: Cr 2 O 7 2 > CrO 4 2 > MoO 4 2 Recently, Foad El-Sherbini et al. in their recent works, show the inhibiting effects of molybdate and tungstate on the pitting corrosion of tin in (0.1 M Na 2 B 4 O 7 + 0.1 M NaCl) and Na 2 CO 3 solutions [14,15]. Nowadays, besides the efficiency of the compound, another important factor has to be taken into account to choose the suitable inhibitor. In this sense, despite the demonstrated efficiency of chromate as inhibitor, the known toxicity and carcinogenic properties of Cr(VI) compounds exert a con- tinuous pressure to use green inhibitors with null toxicity [16]. www.elsevier.com/locate/apsusc Applied Surface Science 253 (2006) 555–560 * Corresponding author. E-mail address: hammoutib@yahoo.fr (B. Hammouti). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.110