Progress in Organic Coatings 45 (2002) 373–378 New synthesised pyridazine derivatives as effective inhibitors for the corrosion of pure iron in HCl medium A. Chetouani a , B. Hammouti a,∗ , A. Aouniti a , N. Benchat b , T. Benhadda b a Laboratoire de Chimie des Eaux et Corrosion, Faculté des Sciences, Oujda, Morocco b Laboratoire de Chimie Organique et Physique, Faculté des Sciences, Oujda, Morocco Received 20 February 2002; received in revised form 23 July 2002; accepted 2 August 2002 Abstract The inhibition of pure iron in 1 M HCl by new synthesised pyridazine compounds has been studied by weight loss, electrochemical po- larisation and electrochemical impedance spectroscopy (EIS) measurements. The results obtained reveal that these compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration and reached 98% at 10 -4 M for 5-benzyl-6-methyl pyridazine-3-thione. Potentiodynamic polarisation studies clearly reveal that the presence of pyridazines does not change the mechanism of hydrogen evolution and that they act essentially as cathodic inhibitors. The temperature effect on the corrosion behaviour of pure iron in 1 M HCl without and with the pyridazines at 10 -4 M was studied in the temperature range from 298 to 353 K. EIS measurements show that the increase of the transfer resistance with the inhibitor concentration. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Pyridazine; Corrosion; Inhibition; Iron; Acid medium 1. Introduction Hydrochloric acid is often used as a pickling acid for iron and its alloys. The main goal is to remove undesirable corrosion products. To make secure from attack of acid, in- hibitors are frequently used. Organic nitrogen compounds on the corrosion behaviour of iron and steel in acidic solu- tions are usually employed for their rapid action [1–13]. The existing data show that most of the organic inhibitors act by adsorption on the metal surface. The adsorption of inhibitors takes place through heteroatoms such as nitrogen, oxygen, phosphorus and sulphur, triple bonds or aromatic rings. The inhibition efficiency should increase in the order O < N < S < P [14]. Nitrogen-containing heterocyclic compounds are considered to be effective corrosion inhibitors. In this work, the influence of the pyridazine rings of a new synthesised class on inhibition of the corrosion of pure iron in 1 M HCl was evaluated. The tested molecules were 5-benzyl-6-methyl pyridazine-3-thione (P1) and 5-benzyl-6-methyl pyridazine-3-one (P2). The study was made by using gravimetric, polarisation and electrochemical impedance spectroscopy (EIS) meth- ∗ Corresponding author. E-mail address: b.hammouti@caramail.com (B. Hammouti). ods. The nature of inhibitor adsorption process was also studied and discussed. 2. Experimental 2.1. Synthesis of pyridazine compounds The pyridazine compounds were synthesised according to the method of Taoufic and coworkers [15,16] and Benchat [17] purified and characterised by NMR, IR spectroscopies and element analysis before use. The molecular structures of the new studied pyridazines are shown in Fig. 1. 2.2. Chemicals Pure iron (99.5%, thickness = 0.05 cm from Good Fel- low, Cambridge, UK) was used. The aggressive solution (1 M HCl) was prepared by dilution of Analytical Grade 37% HCl with double distilled water. 2.3. Weight loss measurements Weight loss was measured on sheets of pure iron of apparent surface area of 2 cm 2 . Sheets were abraded suc- cessively with fine emery paper. The sheets were then 0300-9440/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0300-9440(02)00123-6