ACADEMIA ROMÂNĂ Revue Roumaine de Chimie http://web.icf.ro/rrch/ Rev. Roum. Chim., 2011, 56(8), 793-801 INHIBITION OF BRONZE CORROSION IN AERATED ACIDIC SOLUTION USING AMINO ACIDS AS ENVIRONMENTALLY FRIENDLY INHIBITORS Simona VARVARA, a,* Ileana ROTARU, b Maria POPA, a Liana Maria MUREŞAN b a “1 Decembrie 1918” University, Faculty of Science, Department of Topography, 11-13 Nicolae Iorga St., Alba Iulia 510009, Roumania b “Babes-Bolyai” University, Faculty of Chemistry and Chemical Engineering, Department of Physical Chemistry, 11 Arany Janos St., Cluj-Napoca 400028, Roumania Received July 12, 2010 The inhibiting proprieties of three innoxious amino acids, such as cysteine (Cys), alanine (Ala) and phenylalanine (PhAla) as bronze corrosion inhibitors in a strong acidic solution of 0.2 g/L Na 2 SO 4 + 0.2 g/L NaHCO 3 at pH=3 was studied by electrochemical and scanning electron microscopy (SEM) techniques. Both potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements revealed that these compounds have a protective effect against bronze corrosion and their inhibition efficiencies depend on the structure of amino acids. The anticorrosive efficiencies of the investigated compounds, used in their optimal concentration, decreased in the following order: 10 mM Cys (96.92 %) > 1 M Ala (80.07%) > 10 mM PhAla (52.48 %). EIS measurements also showed that the inhibitor effectiveness of the optimal concentrations of amino acids is time-dependent. SEM analysis of the corroded bronze surface confirmed that the amino acids inhibit the corrosion process, due to their ability to adsorb on the metallic surface. INTRODUCTION ∗ Copper and copper-based alloys are commonly used in heat exchangers, constructions, electronics, coinage, and art works etc. 1 Despite the good corrosion resistance of copper and its alloys, corrosion inhibitors have to be used in order to reduce the damage of metal dissolution in aggressive acidic media. Typical corrosion inhibitors for copper and its alloys are heterocyclic compounds containing nitrogen, oxygen or sulphur atoms. 2-6 The effectiveness of these organic molecules is based on their ability to form a protective film by several mechanisms (i.e. adsorption, polymerization etc.). Nevertheless, an important disadvantage of heterocyclic compounds is their toxicity and the lack of biodegradability. 7-9 In line with the environment protection regulations and ecological policies for the use of chemicals, the latest trend in ∗ Corresponding author: svarvara@uab.ro corrosion research is focused on producing and testing new environmentally-friendly inhibitors as alternatives for the toxic substances. Recently, several works aimed to investigate the use of amino acids as corrosion inhibitors of iron, 10 steel, 11-14 aluminum, 15 vanadium, 16 lead, 17 copper 18-23 and its alloys 24 in various aggressive media. Amino acids are innoxious, biodegradable, soluble in aqueous media, relatively cheap and easy to produce at high purity. 25 These properties would justify the use of amino acids as corrosion inhibitors. Furthermore, in recent papers 26-27 we have reported the beneficial effect exerted by several amino acids, i.e. cysteine (Cys), glutamic acid (Glu), methionine (Met), histidine (His), arginine (Arg) and alanine (Ala) on bronze corrosion in weak acidic electrolyte. We have found that the protection effectiveness of the amino acids on bronze corrosion strongly depends on the size and electronic effects of the substituents