MARTEC 2012 International Conference Kuala Terengganu, Malaysia, 20-22 October 2012 1 Paper Reference ID: UMT/FMSM/MARTEC/MTP-107 SODIUM BENZOATE AS CORROSION INHIBITOR FOR ALUMINUM ALLOY AA 7618 IN TROPICAL SEAWATER Muzathik A.M. 1,2* , Ahmad M.F. 1 , Kamales B. 1 and Wan Nik W.B. 1 1 Department of Maritime Technology, Universiti Malaysia Terengganu, Malaysia. 2 Institute of Technology, University of Moratuwa, Katubedda, Sri Lanka. *E- mail: muzathik64@yahoo.com ABSTRACT Corrosion is chemically induced damage to a material that results in deterioration of the material and its properties. Ships, marinas, pipelines, offshore structures, desalination plants, and heat exchangers are some examples of systems that experienced marine corrosion. Aluminum alloy is commonly used in marine applications. The use of inhibitors is one of the practical methods for protection against corrosion. Sodium benzoate has found considerable application as a corrosion inhibitor in low concentrations. The aim of this study is to analyze corrosion behavior of Aluminum alloy AA 7618 towards tropical seawater with the presence of sodium benzoate as corrosion inhibitor aimed to use in industrial applications. Immersion test and electrochemical test were conducted to measure the corrosion. The immersion period for the Aluminum alloy was 60 days. Seawater sample was collected from South China Sea along Universiti Malaysia Terengganu. This study reports the results of weight loss (%), inhibition efficiency (%), corrosion rate (mm/year), corrosion current densities (i corr ), corrosion potential (E corr ), polarization resistance,(R p ) and capacitance (CPE). The results showed that addition of sodium benzoate acted as inhibitor and minimize the corrosion of the aluminum alloy in seawater. The inhibition efficiency increases with the increase of immersion time. Electrochemical studies showed that there was a significant increase in overall resistance after addition of sodium benzoate. Inhibition efficiency is increased from 50% to 97% during the immersion period and increases with the immersion time. The result obtained lead to the conclusion that sodium benzoate is suitable to use as a corrosion inhibitor of Aluminum alloy AA 7618 in seawater. Keywords: Aluminum alloy, corrosion inhibitor, seawater corrosion, sodium benzoate 1. INTRODUCTION Corrosion is chemically induced damage to a material that results in deterioration of the material and its properties [1]. Moreover corrosion is referred as a process that involves deterioration or degradation of metal as well and as a result of the inherent tendency of metals to revert their more stable compounds which is usually oxides [2]. Ships, marinas, pipelines, offshore structures, desalination plants, and heat exchangers are some examples of systems that experienced marine corrosion. The use of inhibitors is one of the most practical methods for protection against corrosion [3]. Aluminum alloy is commonly used in marine applications. Sodium benzoate has found considerable application as a corrosion inhibitor in low concentrations. Corrosion inhibition has been reported for steel, zinc, copper, copper alloys, soldered joints, aluminum, and aluminum alloys [2]. The aim of this study is to analyze corrosion behavior of aluminum alloy (AA7618) towards tropical seawater with the presence of sodium benzoate as corrosion inhibitor so that it can be used in marine industrial applications in future. 2. METHODOLOGY The study of sodium benzoate as corrosion inhibitor for aluminum alloy AA7618 in tropical seawater was carried out using weight loss experiment and electrochemical impedance spectroscopy (EIS). The samples were immersed in 2 different solution containing seawater and sodium benzoate + seawater wit concentration of 200mg/l. The samples were tested every 5 days for weight loss experiment and every 10 days for EIS experiment to measure corrosion characteristics. Table 1 showed composition of inhibition solutions. Sample preparation was most vital procedure in obtaining better results in this experiment. Initially, the specimens (AA7618) were cut into desirable measurements for immersion tests where the dimension of specimens is 2.5cm x 3.0cm x 0.3cm. Before exposure, more than 108 samples polished using number 600, 800 and 1200 emery papers and lubricated using distilled water to remove layer of oxide from the surface of aluminum alloy samples. The polished samples were cleaned with acetone, washed using distilled water, dried in air and stored over a desiccant.