engleski

Effect of the Cerium(III) chloride on the Corrosion Inhibition of Aluminium Alloy

Aluminium alloys containing copper (2000 series) exhibit high strength and are widely used in the aviation industry but generally they show low corrosion resistance and are susceptible to localized corrosion. The resistance of aluminium against corrosion in aqueous media can be attributed to a rapidly formed surface oxide film, which is composed of Al2O3, Al(OH)3 and AlO(OH) phase. The potential difference between aluminum matrix and other intermetallic particle phases which give strength to these alloys would result in the occurrence of galvanic corrosion reaction in aggressive solution, especially with the presence of chloride ions (Cl−), which shorten its service time significantly. The carcinogenic chromate pretreatments are currently used to hinder the localized corrosion of the AA2024-T3. However, stricter environmental regulations and the needs of industry stimulated an intense research effort to develop novel environmental-friendly pretreatments and inhibitors. The high carcinogenicity and genotoxicity of this method has limited its applications in many countries. Therefore, some rare earth salts are being employed to develop alternative environment - friendly method to inhibit the corrosion protection of aluminium alloys. The salts of rare earth (RE) elements were found to provide an effective corrosion inhibition effect to the aluminum alloys. The inhibition mechanism of rare earth chlorides such as cerium(III) chloride is as follows. In the first stages of corrosion process, oxygen reduction reaction occurs on the cathodic sites resulting in generation of OH− groups over the cathodic intermetallic precipitates. This leads to local increase in pH at the cathodic sites. The hydroxyl group formed over the cathodic sites reacts with the rare earth ions present in the solution. This reaction gives rise to the formation of rare earth oxide/hydroxide islands. The blockage of the cathodic sites by these islands decreases the cathodic current and, therefore, reduces the overall corrosion rate. The precipitates prevent further corrosion by hindering the reduction of oxygen and water.

Aluminium, AA2024-T3, Corrosion, Inhibitor, Cerium(III) chloride

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