Lanthanide compounds as environmentally-friendly corrosion inhibitors of aluminium alloys:: A review

Currently, chromates are among the most common substances used as inhibitors or incorporated in anticorrosive pretreatments of aluminium alloys. However, these compounds are highly toxic and their use produces serious environmental hazards. Consequently, an intense research effort is being undertaken to replace chromates by more ecological compounds. In recent years, several authors have begun studies of the behaviour of lanthanide compounds in the corrosion protection of metallic alloys. After a brief overview of the use of chromates and their ecological alternatives in corrosion protection systems, the paper reviews progress from the literature published to date concerning the application of lanthanide compounds as corrosion inhibitors of aluminium alloys in aqueous solution. Aspects of the mechanism involved in the cathodic inhibition process by lanthanides are also dealt with. In addition, these compounds have been used to prepare chromate-free conversion coatings by full-immersion and electrochemical activation methods. Treatments proposed for these conversion coatings are discussed in detail. From the comprehensive review presented in this article, it is concluded that lanthanide compounds fulfil the basic requirements for consideration as components of more environmentally-friendly formulations: low toxicity and acceptable protective capacity. However, methods proposed up to now present various limitations that restrict their application in practice. Further research efforts are necessary to develop feasible treatments for industry. (C) 1998 Elsevier Science Ltd. All rights reserved.