Rare earth conversion coatings

A. Rudd, C. B. Breshn and F. Mansfeld, The corrosion protection afforded by rare earth conversion coatings applied to magnesium , Corr. Sci. 42,275 (2000). 

X. Yang, G. Wang, G. Dong, F. Gong andM. Zhang, Rare earth conversion coating on Mg-8.5 Li alloys , J. Alloys and Compounds, 487,64 (2009). 

Key words chromate conversion coatings, rare earth conversion coatings, sol-gel coatings, boehmite coatings, rare earth deoxidation, rare earth inhibitors. 

For alutninium treatment the three most common rare earth salt solutions used for rare earth conversion coating are based on Ce(C10 )3 ... 

The preferred method for obtaining a conversion coating on low-Cu alloys is by addition of complexed forms orBi complexes (Bi(EDTA) orBi(HDTA) depending on regulatory regimes). This is the basis of the activation process for the commercial process for rare earth conversion coating. ... 

The review of rare earth conversion coatings presented in this chapter delineates the wide, and ongoing, interest in the rare earths for corrosion protection. The aqueous inhibition qualities of the simple rare earths salts for a range of metals have been known for nearly 30 years. The focus of the rare earths has been primarily on cerium, with a significant amount of research also performed on lanthanum systems. The evolution of the development of the immersion process to viable commercial processes has, however, been slow. Much work has focused on aluminium alloys and a commercial process was developed for non-aerospace applications for aluminium alloys. The development of conversion coatings for other metals has been slower for a range of reasons. 

J. Cai, F. Cao, L. Chang, J. Zheng, J. Zhang and C. Cao, The preparation and corrosion behaviors of MAO coating on AZ91D with rare earth conversion precursor fAm Appl. Surf. Science, 257, 3804 (2011). 

From the viewpoint of corrosion resistance, chromate conversion coatings still play an important role [106] even though a replacement of the toxic chromate is desirable. Rare earth metals are promising superseders for the chromium. They can be incorporated in the layers and enhance the corrosion resistance. 

Hosseini, M.G., Ashassi-Sorkhabi, H., Ghiasvand, H.A.Y., (2007). Corrosion protection of electro-galvanized steel by green conversion coatings. Journal of Rare Earths, Vol. 25, pp. 537-243, ISSN 1002-0721... 

S. Kiyota, B. Valdez, M. Stoytcheva, R. Zlatev and M. Scorr, Electrochemical study of corrosion behavior of rare earth based chemical conversion coating on aerospace aluminum alloy , J. Electrochem. Soc. 158, 666 (2009). 

I. Aziz, Q. Zhang and M. Xiang, Using EIS to evaluate anti-corrosion properties of the Sic /5A06 aluminium MMC treated by cerium conversion coatings , J. Rare Earths , 109 (2010). 

G. Kong, L. Liu, J. Lu, C. Che and Z. Zhong, Study on lanthanum salt conversion coating modified with citric acid on hot dip galvanized steel , J. Rare Earths, 28,461 (2010). 

Hughes, A.E., Gorman, J.D., Miller, P.R., Sexton, B.A., Paterson, P.J.K., et ai. Development of cerium-based conversion coatings on 2024-T3 Al alloy after rare-earth desmutting. Surface and Interface Analysis, 2004. 36(4) 290-303. 

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