Cerium-based coatings

Y. Huang and F. Mansfeld, Evaluation of the Effects of Different Process Parameters on the Corrosion Protection Provided by Cerium-Based Coatings on Galvanized Steels , Corrosion 65,507 (2009). 

Salazar-Banda, G. R., Moraes, S. R., Motheo, A. J. and Machado, S. A. S. 2009. Anticorrosive cerium-based coatings prepared by the sol-gel method. Journal of Sol-Gel Science and Technology, 52,415 23. 

Stoffer et al. [23] recently used cerium-based conversion coatings for corrosion protection of aluminum alloys used extensively for military and commercial aircraft. Results are encouraging for replacement of chromium-based conversion coatings. Work began recently on corrosion protection of steel by cerium ions [23]. 

The most commonly used types of conversion coatings are phosphates and chromates or a process based upon a combination of these two. More recent developments have been in zirconium- and titanium-based chemistry along with cerium-based processes. The impetus behind the more modem conversion coatings is the replacement of hexavalent chromium, which is used in many conventional processes. Conversion coatings have been applied to most metals the most amenable metals along with a number of applications are given in Tables 1 and 2. 

Fahrenholtz, W.G., O Keefe, M.J., Zhou, H., Grant, J.T., (2002). Characterization of cerium -based conversion coatings for corrosion protection of aluminum alloys. Surface and Coatings Technology, Vol. 155, No.2-3, pp.208-213, ISSN 0257-8972... 

Y.-K. Song and F. Mansfeld, Technical note Corrosion protection of electrogalvanized steel by a cerium-based conversion coating . Corrosion 62,1067 (2006). 

Y. Kobayashi and Y. Fujiwara, Effect of SO on the corrosion behavior of cerium-based conversion coatings on galvanized steel , Electrochim. Acta, 51,4236 (2006). 

K. Brunelh, M. Dabala, 1. Calliari and M. Magrini, Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys , Corros. Sci. 4,1, 989 (2005). 

S. Maddela, M. J. O Keefe, Y.-M. Wang, and H.-H. Kuo, Influence of surface pretreatment on coating morphology and corrosion performance of cerium-based conversion coatings onAZ91D alloy . Corrosion 66,115006 (2010). 

M. Dabalh, K. Brunelli, E. Napolitani and M. Magrini, Cerium-based chemical conversion coating on AZ63 magnesium alloy . Surface and Coatings Technology, 172,227(2003). 

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. 

Campestrini, R, Terryn, H., Hovestad, A., and de Wit, J.H.W., Formation of a cerium-based conversion coating on AA2024 relationship with the microstructure. Surface and Coatings Technology, 2004. 176(3) 365-381. 

More recent work on how cerium-based conversion coatings protect high strength aluminum alloys during salt spray testing indicates that the interaction of cerium... 

J. Stoflfer, T. O Keefe, E. Morris, X. Lin, S. Hayes, and P. Yu, Additive-assisted, cerium-based, corrosion-resistant e-coating , US Patent 7,241,371, issue date July 10, 2007. 

F.H. Scholes, C. Soste, A.E. Hughes, S.G. Hardin, and P.R. Curtis, The role of hydrogen peroxide in the deposition of cerium-based conversion coatings , Appl Surf Sci, 253,1770-1780 (2006). 

W. Pine, S. Maddela, M. O Keefe, and W. Fahrenholtz, Formation of subsurface voids in aluminum alloy 2024-T3 during deposition of cerium-based conversion coatings . Surface and Coatings Technology, 204(24), 4095 (2010). 

S. Joshi, E. Kulp, W. Fahrenholtz, and M. O Keefe, Dissolution of Cerium fiom Cerium-based conversion coatings on A17075-T6 in O.lMNaCl solutions . Corn Sci. 60,290 (2012). 

The differences in solubilities of rare earth compounds have led to strategies for developing corrosion resistant coatings. For example, the extremely low solubility of cerium phosphates has led Heller et al. to use phosphate seals on cerium-based conversion coatings, to enhance corrosion resistance of the cerium-based conversion coatings. These approaches are discussed in more detail below. 

Nodular coating structure developed during conversion coating in cerium-based solutions (CeClj/H O /pH 1.9). 

Table 7.S Neutral salt spray performance of silicate-sealed, cerium-based conversion coating (CeCI/HjOj/ph 1.9) with different deoxidation processes.

The performance of chromate replacement processes under paint is varied. But there are examples of processes that perform well under paint, but perform poorly in NSS (without sealing). The cerium-based processes fall into this category. For instance the performance of Ce coatings under paint has been reported to be as good as CrCCs in both aerospace and architectural applications. 

Table 7.7 Comparative performance between a cerium-based conversion coating and chromate under two different paint systems...

Schuman T.P., Shahin A., Staffer J.O. (2002), Cerium based inhibitors of aluminum alloy corrosion, Proc. International Waterborne, High Solids, and Powder Coatings Symposium, New Orleans, LA, February, p. 371. 

A. E. Hughes, S. G. Hardin, K. W. Wittel and P. R. yhWes, Accelerated Cerium-Based Conversion Coatings, NACE, Orlando, USA (2000). 

Plate V(Chapter 7) Appearance of silicate sealed, peroxide accelerated cerium-based conversion coating, without exposure to NSS and after 168 and 336 hours NSS. 

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