Phosphate coatings applications

Surface Preparation of the Substrate. This is extremely important for all methods of paint and coatings application. The failure of a paint system is often due not to the paint itself, but because of a failure in surface preparation. For example, an anticorrosive paint applied to a rusty surface will not be effective if the rust falls off taking the new paint with it. For wood and plastic surfaces, old paint or a weathered surface layer may have to be removed. For older metal objects, the removal of corrosion is often required. Sandblasting is one method to remove both the old paint and any corrosion. For new metal objects, a phosphate or chromate layer is often chemically bonded to the metal to provide a surface to which a coating can easily adhere. 

The waterborne basecoat consists of a urethane or an acrylic dispersion with passivated aluminum for metallic glamour. The aluminum must be passivated to prevent reaction with water and the evolution of hydrogen gas. Passivating agents can include polymers, hexavalent chromium (now mandated for removal), or phosphate esters. The basecoat is pre-baked (with infrared or thermal ovens) to release the majority of the water prior to clear-coat application. 

Shadanbaz, S. and Dias, G.J. (2012) Caclium phosphate coatings on magnesium alloys for biomedical applications a review. Acta Biomater., 8 (1), 20-30. 

Stefanic, M., Krnel, K., Pribosic, I., and Kosmac, T. (2012) Rapid biomimetic deposition of octacalcium phosphate coatings on zirconia ceramics (Y-TZP) for dental implant application. Appl. Surf. Sci., 258 (10), 4649-4656. 

Even though the microhardness of calcium phosphate coatings deposited on metallic implant substrates is not considered to be a critical performance parameter for in vivo applications it can serve to mechanically characterise the coatings and thus shed light on their integrity in service. 

Surmenev, R.A., Surmeneva, M.A., and Ivanova, A.A. (2014) Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis - a review. Acta Biomater., 10, 557—579. Westheimer, F.H. (1987) Why nature chose phosphates. Science, 235, 1173—1178. Zhang, S. (ed) (2013) Hydroxyapatite Coat-ings for Biomedical Applications, Advances in Materials Science and Engineering, CRC Press, 469 pp., ISBN 978-1-4398-8693-9. 

Galvanized steel For galvanized steel, the most prominent conversion layers are phosphate layers for automotive and chromate layers for cod-coating applications [4,185]. 

Narayanan R, SeshadriS, KwonT, Kim K. Electrochemical nano-grained calcium phosphate coatings on Ti-6A1-4V for biomaterial applications. Scr Mater 2007 56 229-32. 

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