Surface treatment chemicals phosphating solutions

Chemical conversion processing is a type of surface treatment that consists only of a chemical reaction. In this respect, metal is immersed in a solution where it dissolves slightly, and an insoluble corrosion product, or an oxide film forms simultaneously on the surface. Examples of such films are corrosion resistant films, undercoat films, and lubrication films. Examples of chemical conversion processing are phosphating and chromic acid treatment. The following is an example of the use of a LCA in the phosphating of zinc plates. 

Phosphating n. Pre-treatment of steel or certain other metal surfaces by chemical solutions containing metal phosphates and phosphoric acid as the main ingredients, to form a thin, inert, adherent, corrosion-inhibiting phosphate layer which serves as a good base for subsequent paint coats. 

The processes are dealt with fully in Chapters 11, 14 and 15. Because many paint systems include an initial surface pretreatment, e.g. chromated aluminium or phosphated steel, BS4479 1990, Part 3 deals with conversion coatings and should be consulted by designers. Whatever the method of treatment, liquids must be able to drain quickly and freely from the surfaces. Crevices where liquids can become entrapped are best avoided. The surface configuration needs to be such that active solutions can be washed away, leaving the surface to be painted completely free from unreacted pretreatment solution. Failure to achieve the requisite level of freedom from the surplus chemicals causes paint failure, e.g. osmotic blistering. 

Figure 31 Emission intensity of a solution of CdSe-ZnS core-shell quantum dots (0.8 pM, 300 pL, CHCI3, 20 °C, A.ex = 430 nm, Xsm = 555 nm) with (a) and without (b) 3 on their surface and BU4NCI (1 M, 50 pL, dichloroethane) after treatment with sodium phosphate buffer (500 pL) and dilution with CHCI3 (4.3 mL). Photographs of solutions of CdSe-ZnS core-shell functionalized quantum dots (0.8 pM, 300 pL, CHCI3) in presence of BU4NCI (1 M, 50 pL, dichloroethane) under ultraviolet illumination after treatment with sodium phosphate buffer (500 pL) at the pH values (I-III) indicated in the plot. (Reproduced with permission from Ref. 66. 2006, American Chemical Society.)...

Phosphate coating is the treatment of iron, steel, galvanized steel, or aluminum with a dilute solution of phosphoric acid and other chemicals in which the surface of the metal, reacting chemically with the phosphoric acid media, is converted to an integral, mildly protective layer of... 

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