Phosphating processes
Phosphating processes: According to heading fall such processes as result in formation of an insoluble phosphate coating on the surface of a metal. The formation of such coatings is invariably linked with the corrosion of the substrate metal. In a narrower definition, phosphating processes are only those which form surface coatings with useful properties. Thus phosphoric acid pickling solutions are a marginal case, since their primary function is removal of corrosion products and their usefulness in forming protective phosphate coating is very much a secon dary one. Technically and economically, the most important processes are those based on aqueous solutions which form protective coatings on metal surfaces, whether by spraying, pouring, immersion or other methods. Depending as to whether or not components are coated on removal from the solution, one may distinguish between the so-called phosphate coating processes and the 'non-coating" alternatives. In addition, there are ph...