Etching and passivation of non-ferrous metals
Etching is a method of cleaning metal surfaces from corrosion products by removing them from the substrate in pickling baths. In practice, the products most often subjected to etching are made of steel (iron alloys), stainless steel and copper brass, whose corrosion products, depending on the conditions in which they appeared, took the form of:
- scale - FeO, Fe3O4, Fe2O3 oxides - iron oxidation products at high temperatures in the manufacturing process
- rust - oxides, hydroxides and alkaline iron salts - atmospheric corrosion products resulting from the action of air and water
During etching, corrosion products are removed from the surface of the metal in various ways:
- they dissolve in acid (e.g. products of atmospheric corrosion in hydrochloric acid)
- they are separated from the substrate by the produced hydrogen (e.g. scale in sulfuric acid)
In order to give the etched surface resistance to further reactions with the surrounding environment, we subject the details to process of passivation.