5 октября, 2015 
Pokraskin Chemical surface preparation can have two different effects on the surface of the adherent:
• Non-oxidizing acids (e. g. hydrochloric acid, dilute sulfuric acid) cause an electrochemical oxide/acid or metal/acid reaction which results in removal of the oxide layer or, if etching times are long, of the deeper metallic interfaces. In this method — called ‘acid degreasing’ — the surface becomes not only chemically clean but also rough in its submicroscopic structure. At the same time, chemically active sites are created on the surface, which are a prerequisite for the formation of adhesive bonds.
• Oxidizing acids (e. g. nitric acid, phosphoric acid, chromic acid), with or without the addition of oxidizing salts such as sodium or potassium dichromate, induce the formation of an additional firmly adhering conversion coating (e. g. phosphate or chromate oxide layer). This method is known as ‘pickling’ or ‘phosphatizing’. The application of an electric current to the adherent can enhance the chemical reaction. Since the parts to be treated are generally used as the anode, this process is called ‘anodizing’. On aluminum alloys, zinc and stainless steel, the process yields an oxide layer of up to several hundred microns thickness which, in the majority of cases, exhibits filigree nanomorphological structures with very good adhesion properties (see Chapter 3 and Section 7.5).
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