Pickling anodic

Pickling—a form of chemical and electrolytic removal of mill scale and corrosion products from the surfaces of metals in an acidic solution. Electrolytic pickling may be anodic or cathodic, depending on the polarization of the metal in the solution. 

Fedotev, N. P. and Grilikhes, S. YA., Eleciropolishing, Anodizing and Electrolytic Pickling of Metals (Moscow, 1957), trans. Robert Draper, Teddington (1959)... 

Acid pickles Some of the acid pickles used to clean and etch aluminium alloy surfaces and remove oxide and anodic films, such as the chromic/ sulphuric acid pickle (method O of DEF STAN 03-2) and other chromic-acid bearing pickles (App. Foi DEF-151) probably leave on the surface traces of absorbed or combined chromate which will give at least some protection against mild atmospheres. 

Anodic and cathodic pickling are forms of eiectroiytic pickling in which the metal is anodically or cathodically polarised in the pickle. 

Hexavalent chromium is used in anodizing baths, and in pickling solutions that remove oxide layers from parts. The chromic acid in these solutions eventually enters the waste stream, either through dragout, or when the pickling or anodizing bath is disposed of. Less... 

Various pre-treatment protocols have been developed including pickling and anodic/cathodic pulses to remove the oxide films. It was apparent that different types of steel require different pre-treatments, i.e. cast pieces behave differently to rolled pieces. Significant success was achieved in electropolishing cast pieces and the finish obtained with the ionic liquid was superior to that with phosphoric add, however, the converse was true for rolled pieces because the oxide film is thicker in the latter samples and hence slower to dissolve in the ionic liquid. 

Summary Bleach can be made using an electrochemical process whereby pickling salt is electrolyzed. During the process, chlorine gas is evolved at the anode, and sodium hydroxide is liberated at the cathode. As the process proceeds, the chlorine reacts with the sodium hydroxide forming sodium hypochlorite (bleach). Some chlorine gas does escape, so use proper ventilation when carrying out this operation. 

Summary Hydrogen and oxygen free chlorine gas can be readily prepared by electrolyzing a solution of ferrous chloride in an open cell. The ferrous chloride can be pre-prepared by electrolyzing a solution of pickling salt using an iron anode in a diaphragm cell. 

Summary Isopropyl hypochlorite is readily prepared by electrolyzing a solution of isopropyl alcohol and pickling salt in the presence of sulfuric acid in a diaphragm salt bridge cell. The electrolysis takes considerable amount time, but produces no significant heat build-up. After the electrolysis process, the anode liquid is filtered, and then extracted with a suitable, low boiling solvent. Afterwards, the solvent is removed via evaporation, and then the desired isopropyl hypochlorite is recovered. 

---