Electrolytic processes for surface conditioning of metals

The uses of electrolysis, for the surface cleaning and descaling of metals, for improving the resistance of aluminium and its alloys to oxidation and abrasion, and for the polishing of metals, are discussed. Compared with direct-immersion processes, electrolytic cleaning and descaling is often speedier, more efficient and easier to control. In cathodic cleaning, adventitious matter is loosened by the nascent hydrogen evolved on the surface of the work, while the gas itself is a powerful reducing agent. Anodic pickling in acid electrolytes is precise in action and avoids the dangers of hydrogen embrittlement and of over-pickling. Alternate anodic and cathodic procedures offer certain advantages that are leading to their wider adoption. Theory and practice in the anodic oxidation of aluminium are discussed; reference is made to the use of this type of process to facilitate photographic reproduction on the surface of the metal, and to modifications of anodizing technique designed to produce especially hard, wear-resisting films. The principles of electrolytic polishing are explained. Industrial practice in the electrolytic polishing of steel, nickel, copper and aluminium is outlined. A comparison is drawn between electrolytic and mechanical polishing, and some reference is made to the economics of the electrolytic process.