Academic journal article European Journal of Sustainable Development

Optimization of Electrolytic Cleaning of Low Carbon Steels

Academic journal article European Journal of Sustainable Development

Optimization of Electrolytic Cleaning of Low Carbon Steels

Article excerpt

(ProQuest: ... denotes formulae omitted.)

1.Introduction

The electrolytic cleaning is a process commonly used in the steel industry for removing contaminants adhered to metal surfaces. This process takes place in two stages: in the first, called cleaning step, the steel is subjected to a series of pre-treatments such as dipping in alkaline solution and brushing or blasting in order to remove grease, oil and particles more weakly attached. In the second, metal surface is submitted to electrolysis by dipping it into a conducting solution and connected to an external power source.

Cleaning can be performed in cathodic or anodic current (Zujur and Rosales, 2012). Under cathodic current, the metal receives a negative charge and hydrogen gas is produced in the metal surface. Under anodic current, the metal receives a positive charge and oxygen gas is produced in the metal surface. This gas bubbling promotes the release of the metal oxides from the surface of the steels.

Electrolytic cleaning can be used for removing the adhered oxides on the metal surfaces due to corrosion processes. Oxidized piece can be placed in the cathode of the cell, and then oxygen release is observed after application of a given current density. Hydrogen, when released, promotes the detachment of the adhered oxides particle by particle (Mantell, 1980). Sometimes, when the piece to be cleaned is extremely delicate, the piece can be submitted to alternate cycles of cathodic and anodic cleaning deliberately, to produce a slow release of the adhered oxides. This effect was applied in cleaning daguerreotypes of the nineteenth century (Da Silva et al., 2010), alternating basic (1% w/v sodium metaborate) and acid electrolytes (0.3% w/v citric acid) with current intensity variations and placing the daguerreotype alternatively as anode and cathode.

Sometimes electrolytic cleaning produces an irregular cleaning, which mainly affects the so-called "high points", i.e., the most outstanding oxide layers within the topography of the steel probe. In the "low points", however, where there is no corrosion or this is insignificant, the pickling process produces an oxidation of the original metal, producing a passivation layer. The result of both processes is an electrolytic polishing; where prominent parts of the roughened surface are reduced and low roughness slightly increase by passivation. The effect is a regularization or continuity of the surface (Mantell, 1980).

Other authors have highlighted the advantages of electrolytic cleaning against different methods. Chaves and Jeffrey (2015) studied the removal of oxides by different techniques, analysing the mass loss, the resulting surface topography, the pit depth and localized corrosion of steel probes after being exposed to corrosion in marine environments of high salinity. These authors found that chemical cleaning is useful for removing recent corrosion, although the effect of the cleaning agent generates the appearance of new oxides, acting itself as a corrosive agent. Exposure to these cleaning agents also produced pitting corrosion of the steel probe. Ultrasonic cleaning did not produce new corrosion products; although their effectiveness was higher in mild to moderate oxidations. Electrolytic cleaning, according to Chaves and Jeffrey (2015) proved to be effective in removing oxides without causing new corrosion products, although it was moderately slow process.

Removal of corrosion is a key step for recovering the oxidized steel probes and the application of new coatings that will serve as protective layer of the clean surface. The electrolytic cleaning is employed as a method for removing impurities, oxides, and small cracks, which can significantly reduce the adhesion of new coatings (Cheng et al., 2010). The electrolytic cleaning is an environmentally friendly method, which results effective also for large pieces with a simple and flexible methodology. However, there are two major problems that can arise from electrolytic treatments: on the one hand, the application of repeated cycles over time can cause a decrease in mechanical properties and on the other hand, the formation of hydrogen which can be incorporated to the material causing fragility of the piece (Cheng et al. …

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