Electrocleaning

Electrocleaning is usually the last step in alkaline cleaning, largely because of its action. By and large, electrocleaners are highly alkaline materials which are very conductive and easily electrolyze water molecules to form both oxygen and hydrogen gas. The half-cell reactions are illustrated below:

Anode Reaction

4(0H) -4e > 2H2O +O2 (Gas)

Cathode Reaction

4H2O +4e + 4(0H) +2H2

Electrocleaners are aided in their cleaning by the evolution of gases at the electrodes. Because water is made up with two molecules of hydrogen and one molecule of oxygen, current passing through it will generate twice the volume of gas at the cathode as at the anode. When a part is placed in an electrocleaner, much of the cleaning is accomplished by the scrubbing action of the gases evolving at the surface of the parts.

In comparison with the soak cleaners, which handle organic materials like oils and greases and are soluble or emulsifiable, an electrocleaner removes smuts and soils. The alkaline nature of electrocleaners does not lend itself to the removal of oils or greases, and should not be used for that purpose. There are, however, crossover compounds available which may do a marginally effective job of removing organic materials.

Cathodic electrocleaningówith twice the scrubbing action because it evolves hydrogen at the surface of the partsó should be used as a preliminary step to remove high volumes of soils on the parts. Cathodic electrocleaning will not passivate sensitive metals like stainless steel or nickel, and in fact, will aid in their activation. Be careful, though, because a cathodic electrocleaner may deposit a metallic smut, which must be removed before finishing.

Anodic electrocleaning is a more traditional method and will remove smut and light oxides from the surface of the parts, as well as remove thin deposits of various materials, such as chromium.

Anodic electrocleaners generate oxygen at the surface of the processed parts and they will tend to passivate sensitive metals such as nickel and stainless steel. When electrocleaners are used to remove chromium from parts, a chromium reducer should be used to keep the chromium in a trivalent form. Unfortunately, the chromium will re-oxidize to hexavalent and the effect will be short-lived.

The best aspect of anodic electrocleaners is the ability to remove smuts and light oxides from the surface of the processed parts. This ability is dependent on, and a function of, the chemical composition of the electrocleaners.