What Does Electrogalvanizing Mean?
Electrogalvanizing is an electroplating technique used to place a layer of zinc metal on top of a steel surface. It involves immersing a steel component into a solution containing zinc salts followed by the application of electricity to induce an electrochemical reaction on top of the steel. Compared to hot dip galvanization, electrogalvanizing provides a thinner coating and more aesthetic appearances.
Bare steel surfaces are prone to corrosion because they contain iron that oxidizes when exposed to oxygen. Zinc, being more anodic than iron, becomes a sacrificial anode and prevents corrosion of the underlying steel.
Steel sheets and wires are often electrogalvanized. Common application of the technique occurs in the automotive and appliance industries.
Corrosionpedia Explains Electrogalvanizing
The electrogalvanizing process produces zinc metal from zinc(II) ions in a solution by electrochemically providing two electrons to each zinc(II) ion to fully reduce the zinc back to its metallic form:
Zn2+ (aq) + 2 e- = Zn (s)
The steel surface acts as the cathode and the resultant zinc metal adheres to the steel surface at the reaction site. Being an electrochemical process, electrolytes are an important component of efficient electrogalvanization and can also affect the brightness of the resulting zinc layer. Alkaline electrolytes are often used, but before the 1980s the alkaline electrolytes contained cyanide (CN-), a highly toxic ion. These solutions contain both sodium hydroxide and sodium cyanide, which solubilize the zinc(II) ions by creating soluble coordination complexes such as Na2Zn(CN)4 or Na2Zn(OH)4. After 1980, alkaline electrolyte solutions for electrogalvanization do not contain cyanide ions. Acidic electrolytes such as ammonium chloride are also used.
The zinc coatings resulting from electrogalvanizing are thinner than those produced by other processes such as continuous sheet galvanizing. Thickness may range up to ~9 μm. As thinner layers are more prone to damage, some electrogalvanized steel surfaces are further protected with an additional paint coating.