Sulfamic acid is an environment-friendly alternative electrolyte for industrial acid cleaning and corrosion inhibition: a mini review

Sulfamic acid (H3NSO3), which is also known as amino sulfuric acid, sulfamidic acid, amidosulfonic acid, and aminosulfonic acid, is an industrially useful water-soluble colorless crystalline solid. Sulfamic acid solutions of different concentrations are widely used for the removal of scales and metal oxides deposits from the surface of metals and ceramics. Sulfamic acid solutions (5-10%) serve as alternative electrolytes for the removal of rusts and lime scales to replace relatively more irritating and volatile hydrochloric and sulfuric acid-based electrolytes. Sulfamic acid solutions can be regarded as relatively more environmentally friendly and less toxic electrolytes for the cleaning of metallic surfaces. However, similar to the popular acidic solutions, sulfamic acid based electrolytes are corrosive to metal and metallic structures. Therefore, organic compounds based corrosion inhibitors of natural and synthetic origin are widely used to prevent corrosive damage of metallic surfaces in such electrolytes. These compounds become effective by adsorbing on the metallic surface following through the Langmuir adsorption isotherm model. Using electrochemical analyses it was observed that organic corrosion inhibitors in sulfamic acid based electrolytes behave as mixed- and interface-type corrosion inhibitors and they become effective by adsorbing at the metal/electrolyte interfaces. The adsorption of most of the corrosion inhibitors mostly follows physiochemisorption mechanism.