Acidic Aqueous General Information Acidic aqueous cleaners are effective for removing rust from ferrous parts. Acidic cleaners are commonly used for the removal of: Mill scale (hot rolled scale) Scale developed during welding Scale developed during heat treating Superficial oxide, which interferes with painting, porcelain enameling, tinning, galvanizing, or electroplating Rust and corrosion products Hard water scale Products of reaction of hard water with soil, especially protein (milkstone, beerstone) Acidic aqueous cleaners show excellent results in removing pigmented drawing compounds. Acidic cleaners can also be used to clean aluminum, a metal susceptible to etching when cleaned with strong alkaline detergents. Magnesium can be affected by slightly acidic cleaners but acid chromate solutions are used. Acidic cleaning solutions can contain mineral acids (nitric, sulfuric, phosphoric, hydrofluoric), chromic acids, or organic acids (acetic or oxalic), plus detergents, chelating agents, and small amounts of water-miscible solvents. Acids commonly used in acidic aqueous cleaners include: sulfuric, nitric, or hydrochloric acids and organic acids such as acetic, oxalic, or cresylic acid. Nitric and hydrofluoric acids are used for brightening aluminum and stainless steel. Some types of stainless steels will rust or dissolve under acidic conditions. Contact between stainless steel and hydrochloric or heated sulfuric acid should be minimized. All stainless steels are pitted by prolonged contact with acidic solutions containing chlorides. Magnesium can be affected by slightly acidic cleaners, especially those containing chlorides. If parts are to be painted, then cleaning in a phosphoric acid solution provides a level of corrosion protection by forming a phosphate coating. Certain soils, especially those that are inorganic, are either removed in acidic cleaners or are dissolved by acids, or both. These cleaners are poor at removing oil, grease, and rosin flux. State Information | Glossary | Conversion Checklist | Comments Home | Process Advisor | Alternatives | Links | Search All SAGE material, Copyright© 1992, Research Triangle Institute Last Update: 06 May 1997 sage@rti.org http://clean.rti.org/alt.cfm?id=ac&cat=gi