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Metal Pickling: Acids and Inhibitors

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Rodine Acid Inhibitor is a series of acid corrosion inhibitors designed to serve worldwide standards for acid inhibitors. They are specially synthesized to provide protection to base metals from acidic corrosion effectively. Rodine Acid Inhibitor products inhibit the corrosion of metals against acids like Hydrochloric, Hydrofluoric, Sulfuric, Phosphoric, Sulfamic, and organic acids blends. The most common products listed in ChemEqual include Rodine 213, Rodine 213 Spl, Rodine 31A, Rodine 103, Rodine 103 NF, Rodine 92B, Rodine 130, and many more.

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Metal Pickling: Acids and Inhibitors

  1. 1. Metal Pickling: Acids and Inhibitors Hot rolling processes associated with various metal industries often leave behind inorganic oxide residues on treated metal surfaces. Exposure to moisture also results in rusting of Ferro-Nickel based metal parts. These oxides interfere with further cold processing like polishing, electroplating, painting or enameling. Rust and scale formation is a thin layer of metal oxide on the surface that is mostly removed by chemical cleaning also called “Pickling”. Pickling is carried out on oxide scaled surfaces of metals with alloy content less than 6%. The ideal pickling solution, known as Pickle Liquor is a 3%-10% solution of Hydrochloric acid (HCl) or Sulfuric acid (H2SO4). Hydrochloric acid is chosen over Sulfuric acid because of faster pickling action all the while minimizing base metal loss. It restricts formation of smut and greatly decreases the risk of excessive attacking. It is also economic as heating expenses needed for sulfuric acid are spared due to possibility of lower temperature pickling. Metal pickling is essential for thoroughly removing scales and inorganic surface contaminants before applying finishing layers like paint, galvanizing and polishing. The result of the process depends on the type, strength and temperature of the pickling liquor. In order to be economical, it is chosen as a continuous cleaning process by mode of manual/mechanized spraying or dipping in large acid vats. For small scale industries like jewellery making and research laboratories, extensive use of pickle pots is observed. Nevertheless, the corrosive action of diluted pickle acids cannot be ignored. In most cases, there is a significant loss of base metal during cleaning operations. For this reason, Acid Inhibitors are used with the acid solution to reduce base metal corrosion. Inhibitors are natural or synthetic organic compounds added to acid solutions to reduce metal surface corrosion. They slow or stop the chemical action of acid on the base metal surface.
  2. 2. Inhibitors are essential to:  Reduce base metal loss  Protect the surface from pitting attack by excessive pickling or from poor surface condition quality  Reduce fumes resulting from excessive acid-metal reactions  Help economize acid consumption without reducing descaling efficacy  Control the rate of pickling Rodine Acid Inhibitor is a series of acid corrosion inhibitors designed to serve worldwide standards for acid inhibitors. They are specially synthesized to provide protection to base metals from acidic corrosion effectively. Rodine Acid Inhibitor products inhibit the corrosion of metals against acids like Hydrochloric, Hydrofluoric, Sulfuric, Phosphoric, Sulfamic, and organic acids blends. The most common products underlined in this range include Rodine 213, Rodine 213 Spl, Rodine 31A, Rodine 103, Rodine 103 NF, Rodine 92B, Rodine 130, and many more. The process is limited to oxides and inorganic scales and contamination by soils, oil, grease, soaps and lubricants need additional processes with the use of Degreasing chemicals. Other limitations of acid pickling include difficulty to handle products because of their corrosive nature, the issue of hydrogen embrittlement popularly associated with some alloy and high-carbon steels, occupational hazards as the reactions produce toxic fumes in the factory shed. To obtain desired descaling, without endangering metal surfaces, acid concentrations and solution temperature need to be monitored quite strictly. Sludge is the ultimate waste product of acid pickling. It contains acid rinse water, metallic dissolved and suspended salts, waste spent acid etc. EPA considers it Hazardous waste and recommends proper treatment before disposal mostly in the form of Lime neutralization.

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