A general definition of corrosion “is the deterioration of materials by chemical interaction with their environment.”[1] The oxygen molecule present in air is highly reactive and will react with the exposed surfaces of most metals forming metal oxide products. These metal oxide products can provide a protective layer for the unexposed metal material, but not all metal oxides are equivalent in their protective capabilities. The process of corrosion or deterioration of the metal materials is often related to the aid or catalyzation of this reaction between exposed metal material and oxygen. The following factors can accelerate or aid corrosion related material damage and deterioration through undermining the metal oxide protective coating.
Sources can include rain, damp conditions, or high humidity,
Water itself provides a medium for countless electrochemical reactions,
Water can easily become acidic or basic which will dissolve the protective metal oxide coating.
There are three common sources of reactive and degrading sulfur compounds that could have reacted with the surface of the analyzed components.
Hydrogen Sulfide[2] - The two common sources of hydrogen sulfide in an environment are paper production and biological decay such as wastewater treatment or slaughterhouse environments.
Sulfur Dioxide[3] - The main source of sulfur dioxide in an environment is the burning of fossil fuels such as exhaust from an engine (heavy equipment, trucks, and generators) and power plant production.
Sulfuric Acid[4] - The main source of sulfuric acid in an environment is industrial processes and production of phosphate fertilizers.
There are four common sources of reactive and degrading chlorine compounds:
Bleach containing Cleaners or Sanitizers;
Main bleach chemical is Sodium Hydrochlorite or NaOCl, [~31% by weight Sodium (Na), ~48% by weight Chlorine (Cl) and ~21% by weight Oxygen (O)],
Salts such as Sodium Chloride [~40% by weight Sodium (Na) and ~60% by weight Chlorine (Cl)] which is commonly found in salt water and used for deicing, and
Hydrochloric Acid, a common processing chemical.
Calcium Chloride (CaCl2) is a common deicing agent (helps to melt ice).
There are two common sources of reactive and degrading nitrogen compounds:
Nitrogen Dioxide commonly created by burning fuel[5],
Ammonia containing products found in cleaning products and fertilizers.
There are two common sources of reactive and degrading sodium compounds found in Commercial Cleaning products like Simple Green which contain the following:[6]
Ingredient CAS Number Percent Range Chemical Formula 2D Structure Relevant Information
Sodium Citrate 68-04-2 < 5%* C6H5O7. 3Na Between 7,5 and 9,0 (5 % aqueous solution)[7]
Sodium Carbonate 497-19-8 < 1%* Na2CO3 Aqueous solutions are strongly alkaline. At 25 °C, the pH of 1, 5 and 10 wt% sodium carbonate solutions are 11.37, 11.58 and 11.70, respectively.[8]
[1] Madkour, P, ‘A SHORT INTRODUCTION TO CORROSION AND ITS CONTROL’, Corrosion, 2019, pp. 1–9 <https://www.academia.edu/14792955/A_SHORT_INTRODUCTION_TO_CORROSION_AND_ITS_CONTROL> [accessed 23 March 2020]
[2] Stopinski, Orin., Hydrogen Sulfide-Environmental Health Effects Research Series, Corrosion (U.S. Environmental Protection Agency, Office of Research and Development, Health Effects Research Laboratory, 1978) <https://nepis.epa.gov/Exe/ZyPDF.cgi/9100B2YD.PDF?Dockey=9100B2YD.PDF> [accessed 21 September 2020]
[3] EPA, ‘Sulfur Dioxide Basics’, Corrosion, 2019, p. 1 <https://www.epa.gov/so2-pollution/sulfur-dioxide-basics#effects> [accessed 21 September 2020]
[4] EPA, ‘8.10 Sulfuric Acid Emission Final Report (AP 42, Fifth Edition, Volume I Chapter 8: Inorganic Chemical Industry)’, Corrosion, 1993, 1–9 <https://www3.epa.gov/ttnchie1/ap42/ch08/final/c08s10.pdf> [accessed 21 September 2020]
[5] EPA, ‘Nitrogen Dioxide ( NO2 ) Pollution’, 2016, pp. 1–2 <https://www.epa.gov/no2-pollution/basic-information-about-no2#What is NO2> [accessed 21 September 2020]
[6] https://simplegreen.com/downloads/SDS_EN-AU_SimpleGreenAllPurposeCleaner.pdf accessed 2021-09-27
[7] https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-citrate accessed 2021-08-17
[8] https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-carbonate accessed 2021-08-17