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Passivation: Difference between revisions
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Text replacement - "https://www.voestalpine.com/welding/content/download/3617/58308/file/BW_Pickling%2BHandbook_EN_2019_GL_128_Preview.pdf" to "https://web.archive.org/web/20200627011337/https://www.voestalpine.com/welding/content/download/3617/58308/file/BW_Pickling%2BHandbook_EN_2019_GL_128_Preview.pdf"
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[[File:Stainless-etched-kettle.jpg|thumb|Stainless kettle]][[Iron]] and other metals are chemically ''reactive''. Upon exposure to air, a metal surface will react with the oxygen, which results in the formation of a thin metal oxide film. This occurs completely spontaneously. The metal oxide film makes the surface more ''passive'' (resistant) to other chemicals in the environment. This is called "passivation" by a chemistry definition.<ref name=a967/><ref name=Crookes>Crookes R. [https://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Passivating_Pickling_EN.pdf ''Pickling and Passivating Stainless Steel.''] 2<sup>nd</sup> ed. Euro Inox; 2007.</ref><ref name=Kremer/><ref name=cluett/> | [[File:Stainless-etched-kettle.jpg|thumb|Stainless kettle]][[Iron]] and other metals are chemically ''reactive''. Upon exposure to air, a metal surface will react with the oxygen, which results in the formation of a thin metal oxide film. This occurs completely spontaneously. The metal oxide film makes the surface more ''passive'' (resistant) to other chemicals in the environment. This is called "passivation" by a chemistry definition.<ref name=a967/><ref name=Crookes>Crookes R. [https://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Passivating_Pickling_EN.pdf ''Pickling and Passivating Stainless Steel.''] 2<sup>nd</sup> ed. Euro Inox; 2007.</ref><ref name=Kremer/><ref name=cluett/> | ||
[[Stainless steel]] is mostly iron, although it also contains a significant percentage of chromium. The chromium oxide in the passive surface layer adds a good deal more resistance to chemical reactions compared to other steel alloys, which means it is less susceptible to rusting. This is what makes the stainless steel "stainless".<ref name=Crookes/><ref name=cluett/><ref name=usa/><ref name=Diversey/><ref name=MB/><ref name=schmidt>Schmidt RH, Erickson DJ, Sims S, Wolff P. [https://www.foodprotection.org/files/food-protection-trends/Oct-12-Schmidt.pdf Characteristics of food contact surface materials: Stainless steel.] ''Food Prot Trends.'' 2012;32(10):574–584.</ref> However, most stainless steel used in the brewery is only about 18% chromium. As such, the relatively high percentage of iron on the surface still leaves it vulnerable to corrosion, and iron can negatively affect beverage [[flavor stability]]. To avoid these problems, the majority of surface iron can be removed with an acid bath. The resulting chromium-rich surface is superbly resistant to corrosion and has lower reactivity with the beverage. This iron removal process is called "passivation" by an industry definition.<ref name=Kremer/><ref name=usa>Yasensky D, Reali J, Larson C, Carl C. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf Citric acid passivation of stainless steel.] Slides presented at: 2011 Aircraft Airworthiness and Sustainment Conference; April 2011; San Diego, CA.</ref><ref name=nasa1/><ref name=a967>ASTM A967 / A967M-17. Standard specification for chemical passivation treatments for stainless steel parts. [http://www.astm.org ASTM International]; 2017.</ref><ref name=Diversey>[https://wine.appstate.edu/sites/wine.appstate.edu/files/Diversey_PassivationofStainlessSteel.pdf Passivation of stainless steel.] ''JohnsonDiversey Tech Tips.'' 2007;15.</ref><ref name=MB/><ref>[https://mmptdpublic.jsc.nasa.gov/prc/PRC-5002_Current.pdf Process specification for passivation and pickling of metallic materials.] National Aeronautics and Space Administration; 2021.</ref><ref name=schmidt/><ref name=bohler>Bornmyr A, Toesch J, Winkler F. [https://www.voestalpine.com/welding/content/download/3617/58308/file/BW_Pickling%2BHandbook_EN_2019_GL_128_Preview.pdf ''Manual for surface treatment of stainless steels.''] 3<sup>rd</sup> ed. Voestalpine Böhler Welding; 2019.</ref> | [[Stainless steel]] is mostly iron, although it also contains a significant percentage of chromium. The chromium oxide in the passive surface layer adds a good deal more resistance to chemical reactions compared to other steel alloys, which means it is less susceptible to rusting. This is what makes the stainless steel "stainless".<ref name=Crookes/><ref name=cluett/><ref name=usa/><ref name=Diversey/><ref name=MB/><ref name=schmidt>Schmidt RH, Erickson DJ, Sims S, Wolff P. [https://www.foodprotection.org/files/food-protection-trends/Oct-12-Schmidt.pdf Characteristics of food contact surface materials: Stainless steel.] ''Food Prot Trends.'' 2012;32(10):574–584.</ref> However, most stainless steel used in the brewery is only about 18% chromium. As such, the relatively high percentage of iron on the surface still leaves it vulnerable to corrosion, and iron can negatively affect beverage [[flavor stability]]. To avoid these problems, the majority of surface iron can be removed with an acid bath. The resulting chromium-rich surface is superbly resistant to corrosion and has lower reactivity with the beverage. This iron removal process is called "passivation" by an industry definition.<ref name=Kremer/><ref name=usa>Yasensky D, Reali J, Larson C, Carl C. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf Citric acid passivation of stainless steel.] Slides presented at: 2011 Aircraft Airworthiness and Sustainment Conference; April 2011; San Diego, CA.</ref><ref name=nasa1/><ref name=a967>ASTM A967 / A967M-17. Standard specification for chemical passivation treatments for stainless steel parts. [http://www.astm.org ASTM International]; 2017.</ref><ref name=Diversey>[https://wine.appstate.edu/sites/wine.appstate.edu/files/Diversey_PassivationofStainlessSteel.pdf Passivation of stainless steel.] ''JohnsonDiversey Tech Tips.'' 2007;15.</ref><ref name=MB/><ref>[https://mmptdpublic.jsc.nasa.gov/prc/PRC-5002_Current.pdf Process specification for passivation and pickling of metallic materials.] National Aeronautics and Space Administration; 2021.</ref><ref name=schmidt/><ref name=bohler>Bornmyr A, Toesch J, Winkler F. [https://web.archive.org/web/20200627011337/https://www.voestalpine.com/welding/content/download/3617/58308/file/BW_Pickling%2BHandbook_EN_2019_GL_128_Preview.pdf ''Manual for surface treatment of stainless steels.''] 3<sup>rd</sup> ed. Voestalpine Böhler Welding; 2019.</ref> | ||
An undue amount of contention in the home brewing world has been caused by using these two definitions of passivation interchangeably. It's clear that they refer to different processes, which results in confusion when the word "passivation" is not well-defined in a particular document or discussion. It's understood that stainless steel naturally "passivates" in a chemistry sense by spontaneously forming an oxide layer. However, the definition of passivation used in this article is the process of using an acid treatment to selectively remove iron, which greatly improves the natural passive layer. | An undue amount of contention in the home brewing world has been caused by using these two definitions of passivation interchangeably. It's clear that they refer to different processes, which results in confusion when the word "passivation" is not well-defined in a particular document or discussion. It's understood that stainless steel naturally "passivates" in a chemistry sense by spontaneously forming an oxide layer. However, the definition of passivation used in this article is the process of using an acid treatment to selectively remove iron, which greatly improves the natural passive layer. | ||