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Acidification of the Electrolyte in the Carbon Steel/ Aluminum Alloys Galvanic Couple: Modeling and Experimental Study

Picture for Acidification of the Electrolyte in the Carbon Steel/ Aluminum Alloys Galvanic Couple: Modeling and Experimental Study
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Product Number: 51321-16334-SG
Author: A. Ortiz/ A. Ruiz-García/J. Genescá/R. Montoya
Publication Date: 2021
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An electrochemical  model  was  developed  to  predict  the  transient  distribution  of  species  generated  during corrosion of  carbon  steel  (CS)  /aluminum  alloy  (AA)  galvanic  couples  under  thin  NaCl  electrolyte  films  at room  temperature  (24  ºC).  Using  specific  geometrical  configurations,  strong  acidification of  the electrolyte,  localized  above  the  AA  surface  and  close  to the  carbon steel  electrode,  was  predicted. However,  a  small  zone evolved (also above  the AA  surface)  between  the  strong  acidified area and  the AA/CS  joint,  where the  pH  was  neutral  due  to the  OH-  production on the CS  surface.  Moderate acidification of  the  electrolyte  was  predicted  above  the  rest  of  the  AA  surface.  Both  diluted  and concentrated  electrolytes  were  taken into account.  Surprisingly,  the  less  concentrated  the  electrolyte,  the more  significant  the  drop  of  pH  on  top  of  the  AA  electrode.   Transient  experimental  measurements  were  achieved  with  the  help  of  an  innovative  setup,  and  findings corroborated  the  theoretical  predictions.  These  results  provide enough evidence to properly  discuss whether  such  an  acidification process  is  due  to  the production  of  intermediate aluminum  compounds  or by  the  fast  consumption  of  hydroxyl  ions  (OH-)  produced by  the  cathodic  reaction on  the  steel  surface.

Keywords:  galvanic  couples,  modeling,  aluminum  alloys,  aluminum  hydrolysis,  acid  corrosion. 

An electrochemical  model  was  developed  to  predict  the  transient  distribution  of  species  generated  during corrosion of  carbon  steel  (CS)  /aluminum  alloy  (AA)  galvanic  couples  under  thin  NaCl  electrolyte  films  at room  temperature  (24  ºC).  Using  specific  geometrical  configurations,  strong  acidification of  the electrolyte,  localized  above  the  AA  surface  and  close  to the  carbon steel  electrode,  was  predicted. However,  a  small  zone evolved (also above  the AA  surface)  between  the  strong  acidified area and  the AA/CS  joint,  where the  pH  was  neutral  due  to the  OH-  production on the CS  surface.  Moderate acidification of  the  electrolyte  was  predicted  above  the  rest  of  the  AA  surface.  Both  diluted  and concentrated  electrolytes  were  taken into account.  Surprisingly,  the  less  concentrated  the  electrolyte,  the more  significant  the  drop  of  pH  on  top  of  the  AA  electrode.   Transient  experimental  measurements  were  achieved  with  the  help  of  an  innovative  setup,  and  findings corroborated  the  theoretical  predictions.  These  results  provide enough evidence to properly  discuss whether  such  an  acidification process  is  due  to  the production  of  intermediate aluminum  compounds  or by  the  fast  consumption  of  hydroxyl  ions  (OH-)  produced by  the  cathodic  reaction on  the  steel  surface.

Keywords:  galvanic  couples,  modeling,  aluminum  alloys,  aluminum  hydrolysis,  acid  corrosion. 

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