Surface potential distribution over a zinc/steel galvanic couple corroding under thin layer of electrolyte

A. P. Yadav, H. Katayama, Kazuhiko Noda, H. Masuda, A. Nishikata, T. Tsuru

Research output: Contribution to journalArticle

51 Citations (Scopus)

Abstract

In this study, surface potential and surface pH changes over a zinc/steel galvanic couple corroding in artificial seawater (ASW) at 60 and 90% RH have been investigated. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test. The potential difference over the zinc and steel surface in 90% RH was very low (less than 200 mV) showing that whole steel surface was under galvanic protection. On the other hand, in 60% RH, after several days of corrosion the potential difference between the zinc coating and the steel surface was very high (more than 500 mV) and hence the galvanic protection was limited to interface region. The X-ray analysis of the sample corroded in 60% RH has shown that the zinc corrosion products were deposited on the steel surface near the interface, the same region has shown a low pH compared to than in other part of the steel surface. This led to conclude that with the progress of corrosion, the coating surface of zinc coated steel acidifies by the hydrolysis reaction of the dissolved zinc ions, and the iron surface showed the alkalinity by the oxygen reduction reaction. Moreover, the parts of the steel surface covered with zinc corrosion products had developed relatively less noble potential than other parts indicating that zinc corrosion products took a role to protect the base steel against corrosion. It was assumed that this behavior was related to a combination of the water absorbing capability of zinc corrosion products and adsorption of zinc ion on the steel surface due to low pH.

Original languageEnglish
Pages (from-to)3121-3129
Number of pages9
JournalElectrochimica Acta
Volume52
Issue number9
DOIs
Publication statusPublished - 2007 Feb 15
Externally publishedYes

Fingerprint

Steel
Surface potential
Electrolytes
Zinc
Corrosion
Ions
Zinc coatings
Steel corrosion
X ray analysis
Alkalinity
Seawater
Hydrolysis
Iron
Oxygen

Keywords

  • Atmospheric corrosion
  • Galvanic corrosion
  • Galvanized steel
  • Surface pH
  • Surface potential

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Analytical Chemistry
  • Electrochemistry

Cite this

Surface potential distribution over a zinc/steel galvanic couple corroding under thin layer of electrolyte. / Yadav, A. P.; Katayama, H.; Noda, Kazuhiko; Masuda, H.; Nishikata, A.; Tsuru, T.

In: Electrochimica Acta, Vol. 52, No. 9, 15.02.2007, p. 3121-3129.

Research output: Contribution to journalArticle

Yadav, A. P. ; Katayama, H. ; Noda, Kazuhiko ; Masuda, H. ; Nishikata, A. ; Tsuru, T. / Surface potential distribution over a zinc/steel galvanic couple corroding under thin layer of electrolyte. In: Electrochimica Acta. 2007 ; Vol. 52, No. 9. pp. 3121-3129.
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AB - In this study, surface potential and surface pH changes over a zinc/steel galvanic couple corroding in artificial seawater (ASW) at 60 and 90% RH have been investigated. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test. The potential difference over the zinc and steel surface in 90% RH was very low (less than 200 mV) showing that whole steel surface was under galvanic protection. On the other hand, in 60% RH, after several days of corrosion the potential difference between the zinc coating and the steel surface was very high (more than 500 mV) and hence the galvanic protection was limited to interface region. The X-ray analysis of the sample corroded in 60% RH has shown that the zinc corrosion products were deposited on the steel surface near the interface, the same region has shown a low pH compared to than in other part of the steel surface. This led to conclude that with the progress of corrosion, the coating surface of zinc coated steel acidifies by the hydrolysis reaction of the dissolved zinc ions, and the iron surface showed the alkalinity by the oxygen reduction reaction. Moreover, the parts of the steel surface covered with zinc corrosion products had developed relatively less noble potential than other parts indicating that zinc corrosion products took a role to protect the base steel against corrosion. It was assumed that this behavior was related to a combination of the water absorbing capability of zinc corrosion products and adsorption of zinc ion on the steel surface due to low pH.

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