Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte

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

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn2+ and Al3+ ions. The low pH value was further confirmed by observing evolution of gas due to H+ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. 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.

Original languageEnglish
Pages (from-to)2411-2422
Number of pages12
JournalElectrochimica Acta
Volume52
Issue number7
DOIs
Publication statusPublished - 2007 Feb 1
Externally publishedYes

Fingerprint

Electrolytes
Steel
Corrosion
Coatings
Zinc
Surface potential
Steel corrosion
Hydrolysis
Dissolution
Gases
Ions
X rays
Water

Keywords

  • Atmospheric corrosion
  • Galvanic corrosion
  • Galvanized steel
  • Surface pH
  • Surface potential
  • Zn-Al coating

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Analytical Chemistry
  • Electrochemistry

Cite this

Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte. / Yadav, A. P.; Katayama, H.; Noda, Kazuhiko; Masuda, H.; Nishikata, A.; Tsuru, T.

In: Electrochimica Acta, Vol. 52, No. 7, 01.02.2007, p. 2411-2422.

Research output: Contribution to journalArticle

Yadav, A. P. ; Katayama, H. ; Noda, Kazuhiko ; Masuda, H. ; Nishikata, A. ; Tsuru, T. / Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte. In: Electrochimica Acta. 2007 ; Vol. 52, No. 7. pp. 2411-2422.
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AB - The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn2+ and Al3+ ions. The low pH value was further confirmed by observing evolution of gas due to H+ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. 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.

KW - Atmospheric corrosion

KW - Galvanic corrosion

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