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Does Zinc still protect Iron at boiling water temp?




Can anyone help regarding the galvanic potential of Zinc at elevated temperatures? Is Zinc still sacrificial to Iron at >100 °C?

Derek Tarrant
- Greeneville, Tennessee, USA
2003


Sorry, I've never seen a chart with the galvanic series at elevated temperature. On the other hand, zinc is very strongly electronegative toward steel, and steel is coated with zinc for galvanic protection in thousands of very common applications; I've never personally heard of reversal of cathodic protection for zinc and steel.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
2003


2003

From Corrosion and Corrosion Control, 3rd Edn., pp. 239-240 (1985): "In many aerated hot waters, reversal of polarity between zinc and iron occurs at temperatures of about 60 °C (140 °F) or above." This reversal is favored by high concentrations of carbonates and nitrates, and inhibited by chlorides and sulphates. It is apparently due to the formation of ZnO rather than Zn(OH)2, the ZnO acting as a semiconductor in aerated waters.

Ken Vlach [deceased]
- Goleta, California
contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.


Thanks for the correction, Ken

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
2007




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