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Does Zinc still protect Iron at boiling water temp?

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

Derek Tarrant
- Greeneville, TN, USA

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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, P.E.
finishing.com
Brick, New Jersey

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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 deg C (140 F) or above." This reversal is favored by high concentrations of carbonates and nitrates, and inhibited by chlorides and sulfates. 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
- Goleta, California

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Thanks for the correction, Ken

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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