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Anne Marie Helmenstine, Ph.D.

Green Rust?

By April 16, 2012

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Green Rust or Iron Hydroxide (Chemicalinterest)Rust is the name given to a collection of iron oxides. You'll find rust in all situations where unprotected iron or steel is exposed to the elements. Did you know rust comes in colors besides red? There is brown, orange, yellow and even green rust! Green rust is an unstable corrosion product typically produced in a low-oxygen environment, such as rebar in the chlorine-rich environment of seawater, which may result in [FeII3 FeIII (OH)8]+ [Cl. H2 O]-, a series of iron hydroxides. Depassivation of steel to form green rust occurs when the ratio of concentration of chloride ions to hydroxide ions is greater than 1. Therefore, rebar in concrete, for example, may be protected from green rust if the alkalinity of the concrete is high enough.

There is a natural mineral which is the equivalent to green rust called fougerite. Fougerite is a blue-green to blue-gray clay mineral found in certain wooded regions of France. The iron hydroxide is believed to give rise to other related minerals.

Have you ever seen green rust? Which colors of rust have you encountered?

Comments

April 14, 2011 at 10:24 am
(1) Lanthanum says:

Hey, how did you get my picture? :) It is made by electrolytic oxidation of iron. Air oxidation produces brown rust because it happens so slow, giving the green rust time to oxidize.

When green rust is pure (oxygen free), it is actually white! Corrosion of iron will probably not produce white rust because the slightest amount of oxygen turns it green.

April 15, 2011 at 8:26 am
(2) VIMALRAJ says:

DOES GREEN RUST OCCURS ONLY IN OXYGEN LESS REGIONS?

April 16, 2011 at 3:46 pm
(3) Lanthanum says:

Either that or extremely rapid corrosion.

April 18, 2012 at 6:09 am
(4) NeedHelp says:

How can I make rust of different colours? Is there a procedure for every different reaction ?

March 25, 2013 at 11:55 am
(5) david bradbury says:

Well well, that settles it, some years back while on DartmoorI found some Vivianite (a phosphate of Iron) a green coating upon the Vivianite was never known until today, thanks for your guidance, Now I have proved it is green Oxide of Fe,,,Wow !

April 2, 2013 at 6:44 pm
(6) r.janarthanam says:

thx anne for ur info. i am working in seawater desalination (yanbu)plant on west coast of saudiarabia. i also observed dark green rust on the victaulic joints of ro membrane vessel (module) outlet line.
the seawtr is pre treated with sodium hypo chlorite& (40%)ferric chloride, sent dual media filter . then 98% sulphuric acid is injected & sent to ro module with pressure for permeation . i also think ur info has relevance with my observation.
regards/thx
r.janarthanam

September 17, 2013 at 12:18 am
(7) chaitanya says:

Lanthanum how did you set up the apparatus? i got green rust formation once but am unable to recreate the experiment

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