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I'm doing a science project in which a put a charge through a tub of sea water. The anode is titanium mesh and the cathode is steel mesh. I am measuring the growth of solids (mainly calcium carbonate and magnesium) on the cathodic steel mesh structure. Everything that is happening so far I've expected except that there is brown and red foam forming on the surface of the water and there is red settlement of the floor. I would greatly appreciate any feed back into what's happening chemically to make this happen.
P.S. Someone suggested that it may be galvanic corrosion. This may be feasible because the steel is galvanized (I'm assuming that that's what's on the steel to stop it from rusting).
Question Date: 2006-05-26
Answer 1:

What you are describing is a very common chemical reaction that occurs when steel is exposed to water, and especially in salty water. The problem is that steel contains a lot of iron, which will eventually form rust in a humid environment. Youre quite correct that galvanized steel is supposed to prevent it from rusting. However, over time, even this protective layer will erode away, exposing the iron underneath.

The rust, or brown and red foam is just iron oxide. The fact that some of it has appeared both on the surface of the water and at the bottom of the container just means that some of the rust has been knocked off from the steel surface. I bet if you looked closely, you would see some rust forming on the steel mesh as well.

The good news is that I wouldnt expect that the presence of a small amount of rust should affect the growth rates of the calcium and magnesium carbonates.

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