Tuesday, December 22, 2009

Oil rigs often have big lumps of magnesium attached to their legs under water. Why?

Just a question in my Science book that i have no idea about. Please help me understand!Oil rigs often have big lumps of magnesium attached to their legs under water. Why?
To stop the oil rig rusting - it's called sacrificial protection.





Sacrificial protection is used for ships, under water pipelines


and oil rigs (for example in the North Sea).





Blocks of a more reactive metal (for example magnesium or zinc)


are attached to the ship's hull or the under water pipe.


The magnesium or zinc can also be connected


to a pipeline or oil rig by conducting cables.





Sacrificial protection is similar to a displacement reaction


with the electrons traveling from the more reactive metal to the steel


either directly or through the conducting cable.


This reverses the oxidation process.





3Zn(s) arrow 3Zn2+(aq) + 6e- Zinc is oxidised as it dissolves.





2Fe3+(s) + 6e- arrow 2Fe(s) Iron ions are reduced to iron atoms. Rusty steel is returned to iron metal.





The block of zinc or magnesium is sacrificed to keep the steel from rusting and must be replaced before it all dissolves.


This is less expensive than rebuilding the ship or replacing the pipe or oil rig





this is what they look like


http://www.ecplaza.net/product/162597_97鈥?/a>

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