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why is iron used for temporary roofing and copper used as a roofing material for large buildings?
Any help would be appreciated.
iron (steel) = temporary because it's cheap but will rust away rather fast. Even galvanized or stainless steel (steel coated with other metals) will rust quickly once the coating is scratched.
copper = permanent because it is more expensive but not very expensive, and it will last forever with no maintenance once the green patina forms.
Water will not eat away at copper metal by way of rusting it to oxides like it does with iron metal, since copper is very inert. Copper does very slowly react with acidic compounds in the air (sulfuric acid, carbonic acid, water) and form copper coordination compounds having copper in the Cu(II) oxidation state. These compounds make a rock-hard, waterproof layer that protects the rest of the copper from corroding. That's why you can see old copper roofs and statues that look just like they did 400 years ago.
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2 Responses to “why is iron used for temporary roofing and copper used as a roofing material for large buildings?”
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January 31st, 2009 at 7:01 am
First of all, that is not iron, but galvanized iron. That means an iron sheet that has been coated with zinc. Galvanized iron is cheap and resists corrosion, because the zinc oxidizes first and keeps the iron from corrosion. Copper is below hydrogen in the electromotive series, so copper resists corrosion. Copper does turn green on its surface, but that's a patina.
References :
January 31st, 2009 at 7:34 am
iron (steel) = temporary because it's cheap but will rust away rather fast. Even galvanized or stainless steel (steel coated with other metals) will rust quickly once the coating is scratched.
copper = permanent because it is more expensive but not very expensive, and it will last forever with no maintenance once the green patina forms.
Water will not eat away at copper metal by way of rusting it to oxides like it does with iron metal, since copper is very inert. Copper does very slowly react with acidic compounds in the air (sulfuric acid, carbonic acid, water) and form copper coordination compounds having copper in the Cu(II) oxidation state. These compounds make a rock-hard, waterproof layer that protects the rest of the copper from corroding. That's why you can see old copper roofs and statues that look just like they did 400 years ago.
References :