Does corrosion decrease the weight of the metal or not ?
Corrosion is the deterioration of a metal. When the metal corrode an oxide will form on the surface exposed to the corrosive medium (water, air..) and the weight increse ’cause the oxide is formed by , for example, iron + oxygen Fe2O3 or Fe3O4 that weight more than Fe. But this is just one case of corrosion, iron + oxygen, there are many different types of corrosion mechanisms for different materials.
The oxides are not so aderent to the metal surface and so maybe at first there is an increase in weight but the final result is a loss of metal and weight.
Phil:
Corrosion of a block of metal – Iron to Iron Oxide (rust), Aluminum to Bauxite, Cooper to Cupric-oxide, or otherwise – does not change the weight of the metal in the system. If does change the weight of the object itself. As long as the object is undisturbed the its weight will increase due to the addition of oxygen molecules.
The density of the object will go down for a number of reasons: oxygen is lighter than the metal and the resulting molecule is larger.
Also remember that metallic oxides easily slough off the parent object. As the parent object is handled or otherwise disturbed it is relatively easy to remove some of the the loose material. This will make it appear that the original object has lost weight, but it is no longer the same object.
