Just a foot note in regards to applied finishes on aluminum.
First, I believe a little background regarding anodized finishes on aluminum is in order.
The chemistry of aluminium (and it's alloys) is interesting. Given that it's a reactive metal (more so than iron) one would expect it to naturally corrode more rapidly than it actually does. The reason it doesn't is that the initial formation of an oxide layer on the surface protects the base metal underneath. Aluminium oxide is a tough material (it's crystalised form is used as an abrasive - Allox), but normally it's formation in air results in an amorphous layer with little mechanical strength, it's a white powder that can easily be scraped off leading to further oxidation.
Anodising on the other hand, is a process which forms a particularly structured and dense oxide layer which resists abrasion and thus protects the underlying metal. This layer is colourless, but it's possible to introduce a dye at one stage in the process to permanently colour the surface. Not all aluminium alloys can be easily anodised, cast aluminium (with a high silica content) is particularly difficult.
Anodising is an electro-chemical process which physically alters the surface of the metal to produce a tough oxide layer on the surface. During the anodising process the oxide layer is at first porous, and at this point it's possible to introduce a coloured dye. 'Porous' in this case refers to the molecular level rather than gaping holes - the dye thus needs to be soluble to penetrate this layer. The porous layer is then 'sealed' by boiling the part in water (which converts the oxide to a different crystalline chemical form) permanently trapping the dye beneath the surface. It should be noted that as the anodised surface is a layer of aluminium oxide, rather than metal, it exhibits a very high resistance to electric current.
Aluminum can be painted. Ask anyone who owns a late model Audi. Due to the chemical composistion of aluminum, and the aluminum oxide layer, you can not direct apply paint to the metal. It must first be acid etched with a chromate type primer, and then the paint applied to on top of that. Upmost care must be taken in properly preparing the surface before priming. Even when such measures are taken, it is still very possible to have the paint chip revealing the shiny metal underneath.
Due to the various layers of material necessary to paint aluminum, the badge would be devoid of detail by the time it was done. Hence the necessary use of anodising.
First, I believe a little background regarding anodized finishes on aluminum is in order.
The chemistry of aluminium (and it's alloys) is interesting. Given that it's a reactive metal (more so than iron) one would expect it to naturally corrode more rapidly than it actually does. The reason it doesn't is that the initial formation of an oxide layer on the surface protects the base metal underneath. Aluminium oxide is a tough material (it's crystalised form is used as an abrasive - Allox), but normally it's formation in air results in an amorphous layer with little mechanical strength, it's a white powder that can easily be scraped off leading to further oxidation.
Anodising on the other hand, is a process which forms a particularly structured and dense oxide layer which resists abrasion and thus protects the underlying metal. This layer is colourless, but it's possible to introduce a dye at one stage in the process to permanently colour the surface. Not all aluminium alloys can be easily anodised, cast aluminium (with a high silica content) is particularly difficult.
Anodising is an electro-chemical process which physically alters the surface of the metal to produce a tough oxide layer on the surface. During the anodising process the oxide layer is at first porous, and at this point it's possible to introduce a coloured dye. 'Porous' in this case refers to the molecular level rather than gaping holes - the dye thus needs to be soluble to penetrate this layer. The porous layer is then 'sealed' by boiling the part in water (which converts the oxide to a different crystalline chemical form) permanently trapping the dye beneath the surface. It should be noted that as the anodised surface is a layer of aluminium oxide, rather than metal, it exhibits a very high resistance to electric current.
Aluminum can be painted. Ask anyone who owns a late model Audi. Due to the chemical composistion of aluminum, and the aluminum oxide layer, you can not direct apply paint to the metal. It must first be acid etched with a chromate type primer, and then the paint applied to on top of that. Upmost care must be taken in properly preparing the surface before priming. Even when such measures are taken, it is still very possible to have the paint chip revealing the shiny metal underneath.
Due to the various layers of material necessary to paint aluminum, the badge would be devoid of detail by the time it was done. Hence the necessary use of anodising.
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