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Brightening aluminium ?


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Hi.

Any suggestions on which household chemicals can be used to restore the bright finish to aluminium parts ?

It is for my automobile engine; aluminium parts used to be shiny and after washing with degreasers lost its new appearance, dull grey now. Nothing of real concern; but would be great if can be restored with something from under the kitchen sink pile of stuff... :rolleyes: ...and your brains...

Miguel

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I'm really sorry, but that last comment you made about the sink and brain cleaning just reminded me of this >.<

 

braincleaner9yu.jpg

 

The aluminum oxide layer that forms around aluminum parts is pretty much non-reactive. Other than physically etching it, I have no idea though x_x

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im pretty sure NaOH wouldnt react with Al2O3

 

You are pretty wrong - aluminum is amphoteric and it reacts both with acids and bases. Al2O3 is stable and highly resistive to corrosion only in pH of around 7. Acid rain or alkalic soap solution are enough to remove oxide layer. New layer is created immediately, but if there is enough acid or base you will be able to dissolve aluminum completely.

 

Best,

Borek

--

Chemical calculators at www.chembuddy.com

pH calculation

concentration calculator

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NaOH reacts with aluminum MUCH faster than HCl does. NaOH eats right through the aluminum oxide coating and the aluminum itself. HCl has a much harder time getting through that coating. Simply take a test-tube and put the same amount of the same concentration of HCl and NaOH in either tube. Then put the same sized piece of aluminum metal into each tube. The reaction will be much quicker, and much more vigorous in the NaOH tube. This is the principal behind draino. Draino is a combination of NaOH pellets/powder and small aluminum pieces. When it's placed in the water, the reaction begins and the H2 that's evolved unclogs the drain.

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well i just tried it and the hcl worked alot faster- pretty much the opposite of what u said. Maybe i have some wrong concentrations or somehting. Btw not all draino has the aluminum in it- the ones that do are the drano crystal things.

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also, the possibile reason why ur engine isnt shiney anymore could be because it was chrom/ watever plated. the degreasers may have taken off the shiney plated layer yeilding a dull motor. If that is the case u couyld go and get it re-plated.

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youll get sodium aluminate from Al2O3 and NaOH, i believe

Almost correct, you will get sodium aluminium hydroxide. If this was then heated to drive off two molecules of water you would get sodium aluminate.

 

The reason that aluminium dissolves at high pH's (ie sodium hydroxide) is the anomalous stability of the Al(OH)4- ion under these conditions. This is the basis of the Bayer process, discovered in 1893, which allows aluminium to be extracted from its ores.

 

Basically the aluminium containing ore is treated with NaOH, the aluminium dissolves, and the waste (usually iron oxides) is left behind. The pH is then dropped again and the aluminium precipitates out as Al(OH)3.

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I agree with coquina. Al is usually anodized or plated someway and if it loses that finish it can not be easily restored. Atempts to chemical etch or polish aluminium tend to make it just more ugly.

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yes, id imagine some fine grit sand paper would do fine if you polished it with a metal polish meant for aluminum afterwards. Then id clear coat it like mmalluck sugested. Steal wool would work better if its greasy though.

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the only problem with that method as with anything too abrasive is that you end up with a brushed aluminium finish instead of a shiney one.

 

bicarb and WD-40 on a rag should give a reasonable finish providing that the alu isn`t too pitted.

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If you use a fine grit sand paper (400-600) and sand it wet,then buff it with fine steel wool it should clean up without a brush effect after you polish it with a polishing compound. Although, if it where my engine, i make it have a brush effect.

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