grg99
asked on
Shiny aluminum foil??
If you've read "The straight dope" series of books, in one of them they explain how and why aluminum foil is shiny on one side and satiny on the other side. But that's not the question here. What I want to know is: Whenever I see bare aluminum, it's usually not shiny. The books say this is because aluminum tarnishes very very quickly-- you can scratch it, and the scratch is shiny for just a few seconds. Airplanes, at least those that are not painted, are usually shined up with some special abrasive and wax compound-- the abrasive removes the tarnish (aluminum oxide Id guess), at the same time the wax quickly covers up the shiny aluminum and prevents immediate tarnishing. You can even buy this polish in many stores, although it's rarely used-- we're just used to screen doors and windows being a dull color. BTW aluminum can take a MARVELOUS shine.
But that's all just background. The real question is: how does the shiny side of the foil STAY shiny? it's probably not a wax-- you can dig up old foil from campgrounds that is still shiny after I'd assume a few years out in the wet world. And a wax would make an ungodly smell in the oven and contaminate the food too. So that seems to rule out waxes, oils, lacquers, etc.... I wonder how it's done, and also why we don't see the same process done to other aluminum items?
Not of earth-shaking importance, but the question popped into my head while I was driving and it really startled me. Almost hit the brake.
But that's all just background. The real question is: how does the shiny side of the foil STAY shiny? it's probably not a wax-- you can dig up old foil from campgrounds that is still shiny after I'd assume a few years out in the wet world. And a wax would make an ungodly smell in the oven and contaminate the food too. So that seems to rule out waxes, oils, lacquers, etc.... I wonder how it's done, and also why we don't see the same process done to other aluminum items?
Not of earth-shaking importance, but the question popped into my head while I was driving and it really startled me. Almost hit the brake.
ASKER
Bzzzt! Nice try, but wrongo, at least for "Reynold's Wrap". Duralumin is mainly used where strength is required. It's rather expensive as it has to be heat-treated. And it still doesnt explain the shinyness, IIRC duralumin can get mighty gray too. The straight info
from Reynold's wrap:
In 1919, the U.S. Foil Company, parent of Reynolds Metals Company was founded in Louisville, Kentucky to produce lead and tin foil. Then in 1926, the company entered the aluminum business, rolling aluminum foil for packaging. Today, Reynolds Wrap is made from 8111 alloy aluminum, at the thickest gauge specifications available in the marketplace. Reynolds Wrap® Aluminum Foil is 98.5% aluminum. The balance is primarily iron and silicon. These are added to give the strength and puncture resistance obtained only in the alloy used in Reynolds Wrap® Aluminum Foil.
And Duralumin:
DURALUMIN:(doorăl´yem
from Reynold's wrap:
In 1919, the U.S. Foil Company, parent of Reynolds Metals Company was founded in Louisville, Kentucky to produce lead and tin foil. Then in 1926, the company entered the aluminum business, rolling aluminum foil for packaging. Today, Reynolds Wrap is made from 8111 alloy aluminum, at the thickest gauge specifications available in the marketplace. Reynolds Wrap® Aluminum Foil is 98.5% aluminum. The balance is primarily iron and silicon. These are added to give the strength and puncture resistance obtained only in the alloy used in Reynolds Wrap® Aluminum Foil.
And Duralumin:
DURALUMIN:(doorăl´yem
>>> So that seems to rule out waxes, oils, lacquers
Just because you cant smell a trace of such material, instead soaking up the aroma of tomato sauce, or broccoli, or whatever, doesn't mean its not there.
The aluminium foil is made by passing a slab through press rollers and continuously decreasing the thickness of it until the final thickness. But on the final pass, the sheet of material is doubled, passing two layers through the final press simultaneously, and the shiny side is the roller side, the matte side is where the two sheets were in contact.
Mineral oil is used to lubricate the contact between the foil and presses during production, but most of the oil is 'burned off' as all that heat is released from pressing the metal. A trace layer MAY remain, perhaps enough to keep it protected evenly? For the most part, shiny is just due to the press surface, dull due to the other surface being the other aluminum sheet, so any metal oxidation after that should still affect both dull and shiny sides equally, so perhaps the alloy composition used primarily for durability has a side-effect of being more resistant to oxidation over time as well?
Just because you cant smell a trace of such material, instead soaking up the aroma of tomato sauce, or broccoli, or whatever, doesn't mean its not there.
The aluminium foil is made by passing a slab through press rollers and continuously decreasing the thickness of it until the final thickness. But on the final pass, the sheet of material is doubled, passing two layers through the final press simultaneously, and the shiny side is the roller side, the matte side is where the two sheets were in contact.
Mineral oil is used to lubricate the contact between the foil and presses during production, but most of the oil is 'burned off' as all that heat is released from pressing the metal. A trace layer MAY remain, perhaps enough to keep it protected evenly? For the most part, shiny is just due to the press surface, dull due to the other surface being the other aluminum sheet, so any metal oxidation after that should still affect both dull and shiny sides equally, so perhaps the alloy composition used primarily for durability has a side-effect of being more resistant to oxidation over time as well?
grg99, Since you asked about aircraft bodies, I told Duralumin.
The reason for shiny may be..
Galvanizing.. generally done for Iron, (coating of Zn), but may be a similar thing for Al??
The reason for shiny may be..
Galvanizing.. generally done for Iron, (coating of Zn), but may be a similar thing for Al??
Alinimium tarnishes as it forms an almost invisible layer of aluminium oxide on it but this then protects the rest of the metal from tarnishing, thus it aways seems shiny if it has been polished. The shiny side of foil (which is dues to the production process) will in time become very slightly less shiny over time. If you have "aliminium" and it goes dull then it is not aluminium but probably an alloy, eg toy cars)
sorry "aluminum" not "aliminium or alinimium "
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aluminium oxide is also known as sapphire.
Also as Alumina ?
ASKER
So I can give my wife a sapphire ring with a chunk of burnt aluminum?
aluminium oxide has many differnt forms saphirre and rubies being a crystaline one. Carbon also has differnt forms, diamond being one.
You can probably shine it up even better by chewing on it, how about give that a try?
Aluminium is also having a special property.. Once it develops the Al2O3 (Aluminium Oxide) layer, then it will not react with most of the chemicals, including highly concentrated acids. So aluminium is used to store and transport acids in chemical laboratories.
ASKER
>So aluminium is used to store and transport acids in chemical laboratories.
Must be a rather limited feature, as ordinary ketchup can dissolve aluminum foil, as anyone that has wrapped a meat-loaf in foil can attest to. Ketchup is a mild acid.
Also spray oven cleaners eat through aluminum foil. They're composed mostly of lye and lemon-scent I think.
Must be a rather limited feature, as ordinary ketchup can dissolve aluminum foil, as anyone that has wrapped a meat-loaf in foil can attest to. Ketchup is a mild acid.
Also spray oven cleaners eat through aluminum foil. They're composed mostly of lye and lemon-scent I think.
See this webpage (scroll down to the specifications table):
http://www.metalagencies.com/aluminium_houshold_use.htm
http://www.metalagencies.com/aluminium_houshold_use.htm
A chemist came back to his car one night, found a layer of ice on his windshield, and realized he had no scraper. "No problem," he thought, there's an aluminum can." Knowing that they're made of pure aluminum and that the Rockwell hardness of aluminum is considerably less than that of glass, he proceded to scrape the ice from his windshield with the bottom of the can. The next morning, after the melt, he found scratches all over his windshield. Why?
It seems he neglected the fact that aluminum oxide has a Rockwell hardness greater than that of glass.
It seems he neglected the fact that aluminum oxide has a Rockwell hardness greater than that of glass.
That is DURALUMIN .. an alloy containing Aluminium
Bye
---
Harish