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Rind of sputtering target.
An example of the element Aluminum

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Rind of sputtering target.
This is the first of several variations of this material I will be posting. Aluminum is widely used for sputtering, a process in which metal is vaporized off a target in a vacuum chamber and deposed in a thin layer on the surface of something else. For example the shiny layer in a CD or DVD disk is sputtered aluminum. To do this you need a sputtering target made of the material you want to deposit.
This very interesting piece of aluminum is scrap from the production of such a target. They started with a cylinder of very pure aluminum and, using tremendous pressure, squashed it down into a pancake about 2" thick and 18" in diameter. Then they sawed off (using a water jet) the outside rim of the pancake to leave a perfect disk. This piece is a slice of the rim that was cut off.
What's most remarkable about it is the strange bumpy ridged surface. I assumed at first it must be formed by some sort of electrodeposition process, as are many bumpy surfaces you'll see typically on raw high-purity metals. But in fact it is formed in a purely mechanical process as the disk is pressed down. There must be internal crystal structures that are sliding and a bumping into each other in way that creates this surface. I will be posting more variations of this material, including a full disk before the rind was cut off, which will show in more detail the strange ridges you see on closer examination.
Source: eBay seller mrj33
Contributor: Theodore Gray
Acquired: 8 December, 2007
Text Updated: 8 December, 2007
Price: $40
Size: 5"
Purity: 99.9996%
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