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3D3DZone refined niobium bar.
From the source:
This is a piece of niobium bar that was zone refined using an electron beam-the metal is heated equally around its circumference in a small band, melting one short area of the bar, and the molten zone is moved along the bar to segregate impurities to one end. Imagine shaking up a container with oil and water, and letting the less-dense oil float up to the top- it is a similar effect, though not necessarily because of density. This is an excellent process for increasing the purity of metals and some other materials, except that it is quite expensive--it requires a high vacuum chamber which must be "baked out" before use to remove moisture and other volatile chemicals, and then the zone refining itself is a slow process which is very delicate and tricky to do just right, resulting in a very small amount of finished material. This sample was zone refined along a short length of it, and was intended to be sliced lengthwise, polished, and etched in a special mixture of acids to view the difference in internal microstructure between the raw bar and the zone-refined section, though this piece was not actually prepared except for the initial slices.

Source: Ethan Currens
Contributor: Theodore Gray
Acquired: 27 December, 2008
Text Updated: 17 March, 2009
Price: Anonymous
Size: 1.5"
Purity: >99.99%