  Zone-refined single crystal.
This is a remarkable object: A bar of pure tungsten that has been zone refined into a single monolithic crystal. As a single crystal, its density should be almost exactly equal to the theoretical maximum density of tungsten, which is not easy to achieve. The bar was created in a large vacuum electron beam furnace by carefully moving a molten zone from one end of the bar to the other, allowing the material to cool at a rate that allows it to align itself to a single, consistent crystal axis from one end of the bar to the other. Zone refining also tends to chase impurities to the end of the bar, resulting in higher purity over the rest of it: To what extent this effect has been utilized to purify this bar I don't know, nor do know the exact purity, but it must be quite high to achieve single-crystal status. Exactly how zone refining is done in tungsten I don't know, but I'd sure like to see it done some day.
This piece is only about an inch long, but I've got another five inches of it that I plan to get polished and beautified one of these days. No, it's not for sale.
Source: Ivan Timokhin
Contributor: Theodore Gray
Acquired: 10 May, 2006
Text Updated: 7 January, 2007
Price: $100
Size: 1"
Purity: >99.99%
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