Sunday, February 17, 2008

Melt techniques used to produce synthetic alexandrite

Today the Czochralski pulled-growth method is used to make synthetic alexandrite.

The ingredient powders are melted in a platinum, iridium, graphite, or ceramic crucible. A seed crystal is attached to one end of a rotating rod and the rod is lowered into the crucible until the seed just touches the melt. The rod is then slowly withdrawn. The crystal grows as the seed pulls materials from the melt, and the material cools and solidifies.

Owing to the surface tension of the melt, the crystal stays in contact with the molten material and continues to grow until the melt is depleted. Crystals formed with this method can be very large, -- more than 50 millimetres in diameter and one metre in length with a high degree of purity.

Although Czochralski pulled boules are much more expensive than flame fusion boules to produce, their cost is still a fraction of the natural materials that they imitate.

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