Verneuil process

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Simplified process scheme of the Verneuil process, the crystal growth takes place on the red marked “cultivation pear”

The Verneuil process is a crucible-free flame melting process for the production of synthetic gemstones that was published in 1902 by the French chemist Auguste Verneuil . Today, the Verneuil process is used to manufacture sapphire glass from synthetic sapphire , originally the process was developed for ruby synthesis .

Synthetic corundum using the Verneuil process

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A metering device contains a high-purity powdery material that is melted in the burner tube of a kiln with hydrogen and oxygen and solidified layer by layer on a crystal nucleus. While the crystal in the form of a so-called “cultivation pear” grows by around 5–20 mm per hour, it is slowly moved downwards using a lowering device so that it remains in the ideal burning zone of the furnace. In industrial plants, a large number of such devices are usually arranged (even 1000 and more). The crystals grown with the Verneuil process are essentially pear-shaped and about 20 to 50 mm in size.

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