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Chromium Metal: Chromic Oxide Reduced by Aluminium (Thermit)
Aluminium takes the oxygen from chromic oxide with so much heat that the chromium comes out molten. Thorpe (1912-13) gives Goldschmidt's thermit: chromic oxide mixed with aluminium powder in a magnesia-lined crucible, lit through a fuse of aluminium powder and barium peroxide with a magnesium ribbon. The heat carries the reaction through the whole charge, and carbon-free chromium sinks under a slag of alumina. White heat: outdoors on dry sand, face shield, stand well back.
The picture: chromium metal (Wikimedia Commons).
Advanced
1 day
Instructions
1
1
Line the crucible
Line the crucible
Line a refractory crucible with a paste of magnesia and water glass, and let it dry fully.
Tools needed:
Clay Crucible - Refractory
Magnesium Oxide
Water Glass (Sodium Silicate Solution)2
2
Mix the charge
Mix the charge
Weigh 150 g of dry chromic oxide and 50 g of aluminium powder, a little less than the 53 g the equation needs, and mix them intimately.
Materials for this step:
Chromic Oxide150 g
Aluminium Powder50 gTools needed:
Balance Scale
Mortar and Pestle3
3
Set the fuse
Set the fuse
Stand the crucible on dry sand outdoors and fill in the charge. On top put a small heap of aluminium powder mixed with barium peroxide, and push a strip of magnesium ribbon into it.
Materials for this step:
Aluminium Powder1 piece
Barium Peroxide1 piece
Magnesium Ribbon1 pieceTools needed:
Dry Sand Bucket4
4
Light it and stand back
Light it and stand back
Face shield on. Light the end of the ribbon and step well back. The fuse fires the charge and the reaction runs through it by its own heat.
Tools needed:
Lighter
Face Shield
Leather Gloves5
5
Break out the regulus
Break out the regulus
Let it cool completely. Break away the alumina slag on top and take out the button of chromium from the bottom. At most 103 g can form from 150 g of oxide.
Tools needed:
HammerLeather GlovesFace Shield
Glass Jars with LidsMaterials
4- 150 gPlaceholder
- 1 piecePlaceholder
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Tools Required
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