Crystal growing Inorganic Synthesis

Growing bismuth crystals and reducing bismuth(III) oxide

bismuth2Bismuth is very interesting stuff in two ways. Firstly for its ability to form amazing hopper crystals and secondly for its beatiful colours. The hoppering is due to ellectrical attraction which is higher along the outer edges and causes faster crystal growth at the edges than near the face centers. Its eyes-catching rainbow tinge isn’t real colour of elemental bismuth in fact. It’s is caused by thin layer of bismuth(III) oxide. Layers of different thickness reflects various colours of light spectrum and that causes the rainbow effect. The crystal was grown on copper wire because of its thermal conductivity and heat dissipation which causes crystalization of the bismuth. After several crystal growing procedures you will be getting more and more dross. You can either throw it away or try to recycle it. There are several reduction methods but I want to describe you one which is accesible for most of amateur chemists. These reactions were used in the reduction:

Bi2O3 + 6HCl → 2BiCl3 + 3H2O
BiCl3 + Al → AlCl3 + Bi
(There also occur some other reactions but they aren’t very important for us).

bismuth

Crystal growing procedure:
Needed equipment:

  • Crucible or steel laddle
  • Pliers
  • Piece of copper wire (about 5mm ∅)
  • Source of heat – a cooker is sufficient
  • And of course, a chunk of bismuth (NOTE: Purity of bismuth is crucial, recomended is 4N or higher).

Chunk of bismuth was placed into the crucible and heated. After all bismuth was molten, the fire was turned off. Then a piece of copper wire was mounted in the pliers and slightly immersed into the molten bismuth. After a while a crystal started forming on the wire. When almost all bismuth was solidified, the wire with crystal was removed from the rest of bismuth.

 Bismuth dross recyclation procedure:                                                                     Needed equipment:

  • Beaker
  • Hydrochloric acid (concetrated preferebly)
  • Crucible or steel laddle
  • Aluminium wool or foil
  • Press

Dross from crystal growing isn’t pure bismuth(III) oxide as it often contains bismuth, which, however can’t be easily separated from the oxide. As bismuth metal doesn’t react with hydrochloric acid, it would also avoid the bismuth(III) oxide to react because it covers the oxide. So the first step was heating the dross with a flame. That produced a yellow solid – bismuth(III) oxide with low amount of elemental bismuth. Then a little of hydrochloric acid was poured into the beaker and bismuth(III) oxide was added. Bismuth(III) oxide reacts with hydrochloric acid to form bismuth chloride and water. When the reaction stoped, there was still something undissolved. Hydrochloric acid was added once again. If this solid isn’t reacting at all, it is probably bismuth. This can be filtered out of the solution. An aluminium wool was then carefully added to the solution and that was followed by vigorous reaction. Bismuth powder has precipitated . Then it was simply filtered. The powder was let to dry out in dry air at room temperature.If the bismuth powder was heated it would oxidize back to bismuth(III) oxide, so it can’t be molten in this way. Instead, it was pressed and then molten.

NOTE: This procedure involves making a lot of gases thus must be done outdoors or in a fume hood.

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