Neme - 7-10-2017 at 09:43
Hello guys,
I prepared some (cca 200g) of very fine bismuth powder by zinc/HCl reduction. When I try to melt it in my ghetto conditions it start oxidizing in air.
I need advice with way to reduce it when melting. I have some ideas:
1) Adding little bit charcoal, but I'm afraid it would contaminate the metal.
2) Adding oxalic acid, it decomposes to carbon monoxide which I think should reduce it.
3) Blowing hydrogen gas, but I'm afraid of this scenario.
If you have better idea please tell me, if not, tell me which one of these is best.
SWIM - 7-10-2017 at 09:52
There was a post covering melting bismuth, and appropriate fluxes to use, last month.
I think they decided that using the search engine was the best way to melt bismuth powder without crowding up the board with redundant posts.
(just do a search for 'melting bismuth'.)
[Edited on 7-10-2017 by SWIM]
crystal grower - 7-10-2017 at 10:20
I had the same problem when I was trying to make crystals from bismuth powder.
Ideal would be a hydrogen atmosphere but I'm not sure if you can afford it 
.
Anyway, you need to compress the powder as much as possible, put it into the crucible and then pour a little of paraffin wax on the top of it. Cover
it with some lid and carefully heat it up.
When it is cooled down, you can easily separate the paraffin layer from the bismuth.
[Edited on 7-10-2017 by crystal grower]
Foeskes - 11-10-2017 at 05:12
Try adding paraffin wax(a little bit of it) and the close the crucible redirect the vent hole of the crucible away from you and torch until the
crucible is red hot, be careful as the wax vapor will catch fire outside the crucible.
I have not tried this with bismuth, but I did try it with lead which has a somewhat similar melting point.
Edit: looks like lead melts at almost 100 degrees more than bismuth.
[Edited on 11-10-2017 by Foeskes]
ninhydric1 - 11-10-2017 at 07:48
If you have a hot enough blowtorch, the oxide can be easily converted back to the bismuth metal with VERY strong heating. It will take time though so
be patient.