Sciencemadness Discussion Board

Melting fine bismuth powder

Foeskes - 16-8-2017 at 01:53

I recently got some bismuth subsalicylate pills, so I'm going to try to make bismuth metal again. A while back I used Mildred's method on making bismuth metal and got some fine bismuth powder. However if I try to melt it, it oxidizes. I am thinking of I way I can melt it without oxidizing the bismuth(I don't have a blow torch or any way of making a effective inert atmosphere). Maybe some kind of low melting point flux? Like boric acid or something?

MrHomeScientist - 16-8-2017 at 06:07

I had the same troubles and the same thought. The requirements for such a flux would be:
- Lower density than Bi
- Immiscible with molten Bi
- Melts well before Bi
- Remains molten to well above Bi's melting point

It's not a trivial problem (or at least, I couldn't find a good solution). Zinc chloride is almost perfect, except its melting point is 20C above Bi. You want the flux to melt well below Bi to head off the oxidization, whatever temperature that happens at. Inert atmosphere might be the way to go.

Elemental Phosphorus - 16-8-2017 at 06:14

You could probably melt it under heavy motor oil or gear oil, since motor oil boils at around 300 degrees Celsius, but bismuth melts at 270 degrees Celsius.

Foeskes - 16-8-2017 at 06:27

What about paraffin wax it boils at temperatures around 370 degrees C maybe it will boil and displace the oxygen in the crucible?
Boiling point from Wikipedia.

[Edited on 16-8-2017 by Foeskes]

elementcollector1 - 16-8-2017 at 08:06

Fluxes can be solid under some circumstances - we used graphite powder as an oxygen-excluding flux to melt tin and lead samples in the labs. As long as there's a decent layer of it over your sample, and it reacts with oxygen at elevated temperatures (scavenging oxygen away from the sample), your flux can still be in solid form at melting temperature.

unionised - 16-8-2017 at 09:15

If you are feeling brave, sodium hydroxide does the job.

Foeskes - 16-8-2017 at 14:41

Wouldn't graphite or charcoal contaminate the bismuth?

[Edited on 16-8-2017 by Foeskes]

VSEPR_VOID - 4-9-2017 at 00:10

Depending on the mineral oil, the boiling point is about 357C. The auto ignition temperature is 366C so there is the possibility it may catch fire. If this were to happen the vapors of oil in the room would also catch fire.

SWIM - 4-9-2017 at 07:42

Quote: Originally posted by Elemental Phosphorus  
You could probably melt it under heavy motor oil or gear oil, since motor oil boils at around 300 degrees Celsius, but bismuth melts at 270 degrees Celsius.

If it's that low melting, couldn't you just melt it under vacuum in some glassware?
Use a cheap or already messed up flask and just break it to get the sample out if you have to?

Or even just melt it sealed in evacuated tubes, like a big version of doing melting point tests in sealed evacuated capillary tubes?

Foeskes - 25-10-2017 at 17:04

I managed to melt it into small nuggets!
After trying the wax thing which failed, I decided to mix the oxide with a bunch of charcoal and heated it orange hot with a spiral butane torch(
After stirring the hot charcoal I noticed a red blob of metal and I quickly poured out the mix into the ceramic floor and got a nice 2.5 gram button of bismuth. Considering I used 20 524mg pills, I got a yield of ~41.67%. This is surprisingly higher than where I got the procedure from(nilered), maybe his method actually vaporized a bit of bismuth.

DionSukhram6 - 28-10-2017 at 13:13

I did the same experiment a few months ago. One thing that worked fairly well was just melting it in a steel crucible under boric acid with a stove or a torch. The one problem with it, depending on the scale of your experiment, is that if you don't have much metal powder it might just get stuck in the boric acid instead of forming a bead, especially if you don't get it hot enough. If you make a pretty good amount though it works fine, the metal comes together, and you can just break it out of the boron trioxide that forms from the boric acid. It might not be the best but it definitely is much safer than 300C mineral oil or molten NaOH