bismuth

[hermanntrude]

Another thread made me think about bismuth. I spent some time researching the stuff and came up with a few facts that surprised me:

 

• bismuth is a metal but forms amazing cubic crystals
  
• bismuth has a low melting point, and can be crystallised at home using a stove-top
  
• bismuth, weirdly, is non-toxic, despite the fact it's next to polonium and lead
  
• bismuth is the largest atom which is (to normal extents and purposes) not radioactive
  
• bismuth expands upon freezing, just like water does
  
• bismuth is the most diamagnetic naturally occuring substance
  

 

The last point on my list made me think about a demonstration i had seen involving a grape and a set of neodymium magnets. It was intended to show that the water in the grape is diamagnetic. I figured if it worked with water it'd work a lot better with bismuth, so I got my lump of bismuth from home and attached it to a pencil, attached a counterweight to the other end, and hung the whole thing from a string on a retort stand. Then I allowed it to come to equilibrium and then approached the bismuth with a set of neodymium magnets. Lo and behold it was noticeably repelled by either pole of the magnets.

[hermanntrude]

look what i found :

 

LINK

 

phwoar!

[frosch45]

http://www.matchrockets.com/ether/diabislev.html

 

Basic, neat link about this.

[Externet]

Questions about these bismuth 'levitators'...

 

Does the thickness or mass of the bismuth affects the amount of repulsion ?

 

Can the same effect be achieved making the bismuth be the one floating above a magnet ?

 

[hermanntrude]

what kind of crucible would you use to melt bismuth in? steel? copper? porcelain (expensive)?

[John Cuthber]

I used an old tin can last time I did it (not expensive).

[hermanntrude]

I used an old tin can last time I did it (not expensive).

 

it doesnt react or melt or cause crystallisation to not work properly in any way?

[John Cuthber]

It worked fine. I think that if the can had been perfectly clean there might have been a problem with the molten Bi dissolving the Fe, but I burned the paint off the tin with a blowtorch so the Bi was in contact with iron oxide which is relatively inert.

Also I was casting 2 lumps of bismuth for a magnetic levitation experiment- I wasn't bothered about great purity.

[Robin Hood]

Here's a woman who loves bismuth (and a few facts about it!)

 

[John Cuthber]

A few facts and the non-fact that Bi isn't radioactive.

[hermanntrude]

Apparently it is, but so slightly that it hardly counts

[qlue]

Isn't all matter technically radioactive?

[John Cuthber]

I'm not sure; has proton decay been observed yet?

[Gilded]

I'm not sure; has proton decay been observed yet?

 

No. According to current results they would have to have a half-life of at least 10^35 years if they decay at all.

[hermanntrude]

OK so i now have my pound of bismuth. I want to crystallise it for myself, but i'm not totally sure what kind of crucible to use, or whether I can use something cheaper.

 

An interesting thing that i've discovered is that my original sample (which belonged to someone else and was already crystallized in that pretty form we all know and recognise) was diamagnetic. When I strung it up on a beam with a counterweight I could visibly repel it with either end of a neodymium magnet. My new sample (which appears to have been simply cooled in a mould and doesnt have the same structure at all), however, seems to be paramagnetic or some other form of attractive magnetism. I wonder if the diamagnetism will come back when I crystallise it?

[emcelhannon]

The bismuth should be diamagnetic regardless of it's form. The crystal structure is still there. It's just filled all the way in. Let your lump sit in hydrochloric acid for a couple of hours, (maybe add a litte h2o2) and you'll see the crystalization patterns that look something like the Widmanstätten patterns on iron/nickle meteorites.

The diagmagnetic properties are very weak compared to magnetism. If you have even small impurities of paramagnet elements, it would overwhelm the diamagetic.

[hermanntrude]

nevertheless, according to the rules taught in first year degree courses, bismuth, due to its three unpaired electrons, should be para, not diamagnetic.

[emcelhannon]

Is it?

[hermanntrude]

Is it?

 

did you read the thread or anything about bismuth?

 

Most sources quote that bismuth is remarkably diamagnetic, and I (not uniquely) have shown it to be true using a torsional balance, but I have also noticed that when it isn't in the crystalline form which is so well known for being beautiful, it seems to exhibit paramagnetism.

[John Cuthber]

How did you get it amorphous?

That's usually a real pig of a problem with metals.

[emcelhannon]

How did you get it amorphous?

That's usually a real pig of a problem with metals.

 

I wasn't aware it was possible. I've made a few chess sets with bismuth, and every piece has revealed it's crystaline structure, when soaked in hcl.. Those that I cool slowly have larger crystals. Those I allow to cool quickly showed small, grain-like structure.

I've never witnessed or heard of bismuth being paramagnetic. I'd like to know how you pulled that off.

[hermanntrude]

that's what's weird, though... it's supposed to be paramagnetic, because it has unpaired electrons. however no-one seems to be able to explain why they teach one thing to the students and ignore the complete opposite in nature.

 

I might be mistaken about the paramagnetism in my experiment... it's not a foolproof experiment, i'm sure, but that's the way it seems.

[John Cuthber]

The diamagnetism of Bi is pretty small. Some rust mixed into it might give a product that was paramagnetic overall.

It is possible to make non-crystaline metals

http://en.wikipedia.org/wiki/Amorphous_metal

but it usually takes some serious deliberate effort.

[hermanntrude]

The diamagnetism of Bi is pretty small. Some rust mixed into it might give a product that was paramagnetic overall.

It is possible to make non-crystaline metals

http://en.wikipedia.org/wiki/Amorphous_metal

but it usually takes some serious deliberate effort.

 

OK let me explain my reasoning just so you don't think i'm crazy:

 

I recrystallised some 99.99% pure bismuth to get some pretty pieces to show off.

 

I also wanted to demonstrate diamagnetism to my students so I hung a skewer from a retort stand, by a string tied around its middle. I then attached a counterweight (clay) to one end and a lump of bismuth to the other. Because I figured it didn't matter if it was particularly pretty, so I used a crappy piece from the edge of the dish. When I approached it with a magnet it was attracted to it. I then repeated the experiment using a better-looking crystal, and this time it was repelled.

[emcelhannon]

My guess

The magnet is pulling on the skewer.

The second crystal is prettier because it's more ornate, and probably larger, so your magnet doesn't need to get close enough to the skewer to attract it.

 

What do you think?