Element Collection

Element Collection

Sunday, May 2, 2010

Experiment: Growing Bismuth Crystals

In this experiment, I'll be growing beautiful iridescent crystals out of pure bismuth metal. These "hopper crystals," as they are known, form completely naturally as molten bismuth cools and solidifies. They aren't found in nature, however, because of the specific circumstances required to make them. People make these in labs and sell some pretty amazing samples on eBay. The process is very simple, and is easy for anyone to do at home.
Bismuth melts at 521 degrees F, so it can be melted on a stove top. As the metal cools from its liquid state, it forms almost perfectly square crystals in a sort of spiraling stair-step pattern. When exposed to air, it immediately tarnishes and forms a very thin layer of oxide. Different thicknesses of this layer reflect light differently and form a beautiful pattern of rainbow colors. To make large single crystals, the metal must be cooled very slowly to give them time to form. To get the best quality crystals with the most colors, very high purity bismuth must be used. I used 99.99% pure bismuth here, but I also have some 99.9999% pure electronics grade stuff that was very generously donated by a coworker. I'm waiting to use this until I perfect my method of cooling and crystal extraction.

This experiment is very simple to do. First, I melted my bismuth by setting my stove top on high. Then, I poured the molten metal into a different, clean container. This eliminates all of the slag that forms on the surface of the metal, and the clean container allows for better crystal growth. Next, I suspended a seed crystal of bismuth in the center of the molten mass. This step allows the crystal to grow unobstructed in all directions, without running into other crystals or the sides of the container, and should result in a larger crystal. If I time it right, this should also allow me to pull the crystal directly out without having to pry it off of anything. Next, I waited until the metal was about halfway cooled. This was hard to gauge, because you don't want to disturb the metal too much while crystals are growing. If you do this, it causes new crystals to start forming rather than continuing to grow a single large one. I tested it by gently tapping the surface with a graphite rod. Once it was half liquid and half solid, I poured off the liquid into another container. The solid contains my newly formed bismuth crystals, which tarnish in air immediately to form the characteristic iridescent sheen.











My melting setup was a small pot on the stove top, with a smaller steel cup inside that actually contained the metal to melt. I did this because the smaller container would make a deeper pool of metal to grow the crystals in. I used about 100g of bismuth.










This is my method for suspending a seed crystal in the metal. I melted a small piece of solid bismuth onto the end of the green copper wire, which will be hung down into the molten metal.


















After the bismuth was fully melted, I poured it into a new, clean container and suspended my seed crystal so it would hang just below the surface of the metal. I turned the stove off and let it cool. This allows for some temperature control, as the heating element cools slowly on its own. I could get better control if I dialed it down slowly myself, which I'll do in future tests. I waited until it was halfway solidified, and poured off the liquid.










The cup on the left holds the liquid I poured off, and the one on the right contains my crystals. I waited just slightly too long, so my central crystal that grew from the seed was attached to the bottom.


















Top and bottom views of my solidified bismuth after knocking it out of the container. All the metal in this picture (except for the copper wire) is pure bismuth. You can see the crystals locked together in the top picture, which I had to pry apart from each other. This is easy to do, because bismuth is very similar to lead and so is soft enough to bend and snap apart easily. This must be done carefully though, to not damage the crystals or scratch the thin oxide layer. The bottom of this piece showed some really beautiful crystal structure and colors as well.









The final product - my bismuth metal crystals. Click the picture for a much larger view so you can really see the details. They were only each about the size of my thumbnail, but that's only because I used a small amount of metal and there wasn't a lot of room or time to grow. Not too bad for only my third try at this!

24 comments:

  1. OMG i did it and it turnd out sooooo sick

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  2. I'll be trying this out soon! This may be a silly question, but can we reuse the pans used for this experiment back for cooking?

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    1. Pardon me but It is a silly question. Use old pots, get something from a charity shop or find something that will do the job. Why would you use good cooking pots for this? I have several pots that are rarely used so I sacrificed one for this, it works fine and I'm now refining my technique. Good luck with it though.

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  3. @ Ketski:
    Well, bismuth and its oxides (formed when heated) are totally nontoxic so that's probably fine. Personally though, I never mix chemistry and food. Anything that goes in the lab stays there. I bought a pan specially for this experiment - IMO it's better to spend a few extra bucks on a pan and be better off safe than sorry. Good luck with this!

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  4. Where do you get the bismuth from ? Do you get this in hardware stores ?

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  5. @Anonymous:
    I bought mine on eBay for about $30/lb, things like that pop up occasionally. You probably won't find it at local stores, although I have heard of "environmentally friendly" bullets made of bismuth instead of lead. Those probably aren't very high purity though.

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  6. Once crystalized, can you melt it back to metal and try again or is it changed forever?

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    1. You can melt it. Bismuth is always in crystaline form, but in bars you don't see them. They are all fused together.

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  7. www.bismuthguy.com

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  8. Have you ever seen the bismuth crystals for perfect triangles, instead of the typical square step pattern? I bought a pound of Bismuth, and the second time I melted it down, the crystals didn't oxidize or tarnish. They remained a shiny platinum-like color/finish. Also, ALL the crystals that time formed only triangles, there wasn't a single right angle anywhere. Since then, I've tried to find some kind of mention of triangle bismuth crystals online, and haven't found anything. Anyone ever seen this happen?

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    1. I've never seen the triangle formations before; if you have pictures I'd love to see them. The lack of color is an interesting subject, actually! Normally to make Bi crystals oxide-free, the melting must be done in an oxygen-free environment like a glove box. However, I have a friend on YouTube that was somehow making silvery bismuth in open air. It was quite a mystery for a while, until he sent a sample in to a university to get it analyzed. Turns out there was a significant impurity of tin alloyed in, which apparently impedes oxide layer formation. Pretty neat, and I really didn't expect that. His name on YouTube is hkparker and he's got some great videos, check him out!

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    2. Thanks for the clear and fantastic way you've set this out! I have a question based on the following: I've been doing the same as you, trying to grow bismuth crystals. Each time I made a molten pot of metal I scraped of the molten slag, as I had seen done on YouTube, and then binned the said slag. The first crystals I made were shades of blue, purple and reddish colours. When I didn't like a crystal I would re-melt it and start again, scraping off any slag which formed. Each crystal had a different colour, up until a point when the molten metal produced silver crystals with no colour whatsoever, which is irritating since the colours are half the beauties of the crystals. Any ideas as to why the metal stopped producing coloured crystals? If you have a reason, and a solution then that would be great. In anticipation of whatever wise words you can give me, thanks for the help!

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    3. The only thing I can think of is that each time you melt it, it picks up impurities from the container. Some of these are removed when taking away the oxide layer, but it looks like enough remain to start messing with the color of your crystals. That's just my hypothesis, though. The higher the purity, the better the colors - my 6N grade semiconductor bismuth produces beautiful reds and golds, while the 4N from eBay shifts more towards blues and greens.

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  9. Hi, thanks for posting. Just yesterday i had fun growing homemade Bismuth crystals. It was fun and rewarding by experimenting , the crystals now are bigger about half inch. the tricky part for me is slowing the cooling process and figuring out when to pour out the excessive molten (for my ladle now its about 30 to 60 seconds). any idea on delaying cooling process to get bigger crystals?

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  10. Hi. Thanks a lot for this complete and clear explanations. Just with the spirit of contributing to general knoledge, I woul like to point out that bismuth crystals do appear in nature. There are a sort of egg-shaped rocks called "geodes" that are formed from molten material expelled from volcanoes. When the surface cools down, it forms a crust that isolates the inner semi-molten material. Then, this stuff cools down very slowly, an so conditions for crystal growing are provided. I´ve seen pictures of geodes from Ehiopia with the inner space filled with beatifuly shaped and colored bismuth crystals (http://imgur.com/RdMJZnM). Again, I only adding informtion to your valuable blog. Best regards

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  11. Fantastic blog.... Thank you for giving all those valuable little details... Actually I am at a Chemistry camp and I want to demonstrate Crystal Growing to my kids here. Could you give me a rough estimate of how long it took you for the entire process?
    I have some Bi from the lab... 99% pure. Will that work?

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    1. Sounds like fun! From start to finish this probably took me 45 minutes, but you can cut that way down to probably 10 minutes for a demonstration. You don't even need the fancy seed crystal setup - I've made plenty of good quality crystals by just melting in a container (takes under 5 minutes with a good heat source), waiting a few minutes, then pouring off the liquid. It takes some practice to know when to pour, since you can't tell how solidified it is without disturbing it, and disturbing it disrupts large crystals from forming! Slow cooling, an undisturbed melt, and high purity all lead to large, well-formed crystals. 99% should work fine. In my experience, higher purity leads to richer colors, too.

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  12. Hi Dan- Thanks for your publication. I'm interested in using this beautiful metal for jewelry. But due to it's fragile nature, it would require some stabilization, and wonder if you have any suggestions. Perhaps a clear coating of some kind.
    Also, have you heard of PMC (precious metal clay)? It's clay made from particles of various metal suspended in clay that is burned off in a kiln, leaving just the metal you've formed as desired. The bronze clay requires firing in an oxy free environ, and this is done in a fire proof container filled with cocoanut fiber inside a programmable kiln. The ramping times and temps can be precisley controlled. I was wondering if this might offer some advantages for forming bizmuth crystals. Have you seen this done? I'd love to hear your thoughts on this.
    Thanks for sharing your experience! MSquid

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    1. Hi,
      I think a resin clear coat would be a good idea. I've seen someone selling Bi jewelry on Etsy which are pretty spectacular looking. It doesn't look like he does anything extra to strengthen them, but it's possible there's a clear coat. You may also be able to alloy it with a very small percentage of antimony to increase strength, similar to what they do for lead. You'd have to experiment to see where the upper limit is before color or crystal structure are impacted.

      I have heard of PMC and did a little reading on it a while back. It sounds really interesting for sure. I'd be surprised if it could keep fine details, though, since surely it has to collapse and wrinkle a bit when the clay burns off. That sort of thing probably wouldn't work for bismuth, because the crystals need to grow out of the melt. Otherwise it's just a bunch of small particles that get sintered together, so there's no chance for crystals to grow. Its low melting point would probably also not be comparable with the clay process. Just speculation, though.

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  13. Hi,
    I have been searching the net about perfect crystals...ie bravais lattices,..crystals which have a perfect ordered structure.they exist in theory afaik but I do read about crystals grown in space and things like that, my question is :has anyone grown a perfect single crystal of a metal like steel or alumunium?if such a thing is possible ...what would be the properties of such a piece.?would it have better strength durablity etc?

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  14. This is amazing! I would like to try it but I have a couple of questions.
    1) Would I be overpaying if I get my Bi from sigma-aldrich (https://www.sigmaaldrich.com/catalog/product/aldrich/95372) that's $52 for 100g as opposed to getting it from ebay?
    2) How do you get your crystal seed exactly?

    Thanks!

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  15. Best place to purchase Bi is www.boltonmetalproducts.com

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  16. Guys check out rotometals for buying the bismuth. Ill be buying some this coming week. Best prices I've found, great reviews, and 99.99 % bismuth...perfect for growing crystals i think.

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