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Saturday, November 12, 2016

Bismuth and My Key to the Amazing World of Crystals

Bismuth is quite an overlooked element in comparison to some like iron and gold. Although it may not be used in everyday life as commonly as iron, and although it may not be as beautiful as gold, it's properties are where it's magic is held.

Last Saturday, I did an interesting experiment that sparked my interest about this element. The theory behind it is the fact that bismuth has an extremely low melting point for a metal at 271.4 degrees Celsius and when it oxidizes it creates really amazing colors.

This is the one I made on Saturday, but the liquid took the shape of the soup ladle rather than the shape of the crystal it makes

I originally got the idea to make this from a YouTube video created by nighthawkinlight who creates several DIY videos. However, it wasn't until later that I realized how interesting crystals actually are. 

A crystal by definition is a solid structure that is made up of a repeating geometric pattern. This pattern is called a crystal lattice or a lattice structure. This is the most stable form of ionic compounds, but crystals can also be formed by covalently bonded molecules when all the molecules share their electrons. Common crystals that you see in every day life include ice, snow, minerals, sand and much more. In fact, 90% of solids are crystalline. 

I started off with my experiment by purchasing 100 grams of bismuth off of for about 6 dollars. Although this is quite an expensive rate, the product is worth it. Utilizing its low melting point, I created a molten form of the metal using a soup pot as a crucible. Then I poured the pure molten metal into a soup ladle leaving the impurities behind. As the molten metal cools, it is exposed to the oxygen in the air. By letting it cool, you can create something similar to the picture above. 

However, I wanted to create a full crystal though; not just a mold of the bottom of a soup ladle. This is when I found something called the Czochralski process, and I used it to redo this experiment a few hours ago.

The Czochralski process is one used by the industrial manufacturing of silicon wafers for semiconductors. The process is defined by taking a seed crystal and dipping it into the molten metal until crystal starts forming around it. Then the crystal is slowly taken out as the crystal continues to grow around it. This creates a long crystal.  A seed crystal is a part of the solid crystal that you are trying to create that speeds up the reaction decreasing its kinetics, because the base of the crystal doesn't have to be formed based on random molecular movement. I will leave a link for a further explanation of the idea of a seed crystal at the bottom of this post. 

However, the process of putting the seed crystal into the molten metal while both accounting for the thermal gradient(the idea that you don't want the seed crystal to melt on contact with the hot liquid metal) and the fact that you have to have some way to draw out the seed crystal slowly. In order to solve this, I froze the seed crystal for a few minutes. Then I used a piece of clay that I wedged the seed crystal into. This was my apparatus to slowly draw the crystal out with. Other things that could work include a hot glue gun stick but an iron rod would work best due to the similar crystalline structure between iron and bismuth. 

This process can be used for any metal that can form a crystal, so I decided to try it with the the bismuth. Below shows my attempt. It created a very small crystal, but it's still a start. I could have created a better crystal, but the bismuth cooled very quickly when I poured it into to the soup ladle. I still got the crystal to form around the seed crystal, but the surrounding metal cooled forming a separate crystal that stuck to the soup ladle. 

Crystal that grew off of the seed 

Crystal that stuck to the soup ladle
I may repeat this experiment in the future using a greater amount of bismuth, better equipment, and now a better understanding on how to create a larger crystal based on the mistakes that I made this time. I highly recommend you guys at home trying this same experiment because actually getting to see the melting and cooling, and see the different oxidized layers is something that is much more valuable that simply watching a video or reading an article. I will leave links of all the videos I watched and sources I read so you can get a better understanding of the process that is going on before you conduct the experiment. Good luck and I hope that you end up with some good crystals.

Nighthawkinlight video: "How to Make Bismuth Crystals"

Explanation of seed crystals:

Czochralski process:

Other sources:

Note: I would personally recommend not using any utensils in this experiment that you intend on using later on, because once the bismuth cools on something, it will most likely never come off and never be clean again. Also, you may want to wear gloves whenot dealing with the molten metal so you don't burn yourself if you mess up!

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