Galavanting with Galena

1/18/13

Today Heather, Daniele and I got quite a bit of work done. Right off the bat Daniele decided that we should try and diffuse the sulfur through a new mineral. Just like the sphalerite, we would use another sulfide called galena. We spent a couple minutes looking for a galena chunk with a smooth surface. This is because since we are measuring how far the sulfur diffuses through the mineral and the sulfur only diffuses a very short distance, it is important that the mineral has a level surface. That way the data of the diffusion across the face of the mineral is consistent. After picking out a prime candidate, I quickly filled the capsule with sulfur and then hooked it up to the vacuum before sealing it. Here is a picture of the crazy goggles I have to wear to protect my eyes while sealing a capsule:

Luckily there were no flaming incidents and I made the capsule easily. Here is the finished product where you can see the furnaces in the background:

We put the capsule in a furnace at 300 degrees Celsius and then headed back to the lab to work with the galena. Since galena does not have the same crystal formation as the sphalerite, the minerals do not naturally cleave to have very smooth faces. As a result, Daniele, Heather and I decided to polish some of the minerals in order to achieve the necessary smooth surface for sulfur diffusion. To do this, we took little circular disks of metal and placed crystal fragments with a very low heat tolerance on the disks. We then placed the disks on a hot plate and melted the fragments into a sticky goo. Picking galena pieces of approximately the same width, we pushed them into the goo. After the disk was taken off the hot plate and the goo allowed to cool, the galena chunks would be held in place for polishing. We polished the mineral basically using strips of sandpaper. We started off with a very rough sandpaper to try to generally start smoothing the bumps in the galena chunks. We then used a smooth sandpaper to begin to work out the scratches. The sandpaper is shown below and I am holding one of the metal disks with the galena chunks on it:

After the sandpaper, we placed the disk in a machine, that sanded the disk back and forth across a mixture of a powder and tap water. The powder contained a special substance that had a even smaller grain to continue to smooth out the surface of the galena on an even tinier scale. While the machine was working, we made another capsule, this time containing our usual sphalerite. We decided to run this sphalerite trial at 750 degrees Celsius to see what results we would get from experimenting with sulfur diffusion at a higher temperature. After finishing the capsule and putting it in the furnace, my time was up and I had to leave before we could get some computer work done. Daniele has promised to show me the programming set-up next week which hopefully will go well.