When I was growing a single crystal recently, I found that the flux Sn residue on the surface of the single crystal was very serious. I repeated centrifugation, but it still didn't seem to work. I then soaked the single crystal with dilute hydrochloric acid (10%), but the single crystal is corroded. I think I should further improve the crystal growth process, so I wonder if there is any special way to overcome flux residue during crystal centrifugation. If you know, please let me know, thanks a lot.
Add some acid like Nitric acid and water (1:1) to the crystal and kept in a ultrasonicate, if that does not work, then heat it to 50 degrees. This should be repeated until the flux is peeled off.
Hi Ziming Wu
There are certain ways to minimize the flux on the surface of crystals.
1. Removing the flux at a little higher temperature. For example, you are using the Sn flux (melting point 231 C), so remove flux at 500-550 C followed by centrifuge at sufficiently higher rpm (~2000-3000 rpm is good).
2. Decrease the flux quantity.
3. Slowing down the crystallization process can also help in getting a good-quality crystal.
4. After centrifuge, use the dil HCl solution and sonication for a few minutes followed by sonication with ethanol/acetone. Repeat the process 3-5 times. The first sonication in dil HCl solution is a test rxn, to check whether it is affecting your crystals or not.
5. The SnCl2 is a white-colored compound. So you can stop the sonication with dil HCl when you observe when there is no change in a color beyond which HCl will start to attack the crystal itself.
For crystal growth, you may also refer to the following article as well.
The metal flux: A preparative tool for the exploration of intermetallic compounds
Hoping this will help.
Cheers
Dear Ziming Wu thanks for posting this interesting technical question on RG. As an organometallic chemist I'm unfortunately not an expert in this field of research. However, I full agree with the previous expert answers. I assume that you just need to be rather quick with the centrifugation process. Personally I would hesitate to clean the crystals with acids because this bears the risk that the crystals are damaged. For some basic information about this issue it might be worth having a look at the following potentially useful article:
Growth of single crystals from metallic fluxes
(see attached pdf file)
Good luck with your work!
Try to centrifuge at a higher temperature by taking the sample out of the furnace at a higher temperature and by minimizing the duration of the transfer from the furnace to the centrifuge.
I would also recommend reducing the etching time and the concentration of the acid.
If that fails, you could try placing the Sn-covered crystals in Hg at 50-100 C. The Hg will dissolve the Sn, which can be poured off. If the crystals are covered in Hg afterwards, it can be evaporated. Be very careful with this procedure though since Hg and Hg vapor are very toxic!
A couple of helpful ideas can be found here:
http://www.physics.fudan.edu.cn/tps/people/jzhao/Book&Paper/Flux%20separation%20methods%20for%20flux-grown%20single%20crystals_Thomas%20Wolf.pdf
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