Ions, Stay! Electrons, Move!

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Well, that’s for thermoelectrics.  For electrolysis, it’s “Electrons, Stay!  Ions, Move!”

What?  You’re still reading?

I’m often asked, “What type of research is your daughter doing at MIT?”  I think when people ask me this question, their expectation is “What leading scientific discovery is she pursuing, and can she get rich off of a business startup?”  Well, maybe the second part is me.  But they probably would like to hear something along the lines of “life changers,” like being four years away from creating a household fissionable energy source or a few months away from making a 3D printer raw material that will form a corn fed, aged beef filet, either of which I’m sure she’d love to do.

My reply usually is along the lines of “Extracting copper from copper sulfide using electrolysis.  It apparently might be useful someday as cost factors change.”  The followup question is asked with glazed over eyes, “Uh, what is her major?”  The third question settles into a comprehensible normalcy, “Does she like Boston?” 

After visiting with her recently, and having her laboratory explained in a little more detail, my mind detoured to the safety details of the lab while she prattled on, but the title of this post is essentially the gist of what I think I heard.  So, to get the story straight, I had her tell it:  “Our group is trying to use electrolysis to extract copper from copper sulfide instead of from copper oxide.”  (Note, at this point, I’m patting myself on the back for the correctness of my abbreviated response to inquiries.)  “Copper sulfide is much more commonly found in minerals, but sulfides haven't been studied as fully as oxides, so it is harder to find an appropriate electrolyte melt to facilitate electrolysis.” 

“We are currently using Barium sulfide (BaS) as our electrolyte, but we don't know what the ideal composition is, the best operating temperature, whether we have to control the partial pressure of sulfur, or even how it is conducting electricity. My part of the project is to look at the conductivity of sulfide melts. The melts conduct electricity both ionically and electronically, which can be a bit of an issue. Ideally, we would only conduct it ionically, so that all power out through the system would be moving ions towards the electrodes where they would react (to form copper on one side and sulfur gas on the other). However, it turns out that around 75-98% of the current flow is due to electrons (again dependent on composition and temperature). The sulfides we are using are strange. Most materials either exhibit ionic, covalent, or metallic natures, but sulfides exhibit all three, with different characteristics dominating in different conditions. Metal sulfides are all semi-conductive as solids, and most carry this behavior over even when they melt. It's my project to figure out why, how, and when the melts will behave with different conductive traits.”  We pause this quote for a deep breath.

“One of the other projects in the lab is to make a thermoelectric device using sulfides as the thermoelectric material. For that project, having a great electronic conductivity (rather than ionic) would be ideal. I get to help find and characterize systems that will help for both projects. To characterize the materials, so far I've been running electrochemical tests to determine total conductivity, electronic and ionic transference numbers (the fraction of current transported by electrons vs ions), and looking at impedance spectroscopy data to see how the system responds to different applied frequencies, hopefully telling us what mechanisms are actually taking place in the melt.”

Here’s an example of what happens when you heat/cool the induction furnace too quickly.  Metal spilled when the crucibles broke while melting gallium in one experiment and copper sulfide in another.  The result was gluing things together that should not be stuck together.  As a side note, copper was accidentally formed.  As an asterisk to the side note, “Probably.  We can’t think of another source of copper that would have been around the set up, but it is vaguely possible we melted a sad stray wire.”  Genius!

Here’s a photo of the “standard variety” furnace she uses.

This is a graphite furnace which is used for the highest temperatures, around 2000oC.

This is an induction furnace with an alumina crucible in it.  It heats incredibly fast, but this can cause the crucible to crack if heated too quickly.  It normally has a metal case around it.

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This is the central work bench, where she doesn’t really work, but at least it looks geeky. 

So… M.I.T.  Massachusetts Institute of Technology.  Impressive.  Here’s her desk.

She shares the same room with eight others, plus one currently un-desked.  Living the high life.

 

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1 comment :

  1. Interestingly enough, my question would be why Cu? Ag or Au are better conductors. Or for lack of better rationale, their value per troy ounce is higher.

    Still, there is a reason to extract Cu and that is what makes me curious.

    ;-)

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