Nanomaterials

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The summer after my freshman year I was looking for a job.  I'd spent the previous summer working on a local farm, and I had no desire to be stuck picking squash for another three months.  I live near Baltimore, and I wanted to get involved in research, so I contacted a bunch of professors at Johns Hopkins University asking to work with them.  Dr. Cammarata in the materials science department emailed me back and I ended up working in his lab for two summers.

The work I did at Hopkins centered around making little metal disks less than a millimeter thick called thin films.  We made these films using a process called electrodeposition.  This involved taking a gold electrode and dunking it in a bath of metal solution, then running a current through it.  The current grabbed metal atoms out of the solution and stuck them to the electrode, eventually building up the thin film.  After a few hours, we took the electrode out of the solution and peeled the film off.

But little bits of nickel or copper aren't interesting on their own.  You can find them in the ground.  The cool stuff happened when we added ceramic nanoparticles to the solution.  Nanoparticles are exactly what they sound like, little tiny grains only a few nanometers across.  When you add them to the mix, they get dragged along by the metal atoms and end up trapped in the film.  The result is a film of pure metal with nanoparticles scattered throughout.

Here's a picture of the setup we used:
RDE.jpg

The blue stuff in the odd shaped jar is copper sulfate solution with nanoparticles floating in it, and the electrode is attached to the big blue thing sticking out the top.  You can see that a layer of nanoparticles has settled to the bottom.  The particles will sink if left alone, so the solution must be stirred continuously to keep that from happening.  We actually did this by spinning the electrode itself at a few thousand rpm.  That big blue thing is the motor that spins the electrode.

The metal-particle composite is a very strong but very brittle material, i.e. it takes a lot to break it, but if you do break it it breaks completely.  The pure metal on the other hand tends to give when a force is applied rather than cracking.  We wanted to have our cake and eat it too, so we worked out a way to get both of these properties in one film.  The fact that the particles sink when the stirring is turned off gave us a way to stop getting particles in our films just by turning off the motor.  By turning the motor on and off while depositing we could get alternating layers of composite and pure metal. 

We started out trying this with copper, but that didn't really work well.  However, the way in which it didn't work looks really cool so I'm adding a picture of it anyway.
copper spiral.jpg

That's supposed to just be smooth, uniform copper.  The grad student I worked with was fond of saying that electrodeposition is kind of a "black magic", so occasionally things like this weird spiral pattern would appear for some unknown reason.  We switched to nickel, which worked better.  Here's an electron microscope image of one of the successful layered nickel composites:
layers.png

You can clearly see the difference between the regions where there are lots of particles and where there are none.  This kind of material has all kinds of possible applications.  Since it's simply plated onto an existing surface, it could be used as a coating to strengthen various objects.  For example, jet engines require strong parts that often need to retain their magnetic properties.  Something like this could be used, since it is considerably stronger than pure nickel, and it could conceivably be deposited in a thin layer onto existing engine components.

So now I've done a summary of the two research experiences I've had.  Hopefully you've enjoyed all the cool science.  Next time I'll start talking about some general observations I've had about what it's like to do undergraduate research.

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