Carbon Nanotubes Harder Than Diamond

purduephotog writes "CDAC has announced the formation of a new form of hexagonal packed carbon similiar to diamond. Carbon nanotubes are compressed at 75 GPa and quenched. The new material is conclusively different via Raman Spectroscopy and both cracked and indented the diamond anvil used in its creation. CDAC is also known to have created via CVD the hardest diamond to date."

Comments

Explanation of Raman spectroscopy

[francisew]

I realize you are kidding... here is what Raman really is... (give or take a few details ;p)

Spectroscopy: study of quantities of light at various wavelengths (or frequencies). Useful because matter interacts with light, so by measuring light passing through unknown matter, you figure out what its passing through.

Raman spectroscopy, is a branch where one looks at the wavelength shift occurring as light passes through a sample. A bit like doppler radar involves a shift of frequency (although it's not a shift due to the movement of molecues, but rather due to energy differences in orbitals as they move/distort).

The cool thing about Raman is that you just need a single wavelength of excitation, meaning you can build a spectrometer with a single laser diode. Then you filter off the laser line, and presto, the only light left will be the spectrum of interest.

Caveats: low intensity, frequency shift is very small, you still need a monochromator. Advantages: you get information that isn't available in standard IR & UV-vis spectra, the spectra are excitation freuency independant (not entirely true), by taking advantage of resonances it's possible to get REALLY intense spectra (resonance Raman and SERS).

background

[cinnamon colbert]

The 2001 edition of the annual review of materials research, http://www.annualreviews.org/, has a nice review of the field of super hard materials. the authors point out that scratching a diamond is not, in intself, much evidence of anything; in the real world lots of soft scratch hard examples can be found. The authors of this article also point out that one of the few flaws of diamond is that it reacts with iron, so you can't diamond coat cutting tools; instead, you have to use much softer things like boron nitride or TiN. Nanotubes could have a major commercial future if they are harder then TiN, non reactive to iron, but softer then diamond.

full citation SYNTHESIS AND DESIGN OF SUPERHARD MATERIALS; J Haines, JM Léger, G Bocquillon
Annual Review of Materials Research, Vol. 31: 1-23

Re:But the real question is...

[Rei]

Ok, lets give some info on this, since I've researched it a lot before when I was on a big space-elevator kick.

First off, the "diamond anvil" is a DAC: Diamond Anvil Cell. It's not an anvil in the typical sense. What you have is a stepping-down system of applying pressure. You have steel apply pressure to a very hard material, such as tungsten carbide, which then applies the pressure to a diamond (incredibly hard), which applies the pressure to whatever you're trying to compress. This means you can have a large area of steel on which to apply pressure, transferring it to a small area of tungsten carbide, transferring it to a tiny area of diamond. DACs are nifty ;)

Secondly, what they've done here had been theorized years ago; I had been trying to convince Highlift (and later, Liftport) to put more research on this front. The concept of coming up with a nanotube epoxy that is as strong as the individual tubes is a bit far-fetched, but it was known that SWNTs, under pressure, can merge:

http://www.ncnr.nist.gov/staff/taner/nanotube/in te rlink.pdf

While carbon sp3 bonds are strong, sp2 bonds are stronger. Nanotubes use only sp2 bonds; diamonds only sp3. In the pressure-induced interlinking, depending on the types of tubes involved, different sp2 bonds will be replaced with sp3, merging the tubes. While this weakens their overall strength, they adhere to each other far, far more strongly than they normallly would from mere van der waals force alone.