Stronger than Diamond!

[TimothyC]

Physics Web

[color:RED]Diamonds are not forever[/color]

26 August 2005

Physicists in Germany have created a material that is harder than diamond. Natalia Dubrovinskaia and colleagues at the University of Bayreuth made the new material by subjecting carbon-60 molecules to immense pressures. The new form of carbon, which is known as aggregated diamond nanorods, is expected to have many industrial applications (App. Phys. Lett. 87 083106).

The hardness of a material is measured by its isothermal bulk modulus. Aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), compared with 442 GPa for conventional diamond. Dubrovinskaia and two of her co-workers - Leonid Dubrovinky and Falko Langenhorst - have patented the process used to make the new material.

Diamond derives its hardness from the fact that each carbon atom is connected to four other atoms by strong covalent bonds. The new material is different in that it is made of tiny interlocking diamond rods. Each rod is a crystal that has a diameter of between 5 and 20 nanometres and a length of about 1 micron.

The group created the ADNRs by compressing the carbon-60 molecules to 20 GPa, which is nearly 200 times atmospheric pressure, while simultaneously heating to 2500 Kelvin. "The synthesis was possible due to a unique 5000-tonne multianvil press at Bayerisches Geoinstitut in Bayreuth that is capable of reaching pressures of 25 GPa and temperatures of 2700 K at the same time," Dubrovinskaia told PhysicsWeb.

The Bayreuth team measured the properties of the samples with a diamond anvil cell at the European Synchrotron Radiation Facility at Grenoble in France. These measurements indicated that ADNRs are about 0.3% denser than diamond, and that the new material has the lowest compressibility of any known material.

In addition to working out why the new material is so hard, the Bayreuth team also hope to exploit its industrial potential. "We have developed a concept for innovative technology to produce the novel material in industrial-scale quantities and now we are looking for partners in order to realize our ideas," said Dubrovinskaia.

Mmmm.... Materials Engineering.

[Alan Bolte]

Yes sir, I chose the right major.

[The Grim Squeaker]

What does the gigapascal rating mean?
Would an object of 20gp be twice as hard as a 10gp object or is it more complicated? (I'd like to understnad the magnitude of the difference between the two materials)

[Edi]

What does the gigapascal rating mean?
Would an object of 20gp be twice as hard as a 10gp object or is it more complicated? (I'd like to understnad the magnitude of the difference between the two materials)

GigaPascal is a unit of pressure. So the process involves using a lot more pressure on the material being worked on than usual, and that alters its physical properties.

Edi

[Il Saggiatore]

Bulk modulus.
For the same external pressure and temperature, the new material deforms -- in volume -- about 10% less than diamond ((491-442)/442 = 11%).

[Mange]

What is the corresponding modulus for fullerene?

[Il Saggiatore]

What is the corresponding modulus for fullerene?

Based on this PDF file, a single fullerene molecule has a bulk modulus of 903 GPa, but solid fullerene has 8.8 GPa or 6.8 GPa, depending on the crystal structure.

[drachefly]

I guess diamond is a bit more regular and thus can shear slightly, while this material is irregular enough to jam earlier. I wonder how much more brittle it is?

Also, note that the tensile strength is also measured in terms of pressure. Carbon nanotubes have already been observed to have a tensile strength of 150 GPa.

But that's pulling, not pushing.

[Zornhau]

So, what would you cut this stuff with?

[GrandMasterTerwynn]

I guess diamond is a bit more regular and thus can shear slightly, while this material is irregular enough to jam earlier. I wonder how much more brittle it is?

Also, note that the tensile strength is also measured in terms of pressure. Carbon nanotubes have already been observed to have a tensile strength of 150 GPa.

But that's pulling, not pushing.

A diamond is a crystal. Crystals have fracture planes built into them. This is why jewelers can cut diamonds with steel blades, in spite of the fact that steel is nowhere near as hard as diamond.

[Hawkwings]

you can probably use lasers to cut this.

[drachefly]

I guess diamond is a bit more regular and thus can shear slightly, while this material is irregular enough to jam earlier. I wonder how much more brittle it is?

...

A diamond is a crystal. Crystals have fracture planes built into them. This is why jewelers can cut diamonds with steel blades, in spite of the fact that steel is nowhere near as hard as diamond.

... I don't see how this contradicts what I said.

The fracture planes naturally occurring in diamonds are spaced much more widely than the irregularities in this supermaterial they invented.



And Hawkwings, yes... you can use lasers to cut it. You can use WATER to cut it, if you move the water fast enough (some high-speed saws actually do this, though not to diamond). Strength only says which material gives way first, but it doesn't preclude both materials from giving way.

[aerius]

I remember some years back that they made a diamond out of pure Carbon-13. There weren't any tests done on it as far as I know, but in theory according to the article, it would be marginally harder than a diamond composed of Carbon-12. Interesting stuff. And now they've outdone themselves.

[The Dude]

What does the gigapascal rating mean?

They're using it in two different senses here. One is pressure (as when they quote the 25GPa processing pressure).

The other is modulus (a material property), which relates the amount of (elastic) deformation in a material to the applied stress. A high-modulus material will deform less than a lower-modulus one, under the same loading conditions.

[The Dude]

I guess diamond is a bit more regular and thus can shear slightly, while this material is irregular enough to jam earlier. I wonder how much more brittle it is?

This material is stated to be denser than diamond, which generally points to a more sophisticated crystal structure (as do the superior mech. properties).

They imply in the article that they don't currently understand why the material is harder than diamond. It may well turn out that it is not universally harder than diamond; the modulus of even very common materials can be highly anisotropic (i.e. the properties change depend upon orientation). This is even more likely to be true of a material comprised of tiny cylindrical elements.

[drachefly]

If they're oriented randomly, though, then it would end up isotropic in the aggregate, unlike a homogeneous crystal.

[The Dude]

If they're oriented randomly, though, then it would end up isotropic in the aggregate, unlike a homogeneous crystal.

It's almost inconceivable that a material made of rigid high-aspect-ratio "rod" elements is not going to be highly textured.

[drachefly]

Again, it all depends on how ordered the material is. On first reading, I thought they said it was random orientation. Rereading, they don't say one way or the other.

In that case, it seems likely there will be long-range order and yes, it will be anisotropic. But if there is no long-range order, it won't be.

Looking over google scholar, I'm not seeing this paper...

Incidentally, my earlier figure for the tensile strength of CNT was off. Estimates go from 300 GPa to 1500 GPa (different CNT variants, different configurations, different purities, etc.)

[The Dude]

Looking over google scholar, I'm not seeing this paper...

It's in the August 22 2005 issue of Applied Physics Letters. I don't have online access, but you can read the abstract at their site.

[Mange]

What is the corresponding modulus for fullerene?

Based on this PDF file, a single fullerene molecule has a bulk modulus of 903 GPa, but solid fullerene has 8.8 GPa or 6.8 GPa, depending on the crystal structure.

Allright, thanks!

[wilfulton]

Okay...so when will they start making knife sharpeners out of this?

[drachefly]

Looking over google scholar, I'm not seeing this paper...

It's in the August 22 2005 issue of Applied Physics Letters. I don't have online access, but you can read the abstract at their site.

Got the whole thing. Looking it over... there seems to be a tendency for them to align, but there are a lot of nanorods which deviate from this alignment.

Also, roughly looking at the images, the length scale over which the alignment changes totally is of order tens of microns. I don't know how far apart the phase boundaries are in diamonds, though...

[The Dude]

Got the whole thing. Looking it over... there seems to be a tendency for them to align, but there are a lot of nanorods which deviate from this alignment.

I'm not clear on what you mean here. It sounds as though the the rods organize into grains of a sort: is there a texture to these grains or is the grain orientation random? Is there any mention in the paper whether the "bulk" material is isotropic or not?

(It 's understandable if there's not a lot of detail there; it's a letter, not a full paper; it may be that the results are preliminary, or that they are protecting their patent application).

Also, roughly looking at the images, the length scale over which the alignment changes totally is of order tens of microns. I don't know how far apart the phase boundaries are in diamonds, though...

Do you mean grain boundaries? Gem-quality diamonds and industrial microdiamonds are single-crystal and are therefore single-phase and have no grain boundaries.


Just to clarify and expound a bit: in solids "phases" means distinct chemistries and/or crystal structures; "grains" are regions of common crystallographic orientation (the boundaries of which are generally defined by a minimum misorientation wrt neighbouring material). For example, brass is single-phase but polycrystalline (many grains), most steels are multi-phase and polycrystalline, diamonds and silicon wafers are single-phase and monocrystalline. It's impossible for a material to be multi-phase and monocrystalline.

[drachefly]

Oh, thanks on 'phase'. Geology class was a long time ago. Yes, I meant grain.

What I said was pretty much what they said on the subject, plus a quick gloss of three images they had (well, two of them. The other was too zoomed to see inhomogeneity).