Carbon-Boron Nitride, Harder and more oxidant resistant than Diamond?

[PB666]

http://www.thelatestnews.com/new-super-hard-diamond-like-material-invented/

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I see super metal potential, possibly better than carbon fiber in terms of weight versus strength. Possibly useful for making struts, standouts, nacell arms, more pressure resistent capsules. In particular is could be combing with carbonfiber to make pressure hulls and fuel tanks for things like xenon or argon gas.

[peadar1987]

I think you're getting a bit too excited about this. It's not as hard as diamond, that's explicitly stated in the article. It is, however, tougher and more oxidation resistant. As the authors of the paper say, it will bridge the gap between diamond, which is incredibly hard, strong, brittle, and vulnerable to oxidation, and more conventional materials, which are softer, but more ductile and less reactive.

Ceramics are the last thing you should be using as pressure vessels, as they are not great in tension, and tend to fail catastrophically via brittle fracture. If this new compound can be made to cheaply form fibres, it could possibly find an application as reinforcement in a composite material, but that's really not what it was designed for (there's a reason we don't already use diamond for this purpose already)

[Kerbart]

Hardness generally goes in hand with brittleness; where construction materials usually need to be tough, the opposite of brittle. (In engineering, "toughness" is the ability to stretch without failing). The article does mention what it is intended for:

This could lead to a new generation of advanced cutting materials.

-- lathes, mills, etc all use cutting tools and the harder those are, the less they wear (become blunt).

[peadar1987]

Exactly (if anybody is interested in the reason, it is, more or less, because if a crack starts to grow through a hard material, it will stay very sharp-edged, and keep propagating. If a crack starts to grow through a soft material, the high stress at the crack tip with deform the material, rounding the crack dip, reducing the stress, and mitigating crack growth.

This is why metals, which are not too hard in the grand scheme of things, will tend to bend or dent, whereas ceramics, which are extremely hard, tend to shatter.

[sgt_flyer]

Interesting though as it was said, materials suitable for pressure vessels are better as fibres.

In that regard the graphene structure is much better (especially in nanotube shape)

Or even better - Carbyne ! (Now, that thing's even more resistant to pull than carbon nanotubes - and can even vary it's stiffness if you incorporate other atoms in it.)

[PB666]

I think you're getting a bit too excited about this. It's not as hard as diamond, that's explicitly stated in the article. It is, however, tougher and more oxidation resistant. As the authors of the paper say, it will bridge the gap between diamond, which is incredibly hard, strong, brittle, and vulnerable to oxidation, and more conventional materials, which are softer, but more ductile and less reactive.

Ceramics are the last thing you should be using as pressure vessels, as they are not great in tension, and tend to fail catastrophically via brittle fracture. If this new compound can be made to cheaply form fibres, it could possibly find an application as reinforcement in a composite material, but that's really not what it was designed for (there's a reason we don't already use diamond for this purpose already)

Didn't I say in combination with carbon fiber, glass, for instance is surprisingly pliable in small layers. If you created layers of the material sandwiched between carbon-fibers, you would have essentially materials for holding pressure combined with plyability.

[peadar1987]

Didn't I say in combination with carbon fiber, glass, for instance is surprisingly pliable in small layers. If you created layers of the material sandwiched between carbon-fibers, you would have essentially materials for holding pressure combined with plyability.

You said you "saw super metal potential", based on, as far as I can see, pretty much no evidence. It's a cutting tool material. The reason we use carbon fibre for composites is because it readily forms long fibres. Things like silicon carbide, CBN and diamond are stronger and harder than carbon fibres, but are not used, because they don't form fibres easily.

CBN is already a thing. Diamond is already a thing. If we don't use either of them as reinforcement in composites already, there's no reason why a mixture of the two would suddenly revolutionise the composites industry.

As somebody who works with composites, mainly glass fibre, quite a lot, I can say that if you put sheets of ceramic between carbon fibre, what you're most likely going to get is delamination of the composite. A macroscale sheet of CBN or diamond is going to be brittle anyway, and will confer no real advantage on the bulk material.

[PB666]

Carbon fiber is not imperviable to gases you have to add other materials to make it impervious but those material are structurally weak, a five or six molecular layer of this stuff would not allow diffusion of gases, and could be bundled in between. Interleave the two.

I think you are discounting this too quickly, boron-carbon-nitrogen this is about as light as structural material gets. We need more of this not less.

[peadar1987]

Carbon fiber is not imperviable to gases you have to add other materials to make it impervious but those material are structurally weak, a five or six molecular layer of this stuff would not allow diffusion of gases, and could be bundled in between. Interleave the two.

I think you are discounting this too quickly, boron-carbon-nitrogen this is about as light as structural material gets. We need more of this not less.

And how would this be any different from, say, a 5 or 6 molecule layer of silicon carbide? Or any other existing ceramic? Is it more easily deposited? Cheaper? Less permeable per unit mass? And for that matter, how would you go about manufacturing an impermeable, 5 molecule thick layer of ceramic in the shape of a pressure vessel? And are you aware of how utterly structurally irrelevant a 5-6 molecule coating will be?

It's a cutting tool material, and you're ascribing to it all sorts of weird and wonderful properties and applications, with no scientific backing to them whatsoever.