[HN Gopher] Hardest amorphous material can scratch even diamond
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Hardest amorphous material can scratch even diamond
Author : gmays
Score : 51 points
Date : 2021-09-03 17:44 UTC (5 hours ago)
(HTM) web link (www.chemistryworld.com)
(TXT) w3m dump (www.chemistryworld.com)
| analognoise wrote:
| Sounds like it would make a great armor plate layer, esp. for
| something like body armor?
| beerandt wrote:
| Not modern body armor. You want lots of deformation before
| failure, which is almost the opposite of brittle.
|
| Like the crush zone of a car.
| analognoise wrote:
| Don't modern body armors have ceramic inserts? - I think the
| idea is to shatter the incoming projectile, then catch the
| pieces while cushioning the impact.
|
| Modern combat body armor, anyway.
| 0-_-0 wrote:
| Wouldn't it be fragile, like diamond?
| sudosysgen wrote:
| It's amorphous, so there is a chance you could make it thin
| enough to bend.
| scythe wrote:
| Partially ordered carbon aggregates which are harder than diamond
| and produced by compressing fullerites have been known for a few
| decades and are usually grouped under the heading "aggregated
| diamond nanorods" or recently "nanodiamond":
|
| http://en.wikipedia.org/wiki/Aggregated_diamond_nanorods
|
| This paper seems to be a step forward, in obtaining a very hard,
| truly amorphous material. Unfortunately, it is not likely that
| this will lead to mass-production any time soon, since the
| synthesis is achieved at 25 GPa, or in familiar terms, about
| 250,000 atmospheres:
|
| https://watermark.silverchair.com/nwab140.pdf
| mauvehaus wrote:
| Does this mean they'll have to turn Mohs hardness scale[0] up to
| eleven?
|
| [0]
| https://en.m.wikipedia.org/wiki/Mohs_scale_of_mineral_hardne...
| conchy wrote:
| "Why don't you just make ten a little harder, and make ten be
| the top number, and make that a little harder?"
|
| https://en.wikipedia.org/wiki/Up_to_eleven
| hasmanean wrote:
| It's a diamond in the rough.
| sebazzz wrote:
| Usually materials that are more hard are also more brittle. I
| don't read anything about that in this article. Anyone any idea?
| fhood wrote:
| See section on "compressive strength".
| jazzyjackson wrote:
| Diamond has a very high compressive strength, but if you drop
| one it will shatter, it is brittle. Since this new material
| has similar hardness & strength, I would assume it is
| similarly brittle.
| jacquesm wrote:
| Brittleness is arbitrarily defined as the ration between
| tensile and compressive strength so GP has a point (high
| compressive strength usually indicates a more brittle
| material), but without knowing the tensile strength it
| remains to be seen if it is more brittle or less brittle
| than say diamond.
| beerandt wrote:
| I don't think a single part of your comment is true.
|
| ASCE, ASTM, and other professional orgs have non-
| arbitrary definitions. They are all versions of some
| measure of deformation _at_ ultimate strength, but don 't
| correlate to that strength value.
|
| Crackers are brittle. Structural steel is not.
| harpiaharpyja wrote:
| Diamond is quite brittle so I think to the point of the
| discussion, it's likely a brittle material even if it's
| somewhat less brittle than diamond.
| beerandt wrote:
| Diamonds are actually tricky, because their practical
| brittleness is mostly due to breaks in the lattice caused
| by impurities. The lines of weakness are defined as
| _cleavage_ , and diamonds will typically _cleave_ along
| those lines when the break.
|
| So there's a bit of ambiguity between the actual
| brittleness of the pure carbon structure and the
| practical brittleness where breaks in that structure
| naturally exist.
| [deleted]
| beerandt wrote:
| Strength is unrelated to brittleness.
|
| Brittleness is a measure of plastic deformation at the
| (ultimate strength) breaking point.
|
| Eg, diamonds, cast iron, and saltine crackers are all very
| brittle.
|
| Resilience and ductility are related technical terms, but not
| quite opposites.
| blix wrote:
| It is probably very brittle. Diamond is a brittle material and
| this is basically a 'disordered' diamond. It is quite unlikely
| that any mechanisms of ductile deformation would be active in
| this material.
| sulam wrote:
| Hmm, not a materials scientist here, but wouldn't some of
| diamond's brittleness derive from its crystalline structure,
| ie that it's easy for it to sheer along a plane? Whereas this
| material, being "disordered", to use your term, won't have
| the same sheer planes and therefore potentially be much less
| brittle?
| bodhiandphysics wrote:
| In general disordered materials are more brittle... think
| glasses, because cracks can propagate in any direction
| instead of just along crystal faces
| jazzyjackson wrote:
| I was pleasantly surprised to find out that diamond and silicon
| share a tetragonal crystal structure, and here they mention their
| buckyball material here is harder than diamond and more
| conductive to boot. So what advantages could carbon computers
| have over silicon I wonder?
|
| "The resulting material's physical properties depend on the ratio
| of sp2 to sp3 carbons. Raising the temperature during synthesis
| increases the sp3 fraction, producing a harder material." - I
| know silicon is doped with impurities to make it more or less
| conductive, so if you can control the band-gap during synthesis,
| perhaps transistors could be baked directly into this carbon-
| glass bucky-stuff.
| phkahler wrote:
| Diamond can be doped - I think with Boron and has very high
| thermal conductivity. Diamond semiconductors are also hard to
| grow.
| blix wrote:
| Diamond's band gap is 5.5eV; it's not too hard to be more
| conductive.
|
| Based on their expeerimental procedure controlling band gap
| carefully would be pretty difficult. Graphene-based materials
| probably represent a better path forward than Diamond-based.
| omegalulw wrote:
| Isn't graphene really prone to shear stress?
| burnished wrote:
| Yes, but it might be easier to work with while producing a
| different carbon based material.
| mikewarot wrote:
| I was expecting an article about BAM [1], which isn't quite as
| hard, but is one of the slickest substances known. Some day I
| hope to own a set of BAM coated tool inserts.
|
| 1 - https://en.wikipedia.org/wiki/Aluminium_magnesium_boride
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