Hardest amorphous material can scratch even diamond | Hacker News Reader

Hardest amorphous material can scratch even diamond

chemistryworld.com

98 pointsgmays39 comments

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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...

"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

I had no idea.

Thank you.

> the IRIX audio panel (when invoked with the undocumented -spinaltap option)

Tchaikovsky's 1880 work 1812 Overture, which is scored for artillery and has passages marked as ffff (in a score, "fortississimo" (fff) instructs the musicians to play the marked passage extremely loudly and is normally the loudest volume specified; "fortissississimo" (ffff), which means to play louder than fortississimo, is sometimes used) has been described as the loudest classical piece. The piece has been played with FH70 155 mm (6.1 in) howitzers and Type 74 Main Battle Tanks included in the orchestra instrumentation (a typical 155mm howitzer generates about 180 dB at the source, sufficient to sometimes cause immediate and permanent hearing damage (artillery crews are issued hearing protection)). The piece is usually performed outdoors or with simulated or recorded cannons, but an indoor performance with live cannon at the Royal Albert Hall has been cited as having been particularly loud.

(edit) Found it while going down deeper the wikipedia rabbit hole: https://en.wikipedia.org/wiki/Loudest_band

Only for the record, there must have been some issues in the English transposition, in Italian those are:

f - forte

ff - fortissimo

fff - fortissimissimo

ffff - fortissimissimissimo

https://it.wikipedia.org/wiki/Dinamica_(musica)#Segni_dinami...

(not that I know anything on music, fortississimo and fortissississimo didn't sound right to me and looked for them)

Per the article, Mahler used fffff the old protorocker.

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

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.

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.

Isn't graphene really prone to shear stress?

Yes, but it might be easier to work with while producing a different carbon based material.

Diamond can be doped - I think with Boron and has very high thermal conductivity. Diamond semiconductors are also hard to grow.

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

Usually materials that are more hard are also more brittle. I don't read anything about that in this article. Anyone any idea?

See section on "compressive strength".

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.

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.

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.

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.

Does that mean diamonds might have ductile fractures if they were flawless? Or just that they would be stronger?

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.

Yes, but this is an informal discussion, so that ratio actually serves a purpose unless you want to attach a complete course in materials science, it's 'good enough' for this level of discussion and sheds some light on why it is a thing to begin with. Oh, and just to fortify this comment here is a reference:

https://subsurfwiki.org/wiki/Brittleness

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.

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.

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?

In general disordered materials are more brittle... think glasses, because cracks can propagate in any direction instead of just along crystal faces

In general if a material is shearing along crystal plains the material is breaking apart. Also I am pretty sure that diamonds are polycrystalline meaning that the a diamond is composed of many crystals with different orientations, so it is generally going to break on the boundaries between those crystals not the crystalline bonds themselves. For an example think of a polycrystal like steel (which I’m a little more familiar with), the atoms in the crystal lattice can be displaced a little (elastic deformation) or the crystalline grains can move or change shape (plastic deformation). Once the crystals (grains) themselves shear that means you’ve applied enough stress to break the crystal’s bonds and the material is going to break. Some materials are different though, and sometimes crystals can slip across grain boundaries. But the bonds between the crystals are generally weaker and more prone to move/change, generally polychrystals break along those boundaries first, before the crystals themselves break apart. This is probably very brittle (and hard) not because there are no shear plains, but because there are no mechanisms for the atoms to move around without breaking chemical bonds.

Makes sense, turbine blades are nowadays a single "crystal" with no seams. The work on it started in te 60s. First application was in the SR-71 Blackbird, nowadays even blades for generators are made like this.

Can they make a drill bit out of it?

It’s a diamond in the rough.

Sounds like it would make a great armor plate layer, esp. for something like body armor?

Wouldn't it be fragile, like diamond?

It's amorphous, so there is a chance you could make it thin enough to bend.

I think that works for crystals too, thin silicon wafers are pretty flexy, particularly if you can grow them relatively free of defects.

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.

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.

Sort of. The ceramic is designed to shatter using as much energy as possible. After spreading the remaining energy sad much as possible. The bullet shattering is only important if it's high powered armor piercing rounds. Otherwise it's usually bc it's a hollow point or is incidental.

But there are lots of different theories and designs.

> which is almost the opposite of brittle.

Brittle failure can actually dissipate more energy than ductile one.

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