## Lighter than Air Solid

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eidako
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### Lighter than Air Solid

Journalists Mangle Scientific Findings, Sky Continues to be Blue
http://news.yahoo.com/worlds-lightest-s ... 09070.html

A metallic lattice of hair-thin pipes is now the lightest solid yet created — less dense than air, scientists revealed.

eidako
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### Re: Lighter than Air Solid

I think the worst part is that it's also 99:1 parts air to metal. Somehow 99% air at 1.275 kg/m3 and 1% of mystery metal has a combined density of 0.9 kg/m3.

Perhaps it uses the same mechanic as ice, which is less dense than water because the crystalline structure creates voids in its volume? I really can't tell if they're using some alternative definition of density or if they actually have made magic carpet cloth.

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### Re: Lighter than Air Solid

It's nickel. density (in normal solid form) is 8.908 g·cm−3, according to wiki.
also: phosphorus.

As per the article:
Next, Schaedler and his colleagues etched away the photopolymer with lye, leaving behind a lattice of hollow nickel-phosphorus struts each 100- to 500-microns wide, or one-to-five times the width of a human hair. The walls of these tubes ranged from 100 to 500 nanometers or billionths of a meter thick, or up to 1,000 times thinner than a human hair.

eidako
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### Re: Lighter than Air Solid

Alright, so
(1.275 kg/m3*0.99) + (8908 kg/m3*0.01) =? 0.9 kg/m3
1.2623 kg/m3 + 89.08 kg/m3 =? 0.9 kg/m3
90.3423 kg/m3 != 0.9 kg/m3

It weighs 1% as much as its raw components.

Nevermind, it's 9999:1

(1.275 kg/m3*0.9999) + (8908 kg/m3*0.0001) =? 0.9 kg/m3
1.2749 kg/m3 + 0.8908 kg/m3 =? 0.9 kg/m3
2.1657 kg/m3 != 0.9 kg/m3

Still heavier, albeit feasible if some kind of vacuum was involved.
Last edited by eidako on Sun Nov 20, 2011 12:38 am UTC, edited 6 times in total.

Glass Fractal
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### Re: Lighter than Air Solid

eidako wrote:I think the worst part is that it's also 99:1 parts air to metal. Somehow 99% air at 1.275 kg/m3 and 1% of mystery metal has a combined density of 0.9 kg/m3.

Perhaps it uses the same mechanic as ice, which is less dense than water because the crystalline structure creates voids in its volume? I really can't tell if they're using some alternative definition of density or if they actually have made magic carpet cloth.

Maybe there's nothing inside the tubes?

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### Re: Lighter than Air Solid

Is it less dense than silica aerogel? If so, it's not the lowest-density solid material

Still an interesting material, though, it's like a metal version of aerogel
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sourmìlk
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### Re: Lighter than Air Solid

This is probably a stupid question, but if this metallic lattice material is lighter than air, shouldn't it float?
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Thesh
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### Re: Lighter than Air Solid

Minerva wrote:Is it less dense than silica aerogel? If so, it's not the lowest-density solid material

That statement makes my head hurt. And, yes, the article states that aerogels have densities as low as 1mg/cm3 and that this stuff has a density of .9mg/cm3.
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Iulus Cofield
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### Re: Lighter than Air Solid

This is cool. Is there anything it can be used for?

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### Re: Lighter than Air Solid

Iulus Cofield wrote:This is cool. Is there anything it can be used for?

My first thought is support structures, if it can be used on a large scale. The article suggests briefly that they recover well from deformation, but if they can be very easily compressed, it may not bode well for weight-bearing structures. Aerogels also got a lot of attention, if I remember, due to their very low thermal conductivity; that made them excellent for insulation uses where additional weight is highly undesirable. This wouldn't seem to have that advantage, but I don't know enough about it.
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Iulus Cofield
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### Re: Lighter than Air Solid

Maybe packing material then? Or maybe this will pave the way for some further down the road technology.

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### Re: Lighter than Air Solid

The article suggests it could be used for acoustic damping? I can certainly see a lot of applications for a very lightweight material for that purpose in the aerospace and automotive sectors. I think it's probably unlikely that we'd see it used for anything structural, though.

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### Re: Lighter than Air Solid

Hawknc wrote:The article suggests it could be used for acoustic damping? I can certainly see a lot of applications for a very lightweight material for that purpose in the aerospace and automotive sectors. I think it's probably unlikely that we'd see it used for anything structural, though.

Yeah, structural use was an off-the-top-of-my-head guess, but the scale would likely be much too large, and the compression behavior doesn't seem ideal. The acoustic damping uses seem a little odd to me, but I'm certainly no expert on the best materials for such purposes. Honestly, though, I'm having trouble imagining a large number of uses where this would be significantly better than aerogels, unless you really need to shave off the extra weight (as you say, could be of great use for aerospace, especially) or unless the cost benefit was significant, but I'd like to see more information on the material properties first (ultimate strength, exactly how well it recovers from compression, etc.). That's what I hate about articles like this: they whet the appetite, but give little of substantial information. I know, it's the nature of the beast in science journalism, but still ...
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eidako
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### Re: Lighter than Air Solid

sourmìlk wrote:This is probably a stupid question, but if this metallic lattice material is lighter than air, shouldn't it float?

That's what makes me incredulous about the claim. Irvine sits 200 feet above sea level. Unless the chunk of metal in the photograph is in a tank of helium, it shouldn't be resting on the dandelion; it should be planted on the ceiling.

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### Re: Lighter than Air Solid

For a moment I was wondering how you knew what city I lived in. But it turns out it's just the local university you were referencing. Yeah, I've been to UCI, and the air density is about normal. It's possible they photographed it in a vacuum, maybe?
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### Re: Lighter than Air Solid

I think the "lighter than air" claim is just terrible reporting. This article manages to convey the whole "low density" thing without the obvious contradiction that it's 99.99% air and yet somehow lighter than air.

sourmìlk
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### Re: Lighter than Air Solid

Holy shit, apparently the terminal velocity of a small piece of that material is something like 6 inches per second.
Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

yurell
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### Re: Lighter than Air Solid

A small piece of what shape? I mean, if I drop a small piece of paper it has really low terminal velocity due to having huge surface area.

Edit: Note to self — 'area' has two 'a's
Last edited by yurell on Sun Nov 20, 2011 3:06 am UTC, edited 1 time in total.
cemper93 wrote:Dude, I just presented an elaborate multiple fraction in Comic Sans. Who are you to question me?

sourmìlk
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### Re: Lighter than Air Solid

Presumably the same sort of rectangular shape there, though they didn't specify.
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curtis95112
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### Re: Lighter than Air Solid

I found a better article.

http://news.cnet.com/8301-30685_3-57327382-264/breakthrough-material-is-barely-more-than-air/

Apparently, it is 0.9mg/cm^3 excluding the air between the tubes.
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sourmìlk
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### Re: Lighter than Air Solid

Oh okay. So to make a light solid, you essentially just have to make the crystalline structure really sparse?
Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

Iulus Cofield
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### Re: Lighter than Air Solid

Wait, they're calculating the density excluding the air, but are they counting area that the air takes up in that density calculation? They...couldn't be, right?

sourmìlk
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### Re: Lighter than Air Solid

.....

So, in other words, if I have a cube of the material taking up 1 cubic centimeter of space, the material itself will weigh .9 grams, but all of the stuff in the space (including the air) will weigh somewhat more?
Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

yurell
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### Re: Lighter than Air Solid

No, if you have a cubic centimetre of the stuff, the material itself will weigh 0.0009 grams, but the space is filled mostly with air (99.99% by volume).

So you have one ten-thousandth of a cubic centimetre of material weighing 0.9 milligrams, giving you the material's density of 9 g cm-3, or 40% the density of iridium.

That makes the entire structure only slightly denser than air, though — the entire cube would be 1.9 times the density of air from what I can calculate (maths in spoiler).

Spoiler:
(0.9 milligrams + 0.9999 cm^3 * density of air) / cm^3

Edit: The video in curtis95112's link is the first time I've heard it pronounced nan-ometers. Here it's always pronounced nano-metres, just like centi-metres.
cemper93 wrote:Dude, I just presented an elaborate multiple fraction in Comic Sans. Who are you to question me?

sourmìlk
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### Re: Lighter than Air Solid

I think I got that but to make sure: if we were to put a 1 cm^3 cube of that material in a vacuum, how much would that cube weigh?
Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

yurell
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### Re: Lighter than Air Solid

0.9 milligrams (0.0009 grams), provided that all the air could get out the gaps.
cemper93 wrote:Dude, I just presented an elaborate multiple fraction in Comic Sans. Who are you to question me?

sourmìlk
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### Re: Lighter than Air Solid

Okay, got it. Excellent.
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### Re: Lighter than Air Solid

In particular, suppose you made a cubic meter of this material (let’s say on a space station so we don’t have to worry about gravity, and the material is essentially uniform throughout.) Next you gently lower the pressure and let the gases escape, until your cubic meter of material is in hard vacuum. Now apply a very thin coat of something hard and airtight, like plastic wrap but good (maybe thin carbon fiber plating), to the surface of the cube. Put the cube back into your spaceship, and return to Earth’s surface.

The interior of the cube has density 0.9mg/cm3, and we may assume the surface coating has negligible mass (if not, just repeat with a bigger cube: volume grows cubically, surface area only quadratically). So the cube has mass of 0.9kg. An equal volume of air has mass about 1.2kg, so the cube has apparent weight equivalent to -0.3kg (yes yes, kg is mass not force. You know what it means.) That means a buoyant force of 2.9 Newtons upward, and when the square-meter top surface bumps into the ceiling, a pressure of 0.00043 psi.

For comparison, helium has density about 0.18mg/cm3, making it 5 times lighter than this new material. A cubic-meter box of helium has mass of 0.18kg, for an apparent weight of -1.0kg. That means a buoyant force of 9.8 Newtons upward, and a pressure of 0.0014 psi.
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csanders
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### Re: Lighter than Air Solid

Calculating the density of something that doesn't fill the space doesn't seem right. Since the article compared it to the Eiffel Tower, I calculated the tower's density the same way. The Eiffel Tower has a density of 4.3 kg/m3 or (5.6 kg/m3 if you include the air). That makes the tower about 1/25 the density of styrofoam, and almost as light as aerogels or this new lattice stuff. We're lucky the Eiffel Tower doesn't just blow away...

This sounds like a really interesting material, I just wish reporters would use a little common sense. The picture doesn't show it floating away, so it's obviously not really lighter than air.

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### Re: Lighter than Air Solid

Iulus Cofield wrote:Wait, they're calculating the density excluding the air, but are they counting area that the air takes up in that density calculation? They...couldn't be, right?

Assuming the air isn't trapped inside, this would get them the density (mass / occupied volume) the material would have in a vacuum.

However, using that number to claim it's "lighter than air" is just misleading. Even if a cubic centimeter of the material, in a vacuum, would have less mass than a cubic centimeter of air, that comparison is useless because it couldn't have that density in air (and therefore float) unless they sealed in the vacuum somehow, which would require more stuff that would increase its mass again.
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Iulus Cofield
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### Re: Lighter than Air Solid

What you say is exactly what I think.

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### Re: Lighter than Air Solid

Besides, if you place a cubic centimeter of air in a vacuum the density will be even less.
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### Re: Lighter than Air Solid

if this stuff was made in a large amount, sealed and then have all the air evacuated, would it (speculate) have the strength to support it's own structure against the pressure of air? if so, could this stuff be used to make lighter-than-air aircraft?

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### Re: Lighter than Air Solid

AvatarIII wrote:if this stuff was made in a large amount, sealed and then have all the air evacuated, would it (speculate) have the strength to support it's own structure against the pressure of air? if so, could this stuff be used to make lighter-than-air aircraft?

Even if it was able to handle air pressure, it'd have to be able to deal with a significant amount of extra forces to be viable for an aircraft. If you're thinking more along the weather-balloon / dumb drone line instead, then I could see this being useful for a long term observation device, assuming it was sturdy enough.

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### Re: Lighter than Air Solid

Just asking, mind you, but density is a function of volume and weight is a function of mass, right? The properties of this pertain to the way air acts with relation to the solid component, is that right? And a thing floats because of the mass it displaces? Take the air out of the lattice and you have the lattice. This thing has no strength. It's value as an insulator derives from the way heat moves through it, It uniqueness is a product of its construction. "Lighter than air solid". face palm for my race.

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### Re: Lighter than Air Solid

morriswalters wrote:Just asking, mind you, but density is a function of volume and weight is a function of mass, right? The properties of this pertain to the way air acts with relation to the solid component, is that right? And a thing floats because of the mass it displaces? Take the air out of the lattice and you have the lattice. This thing has no strength. It's value as an insulator derives from the way heat moves through it, It uniqueness is a product of its construction. "Lighter than air solid". face palm for my race.

I may be misunderstanding what you're saying, but for one thing, density is also a function of mass. And when you say "This thing has no strength", what kind of strength are you referring to? Structural? It's structural strength (to my knowledge) is similar in principle to a bridge; the strength is a function of the materials used in construction and the dissipation of force through the lattice, thus the lattice itself is part of the reason for any strength it has.
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morriswalters
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### Re: Lighter than Air Solid

Density is volume per unit mass. The density of the material occurs because of the way it's constructed. Density varies as the volume changes while the mass stays the same. The material is light because of the amount of material per unit volume is small. Strength is a product of shape and the material composing a shape. The ultimate strength of a material is defined by the strength of the material for a given mass plus other sub-properties such as hardness, elasticity, et al.. Thus we make bridges of steel and not paperlead. The product supports its own weight but its fragile because its light, there not enough material there to give it strength. A steel bridge at a similar scale would be just as fragile..

Edit in italics

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### Re: Lighter than Air Solid

morriswalters wrote:Density is volume per unit mass. The density of the material occurs because of the way it's constructed. Density varies as the volume changes while the mass stays the same. The material is light because of the amount of material per unit volume is small. Strength is a product of shape and the material composing a shape. The ultimate strength of a material is defined by the strength of the material for a given mass plus other sub-properties such as hardness, elasticity, et al.. Thus we make bridges of steel and not paperlead. The product supports its own weight but its fragile because its light, there not enough material there to give it strength. A steel bridge at a similar scale would be just as fragile..

Edit in italics

You've got density backwards: it's mass/volume. Also, density is a function of temperature and pressure. In solids, and to a lesser extent, liquids, this is less apparent or not apparent, but in gases, it's quite so (and you can pump more of a gas into a given volume, showing that mass doesn't always have to stay the same to see a density change. On that side, though, increasing the amount of gas in a container increases the pressure it exerts or, conversely, the pressure the walls of the container must exert to contain it, and thus goes back to the idea that density is a function of pressure, and gas density is generally quoted at specific values of temperature and pressure).

But have you ever seen a competition to build bridges from balsa wood? The structure of the wood makes it so that, while containing relatively little "material" (I'd like to ask you to define this a bit more precisely) and being low-density, it retains a remarkable degree of strength, and can be built to support weights much larger than itself in the right construction because of the material strength (that is, the strength of the cellular material comprising the wood) and because of the way in which such a bridge is built; this is the whole point behind modern bridge-making.

I think we're arguing past each other a little bit here, except for the definition of density. In the case of the micro-lattice, the relatively small amount of nickel-containing compound in the walls of the lattice means there is relatively little "material" to it, which does limit its strength in some applications, but the lattice itself is perhaps even more important to the structural strength of such an object, and is the reason why such an object with so little material to it can be structurally impressive.
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morriswalters
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### Re: Lighter than Air Solid

Sorry mass/volume.

Radical_Initiator wrote:Also, density is a function of temperature and pressure.

Radical_Initiator wrote:gas density is generally quoted at specific values of temperature and pressure

No. Hold the volume fixed and no matter what you do to it density won't change. Density varies by volume.

Strength is a relative function. Shape can let a material reach it's maximum strength, but that's a scaling function. Because it is a micro structure surrounded by air it's as strong as that particular structure can made from that particular material with structural members the cross section that they are. It can't handle weight like a scaled up structure would be able to. Any load that you could put on it in the real world would load all the members at the same time. Think of the Hoover Dam being dropped on the Brooklyn Bridge. An identical structure built of steel would be stronger. How they built it is what is important.

The yahoo writer is an idiot. It's not a solid, it's a structure. And if a materials Scientist that said it is less dense than air than he should give up his degree. Elemental density is the ratio of molecules or atoms per unit measure of volume and is the same for solids. Structural density is a different although related thing. The Iridium in the metal composing the lattice is denser than air. You can't compare a structure and air at all using density. Bad writing and worse Science.

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### Re: Lighter than Air Solid

morriswalters wrote:Sorry mass/volume.

Radical_Initiator wrote:Also, density is a function of temperature and pressure.

Radical_Initiator wrote:gas density is generally quoted at specific values of temperature and pressure

No. Hold the volume fixed and no matter what you do to it density won't change. Density varies by volume.

And how do you hold volume fixed?

morriswalters wrote:Strength is a relative function. Shape can let a material reach it's maximum strength, but that's a scaling function. Because it is a micro structure surrounded by air it's as strong as that particular structure can made from that particular material with structural members the cross section that they are. It can't handle weight like a scaled up structure would be able to. Any load that you could put on it in the real world would load all the members at the same time. Think of the Hoover Dam being dropped on the Brooklyn Bridge. An identical structure built of steel would be stronger. How they built it is what is important.

I'm not 100% sure what you're saying here. No, I would not expect a balsa wood bridge to behave as well as a steel bridge at the same size. I would, however, expect the principles that makes the balsa wood bridge effective at a small size to reflect the same principles that make a steel-and-concrete bridge effective at its size; strength of material is important, but the distribution of load is at the same level of importance, if not moreso. This micro-lattice would probably not have desirable large-scale structural properties, as even watching deformation of the small-scale version suggests it would not be able to support loads of any meaningful size. It would seem to be better suited to shock absorption applications, where the ability to compress without losing structural integrity is important.

morriswalters wrote:The yahoo writer is an idiot. It's not a solid, it's a structure. And if a materials Scientist that said it is less dense than air than he should give up his degree. Elemental density is the ratio of molecules or atoms per unit measure of volume and is the same for solids. Structural density is a different although related thing. The Iridium in the metal composing the lattice is denser than air. You can't compare a structure and air at all using density. Bad writing and worse Science.

No substantive disagreement here, although I tend to think these kinds of articles are a result of Bad Science Writing more than bad science. The latter does occur too frequently, though.
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