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Posts Tagged ‘materials science’

Molten aluminum mixing with water could have ultimately brought the towers down

Simensen’s idea, presented at a materials technology conference in San Diego this week, is thus: after the planes impacted the WTC towers, tons of molten aluminum ran down into the floors below the impact sites, mingling with several hundred liters of water from the buildings’ fire sprinkler systems. This mix of aluminum and water is known to cause a chemical reaction that can not only boost temperatures but also put off combustible hydrogen in the process. Basically, it’s a recipe for a really hot explosion.

The official 9/11 report assigns blame for the collapsing towers to the steel structural beams at the building’s core. Basically, it says that these beams became super-heated by the jet fuel inferno created by the impacting aircraft, and that in turn caused the structures to fail.

But Simensen’s explanation is intriguing. It doesn’t dismiss the official report, but simply claims that it doesn’t tell the whole story. He says the aluminum industry has recorded more than 250 water-aluminum explosions since 1980, and that at one point aluminum maker Alcoa did an experiment involving just 44 pounds of molten aluminum and 20 liters of water (along with a small quantity of rust, which exacerbates the reaction). The resulting explosion destroyed the lab and left a 100-foot crater, he says.

That was under controlled conditions, but extrapolate that to the uncontrolled conditions inside the WTC towers just after the attacks. Jet fuselages contain roughly 33 tons aluminum alloy that melts at roughly 1,220 degrees, Simensen says, turning to a water-like liquid at nearly 1,400 degrees. When the aircraft hit, they exploded and were immediately trapped between floors where debris like plaster quickly melted around them, creating a kind of insulated oven that would push temperatures well north of aluminum’s melting point.

That melted aluminum would then have run down to lower floors, where sprinkler systems were pumping water onto the floors. Once mixed, water and aluminum would’ve immediately reacted, boosting temperatures to up to 2,700 degrees and putting off explosive hydrogen. Thus, just as the steel supports were weakening as a result of the spiking temperatures, the hydrogen blasts would’ve been strong enough and hot enough to blow out a section of the building. That confluence of factors could have easily led to the “pancaking” of the floors above that eventually brought the buildings to their horrifying ends.

Knowing next to nothing about aluminum-water reactions, we’re not out to endorse Simensen’s theory. But it does address some loose ends, like the appearance of explosions from inside the buildings as they began their final collapses. The half hour to 45 minutes that such an aluminum meltdown would require also is roughly consistent with the time elapsed between the impacts and the collapses, Simensen says (once again, we’re not endorsing said math, just reporting what he said).

At this point we’ll never really know what happened. All the same, it’s an interesting bit of chemistry to think about.

[AFP]

In other words, it doesn’t sound easy. But a material like this is necessary if companies like IBM are going to move beyond stacking a few layers of silicon and get down to the business of stacking 100-chip towers that will power the devices of the future.

3-D semiconductors are basically multi-layered chips that can stack computing power, networking, and memory all into one neat system-on-a-chip. Right now companies like IBM can stack a handful of chips, but what they want are silicon towers. That means they need some kind of mortar that possesses these unique properties to hold everything together. That’s what 3M and IBM are striving for: some kind of adhesive that could coat entire silicon wafers, holding them tightly together while still dissipating heat away from heat-sensitive components like logic circuits.

And they want it by 2013--about the same time the first generation of smaller 3-D processors is expected to hit the market in mobile devices. If they get it right, they predict that they could leapfrog today’s existing processor technology, creating a silicon “brick” 1,000 times faster than today’s fastest microprocessors.

Described simply (you can get the more in-depth description via the video below), the system’s key component is a piece of transparent, synthetic rubber coated on one side with a metallic paint composed of very tiny particles. When the non-painted side is pressed against an object--even an object with very small features like the ink on a piece of paper (see image above)--the metallic paint deforms to capture those features.

Cameras set at various angles then capture that deformation from all sides, and computer-vision algorithms turn them into 3-D images. Contrast that with the usual method of obtaining a 3-D image with similar resolution--expensive and sensitive microscopes, vibration isolation tables, high-powered computers--and GelSight, as it is known, looks like a pretty big leap forward for both resolution and sheer simplicity.

GelSight also gets around a key problem with 3-D imaging. By translating an object’s most minuscule features--GelSight can measure features down to less than one micrometer in depth and roughly two micrometers across--through the gel to the metallic paint, it circumvents imaging problems introduced by the various optical properties of various materials (like, for instance, an opaque gel or a clear crystalline object, both of which interact with light differently than, say, a solid object that lets no light pass through).

Potential applications range from distinguishing moles from cancerous growths to quickly and cheaply inspecting manufactured goods to matching spent bullet casings to the firearms that fired them. See GelSight in action below.

[MIT News]

Published as part of a paper recently published by ACS Nano, the Rice lab’s work on Girl Scout Cookies began when lab chemist James Tour mentioned at a meeting that his team had turned table sugar to graphene--a one-atom-thick layer of carbon possessing remarkable properties of strength and conductivity. He claimed that he and his grad students could grow graphene from any carbon source, and it just so happened there were Girl Scout Cookies being passed around the meeting.

And so a challenge was born. The lab invited Girl Scout Troop 25080 to join them in Rice’s nano lab to see exactly how cookies become a prized version of carbon. In their demo, they made graphene from a range of materials--grass, chocolate, a cockroach leg, even dog excrement (special thanks to Sid Vicious the mini dachshund) to show that high-quality graphene is basically waiting to be extracted from all kinds of everyday materials.

To make graphene, the Rice team uses a copper foil and a super-hot argon and hydrogen gas oven burning at more than 1,900 degrees. In this process, the object it placed on one side of the foil and, under high heat, begins to decompose. A thin sheet of graphene forms on the other side of the foil, while the residues and impurities remain on the other side.

Two of the grad students in Tour’s lab did some math given the current commercial price for quality graphene--about $250 per two-inch square--and figured that a box of shortbread cookies could generate a roughly $15 billion profit if converted to graphene.

Of course, that has everything to do with scale, supply, and demand. Right now, graphene is difficult and expensive to produce in large quantities. A box of shortbread could yield a sheet of graphene that would cover three football fields if the means of production were there. And of course if supply were that inexpensive the price would drop substantially.

In other words, the team was trying to demonstrate that--given better manufacturing means of producing graphene in bulk--sources of graphene are all around us, not that you should buy Thin Mints as long-term investment. Although in this economy you might actually come out ahead.

[Science Daily]

Metamaterials to the rescue once again

The team has demonstrated the ability to use metamaterials to engineer emitted “blackbody” radiation with an efficiency that surpasses the natural limits that should be imposed on the material by its temperature. In English, that means better energy conversion efficiency in things like photovoltaics and possibly waste heat harvesting.

A “black body” is an idealized material that absorbs all radiation that strikes it regardless of wavelength. It also emits that energy based on the material’s temperature. Black bodies don’t exist in nature, which is too bad because they are really efficient, in that they achieve a kind of equilibrium. What goes in as electromagnetic radiation comes out as thermal radiation (or “blackbody radiation”). Ideally speaking.

What the duke team has shown using metamaterials--man-made materials not found in nature--is that they can tailor that blackbody radiation in various ways, including in ways that defy the efficiency that a material would have naturally. Put another way, there is a natural limit on the radiation a given material can emit, and that limit depends on the material’s temperature. But the Duke team has shown its metamaterials can emit radiation at efficiencies beyond what nature says they should be able to (more detail on the science behind this hereand here).

The takeaway: a new class of metamaterials could lead to technologies that can harvest waste heat from industrial processes or other heat emitters at unprecedented efficiencies (read: efficiencies that actually make such energy harvesting schemes worthwhile). Or they could lead to thermophotovoltaic cells that can tailor the emitted photons to match the band gap of the semiconductor on the cell, making energy conversion far more efficient.

The acoustic diode works much like the electrical component of the same name, letting current (or, in this case, sound waves) pass in one direction but blocking it in the other. Composed of a structured arrangement of elastic spheres that ferry the sound through the material, the diode can be tuned to work only at certain frequencies or to downshift the frequencies moving through the material to lower frequencies as needed.

That opens the technology up to several potential applications. In the case of soundproofing, the technology could enable true one-way transmission of sound (rather than the simple dispersion and muting performed by “soundproofing” foams). But perhaps more interestingly, the material could be used to harvest energy from sound waves.

For instance, the tunable diode could scavenge energy from noisy machinery and channel it back into a transducer that converts those sound vibrations into electricity that could be fed back to the machine, reducing net energy consumption. It could also downshift sound frequencies to ranges that are optimal for energy conversion.

All that’s a long way off, but the notion is pretty intriguing. In the meantime, the Caltech team is also exploring a range of other technological applications for their wave-manipulating technology, including medical uses (ultrasound), architectural acoustics, and insulating materials that regulate temperature.

[PhysOrg]

Like a delicious, biocompatible computer

The prototypes of the design haven’t yet been outfitted with much memory yet, but the researchers say the capacity is there. That aspect of the material works like a memristor, existing in one of two states at any given time: conductive or resistive. These two states can represent the 1s and 0s of binary computer code, and could someday be used to program the stuff to work inside or on the human body, perhaps in medical monitoring devices or biological sensors.

It’s a pretty cool development, at least for those who think we’re all going to be cyborgs with various machinery augmenting our bodies and optimizing our lives and keeping us healthy at some point in the future. Plus, it has the consistency of Jell-O. I can’t be the only one envisioning a new generation of scrumptious, intelligent desserts.

[NCSU]