Researchers produce strong, transparent carbon nanotube sheets (big advance)

University of Texas at Dallas , physorg.com ^ | 18 Aug 05 | staff

[Arkie2]

Carbon nanotubes are like minute bits of string, and untold trillions of these invisible strings must be assembled to make useful macroscopic articles that can exploit the phenomenal mechanical and electronic properties of the individual nanotubes. In the Aug. 19 issue of the prestigious journal Science, scientists from the NanoTech Institute at UTD and a collaborator, Dr. Ken Atkinson from Commonwealth Scientific and Industrial Research Organization (CSIRO), a national laboratory in Australia, report such assembly of nanotubes into sheets at commercially useable rates.

Starting from chemically grown, self-assembled structures in which nanotubes are aligned like trees in a forest, the sheets are produced at up to seven meters per minute by the coordinated rotation of a trillion nanotubes per minute for every centimeter of sheet width. By comparison, the production rate for commercial wool spinning is 20 meters per minute. Unlike previous sheet fabrication methods using dispersions of nanotubes in liquids, which are quite slow, the dry-state process developed by the UTD-CSIRO team can use the ultra-long nanotubes needed for optimization of properties.

Strength normalized to weight is important for many applications, especially in space and aerospace, and this property of the nanotube sheets already exceeds that of the strongest steel sheets and the Mylar and Kapton sheets used for ultralight air vehicles and proposed for solar sails for space applications, according to the researchers. The nanotube sheets can be made so thin that a square kilometer of solar sail would weigh only 30 kilograms. While sheets normally have much lower strength than fibers or yarns, the strength of the nanotube sheets in the nanotube alignment direction already approaches the highest reported values for polymer-free nanotube yarns.

The nanotube sheets combine high transparency with high electronic conductivity, are highly flexible and provide giant gravimetric surface areas, which has enabled the team to demonstrate their use as electrodes for bright organic light emitting diodes for displays and as solar cells for light harvesting. Electrodes that can be reversibly deformed over 100 percent without losing electrical conductivity are needed for high stroke artificial muscles, and the Science article describes a simple method that makes this possible for the nanotube sheets.

The use of the nanotube sheets as planar incandescent sources of highly polarized infrared and visible radiation is also reported in the Science article. Since the nanotube sheets strongly absorb microwave radiation, which causes localized heating, the scientists were able to utilize a kitchen microwave oven to weld together plexiglas plates to make a window. Neither the electrical conductivity of the nanotube sheets nor their transparency was affected by the welding process -- which suggests a novel way to imbed these sheets as transparent heating elements and antennas for car windows. The nanotube sheets generate surprisingly low electronic noise and have an exceptionally low dependence of electronic conductivity on temperature. That suggests their possible application as high-quality sensors - which is a very active area of nanotube research.

"Rarely is a processing advance so elegantly simple that rapid commercialization seems possible, and rarely does such an advance so quickly enable diverse application demonstrations," said the article's corresponding author, Dr. Ray H. Baughman, Robert A. Welch Professor of Chemistry and director of the UTD NanoTech Institute. "Synergistic aspects of our nanotube sheet and twisted yarn fabrication technologies likely will help accelerate the commercialization of both technologies, and UTD and CSIRO are working together with companies and government laboratories to bring both technologies to the marketplace."

The breakthroughs resulted from the diverse expertise of the article's co-authors. Dr. Mei Zhang and Dr. Shaoli Fang, NanoTech Institute research scientists, first demonstrated the nanotube sheet fabrication process, and this result was translated into diverse applications by the entire team. The other team members include Dr. Anvar Zakhidov, associate director of the NanoTech Institute; Christopher Williams, Zakhidov's graduate student from the UTD Physics Department; Dr. Sergey Lee and Dr. Ali Aliev, research scientists at NanoTech Institute, in addition to Atkinson and Baughman.

The applications possibilities seem even much broader than the present demonstrations, Baughman said. For example, researchers from the Regenerative Neurobiology Division at Texas Scottish Rite Hospital for Children, Dr. Mario Romero, Director, and Dr. Pedro Galvan-Garcia, Senior Researcher Associate, and Dr. Larry Cauller, associate professor in UTD's neuroscience program, have initial evidence suggesting that healthy cells grow on these sheets - so they might eventually be applied as scaffolds for tissue growth.

Baughman said that numerous other applications possibilities exist and are being explored at UTD, including structural composites that are strong and tough; supercapacitors, batteries, fuel cells and thermal-energy-harvesting cells exploiting giant-surface-area nanotube sheet electrodes; light sources, displays, and X-ray sources that use the nanotube sheets as high-intensity sources of field-emitted electrons; and heat pipes for electronic equipment that exploit the high thermal conductivity of nanotubes. Multifunctional applications like nanotube sheets that simultaneously store energy and provide structural reinforcement for a side panel of an electrically powered vehicle also are promising, he said.

UTD researchers began collaborating with their counterparts at CSIRO last year. In November 2004, the organizations achieved a breakthrough by downsizing to the nanoscale methods used to spin wool and other fibers to produce futuristic yarns made from carbon nanotubes.

The latest research was funded by the Defense Advanced Research Projects Agency, an agency of the United States Department of Defense, the U.S. Air Force Office of Scientific Research, the Texas Advanced Technology Program, the Robert A. Welch Foundation and the Strategic Partnership for Research in Nanotechnology.

[marvlus]

If we could just use nano technology somehow to reduce dependence on oil - that could solve a lot of problems!

[from occupied ga]

While nanotube armor may stop bullets (or may not, as I mentioned above), the armor still will not protect from the deadliest effect of a firearm: hydrostatic shock. If you're wearing armor and it stops a 30-06 moving at 3000 feet per second, you will still have to have medical attention within a short period, or you'll still die.

What a load of nonsense. Conservation of energy and momentum guarantees that the same energy and momentum is applied to the shooter as the shootee. If your statement were true, then the recoil would cause as many problens as the bullet. I only know of one case of a person getting killed by recoil and that's when the recoil toppled a heavy automatic weapon on her. What causes in injury in a gun shoot wound is the tearing an puncturing of things that were not made to be torn and punctured.

When you think about how redundant a human body is

Another load of nonsense. Yes, you have two legs - try walking with just one of them. You have two eyes - try doing a task that requires depth perception with just one of them. You have two arms. Try picking up a large package with just one. Sheesh.

[Arkie2]

The article I posted for this thread alluded to improvements in batteries. The article below expands on that and I believe the following article was written before this manufacturing breakthrough. Why does that matter to reducing dependence on oil? Better batteries for electric cars, better batteries for storage at wind farms and solar arrays. Batteries are important in the last two applications because they could serve to even out the production of electricity.

---

Introduction Ultracapacitors or double layer capacitors (DLCs) are energy storage devices whose operation is based on the double layer effect. By utilizing highly porous carbon material with a surface area up to 2000m2/g as electrodes (as in Fig. 3) commercial DLCs can achieve a energy density (6Wh/kg) much greater than the energy density of a conventional capacitor. However, this figure is much lower than the energy density reached by Lithium-Ion batteries (120Wh/kg).

Our analysis shows that the utilization of a matrix of vertically aligned CNTs as electrode structure, can lead to an ultracapacitor characterized by a power density greater than 100kW/kg (three orders of magnitude higher than batteries), a lifetime longer than 300,000 cycles, and an energy density higher than 60Wh/kg.


Double Layer Principle:

The significant energy density improvement of DLCs over other types of capacitors arises from the higher specific capacitance achieved with DLCs that can be up to 180 F/g. This result can be explained by the double layer principle discovered by Helmholtz in 1853. According to the Helmholtz model, when two electrodes, between which a potential is established, are immersed in an ionic solution, ions from the electrolyte migrate to the interface between the oppositely charged electrode and the solution.


Nanotube Enhanced Ultracapacitor:

A matrix of vertically aligned carbon nanotube (CNT) has been investigated as a DLC electrode. Our analysis shows that this configuration can provide a combination of high power density (more than four orders of magnitude greater than fuel cells) and energy density (comparable to Li-Ion batteries). The significant enhancement in the achievable DLC power density derives from the high conductivity obtainable with CNTs, which in the limit of a few microns in length present ballistic conduction. The energy density improvement of a “nanotube enhanced electrode” is due to the higher effective surface area obtainable with a structure based on vertically aligned nanotubes over activated carbon.

Recently, we have been able to grow straight single wall nanotubes (SWNT) with diameters varying from 0.7 to 2nm and a length of several tens of microns. We grew SWNTs via thermal chemical vapor deposition (CVD) on a silicon substrate coated with a catalyst consisting of nanocolloids of aluminum oxide (AlO2) coated with iron nitrogen oxide (Fe(NO3)3). The average diameter of the catalyst seeds was 3nm. The substrate coated with catalyst was processed at 900°C at atmospheric pressure by CVD in an environment saturated with hydrogen (H2) and argon (Ar). As stockfeed gas we used methane (CH4). Single wall nanotubes grew from the Fe(NO3)3 seeds via decomposition of methane at the catalyst interface.

http://lees.mit.edu/lees/projects/cnt_ultracap_project.htm

[nomorelurker]

Maybe we will go back to armored knights. If carbon tube armor is light enough you can start to engineer in other features like shock absorption even using other materials and engineering.

[JamesP81]

What a load of nonsense.

If it were a load of nonsense, then people who are shot while wearing kevlar vests wouldn't have things like broken ribs from the experience. Unless nanotube armor could stop a projectile and completely dissipate the energy away from the wearer, it would be no better than kevlar. Consider: when Kevlar stops a handgun round, it pretty much debilitates the wearer. He's not in the fight anymore. And we're talking about handgun rounds that probly don't exceed 1200 feet per second. Scale that up to 3000 feet per second for your average civilian hunting round (which kevlar is incapable of stopping anyway) and the wearer is still likely to die from the shot even if the armor stops the round. Might want to think about those things before you spout off.

Again, there is nothing in the article that suggests that carbon nanotubes have good ballistic properties. I don't see why we automatically assume that they would. It has high tensile strength, but that doesn't necessarily transfer to stopping a projectile. Hardened steel also has high tensile strength. It's also very brittle and prone to break.

The big advantage I see to this technology is the realistic possibility of aritificial limbs as good as the original.

[Physicist]

just think what might be happening in Texas if Newt and a bunch of penny pinching GOP had not shut down the Super Collider 8 years ago.

The Supercollider was cancelled in October, 1993. It happened on the Dems' watch.

I know this because I was hired at Penn in August, 1993 to do detector design for it.

For the record, I don't know that it would have been of much direct utility for this sort of technology (not that that was its purpose).

[Physicist]

Ping on #46.

[Sloth]

Let's get started on that space elevator.

[Old Professer]

Asbestos is particularly harmful (some species) because they have fishhook-type barbs that attach to the bronchial walls at the bottom of lungs and irritate the lining with the resultant scarring and death of the wall and cilia

Ordinary dust causes a condition characterized as silicosis.

[JeffersonRepublic.com]

I'm shock! Someone who knows what they are talking about. I personally like to just shoot my mouth off about issues I know nothing about - "if I don't understand, I blame Newt or Bush" /sarcasm

[Moonman62]

The Supercollider was cancelled in October, 1993. It happened on the Dems' watch.

Was it the Clintons or members of Congress that killed it?

[KevinDavis]

I think it was shut down in 93..

[doc30]

Thanks for the specifics on that. Do you think there will be health and safety issues associated with carbon nanotubes? This material is so promising, I'd hate to see lawsuit considerations kill it in its infancy.

[KevinDavis]

[KevinDavis]

I think it should be Carbon/Space Age..

[KevinDavis]

Both.. I think it had to do with it being in Texas more than anything..

[Old Professer]

Nothing in the literature points to the use of fibers woven tightly from such structures having a potential for cusing harm to human health; cost of manufacture and practical uses for such esoteria have often been the root causes of their non-penetration into the consumer goods market.

[mudblood]

This is fascinating stuff.

[doc30]

I thought it was democrat senators from states that lost out to Texas that had it killed (e.g. Mass.) If they couldn't get the funds for such a big project, no one would. Too much opportunity for missappropriation to let that one go by.

[Physicist]

Congress killed the SSC. Clinton supported it, at least when the cameras where on him.