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July 05, 2008

Creating strong macroscale Carbon nanotube material


Back in 2006, then Los Alamos researcher Yuntian Zhu was making 4 centimeter long strands of carbon nanotubes and was talking about forming Superthreads out of it with 100 times the strength of steel. The actual GPa strength was not mentioned in the online article.

Yuntian Zhu is now at NC State and is now making shorter arrays of carbon nanotubes This research paper does mention that the tensile strength and stiffness of these CNT fibers were measured in the range 1.35 to 3.3 GPa and 100 to 263 GPa, respectively. CNT fibers have an extremely low density, (0.2 ± 0.01) g cm–3, which is one-tenth the density of a commercial carbon fiber and about one-fortieth the density of steel. Yuntian is working with CNT Technologies to commercialize this material.

This equals 6.5 to 16.5 GPa g/cc.

They calculated the toughness (the work needed to break the fiber) of a CNT fiber as (975 ± 49) J g–1, which is comparable to the toughness of a recently reported single-walled nanotube/poly(vinyl alcohol) (SWNT/PVA) composite fiber (870 J g–1);[15] higher than the toughness of a similar fiber reported previously (570 J g–1);[13] and much higher than carbon fibers(12 J g–1), Kevlar fibers (33 J g–1), and CNT fibers reported previously (14–20 J g–1). The toughness of Zhu's CNT fibers ranged from (110 ±5) to (975 ± 49) J g–1.



From a April, 2008 paper Zhu discusses growth of ultralong (4.7 mm) double wall carbon nanotube (DWCNT) arrays.

The growth of long spinnable arrays has already led to the production of nanotube fibers that are much stronger per weight than any current engineering material or fiber. We expect to grow even longer spinnable nanotube arrays for spinning stronger nanotube fibers (yarns).

An online patent discusses the work and processes

A space elevator site is tracking the progress of carbon nanotubes toward the creation of suitable space elevator tethers.

In recent documents by other researchers:
In 2008, 40 GPa g/cc from Sparse (Carbon nanotubes) CNT Composite was made.

"The extraordinary reinforcing efficiency of single-walled carbon nanotubes in oriented poly(vinyl alcohol) tapes", Wang et al. IOP Nanotechnology vol. 18 –
inferred strength of SWNTs from a 1% CNT reinforced plastic tape.

In 2007, 9 GPa g/cc strenth material for millimeter lengths

"High-Performance Carbon Nanotube Fiber", Krzysztof Koziolet al, Science Magazine, 2007 - Measurement of the strongest of a sample of mm-long pure aggregated carbon nanotube fibers.

Goal 2010, 35 GPa g/cc for 1000 km x mm

Minimal value for Space Elevator ribbon, Taper Ratio=6.3 with 33% safety factor.
Comparative Ribbon Mass = 4.6 - May require more efficient power system.

Goal 2011, 50 GPa g/cc for 1000 km x mm

Basic value for Space Elevator ribbon, Taper Ratio=3.5 with 33% safety factor.
Comparative Ribbon Mass = 2.0

Goal 2012, 80 GPa g/cc for 1000 km x mm

Desirable value for Space Elevator ribbon, Taper Ratio=2.5 with 50% safety factor.
Comparative Ribbon Mass = 1.0

The 2008 work by Z Wang is getting a follow up navy study for increased percentages of carbon nanotubes in plastic

This STTR requests proposals that develop a clear scientific understanding of the main obstacles to ultrahigh CNT loading in nanocomposites and that proposes new methods or approaches to increasing the loading of well dispersed CNTs in structural resins beyond 10% weight fraction.



3 comments:

Brock said...

What aren't I understanding about the cnt-technologies slides? Their "Specific Strength" tables don't have any units. What does it mean they have a specific strength of 172.7? According to wikipedia, steel is better than that and kevlar has an ss of 2514.

I must assume I'm reading something wrong, because CNT Tech's chart says kevlar has an ss of 20. What gives? What am I missing?

Is spaceward.org using the same units of measurement as CNT Tech? They say that an optimal space elevator cable will need an ss of 80. Did CNT Tech really more than double that?

bw said...

They are not using the same units. Spaceward.org is focused on GPa cc/g

Which is the first column of the CNT tech chart g/cc divided into GPa strength. GPa strength is 1.5-3.3 GPa which is listed in the paper. I have calculated the CNT Tech material to be 6-16.5 GPa cc/g. This is in between the two announcments that spaceforward is quoting. Once at 9 GPA cc/g and the other at 40 GPa cc/g.

The specific strength CNT tech is using is different from units for specific strength. I believe the CNT tech units are 1/100th the wikipedia numbers.
http://en.wikipedia.org/wiki/Specific_strength

Brock said...

Thanks bw. They looked about 100:1, but it's been a long, long time since I've used any units like these. The side effects of the schooling and practice of law, I'm afraid.

Still, it's very nice to see such progress. It's been incredibly exciting watching our progress approach the necessary tether strengths so rapidly.