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No limit yet for carbon nanotube fibers:
The Rice lab of chemical and biomolecular engineer Matteo Pasquali reported in Carbon it has developed its strongest and most conductive fibers yet, made of long carbon nanotubes through a wet spinning process.
[...] "The goal of this paper is to put forth the record properties of the fibers produced in our lab," Taylor said. "These improvements mean we're now surpassing Kevlar in terms of strength, which for us is a really big achievement. With just another doubling, we would surpass the strongest fibers on the market."
The flexible Rice fibers have a tensile strength of 4.2 gigapascals (GPa), compared to 3.6 GPa for Kevlar fibers. The fibers require long nanotubes with high crystallinity; that is, regular arrays of carbon-atom rings with few defects. The acidic solution used in the Rice process also helps reduce impurities that can interfere with fiber strength and enhances the nanotubes' metallic properties through residual doping, Dewey said.
"The length, or aspect ratio, of the nanotubes is the defining characteristic that drives the properties in our fibers," he said, noting the surface area of the 12-micrometer nanotubes used in Rice fiber facilitates better van der Waals bonds. "It also helps that the collaborators who grow our nanotubes optimize for solution processing by controlling the number of metallic impurities from the catalyst and what we call amorphous carbon impurities."
The researchers said the fibers' conductivity has improved to 10.9 megasiemens (million siemens) per meter. "This is the first time a carbon nanotube fiber has passed the 10 megasiemens threshold, so we've achieved a new order of magnitude for nanotube fibers," Dewey said. Normalized for weight, he said the Rice fibers achieve about 80% of the conductivity of copper.
"But we're surpassing platinum wire, which is a big achievement for us," Taylor said, "and the fiber thermal conductivity is better than any metal and any synthetic fibers, except for pitch graphite fibers."
I wonder how useful the thermal conductivity would be in cooling computer chips?
Journal Reference:
Lauren W. Taylor, Oliver S. Dewey, Robert J. Headrick, et al. Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers, Carbon (DOI: 10.1016/j.carbon.2020.07.058)
(Score: 0) by Anonymous Coward on Tuesday August 18 2020, @11:43PM (1 child)
This is only a modest improvement past Kevlar, so this particular process is not good enough for a space elevator.
Space elevators in general are not going to be a great idea, at least not for Earth. An orbital ring [wikipedia.org] is easier to build, accessible worldwide, provides faster travel to orbit and doesn't require any new technology, other than traffic volume.
An elevator is only really a good choice if your destination is not so big that the materials are too exotic, big enough that just using a rocket isn't too easy, and rotates fast enough that it doesn't have to be excessively long. Ceres, maybe. Big KBOs that don't have moons. Mars, if you squint.
(Score: 2) by deimtee on Wednesday August 19 2020, @05:12AM
Mars is not only ideal for an elevator, it has a ready-made counterweight. Unless we have some fundamental material breakthroughs I don't think we'll get a stationary one on Earth.
A rotating skyhook could be built with Spectra fiber now, but would probably take out the occasional starlink satellite. It would also require lifting a few thousand tonnes to LEO and draining the Van Allen belts (surprisingly easy to do, when you look into it).
If you cough while drinking cheap red wine it really cleans out your sinuses.