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Fuzzy Fibers

May 4, 2017

When our children were young, my wife would entertain them by reciting the following rhyme
Fuzzy Wuzzy was a bear,
Fuzzy Wuzzy had no hair,
Fuzzy Wuzzy wasn't fuzzy,
was he?

She had heard this venerable rhyme by some unknown author in her own childhood. While fuzz is an adorable characteristic of a teddy bear, it's generally a household nuisance. Fuzz, however, relates to a few technological innovations. On the lighter side, we have the simple fuzz effect electronic circuits that simulate a fuzz bass guitar. In more serious electronics we have fuzzy sets and fuzzy logic that enable fuzzy control systems. There are also fuzzy extractors that convert biometric data to crypotographic keys. Teddy bear

Animal fur is designed to resist and repel water, trapping pockets of dry air near the skin to provide thermal insulation.

In the case of white polar bears and brown forest bears, it also acts as camouflage in their specific environments.

(Wikimedia Commons photograph by Jonik.)


Probably the most important technical use of fuzz is in Velcro® fasteners. As I wrote in a previous article (Insect Velcro, April 22, 2013), Velcro was invented by the Swiss electrical engineer, George de Mestral, who noticed how well burdock burrs, which cover the seeds of burdock as an aid to their dispersal, stuck to his clothing. De Mestral examined the burrs under a microscope and found that they were covered with hooked spines.

De Mestral developed a fastener based on the burdock principle, and received patents for Velcro®, a word formed from the French velours (velvet) and crochet (hook).[2] As is typical for important inventions, expiry of the Velcro® patent in 1978 unleashed a flood of like products into the world. The original Velcro® US patent is currently cited by 210 other patents and patent applications.[2]

Figure 4 of US Patent No. 3,009,235, 'Separable Fastening Device,' by George de Mestral, November 21, 1961

Figure four of US Patent No. 3,009,235, 'Separable Fastening Device,' by George de Mestral, November 21, 1961.

(Via Google Patents.[2]


An interesting illustration of the importance of Velcro® in today's world is its reference in "Carbon Creek," the second episode of the second season of the television series Star Trek: Enterprise, September 25, 2002. In that episode, a Vulcan, stranded on Earth and needing some quick cash, sells the patent rights to the Vulcan version of Velcro® (Vulcro?).

Materials scientists at Rice University (Houston, Texas), Hysitron Inc. (Minneapolis, Minnesota), and NASA's Glenn Research Center have used the Velcro® principle to improve the stability of high temperature ceramic composites for use in rocket engines. They developed "fuzzy fibers" of silicon carbide (SiC) that interlock together to strengthen silicon carbide fiber-reinforced composites.[3-4]

While nickel superalloys are presently used in high temperature engines, ceramic materials are required for operation at higher temperatures. Ceramic is a brittle material, so ceramic matrix composites are used in which silicon carbide fibers strengthen the materials. The fibers are first woven and layered before infiltration with a SiC ceramic matrix.[3-4]

The motivation for the fuzzy fiber concept came from previous experiments with the growth of carbon nanotubes on ceramic wool.[4] In the fuzzy SiC process, a silicon carbide fiber is first coated with an iron catalyst, then a carpet of carbon nanotubes is formed on its surface using a water-assisted chemical vapor deposition process developed in part at Rice. The carbon nanotubes are then converted into an SiC fuzz by heating in the presence of silicon nanopowder at high temperature.[3-4] This synthesis technique ensures a strong bond of the SiC fuzz to the fiber.[3]

Silicon carbide fiber surface fuzz

Electron micrographs of a fuzzy fiber surface. The fuzz (right) is formed by reaction of carbon nanotubes (left) with silicon, and it was found to resist heating to at least 1,000°C.[4] (Ajayan Research Group/Rice University image.)


The surface fuzz on the fibers acts as a nanoscale version of Velcro® hooks and loops that causes contacting fibers to interlock.[4] This tight interlocking provides not only strength, but also resistance to environmental effects such as oxidation.[3-4] The material should offer a longer fatigue life and higher temperature resistance.[3] Tests showed that the shearing force between fibers was greater with the fuzzy coating.[4]

Amelia Hart, a research team member, explains
"Before they used silicon carbide composites, many engine parts were made of nickel superalloys that had to incorporate a cooling system, which added weight to the whole thing... By switching to ceramic matrix composites, they could take out the cooling system and go to higher temperatures. Our material will allow the creation of larger, longer-lasting turbo jet engines that go to higher temperatures than ever before."[4]

Says Chandra Sekhar Tiwary, a Rice postdoctoral associate who participated in this research, "The silicon carbide fiber they already use is stable to 1,600 C... So we're confident that attaching silicon carbide nanotubes and wires to add strength will make it even more cutting-edge."[4] The research team anticipates application of this technique to other materials.[4] Funding was provided by the Air Force Office of Scientific Research through its Multidisciplinary University Research Initiative.[4]

Fuzzy attachment of silicon carbide fibers

Electron microscope image of silicon carbide fibers joined by surface fuzz.

(Ajayan Research Group/Rice University image.)


References:

  1. Margaret Andrews, "FuzzyWuzzy (quickly) Tongue Twister," YouTube Video, December 19, 2015.
  2. George de Mestral, "Separable Fastening Device," US Patent No. 3,009,235, November 21, 1961, (via Google Patents).
  3. Amelia H.C. Hart, Ryota Koizumi, John T Hamel, Peter Samora Owuor, Yusuke Ito, Sehmus Ozden, Sanjit Bhowmick, Syed Asif Syed Amanulla, Thierry Tsafack, Kunttal Keyshar, Rahul Mital, Janet Hurst, Robert Vajtai, Chandra Sekhar Tiwary, and Pulickel M Ajayan, "Velcro®-Inspired SiC Fuzzy Fibers for Aerospace Applications," ACS Appl. Mater. Interfaces, Just Accepted Manuscript (March 28, 2017), DOI: 10.1021/acsami.7b01378.
  4. Mike Williams, "'Fuzzy' fibers can take rockets' heat," Rice University Press Release, March 30, 2017.

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