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January 11th, 2013

Strong, lightweight, and ductile (yes, ductile) silica glass nanofibers

Published on January 11th, 2013 | Edited by: Eileen De Guire

University of Southampton (UK) scientist, Gilberto Brambilla, developed the strongest, lightest known silica glass nanofibers. Credit: U. Southampton.

It looks like a team of optoelectronics researchers from the University of Southampton in Britain may be getting into the structural composites business.

According to the press release, the group discovered how to make “the strongest, lightest weight silica nanofibers,” which it claims are 15 times stronger than steel and potentially can be manufactured in lengths that measure in the thousands of kilometers. They say the discovery could transform the aviation, marine, and safety industries and be used in products like aircraft, speedboats, helicopters, and more.

The discovery was made by Gilberto Brambilla, principal research fellow at Southampton’s Optoelectronics Research Centre (ORC), and David Payne, the center’s director.

The breakthrough came when they found that, paradoxically, the strength of the silica glass nanofibers increased as the diameter decreased. In a press release, Brambilla says, 
”Usually if you increase the strength of a fiber you have to increase its diameter and thus its weight, but our research has shown that as you decrease the size of silica nanofibers their strength increases, yet they still remain very lightweight.”

(Along similar lines, earlier this year a NIST group published a paper documenting that they observed an increase in the fracture strengths in silicon nano wires from 12 to 18 GPa as the radius of nanowires was decreased from 60 to 20 nm.)

The ORC group recognized what that could mean in terms of structural composites. Payne says in the press release, “Weight for weight, silica nanowires are 15 times stronger than high strength steel and 10 times stronger than conventional [glass reinforced plastic]. We can decrease the amount of material used thereby reducing the weight of the object.”

How is it that a team of optoelectronics researchers crossed over into investigating the glass fiber reinforcements? That is not clear, but according to the ORC’s website, Brambilla’s group has a number of active research projects investigating sensors and devices based on optical fibers and nanofibers, so presumably, they would have a natural interest in the mechanical properties of the nanofibers for handling purposes.

Some of Brambilla’s observations may lead to new insights into the relationship between structure and properties of silica glass, too. Not only do the silica nanofibers increase in strength as they decrease in size, he says, “In fact when they become very, very small they behave in a completely different way. They stop being fragile and don’t break like glass but instead become ductile and break like plastic. This means they can be strained a lot.”

The press release says Brambilla shared the work at a seminar he recently organized in the UK. I hope he also publishes a paper on this work so that the ductility secrets of these nanofibers can start to be unlocked.

The topic of glass strength keeps coming up, for example, with the introduction of Gorilla Glass 3 or the recently formed Usable Glass Strength Coalition, but this is the first time I recall seeing glass described as ductile.

I was not able to find out how the fibers are made, and in the press release Brambilla says he handled the nanofibers with his “bare hands,” which conventional wisdom says is a great way to introduce surface flaws. For sure, this is an exciting discovery, but there is a lot more the group could be telling us.


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5 Responses to Strong, lightweight, and ductile (yes, ductile) silica glass nanofibers

  1. Moirraine says:

    I am frustrated that plastics are still the #1 container of foods and are still contaminating them and the people who eat foods sitting in those cans – for months to years.

    Glass – food processors, mixers, ANY kitchen appliance you can think of that HAS PLASTIC NOW, should not, should never have.

    I am chemically damaged by the plastics as well as the other chemicals that were dumped into me as a chronically ill person (wasn’t chronically ill before I was a military dependent, military person, then military dependent again X33 years…)

    No one should have to feel this kind of pain, the incessant nausea and the ruined intestines because this society became greedy and trashed our foods from seed to table – and everywhere in-between – the water that was supposed to be “safe” wasn’t and isn’t, and many are just tired of the marginal attention that has gone into clean water, soil and food – glass should be the ONLY container besides stainless steel or silicone to ever touch food…

    Now if they can just make a REAL ceramic/glass pan that can’t be scratched with this stuff…. yeah, I can see the manufacturing coming back to the US if they are smart.

  2. Eileen De Guire says:

    You’ve done the researchers a favor by providing them a roadmap to the relevant literature on plastic deformation in silica glasses. The article titles alone imply the complexity of the mechanisms, which the University of Shouthhampton team skimmed past.

    Another reader brought a few errors in the university press release to my attention, too. He pointed out that increasing strength of fibers and whiskers with decreasing diameter is a well-known phenomenon seen in glass and other materials, and hardly comprises a “discovery.” He also pointed out that there is ample documentation in the literature to find that a “factor of 15 difference in the strength-to-weight ratios of glass fibers and high strength steel is not at all remarkable. For example, mass-produced optical fibers typically have strength-to-weight ratios 30 times that of steel! Strengths another three time higher than this have been known in smaller diameter silica fibers for many years.”

    The discussion attests to the value of the journal peer review process of authenticating scientific discoveries. This example seems to raise more questions than answers, but not of the good kind.

  3. Sheldon Wiederhorn says:

    Glasses have been referred to as “ductile” in a number of references. Perhaps the best know article on the subject is by D.M. Marsh, “Plastic flow and fracture of glass,” Proc. Roy. Soc. (London) 282A 33-43 (1964). A review of the possibility of plastic flow at crack tips in glass can be found in S.W. Freiman, SM. Wiederhorn, J.J. Mecholsky, “Environmentally Enhanced Fracture of Glass: A Historical Perspective” J. Am. Ceram. Soc. 92 [7] 1371-1382 (2009). A more modern discussion of plastic flow at indentations is given by T. Rouxel, H. Ji, T. Hammouda and A. Moréac, “Poisson’s Ratio and the Densification of Glass under High Pressure,” Phys. Rev. Let. 100, 225501 (2008). I am unaware of any reference of plastic deformation of Silica Glass in tension. It would be nice if the authors of this work would publish a paper on their work in a Peer reviewed journal, so that the work can be critically evaluated.

  4. Peter Wray says:

    Yes, the reference was to Si, but the authors are combined team from NIST Ceramics and Metallurgy Division who are working with pure Si nanowires, and also oxidized Si nanowires in both amorphous and crystalline forms of SiO2. In 2012, Stan et al., for example, reported they measured values of strengths in the range of 10–15 GPa fracture strength of silica glass NWs of elastic modulus around 100 GPa and
    radii in the range of 50–300 nm. Both groups apparently had taken note of the decreasing diameter/increasing fracture strength phenomenon; to a large extent, the NIST group has been developing a standard procedure for determining the bending stress and fracture strength of nanowires using an technique that based on simple AFM manipulation of the NWs. See http://www.ctcms.nist.gov/~davydov/12Stan_SiNW_bending_JMR.pdf

  5. Pathi says:

    If I am not wrong the article what you mentioned is about Si (nanocrystalline silicon-metal)and not silica (SiO2-glass/ceramics). Correct me if I am wrong.
    Thanks.

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