Photograph of a thin, flexible metallic glass fiber (left) and an electron microscopy image of a metallic glass rope weaved from such fibers (right).
The metals we are most familiar with adopt a periodic, crystalline atomic arrangement. Metallic glasses, on the other hand, have an amorphous structure that is well suited for certain fabrication processes such as casting. Glassy metallic wires with widths of micrometers or nanometers are also less brittle than their bulk metallic counterparts, but such wires have proved difficult to fabricate. Wei Hua Wang and colleagues from the Chinese Academy of Sciences in Beijing have now developed a simple method for producing well-controlled and defect-free metallic glass wires.
The researchers found that the resulting wires had high structural uniformity. Their surfaces were as smooth as those of industrial silica glass fibers, and the wires could tolerate a much greater bending angle, in excess of 90° (see image). The diameters of the wires were easily controlled by adjusting the drawing force, allowing the researchers to draw wires as thin as 70 nm—ten times thinner than any wires produced previously.
This work increases the feasibility of using metallic glass fibers as building blocks for microscale and nanoscale devices, with possible applications in composites, sensors, intelligent fabrics, circuit interconnects and optical waveguides. It also holds considerable intrinsic scientific interest, says Wang. “Our fibers can be used as a model system to study many fundamental issues in metallic glasses.”
An ideal fabrication process for such wires should be able to produce narrow wires with uniform surfaces that are free of defects, and should also be applicable to a wide variety of starting materials. Existing methods have not been able to satisfy all of these requirements simultaneously, often because they involve a foreign material, for cooling or filling, that comes in contact with the wires during fabrication.
Wang and his colleagues developed a method that avoided such contact by placing a bulk metallic glass rod inside a steel cylinder, which was then heated by a magnetic induction coil. The rod was heated rapidly from a solid to a ‘supercooled’ liquid state—meaning that it became liquid despite being heated to below its melting point. An ultrathin wire could then be drawn from the low-viscosity liquid using a suspended weight or a rotating shaft.
Other research for metallic glass nanowires for better fuel cells
Electrochemical devices have the potential to pose powerful solutions in addressing rising energy demands and counteracting environmental problems. However, currently, these devices suffer from meager performance due to poor efficiency and durability of the catalysts. These suboptimal characteristics have hampered widespread commercialization. Here we report on Pt57.5Cu14.7Ni5.3P22.5 bulk metallic glass (Pt-BMG) nanowires, whose novel architecture and outstanding durability circumvent the performance problems of electrochemical devices. We fabricate Pt-BMG nanowires using a facile and scalable nanoimprinting approach to create dealloyed high surface area nanowire catalysts with high conductivity and activity for methanol and ethanol oxidation. After 1000 cycles, these nanowires maintain 96% of their performance—2.4 times as much as conventional Pt/C catalysts. Their properties make them ideal candidates for widespread commercial use such as for energy conversion/storage and sensors.