TOTALLY TUBULAR
Their name may not roll off the tongue, but boron nitride nanotubes are poised to be a made-in-Canada tech success story,
When carbon nanotubes emerged on the scientific scene in the 1990s, it sparked bold talk of building ultralight planes, safer and more efficient cars, long-lasting super-batteries and elevators that stretch into space.
This wonder material, composed of a single cylindrical layer of carbon atoms arranged in a honeycomb pattern, proved more than 100 times stronger than steel and one-sixth the weight, not to mention 1,000 times better than copper at conducting electricity. Since their discovery, carbon nanotubes have become a multibillion-dollar market.
But a newer, some say superior, type of nanotube made out of atoms of boron and nitrogen now promises to give carbon nanotubes a run for their money, with the National Research Council of Canada at the forefront of efforts to commercially produce what could kick-start an entirely new industry.
“We hope to keep the lead,” said Benoit Simard, a principal researcher with NRC’s emerging technologies division. “Interest is growing.”
The potential is huge. Boron nitride nanotubes, or BNNTs, are just as strong and light as their carbon cousins, but a crucial difference is their tolerance for extreme heat. Carbon nanotubes start to burn up at 400 C, while BNNTs can withstand temperatures exceeding 800 C.
“For any application that requires flame resistance, the material is fantastic,” said Simard.
Another key difference is that BNNTs don’t conduct electricity, making them excellent insulators. They also have the ability to shield against dangerous neutron and ultraviolet radiation. But perhaps their most distinguishing feature is that they can be made into transparent materials or dyed different colours. With carbon nanotubes, you’re stuck with basic black.
Many materials offer one or a few of these characteristics, but not all, explaining why the U.S. Department of Energy’s Jefferson Lab describes BNNTs as “the most interesting stuff you may have barely heard of.”
The National Research Council became the world’s top producer of BNNTs in August 2014, with the launch of a pilot facility that can produce the material 100 to 200 times faster than previous methods.
Under an electron microscope, individual nanotubes are one tenthousandth the thickness of a human hair, but a few grams of the stuff looks like a fistful of white cotton candy or dryer lint.
Last year, the council struck an exclusive, 20-year manufacturing agreement with Tekna, based in Sherbrooke, Que., which plans to sell the material to customers in the defence, security, aerospace, biomedical and automotive sectors.
The unprecedented combination of strength, lightness and transparency of BNNTs lets the imagination run wild. Could it be possible to make a plane with a transparent fuselage, something similar to Wonder Woman’s invisible, blast-proof jet?
“If you could dream that far out, I guess the answer would be yes,” said Simard, though more practical applications are in the works.
“We have great hope in developing a new type of more-resistant glass and integrating that into anything requiring transparency,” he said. “Take a windshield on an aircraft. It’s thick, heavy. You can imagine making this type of glass much thinner and therefore lighter, meaning a lighter plane overall that uses less fuel.”
The extensive network of wiring within that same plane could be also insulated with BNNT fibres, making the aircraft even lighter. For spacecraft, the reduced weight could substantially lower launch costs while shielding equipment and astronauts from radiation.
The Department of Defence is working closely with the NRC to develop transparent vehicle and body armour that’s better at withstanding blasts and can protect soldiers from fire and electrocution. Over time, as production costs fall, the material could find its way into high-end commercial vehicles, building materials and even medical equipment. Canada has competition. Roy Whitney, president and chief executive officer of BNNT, LLC, a company based in Newport News, Va., re- cently began selling cotton-ball samples of the material using a production method licensed from NASA and the U.S. Department of Energy. However, it seems the NRC and Tekna are still ahead in the race.
Whitney said there is great interest in using BNNTs to add strength and give unique characteristics to polymer, ceramic and metal composites, while reducing their weight.
One promising area is the use of BNNTs in additive manufacturing, known as 3D printing, by which objects are printed in layers using “ink” made of laser-melted powders. Whitney said the temperatures required to liquefy the powders could be tolerated by BNNTs but would burn up carbon nanotubes. Aluminum powder, for example, has a melting point of about 600 C.
Within 10 years, BNNTs will be just as common as carbon nanotubes are today in a range of products, Whitney predicted.
Since BNNTs offer clear advantages and were first developed not long after carbon nanotubes, why has it taken so long to produce them commercially?
The answer, Simard explained, lies in one of their most beneficial qualities: high tolerance to heat makes BNNTs challenging to work with.
The boron nitride powders used to create the material are available in industrial quantities and are relatively inexpensive. But synthesizing them into nanotubes — that is, transforming flat sheets of the molecules into stiffened cylindrical shapes — requires extreme temperatures and pressure, making the process difficult and expensive.
This has limited production capacity to just a few milligrams per batch. But using a super-hot Tekna-supplied plasma torch to vaporize the powder in a special reactor chamber, the NRC proved it could produce kilograms of the fluff every year — and that’s just the start. “We’ll be taking larger strides to stay ahead of the competition,” said Simard.