Nanotube cylinders of boron nitride are nearly as strong as their carbon counterparts, but they also do more.
Boron nitride in its hexagonal form has a structure that is similar to carbon graphite. And like carbon, a sheet of the boron material that has a thickness of just one atom can be rolled into a tube – called a nanotube. The boron tubes are not as strong as the carbon ones, as graphene is the strongest material on Earth, but they come close.
Scientists at the State University of New York in Binghamton have discovered that the boron sheets can be formulated into a strong composite material that is capable of binding polymers.
There are also further advantages. The boron material has a higher thermal conductivity than graphene and can survive higher temperatures. It is capable of absorbing neutron particles and is chemically inert.
The scientists created a composite material of the polymer – in this case polymethyl methacrylate – and the boron nitride sheets. They then used a Nano mechanical probe to test the binding strength at the interface of the two materials. They found that the binding strength on one interface was 35% higher than for the carbon composite equivalent, and on another interface the binding strength was 20% higher than for the carbon material.
The reason that the boron material binds more strongly than carbon to the polymer comes down to the arrangement of its electrons. Carbon atoms within carbon nanotubes share out available electrons in equal measure. But in the case of the boron nitride, nitrogen atoms within the compound dominate the chemical bonding. They effectively monopolise the available electrons.
This type of unequal charge sharing means that in many locations the boron material is capable of creating stronger bonds with the adjacent polymer. The New York State University group joined with colleagues from the University of Georgia to carry out a molecular dynamic simulation of the bonding to demonstrate the strong bonds.
However, the cost of commercialisation means that the new material may not come to the market very easily. Available production of boron nitride is very low worldwide, and the nanotubes themselves emerge in a curved cylindrical form. The production cost of these per gram is $1,000, while with carbon nanotubes the production costs are a mere $10-$20 for each gram.
The challenge now is to develop a high-yield and efficient production method.
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