In chemistry, structure is everything. Compounds with the same chemical formula can have different properties depending on the arrangement of molecules from which they are made. And compounds with a different chemical formula but similar molecular arrangement can have similar properties.
Graphene and a form of boron nitride called hexagonal boron nitride fall into the second group. Graphene consists of carbon atoms. Boron nitride, BN, consists of boron and nitrogen atoms. Although their chemical formulas are different, they have a similar structure; It is so similar that many chemists call hexagonal boron nitride “white graphene.”
Carbon-based graphene has many useful properties. It is thin but strong and conducts heat and electricity very well, making it ideal for use in electronics.
Similarly, hexagonal boron nitride has many properties similar to graphene that could improve computers, smartphones, and LEDs, as well as biomedical imaging and drug delivery. Researchers have been studying this type of boron nitride for many years.
But hexagonal boron nitride isn’t the only useful form this compound comes in.
As materials engineers, our research team is investigating another type of boron nitride called cubic boron nitride. We want to know whether combining the properties of hexagonal boron nitride with cubic boron nitride could open the door to even more useful applications.
Hexagonal and cubic
Hexagonal boron nitride is boron nitride molecules arranged in, you guessed it, a flat hexagon. It looks like a honeycomb like graphene. Cubic boron nitride has a three-dimensional lattice structure and resembles a diamond at the molecular level.
H-BN is thin, soft and is used in cosmetics to give them a silky texture. Will not melt or deteriorate even under extreme heat; This makes it useful in electronics and other applications. Some scientists predict that it could be used to make radiation shields for spacecraft.
C-BN is hard and durable. It is used in manufacturing to make cutting tools and drills and can maintain its sharp edge even at high temperatures. It can also help dissipate heat in electronics.
Although h-BN and c-BN appear different, when combined, our research found that they have much more potential than either alone.
Both types of boron nitride conduct heat and can provide electrical insulation, but one (h-BN) is soft and the other (c-BN) is hard. So we wanted to see if they could be used together to create materials with interesting properties.
For example, combining their different behaviors can make a coating material effective for high-temperature structural applications. C-BN can provide strong adhesion to a surface, while h-BN’s lubricating properties can resist wear and tear. Both together will prevent the material from overheating.
Making boron nitride
Because this class of materials does not occur naturally, scientists must make it in the laboratory. In general, high-quality c-BN is difficult to synthesize, while h-BN is relatively easier to make into high-quality films using so-called vapor phase deposition methods.
In vapor phase deposition, we heat materials containing boron and nitrogen until they evaporate. The evaporated molecules are then deposited on a surface, cool, bond together, and form a thin BN film.
Our research team has worked on combining h-BN and c-BN using processes similar to vapor phase deposition, but we can also mix powders of the two. The idea is to create a material with the right mix of h-BN and c-BN that we can fine-tune for thermal, mechanical and electronic properties.
Our team found that the composite obtained by combining both forms of BN has a variety of potential applications. It flashes brightly when you direct a laser beam at the substance. Researchers can use this feature to create display screens and improve radiation treatments in the medical field.
We also found that we could customize the thermal conductivity of the composite material. This means engineers can use this BN composite in machines that manage heat. The next step is to try to produce large wafers made of h-BN and c-BN composite. If done precisely, we can tailor the mechanical, thermal and optical properties to specific applications.
In electronics, h-BN can act as a dielectric or insulator alongside graphene in some low-power electronics. As a dielectric, h-BN will help electronics operate efficiently and maintain their charge.
C-BN can work with diamond to create ultra-wide bandgap materials that allow electronic devices to operate at a much higher power. Diamond and c-BN both conduct heat well, and together they can help cool those high-power devices that generate a lot of extra heat.
H-BN and c-BN individually can lead to electronics that perform extremely well in different contexts; Together they have many potential applications.
Our BN composite can improve heat spreaders and insulators and work in energy storage machines and rechargeable batteries, such as supercapacitors, which are fast-charging energy storage devices.
We will continue to examine the properties of BN and how we can use it in lubricants, coatings, and wear-resistant surfaces. Developing ways to scale up production will be key to exploring applications from materials science to electronics and even environmental science.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Pulickel Ajayan, Rice University and Abhijit Biswas, Rice University.
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Pulickel Ajayan receives funding from the Army Research Laboratory and the Army Research Office.
Abhijit Biswas does not work for, consult, own shares in, or receive funding from any company or organization that may benefit from this article, and has disclosed no relevant affiliations beyond his academic duties.