Introduction:
Boron Nitride Nanotube also known as BNNTs are the most widely popular and recently developed nanomaterials. BNNTs, due to its unique structure and intrinsic properties, have become a subject of interest in the field of Nanotechnology and commercial industries. In this article, we are going to throw some light on the structure, properties, synthesis, application and future of BNNTs in brief.
3D model of boron nitride nanotubes
Structure of BNNTs:
BNNTs exhibit a unique atomic structure owing to its special combination of Boron and Nitride compounds in a tubular hexagonal structure. They have cylindrical structure with diameter in micrometer and length in micrometer. Its typical honeycomb lattice structure contributes to its most exquisite properties.
(i) Thermal conductivity:
BNNTs have high thermal conductivity of around 3000W/mK. However, thermal conductivity of BNNTs can vary depending on the diameter of nanotubes and the orientation of BNNT film.
(ii) Mechanical properties:
BNNTs have high tensile strength, due to strong covalent bonds between Boron and Nitride compounds. They are very flexible and known to be one of the strongest materials in the world.
(iii) Electrical and Oxidation properties:
BNNTs remain stable up to 900⁰C in air and thermally decomposed around 1500⁰C in air. They can withstand harsh oxidizing environments and a very high temperature. They have superior thermo chemical stability as they are nearly inert and chemically stable.
(iv) Optical Property:
BNNTs are optically transparent in nature. They have transparency in the visible range of spectrum.
(v) Bio-compatibility:
BNNTs are bio-compatible and hydrophobic in nature. When BNNTs molecules come in contact with the molecules of a living compound, it doesn’t produce any adverse reaction.
BNNTs show a very low toxicity in living cells. They have good moisture retention capacity and also they do not impact the immune response system.
(vi) Piezoelectric properties:
BNNTs possess piezoelectric properties. When BNNTs are exposed to mechanical stress, it produces an electric charge in response to it. These effects are also reversible. When mechanical stress is removed, BNNTs stop the discharge of electric charge.
(vii) Neutron shielding:
Due to the presence of Boron elements in BNNTs, it exhibits a high Neutron absorption capacity. Hence, BNNTs act as a Neuron shielding material.
Synthesis of BNNTs:
Boron Nitride Nanotubes
The synthesis of BNNTs first occurred in the year 1995 by using arc discharge method. The other processes through which BNNTs are synthesized are chemical vapor deposition, ball milling, laser ablation, inductively coupled plasma (ICP), pyrolysis and arc jet plasma.
(i) ARC discharge method:
This method is one of the oldest techniques for the preparation of Nanomaterials. In this technique, Boron Nitride rods were inserted into a hollow tungsten anode electrode. This generates the arc plasma. The main disadvantage of this process is that you cannot produce BNNTs at a bulk rate.
(ii) Ball milling method:
This method is very cost effective. In this process, there is a direct reaction of Boron and Nitrogen molecules occur at a specific conditional environment. In this process, a sufficient amount of mechanical energy is applied to achieve this combination. This method has many drawbacks. One of the main disadvantages is that it produces products which have a high level of impurity.
(iii) Thermal plasma jet method:
This method is effective in producing large quantities of BNNTs. This method uses a plasma torch to vaporize Boron in a Nitrogen atmosphere. The main advantage of this method is that it produces at a faster rate and high-quality materials.
(iv) Laser ablation method:
This method produces top quality structure. In this method, Boron nitride undergoes state transition from solid to liquid at a high temperature. The high temperature of around 2000⁰c
is produced due to laser heating. In this process, the direct combination of Nitrogen gas with Boron takes place.
(v) Chemical vapor deposition method:
In this method, both solid and liquid boron nitride are passed through high temperature where Nickel and Cobalt are used as catalysts to produce boron nitride nanotubes. The greater advantage of this method is that you can control the result but this method also fails to produce bulk material.
Application of BNNTs:
Due to its unique and extrinsic properties, BNNTs can be used in various industrial applications. Some of the applications are listed below:
(i) Aerospace industries:
Due to neutron shielding capability, BNNTs can be a gem to the aerospace industry. As Boron combines with Nitrogen, it makes the nanotubes stronger and safer from harmful radiation.
(ii) Nanocarriers:
When BNNTs enter the body, they exhibit a very little or zero toxicity. Therefore, they can be successfully used as nanocarriers. It gives a new hope to the pharmaceutical and biomedical industries. As a nanocarrier, they can be used to target specific organs and sites in the body.
BNNTs give a new hope as a drug carrier and hence can be used to counteract incurable diseases.
(iii) Reinforcement:
Ø Due to its high mechanical strength, BNNTs can be used to produce reinforced materials.
Ø Materials such as high-quality polymers, ceramics are produced by adding BNNTs to aluminum.
Ø BNNTs with aluminum have increased strength and stiffness without making it heavier.
Ø Such materials can be widely used in the aerospace and automotive industry.
(iv) Nanoelectronics:
Ø Due to its high oxidation resistance and high temperature tolerance, BNNTs are preferred materials for nano industries.
Ø Due to its high temperature tolerance, BNNTs can be used as semi-conductors, sensors and other devices which require precise temperature control.
(v) Optometry:
Due to its high optical transparency, BNNTs are ideal materials for the optical industries.
(vi) Piezo electronics:
Due to its piezoelectric behavior, BNNTs can be used as piezo electronics which possess higher strain response than ordinary polymer.
FUTURE OF BNNTs:
The recent research advancement in Boron Nitride Nanotubes has opened new gateways for the potential application of BNNTs. Due to its unique properties like high strength, thermal stability, semiconducting behavior and high mechanical strength, BNNTs are much preferred over CNT (Carbon Nanotubes) used as nanomaterials. With continued experimentation and exploration, BNNTs is expected to yield even more unique applications in future.
CONCLUSION:
Inclusion of BNNTs into our everyday materials and devices has raised the standard of Human lives. With technological advancement, the future of the BNNTs seems to be bright in the coming years. In the coming decade, we are going to experience an advanced Era of BNNTs application into our day-to-day life.