Carbon nanotubes (CNTs) are nanoscale forms of carbon exhibiting exceptional physical and chemical properties. Discovered in 1991, these cylindrical structures are typically one atom thick and one dimensional. They have garnered significant scientific and technological interest due to their unique features such as impressive tensile strength and high thermal conductivity.
Photo of a Carbon Nanotube
CNTs possess remarkable mechanical, electrical, thermal, and optical properties, including a hardness exceeding diamond and tensile strengths surpassing conventional fibers by orders of magnitude. Additionally, their electrical conductivity can rival or even surpass copper, while their thermal conductivity is several times greater than graphite. These impressive attributes, coupled with their tunable electronic structure through chemical modification, make them ideal for a wide range of applications.
Where Carbon Nanotubes Are Used
Carbon nanotubes are currently used in multiple industrial and consumer applications. They have emerged as promising candidates for next-generation electronic devices. Their high conductivity and low weight make them ideal for:
- Interconnects
- Transistors, and
- Supercapacitors
Further, their unique morphology and surface chemistry enable exploration in energy storage, sensing, and composite materials. The integration of CNTs into lithium-ion batteries holds immense potential, offering faster charging times, higher energy densities, extended lifecycles, and improved safety.
Materials with carbon nanotubes significantly improve properties in polymer materials such as: rubbers, silicones, latexes, thermoset resins, and various thermoplastics, as well as materials used in anodes and cathodes.
CNTs also demonstrate potential in biomedical applications. Their biocompatibility and unique surface properties pave the way for biosensors with extremely high sensitivity and selectivity. Additionally, their strength and flexibility offer opportunities for innovative medical implants and drug delivery systems.
Application Requirements
Chemical Vapor Deposition (CVD) is the most widely used method to produce carbon nanotubes. During CVD, a substrate is prepared with a layer of metal catalyst particles. The metal particle size is chosen based on the desired nanotube diameter. The substrate is heated to approximately 700 °C. (See Figure 1)
Figure 1: How CNTs are grown. Image courtesy of OCSiAl.
To initiate the growth of high-quality nanotubes, Brooks Instrument mass flow controllers (MFCs), known for exceptional gas flow control, enabled with digital communication protocols are a critical part of the process in managing and precisely controlling the long-term stability of multiple gas feeds including:
A process gas:
- Ammonia
- Hydrogren
- Nitrogen
Ammonia, Hydrogen, or Nitrogen are examples of process gases.
And, a carbon-containing gas:
- Actetylene
- Ethylene
- Ethanol
- Methane
Actetylene, Ethylene, Ethanol, or Methane are examples of carbon-containing gases.
Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes. The catalyst particles can stay at the tips of the nanotube during growth, or remain at the nanotube base, depending on the adhesion between the catalyst particle and the substrate.
Process Solution
A typical setup starts with Brooks Instrument SLA5800 Series thermal mass flow controllers with the EtherNet/IP or PROFINET interface, enabling real-time data communication between the gas flow controllers and PLC. SLA5800 Series digital mass flow controllers, known for exceptional precision and accuracy, measure and control multiple gas feeds into a furnace.
Mass flow controller accuracy is impacted by long-term stability of the instrument, which ensures more accurate gas flow control, reducing your total cost of ownership. Additionally, Brooks Instrument 122 Series mechanical pressure gauges provide reliable local pressure monitoring. With the inputs to the process in place, the growth of carbon nanotubes can begin.
Pictured here is a gas supply panel of a leading CNT rector tool consisting of four SLA5850 Series MFCs.
The high accuracy, long-term stability, and wide range of available communication protocols offered by SLA5800 mass flow controllers, coupled with Brooks Instrument 122 Series pressure gauges are critical instruments in this application setup. The results will speak for themselves - you will spend less time verifying and recalibrating your mass flow controllers while maximizing system uptime with consistent production.
Flow Scheme
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