Carbon nanotube powder (CNT powder) refers to a fine, powdered form of carbon nanotubes (CNTs). Carbon nanotubes are cylindrical structures composed of carbon atoms arranged in a hexagonal lattice. They can be single-walled carbon nanotubes (SWCNT/SWNT) or multi-walled carbon nanotubes (MWCNT/MWNT). The powder form of carbon nanotubes consists of a large number of individual nanotubes, which are typically entangled or aggregated together.
There are three main ways to produce this product: arc discharge, laser ablation of graphite, and chemical vapor deposition (CVD). All three methods require the use of metals (e.g., iron, cobalt, nickel) as catalysts.2 In the first two processes, graphite is combusted electrically or by means of a laser, and the CNTs that develop in the gaseous phase are separated.
The most common method is CVD, where carbon-containing gases are decomposed on a catalyst to form nanotubes. Here is a general overview of the CNT powder manufacturing process:
The catalyst-coated substrate is placed inside a unit chamber, and the CVD process is initiated. The chamber is typically maintained at high temperatures (around 500–1,000°C) and a carbon-containing gas is introduced.1 The most commonly used method is thermal decomposition of the carbon feedstock, where the carbon atoms from the gas decompose on the catalyst surface. Carbon atoms from the feedstock react with the catalyst, leading to the growth of carbon nanotubes. The CNTs grow vertically from the catalyst particles, forming a forest-like structure. However, this method has its drawbacks, including limited synthesis volume and high costs. As a solution, OCSiAl has developed and patented a pioneering advanced method for producing catalytic metal nanoparticles. In this method, CNTs are produced within the gas phase of synthesis while being suspended inside the chamber of the unit, allowing a production capacity in the flow unit of several kilograms per hour.3 This cost-effective technology makes it possible to offer the market TUBALLTM nanotubes at a significantly lower price than their counterparts.
CNT powder collection
After synthesis, the CNTs are typically collected from the substrate. Various methods can be used for this purpose, including scraping, mechanical agitation, ultrasonication, filtration, or centrifugation.4
CNT powder purification
For many applications, residual iron nanoparticles do not pose a problem, but for some it is very undesirable. In this case, CNT powder purification is applied. The collected CNT material undergoes purification steps to remove catalyst residues, amorphous carbon, and other impurities. Common purification methods include acid treatment, thermal oxidation, chemical functionalization, and electric chemical purification.5 Post-processing techniques such as milling or grinding can be employed to break up agglomerates and obtain a fine powder.6
CNT powder quality control
The CNT powder is analyzed and characterized to assess its structural, morphological, and purity properties. Techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric analysis (TGA), and UV-VIS-NIR spectroscopy are commonly used for characterization.
It's important to note that variations in the manufacturing process exist, depending on the specific requirements and techniques employed by different research groups and companies.
Carbon nanotube powder possesses several key properties that make it a valuable material for various applications:
It's important to note that the properties of CNT powder can vary depending on factors such as the synthesis method, purity, length, diameter, chirality, and functionalization of the nanotubes. These properties can be tailored through specific manufacturing and post-processing techniques to meet the requirements of various applications.
To grant valuable properties to materials, CNT powder should be dispersed using a chemical combination of surfactants along with ultrasonic vibration. To simplify its integration into a wide range of materials and systems, OCSiAl, a leading manufacturer of SWCNTs, developed a line of pre-dispersed concentrates to provide superior electrical conductivity to various materials, while retaining and even enhancing mechanical properties, and with minimal impact on the host matrix. A distinguishing feature of these concentrates is the simplicity of their incorporation into standard production processes during the mixing phase. For instance, TUBALLTM BATT is an ultrafine dispersion of graphene nanotubes within liquid carriers, offering a readily applicable solution tailored for high-energy anodes and cathodes. This innovation bolsters battery energy density and durability. Additionally, the TUBALLTM MATRIX line of nanotube concentrates was specially designed to provide superior electrical conductivity and enhance the mechanical properties of various elastomers, thermosets, and thermoplastics.
Carbon nanotube powder can be used in a variety of applications depending on the required properties. Here are some most common applications of CNT powder:
Above all, the application of CNT powder in electronics, encompassing microprocessors and solar cells, has garnered significant traction in research facilities, progressively nearing practical implementation.
CNT powder is widely used in research and development activities, serving as a versatile starting material for the synthesis of other CNT-based materials. Researchers can functionalize, modify, or further process the powder to create tailored CNT structures for novel applications. The exceptional properties of CNT powder make it a versatile additive able to modify most of materials.
Synthesis Methods of Carbon Nanotubes and Related Materials: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445923/
Carbon nanotubes—what they are, how they are made, what they are used for: https://www.nanowerk.com/nanotechnology/introduction/introduction_to_nanotechnology_22.php
New perspectives in SWCNT applications: Tuball SWCNTs. Part 1. Tuball by itself—All you need to know about it: https://www.sciencedirect.com/science/article/pii/S2667056922000311?via%3Dihub
Synthesis and Purification of Carbon Nanotubes: https://www.intechopen.com/chapters/77073
A review of purification techniques for carbon nanotubes: https://www.researchgate.net/publication/244668507_A_review_of_purification_techniques_for_carbon_nanotubes
Single-walled carbon nanotubes: structure, properties, applications, and health & safety: https://tuball.com/articles/single-walled-carbon-nanotubes
Mechanical properties of carbon nanotubes and its applications—a review: https://www.irjet.net/archives/V8/i8/IRJET-V8I8118.pdf
Electronic and Mechanical Properties of Carbon Nanotubes: https://link.springer.com/chapter/10.1007/0-306-47098-5_22
Electrical properties of nanotubes: https://www.understandingnano.com/electrical-properties-carbon-nanotubes.html
Thermal conductance of an individual single-wall carbon nanotube above room temperature: https://pubs.acs.org/doi/10.1021/nl052145f
Properties that Influence the Specific Surface Areas of Carbon Nanotubes and Nanofibers: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4643664/#:~:text=CNTs%20have%20large%20surface%20areas,et%20al.%2C%202001).
Carbon Nanotube Optics and Their Uses: https://www.azooptics.com/Article.aspx?ArticleID=1507
Carbon Nanotubes and Graphene as Additives in 3D Printing: https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=2714&context=chem_faculty_pubs