Carbon nanofibers - An overview

Carbon nanofibers

Carbon nanofibers are steam-grown carbon fibers or steam-enhanced carbon nanofibers cylindrical nanostructures that are arranged as conifers, cups, or plates decorated with graphene layers. Graphene-coated carbon nanofibers wrapped in a perfect cylinder are called carbon nanotubes.

Carbon nanofibers

History of carbon nanofibers

One of the first technical records was probably patented by Hughes and Chambers in the 1889 filamentous carbon synthesis. They use a methane/hydrogen gaseous mixture and increase the carbon filament through gas pyrolysis and subsequent carbon accumulation and filament growth. The actual realization of these fibers came much later when their structure could be analyzed by electronic microscopy. The first electronic microscopy observations of carbon nanofibers were performed in the early 1950s by Soviet scientists Raduskevich and Lukyanovich, who published a paper in the Soviet Journal of Physical Chemistry stating that 50-nanometer blank graphic carbon fibers.

In 1991, Japanese researcher Sumio Ijima synthesized hollow carbon molecules to determine their crystal structure. In the following years, these molecules were called carbon nanotubes for the first time. VGCNF is produced through basically the same manufacturing process as VGCF, only the diameter is usually less than 200 nm. A number of companies worldwide are actively involved in the commercial-scale production of carbon nanofibers and new engineering applications for these materials are being intensively developed.

Properties carbon nanofibers

1. Carbon nanofibers have a high level of chemical bonding power.

2. It has a number of allotropes including diamond, graphite, and fullerenes.

3. This underscores the versatility of CNFs, which is notable for their thermal, electrical, and electromagnetic protection and an increase in mechanical properties.

4. Since carbon is readily available at a low cost, CNFs are a popular addition to composite materials.

5. CNFs exist on very small, nanometer scales.

6. Carbon nanofibers (CNFs) are clearly used as anode materials for the production of numerous interstitial sites, they show great performance in sodium and lithium storage.

7. Carbon nanofibers (CNF) are produced catalytically in the CVD process.

8. Diameter ranging between 150–300 nm.

The manufacturing process of Carbon nanofibers

Catalytic chemical vapor deposition (CCVD) or only CVDs with thermal and plasma-assisted variants are effective commercial strategies for the manufacture of VGCF and VGCNF. Here, the gas-phase molecules decompose at high temperatures, and the carbon is deposited in a layer in the presence of a metallic catalyst where the subsequent growth of the fibers around the catalyst particles is observed. In general, this process involves the results of individual stages such as gas decomposition, carbon deposition, fiber growth, fiber density, graphitization and purification, and hollow fibers. The nanofiber diameter depends on the catalyst size. The CVD process for VGCF fabrication usually falls into two categories: a. a static-catalytic mechanism, and b. Floating-catalytic mechanism.

In the batch process developed by the Tibetans, the hydrocarbon/hydrogen/helium mixture passes over the mullite by depositing iron catalyst particles at 1000 °C. Methane was 15% concentrated according to the hydrocarbon volume used. With a gas bus time of 20 seconds, the fiber growth is found to be several centimeters at 10 centimeters. In general, the length of the fiber can be controlled by the time of residence of the gas in the furnace. The direction of gravity and gas flow usually affects the direction of fiber growth.

The continuous or floating-catalytic process Koyama and Endo was first patented and later modified by Hatano and colleagues. This process develops VGCF with sub-micrometer diameters and lengths of a few to 100 mm that comply with the definition of carbon nanofibers. They use orthometallic compounds dissolved in volatile solvents such as benzene that obtain a mixture of ultrafine catalyst particles of hydrocarbon gas with a temperature of 1100 °C. In the furnace, the development of fibers begins on the surface of the catalyst particles and continues until the catalyst is poisoned by the impurities of the system. In the fiber growth system described by Bucker and colleagues, only a fraction of the catalytic particles released into the gas mixture contribute to the development of the fiber, i.e. the catalyst is poisoned. Catalyst particles are buried at the final end of a few parts per million at the growing tip of the fiber. At this stage, the fiber is dense.

Advantages of carbon nanofibers

1. Carbon nanofibers are used to deliver therapeutic drugs and developed an elastic material that is embedded with a needle.

2. It works as a carrier material for various catalysts in petrochemistry.

3. Field electron emission sources.

4. The unique structure of these porous carbon nanofibers has resulted in good electrochemical performance and they are used as anodes in rechargeable lithium-ion batteries.

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