Carbon nanofoam

Carbon nanofoam is an allotrope of carbon discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra.[1] It consists of a cluster-assembly of carbon atoms strung together in a loose three-dimensional web. The material is extremely light, with a density of 2–10 mg/cm3 (0.0012 lb/ft3).[1][2] A gallon of nanofoam weighs about a quarter of an ounce.[3]

Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite-like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the opposite of what happens in the case of buckminsterfullerenes, in which carbon sheets are given positive curvature by the inclusion of pentagons.

The large-scale structure of carbon nanofoam is similar to that of an aerogel, but with 1% of the density of previously produced carbon aerogels—or only a few times the density of air at sea level. Unlike carbon aerogels, carbon nanofoam is a poor electrical conductor. The nanofoam contains numerous unpaired electrons, which Rode and colleagues propose is due to carbon atoms with only three bonds that are found at topological and bonding defects. This gives rise to what is perhaps carbon nanofoam's most unusual feature: it is attracted to magnets, and below −183 °C can itself be made magnetic.

See also

References

  1. ^ a b Rode, A.V.; Hyde, S.T.; Gamaly, E.G.; Elliman, R.G.; McKenzie, D.R.; Bulcock, S. (1999). "Structural analysis of a carbon foam formed by high pulse-rate laser ablation". Applied Physics A: Materials Science & Processing. 69 (7): S755–S758. doi:10.1007/s003390051522.
  2. ^ Zani, A.; Dellasega, D.; Russo, V.; Passoni, M. "Ultra-low density carbon foams produced by pulsed laser deposition". Carbon. 56: 358–365. doi:10.1016/j.carbon.2013.01.029.
  3. ^ Kenneth Chang (April 6, 2004). "A Flaky New Carbon: It's Feather Light and Magnetic". The New York Times.
Aerogel

Aerogel is a synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. Nicknames include frozen smoke, solid smoke, solid air, solid cloud, blue smoke owing to its translucent nature and the way light scatters in the material. It feels like fragile expanded polystyrene to the touch. Aerogels can be made from a variety of chemical compounds.Aerogel was first created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid in "jellies" with gas without causing shrinkage.Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromia and tin dioxide. Carbon aerogels were first developed in the late 1980s.Aerogel is not a single material with a set chemical formula; instead, the term is used to group all materials with a certain geometric structure.

Allotropes of carbon

Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include diamond and graphite. In recent decades many more allotropes, or forms of carbon, have been discovered and researched including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3-periodic allotropes of carbon are known at the present time according to SACADA

database.

Carbon

Carbon (from Latin: carbo "coal") is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common element of all known life. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.The atoms of carbon can bond together in different ways, termed allotropes of carbon. The best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen.

The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil, and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with almost ten million compounds described to date, and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions. For this reason, carbon has often been referred to as the "king of the elements".

Currency detector

A currency detector or currency validator is a device that determines whether notes or coins are genuine or counterfeit. These devices are used in many automated machines found in retail kiosks, self checkout machines, arcade gaming machines, payphones, launderette washing machines, car park ticket machines, automatic fare collection machines, railway station ticket machines, and vending machines.

The process involves examining the coins and/or notes that have been inserted, and by using various tests, determining if the currency is counterfeit. Since the parameters are different for each coin or note, these detectors must be programmed for each item that they are to accept.

In normal operation, if any item such as a coin, note, card or ticket is accepted, it is retained within the machine and it falls into a storage container to allow a member of staff to collect it later when the machine is being emptied. If the item is rejected, the machine returns the item to the customer. If a coin or token is rejected, it usually falls into a tray or rolls out of a slot at the bottom where the customer can remove the coin. If a banknote, card or ticket is rejected, it is pushed back out through the machine so that the customer can remove it from the slot into which it was inserted.

Nanofoam

Nanofoams are a class of nanostructured, porous materials (foams) containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam.

Outline of nanotechnology

The following outline is provided as an overview of and topical guide to nanotechnology:

Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is about 1 to 100 nanometers.

Two-dimensional materials

2D Materials, sometimes referred to as single layer materials, are crystalline materials consisting of a single layer of atoms. These materials have found use in applications such as photovoltaics, semiconductors, electrodes and water purification.

2D materials can generally be categorised as either 2D allotropes of various elements or compounds (consisting of two or more covalently bonding elements). The elemental 2D materials generally carry the -ene suffix in their names while the compounds have -ane or -ide suffixes. Layered combinations of different 2D materials are generally called van der Waals heterostructures.

The efficient integration of 2D functional layers with three-dimensional (3D) systems remains a significant challenge, limiting device performance and circuit design.Some 700 2D materials have been predicted to be stable, although many remain to be synthesized. The global market for 2D materials is expected to reach US$390 million by 2025, mostly for graphene in the semiconductor, electronics, battery energy and composite materials markets.

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