Tag: Graphite

What is Difference among Activated Carbon, Graphite, Graphene and Fullerence ?

Charcoal and Activated Carbons

A black, porous, carbonaceous material, 85 to 98 percent carbon, produced by the destructive distillation of wood and used as a fuel, filter, and adsorbent. Charcoal is amorphous and porous carbon, it contains almost no graphite phase and it may contain partially carbonized organizing substances as well as tar and mineral all of these varying tremendously with the source used to generate the Charcoal. Activated carbon is similar but it has been prepared from substrates carefully selected to yield a very high porosity. Some forms come from carbonizing carbohydrate substrates like starch or celluloid yielding very low mineral content.  Activated carbon is a kind of black porous solid carbon, by coal by grinding, molding or with uniform coal particles by carbonization, activation of production.

Graphite

A soft crystalline allotrope of carbon, composed of graphene layers, having a steel-gray to black metallic luster and agreasy feel, used in lead pencils, lubricants, paints and coatings, and fabricated into a variety of forms such as molds,bricks, electrodes, crucibles, and rocket nozzles.  Graphite is 3D
A soft crystalline allotrope of carbon, composed of graphene layers, having a steel-gray to black metallic luster and agreasy feel, used in lead pencils, lubricants, paints and coatings, and fabricated into a variety of forms such as molds,bricks, electrodes, crucibles, and rocket nozzles.
A soft crystalline allotrope of carbon, composed of graphene layers, having a steel-gray to black metallic luster and agreasy feel, used in lead pencils, lubricants, paints and coatings, and fabricated into a variety of forms such as molds, bricks, electrodes, crucibles, and rocket nozzles.

The chemical bonds in graphite are similar in strength to those found in diamond. However, the lattice structure of the carbon atoms contributes to the difference in hardness of these two compounds; graphite contains two dimensional lattice bonds, while diamond contains three dimensional lattice bonds. The carbon atoms within each layer of graphite contain weaker intermolecular bonds. This allows the layers to slide across each other, making graphite a soft and malleable material.

Various studies have demonstrated that graphite is an excellent mineral with several unique properties. It conducts heat and electricity and retains the highest natural strength and stiffness even in temperatures exceeding 3600°C. This material is self-lubricating and is also resistant to chemicals.

Although there are different forms of carbon, graphite is highly stable under standard conditions. Depending upon its form, graphite is utilized for a wide range of applications.

Graphene

Graphene
Graphene
A monolayer of carbon atoms having a hexagonal lattice structure and constituting a basic structural element ofgraphite, fullerenes, and carbon nanotubes. Graphene is 2D.
Graphene is the name for an atom-thick honeycomb sheet of carbon atoms. It is the building block for other graphitic materials (since a typical carbon atom has a diameter of about 0.33 nanometers, there are about 3 million layers of graphene in 1 mm of graphite).
Units of graphene are known as nanographene; these are tailored to specific functions and as such their fabrication process is more complicated than that of generic graphene. Nanographene is made by selectively removing hydrogen atoms from organic molecules of carbon and hydrogen, a process called dehydrogenation.
Harder than diamond yet more elestic than rubber; tougher than steel yet lighter than aluminium. Graphene is the strongest known material.
To put this in perspective: if a sheet of cling film (like kitchen wrap film) had the same strength as a pristine monolayer of graphene, it would require the force exerted by a mass of 2000 kg, or a large car, to puncture it with a pencil.
It is expected that, by strengthening standards and creating tailored high-quality materials, graphene will go beyond niche products and applications to broad market penetration by 2025. Then, graphene could be incorporated in ubiquitous commodities such as tyres, batteries and electronics.  Graphene has unique properties that exceed those of graphite. Although graphite is often used to reinforce steel, it cannot be utilized as a structural material on its own because of its sheer planes. In contrast, graphene is the strongest material ever found; it is more than 40 times stronger than diamond and more than 300 times stronger than A36 structural steel.

What is the Difference between Graphite and Graphene ?

Since graphite has a planar structure, its electronic, acoustic, and thermal properties are highly anisotropic. This means, phonons pass much more easily along the planes than they do when trying to pass via the planes. However, graphene has very high electron mobility and, like graphite, is a good electrical conductor, due to the occurrence of a free pi (p) electron for each carbon atom.

However, graphene has much higher electrical conductivity than graphite, due to the occurrence of quasiparticles, which are electrons that function as if they have no mass and can travel long distances without scattering. In order to fully realize this high level of electrical conductivity, doping needs to be carried out to overcome the zero density of states which can be visualized at the Dirac points of graphene.

Fullerence

A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ellipsoid, tube, or many other shapes and sizes. Graphene (isolated atomic layers of graphite), which is a flat mesh of regular hexagonal rings, can be seen as an extreme member of the family.

Fullerenes with a closed mesh topology are informally denoted by their empirical formula Cn, often written Cn, where n is the number of carbon atoms. However, for some values of n there may be more than one isomer.

The family is named after buckminsterfullerene (C60), the most famous member, which in turn is named after Buckminster Fuller. The closed fullerenes, especially C60, are also informally called buckyballs for their resemblance to the standard ball of association football (“soccer”). Nested closed fullerenes have been named bucky onions. Cylindrical fullerenes are also called carbon nanotubes or buckytubes. The bulk solid form of pure or mixed fullerenes is called fullerite.

Fullerenes had been predicted for some time, but only after their accidental synthesis in 1985 were they detected in nature and outer space. The discovery of fullerenes greatly expanded the number of known allotropes of carbon, which had previously been limited to graphite, diamond, and amorphous carbon such as soot and charcoal. They have been the subject of intense research, both for their chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology.

Types and varieties of Graphite

The principal types of natural graphite, each occurring in different types of ore deposits are:

There are three distinct types of natural graphite which occur in different kinds of ore deposits:

  1. Flake Graphite
  • Less common form of graphite
  • Carbon range of 85-98%.
  • Priced ~4X higher than amorphous graphite
  • Used in many traditional applications
  • Desirable for emerging technology graphite applications (e.g. Li-ion battery anode material)
  • Crystalline small flakes of graphite (or flake graphite) occurs as isolated, flat, plate-like particles with hexagonal edges if unbroken.
  • When broken the edges can be irregular or angular;
  1. Amorphous Graphite
  • Most abundant form of graphite
  • Comparatively low carbon content of 70-80%
  • No visible crystallinity
  • Lowest purity
  • Not of suitable quality for use in most applications
  1. High Crystalline Graphite (vein, lump or crystalline vein)
  • Only extracted from Sri Lanka
  • Carbon content of 90-99%
  • Scarcity and high cost restricts viability for most applications

4. Lump graphite (or vein graphite) occurs in fissure veins or fractures and appears as massive platy intergrowths of fibrous or acicular crystalline aggregates, and is probably hydrothermal in origin.

5.Highly ordered pyrolytic graphite refers to graphite with an angular spread between the graphite sheets of less than 1°.

*Synthetic graphite is a manufactured product made by high-temperature treatment of amorphous carbon materials. In the United States, the primary feedstock used for making synthetic graphite is calcined petroleum coke and coal tar pitch. This makes it very expensive to produce — up to 10 times the cost of natural graphite – and less appealing for use in most applications. The name “graphite fiber” is sometimes used to refer to carbon fibers or carbon fiber-reinforced polymer.

What is Graphene ?

Graphene is an allotrope (form) of carbon consisting of a single layer of carbon atoms arranged in an hexagonal lattice. It is the basic structural element of many other allotropes of carbon, such as graphite, charcoal, carbon nanotubes and fullerenes.


Graphene and its band structure and Dirac cones, effect of a grid on doping

Graphene can be considered as an indefinitely large aromatic molecule, the ultimate case of the family of flat polycyclic aromatic hydrocarbons. Graphene has many unusual properties. It is the strongest material ever tested, efficiently conducts heat and electricity and is nearly transparent. Graphene shows a large and nonlinear diamagnetism, which is greater than that of graphite, and can be levitated by neodymium magnets.

Scientists theorized about graphene for years. It had been unintentionally produced in small quantities for centuries, through the use of pencils and other similar graphite applications. It was originally observed in electron microscopes in 1962, but it was studied only while supported on metal surfaces.

The material was later rediscovered, isolated, and characterized in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester. Research was informed by existing theoretical descriptions of its composition, structure, and properties. This work resulted in the two winning the Nobel Prize in Physics in 2010 “for groundbreaking experiments regarding the two-dimensional material graphene.”

“Graphene” is a combination of “graphite” and the suffix -ene, named by Hanns-Peter Boehm, who described single-layer carbon foils in 1962.


Graphene is an atomic-scale hexagonal lattice made of carbon atoms.

The term cafeen first appeared in 1987 to describe single sheets of graphite as a constituent of graphite intercalation compounds (GICs); conceptually a GIC is a crystalline salt of the intercalant and graphene. The term was also used in early descriptions of carbon nanotubes,  as well as for epitaxial graphene and polycyclic aromatic hydrocarbons (PAH).

Graphene can be considered an “infinite alternant” (only six-member carbon ring) polycyclic aromatic hydrocarbon.

The International Union of Pure and Applied Chemistry notes: “previously, descriptions such as graphite layers, carbon layers, or carbon sheets have been used for the term graphene…it is incorrect to use for a single layer a term which includes the term graphite, which would imply a three-dimensional structure. The term graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed.”

Geim defined “isolated or free-standing graphene” as “graphene is a single atomic plane of graphite, which – and this is essential – is sufficiently isolated from its environment to be considered free-standing.” This definition is narrower than the IUPAC definition and refers to cloven, transferred and suspended graphene. Other forms such as graphene grown on various metals, can become free-standing if, for example, suspended or transferred  to silicon dioxide (SiO2) or silicon carbide.

The theory of graphene was first explored by Wallace in 1947 as a starting point for understanding the electronic properties of 3D graphite. The emergent massless Dirac equation was first pointed out by Semenoff, DiVincenzo and Mele. The earliest TEM images of few-layer graphite were published by Ruess and Vogt in 1948.

A lump of graphite, a graphene transistor, and a tape dispenser. Donated to the Nobel Museum in Stockholm by Andre Geim and Konstantin Novoselov in 2010.

An early, detailed study on few-layer graphite dates to 1962 when Boehm reported producing monolayer flakes of reduced graphene oxide. Efforts to make thin films of graphite by mechanical exfoliation started in 1990, but nothing thinner than 50 to 100 layers was produced before 2004. Initial attempts to make atomically thin graphitic films employed exfoliation techniques similar to the drawing method. Multilayer samples down to 10 nm in thickness were obtained.

One of the first patents pertaining to the production of graphene was filed in October 2002 and granted in 2006. Two years later, in 2004 Geim and Novoselov extracted single-atom-thick crystallites from bulk graphite and transferred them onto thin silicon dioxide (SiO2) on a silicon wafer,which electrically isolated the graphene.

The cleavage technique led directly to the first observation of the anomalous quantum Hall effect in graphene, which provided direct evidence of graphene’s theoretically predicted Berry’s phase of massless Dirac fermions. The effect was reported by Geim’s group and by Kim and Zhang, whose papers appeared in Nature in 2005.  Geim and Novoselov received awards for their pioneering research on graphene, notably the 2010 Nobel Prize in Physics.

Commercialization of graphene proceeded rapidly once commercial scale production was demonstrated. By 2017, 13 years after creation of the first laboratory graphene electronic device, an integrated graphene electronics chip was produced commercially and marketed to pharmaceutical researchers by Nanomedical Diagnostics in San Diego.

What is Graphite ?

Graphite, archaically referred to as plumbago, is a crystalline allotrope of carbon, a semimetal, a native element mineral, and a form of coal. Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Graphite and diamond are the two mineral forms of carbon. Diamond forms in the mantle under extreme heat and pressure. Most graphite found near Earth’s surface was formed within the crust at lower temperatures and pressures. Graphite and diamond share the same composition but have very different structures. Graphite and diamonds are the only two naturally formed polymers of carbon. Graphite is essentially a two dimensional, planar crystal structure whereas diamonds are a three dimensional structure. Graphite is an excellent conductor of heat and electricity and has the highest natural strength and stiffness of any material. It maintains its strength and stability to temperatures in excess of 3,600°C and is very resistant to chemical attack. At the same time it is one of the lightest of all reinforcing agents and has high natural lubricity.

Graphite has a layered, planar structure. The individual layers are called graphene. In each layer, the carbon atoms are arranged in a honeycomb lattice with separation of 0.142 nm, and the distance between planes is 0.335 nm. Atoms in the plane are bonded covalently, with only three of the four potential bonding sites satisfied. The fourth electron is free to migrate in the plane, making graphite electrically conductive. However, it does not conduct in a direction at right angles to the plane. Bonding between layers is via weak van der Waals bonds, which allows layers of graphite to be easily separated, or to slide past each other.

The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), have very similar physical properties, except for that the graphene layers stack slightly differently. The alpha graphite may be either flat or buckled. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1300 °C.

Graphite is a mineral that forms when carbon is subjected to heat and pressure in Earth’s crust and in the upper mantle. Pressures in the range of 75,000 pounds per square inch and temperatures in the range of 750 degrees Celsius are needed to produce graphite. These correspond to the granulite metamorphic facies.

What is graphite used for?

Natural graphite is mostly consumed for refractories, batteries, steelmaking, expanded graphite, brake linings, foundry facings and lubricants.  Graphene, which occurs naturally in graphite, has unique physical properties and is among the strongest substances known. However, the process of separating it from graphite will require more technological development.

What is the Structures of graphite ?

Graphite has a layer structure which is quite difficult to draw convincingly in three dimensions. The diagram below shows the arrangement of the atoms in each layer, and the way the layers are spaced.

Notice that you can’t really draw the side view of the layers to the same scale as the atoms in the layer without one or other part of the diagram being either very spread out or very squashed.

In that case, it is important to give some idea of the distances involved. The distance between the layers is about 2.5 times the distance between the atoms within each layer.

The layers, of course, extend over huge numbers of atoms – not just the few shown above.

You might argue that carbon has to form 4 bonds because of its 4 unpaired electrons, whereas in this diagram it only seems to be forming 3 bonds to the neighboring carbons. This diagram is something of a simplification, and shows the arrangement of atoms rather than the bonding.

What is The properties of graphite ?

 

  • has a high melting point, similar to that of diamond. In order to melt graphite, it isn’t enough to loosen one sheet from another. You have to break the covalent bonding throughout the whole structure.
  •  Graphite’s high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications.
  • has a soft, slippery feel, and is used in pencils and as a dry lubricant for things like locks. Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties. You can think of graphite rather like a pack of cards – each card is strong, but the cards will slide over each other, or even fall off the pack altogether. When you use a pencil, sheets are rubbed off and stick to the paper.
  • has a lower density than diamond. This is because of the relatively large amount of space that is “wasted” between the sheets.
  • is insoluble in water and organic solvents – for the same reason that diamond is insoluble. Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite.
  • conducts electricity. Graphite is an electric conductor, consequently, useful in such applications as arc lamp electrodes. The de-localized electrons are free to move throughout the sheets. If a piece of graphite is connected into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.