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✓ INTRODUCTION ✓ ALLOTROPHIC FORMS OF CARBONS ✓ APPLICATIONS

Carbon from Latin: carbo "coal" is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper (hence its name, from the Greek word "to write"). Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials.
All carbon allotropes are solids under normal conditions with graphite being the most thermodynamically stable form. 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 other 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 more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.
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. It is present in all known life forms, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.
Characteristics

The different forms or allotropes of carbon (see below) include the hardest naturally occurring substance, diamond, and also one of the softest known substances, graphite. Moreover, it has an affinity for bonding with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with such atoms. As a result, carbon is known to form almost ten million different compounds; the large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements. At atmospheric pressure it has no melting point as its triple point is at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330 °C or 7,820 °F), so it sublimates at about 3,900 K
Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature.
Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures carbon reacts with oxygen to form carbon oxides, and will reduce such metal oxides as iron oxide to the metal. This exothermic reaction is used in the iron and steel industry to control the carbon content of steel: Fe3O4 + 4 C(s) → 3 Fe(s) + 4 CO(g) with sulfur to form carbon disulfide and with steam in the coal-gas reaction: C(s) + H2O(g) → CO(g) + H2(g).
Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel, and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.
As of 2009, graphene appears to be the strongest material ever tested. However, the process of separating it from graphite will require some technological development before it is economical enough to be used in industrial processes.

The system of carbon allotropes spans a range of extremes:
|Synthetic nanocrystalline diamond is the hardest material |Graphite is one of the softest materials known. |
|known.[19] | |
|Diamond is the ultimate abrasive. |Graphite is a very good lubricant, displaying |
| |superlubricity. |
|Diamond is an excellent electrical insulator. |Graphite is a conductor of electricity. |
|Diamond is the best known naturally occurring thermal |Some forms of graphite are used for thermal insulation |
|conductor |(i.e. firebreaks and heat shields) |
|Diamond is highly transparent. |Graphite is opaque. |
|Diamond crystallizes in the cubic system. |Graphite crystallizes in the hexagonal system. |
|Amorphous carbon is completely isotropic. |Carbon nanotubes are among the most anisotropic materials |
| |ever produced. |

Allotropy

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Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, known as allotropes of these elements. Allotropes are different structural modifications of an element;[1] the atoms of the element arebonded together in a different manner.
Take carbon for example: 4 common allotropes of carbon are diamond (where the carbon atoms are bonded together in a tetrahedral lattice arrangement), graphite(where the carbon atoms are bonded together in sheets of a hexagonal lattice),graphene (single sheets of graphite), and fullerenes (where the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations).
The term allotropy is used for elements only, not for compounds. The more general term, used for any crystalline material, is polymorphism. Allotropy refers only to different forms of an element within the same phase (i.e. different solid, liquid or gasforms); the changes of state between solid, liquid and gas in themselves are not considered allotropy.
For some elements, allotropes have different molecular formulae which can persist in different phases – for example, two allotropes of oxygen (dioxygen, O2 and ozone, O3), can both exist in the solid, liquid and gaseous states. Conversely, some elements do not maintain distinct allotropes in different phases – for examplephosphorus has numerous solid allotropes, which all revert to the same P4 form when melted to the liquid state.
History

The concept of allotropy was originally proposed in 1841 by the Swedish scientist Baron Jöns Jakob Berzelius (1779–1848) who offered no explanation.[2] The term is derived from the Greek (allotropia; variability, changeableness).[3] After the acceptance of Avogadro's hypothesis in 1860 it was understood that elements could exist as polyatomic molecules, and the two allotropes of oxygen were recognized as O2 and O3. In the early 20th century it was recognized that other cases such as carbon were due to differences in crystal structure.
By 1912, Ostwald noted that the allotropy of elements is just a special case of the phenomenon of polymorphism known for compounds, and proposed that the terms allotrope and allotropy be abandoned and replaced by polymorph and polymorphism. Although many other chemists have repeated this advice, IUPAC and most chemistry texts still favour the usage of allotrope and allotropy for elements only.

Allotropes

Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with different molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Once considered exotic, fullerenes are nowadays commonly synthesized and used in research; they include buckyballs, carbon nanotubes, carbon nanobuds and nanofibers. Several other exotic allotropes have also been discovered, such as lonsdaleite, glassy carbon, carbon nanofoam and linear acetylenic carbon (carbyne).
The amorphous form is an assortment of carbon atoms in a non-crystalline,irregular, glassy state, which is essentially graphite but not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal pressures carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak van der Waals forces. This gives graphite its softness and its cleaving properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a π-cloud, graphite conducts electricity, but only in the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.
Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d–f) fullerenes (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.
At very high pressures carbon forms the more compact allotrope diamond, having nearly twice the density of graphite. Here, each atom is bonded tetrahedrally to four others, thus making a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same cubic structure as silicon and germanium and because of the strength of the carbon-carbon bonds, it is the hardest naturally occurring substance in terms of resistance to scratching. Contrary to the popular belief that "diamonds are forever", they are in fact thermodynamically unstable under normal conditions and transform into graphite. However, due to a high activation energy barrier, the transition into graphite is so extremely slow at room temperature as to be unnoticeable. Under some conditions, carbon crystallizes as lonsdaleite. This form has a hexagonal crystal lattice where all atoms are covalently bonded. Therefore, all properties of lonsdaleite are close to those of diamond.
Fullerenes have a graphite-like structure, but instead of purely hexagonalpacking, they also contain pentagons (or even heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (split into buckyballs, buckytubes and nanobuds) have not yet been fully analyzed and represent an intense area of research in nanomaterials. The names "fullerene" and "buckyball" are given after Richard Buckminster Fuller, popularizer of geodesic domes, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming spheroids (the best-known and simplest is the soccerball-shaped C60 buckminsterfullerene). Carbon nanotubes are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder. Nanobuds were first reported in 2007 and are hybrid bucky tube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure.
Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2 kg/m3. Similarly, glassy carbon contains a high proportion of closed porosity, but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. Linear acetylenic carbon has the chemical structure -(C:::C)n-. Carbon in this modification is linear with sp orbital hybridization, and is a polymer with alternating single and triple bonds. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of the hardest known material – diamond.
"Present day" (1990s) sea surface dissolved inorganic carbon concentration (from the GLODAP climatology)
Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.
In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatonnes of carbon) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Around 1,900 gigatonnes of carbon are present in the biosphere. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well—coal "reserves" (not "resources") amount to around 900 gigatonnes, and oil reserves around 150 gigatonnes. Proven sources of natural gas are about 175 trillion cubic metres (representing about 105 gigatonnes carbon), but it is estimated that there are also about 900 trillion cubic metres of "unconventional" gas such as shale gas, representing about 540 gigatonnes of carbon. Carbon is also locked up as methane and methane hydrates in polar regions. It is estimated that at least 1,400 Gt of carbon is in this form just in (and under) the submarine permafrost of the Siberian Shelf.
Carbon is a major component in very large masses of carbonate rock (limestone, dolomite, marble and so on). Coal is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil carbon fuel. It is also rich in carbon – for example, anthracite contains 92–98%.As for individual carbon allotropes, graphite is found in large quantities in the United States (mostly in New York and Texas), Russia, Mexico, Greenland, and India. Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra Leone. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. However, though diamonds are found naturally, about 30% of all industrial diamonds used in the U.S. are now made synthetically.
Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9–15 km, by a reaction that is precipitated by cosmic rays. Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.

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o COAL o DIAMOND o GRAPHITE o CHARCOAL

COAL

Coal is a combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, with smaller quantities of sulfur, oxygen and nitrogen.
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Physical Properties:

The development of coking property is an intrinsic property. The reason for development of coking property has not yet been clearly established. By physical tests it can be determined whether the coal is coking or non-coking. The following destructive physical test is used for finding the coking propensity of coal.

1. Geisler Plastometer: Equipment should give a reading between 500 to 2000 dial divisions per minute. Higher the fluidity of coal mass, batter will be the dials division per minute.
2. Caking Index: In this test certain amount of powered coal is thoroughly mixed with graded and sized sand. The total quantity of sand and coal should not exceed 25 grams. This mixture when heated at 9250 in the absence of air, after cooling down should a coherent residue. This coherent residue should be able to withstand a weight of 500 grams without generating more than 5% of powder out of the residue. If the solid residue more than 5% then the proportion of coal in the mixture of sand and coal should be increased and vice versa. Normally caking index for coking coal should vary from 20-24 for bee-hive oven the minimum index should be 13 and maximum 24. 3. Swelling Index: During determination of volatile matter in coking coal a solid reside in left, comprising of fixed carbon and mineral matter. The solid residue that is the coke bead is viewed horizontally at the same level of the eye. It will be observed that the top surface of the bead has developed some amount of swelling. This swelling is compared with standard chart indicating There quantum of swelling and a number indicating swelling index. Swelling index varying between 2.-5 is ideal for coke manufacturing. The high swelling coal is not charged for coke making as it would create unnecessary pressure on the side wall of the oven will also produce a coke porous structure.
4. Volatile Matter: The volatile matter of coking coal should vary between 19-26% on DMMF basis. A coal with less VM then 19% will give rise to a coke which will not have proper physical property. A coal with VM higher than 26% will give rise to coke with more porosity and physical strength, such as CSR and CRI. The VM in coal consist of various gaseous products which has generated when the coal is heated in absence of air at temperature more than 900o C. The gases, consists of combination of carbon and hydro-aromatic compound. The gases mainly methane, Acetylene, gaseous Amino – compound. The gases mainly Mathane, Hydrogen and Carbon and some other hydrogen-aromatic compounds such as phenol and benzene. Some amount of tar in gaseous from is also generated.

5. Petrographic Analysis and Reflectance: Another most important nondestructive test of coal which is used for determining of coking coal is the petrographic analysis & reflectance. The coking coal should have a minimum of 60% virtrain (active constituents) and maximum of 40% Inertinite (nonreactive constituent). For finding out the physical strength of the coke, reflectance studies on coking coal are also done. In this study the ideal value of reflectance will be within 1.3 – 1.5. GenerallyC) Physical Properties: The development of coking property is an intrinsic property. The reason for development of coking property has not yet been clearly established. By physical tests it can be determined whether the coal is coking or non-coking. The following destructive physical test is used for finding the coking propensity of coal.

Chemical properties:

1.Carbon: The elements carbon expressed on dry mineral matter free (DMMF) basis should vary between 85-88%. · Hydrogen: The hydrogen DMMF basis should vary between 3.7 to 4.5%. 2. Sulpher: In the suplher both organic & inorganic should not exceed 0.75% on DMMF basis.
3. Phosphorous: The Phosphorous present in the coking coal should not exceed 0.15 – 0.25%.
4. Other elements: Such as Nitrogen, Iron & Other rarer elements must be present in traces.

Applications:

Coal Catalyst Applications
|Cormetech designs and manufactures catalysts unique to coal-fired applications that ensure long-life and highly effective catalyst|
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|caused by poisons such as arsenic and calcium oxide deposits. Our integrated design of the SCR catalyst and its modular frame |
|maximizes NOx reduction and balance of plant operations. |
| | |
|Low SO2 Conversion |[pic] |
|SO3 mitigation is a growing need among coal-fired power plants. A challenge faced |Our low SO2 conversion catalyst achieves less |
|by several power plants is to lower SO2conversion, while maintaining high |than 0.1% SO2 oxidation while maintaining all |
|NOx reduction levels and low ammonia slip. In order to meet this need, we have |other key product performance features. |
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|Greater open area | |
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| | |

DIAMOND

The diamond industry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.
A large trade in gem-grade diamonds exists. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.
The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20 tonnes annually), unsuitable for use as gemstones and known as bort, are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 tonnes) of synthetic diamond is produced annually for industrial use. The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments high-performance bearings, and limited use in specialized windows. With the continuing advances being made in the production of synthetic diamonds, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics

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|PROPERTIES OF DIAMOND | |
| In diamond each C-atom utilizes its four unpaired electrons in bond formation. These bonding electrons are localized. Due |
|to this reason diamond is a bad conductor of electricity. |
| Diamond is the hardest substance ever known. |
| Pure diamond is cloudless. |
| Its melting point is 3500OC. |
| Pure diamond is transparent to x-rays. |
| It has high refractive index i.e. 2.45. |
| Due to impurities it may be colored. |
| Its density is 3.5 gm/cm3. |

PHYSICAL AND CHEMICAL PROPERTIES

1.Hardness and crystal structure
Known to the ancient Greeks as proper, unalterable, unbreakable and sometimes called adamant, diamond is the hardest known naturally occurring material, scoring 10 on the Mohs scale of mineral hardness. Diamond is extremely strong due to the structure of its carbon atoms, where each carbon atom has four neighbors joined to it with covalent bonds. The material boron nitride, when in a form structurally identical to diamond (zincblende structure), is nearly as hard as diamond; a currently hypothetical material, beta carbon nitride, may also be as hard or harder in one form. It has been shown that some diamond aggregates having nanometer grain size are harder and tougher than conventional large diamond crystals, thus they perform better as abrasive material. Due to the use of those new ultra-hard materials for diamond testing, more accurate values are now known for diamond hardness. A surface perpendicular to the crystallographic direction(that is the longest diagonal of a cube) of a pure (i.e. type IIa) diamond has a hardness value of 167 GPa when scratched with an nanodiamond tip, while the nanodiamond sample itself has a value of 310 GPa when tested with another nanodiamond tip. Because the test only works properly with a tip made of harder material than the sample being tested, the true value for nanodiamond is likely somewhat lower than 310 GPa.

2. Toughness
Unlike hardness, which only denotes resistance to scratching, diamond's toughness or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts. Due to diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer. The toughness of natural diamond has been measured as 2.0 MPa m1/2, which is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.[9][10]
3. Color and its causes
Diamonds occur in various colors — black, brown, yellow, gray, white, blue, orange, purple to pink and red. Colored diamonds contain crystallographic defects, including substitutional impurities and structural defects, that cause the coloration. Theoretically, pure diamonds would be transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of defects present and how they affect light absorption:

4. Luster
The luster of a diamond is described as 'adamantine', which simply means diamond-like. Reflections on a properly cut diamond's facets are undistorted, due to their flatness. The refractive index of diamond (as measured via sodium light, 589.3 nm) is 2.417. Because it is cubic in structure, diamond is also isotropic. Its high dispersionof 0.044 (variation of refractive index across the visible spectrum) manifests in the perceptible fire of cut diamonds. This fire—flashes of prismatic colors seen in transparent stones—is perhaps diamond's most important optical property from a jewelry perspective. The prominence or amount of fire seen in a stone is heavily influenced by the choice of diamond cut and its associated proportions (particularly crown height), although the body color of fancy (i.e., unusual) diamonds may hide their fire to some degree.

5. Fluorescence
.Diamonds exhibit fluorescence, that is, they emit light of various colors and intensities under long-wave ultra-violet light (365 nm): Cape series stones (type Ia) usually fluoresce blue, and these stones may also phosphoresce yellow, a unique property among gemstones. Other possible long-wave fluorescence colors are green (usually in brown stones), yellow, mauve, or red (in type IIb diamonds). In natural diamonds, there is typically little if any response to short-wave ultraviolet, but the reverse is true of synthetic diamonds. Some natural type IIb diamonds phosphoresce blue after exposure to short-wave ultraviolet. In natural diamonds, fluorescence under X-rays is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.

GRAPHITE

Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica and feldspars in schists, gneisses and metamorphosed sandstones and limestone as lenses or veins, sometimes of a meter or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 19th century, pencils were made simply by sawing blocks of natural graphite into strips before encasing the strips in wood. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.
There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to very small crystal size rather than complete lack of crystal structure. Amorphous is used for lower value graphite products and is the lowest priced graphite. Large amorphous graphite deposits are found in China, Europe, Mexico and the United States. Flake graphite is less common and of higher quality than amorphous; it occurs as separate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphous. Good quality flakes can be processed into expandable graphite for many uses, such as flame retardants. The foremost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphite is the rarest, most valuable, and highest quality type of natural graphite. It occurs in veins along intrusive contacts in solid lumps, and it is only commercially mined in Sri Lanka.
According to the USGS, world production of natural graphite was 1.1 million tonnes in 2010, to which China contributed 800,00 t, India 130,000 t, Brazil 76,000 t, North Korea 30,000 t and Canada 25,000 t. No natural graphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of $998 million was produced in 2009.

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Graphite (named by Abraham Gottlob Werner in 1789, from the Greek "to draw/write", for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor. Thus, it can be used in, for instance, electrical arc lamp electrodes. Likewise, under standard conditions, graphite is the most stable form of carbon. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds.

PROPERTIES:
Physical Properties of Graphite

1. Graphite is greyish black crystalline substance.
2. It has a soft and greasy texture, but has a metallic luster.
3. The specific gravity of graphite is only 2.2 g cm-3.
4. Due to the presence of a free valence electron, it is a good conductor of electricity.
5. It is also one of the stable forms of carbon.
6. The structure of graphite has hexagonal rings arranged in layers.

Chemical Properties of Graphite

1. Graphite is inactive and inert to almost all chemicals.
2. It does not burn in air, even if heated to high temperature. But if heated in oxygen, it burns completely to form only carbon dioxide
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3. It also gets oxidised to carbon dioxide, when heated with concentrated sulphuric acid and potassium dichromate.

Uses of Graphite

1. Graphite is used in making the 'lead' of pencils.
2. It is used in the production of refractory crucibles, which can withstand very high temperature.
3. Graphite being a conductor of electricity finds application in making electrodes.
4. It is used in making polishes and paints.
5. Graphite is used as lubricant in machines, which have to be operated at high temperatures. All such machines cannot be lubricated with oils, grease, etc. as they vaporize immediately at the high temperature. As a lubricant it is used as dry powder or mixed with water or oil. When mixed with water, it is called 'aqua-dag' and when mixed with oil, it is called 'oil dag'.
6. It is used for making electrotypes for printing, in the following manner. Wax impressions are made and then a thin layer of graphite powder is applied. Copper is deposited on this thin layer. The layer of graphite is used to give the negative electrical connection for carrying out electrolysis to deposit copper on it . After coating the required thickness, the wax can be melted out by dipping it in hot water.
7. Graphite is extensively used in nuclear reactors, to absorb neutrons. This helps in moderating the nuclear reaction.

CHARCOAL

Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetationsubstances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen (see pyrolysis, char and biochar). It is usually an impure form of carbon as it contains ash; however, sugar charcoal is among the purest forms of carbon readily available, particularly if it is not made by heating but by dehydrating with sulphuric acid to minimise introducing new impurities, as impurities can be removed from the sugar in advance. The resulting soft, brittle, lightweight, black, porous material resembles coal.[1]

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Uses

Charcoal has been used since the earliest times for a range of purposes including art and medicine, but by far its most important use has been as a metallurgical fuel. Charcoal is the traditional fuel of a blacksmith's forge and other applications where an intense heat is wanted. Charcoal was also used historically as a source of carbon black by grinding it up. In this form charcoal was important to early chemists and was a constituent of formulas for mixtures such as gunpowder. Due to its high surface area charcoal can be used as a filter, as a catalyst or as an absorbent.

1. Metallurgical fuel

Charcoal burns at intense temperatures, up to 2700 degrees Celsius. By comparison the melting point of iron is approximately 1200 to 1550 degrees Celsius. Due to its porosity it is sensitive to the flow of air and the heat generated can be moderated by controlling the air flow to the fire. For this reason charcoal is an ideal fuel for a forge and is still widely used by blacksmiths. Charcoal is also an excellent reducing fuel for the production of iron and has been used that way since Roman times. In the 16th century England had to pass laws to prevent the country from becoming completely denuded of trees due to production of iron. In the 19th century charcoal was largely replaced by coke, baked coal, in steel making due to cost. Charcoal is far superior fuel to coke, however, because it burns hotter and has no sulfur. Until World War II charcoal was still being used in Sweden to make ultra high-quality steel.

2. Cooking fuel
Prior to the industrial revolution charcoal was occasionally used as a cooking fuel. Modern "charcoal briquettes", widely used for outdoor grilling and barbecues in backyards and on camping trips, imitate this use, but are not actually charcoal. They are usually compacted mixtures of coal or coke and various binders.

3. Industrial fuel
Historically, charcoal was used in great quantities for smelting iron in bloomeries and later blast furnaces and finery forges. This use was replaced by coke during the Industrial Revolution. For this purpose, charcoal in England was measured in dozens (or loads) consisting of 12 sacks or shems or seams, each of 8 bushels.

4. Automotive fuel
In times of scarce petroleum, automobiles and even buses have been converted to burn wood gas (a gas mixture consisting primarily of diluting atmospheric nitrogen, but also containing combustible gasses, mostlycarbon monoxide) released by burning charcoal or wood in a wood gas generator. In 1931 Tang Zhongming developed an automobile powered by charcoal, and these cars were popular in China until the 1950s. Inoccupied France during World War II, wood and wood charcoal production for such vehicles (called gazogènes) increased from pre-war figures of approximately fifty thousand tons a year to almost half a million tons in 1943.
5. Purification and filtration
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Activated charcoal readily adsorbs a wide range of organic compounds dissolved or suspended in gases and liquids. In certain industrial processes, such as the purification of sucrose from cane sugar, impurities cause an undesirable color, which can be removed with activated charcoal. It is also used to absorb odors and toxins in gases, such as air. Charcoal filters are also used in some types of gas masks. The medical use of activated charcoal is mainly the adsorption of poisons, especially in the case of suicide attempts in which the patient has ingested a large amount of a drug. Activated charcoal is available without a prescription, so it is used for a variety of health-related applications. For example, it is often used to reduce discomfort (and embarrassment) due to excessive gas in the digestive tract.[citation needed]
Animal charcoal or bone black is the carbonaceous residue obtained by the dry distillation of bones. It contains only about 10% carbon, the remainder being calcium andmagnesium phosphates (80%) and other inorganic material originally present in the bones. It is generally manufactured from the residues obtained in the glue and gelatinindustries. Its decolorizing power was applied in 1812 by Derosne to the clarification of the syrups obtained in sugar refining; but its use in this direction has now greatly diminished, owing to the introduction of more active and easily managed reagents. It is still used to some extent in laboratory practice. The decolorizing power is not permanent, becoming lost after using for some time; it may be revived, however, by washing and reheating. Wood charcoal also to some extent removes coloring material from solutions, but animal charcoal is generally more effective.
PHYSICAL AND CHEMICAL PROPERTIES
A gram of activated carbon can have a surface area in excess of 500 m2, with 1500 m2 being readily achievable.[3] Carbon aerogels, while more expensive, have even higher surface areas, and are used in special applications.
Under an electron microscope, the high surface-area structures of activated carbon are revealed. Individual particles are intensely convoluted and display various kinds of porosity; there may be many areas where flat surfaces of graphite-like material run parallel to each other, separated by only a few nanometers or so. Thesemicropores provide superb conditions for adsorption to occur, since adsorbing material can interact with many surfaces simultaneously. Tests of adsorption behaviour are usually done with nitrogen gas at 77 K under high vacuum, but in everyday terms activated carbon is perfectly capable of producing the equivalent, by adsorption from its environment, liquid water from steam at 100 °C and a pressure of 1/10,000 of an atmosphere.
James Dewar, the scientist after whom the Dewar (vacuum flask) is named, spent much time studying activated carbon and published a paper regarding its absorption capacity with regard to gases.[4] In this paper, he discovered that cooling the carbon to liquid nitrogen temperatures allowed it to absorb significant quantities of numerous air gases, among others, that could then be recollected by simply allowing the carbon to warm again and that coconut based carbon was superior for the effect. He uses oxygen as an example, wherein the activated carbon would typically absorb the atmospheric concentration (21%) under standard conditions, but release over 80% oxygen if the carbon was first cooled to low temperatures.
Physically, activated carbon binds materials by van der Waals force or London dispersion force.
Activated carbon does not bind well to certain chemicals, including alcohols, glycols, strong acids and bases, metals and most inorganics, such as lithium, sodium,iron, lead, arsenic, fluorine, and boric acid.
Activated carbon does adsorb iodine very well and in fact the iodine number, mg/g, (ASTM D28 Standard Method test) is used as an indication of total surface area.
Contrary to a claim repeated[citation needed] throughout the web, activated carbon does not adsorb ammonia.
Carbon monoxide is not well absorbed by activated carbon. This should be of particular concern to those using the material in filters for respirators, fume hoods or other gas control systems as the gas is undetectable to the human senses, toxic to metabolism and neurotoxic.
Substantial lists of the common industrial and agricultural gases absorbed by activated carbon can be found online.[5]
Activated carbon can be used as a substrate for the application of various chemicals to improve the adsorptive capacity for some inorganic (and problematic organic) compounds such as hydrogen sulfide (H2S), ammonia (NH3), formaldehyde (HCOH), radioisotopes iodine-131(131I) and mercury (Hg). This property is known as chemisorption.
1.Iodine number
Many carbons preferentially adsorb small molecules. Iodine number is the most fundamental parameter used to characterize activated carbon performance. It is a measure of activity level (higher number indicates higher degree of activation), often reported in mg/g (typical range 500–1200 mg/g). It is a measure of the micropore content of the activated carbon (0 to 20 Å, or up to 2 nm) by adsorption of iodine from solution. It is equivalent to surface area of carbon between 900 m²/g and 1100 m²/g. It is the standard measure for liquid phase applications.
Iodine number is defined as the milligrams of iodine adsorbed by one gram of carbon when the iodine concentration in the residual filtrate is 0.02 normal. Basically, iodine number is a measure of the iodine adsorbed in the pores and, as such, is an indication of the pore volume available in the activated carbon of interest. Typically, water treatment carbons have iodine numbers ranging from 600 to 1100. Frequently, this parameter is used to determine the degree of exhaustion of a carbon in use. However, this practice should be viewed with caution as chemical interactions with the adsorbate may affect the iodine uptake giving false results. Thus, the use of iodine number as a measure of the degree of exhaustion of a carbon bed can only be recommended if it has been shown to be free of chemical interactions with adsorbates and if an experimental correlation between iodine number and the degree of exhaustion has been determined for the particular application.
2. Molasses
Some carbons are more adept at adsorbing large molecules. Molasses number or molasses efficiency is a measure of the mesopore content of the activated carbon (greater than 20 Å, or larger than 2 nm) by adsorption of molasses from solution. A high molasses number indicates a high adsorption of big molecules (range 95–600). Caramel dp (decolorizing performance) is similar to molasses number. Molasses efficiency is reported as a percentage (range 40%–185%) and parallels molasses number (600 = 185%, 425 = 85%). The European molasses number (range 525–110) is inversely related to the North American molasses number.
Molasses Number is a measure of the degree of decolorization of a standard molasses solution that has been diluted and standardized against standardized activated carbon. Due to the size of color bodies, the molasses number represents the potential pore volume available for larger adsorbing species. As all of the pore volume may not be available for adsorption in a particular waste water application, and as some of the adsorbate may enter smaller pores, it is not a good measure of the worth of a particular activated carbon for a specific application. Frequently, this parameter is useful in evaluating a series of active carbons for their rates of adsorption. Given two active carbons with similar pore volumes for adsorption, the one having the higher molasses number will usually have larger feeder pores resulting in more efficient transfer of adsorbate into the adsorption space.
3. Tannin
Tannins are a mixture of large and medium size molecules. Carbons with a combination of macropores and mesopores adsorb tannins. The ability of a carbon to adsorb tannins is reported in parts per million concentration (range 200 ppm–362 ppm).
4. Methylene blue
Some carbons have a mesopore (20 Å to 50 Å, or 2 to 5 nm) structure which adsorbs medium size molecules, such as the dye methylene blue. Methylene blue adsorption is reported in g/100g (range 11–28 g/100g).
5. Dechlorination
Some carbons are evaluated based on the dechlorination half-value length, which measures the chlorine-removal efficiency of activated carbon. The dechlorination half-value length is the depth of carbon required to reduce the chlorine level of a flowing stream from 5 ppm to 3.5 ppm. A lower half-value length indicates superior performance.
6. Apparent density
Higher density provides greater volume activity and normally indicates better quality activated carbon.
7. Hardness/abrasion number
It is a measure of the activated carbon’s resistance to attrition. It is important indicator of activated carbon to maintain its physical integrity and withstand frictional forces imposed by backwashing, etc. There are large differences in the hardness of activated carbons, depending on the raw material and activity level.
8. Ash content
It reduces the overall activity of activated carbon. It reduces the efficiency of reactivation. The metal oxides (Fe2O3) can leach out of activated carbon resulting in discoloration. Acid/water soluble ash content is more significant than total ash content. Soluble ash content can be very important for aquarists, as ferric oxide can promote algal growths. A carbon with a low soluble ash content should be used for marine, freshwater fish and reef tanks to avoid heavy metal poisoning and excess plant/algal growth.
9. Carbon tetrachloride activity
Measurement of the porosity of an activated carbon by the adsorption of saturated carbon tetrachloride vapour.
10. Particle size distribution
The finer the particle size of an activated carbon, the better the access to the surface area and the faster the rate of adsorption kinetics. In vapour phase systems this needs to be considered against pressure drop, which will affect energy cost. Careful consideration of particle size distribution can provide significant operating benefits.

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CARBON
Carbon is an indipensable element in industry. By far, the greatest single use of carbon is in the form of coke for the iron and steel industry. The major portion of this coke is used in the reduction of iron ore in blast furnaces.As in the rubber industry, the major applications for carbon blacks are in the printing ink, paint, paper and plastic industries. Minor amounts are used in the manufacture of dry cells and carbon brushes, and as insulation.The largest single application for gas phase activated carbons is in the recovery of volatile organic solvents from air or vapor mixtures. Another large application is in the purification and separation of natural and industrial gases.Main applications for pyrographite and the fiber forms of manufactured graphite are found as components for rockets, missile and other aerospace vehicles.

DIAMOND
Diamond is the only precious stone composed of a single element. Though diamonds have been discovered on all the major continents, over 90% of the world's natural diamond production comes from Africa. Other significant producers are Russia (mainly Siberia), China, Brazil and Angola. In the United States, diamonds can be found in the states of Arkansas, Virginia, Wisconsin and California. India, that was the only producer before the XVIII century, has a very small production nowadays. Diamond crystals can also be found in meteorites.In spite of the first attempt of the Scottish chemist J. Balentine Hannay, in 1880, to produce artificial diamond it was not until 1955 that the General Electric Company first announced the successful development of a reproducible process. The work of Francis Bundy, Tracy Hall, Herbert M. Strong and Robert H. Wentorf complemented the research by Percy W. Bridgman from the University of Harvard. This diamonds have industrial quality being nowadays produced by an identical method, in large scale. Precious-stone quality crystals were obtained in 1970 by Strong and Wentorf in a process involving extremely high pressures and temperatures.In spite of the popular interest on diamonds based on its value as gems, it is on the industrial domain that diamonds play a major role. They can be used in cutting or in turnery and to pierce alumina, quartz, glass and ceramics. Diamond powder is used to polish steel and alloys.

Graphite
Graphite crystals consist of superposed layers of carbon atoms, in an infinite net of hexagonal cycles. The free space between the layers can be occupied by several distint atoms, molecules or ions (oxygen, nitrogen, halogen, alkaly metals etc.), thus producing lamellar compounds.In normal conditions of pressure, the graphite layers easily glide due to the very weak bounds with the vicinity (van der Waals bonding); this is the reason why graphite is used as a lubricant.Graphite occurs mainly in Corea, Austria, Russia, China, Mexico, Madagascar, Germany, Sri Lanka and Norway. However, most of the graphite used nowadays has a synthetic origin.Thanks to its infusibility, hardness and conducting power, this substance is mainly used in the production of refractory coatings and crucibles in the foundry industry. It is also used in the production of pencils, electrodes for multiples purposes, rotary brushes, lubricants corrosion-resistent paints.