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Graphite Elemental Carbon

All grades of graphite, especially high grade amorphous and crystalline graphite having collodial property i.e. remaining in suspension in oil, are used as lubricants.

The History Says

In ancient Rome, scribes wrote on papyrus (an early form of paper) with a thin metal rod called a stylus, which left a light but readable mark. Other early styluses were made of lead. Today we still call the core of a pencil the "lead" even though it is made from nontoxic graphite.

The Present Scenario

Natural graphite occurs in many parts of the world in fair abundance and it has been used for ages in various applications. A dozen countries hold the key position in graphite production. In tonnage, South Korea is the largest producer in the world followed by Austria.

GRAPHITE is a form of elemental carbon. It is one of the three allotropic forms which the element carbon exists in nature, the other two being coal and diamond. It crystallises in hexagonal system in platy form but it is rare that perfect crystals of graphite have been found. Graphite is of metamorphic origin and usually found as veins, lenses, pockets and as thin laminae disseminated in the gneisses, schists and phyllites. Depending upon the mode of occurrence and origin, it is graded into three forms: It has black to steel grey colour, usually leaves a black streak on the hand when touched because of its extreme softness and greasiness. It is opaque even in the finest particles. Graphite is a good conductor of heat and electricity. It has high refractoriness. It can stand a temperature upto 3000ºC in an inert atmosphere though in the presence of oxygen it burns between 620ºC to 720º C. It is unaffected by most of the acids and reagents but yields graphitic acid on treatment with a mixture of potassium nitrate and nitric acid.

In nature, graphite is found usually in mechanical association with felspar, mica, quartz, pyroxene, rutile, pyrites, and apatite. These impurities are associated with vein graphite. The impurities with amorphous graphite are shale, slate, sandstone, quartz and limestone.

Graphite is found in almost every country. Plentiful reserves, however, are possessed the following countries:
Hardness Associated Minerals Streak Colour characteristics Luster Field Indicators
1 - 2 quartz
black gray to brownish gray black, silver thin flakes are flexible but inelastic, mineral can leave black marks on hands and paper, weakly conducts electricity metallic to dull softness, luster, density and streak.

Industrial Applications

Graphite is valued for its good conductivity of heat and electricity and high refractoriness. The utility of graphite is dependent largely upon its type viz., flake, lumpy or amorphous. The flake type graphite is found to possess extremely low resistivity to electrical conductance. The electrical resistivity decreases with the increase of flaky particles. Also the bulk density decreases progressively as the particles become more and more flaky. Because of this property in flake graphite, it finds a large use in the manufacture of carbon electrodes, plates and brushes required in the electrical industry and dry cell batteries. In the manufacture of plates and brushes, however, flake graphite has been substituted to some extent by synthetic, amorphous, crystalline graphite and acetylene black. Graphite electrodes serve to give conductivity to the mass of manganese dioxide used in dry batteries.

The manufacture of crucibles is served best by flake graphite, although crystalline graphite is also used.

Graphite crucibles are manufactured by pressing a mixture of graphite, clay and sand and fixing the pressed article at a high temperature. They are used for melting non-ferrous metals, especially brass and aluminium. Coarse-grained flake graphite from Malagasy is regarded as standard for crucible manufacture.

Flake graphite containing 80 to 85% carbon is used for crucible manufacture; 93% carbon and above is preferred for the manufacture of lubricants, and graphite with 40 to 70% carbon is utilized for foundry facings. Natural graphite, refined or otherwise pure, having a carbon content not less than 95% is used in the manufacture of carbon rods for dry batterry cells. This grade of graphte is imported from Ceylon and England. After the second World War, clay-graphite crucibles were replaced by silicon carbide crucibles bonded by graphite. Such crucibles are now manufactured in the USA and other advanced countries.

All grades of graphite, especially high grade amorphous and crystalline graphite having collodial property i.e. remaining in suspension in oil, are used as lubricants. Graphite has an extraordinarily low co-efficient of friction under parctically all working conditions. This property is invaluable in lubricants. It diminishes friction and tends to keep the moving surface cool. Dry graphite as well as graphite mixed with grease and oil is utilized as a lubricant for heavy and light bearings. Graphite grease is used as a heavy-duty lubricant where high temperatures may tend to remove the grease.

These days, artificially prepared graphite has replaced natural graphite to a great extent. Artificial graphite is prepared by heating a mixture of anthracite, high grade coal or petroleum coke, quartz and saw-dust at a temperature of 3000ºC, out of contact with air. Graphite carbon is deposited as residue. Manufactured graphite is also used for making furnace electrodes and for modes in the manufacture of chlorine and caustic soda.

A considerable quantity of graphite is used in foundry-facing to prevent the moulding sands from adhering to cast articles. Here too, flake graphite is preferred. Dust or powder of flake, crystalline-graphite are also used.

Graphite bricks of high purity are used as moderators in an atomic reactor. In the nuclear field graphite is a good and convenient material as a moderator but this is only true if the graphite is low in certain neutron absorbing elements notably boron and the rare earths and is of consistent quality particularly with regard to density and orientation. The latest invention in the use of graphite is in the blast furnace operation, experimented by Oesterreichisch - Alpine Mountangesellschaft, Austria. In view of the lack of cooking coal in Australia, it is likely that the use of graphite in blast furnace will be developed on a commercial scale.

Other uses of graphite are in the manufacture of paints and pencils. Finely powdered lump graphite of 70% purity is generally employed in paint manufacture. Graphite is a great water repellent and thus makes an ideal protective coating for wood.

Amorphous graphite is generally used in the manufacture of lead for pencils. The suitability of graphite for this purpose is judged by the dark streak it leaves on the paper. It is best done by amorphous graphite. The finer the powder the darker is the smear. The blackness of the smear decreases with increase in flakiness of the graphite. Synthetic graphite, thoughit has less ash content and a fine paricle size, produces very little smears and so it is unsuitable for pencil manufacture.

Mining and Treatment

In Ceylon, the USA and Mexico, graphite is obtained by underground mining. In Ceylon, the deepest working level has gone to depth of 480 metres. In Malagasy Republic, it is obtained by hydraulic method.

Graphite is a natural floater. It does not require a collector and flotation has become the accepted method of beneficiation of graphite.

Flake graphite from disseminated deposits is to be difficult to concentrate. A number of secret processes have been evolved by different countries and firms. It has been found difficult to recover refined graphite from rough concentrates. This difficulty is due to the fact that fine grinding is not allowed in case of flake graphite, because by resorting to this process there is every chance of reducing the grain size of the flake. During the process of grinding there are chances of flakes being cut by quartz and other gangue materials. It reduces the size and also lowers the price and value of the graphite. Graphite required for crucible manufacture must be 8 to 60 mesh.

World Resources

Natural graphite occurs in many parts of the world in fair abundance and it has been used for ages in various applications. A dozen countries hold the key position in graphite production. In tonnage, South Korea is the largest producer in the world followed by Austria.

This country possesses large reserves of amorphous and flake graphite. It is mined in the Muehldorf area and in the Dunkelsteiner forest on the left bank of the river Danube about, 64 to 80 km. west of Vienna in lower Austria. At Muehldorf, graphite beds 2 to 40 metres thick are found in marble and mica gneiss. In south-eastern Austria, a 48 km. long belt extends from Leober to Rottenmann, in the Styrian Alps. It is an important source of amorphous graphite. Two mines are worked in this area. Crude ore contains 50 to 60% carbon. Graphite is refined by flotation and brought to grades of 66-99% C.

Most of the production is now supplied to the Donawitz Iron Works for adding to the blast furnace burden to save coke. Austria supplies a considerable quantity of graphite to the German market. The remaining quantity is used internally for foundry facing, pencils, lacquer, pigments and lubricants.

Crystalline graphite comes from Senja island, north Norway. Here graphite occurs as lenses in mica schists. The rich portion contains 25-30% carbon. The ore is hard and is crushed to recover graphite. Norway produces battery-grade concentrates. A large reserve of amorphous graphite has been discovered in the Lofoten islands, south-west of Senja island.

West Germany
Flake graphite is mined near Passau in eastern Bavaria. It occurs in seams, lenses and disseminated in schists, gneisses 10 to 20 metres thick; the average graphite content is 20 to 25 per cent. At Kropfmuehl, some 20 folds of graphite are found interbedded with crystalline limestone and micaceous gneiss in a stratigraphic thickness of 135 metres. The mine has been worked to a depth of 70 metres. The mineral is concentrated to yield 92-98% carbon of crucible and pencil grades.

The Passau deposits of West Germany extend into this country. Graphite is mined in northern Moravia; the other graphite are in Southern Bohemial ceased production aftere the Second World Wae. It occurs in large lenses in cordierite gneiss containing bands of schist and limestone surrounded by granite. Amorphous graphite is mainly mined.

Flake graphite is mined on a small scale near Rurin, Pinerolo. Anthracite metamorphosed to amorphous graphite is also found and mined for foundry use and paints.

The world's largest reserves of flake graphite are possessed by this country. Formerly, this prized place was held by Ceylon. Mines are located principally south of Tamatave, worked by six French companies. Graphite is found disseminated in Pre-Cambrian metamorphics in the central and eastern parts of the island. The metamorphic rocks have been decomposed to soft rock mass by weathering. Graphite is seen on the surface as bright flakes. The incidence of graphite averages 10 to 12 per cent of the ore. Selected areas may give a higher percentage, up to 25% or more. Most of the deposits are worked by open pits. The ore mined is handpicked, sorted, washed, winnowed and sieved to produce concentrated graphite containingn 90% carbon. Malagasy is noted for coarse flake production.

Graphite mining in this country started in 1907. Most of the production is exported to the USA, the UK and European countries.

This country is famous for the production of high-grade crystalline graphite. Deposits occur on the western flank of the Pre-Cambrian bed-rocks, gneisses, schists and meta-limestone, in the south-central part. Graphite occurs as lenses, cavity fillings, veins and also in the pegmatites intruding the country rocks. The veins, lenses etc. are parallel to the bedding planes. Individual veins are small but graphite-bearing zones extend to many kilomertres. The veins swell, pinch and subdivide into small stringers, just like mica veins. Mostly, the veins show a banded structure. Graphite-pegmatites usually grade into massive graphite. Flake graphite is found disseminated in the schist rocks.

There are over a dozen mechanised underground mines. Others are open pits. The run-of-mine contains about 50% impurities which are hand sorted. At the port of export, the mineral is further processed by crushing, washing, screening and brought to the required specifications according to the consumers' requirement, by blending. Principal graphite mines are worked by Bogala Graphite Ltd., and H.L. de Mel and Co. High carbon ground graphite in different degrees of fineness to minus 200 mesh, is being produced in increasing quantities.

Graphite has been mined in Ceylon since 1834. All production is exported to Canada, the USA and many European and Asian Countries.

Large deposits of bedded graphite associated with metamorphosed Triassic sandstone are found near the town of La Colarada, in the State of Sonora. Graphite has been mined in this country since 1895. The Triassic beds have been sharply folded and intruded by granite and dykes. Seven graphite beds of varying thickness, on an average 2 to 3 metres have been found. Mexico is one of the important producers of amorphous graphite, which is mined here by underground methods. The run-of-mine contains 80-85% carbon which on hand-sorting gives 95% carbon. A major portion of the production is exported to the USA.

Amorphous graphite is found both in North and South Korea formed due to metamorphism of coal and argillaceous graphite. It is found as graphite schist, lenses near the contact of Cretaceous granites. In the Kyeng-Sang district, South Korea, three seams having mineable widths of 24, 6, 15 metres respectively have been found. Korean graphite is of low carbon content and mainly exported to Japan for foundry use.

The production of amorphous graphite in Russia, mainly comes from Siberia. The mines are worked near Inkutsk. Flake graphite occurs in nepheline syenite and schists in North Caucasus.

Graphite is produces mostly in the north-eastern part of China. The average annual production is 40,000 tonnes.

Most of the deposits worked in this country contain on an average 4 to 7% carbon. Occurrences are reported in a large number of States. Pennsylvania, Montana, Central Texas, North-Eastern Albama and New Jersey are the important States where it is mined. Deposits in Michigan, Wisconsin and Nevada have produced amorphous graphite. The main source of amorphous graphite is Rhode Island, in the Narragansette Basin.

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