Uses of Graphite

Graphite is the most stable form of carbon that exists in nature in crystalline form. The colour of graphite is black. It is opaque and has a luster like metals. It is also called plumbago. When subjected to conditions of high pressure and temperature, graphite converts itself to diamonds. In graphite, the carbon atoms arrange themselves in the form of a hexagon and the hexagons are arranged in layers. It may occur in crystalline form, amorphous form, lump form, and graphite fiber. 

It has huge applications in our daily life starting from its use in pencils, lubricants to electrodes, batteries, and many more purposes. It is a very popular material in electricals and electronics for its property of good electrical conductivity. Nowadays synthetic graphite is also produced because of the huge demand for graphite in electrical furnaces fed with anthracite or coke.

Graphite occurrences are reported from different states, but economically significant deposits are located in Chhattisgarh, Jharkhand, Odisha, and Tamil Nadu. 

Consumption of Graphite in India varies from 76 % of total consumption in the crucible and pencil industry to 16% in the Chemical Industry, 5% in Refractory Industry, and 5% in Alloy Steel & Foundry Industry.

Graphite is mostly used for refractory, battery, steel, expanded graphite, brake linings, foundry facings, and lubricants. Graphene, a naturally occurring ingredient in graphite, has unique physical properties and is one of the strongest known substances. The separation process from graphite, however, requires more technological development.

Refractories

Before 1900, the use started with the graphite crucible to carry molten metal but now it is a small part of refractories. The carbon-magnesite brick became important in the mid-1980s, and the alumina-graphite form became a little later. The order of importance at the moment is the shapes of alumina-graphite, carbon-magnesite bricks, monolithics and then crustaceans. 

Crucibles started using very large flake Graphite and Carbon-magnesite brick needing not so large flake graphite; for these and others, the size of the flake required is now much more flexible, and amorphous graphite is no longer restricted to low - end refractories. 

Various forms of alumina-graphite are used as continuous casting ware, such as nozzles and troughs, to transport molten steel from the ladle to the mold, and carbon magnesite bricks lining the steel converters and electric-arc furnaces to withstand extreme temperatures.  

Graphite blocks are used in blast furnace linings where the graphite's high thermal conductivity is very critical. Instead of carbon-magnesite bricks, high-purity monolithic is often used as a continuous furnace lining. 

Batteries

In the last 30 years, the use of graphite in batteries has increased. The anode of all major battery technologies is constructed using natural and synthetic graphite. Approximately twice as much graphite as lithium carbonate is used by the lithium -ion battery.

In the late 1980s and early 1990s, demand for batteries, mainly nickel-metal-hydride and lithium-ion batteries, caused an increase in graphite demand. Portable electronics like portable CD players and power tools have driven this growth. Products such as laptops, mobile phones, tablets and smartphones have increased battery demand. Batteries for electric vehicles increased the demand for graphite. For example, in a fully electric Nissan Leaf, a lithium -ion battery contains almost 40 kg of graphite.

Steelmaking

For this purpose, natural graphite is mostly used to raise carbon in molten steel, although it may be used to lubricate the dies used to extrude hot steel. The supply of carbon pickers is highly competitive and therefore subject to reduced prices from alternatives such as synthetic graphite powder, petroleum coke and other forms of carbon. To raise the carbon content of the steel to the specified level, a carbon raiser is added.

Brake Linings 

For heavier (non-automotive) vehicles, natural amorphous and fine flake graphite is used in brake linings or brake shoes and has become important with the need to replace asbestos. This use has been important for a long time, but organic non-asbestos (NAO) compositions are starting to reduce the market share of graphite. There was no benefit in a brake-lining industry shake-out with some plant closures, nor was there an indifferent automotive market.

Foundry Facings and Lubricants

A mold wash foundry is an amorphous or fine flake graphite paint based on water. Painting the inside of a mold with it and letting it dry leaves a fine graphite coat that will make it easier to separate the cast object after cooling the hot metal. Graphite lubricants are special items that can be used at very high or very low temperatures, such as die-lubricant forging, an antiseize agent, a mining machine gear lubricant, and locks lubricating. It is highly desirable to have low graphite, or even better no - grit graphite (ultra-high purity). It can be used in water or oil as a dry powder or as colloidal graphite (a permanent suspension in a liquid). 

Pencils

Pencils have been made from English natural graphite leads since the 16th century, but modern pencil lead is most commonly a mixture of powdered graphite and clay; it was invented by Nicolas-Jacques Conté in 1795. It is chemically unrelated to the metal lead, the ores of which looked similar, hence the name's continuation. Plumbago is another older term used for drawing natural graphite, typically as a mineral lump without a wood case. The term drawing of plumbago is usually limited to works of the 17th and 18th centuries, mostly portraits. Pencils are still a small but important natural graphite market today. 

Approximately 7 percent of the 1.1 million tons produced in 2011 were used to make pencils. Amorphous graphite of low quality is used mainly from China.

Graphene Technology

Single graphene roller sheets are 10 times lighter than steel, as well as 100 times stronger. Such a rolling sheet is also known as graphene, and this graphite derivative is the strongest identified material in the world and has been used to produce super-strength, lightweight sports equipment. Graphene shows resistance to chemicals, has high electrical conductivity and low light absorption. Its properties make it suitable as a material for future applications. It is used in medical implants such as artificial hearts, flexible electronic components, and in the manufacture of aircraft parts.

Crystalline Structure

Graphite occurs naturally in rock fractures or as amorphous lumps as flakes and veins. A flat sheet of strongly bonded carbon atoms in hexagonal cells is the basic crystalline structure of graphite. These sheets are called graphenes, but the vertical bonds between the sheets are very weak. The weakness of these vertical bonds allows the sheets to slide over each other and to cleave. However, the resulting material is 100 times stronger than steel if a graphene sheet is aligned and rolled horizontally. 

Other Uses

In zinc-carbon batteries, in electric motor brushes, and in various specialized applications, natural graphite has found uses. Different hardness or softness graphite results in different qualities and tones when used as an art medium. The Railway mix graphite with waste oil or linseed oil to create a heat-resistant protective cover for a steam locomotive's exposed portions of the boiler, such as the smokebox or the lower part of the firebox.

Summary

• Crucibles, foundries, pencils, etc. are the traditional uses of graphite. More sophisticated graphite applications include refractories used in steel, cement, and glass manufacturing, expanded graphite-based sealing gaskets, graphite grease, braid, brushes, brake lining, etc.

• It is also used in special applications such as in the nuclear industry, soil conditioners, and graphite foils used for sealing in the chemical and petrochemical industries and in the energy, engineering, and automotive industries.

• It is also used as a vital additive in small amounts to produce foundry coatings to prevent the melting of liquid metal with sand on the mould or core face. Such coatings are either sprayed or painted as a suspension or dusting or rubbed as dry powders.

• The graphite used for coating is of high quality that does not peel off as drying flakes and gives the casting a smooth surface. A major additive in many coating systems, graphite is known for its multiple functions such as refractory, lubricant, thermal conductor, electrical conductor, shield, electromagnetic pulse shield, corrosion shield, and pigment.

• It is also used in nuclear reactors and Lithium-ion (Li-ion) batteries used in electric vehicles that require high purity flake graphite in their anode material as a moderator.