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.
More about GRAPHITE
Graphite is an allotrope of carbon, similar to diamond. It displays a hexagonal crystalline form and is grey/black in colour. Graphite offers high thermal resistance, with a melting point of about 3,927 degrees Celsius. It is the most thermally and electrically conductive of non-metals whilst also being a very good lubricant. Graphite is chemically inert and has a high resistance to corrosion.
There are three distinct types of natural graphite which occur in different kinds of ore deposits. Graphite is characterised by the mode of formation which leads to these physically distinct common varieties: amorphous, vein and flake. Amorphous (micro-crystalline) graphite has a carbon content of 70-85%, high crystalline graphite (vein, lump or crystalline vein) has a carbon content of 90-99% and flake graphite has a carbon range of 80-98%.
Application: Carbon steel forging, Lithium ion batteries, Crucibles, Refractory bricks, Brake pads, dry cell batteries, Lubricants, Casings for electronics, Sporting equipment, Pencils
Specifications: Fixed carbon from 80% to 99.5% with grain size from 35 mesh to 3000 mesh depending on application industry.
Amorphous graphite has a microcrystalline structure. It is normally found as large lumps with flat fracture cleavages. Formed by thermal metamorphism of coal seams, its carbon content is dependent on the parent material. Amorphous graphite is usually lower in purity than other natural graphite. It is the most abundant type of graphite.
Crystalline flake graphite is recognisable by its high metallic lustre, and plate-like particle morphology. It is formed in metamorphic rock, in concentrations of 5%-12% of the ore body. Flake graphite is rarer, thus selling for four times the price of amorphous graphite (Mackie Research Capital).
Flake Graphite is the most widely available crystalline form of natural graphite. While all graphite has a flaky morphology on some level, flake graphite demonstrates this structure regardless of the size of the particle. Ore bodies generally yield graphite of a distinctive purity. For example, flake graphite from Madagascar is typically 85-90% carbon with the balance ash. Graphite from Canada runs 90-97% carbon and graphite from China 90-96% carbon. The size of the graphite flake is commercially important. While small flake graphite can be manufactured from large flake, the reverse cannot be performed. This means the amount of large flake graphite removed from a deposit must be maximized. There are three primary sizes of flake graphite available: fine, medium and coarse flake, with specific particle size distributions. Fine flake graphite is +100 mesh, medium flake graphite is +100 mesh and coarse flake graphite is +80 mesh. From these three grades most other grades, from +32 mesh coarse flake to 3-micrometer powder, are made.
Crystalline vein graphite displays a light metallic sheen and needle like particle morphology. It is found in fissures, fractures or cavities going across igneous and metamorphic rocks through pyrolysis of carbon-bearing gases. It is the most pure type of graphite, with the highest level of crystallinity of the natural forms. It is also the rarest. Sri Lanka is the only place where vein graphite is commercially mined
Traditionally, graphite has been used as a lubricant. This is because the flakes are able to slip over one another, giving the graphite a greasy texture, and thereby making it a desirable alternative to the wetnessEof oil. Changes in technology however, have reduced the need to use graphite as a lubricant, and a range of new applications has arisen.
The majority of the usage of graphite today is in refractory applications. The refractory industry consumes almost 35% of the graphite supply. Refractory applications involve the use of extremely high heat, necessitating the need for materials that are able to withstand such conditions without melting or disintegrating. Other uses of graphite include steelmaking, expanded graphite, brake linings and foundry facings. There are also a variety of other industrial uses which account for the remainder of graphite applications, including zinc-carbon batteries, electric motor brushes and the common pencil.
Graphite has the properties of both metals and non-metals, and this means it is able to be used for many industrial applications. Graphites metallic properties include thermal and electrical conductivity. Its non-metallic properties include inertness, lubricity and high-thermal resistance. As graphite has many desirable properties it can be used in a wide variety of different applications.
Graphites properties of lubricity and thermal conductivity mean it is excellent for use in high temperature applications. This is because it offers effective lubrication at a friction interface whilst providing for a thermally conductive matrix which removes heat away from that same interface. The refractory applications of graphite include alumina-graphite shapes, carbon-magnesite brick, castable ramming, gunning mixtures and crucibles. Carbonmagnesite brick is used in high-temperature, corrosive conditions, for example, in steel or iron blast furnaces or ladles. Alumina-graphite shapes, currently the most important refractory application, are used as continuous casting ware,like nozzles and troughs, and convey molten steel from ladle to mold.
In steelmaking, natural graphite is used as an agent to increase the carbon content of steel.
Expanded graphite can be used to make graphite foil or as a compound which insulates molten metal in a ladle or steel ingots and decreases heat loss. It can also be used as a firestop fitted around a fire door, in sheet metal collars that surround plastic pipes or to make gasket material for use in high temperatures. Graphite foil can be made into heat sinks for laptop computers as it saves on weight whilst keeping them cool. Expanded graphite is created through a process of bathing in chromic acid then concentrated sulfuric acid. This process forces the crystal lattice planes apart and expands the graphite.
Fine flake or amorphous graphite can be added to water-based paint in order to create a foundry facing mold wash. By painting the inside of a mold with this wash, then leaving it to dry, a fine graphite coat is made that is able to ease the separation of an object cast after hot metal has cooled.
Automotive Industry Uses:
Brake linings, Gaskets and Clutch Materials Amorphous or fine flake graphite can be used in brake linings, gaskets and clutch materials as it is now a widespread replacement for asbestos in many automotive functions. If fuel cells begin replacing internal combustion engines as experts predict, then graphite will likely be in very high demand in the automotive industry. Graphite is a central material in the friction industry, especially in the production of brake and clutch linings. With its lubricating properties, graphite modulates the braking effect of friction linings and essentially contributes to braking comfort and to noise reduction. The outstanding thermal conductivity properties of graphite also play an important role in friction linings. The main fields of application are the automotive sector and rail range (e.g. brake and clutch linings) as well as multilayered applications in the industry (e.g. sinter surfaces).
Due to the following versatile properties, graphite is used willingly in the friction industry:
• Friction coefficient: increasing graphite content brings down the friction coefficient
• Thermal conductivity: reduction of Hot SpotsEbr> • Lubricating properties: filling and smoothing of unevenness
• Plastic formability: balancing of unevenness on coat and disc
The main objective of using graphite is to transform kinetic energy into heat in brake linings and for torque transition in clutch linings. The different compositions in the respective brake lining must be mixed homogeneously. The graphite film, applied by the friction, will be removed by the rough petroleum coke. This interaction then leads to the appropriate braking effect.
Advantages of graphite in friction
• Reduction of braking noise and wear
• Encouragement of braking comfort
• Improvement of friction coefficient
• Parting agent in welding process
• Resistance to oxidation and cyclic temperature stress
Most portable devices such as mobile phones, laptops, mp3 players or digital cameras use lithium-ion batteries. However, as these require only small amounts of metal, the demand has stayed relatively small. The evolution of electric vehicles, including hybrid electric vehicles and plug in electric vehicles has changed this the result is rapidly growing demand for lithium-ion batteries. High-purity large-flake graphite is essential for the production of these batteries. There is 10 to 20 times more graphite within a lithium-ion battery than lithium. This is because graphite is the preferred anode material for most battery designs, as the anode requires a carbon material that is porous. An average hybrid electric vehicle requires over 10 kg of graphite, while an average electric vehicle requires 70 kg.
In order to make lithium-ion batteries, only flake graphite can be used. This graphite must be upgraded to 99.9% purity in order to make the sphericalEshape required for lithium-ion batteries. This is an expensive process which wastes 70% of the feedstock flake graphite. Due to this process, spherical graphite currently sells for three times the price of high quality flake graphite.
Graphite powder is mixed in required proportions with clay to achieve specifications of required pencil lead.
A crucible is a container that can withstand very high temperatures and is used for metal, glass, and pigment production as well as a number of modern laboratory processes. While crucibles historically were usually made from clay, they can be made from graphite that withstands temperatures high enough to melt or otherwise alter its contents.
|Graphite Powder Applications|