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Fabric made of woven carbon filaments

Carbon fiber (carbon fibre), alternatively graphite fiber, carbon graphite or CF, is a material consisting of extremely thin fibers about 0.005–0.010 mm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment makes the fiber very strong for its size. Several thousand carbon fibers are twisted together to form a yarn, which may be used by itself or woven into a fabric.[1] Carbon fiber has many different weave patterns and can be combined with a plastic resin and wound or molded to form composite materials such as carbon fiber reinforced plastic (also referenced as carbon fiber) to provide a high strength-to-weight ratio material. The density of carbon fiber is also considerably lower than the density of steel, making it ideal for applications requiring low weight.[2] The properties of carbon fiber such as high tensile strength, low weight, and low thermal expansion make it very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, it is relatively expensive when compared to similar materials such as fiberglass or plastic. Carbon fiber is very strong when stretched or bent, but weak when compressed or exposed to high shock (eg. a carbon fiber bar is extremely difficult to bend, but will crack easily if hit with a hammer).

Contents

History of carbon fiber

from [www.carbonfiber.com.cn][2]

In 1958, Dr. Roger Bacon created high-performance carbon fibers at the Union Carbide Parma Technical Center, located outside of Cleveland(united states), Ohio.[3] Those fibers were manufactured by heating strands of rayon until they carbonized. This process proved to be inefficient, as the resulting fibers contained only about 20% carbon and had low strength and stiffness properties. In the early 1960s, a process was developed using polyacrylonitrile (PAN) as a raw material. This had produced a carbon fiber that contained about 55% carbon and had much better properties. The polyacrylonitrile (PAN) conversion process quickly became the primary method for producing carbon fibers.[1]

The high potential strength of carbon fiber was realized in 1963 in a process developed at the Royal Aircraft Establishment at Farnborough, Hampshire. The process was patented by the Ministry of Defence and then licensed by the NRDC to three British companies: Rolls-Royce, already making carbon fiber, Morganite and Courtaulds. They were able to establish industrial carbon fiber production facilities within a few years, and Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine.

Even then, though, there was public concern over the ability of British industry to make the best of this breakthrough. In 1969 a House of Commons select committee inquiry into carbon fiber prophetically asked: "How then is the nation to reap the maximum benefit without it becoming yet another British invention to be exploited more successfully overseas?" Ultimately, this concern was justified. One by one the licensees pulled out of carbon-fiber manufacture. Rolls-Royce's interest was in state-of-the-art aero-engine applications. Its own production process was to enable it to be leader in the use of carbon-fiber reinforced plastics. In-house production would typically cease once reliable commercial sources became available.

Unfortunately, Rolls-Royce pushed the state-of-the-art too far, too quickly, in using carbon fiber in the engine's compressor blades, which proved vulnerable to damage from bird impact. What seemed a great British technological triumph in 1968 quickly became a disaster as Rolls-Royce's ambitious schedule for the RB-211 was endangered. Indeed, Rolls-Royce's problems became so great that the company was eventually nationalized by Edward Heath's Conservative government in 1971 and the carbon-fiber production plant sold off to form Bristol Composites.

Given the limited market for a very expensive product of variable quality, Morganite also decided that carbon-fiber production was peripheral to its core business, leaving Courtaulds as the only big UK manufacturer.

The company continued making carbon fiber, developing two main markets: aerospace and sports equipment. The speed of production and the quality of the product were improved.

Continuing collaboration with the staff at Farnborough proved helpful in the quest for higher quality, but, ironically, Courtaulds's big advantage as manufacturer of the "Courtelle" precursor now became a weakness. Low cost and ready availability were potential advantages, but the water-based inorganic process used to produce Courtelle made it susceptible to impurities that did not affect the organic process used by other carbon-fiber manufacturers.

Nevertheless, during the 1980s Courtaulds continued to be a major supplier of carbon fiber for the sports-goodsmarket, with Mitsubishi its main customer. But a move to expand, including building a production plant in California, turned out badly. The investment did not generate the anticipated returns, leading to a decision to pull out of the area. Courtaulds ceased carbon-fiber production in 1991, though ironically the one surviving UK carbon-fiber manufacturer continued to thrive making fiber based on Courtaulds's precursor. Inverness-based RK Carbon Fibres Ltd has concentrated on producing carbon fiber for industrial applications, and thus does not need to compete at the quality levels reached by overseas manufacturers.

During the 1970s, experimental work to find alternative raw materials led to the introduction of carbon fibers made from a petroleum pitch derived from oil processing. These fibers contained about 85% carbon and had excellent flexural strength.[1]

Structure and properties

A 6 μm diameter carbon filament (running from bottom left to top right) compared to a human hair.

Carbon fibers are the closest to asbestos in a number of properties.[4] Each carbon filament thread is a bundle of many thousand carbon filaments. A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon. The earliest generation of carbon fibers (i.e., T300, and AS4) had diameters of 7-8 micrometers[5]. Later fibers (i.e., IM6) have diameters that are approximately 5 micrometers[5].

The atomic structure of carbon fiber is similar to that of graphite, consisting of sheets of carbon atoms (graphene sheets) arranged in a regular hexagonal pattern. The difference lies in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The intermolecular forces between the sheets are relatively weak Van der Waals forces, giving graphite its soft and brittle characteristics. Depending upon the precursor to make the fiber, carbon fiber may be turbostratic or graphitic, or have a hybrid structure with both graphitic and turbostratic parts present. In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or crumpled, together. Carbon fibers derived from Polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200 C. Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived carbon fibers have high Young's modulus and high thermal conductivity.

Applications

Tail of an RC helicopter, made of Carbon fiber reinforced polymer

Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as Carbon fiber or graphite reinforced polymers. Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gasses, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component. Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense, compact layer of carbon fibers efficiently reflects heat.[6].

It has also been used in experimental medical procedures to treat severe burns. Brian Eno underwent extensive surgery in early 2009 which complemented a regular skin graft on his arm with carbon fiber threads. Being carbon based, doctors were able to fuse together his skin cells with the carbon fiber.[7]

Most recently, it has been used in Helios braces, braces for Charcot Marie Tooth and other Peripheral neuropathy patients

Synthesis

Each carbon filament is made out of long, thin filaments of carbon sometimes transformed to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer based on acrylonitrile used in the creation of synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing continuous filaments. A common method of manufacture involves heating the PAN to approximately 300 °C in air, which breaks many of the hydrogen bonds and oxidizes the material. The oxidized PAN is then placed into a furnace having an inert atmosphere of a gas such as argon, and heated to approximately 2000 °C, which induces graphitization of the material, changing the molecular bond structure. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, columnar filament. The result is usually 93–95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000 °C (carbonization) exhibits the highest tensile strength (820,000 psi or 5,650 MPa or 5,650 N/mm²), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm²). Since 1995, Nike has used carbon fiber midfoot support shanks in the Air Jordan XI. It is still used today in Nike basketball shoes. It provides torsional rigidity, allowing the heel and forefoot to act as one unit. Many racecars have carbon fiber reinforcing and panels incorporated in them.

Textile

Precursors for carbon fibers are polyacrylonitrile (PAN), rayon and pitch. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding, etc. Carbon fiber yarn is rated by the linear density (weight per unit length, i.e. 1 g/1000 m = 1 tex) or by number of filaments per yarn count, in thousands. For example, 200 tex for 3,000 filaments of carbon fiber is three times as strong as 1,000 carbon fibers, but is also three times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Some commonly used types of weave are twill, satin and plain.

Manufacturers

PAN aerospace/high end carbon fiber
PAN commercial grade carbon fiber
Pitch carbon fiber
  • Sumitomo
  • Kureha Corporation

See also

References

  1. ^ a b c carbon fiber: Definition and Much More from Answers.com
  2. ^ Mr. Jeremy Hierholzer, Assistant Professor of Aviation Technology, Purdue University, 2007.
  3. ^ Bacon's breakthrough
  4. ^ Properties And Fiber Types
  5. ^ a b W.J. Cantwell, J Morton (1991). "The impact resistance of composite materials -- a review". Composites 22 (5): 347–62. doi:10.1016/0010-4361(91)90549-V. 
  6. ^ Z. Zhao and J. Gou "Improved fire retardancy of thermoset composites modified with carbon nanofibers" Sci. Technol. Adv. Mater. 10 (2009) 015005 free download
  7. ^ [1]Interview with Sydney University Radio Group, 18th of May 2009

External links


[[File:|thumb|right|Fabric made of woven carbon filaments]]

Carbon fiber (carbon fibre), alternatively graphite fiber, carbon graphite or CF, is a material consisting of extremely thin fibers about 0.005–0.010 mm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment makes the fiber very strong for its size. Several thousand carbon fibers are twisted together to form a yarn, which may be used by itself or woven into a fabric. Carbon fiber has many different weave patterns and can be combined with a plastic resin and wound or molded to form composite materials such as carbon fiber reinforced plastic (also referenced as carbon fiber) to provide a high strength-to-weight ratio material. The density of carbon fiber is also considerably lower than the density of steel, making it ideal for applications requiring low weight. The properties of carbon fiber such as high tensile strength, low weight, and low thermal expansion make it very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, it is relatively expensive when compared to similar materials such as fiberglass or plastic. Carbon fiber is very strong when stretched or bent, but weak when compressed or exposed to high shock (e.g. a carbon fiber bar is extremely difficult to bend, but will crack easily if hit with a hammer).

Contents

History of carbon fiber

In 1958, Dr. Roger Bacon created high-performance carbon fibers at the Union Carbide Parma Technical Center, located outside of Cleveland, Ohio.[1] Those fibers were manufactured by heating strands of rayon until they carbonized. This process proved to be inefficient, as the resulting fibers contained only about 20% carbon and had low strength and stiffness properties. In the early 1960s, a process was developed by Dr. Akio Shindo at Agency of Industrial Science and Technology of Japan, with using polyacrylonitrile (PAN) as a raw material. This had produced a carbon fiber that contained about 55% carbon.

The high potential strength of carbon fiber was realized in 1963 in a process developed at the Royal Aircraft Establishment at Farnborough, Hampshire. The process was patented by the UK Ministry of Defence then licensed by the NRDC to three British companies: Rolls-Royce, already making carbon fiber, Morganite and Courtaulds. They were able to establish industrial carbon fiber production facilities within a few years, and Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine.

Even then, though, there was public concern over the ability of British industry to make the best of this breakthrough. In 1969 a House of Commons select committee inquiry into carbon fiber prophetically asked: "How then is the nation to reap the maximum benefit without it becoming yet another British invention to be exploited more successfully overseas?" Ultimately, this concern was justified. One by one the licensees pulled out of carbon-fiber manufacture. Rolls-Royce's interest was in state-of-the-art aero-engine applications. Its own production process was to enable it to be leader in the use of carbon-fiber reinforced plastics. In-house production would typically cease once reliable commercial sources became available.

Unfortunately, Rolls-Royce pushed the state-of-the-art too far, too quickly, in using carbon fiber in the engine's compressor blades, which proved vulnerable to damage from bird impact. What seemed a great British technological triumph in 1968 quickly became a disaster as Rolls-Royce's ambitious schedule for the RB-211 was endangered. Indeed, Rolls-Royce's problems became so great that the company was eventually nationalized by Edward Heath's Conservative government in 1971 and the carbon-fiber production plant sold off to form Bristol Composites.

Given the limited market for a very expensive product of variable quality, Morganite also decided that carbon-fiber production was peripheral to its core business, leaving Courtaulds as the only big UK manufacturer.

The company continued making carbon fiber, developing two main markets: aerospace and sports equipment. The speed of production and the quality of the product were improved.

Continuing collaboration with the staff at Farnborough proved helpful in the quest for higher quality, but, ironically, Courtaulds's big advantage as manufacturer of the "Courtelle" precursor now became a weakness. Low cost and ready availability were potential advantages, but the water-based inorganic process used to produce Courtelle made it susceptible to impurities that did not affect the organic process used by other carbon-fiber manufacturers.

Nevertheless, during the 1980s Courtaulds continued to be a major supplier of carbon fiber for the sports-goodsmarket, with Mitsubishi its main customer. But a move to expand, including building a production plant in California, turned out badly. The investment did not generate the anticipated returns, leading to a decision to pull out of the area. Courtaulds ceased carbon-fiber production in 1991, though ironically the one surviving UK carbon-fiber manufacturer continued to thrive making fiber based on Courtaulds's precursor. Inverness-based RK Carbon Fibres Ltd has concentrated on producing carbon fiber for industrial applications, and thus does not need to compete at the quality levels reached by overseas manufacturers.

During the 1970s, experimental work to find alternative raw materials led to the introduction of carbon fibers made from a petroleum pitch derived from oil processing. These fibers contained about 85% carbon and had excellent flexural strength.

Structure and properties

File:Cfaser
A 6 μm diameter carbon filament (running from bottom left to top right) compared to a human hair.

Carbon fibers are the closest to asbestos in a number of properties.[2] Each carbon filament thread is a bundle of many thousand carbon filaments. A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon. The earliest generation of carbon fibers (i.e., T300, and AS4) had diameters of 7-8 micrometers[3]. Later fibers (i.e., IM6) have diameters that are approximately 5 micrometers[3].

The atomic structure of carbon fiber is similar to that of graphite, consisting of sheets of carbon atoms (graphene sheets) arranged in a regular hexagonal pattern. The difference lies in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The intermolecular forces between the sheets are relatively weak Van der Waals forces, giving graphite its soft and brittle characteristics. Depending upon the precursor to make the fiber, carbon fiber may be turbostratic or graphitic, or have a hybrid structure with both graphitic and turbostratic parts present. In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or crumpled, together. Carbon fibers derived from Polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200 C. Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived carbon fibers have high Young's modulus and high thermal conductivity.

Applications

File:Cfk heli
Tail of an RC helicopter, made of Carbon fiber reinforced polymer

Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as Carbon fiber or graphite reinforced polymers. Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gasses, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component. Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense, compact layer of carbon fibers efficiently reflects heat.[4].

Synthesis

Each carbon filament is produced from a precursor polymer. The precursor polymer is commonly rayon, polyacrylonitrile (PAN) or petroleum pitch. For synthetic polymers such as rayon or PAN, the precursor is first spun into filaments, using chemical and mechanical processes to initially align the polymer atoms in a way to enhance the final physical properties of the completed carbon fiber. Precursor compositions and mechanical processes used during spinning may vary among manufacturers. After drawing or spinning, the polymer fibers are then heated to drive off non-carbon atoms (carbonization), producing the final carbon fiber. The carbon fibers may be further treated to improve handling qualities, then wound on to bobbins. Wound bobbins are then used to supply machines that produce carbon fiber threads or yarn.[5]

A common method of manufacture involves heating the spun PAN filaments to approximately 300 °C in air, which breaks many of the hydrogen bonds and oxidizes the material. The oxidized PAN is then placed into a furnace having an inert atmosphere of a gas such as argon, and heated to approximately 2000 °C, which induces graphitization of the material, changing the molecular bond structure. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, columnar filament. The result is usually 93–95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000 °C (carbonization) exhibits the highest tensile strength (820,000 psi or 5,650 MPa or 5,650 N/mm²), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm²).

Textile

Precursors for carbon fibers are polyacrylonitrile (PAN), rayon and pitch. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding, etc. Carbon fiber yarn is rated by the linear density (weight per unit length, i.e. 1 g/1000 m = 1 tex) or by number of filaments per yarn count, in thousands. For example, 200 tex for 3,000 filaments of carbon fiber is three times as strong as 1,000 carbon fibers, but is also three times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Some commonly used types of weave are twill, satin and plain.

See also

References

  1. ^ Bacon's breakthrough
  2. ^ Properties And Fiber Types
  3. ^ a b W.J. Cantwell, J Morton (1991). [Expression error: Unexpected < operator "The impact resistance of composite materials -- a review"]. Composites 22 (5): 347–62. doi:10.1016/0010-4361(91)90549-V. 
  4. ^ Z. Zhao and J. Gou "Improved fire retardancy of thermoset composites modified with carbon nanofibers" Sci. Technol. Adv. Mater. 10 (2009) 015005 free download
  5. ^ "How It Is Made". http://www.zoltek.com/carbonfiber/made.php. Retrieved 2010-04-04. 

External links


Simple English

[[File:|thumb|right|200px|A cloth of woven carbon filaments]]

Carbon fiber or Carbon fibre is also sometimes called graphite fiber. It has the highest compressive strength of all the reinforcing materials (composites), and it has a high strength to weight ratio and low coefficient of thermal expansion. The density of carbon fiber is also much lower than the density of steel. [1] Carbon fiber is in the form of several thousand long, thin strands of material that is composed of mostly carbon atoms.[2]

Contents

Other pages

Chemistry and Synthesis of Carbon Fiber

Notes

  1. Mr. Jeremy Hierholzer, Assistant Professor of Aviation Technology, Purdue University, 2007.
  2. http://www.madehow.com/Volume-4/Carbon-Fiber.html

Other websites









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