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What is Carbon Fiber?

Carbon fiber weave.
High performance aircraft like the Lockheed Martin F-22 Raptor have many lightweight carbon fiber components.
Lightweight carbon fibers are often used to build the hulls of hovercraft.
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  • Originally Written By: Michael Anissimov
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  • Last Modified Date: 15 August 2014
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Carbon fiber is a textile consisting mainly of carbon. It is produced by spinning various carbon-based polymers into fibers, treating them to remove most of the other substances, and weaving the resulting material into a fabric. This is usually embedded in plastic — typically epoxy — to form carbon fiber reinforced plastic or carbon fiber composite. The most notable features of the material are its high strength-to-weight-ratio and its relative chemical inertness. These properties give it a wide range of applications, but its use is limited by the fact that it is fairly expensive.

Manufacture

The production of this material is usually based on either polyacrylonitrile (PAN), a plastic used in synthetic textiles for clothing, or pitch, a tar-like substance made from petroleum. Pitch is first spun into strands, but PAN is normally in fibrous form to start with. They are converted to carbon fiber by strong heating to remove other elements, such as hydrogen, oxygen, and nitrogen; this process is known as pyrolysis. Stretching the fibers during this procedure helps remove irregularities that might weaken the final product.

The raw fibers are initially heated to around 590°F (300°C) in air and under tension, in a stage known as oxidation, or stabilization. This removes hydrogen from the molecules and converts the fibers into a more mechanically stable form. They are then heated to around 1,830°F (1,000°C) in the absence of oxygen in a stage known as carbonization. This removes further non-carbon material, leaving mostly carbon.

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When high quality, high-strength fibers are required, a further stage, known as graphitization takes place. The material is heated to between 1,732 and 5,500°F (1,500 to 3,000°C) in order to convert the formation of the carbon atoms to a graphite-like structure. This also removes the majority of the residual non-carbon atoms. The term "carbon fiber" is used for material with a carbon content of at least 90%. Where the carbon content is greater than 99%, the material is sometimes called graphite fiber.

The raw carbon fiber that results does not bond well with the substances used to make composites, so it is mildly oxidized by treatment with suitable chemicals. The oxygen atoms added to the structure enable it to form bonds with plastics, such as epoxy. After being given a thin protective coating, it is woven into yarns of the required dimensions. These in turn can be woven into fabrics, which are then usually incorporated into composite materials.

Structure and Properties

A single fiber has a diameter of about 0.0002 to 0.0004 inches (0.005 to 0.010 mm); yarn consists of many thousands of these strands woven together to form an extremely strong material. Within each strand, the carbon atoms are arranged in a similar way to graphite: hexagonal rings joined together to form sheets. In graphite, these sheets are flat and only loosely bonded to one another, so that they slide apart easily. In a carbon fiber, the sheets are folded and crumpled, and form many tiny, interlocking crystals, known as crystallites. The higher the temperature employed in manufacture, the more these crystallites orient themselves along the axis of the fiber and the greater the strength.

Within a composite, the orientation of the fibers themselves is also important. Depending on this, the material can be stronger in a certain direction or equally strong in all directions. In some cases, a small piece can withstand an impact of many tons and still deform minimally. The complex interwoven nature of the fiber makes it very difficult to break.

In terms of strength-to-weight ratio, carbon fiber composite is the best material that civilization can produce in appreciable quantities. The strongest are approximately five times stronger than steel and considerably lighter. Research is underway into the possibility of introducing carbon nanotubes into the material, which may improve the strength-to-weight ratio by 10 times or more.

Other useful properties it has are its ability to withstand high temperatures and its inertness. The molecular structure is, like graphite, very stable, giving it a high melting point and making it less likely to react chemically with other substances. It is therefore useful for components that may be subjected to heat and for applications that require resistance to corrosion.

Uses

Carbon fiber is used in many areas where a combination of high strength and low weight are required. These include public and private transport, such as cars, airplanes, and spacecraft; sports equipment, like racing bicycles, skis, and fishing rods; and construction. The material’s relative inertness make it well suited for applications in the chemical industry and in medicine — it can be used in implants as it will not react with substances in the body. In civil engineering, it has been determined that old bridges may be spared from destruction and rebuilding through simple carbon fiber reinforcements, which are comparatively cheaper.

Economics

As of 2013, the uses, and demand, for carbon fiber have been limited by its cost. A bicycle made from composite typically costs around a few thousand US dollars (USD). Formula One racing cars, which travel at speeds over 200 mph (320 kph), may cost over $1 million USD to build and maintain, a cost determined in no small part by the generous use of this material. Demand has risen significantly, however, due largely to the increase in production of large commercial airplanes. If the cost can be significantly reduced, it may become a universal material for vehicles and small products designed for extreme durability and lightness.

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Discuss this Article

anon259491
Post 38

I am doing a project on carbon fiber composites chassis in F1 cars. I have enough information about carbon fibers, but I have very little information about the resin system used. Please, can you help me in this regard?

anon152285
Post 35

Carbon fiber is reaching new levels of manufacturing, processing and cost. A good example is the Boeing 787.

anon150756
Post 34

Who manufactures aircraft containers made of carbon fiber materials? Need comparisons as to comparable weights by container size if available.

Appreciate any information or guidance as to a resource or supplier I could contact.

Thanks for any info you may provide. --Karl B

anon130305
Post 31

list me some of the composite materials used for fabrication of ic engines?

anon125547
Post 30

i am new to carbon fiber and got interested in it. I wonder why carbon fiber is so light and strong compared to other materials like metals.

anon122722
Post 28

the single carbon filament is around 5µm, about a third of a hair's thickness.

To see how much weight that could hold... For one thing, carbon is not at its best when used as a rope, since carbon is very stiff and brittle compared to aramid/kevlar or glass. but in terms of tensile strength, this can vary to the kind of carbon that is used. (from 350Ksi for pitch to 700Ksi for PAN).

This means, in short, is that there is next to nothing you can get your hands on that is better when it comes to sheer stretching resistance.

As for the fire resistance, well they can take up to 6335°F but the resin system you use to contain the fibres in the orientation you desired limits you to an average of 500°F. At that point you just have a bundle of fibres, so the heat resistance depends on the resin system.

a filament is the smallest form of carbon. A strand is a bundle of filaments. A yarn is made of twisted strands, used for weaving and a tow is non-twisted bundles, used for winding or UD placement.

anon118211
Post 27

I'm an a-plus student in South Africa and I found out that carbon fibre can't burn without oxygen.

anon117613
Post 26

Why is it so expensive and why does it have to be transported at 0 frozen?

anon104187
Post 25

I'm currently doing a project on this topic. It is all about the current trends and developments on advance carbon composites, material specific to wind turbine blade technology.

I am seeking help in order for me just to understand what is carbon fibre? when did it start development with its specific production? also, what are the different types of material available in this field?

anon99448
Post 24

How do you compare carbon fiber to,2050 - T84 Plates

Description?

ALCAN patented Aluminium-Lithium 2050 is an

Al-Cu-Li-Mg alloy.

Its application would be bicycle frames.

anon73692
Post 22

i have a project in university, so can you tell me if I should make carbon fibers my topic, because i don't know anything about it and i want to know if it is wide enough to talk about in a project. thank you.

anon59464
Post 21

Excellent article. I am currently researching Carbon Fiber Manufacturers and have found PCT so far to be the best. Any suggestions would be appreciated.

anon55258
Post 19

What is involved with making tables and a bar for a restaurant using carbon fiber?

anon54540
Post 18

I am thinking of using small carbon fiber discs to simulate fish scales in a flexible knee pad for sports. will the impact from a fall on concrete or rocks shatter penny sized discs?

anon54165
Post 17

Carbon fibers will shatter when blunt force is applied. This is useful in a chassis such as an F1 car, is that when the frame is impacted, it will not transfer the force by crumpling, but rather will disperse the energy by shattering, thereby making it safer.

anon53787
Post 15

I read that although carbon fiber can withstand extreme bending due to its flexibility, it is not nearly as resilient when it comes to blunt force and will shatter. if this is true how can it be used in vehicles or aircraft?

anon52265
Post 14

Could carbon fiber be made from carbon waste from coal burning electric generating plants?

anon44877
Post 13

i am in a high school HMV class and i was wondering if it would make sense to use carbon fiber instead of alloys.

anon43604
Post 12

I am doing a project about carbon fibre and I need to know its breaking strength and its cost per square meter.

shramik
Post 10

Can carbon fiber be used in flight(like in blimps not airplanes)?

arch
Post 8

sir

i am 3rd year mechanical engineering student and i am doing project on use of lightweight materials in automobiles. since carbon fiber is the best option can you please give me details regarding the same.

thank you

oconnor
Post 6

I am interested in the question above concerning several strands of carbon fiber known as a tow. Specifically, if it can be wound around an object, what is its strength, how long can it be produced and the approx cost per foot. Thank You

anon22342
Post 5

I am an A-level student studying in england and i am making a presentation about carbon fibre and its use in formula one cars is there any information that you can give me in reference to carbon fibre, its properties and anything of interest to me.

thank you for your time.

anon21038
Post 4

i have a project on how carbon fiber is produced and the time frame it take to produce it by each machine and process by time.

anon19158
Post 3

Dear Sir,

It is a pleasure for me to take the opportunity to contact a real specialist in his field. I was amazed to find out that a personal website can offer the widest scope of information on carbon fibre and its use. Congratulations and thank you!

As you know much better than a dilettante as I am, carbon fibre has already penetrated deeply into world's highest technology. Unfortunately, a small number of people can enjoy the beauty and strenght of this material. As an executive manager of a small Bulgarian company, I would like to give people from my county the chance to touch the might of carbon in different forms, use and design, in different fields of industry. And more, to give them the best carbon fibre in order to improve their production and enter the market with interesting and modern products, made of or combined with carbon fibre.

Unfortunately, I am have already mentioned I am truly a laic in the fully science field and I hope that opening your website shall turn out to be a lucky coincidence.

The questions that first occur to a person that have seen carbon fiber only in formula 1, are what carbon is used for reinforcing car parts or deigning new furniture for example or even making a coffee cup out of carbon fibre, where can such carbon fibre be found, what do I do when I get it, how is it processed etc.

You seem to be only man in the virtual space that seemingly knows the answers of those question! With the fear of too much flattering, I would like to express my admiration and hope to receive your reply!

anon14051
Post 2

Why is it so expensive?

Poe
Post 1

Most of the information I have found on carbon fiber is about woven material, not the single strand. Most of the facts are written for engineers and math majors, not the layman. I would like some information in a straight-forward, user-friendly format.

For example, how thick is a single strand? How much weight will a single strand of carbon fiber hold? Will it oxidize when exposed to a flame of, say, 500 degrees Fahrenheit? Does the process of oxidation weaken the fiber? Is this a fast process, although I do not mean burning or exploding, or does it take place over an appreciable amount of time? When oxidizing, does it come to a point of complete disintegration or will it maintain structural cohesion? (Iron oxide, for example, does not disintegrate but it's structural integrity isn't high, either.)

There is a product called, I believe, a tow: several strands constituting one long line. How thick are these and how much weight do they hold per single line.

I know there are different kinds of carbon fiber, but I'm interested in any that may have the good mix of these abilities: carries a load, relatively inert to a low temperature flame and does not stretch appreciably.

Much obliged

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