Carbon-Carbon Tubes

Carbon-Carbon Tubes

These are eclectic structures that have yet to be used in kites…yet. This is mainly due to the extremely high cost of this material.

What is Carbon-Carbon?

Carbon-Carbon (C/C) has an extremely high stiffness to weigh ratio, but is more in the budget of the aerospace industry, not the average kite builder.

The first stages in the production of C/C is similar to that in the production of Carbon Fiber reinforced phenolic. Subsequent processing usually invokes one or two routes.

In the first route, commonly referred to as LPI, (liquid phenolic impregnation), the phenolic resin composite is heated to high temperatures in the absence of air. This process is known as carbonization and results in the formation of a carbon char. The resultant porous media is then infiltrated with more phenolic resin and further carbonized. This cycle is repeated until a specific carbon content is reached. This is usually measured by the density and, in the case of LPI, C/C is in the range of 1.5 to 1.6 g/cc.

In the second route to C/C commonly referred to as CVI (chemical vapor infiltration), the phenolic resin composites is first carbonized at temperatures up to 2,500° C (4,500° F) to create a porous structure. It is then subjected to the chemical vapor infiltration process. In this step a hydrocarbon gas (natural gas or mixtures of methane and other gases) is “cracked“ at about 1000° C. The resulting carbon is deposited in the porous carbon fiber structure. Although this process is much longer than the LPI route, mechanically superior materials can be made!

Carbon/Carbon has a unique balance of properties. The high temperature capability coupled with its high friction behavior makes it the choice for aircraft and racing car brakes. (Other structural applications rely on its ability to retain high levels of strength at temperature. Specific varieties of C/C exhibit very high levels of thermal conductivity. This coupled with its low coefficient of thermal expansion make it ideal for spacecraft heat exchangers, for example.

C/C Properties:

• Composites consisting of carbon fibers held together by carbon deposits. The carbon deposit is also referred to as the carbon matrix.

• The carbon fibers and carbon matrix are derived from a variety of sources. The most common carbon fibers are those derived from petroleum by-products such as pitch and synthetically produced fibers called PAN fibers. The matrix carbon is produced by the pyrolysis of resins or by reducing hydrocarbon gases such as methane to deposit carbon from the vapor phase.

• The composite properties are largely a function of fiber orientation. Thus, C/C materials are a family of composites, varying from randomly oriented chopped fibers in a carbon matrix to woven fabrics in a carbon matrix. Mechanical strength and stiffness are governed by fibers. The carbon matrix influences thermal properties and fatigue strength.

• Carbon/Carbon materials are used when light weight, chemically inert and/or high temperature strength are important issues. For example, tailored C/C materials surpass superalloys in specific strength, and copper and gold in thermal conductivity.

• Originally developed for high performance aircraft and space vehicles, these composites are used as aircraft and other brakes, vacuum furnace parts, in chemical reactors and a host of other industrial applications.

Further Reading:

Carbon Fiber Tubes

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