Before the fibers are carbonized, they need to be chemically altered to convert their linear atomic bonding to a more thermally stable ladder bonding. This causes the fibers to pick up oxygen molecules from the air and rearrange their atomic bonding pattern.
The stabilizing chemical reactions are complex and involve several steps, some of which occur simultaneously. They also generate their own heat, which must be controlled to avoid overheating the fibers. Commercially, the stabilization process uses a variety of equipment and techniques.
In some processes, the fibers are drawn through a series of heated chambers. In others, the fibers pass over hot rollers and through beds of loose materials held in suspension by a flow of hot air. Some processes use heated air mixed with certain gases that chemically accelerate the stabilization. The lack of oxygen prevents the fibers from burning in the very high temperatures.
The gas pressure inside the furnace is kept higher than the outside air pressure and the points where the fibers enter and exit the furnace are sealed to keep oxygen from entering. As the fibers are heated, they begin to lose their non-carbon atoms, plus a few carbon atoms, in the form of various gases including water vapor, ammonia, carbon monoxide, carbon dioxide, hydrogen, nitrogen, and others. As the non-carbon atoms are expelled, the remaining carbon atoms form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fiber.
In some processes, two furnaces operating at two different temperatures are used to better control the rate de heating during carbonization. After carbonizing, the fibers have a surface that does not bond well with the epoxies and other materials used in composite materials.
To give the fibers better bonding properties, their surface is slightly oxidized. The addition of oxygen atoms to the surface provides better chemical bonding properties and also etches and roughens the surface for better mechanical bonding properties.
Oxidation can be achieved by immersing the fibers in various gases such as air, carbon dioxide, or ozone; or in various liquids such as sodium hypochlorite or nitric acid. The fibers can also be coated electrolytically by making the fibers the positive terminal in a bath filled with various electrically conductive materials. The surface treatment process must be carefully controlled to avoid forming tiny surface defects, such as pits, which could cause fiber failure.
Strength of a material is the force per unit area at failure, divided by its density. Materials such as Aluminium, titanium, magnesium, Carbon and glass fiber, high strength steel alloys all have good strength to weight ratios. Rigidity or stiffness of a material is measured by its Young Modulus and measures how much a material deflects under stress. Carbon fiber reinforced plastic is over 4 times stiffer than Glass reinforced plastic, almost 20 times more than pine, 2.
Although carbon fiber themselves do not deteriorate, Epoxy is sensitive to sunlight and needs to be protected. Other matrices whatever the carbon fiber is imbedded in might also be reactive. This feature can be useful and be a nuisance. In Boat building It has to be taken into account just as Aluminium conductivity comes into play. Carbon fiber conductivity can facilitate Galvanic Corrosion in fittings. Careful installation can reduce this problem.
Resistance to Fatigue in Carbon Fiber Composites is good. However when carbon fiber fails it usually fails catastrophically without much to announce its imminent break. Damage in tensile fatigue is seen as reduction in stiffness with larger numbers of stress cycles, unless the temperature is hight Test have shown that failure is unlikely to be a problem when cyclic stresses coincide with the fiber orientation.
Carbon fiber is superior to E glass in fatigue and static strength as well as stiffness. Tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, or failing.
Necking is when the sample cross-section starts to significantly contract. If you take a strip of plastic bag, it will stretch and at one point will start getting narrow. This is necking.
It is measured in Force per Unit area. Brittle materials such as carbon fiber does not always fail at the same stress level because of internal flaws. They fail at small strains.
Testing involves taking a sample with a fixed cross-section area, and then pulling it gradually increasing the force until the sample changes shape or breaks. Depending upon the manufacturing process and the precursor material, carbon fiber can be quite soft and can be made into or more often integreted into protective clothing for firefighting.
Nickel coated fiber is an example. Because carbon fiber is also chemically very inert, it can be used where there is fire combined with corrosive agents. Carbon Fiber Fire Blanket excuse the typos. Thermal conductivity is the quantity of heat transmitted through a unit thickness, in a direction normal to a surface of unit area, because of a unit temperature gradient, under steady conditions.
In other words its a measure of how easily heat flows through a material. Because there are many variations on the theme of carbon fiber it is not possible to pinpoint exactly the thermal conductivity. Special types of Carbon Fiber have been specifically designed for high or low thermal conductivity.
There are also efforts to Enhance this feature. This is a measure of how much a material expands and contracts when the temperature goes up or down. In a high enough mast differences in Coefficients of thermal expansion of various materials can slightly modify the rig tensions.
However, in modem engineering this is often not acceptable. As an alternative, the use of non-homogeneous, anisotropic materials, with significant stiffness and strength only in the directions these mechanical properties are really needed, can lead to enormous material and weight savings.
This is the case of multiphase systems called composite materials. In these composites, different material parts are added and arranged geometrically, under clearly designed and controlled conditions. Usually, a structure of fibers provides strength and stiffness and a matrix helds them together, whilst providing the geometric form. Carbon fibers are among the high-performance fibers employed in these advanced structural composites, which are profoundly changing many of today's high technology industries.
New research and development challenges in this area include upgrading the manufacturing process of fibers and composites, in order to improve characteristics and reduce costs, and modifying the interfacial properties between fibers and matrix, to guarantee better mechanical properties. The interdisciplinary nature of this "new frontier" is obvious, involving chemistry, materials science, chemical and mechanical engineering.
Other topics, which more often are treated separately, are also important for the understanding of the processes of fiber production.
Carbon filaments is one such topic, as the study of their mechanisms of nucleation and growth is clearly quite relevant to the production of vapour-grown carbon fibers.
Springer Professional. Back to the search result list. The progress achieved with carbon fibres, as compared with glass reinforcement fibres, is based on the superior stiffness of carbon fibres, combined with high strength and low density.
As was shown in [1], the density of polyaramide fibres introduced into the market nearly simultaneously with carbon fibres, is even lower, but strength and stiffness of these organic fibres do not approach the top values of carbon fibres. The pitch fibers and mesophase fibers discussed in this chapter are produced from.
Thus, perhaps they would be more accurately termed isotropic pitch-based and mesophase pitch-based carbon fibers. This, coupled with their unique ability to develop a graphitic structure, makes these fibers extremely attractive candidates for present research and future market growth.
Long before the invention of the electron microscope allowed the discovery of filamentous carbon, or before the march of polymer technology empowered engineers to make the first rayon-based carbon fibers, primitive technology existed for the preparation of vapor-grown fibers. The fibers were thought to be suitable for electric light bulb filaments, but lack of modern process controls made them uncompetitive.
As is discussed elsewhere in this book, the formation of microscopic filaments is a source of harmful carbon deposition when carbonaceous gases carbon monoxide, hydrocarbons The specific conditions in which these filaments have grown to macroscopic dimensions have occasionally been accidentally attained.
These last authors observed not only fibres but also filaments diameters between 10 and 80 nm, length greater than pm both thinner than fibres and longer than carbon filaments which are commonly obtained from the decomposition of carbonaceous gases; they postulated that these thin filaments were the precursors of thicker fibres.
The story of carbon fibres as we know them today begins in the s and 60s when the requirement of the aerospace industry for better lightweight materials became urgent. Following the realisation that low density fibres of high modulus could be used as the reinforcing elements in composites, there were a number of relatively successful attempts to prepare carbon fibres, especially those of Roger Bacon at Union Carbide using viscose rayon see Bacon , of Shindo in Japan using polyacrylonitrile PAN , and of Otani , also in Japan, using an isotropic pitch.
However, all of these procedures incorporated an expensive hot stretching process, and although fibres were produced commercially from viscose rayon Union Carbide and petroleum pitch Kureha Kagaku , now carbon fibres from PAN and mesophase-pitch MP predominate. Carbon fibres are generally used in composites in which they act as the reinforcing material. When the composite is submitted to a mechanical loading the stress transfer from one fibre to the other occurs via the matrix.
In particular the mechanical behaviour of the fibre-matrix interface is critical for the use of composite. Yet the carbon fibres reinforced polymers have usually low interlaminar shear strength and in this prespect their development was subjected to the improvement of their interfacial properties.
As a result, detailed characterization of carbon fibre surface have been carried out in order to investigate possible routes for improving and optimizing the interfacial interactions in composites. Composite materials offer a major growth market for high performance fibers.
It is the reinforcing fiber which gives the composite material its superior strength and stiffness. However, many of the reinforcing fibers have deficiencies which limit the performance of the final composite material. It is vital that these deficiencies be addressed in ongoing fiber research at university and industry research laboratories.
To stimulate thought on needed research, a panel discussion of these critical issues for fibers was held at the NATO Advanced Study Institute on May, 19, Then it can be woven together to form cloth and if needed to take a permanent shape, carbon fiber can be laid over a mold and coated in resin or plastic. Because of this, carbon fiber is very popular in many industries such as aerospace, automotive, military, and recreational applications.
Carbon fiber dates back to when Thomas Edison baked cotton threads or bamboo silvers at high temperatures, which carbonized them into an all-carbon fiber filament. By , high-performance carbon fibers were invented just outside of Cleveland, OH.
Carbon fiber is made from a process that is part chemical and part mechanical. It starts by drawing long strands of fibers and then heating them to a very high temperature without allowing contact to oxygen to prevent the fibers from burning. This is when the carbonization takes place, which is when the atoms inside of the fibers vibrate violently, expelling most of the non-carbon atoms.
This leaves a fiber composed of long, tightly inter-locked chains of carbon atoms with only a few non-carbon atoms remaining.
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