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1993 | Buch

Carbon-Carbon Composites

verfasst von: G. Savage

Verlag: Springer Netherlands

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Über dieses Buch

Carbon fibre reinforced carbon composites form a very specialized group of materials. They may be considered as a development of the family of carbon fibre reinforced polymer composites which are becoming ever more prevalent in modern engineering. Since the early 1960s a large number of so-called 'advanced materials' have appeared on the scene. Carbon~arbon is arguably the most successful of all these products finding many and varied applications. In the field of Formula 1 motor racing for example, the present levels of performance simply could not be achieved without the use of carbon-carbon brakes and clutches. Despite the materials' obvious assets, they have not, and will not, reach their full potential until their inherent problems of excessive production costs and oxidation resistance have been addressed properly. In this respect the 'carbon-carbon story', of much potential but only limited success, serves as a lesson to all those involved in materials research, development and application. In writing this book I have tried to set up a logical progression of what the materials are, how they are made, what their assets and deficiencies are, what they are used for and to what extent they are commercially exploited. Each specialized chapter may be considered in isolation or as part of a sequence, whereas the final chapter provides a summary of the principal concepts as well as a basic review of the economic situation past, present and, hopefully, future.

Inhaltsverzeichnis

Frontmatter
1. Introduction
Abstract
Carbon has an atomic weight of 12.011 and is the sixth element in the periodic table. Three isotopes are known to exist, these being C12, C13 and C14, the first two of which are stable. C12 accounts for around 99% of the naturally occurring carbon and is used as the reference definition of atomic mass. It is defined as having a ‘relative atomic mass’ of 12[1]. C13 has a magnetic moment (spin = 1/2) which results in its being used as a probe in nuclear magnetic resonance (NMR) studies, although its low abundance induces lengthy acquisition times. The radioactive isotope C14 is generated in the earth’s upper atmosphere by the interaction of neutrons with nitrogen:
$${{N}^{14}}+n\to {{C}^{14}}+{{H}^{1}}$$
(1.1)
C14 has a very long half-life of 5730 years and is used extensively in the dating of archaeological artefacts and as a ‘label’ in the study of organic reaction mechanisms.
G. Savage
2. Carbon Fibres
Abstract
The measured strengths of materials are several orders of magnitude less than those calculated theoretically. This discrepancy is believed to be due to the presence of inherent flaws within the material [1]. It follows that the strength of a material can therefore be enhanced by eliminating or minimizing such imperfections. Cracks lying perpendicular to the direction of applied loads are the most detrimental to the strength. Fibrous or filamentary materials thus exhibit high strengths and moduli along their lengths because in this direction the large flaws present in the bulk are minimized.
G. Savage
3. Gas Phase Impregnation/Densification of Carbon-carbon and other High-temperature Composite Materials
Abstract
Chemical vapour deposition (CVD) is a process in which a solid product nucleates and grows on a substrate, by decomposition or reaction of gaseous species, and involves the heating of a fibre preform in a gaseous environment so that the matrix is deposited from the gas phase. The technology developed to date allows fine control over the composition and morphology of the solid deposit. Various processes have been used for the production of thin film semiconductor devices for the communications industry and the production of hard, abrasion-resistant coatings on cutting tools and coatings on radioactive pellets. The CVD techniques have also been widely used for the preparation of oxidation- and wear-resistant coatings to carbon-carbon composites. Well-processed CVD-derived composites generally possess excellent mechanical properties as a consequence of the slow, steady build-up of matrix material around the fibre network. The CVD method has proven especially useful for the production of ceramic matrix composites, where melt-processing techniques are inapplicable and conventional powder-processing methods — such as those used for the production of monolithic ceramics — result in serious fibre degradation. The major drawback of CVD is the very slow rate of deposition, leading to large material/energy inputs and a high final cost.
G. Savage
4. Thermosetting Resin Matrix Precursors
Abstract
Thermosetting resins are used as matrix precursors in carbon-carbon composites because they are relatively easy to use to impregnate fibres, and a large technology base exists from their use in ‘conventional’ composites processing. The resin impregnation/carbonization route is extremely flexible. Large structures, often with complex geometries, can be manufactured using all of the methods proven in the composites field, e.g. filament winding, prepreg, hand lay-up or pultrusion. In general, thermosetting resins polymerize at low temperatures (<250 °C) to form a highly three-dimensionally cross-linked non-softening amorphous solid. When pyrolysed, the resins form a glassy, isotropic carbon [1] which does not graphitize at temperatures up to 3000 °C.
G. Savage
5. Thermoplastic Matrix Precursors
Abstract
It has been discussed, thus far, how the fabrication of carbon-carbon composites is achieved by the impregnation of fibre tows, weaves or skeletons (3-D structures or felts) with thermosetting resins or by chemical vapour infiltration with gaseous hydrocarbons. All of the processes presently practised are slow and expensive, and fail to exploit fully the strength of the reinforcing fibres [1]. Vapour infiltration methods require low reaction rates to maintain a uniform deposition throughout a porous body.
G. Savage
6. Oxidation and oxidation protection
Abstract
Over the past decade the development of structural carbon-carbon materials has received a great deal of attention. Potential uses have been cited in future generation military aircraft, missile systems and a number of proposed hypersonic aerospace vehicles. All of the possible applications take advantage of the excellent high-temperature properties of carbon and the benefits of fibre reinforcement, most especially high strength and strength retention at temperatures in excess of 2000 °C. It is important to note that all such applications involve operation for extended periods of time in oxidizing environments. Since the composites have already demonstrated the mechanical requirements, it is generally concluded that the development of reliable oxidation protection is crucial to carbon-carbon attaining its full potential. The method accepted as the most feasible way to protect carbon-carbon composites involves coating of the outer surfaces of the material with appropriate refractory materials in order to prevent oxygen attacking the substrate. Additionally, protective compounds, known as inhibitors, may be placed within the composite.
G. Savage
7. Laboratory scale production and evaluation of carbon-carbon
Abstract
In earlier Chapters the principles and processing involved in the various industrially exploited methods of carbon-carbon manufacture have been discussed. The aim of this Chapter is to detail the production, testing and evaluation of the materials on a laboratory scale for research purposes.
G. Savage
8. The Properties of Carbon-carbon Composites
Abstract
The microtexture, that is to say the microstructure and morphology, of the various types of carbon-carbon composite will differ according to the type of raw materials and the processing conditions. Further complication will arise from the use of ‘subtle’ treatments such as surface modification of the fibres and inclusion of oxidation protection. All such differences in microstructure exert a considerable influence on the properties of the materials.
G. Savage
9. Applications of Carbon-carbon Composites
Abstract
Something like 63% by volume of the carbon-carbon produced in the world is used in aircraft braking systems. Carbon-carbon brake materials were originally developed by the Super Temp Division of B. F. Goodrich Inc. in the USA. Their process was licensed by Dunlop in the UK. Dunlop were the first company to manufacture and fit carbon-carbon composite brakes into regular service.
G. Savage
10. Technology Summary and Market Review
Abstract
Carbon-carbon composites consist of carbon fibres in a carbon matrix. The fibres may be chopped, continuous or woven and may be produced from rayon, polyacrylonitrile (PAN) or pitch (mesophase or isotopic). The carbon matrix may be deposited by chemical vapour deposition (CVD), by the carbonization of a thermosetting or thermoplastic organic material or by a combination of these. The result is a family of composites whose microstructures and properties may be multi-dimensionally tailored to a great degree for a range of applications. Unlike metals and ceramics, carbon-carbon composites retain their strength at very high temperatures. High thermal conductivity and low thermal expansion give carbon-carbon materials an excellent resistance to thermal shock. A high heat of sublimation and low CTE for carbon and graphite result in good ablation resistance. Other advantages include chemical resistance, excellent high-temperature wear characteristics, biocompatibility, shape stability and pseudo-plastic fracture behaviour.
G. Savage
Backmatter
Metadaten
Titel
Carbon-Carbon Composites
verfasst von
G. Savage
Copyright-Jahr
1993
Verlag
Springer Netherlands
Electronic ISBN
978-94-011-1586-5
Print ISBN
978-94-010-4690-9
DOI
https://doi.org/10.1007/978-94-011-1586-5