Thermal stabilization of 2D carbon-carbon composite material object geometry (1)

High-temperature treatment (HTT) of billets after carbonization is an integral part of industrial and laboratory production processes for manufacture of carbon composites, and also a number of varieties of structural graphite. High-temperature treatment regulates carbon material true density, its thermal and electrical conductivity, and also object geometric properties.

The aim of this work is analysis of conditions providing a stable geometric shape for carbon-carbon composite material (CCCM) objects during high-temperature treatment, based on directive specifications for production processes and schemes for making up a change of large billets. Recently in the domestic industrial base series production has been restored for manufacture from CCCM with the aim of providing primarily electrical engineering and chemical enterprises with high-strength and heat-resistant carbon materials in large thin-walled forms. Objects of CCCM in the current period of their production due to unique thermophysical and physicomechanical properties compared with structural graphites only in the case of creating from them medium-size and large and thin-walled objects. Industrial production of objects of composite carbon materials provides this segment of market demand with structural graphite materials. Recently the size of carbon billets of industrial production in the USA has already exceeded 5000mm. In China mass production has been set up for carbon-carbon plates from 2mm thickness with sizes up to 1500*1300mm. This increases the importance of the purpose of the present work.

Previously with participation of one of the authors a fundamental production scheme has been described for manufacturing products from CCCM, and some questions have been considered of providing high reliability of industrial production for large objects, which in that period found main use in special technology. It has been shown that the main production method for processing all carbon-containing substances in structural carbon materials is high-temperature processing in an inert or reducing atmosphere. The most critical stages in preparation of CCCM are:

– shaping of billets in spatial dimensions for finished objects;

– formation of a carbon matrix in a pore space of a carbon fibrous carcass; here extreme physicomechanical and thermophysical properties of CCCM are achieved.

Use of a production scheme for preparation of carbon-reinforced plastic as a precursor for a carbon-carbon billet for structural purposes in recent years has become the method used most often. This is due to the fact that primary polymer binder penetrates into pores between fibers of threads with greater probability and reliability than a smaller radius capillary.

Raw materials, used for preparing industrial CCCM are phenol formaldehyde resins, coal-tar pitch, carbon fibers and cloths of polyacrylonitrile or viscose, and also hydrocarbon natural gas, containing up to 95% carbon.

After carbonization and high-temperature treatment in the area of a resin layer there is formation of pores with a diameter of about 60% of the initial thickness of a polymer binder layer. Therefore, the capillary structure of reinforcing filler, depending on its texitile form, and binder content, governs the structure of a layer of polymer binder. Subsequently, after carbonization, the pore structure of a carbon-carbon carcass completely inherits features of the structure of the original composite mateiral in a plastic state. Choice of raw materials for filling pores of carbonized CM of carbon matrix and methods for this process depend on the change in CM structure in all preceeding production processes. Compaction of carbonized CM with a carbon matrix finally realizes a change-over from an unbonded cluster of fibers to a bonded cluster (composite material)


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