Carbon-fiber composites processing steps

Processing is lengthy, difficult, eind expensive. Typical steps in the processing of a 2D phenolic-carbon fiber composite are as follows ... 

More than 95% of current carbon fiber production for advanced composite appHcations is based on the thermal conversion of polyacrylonitrile (PAN) or pitch precursors to carbon or graphite fibers. Generally, the conversion of PAN or pitch precursor to carbon fiber involves similar process steps fiber formation, ie, spinning, stabilization to thermoset the fiber, carbonization—graphitization, surface treatment, and sizing. Schematic process flow diagrams are shown in Eigure 4. However, specific process details differ. 

The production of carbon fibers or filaments by decomposing a hydrocarbon gas over a transition metal catalyst has been the subject of extensive research. The product consists of filaments with diameters in the range of 1-100 pm and lengths up to 100 mm. In microstructure, it is different from traditional carbon fibers, resulting in a sword and sheath fracture mode without catastrophic failure. Since, in addition, these fibers are produced in a single step with no really expensive processing, they are attractive candidates for reinforcing composites. 

The strength and tensile behavior, at room and high temperatures, as well as the structure of three dimensional earbon fiber/SiC composites, fabricated by the slurry pulse/CVI combined process, were eharacterized by Suzuki et al [207-209]. Carbon fiber preforms, constructed with 4-step braid, 4-step/axial braid, 2-step braid and orthogonal weave, were used as reinforcements of the composites. The composites were fabrieated by a process consisting of slurry and dissolved organosilicon polymer infiltrations, followed by the application of pulse CVI. 

Copper can be coated on carbon fibers [47] and Zhu and workers have used a three-step electrodeposition process for the fabrication of Cu composites [48]. 

The diffusion of the volatile compounds to the atmosphere is a critical step and must occur slowly to avoid disruption and rupture of the carbon network. As a result, carbonization is usually a slow process. Its duration may vary considerably, depending on the composition of the end-product, the type of precursor, the thickness of the material, and otherfactors. Some carbonization cycles, such as those used in the production of large electrodes or some carbon-carbon parts, last several weeks. Others are considerably shorter, such as the carbonization cycle to produce carbon fibers, since these fibers have a small cross-section and the diffusion path is short. The specifics of each cycle will be reviewed in more detail in the following chapters. 

TGA is a thermal method that measures the weight loss as a function of temperature or time. Polypropylene decomposes at a lower temperature than polyethylene because of the substitution of a methyl group. Some works showed an increase of the degradation temperature of composites with the addition of carbon nanotubes and other synthetic fibers [52]. PE with natural fiber composites show two steps degradation processes because of cellulose, Thermal stability of PE/cellulosic fiber composites decreases with increase in fiber loading, showing two degradation processes. However,... 

The first useful organosilicon preceramic polymer, a silicon carbide fiber precursor, was developed by S. Yajima and his coworkers at Tohoku University in Japan [5]. As might be expected on the basis of the 2 C/l Si ratio of the (CH3)2SiCl2 starting material used in this process, the ceramic fibers contain free carbon as well as silicon carbide. A typical analysis [5] showed a composition 1 SiC/0.78 C/0.22 Si02- (The latter is introduced in the oxidative cure step of the polycarbosilane fiber). 

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