Characterization Of Commercial Carbon Fiber From Standard Pan Precursors And Low Cost Carbon Fiber From Textile Pan Based Precursors

Author : Joseph Sengeh
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (133 download)

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Download or read book SYNTHESIS, CHARACTERIZATION AND EVALUATION OF CARBON PRECURSORS AND THEIR APPLICATIONS IN CARBON FIBER, CARBON-CARBON COMPOSITES, AND GAS SORPTION SYSTEMS. written by Joseph Sengeh and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon products, especially carbon fibers (CFs) and carbon-carbon composites (C/C), are essential to many high-tech industries such as aerospace, green renewable energy, compressed gas storage, sporting goods, automobiles, and bioengineering, for producing high-end, high-performance products. They offer a unique combination of lightweight, high mechanical strength, low thermal expansion coefficient, and high-temperature stability, which are desirable for structural materials. For example, in the wind turbine industry, longer and lighter windmill blades are more efficient in harvesting wind energy. The blades 60 meters long are usually fabricated using CF-based composites. There is a strong desire to maximize and expand the use of CFs and carbon materials to many industries, including areas addressing energy and environmental concerns. Yet the key factor that prevents the widespread use of carbon products is their high cost. The cost of producing high-strength CFs from common polyacrylonitrile (PAN) precursor is high in all fabrication steps: the precursor synthesis, solution spinning, stabilization, and carbonization with low carbon conversion yield (C-yield). In addition, C/C composite manufacturing requires multiple impregnation and pyrolysis cycles because of the low C-yield of traditional phenolic resin precursors. Chapters 1 and 2 of this dissertation summarize the history and relevance of carbon materials, including CFs, C/C composites, and carbon materials for gas storage, as well as the challenges faced by the carbon industry. They also highlight the currently available carbon precursors, their design principles, advantages, and limitations. Chapters 3 and 4 introduce and investigate ways of developing a new set of polymeric and carbon precursors, including derivatives of poly(phenylacetylene) and poly(ethylene), which show incredible carbon yields as high as 90% and which are processable by both electro and solution spinning techniques. The fibers obtained from these precursors also show a polymorphous morphology similar to those of PAN fibers. These properties create the potential for these polymers to be used as alternatives to PAN, which is the major contributor to the precursor cost. The poly(ethylene) precursor fibers, in addition to a high carbon yield, good processability, and carbon properties have the potential to be cost-efficient compared to poly(phenylacetylene) and other polymers used to make carbon. Their high carbon yield also provides the opportunity for these polymeric precursors to be used as fillers in C/C composite systems. In addition to developing new polymer precursors for carbon fibers, a new practical synthetic route is developed in Chapter 5 to fabricate boron-doped carbon (CBx) materials using a new family of boron-doped pitch precursors that show a char yield as high as 81% with a softening temperature of 300 oC. These melt-processable boron-doped pitch precursors can serve as alternatives to polymer precursors for the fabrication of C/C composites. In addition to their low cost, this new precursor can dramatically reduce the current 6 impregnation/pyrolysis cycles to 1 cycle, which will significantly reduce the cost and time of manufacturing C/C composites. The resulting boron-doped carbon (CBx) materials exhibit a highly graphenic structure with a d-spacing of 0.3357 nm due to the presence of boron, which catalyzes the carbonization and graphitization processes at lower temperatures. When compared to synthetic graphite, which is stable in air up to 500 oC, these CBx materials are highly oxidatively stable. In air at 600 °C, these CBx materials lose no weight for as long as six hours. When the temperature is further increased to 700 and 800 °C, there is no detectable weight loss for 80 minutes. Evidently, the homogeneous distribution of B atoms in the CBx matrix is essential in continuously providing a protective B2O3 surface layer to slow down the oxygen diffusion into the matrix and delay the thermal/oxidative degradation process. Lastly, in Chapter 6, a highly microporous amorphous carbon material containing ~1% boron atoms is synthesized by chemically activating the boron-doped pitch precursor using potassium hydroxide (KOH) powder at 600 oC. The boron atoms in the amorphous carbon template provide sites to enhance the activation process with the KOH to produce a highly porous activated carbon; moreover, the remaining boron atoms are instrumental in enhancing the binding energy up to 20 kJ/mol between the sorbent and methane gas. The activated carbon obtained is influential in serving as a sorbent material for methane gas storage. The maximum amount of methane gas uptake that is recorded for this adsorbent at a pressure of 100 bars at 298 K is 0.426 g/g (gravimetric capacity) and 150 V/V STP (volumetric capacity), which is low compared to the DOE standard of 250 V/V STP (volumetric capacity) under similar conditions. Thus, this volumetric capacity value is enhanced to ~231 V/V STP at RT and 80 bars when the activated carbon material is densified to reduce the interparticle spacing as well as the meso and macropore structures. When the measurements were completed at a lower temperature of 0 oC and pressure of 80 bars for the densified samples, the methane uptake increased by ~60% to 370 V/V STP, which is much higher than the current methane capacity of compressed natural gas (263 V/V STP) at 200-250 bars and RT and that of the DOE standard (250 V/V STP) at RT and 100 bars. Results of a high pressure 13C magic-angle spinning NMR highlighted the potential for swelling within the carbon network during CH4 adsorption. The methane sorption capacity level in our activated carbon material is very high, compared with those reported in other precursors that were developed for methane gas storage.