RESUMO
Carbon fibers are highly valued for their lightweight characteristics, outstanding mechanical properties, and cost-efficiency. However, their limited oxidation resistance and low thermomechanical stability in hot air impose constraints on their utilization. Here, we present an approach to simultaneously achieve high thermomechanical properties and high-temperature oxidation resistance in carbon-ceramic hybrid fibers featuring a highly aligned co-continuous topological structure through a continuous process. These hybrid fibers exhibit superior mechanical properties compared to pure carbon fibers with the same diameter (20 µm), including a tensile strength of 2.0 ± 0.2 GPa, Young's modulus of 175 ± 34 GPa, and elongation at break of 1.3 ± 0.2%. Moreover, when subjected to thermal exposure under stress loading conditions in air, the ceramic constituents form a protective oxidized ceramic layer that effectively mitigates thermal oxidation and mechanical loading effects at elevated temperatures, surpassing the performance of carbon fibers. Our discovery offers a promising avenue for bridging the performance gap between cost-effective high-strength carbon fibers and expensive SiC counterparts with exceptional oxidation resistance, which can be applied in many fields wherever high thermomechanical loading and oxidation-resistant properties are important.
RESUMO
In this study, multifibrillar carbon and carbon/ceramic (C/SiCON) fibers consisting of thousands of single nanofibers are continuously manufactured. The process starts with electrospinning of polyacrylonitrile (PAN) and PAN/oligosilazane precursors resulting in poorly aligned polymer fibers. Subsequent stretching leads to parallel aligned multifibrillar fibers, which are continuously stabilized and pyrolyzed to C or C/SiCON hybrid fibers. The multifibrillar carbon fibers show a high tensile strength of 911 MPa and Young's modulus of 154 GPa, whereas the multifibrillar C/SiCON fibers initially have only tensile strengths of 407 MPa and Young's modulus of 77 GPa, due to sticking of the nanofibers during the stabilization in air. Additional curing with electron beam radiation, results in a remarkable increase in tensile strength of 707 MPa and Young's modulus of 98 GPa. The good mechanical properties are highlighted by the low linear density of the multifibrillar C/SiCON fibers (~ 1 tex) compared to conventional C and SiC fiber bundles (~ 200 tex). In combination with the large surface area of the fibers better mechanical properties of respective composites with a reduced fiber content can be achieved. In addition, the developed approach offers high potential to produce advanced endless multifibrillar carbon and C/SiCON nanofibers in an industrial scale.
RESUMO
Materials with an extremely low thermal and high electrical conductivity that are easy to process, foldable, and nonflammable are required for sustainable applications, notably in energy converters, miniaturized electronics, and high-temperature fuel cells. Given the inherent correlation between high thermal and high electrical conductivity, innovative design concepts that decouple phonon and electron transport are necessary. We achieved this unique combination of thermal conductivity 19.8 ± 7.8 mW/m/K (cross-plane) and 31.8 ± 11.8 mW/m/K (in-plane); electrical conductivity 4.2 S/cm in-plane in electrospun nonwovens comprising carbon as the matrix and silicon-based ceramics as nano-sized inclusions with a sea-island nanostructure. The carbon phase modulates electronic transport for high electrical conductivity, and the ceramic phase induces phonon scattering for low thermal conductivity by excessive boundary scattering. Our strategy can be used to fabricate the unique nonwoven materials for real-world applications and will inspire the design of materials made from carbon and ceramic.