Structural Regulation And Properties Of Electrospun Sioc Fibers And Their Composites

Preceramic polymer pyrolysis is able to produce ceramics with low sinteringtemperature and complex shapes, and electrospinning is considered as a simple andversatile method for the fabrication of nanofibers. In this thesis, a combination of theabove-mentioned two methods was applied for the fabrication of SiOC fibers. Thewhole fabrication procedure and the characterization of the porosity were discussed indetail. Furthermore, based on the occurrence of the carbothermal reduction in SiOCceramics at high temperature, hierarchically structured polymer-derived ceramicfibers and metal/SiOC composite fibers were successfully produced by theintroduction of the transition-metal catalyst or the metal source.For the fabrication of the SiOC fibers, in order to prepare uniform fibers, a seriesof methods were applied: firstly, the selection of appropriate solvent, spinningassistant and cross-linking catalyst ensured the formation of the fibers with uniformmorphology and prevented fibers from melting during the cross-linking process.Secondly, the increase of the dielectric constant of MK electrospinning solvent andthe improvement of the evaporability of H44electrospining solvent enabled to reducethe diameter of the MK/PVP fibers and prevent the formation of beads in H44/PVPfibers. The SiOC fibers produced in this work exhibited both a smaller averagediameter (~1μm) and a more controlled morphology than those reported by previousliterature.For the characterization of the SiOC fibers, we focused on investigating themethods of measuring the porosity. The results show that the weight-volume-truedensity method and the improved mercury intrusion porosimetry could provide acorrect porosity. The X-ray computed tomography was able to construct a3Dstructure morphology of the fiber mats but it is not suitable for detecting the fiberswith a small diameter. Due to the complicated structure of the fiber mat, the SEMimage analysis was not suitable for measuring the fiber mat porosity. The porosities ofboth fibers were around90%and the MK-derived SiOC fibers possess a higherporosity than the H44-derived SiOC fibers, which results in a high permeability andlow tensile strength of the MK-derived SiOC fibers.Hierarchically structured polymer-derived ceramic fibers were successfullyproduced by electrospinning and catalyst-assisted pyrolysis with the addition of cobalt-based catalyst. The formation of nanowires improved the specific surface areaof the fiber mat from4.37m2/g to14.45m2/g and provided the material withsignificant additional meso-pores. Various kinds of metal/SiOC composite fibers(Ag/SiOC, Co/SiOC and Cu/SiOC composite fibers) were successfully fabricated by acombination of electrospinning and carbon thermal reduction method with themetallic oxide or metallo-organic compound as the starting material. The introductionof different metals further functionalized the SiOC fibers. Compared to other methods,the carbon thermal reduction method used in this paper is very simple and versatile.