Fabrication Of Hollow And Multi-channel SiC Ultrafine Fibers By Emulsion Electrospinning

Silicon carbide（SiC）ultrafine fibers are widely used in the fields of high temperature insulation,wave absorption,catalyst support,sensor,electromagnetic shielding and field emission because of their properties of good thermostability,corrosion resistance and high thermal conductivity.Hollow SiC ultrafine fibers（HSiC fibers）possess the characteristics of large specific surface area and numerous active sites,because of its unique internal structure,can be applied in the high-temperature insulation material absorbing materials,catalyst carrier etc.other fields.Among the present fabrication methods of HSiC fibers,the complex equipment and imprecise preparation parameters of coaxial electrospinning hinder the quantity production,and the complex procedures and low efficiency of template method limit its extensive application.Aiming at the problems such as low efficiency,complex steps and poor morphology,an efficient and simple method was designed in this thesis.The hollow SiC fibers were prepared by emulsion electrospinning combined with the Polymer drived ceramics method.The structures and composition of the fibers were characterized,and the formation mechanism of HSiC fibers was analyzed.HSiC fibers showed good high temperature insulation performance.According to the formation mechanism of HSiC fibers,multi-channel SiC ultrafine fibers were prepared by regulating the dimension and number density of emulsion dispersed phase.Employing PCS,polystyrene（PS）and solvent to prepare PS/PCS emulsion as spinning emulsion,PS@PCS core-shell structure fibers was prepared by electrospinning technology.The fiber was transformed into PS@Crosslinked-PCS core shell structural fiber after preoxidation treatment,and HSiC fibers were obtained after pyrolysis treatment.After proportional optimization,the HSiC fibers prepared by PCS_0.4-PS_0.2 emulsion have good morphology,the average diameter is about 1.7μm,the average wall thickness is about250 nm,and there are nanospheres attached on the wall.Through the characterization of the PS@PCS core shell structure fiber,the formation mechanism of HSiC fiber was analyzed.It was found that the continuous PS@PCS core shell structure fiber formed by emulsion electrospinning was related to the redistribution of solvent in the PS dispersed phase of the emulsion.The dimension and number density of the PS dispersed phase could affect the morphology of the core-shell structure fiber.The nanospheres on the wall of micro nanofibers are composed ofβ-SiC,and the nanospheres are dericed from PCS microdrops which trapped in PS dispersed phase.PCS microdrops form the core layer of PS@PCS fibers along with PS dispersion phase,and then transform into SiC nanospheres after heat treatment.The thermal insulation property of HSiC fiber was tested by laser flash diffusivity apparatus.The thermal conductivity of HSiC fiber mat was 104.9 m W·（m·K）^-1 at800℃,only 29%of that of the solid SiC fiber mat.Based on the formation mechanism of HSiC fibers prepared by emulsion electrospinning,multi-channel SiC fibers were prepared by regulating the composition of emulsion and spinning conditions,and their formation mechanism was also analyzed.According to the spatio-temporality of emulsion behavior in Taylor cone,through decreasing the shear rate or lowering the environmental temperature,the coalescence efficiency of PS droplets is reduced,and it coalesced to a certain node,namely,leaving the Taylor cone to solidify and stretch to form multi-core fibers.After heat treatment,multi-channel SiC fibers were obtained.