The Relationship Between Microstructure Evolution And Mechanical Properties Of Pre-oxidized Silk And Carbon Fiber Under Irradiation

Carbon fibers(CFs)is a kind of high strength and high modulus carbon materials,and its carbon content is more than 95%.CFs have been widely applied in variety of applications such as aviation,building and transport and so on owing to their superior mechanical properties.However,practical mechanical properties of CFs were far lower than theoretical value.The y-irradiation had attracted tremendous attention because this technology could simultaneously improve surface activity and mechanical performance of CFs.However,as an important part in the microstructure of carbon fiber,there was not any research in previous literatures to report the evolution of microvoid for y-irradiated CFs.Pre-oxidized fiber is an important stage of carbon fiber preparation.So far,few studies have been made on it.There are also few studies on the evolution of pre-oxidized fiber structure under irradiation.In this paper,XRD,Raman,SAXS and SEM were used to study the microstructure of CFs,combined with mechanical properties analysis,to explore the relationship between the microstructure evolution and mechanical properties of carbon fibers irradiated by y-rays.The pre-oxidized fiber was irradiated by ?-ray,and the microstructure evolution of the pre-oxidized fiber was characterized by XRD,SAXS,EDS and so on.X-ray diffraction,small angle X-ray scattering and Energy Dispersive Spectrometer are used to study the evolution mechanism of microstructures for pre-oxidized fiber.The results show that the(002)layer spacing of pre-oxidized fiber decreases from 3.4824nm to 3.4513nm after irradiation.The radius of rotation increases from 1?5nm to 1?6nm(air)and 1?7nm(Ar),and the radius of the micropores is also increased from 1?7nm(original)to 1?8nm(air)and 1?9nm(Ar).The volume fraction of small size micropore is smaller than that of large size micropore.It is proved that y-irradiation makes the micropores of pre-oxidized fiber increase.The cross-sectional variation of oxygen content of pre-oxidized fiber is different under different irradiation medium,the oxygen content of cross section of pre-oxidized fiber irradiated in argon atmosphere are decreased,the precursor throughout the oxygen content in the air of irradiation increased,suggesting that y-ray irradiation promoted the process of pre oxidation pre-oxidized fiber.After irradiation,(002)layer spacing and ID/IG of T700 are smaller than before,L of pristine fibers was around 3?9nm,but minished to 1?7nm(ECP)and 1?5nm(Ar)for y-irradiation CFs.R of CFs irradiated in ECP and Ar respectively was 3.6868nm and 3.4223nm,decreasing 23.83%and 25.16%compared with the 4.8406nm for pristine fibers.But R of CFs irradiated in Ar was smaller than that in ECP,indicating activity media would enlarge the microvoid of CFs surface.But there was little difference of(002)layer spacing and ID/Ig of T700 between samples irradiated in ECP and Ar.It shows that the irradiated medium has little effect on the microcrystalline structure and the degree of graphitization of carbon fiber.Compared with the change of the mechanical properties of carbon fiber,it could be found that medium had little effect on crystal structure and the graphitization degree of CFs.On the contrary,the active medium(ECP)had remarkable influence to microvoid.Meanwhile,evolution of mechanical property in different irradiation media was consistent with the evolution of microvoid.Therefore,we could conclude that mechanical property of CFs was enhanced along with the decrease of microvoid caused by y-irradiation.