Preparation And Research Of Antioxidation Coating Of Carbon Fiber And Its Reinforced Composites

Carbon fiber has lots of excellent properties,such as high specific modulus,high specific strength,good fatigue resistance,thermal conductivity and electromagnetic properties.Besides,the thermal expansion coefficient of carbon fiber is small,which can be used as structural materials and functional materials for the preparation of reinforcing phase.Currently,carbon fiber has been applied in various fields including chemical engineering,biology,automobile and aerospace.However,the antioxidation ability of carbon fiber in the air environment is bad.When the temperature is over400℃,carbon fiber wound be oxided rapidly.It limits the application of carbon fiber in high temperature with air.Improving the heat resistance of carbon fiber is very important to broad the using range of such materials.In this paper,the modified sol-gel method and composites plating has been used to fabricate the SiC/SiO₂ coating and SiC-ZrO₂-MoSi₂/Ni coating for carbon fiber.The factors that affect the structure and property of coating have been studied,and the mechanism of coating process and antioxidation process has been discussed.The coated carbon fiber reinforced phenolic resin composite has been manufactured and tested.The results show that while the antioxidation property of fibers and composite have been increased,the mechanical property of them only decrease a little.First,the paper modified traditional sol-gel mtheod by adding KH560 and DMF with the weight ratio 5%and 3%.Coating factors that affect sol-gel properties and oxidation performance has been analyzed.The results show that modified sol-gel mehod can get more stable SiO₂ sol and better antioxidation ability SiO₂ coating.The initial oxidation temperature and final oxidation temperature have been improved nearly 70 ℃ and 100 ℃.Then the paper uses this modified SiO₂ sol,simethicone and Tween 80 to synthesize the modified sol-emulsion system.By dispersing the SiC nanoparticles into the system,SiC/SiO₂ coating can be fabricated at the surface of CF.The scanning electron microscope（SEM）,X-ray diffraction（XRD）and Thermogravimetric Analysis（TG）have been used to characterize the sol mass fraction,thermoforming temperature,nanometer SiC particle concentration and other factors which may affect the structure and performance of coating.Compared with the SiO₂coating,the composite coating is more smooth,and nanoparticles were disperse more uniform,the crystallinity of SiO₂ and the oxidation resistance ability of carbon fibers have also been increased.The initial oxidation temperature has been increased nearly300 ℃.The residual weight of coated carbon fibers is 65%after 1000 ℃ oxidation treatment for 15min.Due to the thickness of the composite coating,the mechanical property of coated carbon fibers has only slightly been decreased.To make a further step to incrase the interface strength between carbon fiber and coating,the paper proposed composite plating to fabricate the SiC-ZrO2-MoSi2/Ni coating onto carbon fibers,which shows much more powerful antioxidation ability.SEM,Energy Dispersive Spectroscopy（EDS）and TG analysis have been used to explore the best production conditions.Then,to characterize the chemical compostion,surface morphology molecular structure and antioxidation property of SiC-ZrO2-MoSi2/Ni coating,SEM,XRD,Fourier Transform infrared spectroscopy（FTIR）and TG have been used as testing method.Compare with SiC/SiO₂ coating,the SiC-ZrO2-MoSi2/Ni coating shows better oxidation resistance performance.Since it has stronger interface strength,the coefficient of thermal expansion between coating and fiber is much closer.What’s more,the intermediate products ZrSiO₄ can keep the composite coating intact at higher temperatures.The antioxidation ability has been improved magnificently.When the temperature is over 1400 ℃,the residual weigh of SiC-ZrO2-MoSi2/Ni coated carbon fiber is over 67%.After 10 min oxidation under 800 ℃ and 1000 ℃,the carbon fiber remains intact.Only few mechanical properties have been decreased.It means that while the composite coating increased the antioxidation performance of carbon fiber,the mechanical property of carbon fiber has been reserved.Last,the paper uses these two kinds of coated carbon fibers to make phnolic resin based composites,and the oxidation resistance property and mechanical property have been tested.The coated carbon fiber reinforece composite shows much better antioxidation performance while compares with uncoated carbon fiber reinforeced composites.Once the oxidation temperature is over 800 ℃,the uncoated carbon fiber reinforeced composites can be oxided rapidly.After 10min oxidation under 1200 ℃,the residual weight of SiC/SiO₂ coated carbon fiber reinforeced composite is over 50%.After 10min oxidation under 1600 ℃,the residual weight of SiC-ZrO2-MoSi2/Ni coated carbon fiber reinforced composites is 53%.From the results of mechanical testing,it can deduce that the coated CF reinforced composites have similar bending property with uncoated CF reinforced composites.Before the oxidation treatment,the bending strength of uncoated carbon fiber reinforced phenolic resin composites is 145.43 MPa,the bending modulus is 11.9 GPa.The bending strength of SiC/SiO₂ coated carbon fiber reinforeced composites is 137.14MPa,the bending modulus is 11.5 GPa.The bending strength of SiC-ZrO₂-MoSi₂/Ni coated carbon fiber reinforeced composites is 135.07 MPa,the bending modulus is11.4 GPa.It can deduce that two antioxidation coating has reserved the mechanical property of carbon fibers,and interface between coating and phenolic resin matrix is excellent.After 1200 ℃ treatment,the antioxidation coating has been peeled off from the fiber,leading the rapid decrease of mechanical properties.However,after 10min oxidation treatment under 1600 ℃,the bending strength and modules of SiC-ZrO₂-MoSi₂/Ni coated carbon fiber reinforeced composites are 43.97 MPa and3.6 GPa,which are still available.