| Abstract:Carbon fiber(CF) is a kind of high performance reinforcing material which has great development prospect because of its excellent properties in mechanical, thermology, electricity and chemical resistant.It has become a strategic material and being widely used in various fields such as aerospace, machinery, electronics, energy, etc.However,our country’s consumption of carbon fiber,especially high-performance carbon fibers used in the field of defense and military,mostly depend on import.With the development of production technology,it has being possible to substitute import with domestic carbon fiber.In this paper, a comparative study between three kinds of demostic and import carbon fibers with the same level has been demonstrated firstly to obtain the basic material parameters,and to understand the differences of structure and properties. Then oxidation modified with nitric acid and air was carried out to discuss the changing rule of the surface composition and microstructure. The following conclusions:1、The study shows that the surface groove structure of domestic carbon fibers appeared deeper. The tensile strength of ST300fiber which performed poor stability is only2.7GPa, and the CV value is as high as7.5%. The tensile strength of CCF300fiber is about3.31GPa which approach import carbon fiber.There are still large gap in terms of performance and stability between domestic CCF700and T700.2、The interplanar spacing、laminated thickness and crystallite size of domestic fibers are smaller than the import fibers.The R value of ST300fiber is maximum, indicating the worst degree of order.In addition, The amorphous carbon and functional groups of T300and T700are higher than domestic fiber.3、There exist a large number of oxygen-containing groups on the surface of untreated fibers.The content of C-OR and C=O on the surface of import fibers is high,as with higher content of COOR to domestic fibers.4、With the extension of oxidation time of CCF700fibers treated by nitric acid at80℃, the tensile strength declined firstly,and then increased with the time extended,and it would be increased slightly after treated at80℃,60min and100℃,90min.Not by over20min soking CCF700fibers in mixed acid, the tensile strength changed little,however,the modulus declined obvious.5、By CCF700fiber’s surface oxidation treatment with nitric acid,the total and the external oxygen concentration increased the overall content was significantly lower than the surface, and the growth is above the surface. After80℃treatment, with the extension of oxidation time, the whole oxygen content increased, but the surface oxygen content declined slightly, nitrogen content changed with fluctuations.It would not only introduce new groups, low reactive groups also happened to evolve to higher.With the increase of oxidation temperature and the extension of time, the disorder of the fiber surface reduced.6、With the increase of oxidation temperature, specific surface area of oxidated CCF300fiber increased,the total pore volume and the medium pore volume declined first and then rising, micropore volume increased.Total average pore diameter declined first and then increased.With the extension of oxidation time, The specific surface area increased first,and then fell to0.980m2/g after treated120min;the volume of total pore、midium pore and micropore rised first and then declined; the average pore diameter decreased from7.145nm to3.511nm.The specific surface area of air oxidated carbon fibers increased by more than27times, total pore volume increased by more than7times, the average pore diameter reduced to2.189nm, the volume of medium pore and micropore increased, the average pore diameter decreased.7、The oxygen content of carbon fiber oxidized by nitric acid or air were increased, and its activity increased.Air oxidation treatment to enhance the surface activity is not as good as nitric acid oxidation treatment,and air oxidation treatment mainly increased the content of C-OR and C=O structures,but reduced the content of COOR... |
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