Preparation And Properties Of Carbon Based Composite Materials

Carbon nanotubes (CNT) is a kind of one dimensional carbon material with extraordinary mechanical, electrical and thermal properties. Therefore, it has often been used as reinforcement with the polymer matrix to form composite material, so as to get high performances.Graphene is a new type of carbon material which was found following carbon nanotubes, It has not only the unique two-dimensional structure, but also the high thermal conductivity that can reach 5×103 W/n·K.In recent years, the preparation and application of graphene have attracted wide attention from researchers to engineers.Silver metal has been widely applied to electronic and aerospace and other fields,due to its good conductivity and ductility.If we can introduce the high strength, high electrical conductivity, high thermal conductivity and excellent performance of graphene to the silver based composite materials,it will greatly enhance the thermal properties of the composite.Therefore, in this paper by melt blending of carbon nanotubes and polyvinylidene fluoride(PVDF), oxidation reduction for preparation of graphene and powder metallurgy technology for preparing graphene/silver composites, then the structure and properties of the prepared materials were studied.The research contents and results of this paper are mainly summarized as follows:1. MWCNT/PVDF composites were prepared by a melt blending method.We prepared MWCNT/PVDF composites using PVDF as the matrix, carbon nanotubes as the filler.The micro structure, electric resistivity and thermal conductivity of the composite were characterized through X-ray diffractometer (XRD), impedance analyzer (LCR) and thermal conductivity analyzer (LFA447). At the same time, the relationship between the real part and the imaginary part of the impedance is illustrated using the Cole-Cole model.The results show that the conductivities of composites were significantly increased after surface oxidation passivation of MWCNT; and the thermal conductivity of the composites linearily increases with the volume fraction of the carbon nanotube.2. Graphene was prepared by oxidation reduction method.We prepared graphene using flake graphite as raw material, potassium permanganate as oxidant, concentrated sulfuric acid and concentrated phosphoric acid as intercalation agent, ascorbic acid as a reducing agent. The experiment of the system was carried out by controlling the compositions, changing the temperature and time of reduction. And then we used XRD, scanning electron microscope (SEM), Raman spectroscopy (Raman) and transmission electron microscopy (TEM) to study the morphology and structure of the graphene obtained under 150℃ 8h,150℃ 10h,150℃ 12h,180℃ 10h,200℃ 10h hydrothermal conditions.The results show that the macro morphology of the graphene showes a stable columnar hydrogel morphology. When the reduction temperature is fixed, the size of the graphene hydrogel increases with the reduction time.And when the reduction time is fixed, the size of the graphene hydrogel increases with the increase of the reduction temperature.The reduced graphene were 3-D porous network structure.The best quality of the micro morphology of graphene was obtained under the condition of 150℃ 10h, with a transparent thin slice structure.The XRD characteristic diffraction peak of graphene appears in the vicinity of the 23-26 degree.When the temperature is 150℃, the D-spacing of graphene is increased with the increase of the hydrothermal time; And at the same reaction time (10 h), the D-spacing increase with the increase of hydrothermal temperature. The D and G peak of Raman scattering of graphene appeared in the vicinity of 1356 cm-1 and 1615 cm-1 respectively.When the temperature is fixed (150℃), the ID/TG value of graphene decreases firstly and then increases with the increase of hydrothermal reduction time.However, when the reaction time is the same (10 h), the ID/IG value of graphene increases gradually with the increase of hydrothermal temperature.Under the low magnification TEM,the obtained graphene is of a sheet structure with folded parts,and the edge is clear and transparent.3. Graphene/silver composite materials were prepared by a powder metallurgy technology.We prepared graphene/silver composite using graphene as the filler, silver metal as the matrix. The morphology of graphene/silver composite was characterized by SEM.It was found that the porosity of the composites increases with the increase of the mass fraction of graphene.Between the silver particles and graphene does not form close compact, but only form the point contact and surface diffusion between silver particles.The incorporation of graphene hindered the surface diffusion between silver particles.The densities of the composites containing different graphene mass fraction were measured by the Archimedes method. The results indicate that the density of the composites almost linearly decreases with the increase of the mass fraction of graphene. The density and thermal conductivity of the composites by isostatic pressing and firing process were measured by the Archimedes method and LFA447.The results showed that:for composite material with lwt% content of graphene,when the time is fixed,with the increase of the pressure of isostatic pressing, the density of the composites increases by 6.2% and the thermal conductivity of the composites increases from 37.10 W/m·K to 64.56 W/m K.With the same holding time(5 h), the density of the composite increases with the increase of sintering temperature. And with the sintering temperature increases from 500℃to 800℃, the thermal conductivity of the composites also increases from 37.79 W/m·K to 92.89 W/m K,almost 1.46 times larger.As a result, the thermal conductivity of the composites is increases with the increase of the density of the composites.