Evaluation Of Low Density And Highly Thermal Conductive Carbon Bonded Carbon Fiber Network With Mesophase Pitch As Binder

With the continuous miniaturization and high density of electronic devices,the large amount of heat generated during their service needs to be exported in time to ensure the working efficiency and life of the device.Therefore,the development of high thermal conductivity,low density and corrosion resistant materials has become an important direction for the development of heat management materials.In this paper,mesophase pitch(MP)was used as binder to prepare low density and high thermal conductivity carbon-viscose carbon fiber network by slurry forming method,and phase change energy storage composites with high thermal conductivity were obtained by vacuum impregnation of phase change energy storage materials.The preparation process of the new thermal conductive reinforcement was systematically explored,and focuses on the influence of binder and carbon fiber heat treatment process on the thermal conductivity of the sample.Firstly,the asphalt precursor fibers made in laboratory were pre-oxidized at different temperature and time,and the influence of different pre-oxidation processes on the dispersion of carbonized fibers was analyzed.Then,Thermogravimetric analyzer(TG)was used to simulate the pre-oxidation and carbonization of asphalt fibers to analyze the difference of oxidation weight gain and carbon yield.Results show that the fibers oxidized at a constant temperature of 250℃for 150 min and 270℃for 80 min,causing the fibrillation process to stick to each other and cannot be dispersed in the alcohol solution because the former has a lower oxidation temperature and the latter has a shorter time.After being oxidized at 290℃ for 150 min,although the fiber can be uniformly dispersed in the alcohol solution,excessive pre-oxidation can easily cause internal defects of the fibers.Therefore,it can be inferred that the constant temperature of 270℃for 150 min is the best process for fiber pre-oxidation.The preoxidized fibers were carbonized at different temperatures(500℃,700℃,900 ℃)to investigate the effect of the carbonization process on the properties of carbon fibers and their network.The experimental results show that the diameter of carbon fibers shrinks continuously with the increase of carbonization temperature,and the shrinkage rate is the smallest at 500 ℃,which is 1.5%.Observation of the bonding of the network by scanning electron microscopy(SEM)revealed that the fiber network prepared by the oxidized fiber was bent and deformed,and the fiber surfaceexhibited a wrinkled coating structure.the diameter and chemical composition of the carbon fibers treated at 700℃and 900℃have changed greatly,which results in the difference of thermal expansion coefficient and composition between the carbon fibers and pitch,and there is obvious cracking at the bonding point.The carbon fiber carbonized at 500 ℃ can form a good bonding state with the binder,so it is considered that 500℃ is the optimum carbonization temperature.Using mesophase pitch as binder,carbon-viscose carbon fiber network was obtained by low pressure moulding,carbonization and graphitization with carbonized fibers at 500℃.In order to investigate the influence of binder and bonding state on the performance of the network,compared with the sample prepared by using 1300 ℃carbonized fiber and phenolic resin as a binder.Since the binder mesophase pitch and low-temperature carbonized fibers undergo subsequent carbonization and graphitization treatment,they have similar thermal expansion properties and show good bonding performance,and the highly oriented graphite sheet layer produces riveting effect at the bonding site,which makes the thermal conductivity improved significantly.The graphitized carbon fiber network has a density of 0.317 g/cm3,and the in-plane thermal conductivity of the phase change energy storage composite is19.30 W.m-1.K-1,which is 80 times higher than that of the pure phase change material(paraffin).