Experimental Study On Thermal Conductivity Of Carbon Fiber In Wide Temperature Range

With the rapid development of material science and technology,a variety of high-performance carbon fibers and its Composites have been continuously developed and applied to industrial production.As a new type of fiber material with high strength and Young's modulus,the exploration and improvement of the factors that affect the physical properties of carbon fiber has aroused extensive attention of researchers all over the world since its birth.Thermal conductivity is one of the important technical parameters of carbon fiber physical properties.Accurate measurement and finding out the internal factors that affect the thermal conductivity of carbon fiber has always been an important content of its research.Based on the transient electrothermal method(TET),an experimental measurement system for thermal conductivity in a wide temperature range was designed and developed.The thermal diffusivity,thermal conductivity and specific heat capacity of different types of carbon fiber at different ambient temperatures were measured.By combining Raman scattering,X-ray photoelectron spectroscopy(XPS),phonon mean free path and thermal reffusivity,the micro mechanism of thermal conductivity of carbon fiber materials in a wide temperature range was studied.The possible errors of experimental results are analyzed and discussed from the aspects of basic data measurement,the use of silver glue and the amount of heating.Based on the accurate measurement of thermal physical parameters of different carbon fibers at room temperature,the differences of thermal conductivity were analyzed by using Raman scattering spectrum and phonon mean free path.The research shows that the thermal conductivity is strongly determined by a material's internal micro-structure.In order to study the influence of temperature on the thermal conductivity,the thermal diffusivity,thermal conductivity and specific heat capacity of two kinds of CF were measured in the temperature range from room temperature(290K)to low temperature(10K),the curves of thermal conductivity of CFs versus temperature were drawn.Combined with XPS and the thermal expansion coefficient(TEC),the reason why the critical temperature appears in the curve of thermal conductivity versus temperature was explained.The thermal reffusivity as a new physical parameter,which is introduced to represent the phonon thermal resistance,so the internal micro-structure size of the material can be researched and analyzed.On the premise of fully analyzing the composition of phonon mean free path close to 0K and the relationship between phonon mean free path and the size of internal micro-structure of CF materials,the size data of micro-structure before and after the critical temperature were studied by using the fitting value of thermal reffusivity close to 0K.The results of the size data before and after the structure deterioration are317.1nm?6.23 nm and 234.1 nm?5.16 nm,respectively.The change ratio of micro-structure can be calculated as 26.2% and 17.2%,respectively.The experimental result shows that the internal micro-structure have changed due to the influence of low temperature,which can further prove the influence of internal micro-structure on the thermal conductivity of these materials.Through the study of the thermal conductivity of CF materials at different temperatures,the relationship between the thermal conductivity and the internal micro-structure can be determined.Especially through the research on the thermal conductivity at extremely low temperature,the paper systematically reviews the development of a new concept: thermal reffusivity to determine a material's structure domain size.So the influence of the change of micro-structure on thermal conductivity can be further understudied.Based on the research on thermal conductivity,those key factors that can affect the ability of thermal conduction are explored,which can be used to guide the research and development of high-performance CF materials from the selection of raw materials and the optimization of processing technology.It can provide better solutions to the two problems of heat dissipation and heat preservation encountered in the real application environment,and also it can provide a strong theoretical and material support for the exploration of outer space and abysmal sea.