Study On Thermal Conductivity Of Silicon Carbide Fiber In Variable Temperature Environment

With the rapid development of the aerospace industry,the demand and requirements for high-performance materials are getting higher and higher.As one of the critical materials of the third generation semiconductor,silicon carbide(Si C)has plenty of advantages such as wide band gap and excellent chemical stability.Therefore,it is very suitable for high frequency,radiation resistance,high power and high density integrated electronic devices.Nowadays,silicon carbide has been recognized in many fields such as electronics,information,biomedicine and green energy.Silicon carbide fibers can be woven into complex structures and enhance their performance.As a reinforcement material,Si C fibers are located in the upstream of ceramic matrix composites(CMC),which is a significant factor in the composite production process.The thermal conductivity of single Si C fiber plays a crucial role in the heat dissipation of the entire CMC component.The development of low temperature technology also provides opportunities for the realization of silicon carbide in various fields such as biomedicine.At present,the focus of research on silicon carbide products is to understand their physical and chemical properties and continuously optimize their potential performance.By building a low temperature experimental system,the thermal conductivities of the Si C fiber samples at 18 different temperatures within 10 K-290 K were measured by using the transient electric technology(TET).The experimental data of thermal diffusivity,thermal conductivity and volume specific heat of the Si C fiber were obtained.The thermal conductivity of Si C fiber sample at room temperature is 4.97 W/(m·K),which is significantly different from that of single crystal Si C.The significant decrease of the thermal conductivity of Si C fiber confirmed that the thermal conductivity of nanocrystalline materials was limited due to the size effect.As the temperature goes down,the thermal diffusivity of the silicon carbide fiber increases monotonously,while the thermal conductivity decreases first and then increases with the decrease of temperature.When the temperature reaches 10 K,the thermal conductivity of silicon carbide fibers has been reduced by more than 60% compared with room temperature.According to the phonon scattering theory,phonon-phonon scattering abates with temperature reduces,and the phonon-defect scattering becomes dominant.As a result,less mean free path leads to the thermal conductivity decrease.The model of thermal reffusivity is used which analogizes the electrical resistivity model of metal materials.It can be used to evaluate the defect grade of nonmetallic materials effectively.The residual thermal reffusivity and grain size are obtained by fitting the experimental data at 0 K.According to the definition of residual thermal reffusivity,it represents the defect degree inside the material.The residual thermal reffusivity accounted for 11.88% of the total thermal reffusivity at room temperature.So that the ideal thermal conductivity of the sample without defects can be predicted.