Synthesis And Electromagnetic Wave Absorption Properties Of Silicon Carbide Nanomaterials From Rice Husks

Silicon carbide?SiC?nanomaterials,as one core material of the third generation semiconductor,have numerous potential application in composite,optoelectronic devices,field emission,catalyst supports,electromagnetic?EM?wave absorbing materials as well as biologically compatible materials due to their high hardness,large strength,good thermal conductivity,wide bandgap,high breakdown voltage,excellent antioxidant ability and corrosion resistance.The common preparation method of SiC namomaterials are chemical vapor deposition,carbothermal reduction and solvothermal method.However,those synthesis procedure are high-cost due to the high reaction temperature and expensive equipment.Therefore,large-scale and low-cost synthesis of SiC nanomaterials is very important for its wide application.In this dissertation,a low-temperature and scalable process to produce?-phase SiC nanoparticles?NPs?from rice husks?RHs?by magnesiothermic reduction?MR?at a relative low temperature of 600°C is described.The morphology,structure and physical properties of the RHs-derived SiC NPs were comprehensive characterized.The reaction mechanism of MR also be studied,and a new reaction model be proposed on the base of previous work.In the end,the EM wave absorbing application of RHs-derived SiC NPs were preliminary studied.The main contents are as follows:?1?A facile,low-cost,and large-scale MR process is described to synthesize?-phase SiC NPs from the waste RHs and the yield?-SiC from RHs is 7-10 wt%.The as-synthesized SiC NPs have an average size of 20-30 nm,which have morphology similarities to the biogenetic SiO₂ NPs in RHs.The reaction mechanism of the formation of SiC from the mixture of carbonized RHs and Mg is proposed.The reaction process consists of two steps:?1?reduction of the surface of the SiO₂ nanoparticles to the Mg2Si layer based on the fast exothermic reaction and?2? reaction between the intermediate Mg2Si and residual SiO2 and diffused C to form SiC.?2?The RHs-derived SiC NPs were applied to the EM wave absorbing materials.The different carbon content SiC NPs/C composite were prepared from RHs,and the EM wave absorption performance were also be tested.The EM wave absorption properties of 1.5 wt%carbon content sample have the best performance,the reflection loss reached the maximum value of-22.8 dB at 7.1 GHz,and the frequency width less than-10 dB?absorb 90%?is 1.9 GHz.