| Electromagnetic（EM）shielding and absorbing materials can suppress or eliminate electromagnetic pollution.Unlike metal materials,polymer materials and magnetic materials with high density,poor weather resistance,poor mechanical properties and other shortcomings,carbon-based and carbide materials due to the physical and chemical properties of low density,high conductivity,excellent corrosion resistance and good thermal stability,it is easier to realize the strong,wide,thin and light targets of EM wave shielding and absorbing materials,and has shown great potential for applications in the field of EM wave shielding and absorption.Pure carbon materials,such as graphene and carbon nanotubes,are prepared with low efficiency,low yield and high cost,and the harvesting of their complex usually requires preparation of pure carbon materials supplemented by high-temperature and high-pressure operations;carbides,such as titanium carbide,silicon carbide,also suffer from time-consuming,energy-consuming and costly preparation process.Flash Joule heating（FJH）,which instantaneously converts electrical energy into high heat and quenches it,provides a new way for materials to be prepared with high efficiency,high yield,low energy consumption and low cost,and has demonstrated distinct advantages in the fields of waste conversion and energy catalysis.Carbon-based and carbide materials derived from FJH have rarely been reported for EM wave shielding and absorption applications.It is also unknown how FJH parameters affect the product structural features,physical phase characteristics and EM parameters,and thus the shielding and wave absorbing properties of carbon-based and carbide materials.Based on it,this dissertation starts from the preparion of porous graphene by FJH,expands to carbon-based and carbide materials,constructs the relationship between FJH parameters and the structural features,physical phase characteristics and EM parameters of the products,and investigates the EM shielding and absorption mechanisms of the products in detail and in-depth.The main contents are as follows:（1）Based on the strategy of molten sugar bubbling,porous carbon obtained from bubbling of inexpensive carbon source was used as the reaction intermediate,and porous graphene,a pure carbon material,was then prepared by FJH.Porous graphene with different defect degrees was obtained by adjusting the FJH voltage and time to regulate the graphitization transition and the defect degree of the resulting products.Based on the successful preparation of porous graphene by FJH,the micro-nano structure,electrical and EM properties of the porous graphene were studied in depth.The porous graphene was applied into EM wave shielding and absorption.The enhanced conductivity after FJH,the tunable graphene defect degree and the porous structure of micro-and nanopore coexistence endow the porous graphene with absorption-enhanced shielding properties in the gigahertz band.The porous graphene Gr-220/300 achieved a shielding effectivenss of32.5 d B with an effective shielding bandwidth of 2.5-18 GHz at a thickness of 2 mm with20 wt%filler,which was comparable to the shielding effectivenss of graphene obtained by other methods.Expanding the porous graphene Gr-180/300 with suitable conductivity and abundant defects to the terahertz band,the suitable surface reflection and polarization-enhanced dielectric loss endowed Gr-180/300 excellent shielding（average shielding effectiveness of 40.7 d B）and absorption（average reflection loss of 12.9 d B）performance in 0.2-1.2 THz at a thickness of 1 mm with 5 wt%filler.The above results indicate that the FJH parameters can be regulated to obtain products with different defect degrees and conductivities depending on the applying requirements for shielding or absorption.This study is instructive for the FJH preparation of carbon-based shielding and absorption materials,especially practical for the wide application of multi-band integrated devices based on 6G communication technology.（2）FJH was extended to the preparation of carbon-based metal composites.Similarly,inexpensive carbon and copper sources were employed to acquire intermediates（carbon pre-coated copper particles,Cu/C@C）by molten sugar bubbling,and then graphene-coated copper particles（Cu/Gr@Gr）were harvested after FJH.By real-time monitoring of voltage and current during FJH,the effects of FJH voltage,filler loading and reaction time on graphene defects were investigated,revealing that the above factors affect graphene crystal structure through the mass energy density and reaction time.Increased mass energy density and prolonged reaction time lead to high quality homogeneous graphene.By comparing the thermal stability as well as shielding performance of the samples before and after FJH,it was found that the graphitized cladding layer improved thermal stability of FJH products.Their conductivity and average shielding effectiveness were retained by 89.8%and 95.1%after thermal oxidation,respectively,both higher than those before FJH.Subsequently,the universal preparation method of graphene cladding synthesized by FJH based on different copper sources,carbon sources,conductive agents and mixing methods was investigated by taking graphene-coated copper particles as an example.The feasibility of the mentioned strategies was experimentally comfirmed,which promoted the application of FJH in synthesizing graphene-coated（non）metallic particles.（3）FJH was further extended for carbide synthesis.The high heat and quench cooling of FJH was used for carbothermal reduction of inexpensive titanium dioxide to prepare Ti C-Ti O2/C with multi-phase loss media and interfaces of titanium carbide and titanium dioxide.By reducing the carbon reductant dosage below the stoichiometric ratio of titanium dioxide carbothermal reduction reaction,AR-Ti O2/C with multi-phase loss media and interfaces of the thermotropic phase transfer product（rutile titanium dioxide）and the feedstock（anatase titanium dioxide）was obtained.When Ti C-Ti O2/C and AR-Ti O2/C were used as EM wave absorption materials,the enhanced permittivities and abundant heterogeneous interfaces after FJH improved impedance matching and dielectric loss to EM wave,resuling in the Ti C-Ti O2/C exhibiting reflection loss-33.3 d B at a thickness of 1.6 mm（with an effective absorption bandwidth of 4.5 GHz）and AR-Ti O2/C exhibiting reflection loss-36.1 d B at a thickness of 1.8 mm（with an effective absorption bandwidth of 5.1 GHz）.Further,by comparing EM parameters and absorption properties of FJH products and the mixture（formed by simple blending of raw materials in equal proportions）,the mechanism of multi-phase loss media and interfaces on enhanced absorption performance was illustrated. |
