Research On Preparation And Microwave Absorption Properties Of Biomass Carbon/Nickel Oxide Composites

Nowadays,a large number of electromagnetic(EM)devices are used in civil and military fields due to the rapid development of electronic and communication technology.So,great efforts are still on the way to design novel absorbing materials with thin thickness,light weight,strong absorption and wide bandwidth and to analyze their absorbing mechanism.Due to its matching of permittivity and permeability,NiO as a kind of transition metal oxide,has been drawn much attention in the field of microwave absorbing materials.However,both the dielectric loss and magnetic loss of NiO are all relatively weak,which need to be compounded with high conductive carbon materials.Among them,the biomass porous carbon(BPC)material derived from biochar sources has the advantages of abundant source,environmental friendliness,large specific surface area,lower density and porous structure.In order to obtain BPC/NiO composites with excellent microwave absorption properties,different BPC materials are synthesized and the influence mechanism of their microwave absorbing properties are discussed.The main research work and conclusions are as follows:(1)Porous carbon materials were prepared by a grinding mixing-activation process and a solution mixing-activation process,respectively.It is found that the porous carbon materials prepared by solution mixing-activation have smaller particle size,more abundant pore structure and better activation effect.Better activation effect can be obtained by increasing activation temperature and prolonging activation time.(2)Biomass porous carbon materials were prepared by carbonization-activation process and one-step direct activation process.It is found that the graphitization level,specific surface area,pore structure and dielectric properties of directly activated carbon are comparable to those of conventional activated carbon.(3)Biomass porous carbon was prepared from walnut shell,pine nut shell and pine pollen,and combined with nickel hydroxide and nickel oxide.Different biomass porous carbon/nickel oxide composites were prepared by changing the ratio of nickel source and biomass porous carbon.The microwave absorption properties of the materials have been improved by compounding with biomass porous carbon which can change the polarization in the electromagnetic field and improve the conductivity and dielectric properties of the material.(4)Pine pollen biomass derived porous carbon decorated with NiO nanoflakes have interconnected porous structure and uniformly distribution of NiO nanoflakes on the surface and voids of carbon materials.The composite has small particle size and moderate dielectric constant and thus the best microwave absorption performance.When the composite ratio is 0.1-1.0,a large reflection loss peak of-42.6 dB is achieved for the BPC/Ni(OH)2 composites,and the effective absorption bandwidth(EAB)less than-10 dB can reach up to 3.52 GHz with a thickness of 2.0 mm.And with a thickness of 2.4 mm,the maximum absorption peak reaches-38.3 dB and the EAB is 5.52 GHz.After calcined to NiO,the maximum reflection loss of the BPC/NiO composites reaches-52.64 dB and an EAB is 4.88 GHz.