Preparation And Characterization Of Ni Or Co Absorbing Materials Supported By Coal Hydrogasification Residue

With the development of the "big data" society and the popularization of the awareness of healthy life,people’s aspiration for a green environment and green life has gradually increased.The widespread use of radio communication equipment and the rapid development of electronic technology have brought convenience to people’s life,but also brought serious electromagnetic radiation.In order to solve the electromagnetic pollution caused by the enrichment of electromagnetic radiation,it is urgent to develop and apply low-cost,high-performance microwave absorbing materials.Among them,the high performance of carbon-based microwave absorbing materials has attracted a large number of researchers.Based on this,this paper attempts to recover and utilize coal hydrogenation residues loaded with Ni or Co magnetic elemental particles to prepare composite microwave absorption materials,and tries to find a kind of absorbing material with low-cost,easy-to-obtain and high-performance wave absorbing material,and to realize the high value-added utilization of coal hydrogasification residue,and also meet the concept of environmental protection.The main research work is as follows:(1)The Ni/coal hydrogasification residue composite microwave absorption materials was simply prepared by liquid-phase impregnation and carbothermal reduction.The coal hydrogasification residue was used as raw material,which was ground and sieved,dried at 120 °C,and then immersed in the nickel nitrate precursor solution.By adjusting the carbothermic reduction temperature and changing the concentration of nickel nitrate solution to adjust the loading of Ni,a composite material with excellent wave absorbing properties was obtained.Compared with the coal hydrogasification residue,the microwave absorption performance of Ni/coal gasification residue composite microwave absorbing material is obviously improved.When the coating thickness is 2.5mm,the minimum reflection loss is-42.6 d B,and the effective absorption bandwidth is 4.1 GHz.When the coating thickness is 2 mm,the effective absorption bandwidth is up to 5.6 GHz and the corresponding minimum reflection loss is-35.6 d B.This can be attributed to that the introduction of Ni particles can adjust the impedance matching characteristics of the material so that a large number of electromagnetic waves can enter the material,and the conduction loss caused by residual carbon and the polarization loss between the interfaces contribute to the energy loss of electromagnetic waves.The combined effect of the two leads to the excellent properties of the Ni/coal hydrogasification residue composite microwave absorbing material.(2)In order to explore the change of material properties loaded with other magnetic components and the generality of this study,we replaced Ni with Co with a smaller particle size,and prepared a Co/coal hydrogenation residue composite microwave absorbing material by the same method.The microwave absorption properties of the Co-loaded composites can be effectively adjusted by changing the carbothermal reduction temperature and the amount of Co added.At 700 ℃,when the Co loading is 20% and the coating thickness is 2mm,the minimum reflection loss is-40.1 d B,and the effective absorption bandwidth is 5.0 GHz.The high performance of the Co/coal hydrogenation residue composite microwave absorbing material at the same thickness can be attributed to the good impedance matching characteristics of the material and the high loss capability caused by the high conduction loss,polarization loss and multiple reflections inside the material.This shows that the change of the magnetic composition can meet the application of microwave absorbing materials under different conditions to a certain extent,and can also provide a certain idea for the recovery of Co catalysts in the subsequent coal hydrogenation catalytic gasification process.(3)In order to explore whether the sample can meet the application in high temperature environment,we selected Ni with lower cost to prepare Ni/coal hydrogenation residue composite microwave absorbing material,and selected the sample with the best absorbing performance to conduct a preliminary study on thermal stability.The samples were calcined in air atmosphere at 300 ℃,400 ℃ and 500 ℃,respectively,and the changes of microwave absorption properties were tested.We can find that as the temperature increases,Ni in the sample is gradually reduced to Ni O,and the residual carbon is oxidized.The impedance mismatch of the material and the decrease of the internal loss ability of the material make the absorbing performance gradually decrease,but the material is below 400 ℃.It can still maintain a certain microwave absorption capacity,indicating that the performance of the material will not be greatly affected at room temperature.