基于煤加氢气化半焦制备Ni/碳基复合吸波材料及组成优化

Preparation and composition optimization of the composite Ni/carbon-based microwave absorbents from coal hydrogasification semicoke

利用煤加氢气化半焦作载体、其中的炭作还原剂与介电组分,采用硝酸镍溶液浸渍结合碳热还原工艺制备Ni/碳基复合微波吸收材料;研究磁性组分Ni负载量对复合物微观结构与性能的影响作用及相关机制。结果表明,通过改变复合物的碳含量、碳的石墨化程度以及引入界面与缺陷,调整Ni的负载量可以方便地调控复合物的电磁参数,从而实现良好的阻抗匹配。在碳热还原温度为700℃时,Ni负载量为20%的复合物显示了最优的微波吸收性能。在涂层厚度为2.5 mm条件下,其最低反射损耗可达−42.6 dB,相应的有效带宽为4.1 GHz;而在2 mm涂层厚度条件下,其有效带宽可达5.6 GHz。复合物中起主导作用的微波吸收机制是介电损耗,主要源于石墨化炭引起的漏导损耗及界面与缺陷引起的极化驰豫损耗。

With the residual carbon in coal hydrogasification semicoke as both reducing agent and dielectric component,Ni/carbon-based composite materials for microwave absorption were prepared.The synthesis process mainly involved loading of Ni species via an impregnation of nickel nitrate solution and then an in-situ carbothermic reduction.The effects of Ni load on the microstructure and properties as well as the related mechanism were studied.The experimental results showed that the electromagnetic parameters could be readily regulated by changing the Ni load,which occurred as a result of the accompanied changes in carbon content,graphitization degree,as well as the number of interfaces and defects.Hence,a good impedance matching could be easily achieved.At a carbothermal reduction temperature of 700℃,the composite with 20%Ni load showed the best microwave absorption performance.For a coating thickness of 2.5 mm,the minimum reflection loss was−42.6 dB and the corresponding effective bandwidth was 4.1 GHz;while the effective bandwidth could be up to 5.6 GHz under 2 mm coating thickness.The dominant microwave absorption mechanism was the dielectric loss,which mainly derived from the conduction loss due to graphite carbon and the polarization relaxation losses because of the existence of interfaces and defects.