Synthesis Of Composite Microwave Absorbing Materials Loaded With Fe₃O₄ And Fe Derived From Red Mud And Coal Gangue Solid Wastes

With the advent of the electronic era,electromagnetic pollution has seriously threatened the living environment of mankind.Researchers have continuously developed various wave absorbing materials to treat electromagnetic pollution.Among them,magnetic/carbon matrix composites are widely used due to their excellent wave absorbing properties and stable physical and chemical properties.On the other hand,as bulk solid wastes,coal gangue（CG）and red mud（RM）are accumulated over the years,which leads to serious environmental pollution problems.If their application fields are expanded,it is not only beneficial to the resource utilization of both,but also has important significance to the sustainable development of coal development industry and aluminum making industry.Based on the above background,this paper uses coal gangue and red mud as raw materials to prepare composite microwave absorbing materials（GRM）.This work not only helps to reduce the preparation cost of composite materials,but also provides effective value for the comprehensive utilization of red mud and coal gangue.In this paper,a series of GRM composite absorbing materials with magnetic components Fe₃O₄and Fe were prepared by carbothermal reduction method.The phase composition,thermodynamic reactions,micromorphology,and microwave absorbing properties of the composite material during calcination were systematically analyzed.The microwave absorbing mechanism of the composite material was discussed through the analysis of electromagnetic parameters.The results showed that the preparation can be through the control of heat treatment temperature load different magnetic composite absorbing material components.When the calcination temperature is 600～700℃,the magnetic component in the composite material is Fe₃O₄,and when the calcination temperature is 900～1000℃,the magnetic component is Fe/Fe₂C.At the same time,the sample GRM700 exhibits excellent microwave absorption performance at a thickness of 5.0 mm,with a RL_minof-35.9 d B.When the coating thickness decreases to 2.0 mm,its effective frequency band width can reach 4.5 GHz.When the coating thickness of composite material GRM900 is 1.5 mm,its RL_minvalue is-18.2 d B,and the matched effective frequency band width is 3.3 GHz.After the raw material is roasted,there are a large number of interfaces（Fe₃O₄/Fe-C interface,Fe₃O₄/Fe-Na Al Si O₄interface,etc.）,defects,and conductive networks formed by magnetic components and carbon,which cause conductivity loss and interface loss under the action of electromagnetic waves,making the composite material have good absorption performance.In addition,the goal of optimizing the microwave absorbing performance of composite materials can be achieved by changing the ratio of raw materials.When the temperature is 700℃and the mass ratio of coal gangue to red mud is1.1:1,the RL_minvalue of composite material GRM700-1.1 at 7.3 GHz is-50.1d B when the coating thickness is 3.5 mm.The effective absorption bandwidth（EAB）of the sample reached 4.8 GHz when the coating thickness was 2.0 mm;When the heat treatment temperature of 900℃,the quality of the coal gangue with red mud ratio was 0.8:1,the composite material GRM900-0.8 achieves RL_minof-38.5 d B at 5.6 GHz when the coating thickness is only 3.5 mm,and the corresponding effective absorption bandwidth is 3.7 GHz when the coating thickness is only 1.5 mm.