A Study On The Electromagnetic Properties Of Carbon Nanotube Reinforced Geopolymer Composites

With the development of modern radar detection technology and the widespread application of electromagnetic waves,the high performance of microwave absorbing materials are urgently needed for construction applications.In this work,the sustainable and green geopolymer(GP)were used as the matrix instead of traditional Ordinary Portland cement(OPC).Carbon nanotube(CNT)was used as the reinforcement.5S@CNT,10S@CNT,20S@CNT and 40S@CNT with a single core-shell structure were obtained by adding different amounts(5,10,20 and 40 ml)of tetraethylorthosilicate(TEOS)to the acidified CNT(a CNT)suspension by a sol–gel method and compounded with GP to fabricate GP composites(5S@CNT/GP,10S@CNT/GP,20S@CNT/GP and 40S@CNT/GP).It was found that the electromagnetic interference shielding effectiveness(SE)of 5S@CNT/GP,10S@CNT/GP and 20S@CNT/GP composites reached 24.2,16.4 and 11.8 d B,respectively,when the CNT content was 5 vol%.This was ascribed from the fact that the thinner Si O₂shell was dissolved during the curing process of GP to restore the conductive nature of CNT.In contrast,the thicker Si O₂shell formed a barrier to hinder the electrons transfer in the three-dimensional CNT network,and thus reduced the reflection of the incident wave.With the further increase of the thickness of the Si O₂shell,a capacitive network was formed by S@CNT in the GP matrix.The minimum reflection loss(RL_min)of 40S@CNT/GP composite at a frequency of 8.4GHz was-53.4 d B when the CNT content was only 0.5 vol%.To further increase the microwave absorbing performance,the nickel(Ni)layer and Si O₂layer were introduced on the surface of CNT by electroless nickel plating and sol-gel methods,respectively,to form S@Ni@CNT with double core-shell structure.The RL_minof40S@Ni@CNT/GP composite at a frequency of 6.7 GHz reached-68.3 d B when the CNT and Si O₂content were kept the same as the system of 40S@CNT/GP composite.The introduction of the double core-shell structure not only optimized the impedance matching and attenuation characteristics of the GP composite,but also facilitated the dispersion of CNT in the GP matrix.In the terms of mechanical properties,the K_1cvalue of GP increased from 0.41 to 0.56 MPa·m^1/2with the addition of 0.5 vol%40S@Ni@CNT,which was mainly attributed to the well dispersion of CNT and good interfacial bonding between CNT and GP matrix.