High-rate carbon nanotube/magnetic-sheet composites in situ synthesized using a fluidized bed for high-frequency microwave absorption

At present, the large-scale preparation of carbon nanotubes (CNTs) can be achieved by using fluidized bed devices and a chemical vapor deposition (CVD) process. We selected a layered double hydroxide (LDH) as the catalyst carrier, and investigated the effects of different catalyst particle sizes and temperature conditions on the growth of CNTs using a fluidized bed. The catalyst particles of an appropriate size have a significant impact on the fluidization performance and the yield of the final CNTs. Comparing the catalyst particles of 120 mesh, 60 mesh, and 40 mesh sizes, the volume of the product after the 40-mesh catalyst growth is more than 32 times the volume of the initial feedstock added. The ferromagnetic material in the CNTs/magnetic-sheet composite obtained from this bulk in situ preparation combines well with the highly conductive CNTs to achieve a better impedance matching. Benefiting the "wire/capacitor" composite structure, the minimum reflection loss (RL) value of -40.0 dB is achieved at a frequency of 5.0 GHz. More importantly, the effective absorption bandwidth (RL < -10.0 dB) is 3.7 GHz, which occurs in the high frequency (14.3-18.0 GHz) region at a thickness of 1.5 mm. The results show that the composite can be applied to the field of high-frequency microwave absorption.