Dispersing of functionalized CNTs in Si–O–C ceramics and electromagnetic wave absorbing and mechanical properties of CNTs/Si–O–C nanocomposites

Abstract

Advanced structural materials with excellent electromagnetic wave (EMW)-absorbing properties and outstanding mechanical properties have stimulated attention in recent years. The application of CNTs as excellent EMW absorbers in ceramic matrix composites has been limited due to the difficulty of homogeneously dispersing these CNTs. Herein, CNTs/Si–O–C nanocomposites were synthesized by a polymer-derived ceramics method using polysiloxane (PSO) as a precursor and functionalized CNTs as fillers, and the CNTs/PSO precursors were pyrolyzed at 800 °C under Ar atmosphere. The carboxyl CNTs (CNTs-COOH) could be steadily suspended in PSO/ethanol solution for a longer time compared with pristine CNTs and hydroxylated CNTs (CNTs-OH); these results revealed that CNTs-COOH can disperse homogeneously in PSO/ethanol solution due to stronger electrostatic repulsions with each other and strong binding forces with PSO and ethanol. The effects of the loading ratio of CNTs-COOH on the EMW-absorbing properties at the X band (8.2–12.4 GHz) and the mechanical properties of CNTs/Si–O–C nanocomposites were investigated. When the filler loading ratio was 7.5 wt %, CNTs/Si–O–C nanocomposites had a minimum reflection loss of -60.40 dB at 10.15 GHz with a thickness of 2.5 mm, and the effective wave absorbing band covered 3.11 GHz (8.78 GHz–11.89 GHz). The flexural strength was significantly enhanced from 5.70 MPa of Si–O–C ceramic to 12.50 MPa with 7.5 wt % CNTs and 23.74 MPa with 10.0 wt % CNTs.