Mechanical and Electrical Properties of Multiwalled CNT-Alumina Nanocomposites Prepared by a Sequential Two-Step Processing of Ultrasonic Spray Pyrolysis and Spark Plasma Sintering

Abstract

The high tensile strength and electrical conductivity as well as high aspect ratio of carbon nanotube (CNT) are known to effectively improve the brittleness and electrical properties of ceramic materials; however, the agglomeration of CNTs during in the synthetic process and the poor interfacial bonding between CNTs and matrix materials still present challenges. Herein, multiwalled carbon nanotube (MWNT)-alumina composites were prepared, with homogeneously dispersed MWNTs in an alumina matrix, using a sequential two-step process via ultrasonic spray pyrolysis followed by a spark plasma sintering process. To mix these two materials at the molecular level, MWNT-alumina composites were prepared using a precursor solution containing Al ions instead of solid aluminum oxide particles as the starting material. The agglomeration of MWNTs at high concentration, which is a main obstacle to solution processing, was minimized using ultrasonic spray pyrolysis. The dc conductivity of pure a-alumina, possessing substantial insulating properties, was increased to 12.2 S/m by incorporating 2.48 wt% of MWNTs with a low percolation threshold under 0.18 wt%. With the same amount of MWNT, the fracture toughness of the composite was increased 2.5 times. The improved electrical and mechanical properties of the composites are discussed based on the microstructural characteristics of the composites.