Heterocoagulation System Assisted Adsorption of Carbon Nanotubes on Alumina for Toughening Ceramics

A heterocoagulation process was adopted to disperse homogenously multi-walled carbon nanotubes (CNTs) into alumina powders via liquid medium and deposit uniform CNTs on the surfaces of alumina particles. Alumina composites with an addition of 2wt% CNTs were prepared by spark plasma sintering (SPS). The mechanical properties of the composites were characterized as a fracture toughness of 6.35 ± 0.15 MPa m0.5, 1.7 times that of pristine alumina ceramics, and also much improved compared to that of alumina ceramics added with pristine CNTs but without the heterocoagulation processing with surfactants. The fracture morphologies showed visually the bridging and pull out effects of the CNTs at interfaces between the alumina grains. The results indicated that the loads during the mechanical tests were efficiently transferred from the alumina matrix to the CNTs and dissipated, and then led to the improvement of mechanical properties.