Multi-functional fullerene soot/alumina composites with improved toughness and electrical conductivity

We present the results of characterization and mechanical testing of alumina matrix composites reinforced with fullerene soot. The composites were manufactured by mechanical milling, sonication, and spark plasma sintering (SPS). Addition of 2 wt% Ni serves as an efficient catalyst for in situ transformation of soot into diamond and nanoparticles of fullerite and graphitic carbon during thermomechanical processing. The carbon nanostructures act as an effective reinforcement in the composite that results in an enhancement of the fracture toughness to 16.5 MPa m1/2. Electrical resistivity decreases by 15 orders of magnitude. The improvement of composite properties is attributed to the formation of a homogeneous carbon coating on the alumina particles. The type of synthesized carbon nanostructures is shown to depend on the catalyst, SPS conditions, and the amount of fullerene soot added. A small amount of ruby is present as an impurity in the alumina, and serves as a convenient pressure sensor through its stress-dependent luminescence and gives additional multi-functionality to the composite.