M. Singh, R. Vander Wal
Pennsylvania State University,
Keywords: carbon-carbon composite, graphene, TEM, nanostructure, carbonization, graphitization, high-temperature heat treatment
Summary:Carbon-carbon composites, originally developed for aerospace applications, are materials that consist of a carbonaceous matrix with an embedded carbon filler providing the required reinforcement for thermal and mechanical stability. An important aspect of composites is the interdependence of the matrix and additive phases to strengthen one another and the material as a whole with the interfacial stress transfer being key to this reinforcement. Thus, the bonding between the matrix and the additive is crucial in understanding its behavior at the macro-scale. Understanding the material’s nanostructure in order to shed light on its interfacial dynamics is an unexplored aspect owing to experimental and probing challenges. This study attempts to probe nanostructure and its impact on carbon-carbon composites by embedding pre-synthesized nano-carbons in an amorphous carbonaceous matrix of varying chemistry. The resin-nanocarbon mix is subjected to carbonization at 500 °C followed by high temperature heat treatment at 2700 °C in order to realize the final product. Variation in nano-carbon additive morphology helps shed light on the spatial direction and lateral extent of nanostructure development at the interface. The effect of additive morphology (i.e. shape) is comparatively examined here by testing pseudo-spherical particles (in the form of a carbon black), 1-dimensional nanotubes and 2-dimensional graphene sheets. It is shown that the filler provides a physical boundary that directs the development of the matrix structure during the course of thermal processing, consequently impacting the material’s bulk properties such as its electrical conductivity and mechanical hardness. Mechanical hardness is inferred using nano-indentation. Evolution of matrix-additive interfacial nanostructure is observed and analyzed using high resolution transmission electron microscopy (HRTEM). Other analyses include differences based on the material’s electrical conductivity and mechanical hardness that are telling of the material’s performance at the macro-scale. Increased interfacial structure and stronger matrix-additive interaction is correlated to the composite’s thermal and mechanical properties.