Investigation of Multiwalled Carbon Nanofiber - Graphite Layer Composites and Analysis of Natural Chalks

Abstract

The first part of this dissertation focuses on self-assembled composites. Self-assembled composites composed of vertically aligned multiwalled carbon nanofibers (VA-MWCNF) combined with a graphitic layer (GL) arranged perpendicular to MWCNF axes‘ have been produced at low temperature (445 °C) using low pressure thermal chemical vapor deposition (LPCVD). Electron microscopy and Raman spectroscopy were used to analyze composite morphology, structure and quality. It is found that different composite morphologies and modification of the GL structure can be obtained by varying the nickel (Ni) catalyst underlayer materials, the catalyst pre-treatment method, the gas recipe, the gas flow rates and the pressure conditions of the LPCVD process. Pre-treatment of the catalyst with H2 plasma or NH₃ gas was also investigated. It is found that even a short, one minute H2 plasma pre-treatment of the catalyst results in a significant break-down of the VA-MWCNF/GL composite structure. On the other hand, a one or ten minute catalyst pre-treatment with NH₃ gas results in a structural modification of the GL but retains the VA-MWCNF/GL composite structure. An increase in time of NH₃ gas pre-treatment leads to reduced VA-MWCNF/GL composite height. A growth mechanism for VA-MWCNF/GL composites was proposed. The focus, of the second part of this dissertation, is on the analysis of natural chalks used in traditional old master drawings. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis were performed on bulk samples of natural black chalk, steatite and calcite natural white chalks and on samples of these chalks applied to paper using various techniques. Critical information was obtained about the morphology and sub-micron features of the chalk particles, the chalk/paper interaction of each application technique and elemental composition of the bulk chalk samples. It was found that the particle size and morphology of the natural white chalks reduced their ability to hold to the paper. This information provides insight as to why black chalk is more resistant to abrasion than the natural white chalks which is important for the conservation of extant chalk drawings.