Sharmila M. Mukhopadhyay (Advisor), P.Terry Murray (Committee Member), Ajit K. Roy (Committee Member), Raghavan Srinivasan (Committee Member), H. Daniel Young (Committee Member)
Doctor of Philosophy (PhD)
Multi-scale hierarchical carbon structures have been developed by growing strongly attached carbon nanotubes (CNT) on high surface area substrates having open, interconnected porosity. This investigation was developed on cellular carbon foams but the process is equally suitable for other geometries including flat, fibers, and other porous substrates (interconnected). It is also adaptable to other substrate materials such as metals, alloys or ceramic compounds. Multiwalled carbon nanotubes are grown using a floating catalyst chemical vapor deposition (CVD) method after pre-coating the substrate with a silica nano-layer. The silica-coated graphitic substrates are seen to grow 280 times more nanotubes per unit area compared to bare graphite. Detailed spectroscopic and microscopic studies indicate that this significant improvement can be attributed to improved adhesion and distribution of the iron catalysts and enhanced catalytic activity from substrate interactions. Failure analysis of the nanotube layer under several types of loading demonstrates strong adhesion between CNT and substrate, with failure occurring in the underlying substrate. Attachment of carbon nanotubes can result in more than two orders of magnitude increase in specific surface area as independently confirmed by modeling the microstructure and direct surface area measurement using Brunauer-Emmett-Teller (BET) technique. These hierarchical materials are tested as encapsulation structures for phase change materials (PCM). The CNT can act as nanofin radiators enhancing energy exchange between the thermally conductive encapsulation and the PCM, hence improving thermal response time. A heat cell was designed to compare the response times of foam encapsulation with and without CNT. Encapsulation with CNT is found to have and significantly faster thermal response. DSC measurements demonstrate that CNT/foam hierarchical encapsulation provides 15% higher storage of latent heat. The improvements in thermal responsiveness and storage capacity from CNT/foam encapsulation provide 150% higher specific power (W/g) while transferring the heat into the paraffin wax when compared to the foam without CNT.
Department or Program
Ph.D. in Engineering
Year Degree Awarded
Copyright 2012, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.