Combustion and Self-Assembly of Nanoenergetic Materials
Open Access
- Author:
- Malchi, Jonathan Yaniv
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 13, 2007
- Committee Members:
- Richard A Yetter, Committee Chair/Co-Chair
Robert John Santoro, Committee Member
David Lawrence Allara, Committee Member
Vigor Yang, Committee Member
Grant Alexander Risha, Committee Member
Steven Son, Committee Member
Timothy Foley, Committee Member - Keywords:
- thermite
self-assembly
combustion - Abstract:
- This work examines how nanotechnology and self-assembly can benefit the field of energetic materials. Nanoaluminum (nAl) is subjected to a progression of experiments to analyze its reactivity in various combustion environments and experimental setups. The set of tests consists of: 1) a fully heterogeneous flame spread system, 2) a semi-homogeneous sonicated thermite system and 3) a quasi-homogeneous self-assembled thermite system. The flame spread experiment physically separates the nAl from the gaseous oxidizer allowing for a well-understood convective, diffusive, reactive system to be analyzed. Spread rates for nAl are 2 to 3 orders of magnitude greater than typical solid fuels, such as poly(methyl methacrylate) and cellulose. This brings about a fingering combustion instability in normal gravity conditions that previously, has only been demonstrated in microgravity conditions. A scaling analysis is used to predict trends, and a stability map is created based on the non-dimensional Lewis and Damköhler numbers that predicts when a continuous flame front will transition to a fingering instability. A nanoscale thermite is created via sonication of nAl and nanocopper-oxide (nCuO) particles and experiments are performed to examine the effect of adding a diluent to the system. Both aluminum-oxide and long alkyl chain hydrocarbons severely hinder the propagation rate, however, experiments suggest that hydrocarbon addition could help with the material’s sensitivity to electrostatic discharge. Because of the hydrocarbons required for self-assembly, these experiments also give an indication of how the self-assembled material will react. A nAl/nCuO thermite is self-assembled via electrostatic forces. Scanning Electron Microscopy images show a portion of the material has assembled into microspheres having diameters from 1-5μm. This is the first known energetic nanocomposite built with a bottom-up engineering approach. The combustion properties of the self-assembled material are compared to that of the sonicated material, with similar amounts of added hydrocarbons. Unlike the sonicated material, the self-assembled material is able to achieve ignition and propagate the full length of the microchannel. This gives indication that electrostatic self-assembly is a viable method for building energetic materials from the bottom-up, and could potentially increase the intimacy of the mixing and allow for custom tailoring of the combustion properties.