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Two papers from undergrad

Yr. corresps has been published twice this year as a co-first author and a second author both in Combustion & Flame volume 196. Funny that two research projects conducted years apart wound up in the same volume of journal.

Nothing to do with fuel cells, and only a tenuous connection to energy in that these reactive laminate systems release it in high amounts per gram. Much of the money funding these projects stems from their potential as means of bioagent defeat, eg thermal kill of anthrax.

Below are the titles, authors, and abstracts in chronological order:

The influence of sample thickness on the combustion of Al:Zr and Al-8Mg:Zr nanolaminate foils
Kyle R.Overdeep, Travis A. Schmauss, Atman Panigrahi, and Timothy P. Weihs

Al:Zr and Al-8Mg:Zr nanocomposite foils do not combust completely in air because the penetration of oxygen and nitrogen into the foils can become limited as the product phases grow. The heat produced during the combustion of these foils could feasibly depend upon the volume fraction of the surface oxide layer that forms and therefore the initial foil thickness as well. To test this, Al:Zr and Al-8Mg:Zr foils of various thicknesses (9–61 µm) were fabricated by Physical Vapor Deposition and their heats of combustion were measured using bomb calorimetry in 1 atm of air. We found that combustion efficiency decreased significantly for Al:Zr foils as thickness increased, but Al-8Mg:Zr foils had a nearly constant combustion efficiency for the range of thicknesses studied. SEM-EDS measurements across the foil cross-sections showed that for Al:Zr foils, a distinct oxide layer formed on the external surfaces and there were low levels of oxygen and nitrogen toward their centers. For Al-8Mg:Zr foils though, there was minimal dependence between heat output and foil thickness, the surface oxide layer was more diffuse, and the oxygen and nitrogen contents were higher throughout the foil. We propose that the addition of magnesium improves heat generation by increasing the rates of oxygen and nitrogen diffusion and thus enabling the formation of solid solutions that are richer in oxygen and nitrogen throughout the bulk of the foils.

Observations during Al:Zr composite particle combustion in varied gas environments
Elliot R. Wainwright1, Travis A. Schmauss1, Shashank Vummidi Lakshman, Kyle R.Overdeep, and Timothy P.Weihs
1Both authors contributed equally to this work

This work presents observations of Al:Zr bi-metallic composite particle combustion in multiple gas environments using particles that were synthesized by both arrested reactive ball milling and physical vapor deposition (PVD). We report on combustion and microexplosion behavior using high speed videography and emission spectroscopy in four different environments: air, Ar + O2, Ar + N2, and Ar. We report multiple final morphologies including thin, hollow-shelled combustion products that imply gaseous expansion of the particles during combustion at temperatures ranging from 2700 to 3500 K. Scanning electron microscopy and energy dispersive spectroscopy are performed on these post-reaction products to analyze their morphologies and elemental compositions. We also report evidence of Al burning in the vapor-phase in air and in Ar + O2. Ball milled and PVD particles microexplode extensively and repeatedly in air. In the Ar + O2 environment, ball milled particles show no secondary or tertiary explosions, while the PVD particles rarely microexplode. In Ar + N2 and Ar environments, the particles react to form hot intermetallic particles but show very little combustion and no microexplosions. We propose a two-phase reaction mechanism for Al:Zr in which Al vaporizes and combusts in the vapor phase, then exhibits a critical shift to a condensed phase reaction and burns similarly to pure Zr.

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