Effect of Hydration on Promoting Oxidative Reactions with Aluminum Oxide and Oxyhydroxide Nanoparticles

I. Shancita, Loudon Lee Campbell, Chi Chin Wu, Adelia J.A. Aquino, Scott D. Walck, Daniel Tunega, Michelle L. Pantoya

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

To harness greater power from aluminum (Al) combustion, one approach is to chemically transform the aluminum oxide (Al2O3) passivation layer surrounding the Al core particle by exploiting surface reactions via a wet chemistry approach. The goal of this study is to identify key parameters affecting interfacial chemistry on Al particles. As models for the surface layer of Al particles, γaluminum oxide (γ-Al2O3) and boehmite (γ-AlO(OH)) nanoparticles are examined. Density functional theory calculations of dehydroxylation and dehydration energies are conducted on γ-Al2O3 and γ-AlO(OH). The calculations predict that OH bridge bonds throughout γ-AlO(OH) require similar energy to break compared with terminal OH groups abundant on the surface of γ-Al2O3 and are the most reactive sites. Experimentally, the predictions are confirmed by isolating representative surface reactions using γ-Al2O3 and γ-AlO(OH) nanoparticles suspended in an iodic acid solution to synthesize an oxidizing salt, aluminum iodate hexahydrate (AIH). Powder X-ray diffraction and X-ray photoelectron spectroscopy identify species of whole materials and surfaces, respectively. The structural and compositional details are revealed by acquiring images, spectra, and determining component phase maps in the scanning mode via transmission electron microscopy. The AIH yield is higher for γ-Al2O3, AIH formation is linked to the removal of terminal OH bonds, and AIH appears isolated on the particle surface. AIH formation from γ-AlO(OH) is linked to the removal of OH bridge bonds, and AIH formation does not appear localized on particle surfaces. These results link dehydroxylation and dehydration energies to reactions that produce AIH and provide a fundamental understanding of how to use hydration to control Al2O3 surface reactions and transform the reactivity of Al particles. Also, AIH is newly discovered as a highly reactive oxidizer used in energetic material studies that show tremendous potential for increasing the energy release rate from Al combustion.

Original languageEnglish
Pages (from-to)15017-15026
Number of pages10
JournalJournal of Physical Chemistry C
Volume123
Issue number24
DOIs
StatePublished - Jun 20 2019

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