TY - JOUR
T1 - Effect of Polar Environments on the Aluminum Oxide Shell Surrounding Aluminum Particles
T2 - Simulations of Surface Hydroxyl Bonding and Charge
AU - Padhye, Richa
AU - Aquino, Adelia J.A.
AU - Tunega, Daniel
AU - Pantoya, Michelle L.
N1 - Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/6/8
Y1 - 2016/6/8
N2 - Density functional theory (DFT) calculations were performed to understand molecular variations on an alumina surface due to exposure to a polar environment. The analysis has strong implications for the reactivity of aluminum (Al) particles passivated by an alumina shell. Recent studies have shown a link between the carrier fluid used for Al powder intermixing and the reactivity of Al with fluorine containing reactive mixtures. Specifically, flame speeds show a threefold increase when polar liquids are used to intermix aluminum and fluoropolymer powder mixtures. It was hypothesized that the alumina lattice structure could be transformed due to hydrogen bonding forces exerted by the environment that induce modified bond distances and charges and influence reactivity. In this study, the alumina surface was analyzed using DFT calculations and model clusters as isolated systems embedded in polar environments (acetone and water). The conductor-like screening model (COSMO) was used to mimic environmental effects on the alumina surface. Five defect models for specific active -OH sites were investigated in terms of structures and vibrational -OH stretching frequencies. The observed changes of the surface OH sites invoked by the polar environment were compared to the bare surface. The calculations revealed a strong connection between the impact of carrier fluid polarity on the hydrogen bonding forces between the surface OH sites and surrounding species. Changes were observed in the OH characteristic properties such as OH distances (increase), atomic charges (increase), and OH stretching frequencies (decrease); these consequently improve OH surface reactivity. The difference between medium (acetone) and strong (water) polar environments was minimal in the COSMO approximation.
AB - Density functional theory (DFT) calculations were performed to understand molecular variations on an alumina surface due to exposure to a polar environment. The analysis has strong implications for the reactivity of aluminum (Al) particles passivated by an alumina shell. Recent studies have shown a link between the carrier fluid used for Al powder intermixing and the reactivity of Al with fluorine containing reactive mixtures. Specifically, flame speeds show a threefold increase when polar liquids are used to intermix aluminum and fluoropolymer powder mixtures. It was hypothesized that the alumina lattice structure could be transformed due to hydrogen bonding forces exerted by the environment that induce modified bond distances and charges and influence reactivity. In this study, the alumina surface was analyzed using DFT calculations and model clusters as isolated systems embedded in polar environments (acetone and water). The conductor-like screening model (COSMO) was used to mimic environmental effects on the alumina surface. Five defect models for specific active -OH sites were investigated in terms of structures and vibrational -OH stretching frequencies. The observed changes of the surface OH sites invoked by the polar environment were compared to the bare surface. The calculations revealed a strong connection between the impact of carrier fluid polarity on the hydrogen bonding forces between the surface OH sites and surrounding species. Changes were observed in the OH characteristic properties such as OH distances (increase), atomic charges (increase), and OH stretching frequencies (decrease); these consequently improve OH surface reactivity. The difference between medium (acetone) and strong (water) polar environments was minimal in the COSMO approximation.
KW - DFT calculations
KW - alumina catalysis
KW - aluminum combustion
KW - fluoropolymer reactions
KW - implicit solvent model
KW - modified alumina structures
UR - http://www.scopus.com/inward/record.url?scp=84974786984&partnerID=8YFLogxK
U2 - 10.1021/acsami.6b02665
DO - 10.1021/acsami.6b02665
M3 - Article
AN - SCOPUS:84974786984
SN - 1944-8244
VL - 8
SP - 13926
EP - 13933
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 22
ER -