Fluorination of an Alumina Surface: Modeling Aluminum–Fluorine Reaction Mechanisms

Abstract

Density functional theory (DFT) calculations were performed to examine exothermic surface chemistry between alumina and four fluorinated, fragmented molecules representing species from decomposing fluoropolymers: F, HF, CHF, and CF. The analysis has strong implications for the reactivity of aluminum (Al) particles passivated by an alumina shell. It was hypothesized that the alumina surface structure could be transformed due to hydrogen bonding effects from the environment that promote surface reactions with fluorinated species. In this study, the alumina surface was analyzed using model clusters as isolated systems embedded in a polar environment (i.e., acetone). The conductor-like screening model (COSMO) was used to mimic environmental effects on the alumina surface. Four defect models for specific active -OH sites were investigated including two terminal hydroxyl groups and two hydroxyl bridge groups. Reactions involving terminal bonds produce more energy than bridge bonds. Also, surface exothermic reactions between terminal -OH bonds and fluorinated species produce energy in decreasing order with the following reactant species: CF > HF > CHF. Additionally, experiments were performed on aluminum powders using thermal equilibrium analysis techniques that complement the calculations. Consistently, the experimental results show a linear relationship between surface exothermic reactions and the main fluorination reaction for Al powders. These results connect molecular level reaction kinetics to macroscopic measurements of surface energy and show that optimizing energy available in surface reactions linearly correlates to maximizing energy in the main reaction.

Highly reactive energetic films by pre-stressing nano-aluminum particles

“…The SQ nAl + PVDF exhibits a two-stage pressure rise: an initial spike followed by a slower rise suggesting a two-stage ignition and reaction behavior. In this case, the extended rise time to peak pressure may allow HF gas generated in the conned cell to react with Al and favor production of condensed phase AlF 3 as shown by Padhye et al 26 For the second-stage in the SQ nAl + PVDF reaction there is similarity in the pressure history for the UN nAl + PVDF reaction with a plateau in pressure following the peak. The shoulder could be related to gas generation behavior which is more rate limited in these two lms and may be produced in stages.…”

“…Generalization of eqn (20)-(23) for the case with delamination during quenching without creep is shown in eqn (24)- (26).…”

Applying Mechanically Activated Al/PTFE in CMDB Propellant

“…This is of significant practical importance for the disadvantages of nanoparticles mentioned above. Pantoya et al [23,[27][28][29] investigated factors affecting pre-ignition reaction (PIR, the initial exothermic reaction between metal and fluorocarbon) and found that alumina surface structure could be transformed due to hydrogen bonding effects resulting in enhancing in oxidation reactivity of Al in Al/PTFE mixtures. Dreizin et al [19] studied much mechanical milling prepared reactive materials.…”

Sequential synergetic sorption analysis of Gracilaria Rhodophyta biochar toward aluminum and fluoride: A statistical optimization approach

“…The aim of the present investigation was to develop an economical bio‐adsorbent for the sequential removal of Al(III) and fluoride from contaminated water by optimizing various physicochemical parameters by integral optimization technique, RSM, and to study the thermodynamics, isotherms, and kinetics of the sorption process (Padhye, Aquino, Tunega, & Pantoya, ).…”