Miller Kelsea K, de Rezende Armando, Aquino Adelia J A, Tunega Daniel, Pantoya Michelle L
Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409, USA.
Institute for Soil Research, University of Natural Resources and Life Sciences, Peter-Jordan-Strasse 82, Wien A-1190, Austria.
Phys Chem Chem Phys. 2022 May 18;24(19):11501-11509. doi: 10.1039/d1cp05924f.
Harnessing aluminum oxidation energy requires navigating the particle's passivation shell composed of alumina. The shell is a barrier to aluminum oxidation but can also exothermically react with halogenated species and therefore contribute to the overall energy generated during aluminum particle combustion. Fluorination reactions with alumina have been studied because fluorine is abundant in binder formulations that commonly surround aluminum particles in an energetic mixture. However, iodine has emerged as an alternative halogenated-based binder or oxidizer because iodine gas provides ancillary benefits such as chemical neutralization of biological agents or sterilization of contaminated environments. This study used density functional theory (DFT) calculations to evaluate potential reaction pathways for aluminum-iodine combustion. Relative to fluorinated fragments such as HF and F, the adsorption energies associated with HI and I are nearly triple the exchange reaction energy available from fluorination reactions with alumina (-189 and -278 kJ mol for HI and I, respectively). However, exchange reactions between iodinated species and the alumina surface are energetically unfavorable. These results explain that through adsorption, alumina surface exothermic reactions with iodine are more energetic than with fluorine fragments. Experiments performed with differential scanning calorimetry (DSC) confirm the higher magnitude of energy generated for iodination compared with fluorination reactions with alumina. Additionally, strong adsorption energies can promote synthesis of new shell chemistries. Adsorption in solution will promote alumina dissolution and iodine precipitation reactions to produce hydroxyl complexes and iodinated species synthesized on the surface of the particle, thereby replacing alumina with alternative passivation shell chemistry.
利用铝氧化能需要克服由氧化铝构成的颗粒钝化壳层。该壳层是铝氧化的障碍，但也能与卤化物质发生放热反应，因此有助于铝颗粒燃烧过程中产生的总能量。由于氟在含能混合物中通常包围铝颗粒的粘结剂配方中含量丰富，所以已经对氧化铝的氟化反应进行了研究。然而，碘已成为一种替代的基于卤化的粘结剂或氧化剂，因为碘气具有诸如对生物制剂进行化学中和或对受污染环境进行消毒等辅助益处。本研究使用密度泛函理论（DFT）计算来评估铝 - 碘燃烧的潜在反应途径。相对于氟化片段如HF和F，与HI和I相关的吸附能几乎是氧化铝氟化反应可获得的交换反应能的三倍（HI和I分别为 - 189和 - 278 kJ/mol）。然而，碘化物质与氧化铝表面之间的交换反应在能量上是不利的。这些结果表明，通过吸附，氧化铝表面与碘的放热反应比与氟片段的反应更剧烈。用差示扫描量热法（DSC）进行的实验证实，与氧化铝的氟化反应相比，碘化反应产生的能量更高。此外，强吸附能可以促进新壳层化学物质的合成。溶液中的吸附将促进氧化铝溶解和碘沉淀反应，以产生在颗粒表面合成的羟基络合物和碘化物质，从而用替代的钝化壳层化学物质取代氧化铝。
