Agarwal Prawal P K, Matsoukas Themis
Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
ACS Appl Mater Interfaces. 2022 Aug 3;14(30):35255-35264. doi: 10.1021/acsami.2c08300. Epub 2022 Jul 21.
The performance of Al as nanoenergetic material in solid fuel propulsion or additive in liquid fuels is limited by the presence of the native oxide layer at the surface, which represents a significant weight fraction, does not contribute to heat release during oxidation, and acts as a diffusion barrier to Al oxidation. We develop an efficient technique in which the oxide layer is effectively turned into an energetic component via a reaction with fluorine that is coated in the form of a fluorocarbon nanofilm on the Al surface by plasma-enhanced chemical vapor deposition. Perfluorodecalin vapors are introduced in a low-pressure plasma reactor to produce nanofilms on the surface of Al nanoparticles, whose thickness is controlled with nanolevel precision as demonstrated by high-resolution transmission electron microscopy images. Coated particles show superior heat release, with a maximum enhancement of 50% at a thickness of 10 nm. This significant improvement is attributed to the chemical interaction between AlO and F to form AlF, which removes the oxide barrier via an exothermic reaction and contributes to the amount of heat released during thermal oxidation. The chemistry and mechanism of the enhancement effect of the plasma nanofilms are explained with the help of X-ray photoelectron spectroscopy, X-ray diffraction, high-angle annular dark-field scanning transmission electron microscopy-energy dispersive spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.
铝作为纳米含能材料在固体燃料推进或液体燃料添加剂方面的性能受到其表面天然氧化层的限制，该氧化层占显著的重量分数，在氧化过程中不参与放热，并且对铝的氧化起到扩散阻挡作用。我们开发了一种有效技术，通过与氟发生反应，将氧化层有效地转化为含能组分，氟以碳氟纳米薄膜的形式通过等离子体增强化学气相沉积涂覆在铝表面。将全氟萘烷蒸气引入低压等离子体反应器中，以在铝纳米颗粒表面制备纳米薄膜，高分辨率透射电子显微镜图像表明其厚度可控制在纳米级精度。涂覆后的颗粒表现出优异的放热性能，在厚度为10 nm时最大增强幅度为50%。这种显著的改善归因于AlO与F之间的化学相互作用形成AlF，其通过放热反应去除了氧化阻挡层，并增加了热氧化过程中释放的热量。借助X射线光电子能谱、X射线衍射、高角度环形暗场扫描透射电子显微镜 - 能量色散光谱、热重分析和差示扫描量热法对等离子体纳米薄膜增强效应的化学过程和机理进行了解释。
