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A quantitative study on the aging behavior of aluminum nanopowders is presented. While previous studies in literature focused on a few conditions of temperature and/or humidity, towards an understanding of the physical process behind the aging, no study investigated yet sufficient conditions to develop an accelerated aging model specific to aluminum nanopowders. This study investigated aluminum nanopowders obtained by plasma electro-condensation, submitted to a range of 11 conditions of humidity (25 to 75%) and temperature (298 to 348 K) over periods of 1 h to 71 days. Apart from the storage time in the climatic chamber, the powders were stored in a low-oxygen and low-humidity glovebox to prevent the influence of natural aging. The powders were then analyzed through thermo-gravimetric analysis (TGA) combined with differential scanning calorimetry (DSC) to retrieve the aluminum content as well as the humidity content. The decrease in aluminum content over time for each storage condition was then modeled with a power law. Finally, the fitting coefficients determined from the power law were used to build an accelerated aging model taking into account temperature and humidity effects, and that can predict the oxidation due to natural aging. Furthermore, the activation energy of the aging process determined through the model can also be used in the accelerated aging model of Bohn with a similar F coefficient. [ABSTRACT FROM AUTHOR]

Aluminum nanopowder oxidation is mostly experimentally studied through thermogravimetric analysis (TGA) combined with differential scanning calorimetry (DSC). These types of analyses are very sensible to a variety of parameters such as the heating rate, oxidizing gas composition or sample mass. Also, theoretical models of aluminum nanopowder oxidation are based on the evolution of the oxide thickness, whereas the outcome of TGA experiments provides a mass evolution. Moreover, the determination of the oxide thickness from a tested sample of aluminum nanopowder is not straightforward. Models are available in the literature but are not always validated and have never been compared with each other. This article first summarizes a literature survey on the influence of different parameters on TGA/DSC experiments and secondly discusses the analyses of TGA/DSC experiments with aluminum nanopowders produced by inductively coupled plasma. Guidelines on the best parameters to use for TGA/DSC experiments are provided. In parallel, three models, found in the literature, used to calculate the oxide thickness from a given mass increase by TGA/DSC experiments, but with different input variables and assumptions, are summarized and compared theoretically. The models are then applied to estimate the thickness of the oxide layer of aluminum nanoparticles produced by inductively coupled plasma. The calculated thicknesses are then compared with each other and validated against the oxide thickness determined using TEM images. [ABSTRACT FROM AUTHOR]

A theoretical and experimental analysis of the oxidation of aluminum nanoparticles is presented. The modeling of the oxidation is based on a modified Mott–Cabrera model. Mass and heat transfer, both at individual particle level are implemented. An investigation of the final oxide layer in the passivation process is carried out for nanometer sized particles. The model predicts the effect of the particle’s radii on the oxide layer growth and on the particle’s temperature. A 2 nm particle reaches a passive layer of 8 Å in almost 2000 s increasing its temperature from 300 K to a peak of almost 500 K. Parametric analysis on the influence of temperature and partial pressure of oxygen are performed. Thermo-gravimetry measurements are used and compared to the model’s results. Good agreement between the model and the experimental results, especially at low temperatures, makes it possible to estimate and devise a strategy for efficient and safe passivation of aluminum nanopowders. [ABSTRACT FROM AUTHOR]