Characterization of Nanometer- to Micron-Sized Aluminum Powders: Size Distribution from Thermogravimetric Analysis

Abstract

Thermogravimetric analysis was used to study the reactivity of aluminum powders in air, oxygen, and nitrogen. In addition, the data were used to characterize active Al content, Al oxide content, volatile impurity content, particle size, and particle size distribution. Weight gains from complete oxidation of the Al were used to calculate average particle sizes in the range of 30 to 500 nm. These particle sizes correlated well with particle sizes derived from surface area measurement. Particle size was also examined by scanning electron microscopy, and compared with crystallite size determined by x-ray diffraction. Particle size distributions were derived from thermogravimetric analysis data based on a model of uniform oxidation of Al from the exterior to the interior of the particle. The method is well suited for analyzing samples with broad particle size distributions, and in particular, for monitoring the presence of 500-5000 nm particles within nominally nanosized samples. Quantitative information was not obtained for particles around 100 nm or smaller, due to large variations in oxidation behavior below 700° C. Nitridation of Al powders was studied for extended times at 600° C. Surprisingly, 2 μm powder was nearly completely nitrided in 1 h, indicating that the nitride product has little inhibiting effect on the reaction.