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Abstract
A comparison of different experimental techniques for metallic particle size evaluation including light diffraction, scanning electron microscope analysis and nitrogen adsorption is presented. Nitrogen adsorption as an appropriate experimental method for particle size evaluation is proposed. Certain aspects of chemical reactivity of micron and submicron aluminum powders in the air, using thermogravimetry and differential thermal analysis (TG/DTA), are discussed.
Three metallic Al powders were analyzed: S-400 (Reynolds Co.), ALEX (Argonide Corp.) and WARP-l (Ceramic and Materials Processing, Inc.). TG/DTA analysis revealed that S-400 (specific surface area = 0.3m2 /g) does not react below melting point of Al (2% conversion); ALEX powder (specific surface area = 12.0 m2/g) starts reacting around T = 440°C and 16% reacts before melting point temperature is reached. WARP-1 samples (specific surface area between 16.0 and 26.5 m2/g) react already at T = 200°C and 25 wt% of aluminum is oxidized below melting point temperature. Differential thermal analysis did not discover any “stored” energy in S - 400 or ALEX materials; however, WARP-l samples released thermal energy already at 130 and 230°C, which is assigned to “stored energy”.
