Particle size and reactivity of aluminum powders

A comparison of different experimental techniques for metallic particle siz e evaluation including light diffraction, scanning electron microscope anal ysis and nitrogen adsorption is presented. Nitrogen adsorption as an approp riate 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 (Argoni de Corp.) and WARP-1 (Ceramic and Materials Processing, Inc.). TG/DTA analy sis revealed that S-400 (specific surface area = 0.3 m(2)/g) does not react below melting point of Al (2% conversion); ALEX powder (specific surface a rea = 12.0 m(2)/g) starts reacting around T = 440 degrees C and 16% reacts before melting point temperature is reached. WARP-1 samples (specific surfa ce area between 16.0 and 26.5 m(2)/g) react already at T = 200 degrees C an d 25 wt% of aluminum is oxidized below melting point temperature. Different ial thermal analysis did not discover any "stored" energy in S - 400 or ALE X materials; however, WARP-1 samples released thermal energy already at 130 and 230 degrees C, which is assigned to "stored energy".