(7b) Dispersion of High Aspect Ratio Particles in Air

Powder dispersion is a vital aspect of powder technology impacting traditional and emerging technologies in many diverse areas including health, industry, the environment, and the military. In such applications, the properties and quality of the resultant product will be directly and noticeably affected by the degree to which the particles are dispersed. As powder technology moves into the nano-age, new, more complex challenges arise. Decreasing particle size into the submicron range significantly increases the effect of surface forces leading to an increase in the cohesiveness of the powder. The focus of this research is to systematically investigate factors that impact the dispersion in air of particles with one dimension in the nano size range, including second phase particles, coatings, and supercritical fluid processing.

Aluminum particles have been characterized using scanning electron microscopy (SEM), image analysis, laser diffraction, nitrogen absorption (BET), and Fourier transform infrared microscopy (FTIR). It was determined that the particles have a mean diameter of 10±5um and a process-controlled thickness of approximately 15nm. These dimensions, combined with the smooth surface characteristic of the vapor deposition process lead to a high degree of agglomeration. Preliminary research shows that the second phase material can increase dispersion by reducing the contact area between particles; coatings can be used to control the particle hydrophobicity, thus the effect of capillary forces; and supercritical fluid processing can be used to eliminate agglomeration due to capillary attraction during drying. Further investigation will facilitate a better understanding of the extent to which these factors are effective leading to the development of novel dispersion methods for high aspect ratio particles in air.