Mixing and Packing of Fine Particles of Different Sizes

Two different approaches for mixing different sizes of fine particles without segregation and simultaneously increasing the packing density of the mixture are presented. The first application requires uniform mixing of 300 and 30 mu m aluminum oxide particles acting as surrogates for the explosive RDX. The packing density needs to be as high as possible and the particles need to be well-mixed to prevent local hot spots. This was accomplished by adding moisture to uniformly mix the particles and then removing the moisture to increase the packing density. The second application requires mixing coarse (2.3 mm) and fine (65 mu m) silica aerogel particles; the aerogels are very porous and light and have a very low thermal conductivity. Here we want to fill the voids between the coarse particles with fine particles so that the bulk (or packing) density of the mixture is increased, thereby further increasing their insulating properties. This was done by combining a negative pressure (vacuum) with an external force field, such as sound waves or vibration.