The effect of particle size on interparticle adhesive forces for small loads

We have measured the tensile strength and average free volume of fine cohes ive powders as a function of consolidation stress in the range of low conso lidation stresses. All the measurements start by fluidizing the powder. Onc e the powder is homogeneously fluidized, the fluidizing gas is reduced to a value below the minimum fluidization flow. In this way, the powder bed set tles down under a consolidation stress below its weight per unit area. The average free volume is calculated by measuring the powder bed height by mea ns of an ultrasonic sensor. Then the gas flow is slowly increased until the powder breaks, enabling us to measure the powder tensile strength. This pr ocess is repeated for different values of the decompressing gas flow. We sh ow that at low consolidations, there exists a linear relationship between t he tensile strength and the consolidation stress. From the measured consoli dation stress. tensile strength and average free volume, we estimate the in terparticle consolidation force per contact, F-c and the interparticle tens ile force per contact, F-t. We show that F-t increases linearly with F-c an d is independent of particle size. This result implies that, at low consoli dations, the contact between fine cohesive particles is plastic. (C) 2001 E lsevier Science B.V. All rights reserved.