Powder Structure Control

In previous years the experimental set-up was about granules composed of only two phases, a particle phase and a binder phase. The particle phase consisted of insoluble limestone particles with different particle size distributions. The particle size distribution was varied systematically by changing the ratio of coarse to fine primary particles. It was found that the composition of primary particles plays an important role for the granule properties, especially the amount and distribution of coarse primary particles.

The aim of this years project

was to amplify the knowledge about structure - functionality correlation. Therefore a set of experiments with two different primary particle phases was investigated. The materials were chosen to have a soluble and an insoluble particle phase. As soluble particle phase sodium chloride was chosen because it allows the measurement of conductivity during dissolution. The insoluble particle phase was again chosen to be limestone. Also the binder was hold constant to be polyethylene glycol but it was now used in a melted state and not in concentrated solution as before.

Granulation method

Additionally the granulation method was changed into a two step method involving casting and milling. This step was necessary because it was aimed to generate a random close structure of primary particles in binder. In more detail a mixture of primary particles was mixed with melted binder and casted on a plate for cooling. The amount of binder was adapted to generate a saturated system without porosity. Afterwards the hardened plate was milled down to the desired granule size between 250 and 710m.

Investigation of granules

The granules were investigated in two ways as done in previous work. The structure was determined from X-ray micro-tomography images calculating structure measures like chord length distribution, covariance function and star volume of different phases. The granule properties were determined by different measurements including single particle crushing and dissolution behavior.