Flow behaviour of zeolite powders at high process temperatures

Zeolite powders are an active ingredient for various applications and processing condition could affect powder flow behaviour. One of the important process conditions that changes during the manufacturing process is temperature. Temperature can change the particle properties affecting the powder flow properties and, therefore, the latter need to be tested at the process conditions. The flow properties of two types of zeolite powders, Z302 and T804, were evaluated at temperatures of 150, 300, and 500 ?C in the range of 1-8 KPa of normal consolidation stresses by an Anton Paar shear cell. The two materials show a very different flowability behaviour, even at the lowest temperature tested. The temperature appears much more significant effect on the T804 zeolite at 500 ?C and the flow function falls into the cohesive range while the Z302 zeolite flow function changes only for large values of consolidation stresses, by showing a flow function falling entirely within the very cohesive range. To find an explanation for understanding such a different behaviour of these two materials at changing temperature and consolidation stress, a theoretical framework was developed to take into account the different particle size distributions of the two powders. The resulting analysis, which is specific to the system taken into account, supports the goodness of the general approach that an adequate estimate of the average material fabric provides averaged estimates of contact forces that are able to explain the different behaviours of temperature and consolidation changes shown by powders. An original analysis of flowability based on the calculation of a structural length is also introduced to account for different powder bulk densities.