From particle to powder properties – A mesoscopic approach combining micro-scale experiments and X-ray microtomography

Abstract

The detailed understanding of particle flow is of special interest from the academic point of view and crucial for a safe and reliable process design. Due to poor flowability and heterogeneous bulk structures, the handling of fine and cohesive powders is particularly challenging. Recently, high resolution X-ray microtomography (XMT) has proved to be a reliable tool for analysing powder structures on bulk and particle level. This study now presents a complementary approach of micro-scale experiments and XMT analysis to improve the general understanding of particle flow. Centrepiece of the experimental investigation is a novel micro shear tester (μST) for very small powder samples (volumes from 0.005 to 0.1 mL), which has been integrated into a high resolution XMT system. By combining μST and XMT it is possible to extract detailed 3D images of precisely compacted and sheared powder samples. A SiO2 powder consisting of spherical, adhesive particles (x50,3 ≈ 11,2 μm) and a limestone powder consisting of irregular shaped particles (x50,3 ≈ 4,8 μm) are scanned before and after various shear and compaction tests. A detailed analysis of the sample microstructure reveals important information on the particle network and the bulk structure. The impact of the test procedure on mesoscopic heterogeneities and shear zones inside the sample is discussed. Moreover, the measurement of yield loci in the novel μST is presented.