Measuring granule phase volume distributions using X-ray microtomography

Although granule microstructure has been shown to have a significant influence on granule performance, e.g., impact attrition resistance, dissolution rate, and granule strength, there has been a lack of research on methods to identify granule components in 3D space to describe granule microstructural properties. This paper presents techniques to non-destructively identify and describe spatial distributions of particle, binder, and air volumes within wet-granulated granules using X-ray microtomography (XRμT). anules were produced from glass ballotini particles and aqueous PVP binder and were imaged using XRμT. Particle and binder volumes were identified from the output images by using a combination of gray intensity value thresholds and image processing techniques. A new technique, utilizing the intersection of convex hulls defined along the granuleʹs three principal planes, was developed to distinguish between the intra-granular and extra-granular air space. ted glass ballotini masses were accurate and insensitive to the gray value thresholds. Segmented PVP mass was sensitive to both the lower gray value threshold and the elimination of particle partial voxels. Therefore, the effect that the segmentation method had on image measurements was investigated. Identified internal air volumes gave good agreement when compared to the powder bed porosity and to the predicted average particle coordination number. atial distributions of the phases are described both radially from the granuleʹs center of mass and with planes starting from the top of each granule. While phase volume fractions are uniformly distributed in the radial direction, axial distributions show that the binder volume fractions at the top of the granules are approximately 3% larger than at the bottom of the granules. This localization of binder was found to be consistent regardless of the binder identification method and is the first quantitative proof of intra-granular binder segregation for granules formed with a binder solution.