Preparation techniques for micron-sized particulate samples in X-ray microtomography

New application fields of particle technology, e.g. coatings, pharmaceuticals or electronic components require more and more highly defined particles in the lower micrometer range. In this case the particle size distribution (PSD) is no longer sufficient to define the specifications alone. The particle system has to be described by further distributed properties, which are for instance particle shape or particle composition. Tomographic particle characterization is one key methodology to provide the data, required to quantify these specifications. The tomogram of a representative particle sample contains information on the size and shape of each individual particle. The data of X-ray absorption furthermore gives hints about the material properties and structure of intergrown or composite structures. One central challenge in the tomography of a particle sample is the segmentation of the image data. When the particles in the sample are too close to each other, the algorithm is not able to separate individuals. On the other hand, oversegmentation can occur, when a particle is separated into two or more individuals during the image processing. Therefore, the physical sample preparation, which keeps the particles at a defined distance, strongly facilitates any automated segmentation. The established techniques known from SEM, TEM or automated mineralogy (MLA) cannot be transferred to X-ray microtomography (XMT), because they only have to provide a representative 2D-measuring plane. The 3D-sample preparation introduced here is able to provide a homogeneous particle sample immobilized within a matrix material with low X-ray absorption. In the sample, all particles have a minimum distance which amounts to more than a defined minimum multitude of the voxel size. The carrier matrix is a wax structure, that is shock frozen within a small polymeric tube with inner diameter from 0.5 mm to 2 mm. This corresponds to the requested sample size for the tomographic measurements (X-ray microscopy system Zeiss VERSA 510), which is 1024 times voxel size (approximate to 0.5 mu m to 2 mu m), allowing multi-dimensional characterization of particles from 5 mu m to 50 mu m in size and shape. (C) 2019 Elsevier B.V. All rights reserved.