X-ray micro tomography and image analysis as complementary methods for morphological characterization and coating thickness measurement of coated particles

This work demonstrates the potentiality of X-ray micro tomography as a powerful tool for morphological characterization of coated particles and, in particular, of their coating layer. X-ray micro tomography provides a high level of details at both micro and macro-scale. It was, in this work, used in the determination of density, porosity, surface/volume ratio, and thickness of the coating layer. Special emphasis was put on evaluation of the adhesion core/coating shell due to its strong influence on the acceptance and goodness of the final coated compound. Different definitions of coating thickness are evaluated. The variance of these properties is assessed within particles and between particles. A novel protocol was developed in order to segment the coating shell out from the core particles. The segmented out images were used to create 3D models of such coating shells. General aspects of theses models are discussed. The potential and limitations of X-ray micro tomography are finally highlighted based on the experimental work. Image analysis was used to determine the coating thickness applied on the core particles as complementary and reference method. As case study, two series of coated particles, prepared using top-spray fluidized bed coater, were obtained, each one employing three standard well-know coating agents.