Disorientation angle distribution of primary particles in potash alum aggregates

Abstract

In order to fully characterize crystal aggregates, the orientation of primary particles has to be analyzed. A procedure for extracting this information from three-dimensional microcomputed tomography (µCT) images was recently published by our group. We here extend this method for asymmetrical crystals and apply it for studying the disorientation angle distribution of four potash alum crystal samples that were obtained under various experimental conditions. The results show that for all considered supersaturation profiles, primary particle pairs tend to have the same orientation significantly more often than in theoretical considerations, in which the orientations of primary particles are assumed to be distributed randomly.

Simulations of crystal aggregation and growth: Towards correct crystal area

“…However, the method must be further adapted in case that particles aggregate by aligning their faces. It is therefore important to experimentally measure the orientation between particles, as well as to estimate the amount of overlapping area at the moment of aggregation. Such experimental studies must furthermore ensure that the observed particles were indeed created by fluid shear and not by a crystal twinning.…”

“…This work follows the crystal representations used in prior publications of the Briesen group and therein developed MATLAB code. In the “geometrically complex” method, each primary particle is described by a set of unit face normals a i , as well as their distances h i from the coordinate system origin (H‐Representation).…”

“…Crystals may change the set of visible faces through growth and dissolution, as well as undergo breakage or form aggregates of several crystals. While two‐dimensional (2D), as well as three‐dimensional (3D) imaging methods have recently been established for characterizing complex particle shapes, simplifications are typically undertaken in order to model these processes. In this contribution, we focus on growth and aggregation while neglecting breakage.…”

“…The assumption of point or line contact, however, should be experimentally verified and the method properly adapted before simulating a realistic system. The necessary experimental information can be obtained using microcomputed tomography …”

Application of Transformation Matrices to the Solution of Population Balance Equations

“…Despite the fact that most models in solids processing technology consider particle size distribution as one of the main material parameters, many of them additionally incorporate various other attributes. For example, the shape and orientation of primary particles are important in crystallization processes [1]; the size and yield strength of the colliding granules can be considered as parameters for wet granulation models [2]; the distributions of granules by porosity and saturation are important for breakage rate in some apparatuses [3]; and the moisture content of particles plays a significant role in dryers [4].…”