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Automated evaluation of contact angles in a three-phase system of selective agglomeration in liquids
(2020)
This study aims to an automated evaluation of contact angles in a three-phase system of selective agglomeration in liquids. Wetting properties, quantified by contact angles, are essential in many industries and their processes. Selective agglomeration as a three-phase system consists of a suspension liquid, a heterogeneous solid phase and an immiscible binding liquid. It offers the chance of establishing more efficient separation processes because of the shape-dependent wetting properties of fine particles (size ≤ 10 µm). In the present paper, an experimental setup for contact angle measurements of fine particles based on the Sessile Drop Method is described. Moreover, a new algorithm is discussed, which can be used to automatically compute contact angles from image data captured by a high-speed camera. The algorithm uses a marker-based watershed transform to segment the image data into regions representing the droplet, the carrier plate coated by fine particles, and the background. The main idea is a parametric modelling approach forthe time-dependent droplet’s contour by an ellipse.
The results show that the development of the dynamic contact angles towards a static contact angle can be efficiently determined based on this novel technique. These findings are useful for a detailed discrimination of wetting properties of spherical and irregularly shaped particles as well as their wetting kinetics. Also, a better understanding of selective agglomeration processes will be promoted by this user-friendly method.
The aim of this work was to develop a novel method for studying the 3D morphology of agglomerates obtained by spherical agglomeration. It has been found, that the combination of shock-freezing the samples in a mixture of ethanol and dry ice followed by an X-ray microtomography measurement leads to useful results. Hereby, the image quality for low absorbing material like the used graphite was enhanced by propagation-based X-ray microtomography, which results in phase contrast images. We also discuss our 3D image post-processing routine, which is used to determine the morphology parameters sphericity, fractal dimension and packing density. Furthermore, a two-dimensional kernel density estimation is used to calculate the joint probability density of agglomerate size and the morphology parameter. In future, this method will be used to determine the morphological behaviour of agglomerates during the different phases of spherical agglomeration.
Die Umbenetzungsagglomeration bietet die Möglichkeit einer Trennung nach zwei Partikeleigenschaften. Hierbei wird nach den Benetzungseigenschaften des Feststoffs in Bezug zur Suspensions- und Bindeflüssigkeit getrennt und nach der Größe. Ziel dieser Arbeit ist, die Reinheit der entstehenden Graphitagglomerate in einer Mischung mit Quarzsand gravimetrisch zu bestimmen und diese mit den Benetzungseigenschaften zu korrelieren. Die Güte dieser Ergebnisse wird mit einer Mikroröntgentomographie (µ-CT) untersucht. Es konnte gezeigt werden, dass sich Quarzsand mit Paraffinöl nicht benetzen lässt und somit Reinheiten von 99,5 % bis 99,9 % erreicht werden, was das Ergebnis der µ-CT bestätigt. Einen Einfluss der Partikelgröße des Quarzsandes konnte im untersuchten Bereich nicht bestätigt werden.