(376a) Dry Particle Coating for Tailor-Made Product Properties: Coating and Decoating Processes | AIChE

(376a) Dry Particle Coating for Tailor-Made Product Properties: Coating and Decoating Processes

Authors 

Bluemel, C. - Presenter, Friedrich-Alexander University of Erlangen-Nuremberg
Wirth, K. E., Friedrich-Alexander University Erlangen-Nuremberg



Today tailor-made particle properties of highly dispersed powders are of increasing interest in industrial applications. Theses powders consist of particles with small diameters (≤ 10 µm). With decreasing particle size, the influence of van-der-Waals forces in comparison to their weight-force is increasing resulting in agglomeration. The outcome is bad flowability of the powders leading to problems in further processing.

Dry particle coating is a cost-efficient and easy-handling mixing process for assembling tailor-made composite particles. Therefore nanoscale guest particles are adhered to microscale host particles. This process mainly bases on van-der-Waals forces. Within the adhesion of nanoparticles the distance between the host particles is increased. This results in decreased adhesion forces and increased flowability. Additionally properties of the particles can be modified or changed, for example wettability, solubility, adsorption properties or higher cycle stability of electrode materials. These tailor-made particle properties influence the resulting product properties and enable the production of complex devices.

The processing of such composite particles can for example be conducted in a tumbling mixer or a rotary drum mixer for understanding the major influences to create scale-up criteria. The number of host particle contacts as well as the applied energy have major impact on the dry particle coating results. The guest particle agglomerates should be deagglomerated ideally whereas the host particles should not be comminuted. There is an optimum distribution of guest particles on the surface of the host particles. To increase the applied energy, mixing agents can be added to the host particles and guest particles in order to improve the mixing intensity and thereby deagglomeration of the cohesive host and guest particles.

Longer process times respectively great applied energy lead to decoating processes of the host particles. Guest particles are removed from the host particles surface and agglomerate again to agglomerates with low porosity. A model has been developed for the coating process as well as for the decoating processes. The variation in time can be described as a first order reaction. The quality of the coating has been characterized by several methods, for example: SEM and TEM.

Flowability measurements of the host particles and composite particles were conducted in Schulze ring shear tester; Zimmermann tensile strength tester and AFM. These three methods enable to measure complementary data ranging from the single particle level to bulk as well as from small to higher loads.

The surface properties of the host particles and guest particles are important for the dry particle coating process. Hydrophobic guest particles only adhere to hydrophobic host particles as well as hydrophilic guest particles only adhere to hydrophilic host particles.

The dry particle coating process in a tumbling mixer is quite complicated, because rotation, translation and inversion are taken place simultaneously. Since mixing is conducted in a closed vessel, in-situ-observations are of great interest. Positron Emission Particle Tracking (PEPT) measurements enable such observations and therefore were conducted to learn more about the dry particle coating process. Via these measurements, a single mixing agent (diameter: 1 mm) was tracered with a positron (β+) emitter. Thereby the mixing intensity can be determined for example by velocity distributions, movements and collisions of the mixing agents. The applied energy is proportional to the velocity of the glass beads and can be calculated in this way. The quality of the coating depends on the velocities of the mixing agents.

The composite particles assembled in this process open new possibilities in different applications, for example: selective laser beam melting (SLM), light weight construction as well as in lithium ion batteries. The fundamentals of the dry particle coating process, the description of the occurring mechanisms of coating and decoating as well as examples for applications will be given in the presentation.