Granule Formation, Structure and Content Uniformity from Single Drop Impact on Heterogeneous Powder Beds

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Description
Single drop impact of liquid on a static powder bed was studied to investigate the granule formation mechanism, droplet penetration time, the characterization of granules (morphology, surface structure and internal structure), as well as the formation regime map. Water was

Single drop impact of liquid on a static powder bed was studied to investigate the granule formation mechanism, droplet penetration time, the characterization of granules (morphology, surface structure and internal structure), as well as the formation regime map. Water was used as the liquid and two pharmaceutical powders, microcrystalline cellulose (MCC) and acetaminophen (APAP), were mixed to make heterogeneous powder beds. The complete drop impact and penetration was recorded by a high-speed camera. Two granule formation mechanisms identified previously occurred: Spreading and Tunneling. Spreading occurred for mixtures of large particle sizes, while Tunneling started to occur when the particle sizes of the mixtures decreased. With an increase of APAP concentration, the overall drop penetration time increased, which was in good agreement with previous literature. The granule morphology, surface structure, and internal structure were characterized by a prism method with image analysis, scanning electron microscope, and X-ray microtomography, respectively. The Spreading mechanism produced flat disks with porous internal structures, while the Tunneling mechanism produced round granules with dense internal structures. Granules that were formed via a hybrid of the mechanisms, Spreading/Tunneling, were hybrid granules, with some dense areas and some porous areas. The results of the granule content uniformity from UV-vis spectrometry revealed that with the increase of APAP proportion, the overall uniformity was compromised for mixtures with fine ingredients, while the content was much more uniform for coarse mixtures. It is believed that the mean particle size of the powder bed is the predominant factor in influencing the formation mechanism, drop penetration time, and granule properties, while the content uniformity is affected by both the particle sizes and the mixture hydrophobicity.
Date Created
2020
Agent

Conductive polymeric binder for lithium-ion battery anode

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Description
Tin (Sn) has a high-specific capacity (993 mAhg-1) as an anode material for Li-ion batteries. To overcome the poor cycling performance issue caused by its large volume expansion and pulverization during the charging and discharging process, many researchers put efforts

Tin (Sn) has a high-specific capacity (993 mAhg-1) as an anode material for Li-ion batteries. To overcome the poor cycling performance issue caused by its large volume expansion and pulverization during the charging and discharging process, many researchers put efforts into it. Most of the strategies are through nanostructured material design and introducing conductive polymer binders that serve as matrix of the active material in anode. This thesis aims for developing a novel method for preparing the anode to improve the capacity retention rate. This would require the anode to have high electrical conductivity, high ionic conductivity, and good mechanical properties, especially elasticity. Here the incorporation of a conducting polymer and a conductive hydrogel in Sn-based anodes using a one-step electrochemical deposition via a 3-electrode cell method is reported: the Sn particles and conductive component can be electrochemically synthesized and simultaneously deposited into a hybrid thin film onto the working electrode directly forming the anode. A well-defined three dimensional network structure consisting of Sn nanoparticles coated by conducting polymers is achieved. Such a conductive polymer-hydrogel network has multiple advantageous features: meshporous polymeric structure can offer the pathway for lithium ion transfer between the anode and electrolyte; the continuous electrically conductive polypyrrole network, with the electrostatic interaction with elastic, porous hydrogel, poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) (PAMPS) as both the crosslinker and doping anion for polypyrrole (PPy) can decrease the volume expansion by creating porous scaffold and softening the system itself. Furthermore, by increasing the amount of PAMPS and creating an interval can improve the cycling performance, resulting in improved capacity retention about 80% after 20 cycles, compared with only 54% of that of the control sample without PAMPS. The cycle is performed under current of 0.1 C.
Date Created
2015
Agent