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Relationship between Surface Area Coverage of Flow-Aids and Flowability of Cohesive Particles

Fulchini, Fabio, Zafar, Umair, Hare, Colin, Ghadiri, Mojtaba, Tantawy, Hossam, Ahmadian, Hossein and Poletto, Massimo (2017) Relationship between Surface Area Coverage of Flow-Aids and Flowability of Cohesive Particles Powder Technology, 322. pp. 417-427.

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Poor and inconsistent flow of cohesive powders is a major issue in powder processing. A common solution is to coat the surfaces of the cohesive particles with finer particles, referred to as flow-aids. Such particles adhere to sticky surfaces and act as spacers preventing them from contacting each other and thus reducing the inter-particle forces and bulk powder cohesion. A question which naturally arises is how much flow-aid is needed to enhance the flowability to an optimum level. This work aims to establish a relationship between the degree of Surface Area Coverage (SAC) of flow-aids and the flowability, the latter as determined by a quasi-static shear cell method, as well as the angle of repose test and the FT4 powder rheometer. Glass beads of 90-150 μm sieve cut are made cohesive by silanising their surfaces with a commercial chemical reagent, Sigmacote® and are used as host particles. Two types of zeolite particles are used as flow aids. The mass fraction of the flow aids required to achieve a theoretical SAC of 1, 5, 10, 20, 50 and 100% is first estimated and then the host particles are coated in a pan mixer. The SAC is measured by Scanning Electron Microscopy, coupled with image analysis, and found to correlate well with the estimated value. The optimum surface coverage is found to be when SAC is 10-20%, as this provides the greatest flowability. An increase in SAC beyond this range leads to a gradual reduction in flowability.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Chemical and Process Engineering
Authors :
Fulchini, Fabio
Zafar, Umair
Ghadiri, Mojtaba
Tantawy, Hossam
Ahmadian, Hossein
Poletto, Massimo
Date : 18 September 2017
Funders : Engineering & Physical Sciences Research Council (EPSRC)
DOI : 10.1016/j.powtec.2017.09.013
Grant Title : EP/K503836/1
Copyright Disclaimer : © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (
Uncontrolled Keywords : Cohesive; Flowability; Flow aids; Processing; Surface area coverage; Coating
Depositing User : Clive Harris
Date Deposited : 06 Sep 2017 13:44
Last Modified : 11 Dec 2018 11:23

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