Effect of mechanical vibration on the size and microstructure of titania granules produced by auto-granulation

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.Effect of mechanical vibration on the size and microstructure of titania granules produced by auto-granulation Nicholas Ku, Colin Hare, Mojtaba Ghadiri, Martin Murtagh, Richard A. Haber Abstract Auto-granulation is the growth of particle clusters within a dry, fine powder bed due to the bulk powder cohesion. This clustering occurs without the addition of any binder to the system due to simple agitation of a powder, such as during storage or handling. For this reason, it is important in powder processing to be able to characterize this behavior. In this study, a submicron titania powder is mechanically vibrated under controlled conditions to induce clustering and promote auto-granulation. The amplitude and frequency of the vibration is varied to view the effect on the equilibrium granule size. A statistical model of the effect is also developed to determine that the granule size increases linearly with vibrational energy. Furthermore, imaging of cross-sections of the granules is conducted to provide insight into to the internal microstructure and measure the packing fraction of the constituent particles. It is found that under all vibrational conditions investigated the particles exhibit a core-rim microstructure.

Modelling of auto-agglomeration of cohesive powders

“…The primary particle size is reported to be around 0.1 m, although it is likely that the powder will be endowed with a certain degree of agglomeration even before starting the vibration process. In Figure 1, the solid fractions calculated with dp=2.1 m from Eq.4 are reported as a function of V. In the same figure, the average values of the experimental solid fractions obtained from Ku et al [1] are shown for comparison. Inspection of Figure 1 reveals that the proposed model is capable of capturing the variation of the packing fraction with the vibration intensity apart from one data point.…”

“…The model is first validated with the experimental data provided by Ku et al [1]. The primary particle properties are given in Table 1.…”

“…Auto-granulation is the agglomeration of fine powder without any additives, due to the highly cohesive nature of the inter-particle contacts. With fine and cohesive powder stable agglomerates can be formed by mechanical vibration or fluidization [1][2][3][4][5][6][7]. However, the mechanism by which clusters form has not been elucidated sufficiently.…”

“…However, the development of an accurate macroscopic model for dry granulation requires a description of the processes of densification and breakage [13][14][15][16][17][18]. Ku et al [1] found that mechanically vibrated fine titania particles cluster to a maximum equilibrium size which increase with the level of vibration, i.e. by increasing the vibration amplitude and/or frequency.…”

Flowability assessment of weakly consolidated powders

“…The appearance of the powder is white and cohesive, with loose clusters easily forming during powder handling and storage. Titania has the ability to autoagglomerate, due to possible agitation of the powder bed, such as mechanical vibration [6].…”