Understanding the electrosteric dispersion of α-alumina particles using a sulfonated tannin of natural origin

This work explores the stabilization effect of a sulfonated tannin (black wattle extract) on water-suspended α-alumina particles. Results showed that first additions lead to particle agglomeration. A minimum of 0.5 wt% tannin (relative to the alumina content) is required to cover the whole particle...

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Published in:Powder technology 2022-02, Vol.399, p.117164, Article 117164
Main Authors: Webber, Jaíne, Zorzi, Janete E., Segadães, Ana M., Mantas, Pedro Q., Cruz, Robinson C.D.
Format: Article
Language:English
Subjects:
Adsorption
Alumina
Alumina particles
Aluminum oxide
Colloidal stability
Diameters
Double layer potential
Electric double layer
Hydrodynamic diameter
Ionic strength
Surface stability
Tannin
Tannins
Thickness
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Summary:This work explores the stabilization effect of a sulfonated tannin (black wattle extract) on water-suspended α-alumina particles. Results showed that first additions lead to particle agglomeration. A minimum of 0.5 wt% tannin (relative to the alumina content) is required to cover the whole particle surface. Suspensions regain stability at ca. 1.0 wt% tannin (ca.1 mg tannin/m2 alumina surface area), due to a high negative ζ-potential (−60 mV, pH = 8.0). Both ζ-potential and particle hydrodynamic diameter are then close to those in electrostatically dispersed alumina particles. Changes in ionic strength cause changes in ζ-potential and hydrodynamic diameter but hardly affect the tannin adsorption. The electrosteric stabilization results from the repulsion provided by the ~15 nm thick adsorbed tannin layer (steric effect) and the enveloping electric double layer, which remains sensitive to the suspension ionic strength (electrostatic effect). Changes in hydrodynamic diameter can be used to infer the electric double layer thickness. [Display omitted] •Incomplete surface coverage lowers ζ-potential and causes particle agglomeration.•Full surface coverage reverses the particles surface charge (stable dispersion).•An electric double layer sensitive to ionic strength envelops the tannin barrier.•The electric double layer thickness can be inferred from the hydrodynamic diameter.•Stabilization tannin content should be referred to particles specific surface area.
ISSN:0032-5910
1873-328X
DOI:10.1016/j.powtec.2022.117164