Ions effects on sol–gel transition and rheological behavior in alumina slurries

Colloids and Surfaces A:Physicochem.Eng.Aspects 430 (2013) 39–45

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Colloids and Surfaces A:Physicochemical and

Engineering

Aspects

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r f

a

Ions effects on sol–gel transition and rheological behavior in alumina slurries

Romain Castellani a ,Arnaud Poulesquen a ,∗,Frédéric Goettmann a ,Philippe Marchal b ,Lionel Choplin b

a CEA,DEN,(DTCD/SPDE/LCFI)-Marcoule,F-30207Bagnols-sur-Cèze,France

b

CNRS,GEMICO-LRGP (UMR CNRS 7274),Universitéde Lorraine,Nancy,F-54001,France

h i g h l i g h t s

•We studied sol–gel transitions in alu-mina slurries.

•When pH and ionic content vary,

multiple sol–gel transitions are observed.

•Zeta potential variations can be linked to these transitions.

•Different gel structures are thus found by rheological measurements.

g r a p h i c a l

a b s t r a c

t

a r t i c l e

i n f o

Article history:

Received 29January 2013

Received in revised form 25March 2013Accepted 26March 2013Available online 8 April 2013

Keywords:

Colloidal suspensions Zeta-potential Alumina Rheology Physical gel

a b s t r a c t

Aqueous slurries made of silica or alumina particles may behave like sols or like gels depending on the particle concentration,but also the pH or the ion force of the medium.The present study aimed at inves-tigating the different sol–gel transitions observed in systems between a diluted state and concentrated formulations.For this purpose zeta potential and G ,G measurements,reflecting elastic and viscous behaviors,were selected as the tools of choice to get insights into the mechanisms accounting for the sol–gel transition.We discuss about the relevancy of these simple measurements and affirm that they are sufficient to explain the evolutions in an alumina based system.Indeed,particles can adopt a “repulsive”organization at low salt concentration values (i.e.high surface potential values)or form an attractive percolating network,when the ion strength reaches a critical level.Moreover,the addition of NaOH can lead to very complex moduli variations as both the electrostatic shielding and the pH change;yet,these variations are easily predictable using our reasoning.

© 2013 Elsevier B.V. All rights reserved.

1.Introduction

The study and comprehension on how colloidal suspensions and slurries behave play a major role in several industrial fields.Ceramics crafting for example requires a good comprehension on these systems as slight modifications in the processing parame-ters (pH,salt concentrations [1,2])may influence the final aspects of many products or synthesis.In a different approach,some

∗Corresponding author.Tel.:+330466791801;fax:+330466397871.E-mail address:arnaud.poulesquen@cea.fr (A.Poulesquen).

techniques derived from the comprehension of these mechanisms can lead toward industrials improvements,as for filtration tech-niques [3].

In dispersed solutions,the rheological behavior and interactions between particles are well known,at least for a large number of systems.Theories like the classic Derjaguin–Landau–Verwey–Overbeek (DLVO)are striving to describe them;a simple approach derived from them is to state that the total interaction energy between particles is the combi-nation of van der Waals attraction and electrostatic repulsion of each particle surfaces [4].When ionic compounds are added,they may interact with positively and negatively charged surface sites.

0927-7757/$–see front matter © 2013 Elsevier B.V. All rights reserved./10.1016/j.colsurfa.2013.03.056