Citric Acid A Dispersant for Aqueous Alumina Suspensions

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Citric Acid A Dispersant for Aqueous Alumina
Suspensions
2001. 6 .11 Yi-Koan Hong Department of Metallurgy
and Materials Engineering Hanyang University,
Ansan, Korea
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Outline

• Introduction
• - Citric acid
• - Zeta Potential
• 2. Motivations
• 3. Experimental Materials and Procedure
• 4. Experimental Results
• 5. Discussion and Conclusions

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Citric acid ( I )

• Organic additives are widely used to control the
  force between the particles.
• - The suspension properties are determined by
  attractive and repulsive force.
• - By adsorption on the particle surfaces, citric
  acid causes a change of the surface charge result
  in a change of the double layer repulsion.
• - The specific adsorption of a carboxylic acid
  can be describes as a ligand exchange, where the
  hydroxyl group is exchange for a carboxylate
  group.

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Citric acid ( II )

• Structure of Citric acid and tricarballlyic acid

COOH

• Speciation of citric acid as a function of pH

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Zetapotential
Adsorbed Layer
Electrical double layer for electrostatic behavior
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Motivation

• The investigation of the adsorption behavior of
• citric acid
• Citrate Alumina surface complex
• The rheological properties of alumina suspension
• The influence of citric acid on the viscosity

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Experiments
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Methods ( I )
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Methods ( II )

• Measurement of the Electrokinetic properties
• - The Measurement of dynamic electrophoretic
  Mobility (µd)
• ? µd(?)?G(?)-1?-1
• Rheological Measurements
• Rheological characteristics of the alumina
  suspensions were
• determined using a concentric rotational
  viscosity meter.

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Adsorption curves of citric acid

• The Citric acid adsorption decrease with
  increasing pH

• With citric acid additions lt 0.2 wt, an almost
  complete adsorption of the added dispersion is
  observed for pH between 3 and 7
• The Maximum in the citrate adsorption at pH 3
• With Increasing pH, adsortion of citric acid
  decrease. mainly because the electrostatic
  attraction between the positively charged alumina
  surface and citrate anion decreases. Eventually,
  the electrostatic interaction becomes repulsive

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Citrate Alumina surface ( I )

• To clarify the influence of the hydroxyl group,
  the dynamic electrophoretic mobility of the
  alumina particle were compared
• The structure of tricarballylic acid is
  identical to that of citric, except for the
  missing hydroxyl group
• Given this result, the hydroxyl group of the
  citrate is assumed also to be coordinated to an
  aluminum atom of the alumina surface. It acts as
  an anchor group and charge carrier

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Citrate Alumina surface ( II )

• Citrate Alumina surface complex was
  investigated ATR-FTIR

Citrate dissolved in D2O
Citrate Alumina Complex

• ATR FTIR spectrum of the interfacial citrate
  at pD 6.1
• - Not all three carboxylate groups of citrate
  anion are coordinated to an alumina
• particles
• - Spectroscopy of the Citrate Alumina complex
  gives evidence of the formation
• of a Citrate- Alumina surface complex

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Measurement of the Electrokinetic properties
0 wt of citric acid
0.1 wt
0.2 wt
0.6 wt

• With increasing the overall citric acid
  concentration,
• - IEP is pushed further into the acidic pH
• - Any further increase in the concentration
  of the dispersant has a very limited effect,
• not only on the IEP but also on the
  electrophoretic mobility

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Rheological Measurement
IEP

• The disappearance of the repulsive double- layer
  force near the IEP line lead to an increase in
  viscosity. In this region, designated as
  unstable and the viscosity is gt200 mpas
• Approaching the IEP, the zetapotential
  decreases. because of the decreasing repulsive
  electrical double-layer force. Eventually, the
  attractive force predominant

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Summary

• With Increasing pH, adsortion of citric acid
  decrease.
• The hydroxyl group of the citrate is assumed
  also to be coordinated to an aluminum atom of the
  alumina surface. At the comparison with
  tricarballylic acid.
• The spectroscopy gives evidence of the
  formation of a Citrate- Alumina surface complex
• With increasing the overall citric acid
  concentration, Any further increase in the
  concentration of the dispersant has a very
  limited effect, not only on the IEP but also on
  the electrophoretic mobility
• The disappearance of the repulsive double- layer
  force near the IEP line lead to an increase in
  viscosity