Abstract

Abstract

Rapid development of technologies requires introduction of new materials as well as

improvement of the existing one (Kudyba-Jansen et al. 2000).

The very fine fumed metal oxide -

Al

2 3

O

(d50 = 0.13nm, Desussa, Germany) has

been investigated on the possibilities for development of green bodies though the

innovative wet shaping process gel casting.

Thus, this study in particular is focused on characterisation of the suspension

stabilities promoted by two commercially produced polyelectolytes Dolapix CE64 and

Dolapix A88 (Zschimmer-Schwarz, Lahnstein, Germany). The optimal dispersant

dosage has been found and the suspension stability has been further evaluated.

Finally Dolapix CE64 has been found to be most favourable for enhancing the stability

of aqueous -

A

2

l

3

O

.

iii

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Acknowledgements

Acknowledgements

I would like to thank Prof. Ay and Dr. Gaydarzhiev (Chair of Mineral Processing, BTU

Cottbus) for giving me the opportunity to carry out this interesting and exciting

project. I am especially grateful to Stoyan for the scientific discussions with him which

helped me to conduct and analyze my experiments for his valuable and constructive

advice and for the numerous reviews of the manuscript.

I also appreciate the partial financial support of the chair of Mineral Processing for the

time the measurements were made.

I would like to thank to Dr. Hitzen (Laboratory of Solid State and Materials Chemistry,

Eindhoven University of Technology, The Netherlands) who gave me access to some

valuable literature sources that helped me in writing this paper.

iv

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Table of Contents

ABSTRACT

CHAPTER I

INTRODUCTION

1

1.1. Task Description and Objectives

1

1.2. Work Load and Study Project Requirements Agreement

3

CHAPTER II

COLLOIDAL PROCESSING OF CERAMICS­ PARTICLE INTERACTIONS

4

2.1. van der Waal Forces

5

2.2. Electrostatic forces

8

2.3. Steric Forces

10

2.4. Electrosteric Forces

10

2.5. Depletion Forces

11

CHAPTER III

MATERIALS AND METHODS

12

3.1. -

Al O

Properties

12

2

3

3.2. Dispersants Properties

14

3.3. Suspension Preparation

15

3.4. Investigation Techniques

16

CHAPTER IV

RESULTS AND DISCUSSION

22

4.1. -

Al

2 3

O

Suspension Characterization

22

4.2. Dispersant Dosage Optimization

23

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Table of Contents

4.3 Comparison of the dispersants effect on the zeta potential of the 5%

-

Al O

suspension

25

2

3

4.4. Comparison of the dispersants effect on the ionic strength of the 5%-

-

Al O

suspension

26

2

3

4.5. Assessment of the Dispersants with Reference to Point of Zero Charge (pzc) 27

4.6. Dispersant Behaviour Model

30

4.7. Experimental comparison of zeta potential and streaming potential of

-

Al

2 3

O

slurry

32

CHAPTER V

CONCLUSION

36

REFERENCES

38

APPENDIX I

42

APPENDIX II

43

APPENDIX III

44

vi

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List of Tables

TABLE 1. ILLUSTRATION OF THE INTERACTION POTENTIAL ENERGY AND RELEVANT LENGTH SCALE FOR

DIFFERENT INTERPARTICLE INTERACTIONS, ADOPTED FROM LEWIS (2000)

7

TABLE 2. CHARACTERISTICS OF -

Al O

SAMPLE (SOURCE: WWW.DEGUSSA.DE)

12

2

3

TABLE 3. SOME IMPORTANT PROPERTIES OF THE DISPERSANTS IN USE

14

TABLE 4. ZETA POTENTIAL [MV] AS MEASURED WITH PCD AND ESA AND THE RESPECTIVE PH AT

DIFFERENT DOSAGES OF DOLAPIX A88/ DOLAPIX CE64

32

TABLE 5. STATISTICAL DATA FROM LINEAR REGRESSION ANALYSIS OF SUSPENSIONS WITH 5% SOLIDS

LOADING AS EVALUATED FROM THE DATA AT FIG.13. ACCORDING TO EQ.(11.)

33

TABLE 6. HAMAKER CONSTANTS FOR SEVERAL CERAMIC MATERIALS INTERACTING UNDER VACUUM

AND ACROSS WATER AT 289K

42

TABLE 7. ISOELECTRIC POINTS FOR SEVERAL CERAMIC MATERIALS

42

vii

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List of Figures

FIG. 1. STATE OF COLLOIDAL SYSTEMS AND PREDOMINANT INTERACTIONS (AFTER LEWIS 2000)

4

FIG. 2. -

Al O

SAMPLE

13

2

3

FIG. 3. SCHEMATIC REPRESENTATION OF SEDIMENT BED FORMED BY (LEFT) DISPERSED SUSPENSION

AND (RIGHT) AGGREGATED PARTICLES (AFTER BESRA ET AL. 2005)

17

FIG. 4. SCHEMATIC ILLUSTRATION OF THE CST APPARATUS

18

FIG. 5. SCHEMATIC ILLUSTRATION OF DOUBLE LAYER FORMATION IN THE MEASURING GAP

19

FIG. 6. SCHEMATIC PRESENTATION OF CVI/ESA MEASUREMENT CELL SHOWING POLARIZATION OF THE

ELECTRIC DOUBLE LAYER FOR A NEGATIVELY CHARGED PARTICLE (AFTER WÄSCHE ET AL. 2002) 21

FIG. 7. POTENTIOMETRIC TITRATION OF 1% AND 5% -

Al O

SUSPENSION

22

2

3

FIG. 8. CST TEST RESULTS FOR DISPERSANT OPTIMIZATION

23

FIG. 9. VOLUMETRIC TITRATION OF 5% ALU-C AT DIFFERENT DISPERSANT DOSAGES WITH RESPECT

CHANGE IN ZP

25

FIG. 10. VOLUMETRIC TITRATION OF 5% ALU-C AT DIFFERENT DISPERSANT DOSAGES WITH RESPECT

TO CHANGE OF SUSPENSION CONDUCTIVITY

26

FIG. 11. COMPARATIVE POTENTIOMETRIC TITRATION AT DIFFERENT DISPERSANT DOSAGES

29

FIG. 12. SCHEMATIC ILLUSTRATION OF ADSORBED ANIONIC POLYELECTROLYTE SPECIES ON CERAMIC

SURFACE AS A FUNCTION OF PH AND IONIC STRENGTH - IS THE ADLAYER THICKNESS

30

FIG. 13. ZETA POTENTIAL AS MEASURED BY THE CVI AS A FUNCTION OF THE STREAMING POTENTIAL

AS MEASURED BY THE PCD METHOD FOR SUSPENSIONS AT A PARTICLE VOLUME FRACTION 5%

W/V IN THE PRESENCE OF DISPERSANT

34

FIG. 14. GELCASTING FLOW CHART AS SUGGESTED BY THE OAK RIDGE NATIONAL LABORATORY

43

viii

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Annotation and Abbreviations

a

particle radius

A

Hamaker constant

F

Faraday constant

h

minimum separation distance between particle

surfaces

V

electrostatic potential energy between charged

elect

particles

V

steric potential energy between particles resulting

steric

from adsorbed species

V

structural potential energy between particles

structural

resulting from non-adsorbed species

V

total interparticle potential energy

tot

V

total interparticle potential energy

vdW

F

Keesom forces

Keesom

F

Debye forces

Debye

F

London forces

LD

relative dielectric constant

r

permittivity of free space

0

zeta potential

N

number density of ions of type i in solution

i

r

valance of ions of type i in solution

i

Flory­Huggins parameter

surface potential

0

Ad-layer thickness

1/

Debye­Huckel screening length

CVI

Colloid Vibration Current

CST

Capillary Suction Test

ESA

Electrokinetic Sonic Amplitude

GC

Gelcasting

IEP

isoelectric point

PCD

Particle Charge Detector

PZC

point of zero charge

ix

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1. Introduction

Chapter I

Introduction

1.1. Task Description and Objectives

The overall idea for this study project originates from the intention to investigate the

possible use of the very fine fumed hydrophilic metal oxide, -

Al O

2

3 , produced by

Degussa, Germany for sintering a green body with a homogenous, high density and

optimal particle packing microstructure by gelcasting.

Gelcasting (GC) is a new shaping process for making high-quality complex-shaped

ceramic parts developed by the scientists from Oak Ridge National Laboratory, USA in

1984 (Janney et al. 1998). An aqueous system using acrylamide as monomer was

completed in 1988 (Omamete et al. 1991). However, concerns regarding health, safety

and disposal of acrylamide, referred to as neurotoxin caused industrial rejection of the

process. Development of a low toxicity process was initiated to deal with the lack of

acceptance, and it was fully demonstrated in 1990 (Janney et al. 1998). In the

gelcasting process, a small amount of organic monomer and cross linker is added to the

ceramic aqueous slurry. The most successful systems are based on the monofunctional

monomers methacrylamide (MAM), methoxy poly(ethylene glycol) monomethacrylate

(MPEGMA), and n-vinyl pyrolidone (NVP), the difunctional monomers methylene

bisacrylamid (MBAM) and poly(ethylene glycol) dimethacrylate (PEG(1000) DMA)

(Janney et al. 1998, Rak 2000). None of the monomers interact adversely with

standard ceramic processing aids such as dispersants and defoamers. Solids loading as

high as 55-60 w/v were achieved in alumina slurries and 45-57 w/v in silicon nitride

suspensions using these systems (Rak 2000). Upon heating, the monomer polymerises,

and the resulting gel (which is ca. 90% water) stiffens the ceramic powder slurry into

1

Electrokinetic Properties of Advanced Powders in View of Their Colloidal Processing

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