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 - Al2 3O (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 y -  Al2O3

iii

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

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
3.2. Dispersants Properties 14
3.3. Suspension Preparation 15
3.4. Investigation Techniques 16
CHAPTER IV
RESULTS AND DISCUSSION 22
4.1. y - Al2O3 Suspension Characterization 22
4.2. Dispersant Dosage Optimization 23

v

4.3 Comparison of the dispersants effect on the zeta potential of the 5% y- Al2O3 suspension 25

4.4. Comparison of the dispersants effect on the ionic strength of the 5%- y- Al2O3 suspension 26

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 y- Al2O3 slurry 32

CHAPTER V

CONCLUSION 36

REFERENCES 38

APPENDIX I 42

APPENDIX II 43

APPENDIX III 44

vi

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 - y - Al2O3 SAMPLE (SOURCE: WWW.DEGUSSA.DE) 12
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

List of Figures

FIG. 1. STATE OF COLLOIDAL SYSTEMS AND PREDOMINANT INTERACTIONS (AFTER LEWIS 2000) 4
FIG. 2. y - Al2O3  SAMPLE 13
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% y - Al2O3  SUSPENSION 22
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