Ceramic powder dispersion should be evaluated using viscosity, zeta potential, sedimentation stability and particle-size distribution together. Viscosity indicates resistance to flow, zeta potential reflects electrostatic interactions, sedimentation reveals time-dependent stability, and particle-size measurements identify remaining agglomerates.
Four Core Testing Methods
1. Viscosity and rheology
Compare slurry viscosity under the same solids loading, temperature and shear conditions. Better dispersion generally reduces apparent viscosity and yield stress because particle agglomeration is reduced.
ISO 19613 specifies rotational-viscometer measurement of ceramic slurry viscosity. For formulation screening, viscosity should be measured across several dispersant dosages rather than at only one concentration.
2. Zeta-potential measurement
Zeta potential provides information about electrostatic interactions between particles. ISO 13099-2:2025 specifies optical measurement of electrophoretic mobility for calculating zeta potential.
Suspensions close to their isoelectric point are generally more susceptible to flocculation. However, a high absolute zeta potential does not automatically guarantee stability in every ceramic slurry because steric stabilization, ionic strength and solids loading can also dominate behavior.
3. Sedimentation stability
Place identical slurry samples in graduated containers and record sediment height, supernatant formation and redispersibility over time.
Research on alumina dispersion stability evaluated particle size, sedimentation, viscosity and zeta potential together and found good agreement between these methods when identifying optimum dispersion conditions.
A hard sediment that is difficult to redisperse usually indicates an unsuitable dispersion state even when the initial viscosity appears acceptable.
4. Particle-size distribution
Laser diffraction can identify changes in agglomeration. ISO 13320 provides guidance for particle-size analysis by laser diffraction.
Compare D50, D90 and the coarse-particle tail before and after dispersant addition. A reduction in D90 may indicate that larger agglomerates have been broken down. The dispersion and ultrasound procedure must remain identical between samples.
Testing Checklist
Use the same powder lot and solids loading;
Fix pH, temperature and mixing conditions;
Test several dispersant dosage levels;
Combine viscosity, sedimentation and particle-size results;
Verify the selected condition through green-density and fired-property tests.
Conclusion
No single measurement fully describes ceramic powder dispersion. Viscosity measures flow, zeta potential describes particle interactions, sedimentation tests stability over time and particle size reveals agglomeration. Combining these methods provides a practical way to identify the optimum dispersant dosage and a stable slurry-processing window.
FAQ
Q1: Is the lowest viscosity always the optimum dispersion condition?
A: No. Sedimentation stability, redispersibility and forming performance should also be checked.
Q2: Is a higher absolute zeta potential always better?
A: No. Steric stabilization, solids loading and ionic conditions may also control slurry stability.
Q3: Why can excessive dispersant reduce stability?
A: Excess additive can alter surface adsorption and solution chemistry, potentially increasing viscosity or promoting instability.