Ceramic additive stability should be judged by whether an additive continues to perform during storage, slurry preparation and heating—not only by its original certificate values. The main indicators are viscosity drift, pH change, sedimentation, redispersibility and thermal-decomposition behavior.
How Do pH, Viscosity and Sedimentation Indicate Stability?
Additive stability is the ability of a dispersant, binder, plasticizer or other functional material to retain its chemical condition and processing function under defined time, temperature and formulation conditions.
A liquid additive may remain visually stable in its container but perform poorly after contact with ceramic powders, dissolved ions or other additives.
Four Ceramic Additive Stability Tests
1. Storage-stability testing
Compare fresh and stored samples for appearance, odor, pH, density and viscosity. Ambient and accelerated-storage groups can be used to identify crystallization, separation, gel formation or color change.
The test temperature and duration should reflect actual warehouse and transport conditions rather than an arbitrary laboratory period.
2. Slurry-stability testing
Add the material to a standardized ceramic powder and compare sediment height, supernatant clarity, redispersibility and viscosity after controlled storage.
ISO/ASTM 52940:2025, developed for ceramic slurries used in vat photopolymerization, includes solids content, dynamic viscosity, particle-size distribution and solid-dispersion stability among the main characterization items. The same principle is useful for broader ceramic-slurry evaluation.
3. Rheological-aging testing
Measure viscosity and thixotropic behavior at a fixed temperature and shear history immediately after preparation and at later time points. Ceramic-slurry viscosity can be measured using the rotational-viscometer method in ISO 19613.
Research on aged ceramic suspensions shows that dispersant type, dosage, ionic conditions and pH can change viscosity and structural rebuilding over time. A stable additive should keep these changes within the process-control range.
4. Thermal-stability testing
Binders and organic dispersants should be examined by TGA, DSC or coupled TG-MS analysis to determine decomposition temperatures, mass-loss stages and evolved gases.
A study of thermal degradation of organic additives used in ceramic colloidal shaping found major differences between additives. Rapid gas release during heating can contribute to pores, deformation or cracking, so thermal data should be used when designing debinding and firing schedules.
Evaluation Checklist
Item | Requirement from the Source Draft |
1 | Include additive-free and fresh-additive reference samples |
2 | Fix solids loading, pH, temperature and mixing conditions |
3 | Evaluate both the original additive and the formulated slurry |
4 | Track change over time, not only one measured value |
5 | Retest forming and fired properties after aging |
6 | Define acceptance limits from stable production history. |
Conclusion
Additive stability is not simply the absence of visible deterioration during storage. A stable additive must still control dispersion, flow, forming and burnout after aging. Combining storage observation, rheology, sedimentation testing and thermal analysis provides a practical basis for setting shelf life, incoming-inspection limits and a reliable processing window.
FAQ
Q1: Does a clear, non-separated liquid prove that an additive is stable?
A: No. Its performance must also be verified after it is mixed with the actual ceramic powder and other formulation components.
Q2: Does rising slurry viscosity always indicate additive failure?
A: No. Temperature, pH, powder dissolution, evaporation and microbial contamination may also cause viscosity drift.
Q3: How long should stability testing continue?
A: The test should cover the intended storage period and include retesting after supplier, formulation or processing changes.