Preparation of optimum ceramic slurries can be considered as the first critical step in many ceramic processes. Some significant factors in processing ceramic slurries are mixing speed, time, temperature, specific gravity, viscosity and pH value, of the slurries.
So, how can one know the proper, if not optimal, time and temperature while preparing a slurry?
It is true that it depends on what are the desired properties of the slurry but let's say just for a start to obtain well-dispersed one.
Thanks a lot.
In preparing ceramic slurries for e.g. slip casting or spray drying - at least in the high preformance sector - mixing is not enough, the slurry has to be milled to break down agglomerates unless powders are used which are agglomerate free (this practically does not exist in powders finer than 1 micron).
For a simple lab procedure disperse the slurry in solvent (usually water) using proper surfactants (~ 1 wt-% of powder) by stirring and add further additives necessary for the following process step (binder, plasticizer etc.) Put the slurry in a PE container, add milling balls (diameter 2-5 mm) and mill for some hours by rotating the container around the length axis.
If the powders are not severely hard agglomerated this is sufficient to obtain a homogeneous slurry which can be further processed.
You may check the particle size frequently before and during gentle milling to find out when to stop. You may also check viscosity a good value is something between 0.1-1 Pas at shear rates of 10-100 1/s.
If you are going to use spray drying or spray coating processes you will need to use dispersants, surfactants for a uniform particle distribution.
Since your milling system is not described it is very hard to comment on this question.
However, for a good mixing of the already milled powders ( assuming that you will be working with certain particle size you will need to use a good ratio between water:dry mass and all depends on your process. The optimal mixing angle of the mixer arm is 25 degrees. But this also depends on your system. You need to continiously mix the slurry otherwise you will form a thin fil at the surface depending on your system again, or your particles may segregate.
Good luck!
1- Rheological properties of slurries prepared using a planetary mixer
Naoki Adachi,
Minoru Hashiba,
Osamu Sakurada,http://www.sciencedirect.com/science/article/pii/S0272884204000021
2- Spray-Drying Ceramic Powders
Stanley J. Lukasiewicz
http://onlinelibrary.wiley.com/doi/10.1111/j.1151-2916.1989.tb06184.x/pdf
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science