I want to combine some micron-sized ceramic particles with a 'fire-resistive' binder to form a slurry which can be spray-dried afterwards. In that case, what are the important factors that I need to consider in choosing the suitable binder? An example of a binder for this type of application would be greatly appreciated.
Thanks!
Binders for ceramic slurries for spray drying are polymers which must be soluble in the solvent( most of the time water), must withstand the drying conditions and must be entirely combustible during the debindering/firng process.
Popular binder systems are acrylates or polyvinylalcoholes.
How to select the binder and its amount ?
Organic additives (surfactants, plasticizers, binders) do not apply for any powder and may in combination interfere with each other leading to unfavorable rheological properties or other unexpected things that may happen when you mix some components together.If you have not enough binder the green strength will be low, with risk of failure during pressing, handling or machining, if you have too much the feedstock will stick to the punches after pressing.
The simplest way is to buy a ready made binder from company supplying the ceramics industry such as Z&S or BYK. They will be able to give some application know-how for the amount necessary for a certain powder and the proper choice depending on the material (e.g. SiC or Al2O3). The problem is the product has some phantasy name and you will never know what substances you are actually using.The second and more scientific way is to use chamicals of known composition and do anything by your own.
A binder which works for almost all oxide ceramics is PVA 4-88.
Some rule of the thumb: For alumina you will need approximately 0.1 x BET surface [%] binder, this means for a powder with 10 m2/g about 1 wt-% calculated to the solid in the slurry. As a plasticizer you may add about 25 % of the binder amount. Suitable plasticizers are low molecular weight PEGs.
Probably you will need some iterations to fine tune the recipe, if it sticks reduce the binder, if its too weak increase the binder.
You will need oxidizing debindering process at 800°C for at least 1h to get rid of the PVA binder, this may cause problems with fine grained non-oxide powders.
So good luck for your experiments !
In addition to comments from Dr. Kern, it is also recommended to add surfactants (SKW-BASF Castaments are a good option for ceramic slurries) in order to adjust rheological properties of suspension prior the spray drying step. Molecular weight of surfactants and binders, required pH, temperature of working suspension and surface area of ceramic powders need to be considered. I suggest a talk with the following person: [email protected]
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science