Surface Modification of Ceramic Powders
in cooperation with LS Polymeric Materials of BTU Cottbus - Senftenberg
Many technologies are based on powders of anorganic non-metal materials. The powders can be dry (e.g. dry press mass) or in suspension (e.g. resin matrices, composite precursors). In any case the handling of the powders requires control of their surface characteristics. Through the reaction of the functional groups on the powder surface (generally OH-groups) with suitable reactants, the surface properties can be adjusted selectively. Treatment with (functionalized) alkyl silanes is generally well suitable. In addition, specific processes like acid-base-reactions or complex formation can be used for the modification of surfaces as well.
Resin matrices based on surface modified powders show a significantly improved densification behavior [1-3].
Surface modification affects the rheological behavior of powder suspensions. Steric stabilization reduces the viscosity of non-aqueous suspensions significantly [1-6]. The agglomeration behavior can also be modified [4,5]. Therefore modification of the surface is a suitable method for the improvement of ceramic molding technologies (e.g. hot molding or injection molding) as well as the production of plastic-ceramic-composites.
Powders tested so far (selection): silicon nitride, aluminum oxide, zirconium oxide, magnesium silicide, eukryptite.
The effect of surfactants on the densification of powders was studied in detail. Tensides reduce friction in the sense of lubricating the surface.
Modifying reagents that stick to the powder well significantly reduce the powder-powder-friction, those that are only lightly attached reduce the powder-wall-friction [1-3].
In respect of the behavior of modified powder many analogies can be shown between dry presses, rheology and chromatography [1-3, 7]. Especially important here is the connection between the powder-powder-friction coefficient of the dry pressing and the viscosity values from rheological testing.