Emulsion Processing and Size Control of Polymer‐derived Spherical Si/C/O Ceramic Particles

Abstract

Ultrasonic or stirring agitation of silicon‐based pre‐ceramic polymer emulsions in water, followed by crosslinking and consecutive pyrolysis was used to produce fine disperse powders of Si/C/O ceramic particles with spherical morphology. Depending on the shear forces introduced during the formation of the emulsions the diameters of the ceramic spheres can be controlled. Nanosized spheres in the range of 50–600 nm are formed upon sonication of the emulsion with ultrasound, while micrometer‐sized particles in the range of 1–10 and 10–100 μm are obtained when the emulsion is prepared with a high‐performance homogenizer at 20,000 rpm or by magnetic stirring at 1000 rpm, respectively. Dynamic light scattering (DLS), scanning electron microscopy (SEM), simultaneous thermal analysis (TGA/DTA), powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption measurements (BET), infra red spectroscopy (FTIR) and ²⁹Si as well as ¹³C solid‐state NMR investigations were applied to characterize the products. The novel precursor processing method is a general way to produce fine disperse ceramic powders for advanced ceramics and composites, which have spherical particle morphology, offering an alternative to the sol‐gel and vapor phase routes.

Keywords:

• Cross‐linking
• Micro‐spheres
• Nano‐spheres
• Polymer derived ceramics
• Poly(methylsilsesquioxane)

Acknowledgments

This work was supported financially in the framework of the Research Priority Program of the State of Baden‐Wuerttemberg (Project‐title: Functional Materials; subproject: Polymer‐Derived Metal‐Ceramic Nanocomposites). The authors are grateful to Dr. Erica Brendler (TU Bergakademie Freiberg/TU‐BAF) for the solid‐state NMR studies and Dr. Marina Krumova (Universität Konstanz) for the TEM‐investigation. Further valuable support was provided by the TU‐BAF Institutes for Materials Science (SEM, Brigitte Bleiber) and for Ceramic Materials (BET Measurements, Susann Rabe and Dr. Reinhard Herbig).