Intermediate Processing of Polymer-Silica Hybrid Nanoparticles using X-ray Microtomography

For certain product applications in pharmaceutical, chemical and material sectors, sintering of powders while retaining grain sizes in the sub-micron range becomes a critical processing step. The key to nanosintering and compaction is to achieve densification by limiting coarsening and undesirable microstructural transformations. Densification commonly results in grain coarsening. Nanosintering brings on additional challenges as compared to sintering of micron-size powders due to high rate of agglomeration, high reactivity, grain coarsening and ultimate loss of nanofeatures. One of the most severe limitations is the apparent inability to retain initial micro structural features during consolidation and sintering. These limitations are mainly related to powder agglomeration and interparticle friction. Polyviologens (PVs) are mainly used as potential templating agents in the hydrolytic sol-gel process. The resultant hybrid materials are amorphous aggregates of roughly spherical silica particles. Particle size range is between 100-300 nm and there is a large degree of agglomeration. Sol-gel process has become an important synthesis route for nanopowder applications over the last decade despite the fact that it has been around much longer than that. In this paper, we describe an experimental system which has been designed to examine an assembly of nanoparticles in a wide range of process engineering applications. These applications include harvesting from solutions of nano-particles into green parts and subsequent sintering into finished components. The system is based on an X-ray microtomography with a spatial resolution down to 5 μm. The application of the microtomography technique to the study of thermally induced morphological changes in silica-polymer hybrid nanoparticles is described under different experimental conditions.