In situ observation of nanoparticle sintering via room temperature ion irradiation

Ceramic particles typically require significant temperatures to densify or sinter–the process of joining to individual particles into one larger body.  High temperatures are necessary to activate diffusion mechanisms, that allow for mass to redistribute based on driving forces such as curvature and surface energy.  However, when a ceramic is irradiated with ions, collisions between the energetic ions and the atoms on the crystalline lattice result in a high density of point defects–vacancies and interstitials.  Vacancy mediated diffusion is characterized by that thermal activation barrier described earlier.  Interstitial diffusion, has an even higher activation barrier, but if the collision events overcome this, the actual motion of interstitial is expected to be quite easy therefore allowing mass transport at much lower temperatures.  Using in situ transmission electron microscopy to observe the evolution of ceramic nanoparticles subject to ion irradiation, we can see the consequences of this interstitial diffusion–room temperature sintering!  The video below, of ceria nanoparticles, is captured at room temperature and compressed to show 60 minutes of imaging in just a few seconds.  Can you see how the agglomerate changes shape?  Ex situ irradiation gives rise to the same evolution, so the electron beam used in imaging does not significantly contribute to the microstructural changes.  Likewise, the temperature only increases by a few degrees Celsius during the experiment.