The effect of pulverization methods on the microstructure of carbon aerogels

Kurzfassung

Carbon aerogels are suitable for many fields of application. In many cases powders are required and pulverization is necessary. But how can we take care on material quality as various changes in the microstructure of carbon aerogels are induced by pulverization?. The extent of changes depends not only on the dominant forces of used technique, but also on the mechanical and structural properties of initial monolithic samples. Various methods are available to produce carbon aerogels in a powdered form. the first of all monolithic samples of carbon aerogels can easily be grinded manually using sand paper. The accruing powder is collected from the surface and can be used for any application. During the grinding process, only low forces are applied to the sample which makes the method applicable for fragile or soft materials. Among many milling techniques, shaker milling is based on frequent percussions of a steel or ceramic bar or balls inside of the milling container. Depending on frequency, the steel bar will oscillate in the container and through the powerful impacts, crush the sample. Shaker mills are often used under cryo temperatures, whereby the container is arranged in liquid nitrogen. On the other hand milling in a planetary ball mill is the most frequently used method to get carbon aerogel powder, where the monolithic aerogel is placed in a container with balls. In the present work, we discuss the influence of grinding, milling in shaker cryo mill and planetary ball mill on stiff, ductile and flexible carbon aerogels. Results show that stiff carbon aerogels do not undergo noticeable changes. In contrast, ductile carbon aerogels are very sensitive to friction forces. Soft and flexible carbon aerogels undergo drastic changes in the microstructure.