The effect of pulverization methods on the microstructure of stiff, ductile, and flexible carbon aerogels

Abstract

Carbon aerogels find application in many fields. In most of the applications, they are used as powders and thus need to be pulverized. However, the pulverization could induce various changes in the microstructure of carbon aerogels. 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. 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. Scanning electron microscopy and transmission electron microscopy images, gas sorption techniques, wide-angle X-ray scattering, and Raman spectroscopy show a strong dependency of the introduced energy amount while pulverization on the structure modification. 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.

Wet Milling of Alginate Alco‐ and Hydrogel Composites: A Facile Top‐Down Approach for Continuous Production of Aerogel Microparticles

“…It is interesting to note that this trend is in accordance with results reported by Schwan et al., who observed that the mesopore volume of ductile carbon aerogels increased after dry milling, while the mesopore volume of stiff carbon aerogels remained nearly unchanged. [ 17 ] In our case, we can conclude that stiffer and more rigid biopolymer fibers of alcogels are better able to withstand the friction forces in the wet milling process than the more flexible fibers of hydrogels, which are comparably easily deformed.…”

“…Principally, milling of gels is feasible at any step of the aerogel production: in dry aerogel‐ as well as wet alco‐ and hydrogel state. Since the application of friction and shearing forces on carbon‐ and silica gels results in relatively easy breakup due to their brittle and stiff nature, milling in dry aerogel state may be a preferred approach for these material classes: grinding of carbon and silica aerogels has been carried out via manual mortar grinding, ultrasonic‐, shaking‐, and ball‐milling processes, [ 16–18 ] among others. Depending on the milling process and applied forces, changes of the microstructure can occur, which depend on the amount of introduced energy.…”

“…Depending on the milling process and applied forces, changes of the microstructure can occur, which depend on the amount of introduced energy. [ 17 ] Dry milling is, however, considered less suited for biopolymer‐aerogels since they exhibit mechanical properties very different from inorganic aerogels, such as a certain degree of flexibility and plasticity, which is rooted in their fibrillar, foam‐like microstructure. [ 19 ] Wet milling of suspended hydro‐ and alcogel biopolymer beads may be considered as an alternative due to the different viscoelastic properties of wet and dry gels.…”

Improved Dimethyl Ether Production from Syngas over Aerogel Sulfated Zirconia and Cu-ZnO(Al) Bifunctional Composite Catalysts

“…The CZA-ZrO 2 /SO 4 bifunctional composite catalysts were prepared by the physical mixing of aerogel or xerogel sulfated zirconia (calcined at T = 300 • C) with the CZA solid in a mass ratio of 1:2. It is well known that the characteristics of bifunctional catalysts are highly dependent on the mixing process (manual grinding with mortar, agitation, ultrasound, or balls) and the applied forces [26,27]. Thus, to avoid changes of the catalyst surface properties, both of the solids were mixed in agate mortar for a short time (5 min) and without hard pressing to form the homogenous mixture.…”

False Morphology of Aerogels Caused by Gold Coating for SEM Imaging

“…Hence, structural elements, including variations in the geometry of the network forming entities down to the nanoscale, can be differentiated. These differences in fine structure are related to the chemical composition of the source material(s) and the conditions of gel syntheses [ 13 , 14 , 15 , 16 ]. The archetypes of aerogels (silica, cellulose, alginate, polyurea, etc.)…”