The Use of Contrast-Matching Small-Angle Neutron-Scattering Techniques to Monitor Closed Porosity in Carbons

“Real time” determination of porosity development in carbons: a combined SAXS/TGA approach

“…By 100 min the entire difference curve has become negative; i.e., scattering has decreased with respect to the initial material. This behavior is similar to that observed for phenolic resin char at low q at low burn-offs, that was attributed primarily to preferential gasification of amorphous carbon clusters of characteristically large sizes [2]. By 200 min, the curve is still negative at low q, but becomes positive again at higher q, proceeds through a maximum at about 0.08 Å -1 , and then falls to zero again.…”

“…In the absence of other effects, scattering at high wave vector (q) values is primarily due to microporosity, while that in the low range is due to meso-and larger porosity [2].…”

“…Early activation of these types of carbons primarily involves preferential burn-off of the amorphous carbon, exposing the intrinsic underlying microporous structure. For example, using contrastmatching small angle neutron scattering, no new microporosity development was observed upon activation of a char produced from a highly crosslinked phenol-formaldehyde resin up to 21% burn-off [2]. The only mechanism observed was burn-off of amorphous carbon and unblocking of initially "closed" microporosity.…”

The application of small angle scattering techniques to porosity characterization in carbons

“…This approach was used to fit scattering data from a resin char using a correlation function constructed from a bimodal Schulz distribution [15]. For fractal models, Texeira [16] and Schmidt et al [17] have shown that the scattering intensity is given by…”

Neutron and X-Ray Porosimetry

“…In this context, the existing pores may be divided into two classes: interconnected pores that have access to the exterior of the particles, and pores that are disconnected from the surface and are effectively inaccessible to fluid transport from the exterior [44]. During the activation or gasification process, the volume of accessible pores may increase, previously inaccessible porosity may be opened, and new porosity may be developed.…”