The Use of Contrast-Matching Small-Angle Neutron-Scattering Techniques to Monitor Closed Porosity in Carbons
✍ Scribed by M.Mirari Antxustegi; Peter J. Hall; Joseph M. Calo
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 207 KB
- Volume
- 202
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
Small-angle neutron scattering has been performed on samples inaccessible porosity may be opened, and new porosity may of phenolic resin char activated from 0 to 21% burn-off in oxygen. be developed (5). Thus, the presence of ''closed'' or inac-Comparisons of scattering intensities from samples of these cessible porosity can have a significant effect on how poroschars, both dry and contrast-matched with perdeuterated toluity develops. Despite its importance, however, this process ene, were used to elucidate the behavior of this carbon with prois still not well understood, primarily because only a limited gressive reaction. It was found that the total scattering intensities number of techniques can be used to accurately characterize from the dry samples decreased with burn-off, in contrast to closed porosity.
those for other carbons, where they typically increase due to
A number of techniques have been applied to the investiporosity development at low burn-offs. This behavior was shown to be due to the selective burn-off of disordered carbon material gation of porosity in carbons in general. These include gas exhibiting a broad distribution of sizes up to about 300 A ˚, with adsorption (6-8), mercury intrusion porosimetry (2), TEM a mean size ca. 102 A ˚, which originally blocked access to almost (9), and small-angle scattering techniques (10, 11). By their the entire intrinsic underlying porosity. The distribution of intrinvery nature, gas adsorption and mercury intrusion porosimesic porosity was found to be well fit by a bimodal Schulz distributry do not provide information about closed porosity, and tion of fully penetrable polydisperse spheres, comprising a nar-TEM gives only limited information concerning pore conrow distribution in the micropore size range with a mean of about nectivity (12). Small-angle X-ray scattering provides scat-9.4 A ˚, superimposed on another broad distribution of pore sizes.
tering data from both open and closed porosity, which cannot
The primary effect of burn-off of this carbon material is progresbe decoupled. sive removal of the disordered carbon, resulting in the conversion Recently, Hall et al. (12-14) have applied contrastof initially inaccessible to accessible porosity. There was no evimatching small-angle neutron scattering (CM-SANS) to indence of significant widening or alteration of the intrinsic underlying porosity, nor of the development of new porosity up to 21% vestigate closed porosity in a variety of materials, including burn-off. ᭧ 1998 Academic Press polymer resins (12), coal char (13), and vapor-deposited Key Words: small-angle neutron scattering; contrast matching; metal alloys (14). The technique consists of performing phenolic resin char porosity and porosity development.
SANS on ''dry'' samples where the total scattering is from all the porosity, including both accessible (open) and inaccessible (closed) pores. The pores accessible from the exte-