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An investigation of surface area and porosity in solids by small-angle neutron scattering (SANS)

A number of adsorbents have been characterized using small-angle neutron scattering (SANS) and the results compared with those obtained by analysis of nitrogen sorption isotherms. The adsorbents include the microporous Gasil 200 and 60 120 mesh silicas, charcoal cloth, and activated charcoal; the me...

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Bibliographic Details
Published in:Journal of colloid and interface science 1985-01, Vol.104 (1), p.151-174
Main Authors: Hall, P.G, Williams, R.T
Format: Article
Language:English
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Summary:A number of adsorbents have been characterized using small-angle neutron scattering (SANS) and the results compared with those obtained by analysis of nitrogen sorption isotherms. The adsorbents include the microporous Gasil 200 and 60 120 mesh silicas, charcoal cloth, and activated charcoal; the mesoporous Gasil 35, Spherisorb S20W, and S7W silicas, the Spherisorb AIOY, Harshaw (support and supported catalysts) aluminas; the nonporous Cabosil and precipitated silicas, Alon alumina, a graphitized and ungraphitized carbon black (Sterling FT), Koch-Light graphite, and two naturally occurring iron pyrite samples (EOD and MT. ISA); a series of electrofurnace graphites A to H having N 2 BET areas in the range 5 to 540 m 2 g −1. Guinier plots of the small-angle neutron scattering data indicate that the porous materials studied are particularly well defined in terms of their porosity. Linear Guinier behavior suggests that the pores approximate to a monodisperse phase in a binary phase system. With the exception of activated charcoal, the scattering is best approximated by the Guinier “cylinder” relationship. The SANS pore sizes (from Guinier analysis, assuming a cylindrical pore shape) agree reasonably well with those from conventional analysis, e.g., by application of the Kelvin equation to desorption isotherms and porosimetry. This was shown by the Spherisorb silicas (48 to 76 Å (SANS), 89 Å (other)), Gasil 35 (76 Å (SANS), 120 Å (other)), Gasil 200 (23 to 39 Å (SANS), 21 Å (other)), mesh silica (14 Å (SANS), 21 Å (other)), Spherisorb alumina (101 Å (SANS), 134 Å (other)), Harshaw support (51 Å (SANS), 79 Å (other)), Harshaw catalysts (100 Å (SANS), 100 Å (other)). The SANS technique was also used in the detection of a change in the pore form of a catalytic alumina support. The process used to introduce the copper chloride Harshaw catalyst into the supporting alumina appeared to increase the size in terms of an increased radius. Additionally, the pore shape changes from one which gives rise to scattering according to an isodiametric cylinder. The presence of a monodisperse phase consisting of micropores within charcoal cloth and activated charcoal was confirmed by Guinier analysis. The nonporous solids show universal nonlinear Guinier behavior as a result of the polydisperse nature of the heterogeneities present. Normal Porod behavior, i.e., Q −4 dependence of the scattered intensity, I, at high momentum transfer, Q, was shown by the mesoporous and nonporous si
ISSN:0021-9797
1095-7103
DOI:10.1016/0021-9797(85)90020-7