Work

Joule-discharge heating studies of pore connectivity in silica gel: influence of pore diameter, chemical modification, and particle size

Year: 1993

Type: article

Abstract: Studies of Joule-discharge heating of packed beds of chemically-modified silica gel address the influence of pore diameter, particle size, and chemical modification on the heating kinetics of the silica gel. The results reveal that surface modification and pore diameter affect the connectivity of the intraparticle pore network. Heating of packed beds consisting of 60 Å, 100 Å, and 147 Å pore-diameter silica gels modified with n-triacontyldimethylsilyl (C30), dimethyloctadecylsilyl (C18) or trimethylsilyl (C1) ligands are monitored by observing the temperature-dependent fluorescence of NBD-hexanoic acid in MeOH/H2O solvents. A decrease in the silica pore diameter, an increase in the length of surface ligands, or an increase in bonding density of the ligands causes a reduction in the rate of the energy dissipation in the temperature-jump cell. The temperature equilibration time or minimum heating time, τh,min, depends on particle size with 5 μm, 10 μm, and 40-63 μm octadecylsilica exhibiting τh,min values of ca. 5 μs, 10 μs, and 250 μs, respectively. Joule-heating at a discharge rate of 2 x 105 s-1 of 5 μm and 10 μm silicas is uniform as indicated by a single exponential response of the fluorescence thermometer; while a bi-exponential response for larger particle silica shows evidence of non-uniform heating. Furthermore, the rate and uniformity of heating depend upon the particle size and length of the alkyl ligands attached to the surface.

Source: Analytical Chemistry

DOI: 10.1021/ac00072a015

Authors: E. H. Ellison, S. W. Waite, D. B. Marshall, J. M. Harris

Institution: Utah State University

Language: English

Topic: Heat and Mass Transfer in Porous Media

Subfield: Computational Mechanics

Field: Engineering

Domain: Physical Sciences

Open Access status: green