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

Journal Article · Wed Dec 15 00:00:00 EST 1993 · Analytical Chemistry (Washington); (United States)

DOI:https://doi.org/10.1021/ac00072a015· OSTI ID:5041333

Ellison, E H; Marshall, D B ^[1]; Waite, S W; Harris, J M ^[2]

---

1. Utah State Univ., Logan, UT (United States)
2. Univ. of Utah, Salt Lake City, UT (United States)

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-, 100-, and 147-[angstrom] 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/H[sub 2]O 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, [tau][sub h,min], depends on particle size with 5-, 10-, and 40-63-[mu]m octadecylsilica exhibiting [tau][sub h,min] values of ca. 5, 10, and 250 [mu]s, respectively. Joule heating at a discharge rate of 2 X 10[sup 5] s[sup [minus]1] of 5- and 10-[mu]m silicas is uniform, as indicated by a single-exponential response of the fluorescence thermometer, while a biexponential response for larger particle silica shows evidence of nonuniform heating. The rate and uniformity of heating depend upon the particle size and length of the alkyl ligands attached to the surface. 18 refs., 4 figs., 8 tabs.

• OSTI ID: 5041333
• Journal Information: Analytical Chemistry (Washington); (United States), Vol. 65:24; ISSN 0003-2700
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
POROUS MATERIALS
SURFACE PROPERTIES
SILICA GEL
JOULE HEATING
POROSITY
ALKYL RADICALS
COMPILED DATA
FLUORESCENCE
LIGANDS
PACKED BEDS
PARTICLE SIZE
SURFACE TREATMENTS
THERMOMETERS
ADSORBENTS
DATA
ELECTRIC HEATING
HEATING
INFORMATION
LUMINESCENCE
MATERIALS
MEASURING INSTRUMENTS
NUMERICAL DATA
PLASMA HEATING
RADICALS
RESISTANCE HEATING
SIZE
400201* - Chemical & Physicochemical Properties
661300 - Other Aspects of Physical Science- (1992-)