Adsorption Studies of Two Silica Gels and a Gel-Type Catalyst.

Nordstrand, Van; We, Kreger; He, Ries

doi:10.1021/j150488a001

Cited by 16 publications

(8 citation statements)

References 10 publications

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“…4. Similar results have been reported by Milligan and Rachford 23 and Van Nordstrand et aZ., 24 calcination of silica gel to above 900" not appreciably modifying the size-distribution of pores but diminishing their number.…”

Section: S O R P T I O N Resultssupporting

confidence: 89%

Dielectric behaviour of water sorbed on silica gels. Part 2.—Purified silica gel and samples calcined at different temperatures

Nair¹,

Thorp²

1965

Trans. Faraday Soc.

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Sorption isotherms, reversible dielectric isotherms (over a frequency range from 2.5 Kc/sec to 1 Mcjsec) and corresponding reversible loss curves are reported for water, both adsorbed and desorbed, on a purified commercial silica gel and on two samples calcined at 610 and 810"C, respectively. The first linear, frequency-independent, region in each dielectric isotherm corresponded to water molecules adsorbed on surface silanol groups. Dispersion phenomena observed in the second region, up to 500 Kclsec, was attributed to Wagner-type dispersion due to the heterogeneous nature of the system and to the conductivity of the adsorbed film after monolayer completion.Differences in the dispersion phenomenon exhibited by the uncalcined and calcined gels could be explained on the basis of progressive reduction in the conductivity of the adsorbed f i l m on increasing the calcination temperature, partly due to progressive removal of ions still present on the surface of the uncalcined gel. At 1 Mc/sec, no dispersion is observed and then each dielectric isotherm consists of two linear regions, with the second (extending to near saturation) being of smaller slope than the first, and apparently characteristic of the dielectric behaviour of polar adsorbates on porous adsorbents.

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Section: S O R P T I O N Resultssupporting

confidence: 89%

Dielectric behaviour of water sorbed on silica gels. Part 2.—Purified silica gel and samples calcined at different temperatures

Nair¹,

Thorp²

1965

Trans. Faraday Soc.

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“…It should be noted, particularly for the alkoxide gels that P and S vary little with temperature until densification begins around 800-850 This is in contrast to the pore size which increases linearly in the same temperature range. This is not easily understood and similar previous studies [10,11,12] are contradictory in that they showed either no or slight increases in pore diameter with temperature. For the "colloidal type" gels, this behavior can possibly be explained by a combination of two effects.…”

Section: Resultscontrasting

confidence: 57%

Structural Observations of Porous Silica Gels

et al. 1986

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Silica gels were prepared by two methods; from the alkoxides under cc ditions where moderate degrees of crosslinking are expected and from LUDOX -alkaline silicate sols from which the alkali was subsequently removed. By selective thermal treatment from 300 to 850'C, pore diameters (excluding micropores) in the range 35,A to 400,A are seen. The pore size increased with temperature while the surface area and total porosity remained essentially constant. Extensive high resolution TEM analyses showed both colloid and polymeric structures with particle sizes between 60A and 250A which decreased on heating. An intra particle structure, presumably micropores of 10 A to 30A is also seen. By using a shadow cast Pt-C replica technique, stereoimages show the particles to have a filamentry type structure.

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“…The method of calculation used is similar to the one employed by Barrett, Joyner, and Halenda (7). The main difference is that in the present method the surface area of the representative pore of 10 A. radius is taken to be the difference between the total BET surface area and the surface area of representative pores larger than 10 A.…”

Section: Silica-alumina Catalystsmentioning

confidence: 99%