The Effect of Heat-treatment on the SorptionDesorption Hysteresis Characteristics of Silica Gel.

Milligan, W. O.; Rachford, H.H.

doi:10.1021/j150451a026

Cited by 18 publications

(7 citation statements)

References 14 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: 88%

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: 88%

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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“…Further confirmation of the present results is to be found in the work of other authors (10,18,21). The observations are consistent with sintering of the material in the region of its Tammann temperature; for silica, this is about 790°C.…”

Section: T H Isupporting

confidence: 92%

“…Low-temperature gas adsorption isotherms have been widely used in the past to evaluate the effects of heat treatment on silica gel and gel-like structures (1,2,3,5,10,18,21,22), particularly by the application of the B.E.T. equations (5).…”

mentioning

confidence: 99%

Effect of temperature on silica and silica xerogels as measured by low-temperature (-196.deg.C.) nitrogen adsorption

Taylor¹,

Ross²

1969

J. Chem. Eng. Data

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low-temperature (-1 96' C.) nitrogen adsorption-desorption isotherms have been measured on pure silica and a range of silica xerogels thermally modified from 240' to 1 1 0 0 O C. B.E.T. surface areas and pore distribution characteristics are reported for each material. Results indicate that thermal modification has a significant effect on the surface areas and distribution data, especially above 700OC. In the majority of cases, B.E.T. areas are greater than the equivalent cumulative data. A range of noncylindrical pores is indicated in each material. With the exception of Macroporous silica gel, both the adsorption and desorption branches of the isotherms can be used for pore volume and surface area distribution determinations. In the former case, the desorption branch of the isotherm seems to lead to more apt results.S I L I C A gels and silicas are widely used in industry, and a close understanding of the surface and bulk properties of such materials is of practical importance in the technology of cracking catalysts, catalyst supports, mineral processing, ceramics, and adsorbents. Such an understanding is, in addition, directly involved in the manufacture and use of siliceous fillers and thickening agents in organic systems, including paints, inks, elastomers, and lubricating greases.Recent studies have been reported of the sorption of ammonia ( 6 ) , ethylamine (23, 24), and sulfur dioxide (14) on silicas and silica xerogels of high purity. Surface and structural modifications were achieved by thermal treatments, largely in the range 240" to 1100" C. T o characterize the materials, a large number of low-temperature (-196" C.) nitrogen adsorption-desorption isotherms were determined.Low-temperature gas adsorption isotherms have been widely used in the past to evaluate the effects of heat treatment on silica gel and gel-like structures (1, 2, 3, 5, I O , 18, 21, 22), particularly by the application of the B.E.T. equations (5). The method was used here to characterize materials, with special regard to surface area. Additional detailed information on pore-size distributions has been obtained by applying the Cranston and Inkley method (7) to the isotherms. This method provides independent comparative surface area data (to the B.E.T. values) and can be applied to both the adsorption and desorption branches of the isotherms. The results were calculated on the assumption of a molecular cross-sectional area for nitrogen of 16.2 A.2 (the most frequently used figure). However, there have been suggestions that the quadrupole moment of nitrogen can interact with hydroxyl or other polar groups, leading to a change in cross-sectional area (19). In spite of this, nitrogen adsorption generally gives the most meaningful results in low-temperature adsorption studies.Results from the adsorption measurements and from the isotherms were analyzed with the aid of an Elliott 803 computer . EXPERIMENTAL Materials. The major portion of the study was carried out with Davison 923 chromatographic grade silica gel (> 99.98% pure). Its surf...

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“…Temperature was controlled to within 5°C. These evacuation-sintering treatments extended for approximately 12 hr. at the temperature indicated.…”

Section: Methodsmentioning

confidence: 99%

“…The changes investigated include those produced by sintering in vacuo, by use as a catalyst, and by grinding to a fine powder. Recently Milligan and Rachford (12) reported the sintering of a silica xerogel (type IV isotherm) in air. They used adsorption of water vapor to characterize the gel at different stages and found that sintering caused destruction of pores but no change in average pore size or pore-size distribution.…”

Section: Introductionmentioning

confidence: 99%

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

Nordstrand¹,

We²,

He³

1951

J. Phys. Chem.

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The Effect of Heat-treatment on the SorptionDesorption Hysteresis Characteristics of Silica Gel.

Cited by 18 publications

References 14 publications

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

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

Effect of temperature on silica and silica xerogels as measured by low-temperature (-196.deg.C.) nitrogen adsorption

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

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