Volume 66, 1970

Dielectric constant of silica gel activated at different temperatures

Abstract

The dielectric constant ε(25°C, 1 Kc/s) of a chromatographic gel was determined after activation in vacuo at temperatures from 150 to 1015°C. The specific surface was evaluated from nitrogen sorption isotherms (–195°C). The total hydroxyl content, which may have included some intra-globular hydroxyl groups, in addition to “perturbed” and “free” surface hydroxyls, was determined by thermogravimetric analysis. For activation temperatures up to near the Tamman temperature (755°C) the composite polarization per gram of silica gel was a linear function of the total hydroxyl concentration, COH(mol g–1). Above this temperature, the polarization was independent of COH. These results can be explained on the basis of a polarization contribution from “perturbed” hydroxyl groups (where the hydroxyls can rotate from one hydrogen-bonded position to another), that from the isolated “free” surface hydroxyls remaining after activation above 755°C being negligible. Additional measurements of ε were made on silica gel (activated at 664°C) at –85 and –195°C. The increase in ε observed with decrease in temperature confirmed that part of the polarization of the system was contributed by surface hydroxyls constrained to rotate within cones about the Si—O axes.

Article information

Article type
Paper

Trans. Faraday Soc., 1970,66, 1741-1747

Dielectric constant of silica gel activated at different temperatures

L. B. Nichols and J. M. Thorp, Trans. Faraday Soc., 1970, 66, 1741 DOI: 10.1039/TF9706601741

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements