Microwave dielectric relaxation of bound water to silica, alumina, and silica-alumina gel suspensions

Tomoyuki Ishida, Tomoyuki Makino

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

By the use of a time domain reflectometry method, dielectric measurements were carried out on silica, alumina, and silica-alumina gel suspensions (five types with composition varying between 0.3 < Si/Al atomic ratio <0.8) in the frequency range of 100 kHz to 20 GHz. For all the gels, a relaxation peak due to bound water was observed. This peak locates at around 1-10 MHz, indicating that the peak is a decade or 10 decades lower than those of biological polymers such as an aqueous DNA solution. The silica and alumina gels have a different bound water structure, judging from the fact that the peaks are different in their locations and shapes between the two gels. The silica-alumina gels exhibit two different peaks other than the peak of bulk water. The sum of the relaxation strength on the two peaks is proportional to the monolayer capacity obtained from water vapor isotherms. The shape of the one peak holds that of the silica gel, whereas the other retains that of alumina gel, and furthermore the ratio of the relaxation strength on the former peak to that on the latter depends on Si/Al atomic ratio. It is suggested that both peaks are caused by the orientation of bound water molecules.

Original languageEnglish
Pages (from-to)144-151
Number of pages8
JournalJournal of Colloid And Interface Science
Volume212
Issue number1
DOIs
Publication statusPublished - 1999 Apr 1
Externally publishedYes

Keywords

  • Bound water
  • Complex permittivity
  • Dielectric relaxation
  • Silica-alumina gel

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry

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