The present study was performed to shed light on the migration of ions in field-assisted ion-exchanged glasses in which K<SUP>+</SUP> and other cations (Ag<SUP>+</SUP> and Li<SUP>+</SUP>) ions are introduced and removed with the aid of an electric field. Emphasis is placed on understanding the basic science of ion exchange processes. Also, comparisons are made between thermal and field-assisted diffusion. A systematic series of field-assisted ion-exchange experiments was investigated by electrolysing K<SUP>+</SUP> ions into commercial soda-lime silicate glass at temperatures from 260 to 450<SUP>o</SUP> C. The electrical properties of ion-exchanged glass were investigated <I>in situ</I> by a.c. impedance spectroscopy over the range 1 Hz to 1 MHz. The diffusion profiles of K and Na were determined by EPMA. The local cation motions and the vibrations of the silicate network were determined by IR spectroscopy. The glass transition temperatures of exchanged glasses were also measured using DSC. After electrolysis, the formation of a K<SUP>+ </SUP>-rich layer is indicated by the growth of a new semi-circle at a lower frequency in the complex Z* plots, and confirmed by the presence of a step-like surface layer in the concentration profiles. Thus, a high resistance is built-up in the surface layer as a direct result of insertion of K<SUP>+</SUP> ions. The quantitative measurements showed that nearly 90% of Na<SUP>+</SUP> ions were replaced by the incoming K<SUP>+</SUP> ions. In effect, it was found that the character of the electrolysed layer cannot be changed, except by changing the composition of the molten salt. Increasing the electrolysis decreases the corresponding surface resistance when measured to a given temperature, indicative of a loss of the stress and the occurrence of more stress relaxation at higher temperatures. This result suggests that the impedance experiments may provide a useful guide to the stresses built-up during initial electrolysis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:593852 |
| Date | January 2000 |
| Creators | Wu, M-H. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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