Browsing by Author "Varshneya, Arun K."

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    Transient and steady state ionic conductivity in type-III fused silica
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Jain, Vijay; Varshneya, Arun K.; Bihuniak, Peter P.
    Measurements of the transient and the steady state ionic conductivity in type-III fused silica were carried out in a non-blocking mode setup. Alkali (Li+, Na+ and K+) ions were electrolysed through the sample under a dc applied field in a 300 to 800 °C temperature range. The change in conductivity with time and the time required to attain steady state depended upon the type of alkali ion electrolysed through the sample as well as the electrolysing temperature. Except for the 350 °C transient conductivity profile, a maximum in the current-time behavior of K+ ion was observed at higher temperatures. In the dried as well as heat-treated samples, K+ ion transient conductivity at 600 °C showed a smooth approach to steady state. Li+ ion transient conductivity showed a minimum in the early stages of conduction for samples dried at 140 °C. This minimum shifted to lower times on increasing either the electrolysing temperature or the applied field. The minimum disappeared when the samples were heat treated at 600 to 650 °C for 1 to 2 d. Na+ ion electrolysis on the 140 °C dried sample showed instability in the early stages of transient conduction at 600 °C. The heat-treated samples always showed a higher instantaneous conductivity compared to the dried samples irrespective of the electrolysing ions but the steady state conductivities were similar. The protonic and the anionic (Cl-) species produced as a result of the interactions between the ≡SiCl groups and the dissolved H2 and H2O in the interstitial volume can account for the differences in the observed behavior. The steady state analysis showed that the Na+ ions were the most mobile ions followed by Li+ and K+ ions. The steady state conductivity was apparently independent of electric field strength and the different reactions which produce protons and Cl- ions.
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    Transient ionic conductivity in fused silica
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Varshneya, Arun K.; Jain, Vijay; Bihuniak, Peter P.
    Transient currents in doped and commercial type-I fused silica glasses were monitored by electrolyzing alkali ions (Na+ , Li+ and K+) through a sample disk in a U-tube dc non-blocking conductivity cell until steady state was achieved. The experiments were carried out either at 600 or 650 °C. Approach to steady state varied from sample to sample depending not only on the electrolyzing ion but also on the alumina/alkali ratio and the concentration of Li+ and Na+ impurity level in the silica. Results indicated that the transient behavior (current versus time) at a particular temperature was best expressed as a lg — lg plot showing two linear regions. The initial slope was attributed to the flushing of more mobile species and the final slope to the disappearance of interdiffusional coupling effects. The nature of the interdiffusional coupling, in some cases, was typical of the mixed-alkali effect in silicate glasses containing much higher levels of mixed alkali.