Measurements are reported of the dielectric response of Na-X, Na-Y and Ca-A zeolites in the frequency range 10 mHz to 10 kHz for a range of humidities and also over a range of temperatures. The extended frequency range compared with earlier studies has enabled a more detailed understanding to be obtained of the low-frequency behaviour, which is dominated by a strongly dispersive dependence on frequency of both the real and the imaginary components of the complex capacitance and has shown the complete absence of proper direct current conduction, contrary to earlier beliefs. The magnitude of the low-frequency behaviour shows an approximately exponential dependence on the water content of the pellets, suggesting that some form of percolation process is determining the low-frequency transport. Strongly non-linear behaviour is seen with respect to the amplitude of the applied voltage signal and this is also responsible for the absence of Kramers-Kronig compatibility in some of the low-frequency data. The observed dielectric spectra are related to the known structural characteristics of the three types of zeolites.
Measurements are reported, we believe for the first time, of the time-domain response of humid zeolites of types Na-X, Na-Y and Ca-A, in the time range 100 ,us to lo3 s. The results show the presence of non-linear responses with respect to the amplitude of the applied step voltage and they also reveal strong discrepancies with respect to the frequency-domain response, but exact correlation is absent on account of the non-linearities mentioned above. The discharge currents at intermediate and long times are very different according to whether the measurements are taken in the humid atmosphere or in vacuum, the former data showing a strong rise before the final fall. This is very unusual behaviour and its significance is not yet understood. The importance of time-domain measurements in non-linear systems is stressed and the relevance of electrochemical energy storage is introduced.
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AbstractA technique is described for making dielectric spectroscopy measurements of very small quantities (< 1 µl) of oil. The technique utilises surface tension to hold the oil between the plates of a capacitor, the inter-electrode distance being controlled by a micrometer.Breakdown strength can also be estimated using this technique. Three samples of silicone oil, used in cable sealing ends, were tested: virgin, used and failed. A major component in the frequency dependent impedance had the form ( ) (
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