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This work reported the investigation on the effect of relaxation to the permittivity (epsilon' r ) characteristic of Mg1-x Zn x TiO3 ceramics for x = 0 – 0.5 (MZT0 – MZT0.5) measured from 1 Hz to 330 MHz. Within that frequency range, the relaxation effect that consists of the space charge (SC) and the dipolar (D) polarization mechanisms were identified. The contribution of the D relaxation in MZT0 – MZT0.2 systems extents overall from about 100 Hz to 330 MHz, while that in MZT0.3 – MZT0.5 systems is from 50 kHz to 330 MHz. The remaining frequencies, i.e. from 1 to 90 Hz for MZT0 – MZT0.2 and from 1 Hz to 50 kHz for MZT0.3 – MZT0.5, are attributed to the SC relaxation. The D polarization mechanism provides constant epsilon' r values which vary from (15.4 – 17.0) ± 0.3 throughout the samples. Contribution of the SC polarization mechanism to the characteristic is supported by the simultaneous presence of different content and level of resistivity of the secondary phase of (Mg1-αZnα)2TiO4 in MZT0 – MZT0.2 systems and of (Zn1-αMgα)2TiO4 in MZT0.3 – MZT0.5, along with the presence of the main Mg1-x Zn x TiO3 phase, as a result of the variation of zinc content in the systems.
Trace humidity was measured by using miniaturized planar coulometric sensors in technical gases such as hydrogen, nitrogen, helium, nitrous oxide, and synthetic air. Frost point temperatures tf in the gases ranged from −60 °C to −30 °C, which is equivalent to a vapour mole fraction xv from 10 μmol mol−1 to 376 μmol mol−1. In addition, the generated humidity was determined by using a precision dew point hygrometer as reference. Nonlinear calibration functions were calculated that correlated electric current (sensor signal) and reference humidity. Parameters of functions were tested with one-way analysis of variances (ANOVA) to prove if all used sensors had a similar behavior in the same gas during experiments. Results of ANOVA confirmed that averaged functions can be applied for trace humidity measurement in nitrogen, helium, nitrous oxide, and synthetic air. The calculated functions were negligibly different for nitrogen, helium, and synthetic air. In humidified nitrous oxide, a minor change of parameters was observed due to lower electrical currents. In total contrast to that, the measured sensor signals were significantly higher in humidified hydrogen and each sensor required its own calibration function. The reason was a recombination effect that favoured multiple measurements of water molecules. Nevertheless, it was possible to measure continuously trace humidity in all tested gases by using coulometric sensors with an expanded uncertainty below 2 K (k = 2).
Especially trace amounts of water vapour in gases can be reliably determined by coulometric trace humidity sensors. The principle of these sensors is based on water vapour absorption in a hygroscopic layer and its subsequent electrolytic decomposition. The calibration of sensors was performed in the humidity range, expressed as frost point temperature, from −30°C to −80°C . This range is equivalent to volume fractions smaller than 376 µL·L−1. Generated humidity was measured with coulometric sensors and a chilled dew point hygrometer that was used as reference. An empirical non-linear function was found between sensor signal and measured reference humidity. This function consists of two parameters with a measurement uncertainty. Both calibration parameters were checked by means of one-way analysis of variance. It showed that gas specific function can be used for humidity measurement in nitrogen, hydrogen, dinitrogen monoxide, compressed and synthetic air. It is possible to determine trace humidity in all tested gases with an expanded uncertainty less than 2.1 K (coverage factor k=2 ) regarding frost point temperature.