Potential sensors

SM-2) A measure of effectiveness of each potential sensor mode. This should be a function of both the mode (as defined above) and of the environment, or at least the estimate of it mentioned in... 

Fulco, M., Schiltz, R.L., lezzi, S., King, T.M., Zhao, P., Kashiwaya, Y., Hoffman, E., Veech, R.L. and Sartorelli, V. (2003) Sir2 regulates skeletal muscle differentiation as a potential sensor of the redox state. Molecular Cell. 

The analyze phase of the project consists of the activities which are typically associated with , including identification and assessment of potential sensor technologies, method development, qualification, and validation. In addition, designed experiments (DOE) or data-mining exercises may be performed to... 

Unfortunately, -alumina cannot be used as a fuel cell electrolyte since its oxygen ions are immobile and so any oxygen electrodes in the corresponding galvanic cells will not be reversible. However, under open circuit conditions, /1-alumina has been successfully used as an oxygen potential sensor. In this mode of application, the oxygen electrode equilibrates with the Na+ ions of the electrolyte as follows... 

Most factors in parameter G (Chapter 4, Equations 4.55 and 4.56) and the potential of the reference electrode are temperature-dependent this is possibly also the case for factor x. Equation 4.56 also represents the concentration of the hydroxide ion. This means that a potential sensor based on the prewave will also have to contain a pH sensor. The hydroxide ion concentration derived from the output signal of this additional sensor needs to be introduced in the algorithm for the calculation of the hydrogen peroxide concentration. As an additional sensor, a glass electrode is an obvious choice, with a temperature-dependent potential, which is the case also for the potential of the reference electrode associated with the glass electrode and for the pH of the buffers. In this research work, the influence of... 

M. George, W.J. Parak and H.E. Gaub, Highly integrated surface potential sensors, Sens. Actuators B Chem., 69(3) (2000) 266-275. 

As the reflected radiation is emitted from the sample in a random direction, diffusely reflected radiation can be separated from, potentially sensor-blinding, specular reflections. Common techniques are off-angle positioning of the sensor with respect to the position(s) of the illumination source(s) and the use of polarisation filters. Application restrictions apply to optically clear samples with little to no scattering centres, thin samples on an absorbing background and dark samples. In either of these cases, the intensity of radiation diffusely reflected off such samples is frequently insufficient for spectral analysis. While dark objectives remain a problem, thin and/or transparent samples can be measured in transmission or in transflectance. 

Biomimetic sensors, prepared by catalase adsorption on diasorb and agarose (treated with trypsine) and adhered to an aluminum electrode surface by Pattex adhesive, displayed an abrupt decrease of the electrode potential. Sensors prepared by catalase adsorption on A1203 (without trypsine treatment) and adhesion to the aluminum electrode with Pattex adhesive displayed a high oscillation of the electrode potential, which induces extreme instability of the operation. Hence, it should be noted that sensor operation was always better in the case of enzyme treatment with trypsine. 

Gas sensors — (b) Gas sensors with solid electrolytes — Figure 5. Schematic drawing of the layer structure of a mixed potential sensor... 

Other spectroscopic studies have been focused on the UV-Vis absorption properties of rhodium and iridium complexes of A -(2 -hydroxyphenyl)pyrrole-2-aldimine <2005MI167>, and of l,l, 5,5 -tetraaryl-2,2 -bipyrroles <2005H(66)319>. The spectrophotometric properties of calix[4]pyrroles as potential sensors and receptors are also the focus of much ongoing work <1998PAC2401, 2004JA16296, 2005JA8270>. 

Figure 13.2 Mixed potential sensor mechanism, (a) Mixed...

One of the advantages of mixed potential sensors is that it is possible for both electrodes to be exposed to the same gas. The elimination of a need to separate the two electrodes simplifies the sensor design, which in turn reduces fabrication costs. Although this simpler planar design is often used, the electrodes are sometimes separated to provide a more stable reference potential. As with equilibrium potentiometric sensors, the minimum operating temperature is often limited by electrolyte conductivity. However, the maximum operation temperatures for nonequilibrium sensors are typically lower than those of equilibrium sensors, because the electrode reactions tend towards equilibrium as the temperature increases. This operating temperature window depends on the electrode materials, as will be discussed later in the chapter. 

The mixed potential mechanism was described above, using CO as an example. However, the mechanism can be applied to any pair of oxidation and reduction reactions. Thus, mixed potential sensors have been reported for other reducing gases, such as hydrocarbons. Figure 13.20 shows that gold and platinum electrodes can be used to measure the amount of propylene (CsHe) [228, 229, 231, 233, 236-238]. Mixed potential hydrocarbon sensors have also been reported using proton-conducting electrolytes [239-242]. 

Among mixed oxides employed in mixed potential sensors is ITO, this having been used for both NO [291] and CO [292-294] sensors. A further example of a doped oxide being used as an electrode is TiO2, which has been doped with tantalum for hydrocarbon sensors [295] or vanadium for SO2 sensors [296]. 

Two-phase mixtures of oxides have also been used in mixed potential sensors. Such examples include Cr2O3 + NiO [297] for NO sensors, CuO + ZnO [298, 299] or SnO2 + CdO [300] for CO sensors, and In2O3 + MnO2 [301, 302] for hydrocarbon sensors. Some examples ofthe outputs of NO -and CO sensors with two-phase oxide mixtures as electrodes are shown in Figure 13.24 [270, 297, 298, 300]. 

Mukundan, R.. Brosha, E.L., Brown, D.R. and Garzon, F.H. (1999) Ceria-electrolyte-based mixed potential sensors for the detection of hydrocarbons and carbon monoxide. Electrochem. Solid-State Lett.. 2 (12), 412-14. 

Lalauze, R., Visconte, E., Montanaro, L. and Pijolat, C. (1993) A new type of mixed potential sensor using a thick film of beta alumina. Sens. Actuators B, 13-14, 241-3. 

Szabo, N.F. and Dutta, P.K. (2004) Correlation of sensing behavior of mixed potential sensors with chemical and... 

F., Vashook, V. and Guth, U. (2008) Perovskite related electrode materials with enhanced no sensitivity for mixed potential sensors. Solid State Ionics, 179, 1628-31. 

F. (2003) The role of heterogeneous catalysis in the gas-sensing selectivity of high-temperature mixed potential sensors. Proceedings of the Electrochemical Society, 2002—26 Solid-State Ionic Devices 111, The Electrochemical Society, Pennington, New Jersey, pp. 261—71. 

In 2005, it was experimentally found that the slow recovery rate to NO2 of the YSZ-based mixed-potential sensor with the NiO-SE can be significantly improved when the sample gas was humidified with 5 vol. % water vapor. These results were published in 2006 [13]. Figure 2.12 [41] illustrates numerical and experimental values for the response/recovery transients to 400 ppm NO2 in 5 vol. % O2 with a N2 balance in the absence (a) and presence (b) of 5 vol. % H2O at 850°C. Sample... 

Brosha, E.L. et al.. Development of ceramic mixed potential sensors for automotive... 

The mixed potential developed is a function of various electrode parameters including, morphology, adsorption, catalytic, and electrocatalytic properties [54], To get a measurable potential difference between two electrodes, there must be asymmetry between them. Therefore, in most of the mixed-potential sensors the RE is usually Pt and the SE is oxide and/or an oxide mixture [13]. As a result, depending on the nature of the SE, it is possible that both reducible and oxidizable gases can be analyzed by the single sensor having a simple design. 

Consequently, it can be concluded that the enhancement of the NO2 sensitivity and selectivity for the zirconia mixed-potential sensors with the oxide-SE will be focused on the technological improvements in fabrication of the SE. Eurther development of the sintering technology for the SE will be based on predicted calculation of how the initial binary oxide mixtures will be transferred into solid solutions with domination of one oxide phase and trace of another. In these solid solutions, the electrode kinetic of the bulk reactions within the SE will be responsible for sensitivity and selectivity of the sensor. 

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