Palladium sensors

There are three major classes of palladium-based hydrogen sensors [4], The most popular class of palladium-based sensors is based on palladium resistors. A thin film of palladium deposited between two metal contacts shows a change in conductivity on exposure to hydrogen due to the phase transition in palladium. The palladium field-effect transistors (FETs) or capacitors constitute the second class, wherein the sensor architecture is in a transistor mode or capacitor configuration. The third class of palladium sensors includes optical sensors consisting of a layer of palladium coated on an optically active material that transforms the hydrogen concentration to an optical signal. 

One attractive feature of the palladium sensor is that it does not require operation at elevated temperatures like the metal oxides and can therefore realize significant power consumption savings. 

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

Fig.4.12. The sample construction 1 - polished quartz plate 2 — semiconductor sensor (ZnO) i - a strip of marblyte glass 4 - a layer of titanium (palladium) X = 0.027 cm ( the length of surface migration of H atoms h = 0.0025 cm ( the air gap between the quartz plate and the glass strip).

Fig. 4.17. Kinetics of variation of electric conductivity of ZnO sensor following leaking-in H2 into the reaction cell and subsequently pumping it out (indicated by pointer) before (curve /) and after O - 4) activation of the working plate with palladium 0pj = 510 5 cm 2, = 6.7 Pa, T = 295 K O), 378 K (3),...

Resonant photoacoustic gas spectrometry was adapted to fiber optic sensor technology32 as early as in 1984. A Mach-Zehnder arrangement was combined with a resonant photoacoustic cell for gap analysis. The pollutant gas NO2 was detectable in a concentration of 0.5 ppm. In a smart optical fiber hydrogen sensor, the fiber is coated with palladium metal which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometry33. 

A wide variety of solid-state sensors based on hydrogen-specific palladium, metal oxide semiconductor (MOS), CB, electrochemical, and surface acoustic wave (SAW) technology are used in the industry for several years. Microelectromechanical systems (MEMS), and nanotechnology-based devices for the measurement of hydrogen are the recent developments. These developments are mainly driven by the demands of the fuel cell industry. Solid-state approaches are gaining rapid popularity within the industry due to their low cost, low maintenance, replacements, and flexibility of multiple installations with minimal labor. 

Operation Mechanisms of Solid-State Sensors 15.3.1 Theory of Palladium-Based Hydrogen Sensors... 

Several types of palladium-based hydrogen sensors have been reported in the literature. The most notable ones are based on Pd thin-film resistors, FETs, Pd nanowires, Pd nanoparticle networks, Pd nanoclusters, and Pd nanotubes as shown in Table 15.2. 

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