Solid-state sensors performance

Lin Q, Jiang F, Wang X-Q, Han Z, Tai Y-C, Lew J, Ho C-M (2000) MEMS Thermal Shear-Stress Sensors Experiments, Theory and Modehng, Technical Digest, Solid State Sensors and Actuators Workshop, Hilton Head, SC, 4—8 June 2000, pp 304-307 Lin TY, Yang CY (2007) An experimental investigation of forced convection heat transfer performance in micro-tubes by the method of hquid crystal thermography. Int. J. Heat Mass Transfer 50 4736-4742... 

Most solid-state sensors are heated to well above 100°C and can operate in the "cold start" condition in a fuel cell. Another important performance parameter for a hydrogen sensor in a fuel cell is its resistance to water entry. Most fuel cells have excess of liquids including water during operation. It is highly possible that water will splash or penetrate into the hydrogen sensor mounted in the ventilation or outlet of a fuel cell. Hydrophobic... 

The performance of common multisensor arrays is ultimately determined by the properties of their constituent parts. Key parameters such as number, type and specificity of the sensors determine whether a specific instrument is suitable for a given application. The selection of an appropriate set of chemical sensors is of utmost importance if electronic nose classifications are to be utilised to solve an analytical problem. As this requires time and effort, the applicability of solid-state sensor technology is often limited. The time saved compared with classic analytical methods is questionable, since analysis times of electronic nose systems are generally influenced more by the sampling method utilised than the sensor response time [185]. 

To optimize the OLED-based hydrazine sensor performance, the OLED pulse width and voltage were varied. The optimal values were found to be 20 ps and 30 V, respectively. The corresponding results of the change in the PL of the hydrazine/ADA solution are shown in Fig. 3.16. They clearly show that the LOD of hydrazine by this system is 60 ppb in 1 min, i.e., roughly equivalent to 1 ppb in 1 h. That is, the sensitivity of this system exceeds the OSH A requirements by a factor of 80. Methods to develop ADA-based solid state sensors are currently being explored. 

A new kind of all solid-state sensors was first reported by Cattrall and Preiser in 1971 in which the internal reference element was in direct contact with the sensing membrane and thus contained no aqueous solution. The first group of such simplified sensors was those of the so-called coated wire construction type (CWE). In this approach, a metal wire was dipped with a solution of PVC in THF containing also a suitable electroactive material. During evaporation of the solvent, a PVC film on the metal wire surface was formed. Although different materials such as platinum, silver or sliver chloride, and aluminum could serve as central conductors, the nature of the wire support had no substantial influence on the electrode performance if it did not react with the membrane components. ... 

Poor adhesion of membrane to metal is the leading cause of failure in solid-state potentiometric sensors [116], For glass membranes, the mismatch of thermal coefficients of expansion between thin glass membrane and metal (mostly Pt) has been attributed to premature failure due to hairline crack formations in the glass layer [60], For polymer-based membranes, water vapor penetration was reported to compromise the membrane-metal interface, therefore affecting the sensor s performance. 

In this review the basis for the chemical sensitivity of these devices will be explored and the various device structures used for these sensors will be discussed. A survey of the performance of the diode-type and capacitor-type structures will be presented and a comparison of characteristics of these two classes of solid state gas sensors will be given. 

Conducting polymers have been studied as potentiometric ion sensors for almost two decades and new sensors are continuously developed. The analytical performance of solid-state ion sensors with conducting polymers as ion-to-electron transducer (solid-contact ISEs) has been significantly improved over the last few years. Of particular interest is the large improvement of the detection limit of such solid-contact ISEs down to the nanomolar level. Further optimization of the solid contacts as well as the ion-selective membranes will most certainly extend the range of practical applications. 

Ion selective membranes are the active, chemically selective component of many potentiometric ion sensors (7). They have been most successfully used with solution contacts on both sides of the membrane, and have been found to perform less satisfactorily when a solid state contact is made to one face. One approach that has been used to improve the lifetime of solid state devices coated with membranes has been to improve the adhesion of the film on the solid substrate (2-5). However, our results with this approach for plasticized polyvinylchloride (PVC) based membranes suggested it is important to understand the basic phenomena occurring inside these membranes in terms of solvent uptake, ion transport and membrane stress (4,6). We have previously reported on the design of an optical instrument that allows the concentration profiles inside PVC based ion sensitive membranes to be determined (7). In that study it was shown that water uptake occurs in two steps. A more detailed study of water transport has been undertaken since water is believed to play an important role in such membranes, but its exact function is poorly understood, and the quantitative data available on water in PVC membranes is not in good agreement (8-10). One key problem is to develop an understanding of the role of water uptake in polymer swelling and internal stress, since these factors appear to be related to the rapid failure of membranes on solid substrates. 

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

PEVD has been applied to deposit auxiliary phases (Na COj, NaNOj and Na SO ) for solid potenfiometric gaseous oxide (CO, NO, and SO ) sensors, as well as a yttria stabilized zirconia (YSZ) ceramic phase to form composite anodes for solid oxide fuel cells. In both cases, the theoretically ideal interfacial microstructures were realized. The performances of these solid state ionic devices improved significantly. Eurthermore, in order to set the foundation for future PEVD applications, a well-defined PEVD system has been studied both thermodynamically and kinetically, indicating that PEVD shows promise for a wide range of technological applications. 

The present availabihty of numerous types of solid electrolytes permits transport control of various kinds of mobile ionic species through those solid electrolytes in solid electrochemical cells, and permits electrochemical reactions to be carried out with the surrounding vapor phase to form products of interest. This interfacing of modem vapor deposition technology and solid state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). PEVD has been applied to fabricate two types of solid state ionic devices, i.e., solid state potenfiometric sensors and solid oxide fuel cells. Investigations show that PEVD is the most suitable technique to improve the solid electrolyte/electrode contact and subsequently, the performance of these solid state ionic devices. 

Improvement of the geometric structure of the working electrode by a well-controlled PEVD process benefits the performance of a CO sensor in many ways. To optimize kinetic behavior, the response and recovery times of CO potentiometric sensors were studied at various auxiliary phase coverages. This was realized by a unique experimental arrangement to deposit the Na COj auxiliary phase in-situ at the working electrode of type III potentiometric CO sensors by PEVD in a step-wise fashion. Since the current and flux of solid-state transported material in a series of PEVD processes can be easily moiutoredto control the amount of deposit... 

The performance of the photomultiplier (representative of a very fast responding sensor even in terms of modern solid state devices) is shown in the lower curves and its performance is in complete contrast to that of the cadmium sulfide cell. The time constant, determined again from the slope of the log curve, was found to be only 40 milliseconds. Such a response time is generally acceptable for most GC and LC separations. Nevertheless in both fast GC and fast LC solutes can be eluted in less than 100 milliseconds in which case an... 

Ono, T., Hasei, M., Kunimoto, A., and Miura, N. 2004. Improvement of sensing performances of zirconia-based total NO sensor by attachment of oxidation-catalyst electrode. Solid State Ionics 175, 503-506. 

Pasierb. P., Komornicki, S., Gajerski, R., Kozinski. S. and Rfkas, M. (2003) The performance and long-time stability of potentiometric CO2 gas sensors based on the (Li-Ba)COj NASICON (Na-Ti-O) electrochemical cells. Solid State Ionics,... 

Satyanarayana, L., Choi, G.P., Noh, W.S., Lee, W.Y and Park, J.S. (2007) Characteristics and performance of binary carbonate auxiliary phase CO2 sensor based on Li3PO4 solid electrolyte. Solid State Ionics, 177 (39-40). 3485-90. 

D.K. and Meng, G.Y (1996) Performance evaluation of SO (x = 2.3) gas sensors using Ag-p-alumina solid elech olyte. Solid State Ionics, 86-88, 1095-9. 

Elumalai, P. and Miura, N. (2005) Performances of planar NO2 sensor using stabdized zirconia and NiO sensing electrode at high temperature. Solid State Ionics, 176, 2517-22. 

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