Mercury vapor sensor

One of the simplest, albeit least discussed, chemiresistors is the mercury vapor sensor. The heart of this device is a thin (7-40 nm) film of gold evaporated on a ceramic or glass substrate. At such thicknesses, the films are continuous, with the resistivity between 300 and l,500Qcm. The sensors are usually connected as a pair in a DC bridge configuration with one sensor acting as the reference. 

Sabri YM, KojimaR, Ippolito SJ, Wlodarski W, Kalantar K, Kaner RB, Bhargava SK (2011) QCM based mercury vapor sensor modified with polypyrrole supported palladium. Sens Actuator B Chem 160(l) 616-622. doi 10.1016/j.snb.2011.08.038... 

Fig. 8.5 Thin Au film sensor for mercury vapor and other adsorbing species...

Fig. 15.1. Chemical sensors for detection of mercury vapor. The thickness of the gold electrodes is 42 nm. The sensor geometry is shown schematically and cannot be used for recalculation of the total length.

Although the sensor signal is changed during about 30-40 min after exposure to mercury vapor, an estimation of the concentration can be performed from the data measured within the first 5-10 min. 

McNicholas, T. E, Zhao, K., Yang, C., Hernandez, S. C., Mulchandani, A., Myung, N. V. and Deshusses, M. A. (2011), Sensitive Detection of Elemental Mercury Vapor by Gold-Nanoparticle-Decorated Carbon Nanotube Sensors , Journal of Physical Chemistry C, 115,13927-31. 

EPA and ATSDR accept Jerome findings for cieanup. With on-board data iog-ging, battery powered sensor regeneration, and storage of 20,000 data points, the Jerome J405 is the best instrument for mercury vapor detection on the market. Find out more at www.azic.com. 

The generation of UV light is typically achieved by placing a voltage across a gas mixture contained in lamp tubes. The gas is temporarily excited by the voltage and emits photons as it returns to a lower energy state. The gas mixture determines the wavelength emitted. Common lamp types are mercury vapor, metal halide, pulsed UV, and excimer or LED. The most common water treatment lamp is the mercury vapor. A typical system consists of the UV lamps, reactor, ballasts, lamp sleeves, and sensors. ... 

A quartz plate equipped with a gold electrode on each face can detect the adsorption of mercury vapor on the gold. A carbon monoxide sensor can therefore be constructed since this gas reacts with mercury oxide at 210 liberating mercury vapor [224] which is detectable with the piezoelectric sensor. Similarly, the deposition of copper complexes on a quartz crystal is used to detect organophosphates [225] such as diisopropylmethylphosphonate (DIMP), and modified cyclodextrins are us to detect benzene vapors [226]. The piezoelectnc sensor is also used in the liquid phase to monitor the viscosity of fluids and gelation, and deduce, for example, the concentration of fibrinogen [227]. 

The sensor is based on high affinity of gold to mercury and on chemo-resistive properties of ultrathin gold layers adsorption of mercury leads to increase in the surface resistance [1,2]. However, this effect is not selective similar changes are caused by adsorption of water vapor and sulfuric compounds. The use of monomolecular layer of alkylthiols as a filter excludes this interference completely [3]. Sensor calibration is performed by thermoinjection of nanogram-amount of mercury quantitatively deposited by electrochemical reduction [4],... 

A simple distilling apparatus that can be nsed for this experiment is shown in Fig. 4. The mercury thermometer bulb (or any other thermometer sensor) should be about level with the side arm to the condenser so that the temperature of coexisting vapor and Uqnid is measured. Except when samples of distillate are being taken for analysis, an adeqnate receiving flask should be placed at the lower end of the condenser. 

The electrode elements of an electrochemical sensor are often metallic, semiconductive, or inert. For metallic electrode elements, noble metals such as gold, platinum, and silver are often used in conventional electrochemical sensors. Mercury or amalgam as electrode materials for microfabricated electrochemical sensors are seldom used due to the difficulty involved. Because mercury has a relatively high vapor pressure, it does not lend itself well in any fabrication process using a vacuum or low-pressure environment. The formation of amalgam requires the use of mercuric ion containing reagent. This step can be elaborate and complicated. 

The WE, typically a cathode, is generally where the reaction of interest occurs. Typical WEs (see Chapters 5 and 6) include the noble metals (especially gold and platinum), carbon (including pyrolytic carbon, glassy carbon, carbon paste, nanotubes, and vapor-deposited diamond), liquid metals (mercury and its amalgams), and semiconductors (indium-tin oxide. Si, see Chapter 9). WEs can be chemically modified (see Chapter 8) in order to increase their sensitivities toward specific species (i.e., become chemical sensors) or to decrease the potential required to drive a particular reaction (i.e., catalysis). 

The direct pressure measurement has the advantage that absolute pressures can be obtained and pressure fluctuations can be observed. More modem equipment applies electronic pressure sensors instead of Hg-manometers to avoid the problems caused by the contact of solvent vapor with the mercury surface and to get a better resolution of the measuring pressure. 

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