Conference Paper

Hydrogen Sensor for Oil Transformer Health Monitoring

Appl. Nanotech, Inc., Austin, TX
DOI: 10.1109/NANO.2008.69 Conference: Nanotechnology, 2008. NANO '08. 8th IEEE Conference on
Source: IEEE Xplore

ABSTRACT A hydrogen sensor for detection of H2 dissolved in transformer oil has been developed for the use in a stand-alone dissolved gas analyzer (DGA) which will also assess the relative humidity saturation of oil. The sensor uses palladium nanoparticles as a sensitive material that is selective to hydrogen. The DGA will be capable of measuring dissolved hydrogen in concentrations from 50 ppm to 4000 ppm.

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    ABSTRACT: In situ X-ray diffraction (XRD) measurements for Pd-clusters (3.8 and 6.0 nm) are performed during hydrogen loading and unloading. The lattice parameter increases as a function of the hydrogen partial pressure. The expansion is smaller than that of bulk palladium and is shown to be cluster-size dependent. An (α–α′) phase transition was observed for the large clusters but small clusters do not show this transition. XRD analysis of the as-prepared clusters show that the 3.8-nm sized clusters predominantly have an icosahedral structure, while the 6.0-nm sized clusters have a cubic structure. The effect of size and structure of the cluster on the lattice expansion and on the phase transition will be discussed.
    Journal of Alloys and Compounds 01/2003; 356:644-648. · 2.73 Impact Factor
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    ABSTRACT: The hysteresis effect observed in the palladium-hydrogen system when the pressure of the gas is taken through a cycle of changes has been examined by the X-ray method. Measurements of the parameter of charged palladium at different pressures were made when the temperature was kept constant. When the pressure was increased and the temperature kept at 100° C. the α phase appeared alone up to a pressure of about 20 cm. of mercury, the parameter increasing as the pressure was increased. Between pressures of 20 and 45 cm. of mercury the α and β phases appeared together and on further increase of pressure the β phase appeared alone. With decreasing pressures, starting from an initial pressure of 66 cm. of mercury, the β phase appeared alone until a pressure of about 21 cm. of mercury was reached. Over the range of pressure from 21 to about 17 cm. of mercury the α and β phases appeared together, but at a pressure of 17 cm. of mercury the β phase disappeared, the α phase remaining alone until the pressure was reduced to zero. Those parts of the ascending or descending isothermals in which a single component existed, could be retraced by altering the pressure but this reversibility disappeared when the second component made its appearance. The concentration of hydrogen in palladium changed rapidly when the β phase appeared or disappeared. The measurements support the view that the palladium-hydrogen system consists of two solid solutions at the two temperatures chosen, namely 100° and 120° C., the hydrogen rich phase being closely associated with the combination Pd2H, which is capable of taking hydrogen into solution. The β phase lattice was always found to be distorted; every attempt to obtain this phase free from distortion failed. No such distortion was found with the α phase. The distortion of the β phase lattice remained after the gas had been removed from the metal. It required a temperature well above that necessary to displace the hydrogen from the metal to remove the distortion. It is concluded that the gas is not in its normal state when it leaves the metal.
    Proceedings of the Physical Society. 12/2002; 49(5):603.
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    ABSTRACT: In this work we have studied the steady-state reaction of molecular and atomic hydrogen with oxygen on a Pd(111) surface at a low total pressure (<10(-7) mbar) and at sample temperatures ranging from 100 to 1100 K. Characteristic features of the water formation rate Phi(pH2; pO2; TPd) are presented and discussed, including effects that are due to the use of gas-phase atomic hydrogen for exposure. Optimum impingement ratios (OIR) for hydrogen and oxygen for water formation and their dependence on the sample temperature have been determined. The occurring shift in the OIR could be ascribed to the temperature dependence of the sticking coefficients for hydrogen (SH2) and oxygen (SO2) on Pd(111). Using gas-phase atomic hydrogen for water formation leads to an increase of the OIR, suggesting that hydrogen abstraction via hot-atom reactions competes with H2O formation. The velocity distributions of the desorbing water molecules formed on the Pd(111) surface have been measured by time-of-flight spectroscopy under various conditions, using either gas-phase H atoms or molecular H2 as reactants. In all cases, the desorbing water flux could be represented by a Maxwellian distribution corresponding to the surface temperature, thus giving direct evidence for a Langmuir-Hinshelwood mechanism for water formation on Pd(111).
    The Journal of Chemical Physics 03/2004; 120(8):3864-70. · 3.12 Impact Factor


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