David L. West

Electrically Biased NO x Sensing Elements with Coplanar Electrodes

Fabrication and characterization of electrically biased NO x sensing elements operative at 500-600°C are described. The sensing elements were produced by screen-printing Pt and transition metal oxide electrodes on yttria-stabilized zirconia substrates. DC electrical biasing greatly enhanced the response of the sensing elements to nitric oxide (NO), with voltage changes on the order of 10% observed as the sensing response to 450 ppmv NO at 600°C and 7 vol % O 2 . Voltage and current biasing techniques were employed with a sensing element using NiCr 2 O 4 as the oxide, and the computed changes in resistance due to NO were nearly identical, suggesting that the response mechanism of the elements is a change in dc electrical resistance. The sensing response was minimally affected by O 2 concentrations between 7 and 20 vol % at [NO] concentration levels from 0 to 1500 ppmv. These sensing elements and techniques may be useful in sensors for measuring [NO] at temperatures near 600°C.

Stable and selective sulfur dioxide sensing elements operating at 800–900 centigrade

Sensing behavior of electrochemical transducers for the detection of sulfur dioxide (SO2) is described. These elements operate at temperatures in the range 800-900 °C, and are constructed from oxide and precious metal electrodes on oxygenion conducting substrates. The responses to SO2 at oxygen contents around 5% can be large, with 25 ppm SO2 causing a 30-40% change in the sensing signal. This SO2 response is shown to be little affected by oxides of nitrogen (NOx), carbon monoxide, and propylene, present at the 100s of ppm level. Element stability is demonstrated over about 50 days of operation at temperature.

Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury

The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering the beam “window”, through which the high-energy proton beam passes, with a protective layer of gas. The difficulty lies in establishing a stable gas/liquid interface that is oriented vertically with the window and holds up to the strong buoyancy force and the turbulent mercury flow field. Three approaches to establishing the gas wall have been investigated in isothermal mercury/gas testing on a prototypical geometry and flow: (1) free gas layer approach, (2) porous wall approach, and (3) surface-modified approach. The latter two of these approaches show success in that a stabilized gas layer is produced. Both of these successful approaches capitalize on the high surface energy of liquid mercury by increasing the surface area of the solid wall, thus increasing gas hold up at the wall. In this paper, a summary of these experiments and findings is presented as well as a description of the path forward toward incorporating the stabilized gas layer approach into a feasible gas/mercury SNS target design.Copyright

DETECTION OF SO2 AT HIGH TEMPERATURE WITH ELECTRICALLY BIASED, SOLID-ELECTROLYTE SENSING ELEMENTS

Design and operation of sensing elements for the detection of sulfur dioxide (SO2) at high temperature (800 900 oC) is described. The sensing elements consisted of three (two oxide and one Pt) electrodes on yttria-stabilized zirconia substrates. To operate the elements, a constant current (usually on the order of 0.1 mA) was driven between two of the electrodes and the voltage between one of these electrodes and the third electrode was monitored and used as the sensing signal. In one example, 31 ppm SO2 caused an approximately 40% change in the element output, and 2 ppm of SO2 could be easily detected. The cross-sensitivity to several interferents such as NOx was evaluated and found to be relatively small in comparison to the SO2 response.

Supply Chain Based Solution to Prevent Fuel Tax Evasion: Proof of Concept Final Report

The goal of this research was to provide a proof-of-concept (POC) system for preventing non-taxable (non-highway diesel use) or low-taxable (jet fuel) petrochemical products from being blended with taxable fuel products and preventing taxable fuel products from cross-jurisdiction evasion. The research worked to fill the need to validate the legitimacy of individual loads, offloads, and movements by integrating and validating, on a near-real-time basis, information from global positioning system (GPS), valve sensors, level sensors, and fuel-marker sensors.

High-T NOx Sensing Elements Using Conductive Oxides and Pt

Development of NOx sensing elements intended for operation at T ∼600 °C are described. The elements were fabricated by depositing co-planar La1-x Srx BO3 (B = Cr, Fe) and Pt electrodes on yttria-stabilized zirconia substrates. Characterization of the elements included response to NO2 and NO as well as the [O2 ] dependence of the NO2 response. Much stronger (∼ 40 mV for 450 ppm NO2 in 7 vol% O2 at 600 °C) sensing responses were observed for NO2 than NO, indicating these elements are best suited for detection of NO2 . Pronounced asymmetries were observed between the NO2 step response and recovery times for the elements, with temperature being the primary variable governing the recovery times in the temperature range 500–700 °C.Copyright