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Synthesis of γ-WO3 By Reactive Spray Deposition Technology for NOx and H2 Sensing

Wednesday, May 14, 2014: 08:00
Sarasota, Ground Level (Hilton Orlando Bonnet Creek)
R. Jain (Department of Materials Science and Engineering at the University of Connecticut), Y. Liu (Department of Chemical and Biomolecular Engineering at the University of Connecticut), Y. Wang (Department of Materials Science and Engineering at the University of Connecticut), Y. Lei (Department of Chemical and Biomolecular Engineering at the University of Connecticut), and R. Maric (Department of Chemical and Biomolecular Engineering at the University of Connecticut, Department of Materials Science and Engineering at the University of Connecticut)
Metal oxide semiconductors such as n-type WO3 has remarkable sensing properties for NOx, NH3, acetone, ethanol, H2 and O3. Sensor response (S) is a function of the conductivity of the WO3 film on interdigited Pt or Au electrodes in given by the following equation:

S = Canalyte/Cair -1

where Canalyte is the conductivity of the film in presence of testing analyte and Cair is the conductivity of the film in air.

The gas detection occurs because of the reaction on the WO3 surface in presence of these gases causing a change in electron concentration and hence fluctuation in electrical conductivity.

In this work Reactive Spray Deposition Technology (RSDT) has been employed as a single step flame based open atmosphere direct deposition process for synthesizing 5-10 nm WO3 particles of primarily γ phase. RSDT is able to synthesize some unique phases of WO3 nano particles by rapidly quenching the particles by a ring of cold air flowing at 28 L/min as soon as they are produced in the hot zone of the flame at temperature around 700 ˚C. The particles reside in the hot zone for 6 milli sec and are quenched immediately.  This causes the formation of some very unique phases and incorporation of defects which are otherwise not stable at room temperature.

The RSDT process with optimization of conditions such as temperature of the flame, flow rate of quench air and residence time of the particles in flame is able to synthesize materials with different structures and varying concentration of dopants. The influence of crystal structures on sensing activities will be largely explored.

The structure and morphology of the WO3 films prepared by RSDT has been probed by XRD, Raman Spectroscopy, BET, mercury porosimetry, profilometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Fig 1 shows the WO3 nano particles synthesized by RSDT.

Fig 2 shows the sensors used for depositing WO3. The as-prepared WO3 sensors will be applied for the detection of NOx and H2 sensitivities in the range of 30-400 ˚C, and characteristics such as sensitivity, limit of detection, reproducibility, stability will be reported. The selectivity for the interfering analytes such as CO2, NO2, SO2 and humidity will also be investigated. Finally the sensing mechanism will be discussed.

See more of: Gas Sensors
See more of: B1: Sensors, Actuators, and Microsystems General Session (Chemical and Biological Sensors)
See more of: Chemical and Biological Sensors
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