AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS1-TuA

Paper PS1-TuA4
Microhollow Cathode Discharge Microreactor Chemistry

Tuesday, November 5, 2002, 3:00 pm, Room C-103

Session: Microdischarges
Presenter: D.D. Hsu, University of California, Berkeley
Authors: D.D. Hsu, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
The peak neutral temperature of a microhollow cathode discharge (MHCD) has been found from optical emission spectroscopy to be on the order of 2000 K, although adjacent temperatures rapidly drop off to near room temperature. These thermal properties suggest that MHCDs are suited to promote endothermic chemical reactions. Thin-film resistive heaters often are employed to heat reactants in microreactors. Unlike resistive heaters, the electrical power of the microdischarge heats the gas directly, offering the possibility of higher peak temperatures and greater energy efficiency. Ammonia decomposition is a highly endothermic reaction, and such a reaction could be used as a source of hydrogen for a microfuel cell. Pure ammonia was flowed through a 200 µm diameter microhollow cathode at flowrates up to 64 sccm and pressures up to atmospheric pressure. Ammonia conversion was measured by FTIR, and production of hydrogen and nitrogen was monitored by a mass spectrometer. A discharge at 490 V and 9 mA converted 16 percent of ammonia flowing at a rate of 2.5 sccm at 100 Torr. Conversion was largely dependent on the residence time of the gas in the plasma. Based on published kinetic data, the conversion and residence time data are consistent with thermal decomposition at temperatures near 3000 K. We discuss the behavior of these microplasmas as reactors for ammonia and other chemistries, and we explore methods for increasing reaction conversion.