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Effect of heating on dissociation of water vapor in high-frequency plasmas and formation of hydrogen peroxide in a cold trap downstream of the plasma

Journal Article · · Plasma Chem. Plasma Process.; (United States)
DOI:https://doi.org/10.1007/BF00633131· OSTI ID:5345101
;

At low flow rates (0.7-2.8 mmol hr/sup -1/) and long residence times (2.3-8.5 s) nearly 60% of the input water vapor was decomposed by a 13.56-MHz rf discharge. Downstream of the discharge a trap cooled by liquid nitrogen collected nearly constant yields of H/sub 2/O/sub 2/. The decomposition is representable by the equation 2H/sub 2/O = H/sub 2/O/sub 2/ + H/sub 2/. The overall rate of decomposition was found to depend on the absorbed power density. Heating the rf plasma and its spatial afterglow from 25 to 600/sup 0/C did not significantly change the percent decomposition of H/sub 2/O and the formation of H/sub 2/O/sub 2/. Above 600/sup 0/C, however, a continuous decrease in H/sub 2/O/sub 2/ yield was observed with increasing temperature, and this was associated with the increasing formation of H/sub 2/O from the dissociated products such as highly excited OH radicals which otherwise produce the precursors of H/sub 2/O/sub 2/. The same heating effects were observed in the case of the spatial afterglow of a 2.45-GHz microwave cavity discharge in water vapor under essentially similar conditions. It appears that at the high temperatures the reaction OH + OH..-->..H/sub 2/O + O is favored over the reaction O + OH..-->..O/sub 2/ + H. This limits the formation of O/sub 2/ and consequently decreases the H/sub 2/O/sub 2/ yield.

Research Organization:
Western Illinois Univ., Macomb, IL
OSTI ID:
5345101
Journal Information:
Plasma Chem. Plasma Process.; (United States), Journal Name: Plasma Chem. Plasma Process.; (United States) Vol. 2:2; ISSN PCPPD
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
COLLISIONS
COOLING
DISSOCIATION
ELECTRIC DISCHARGES
ELECTRON COLLISIONS
ELECTRON TUBES
ELECTRON-MOLECULE COLLISIONS
FLUIDS
GAS DISCHARGE TUBES
GASES
HEATING
HIGH-FREQUENCY DISCHARGES
HIGH-FREQUENCY HEATING
HYDROGEN COMPOUNDS
HYDROGEN PEROXIDE
KINETICS
MICROWAVE HEATING
MOLECULE COLLISIONS
OXYGEN COMPOUNDS
PEROXIDES
PLASMA
PLASMA HEATING
REACTION KINETICS
SYNTHESIS
TEMPERATURE EFFECTS
VAPORS
WATER VAPOR
YIELDS