Reactions in the system O-2-NO-SiO2 in a conventional furnace - I. Oxygen exchange reactions

Different oxygen exchange reactions have been studied in the NO-O-2-SiO2 sy stem. The exchange rates have been measured by monitoring the isotopic conc entration in a closed system and using isotopic labeled (with N-14, N-15, O -16, and O-18) NO and O-2 gas mixtures. Pressure dependency and activation energies for the different exchange reactions O-2 reversible arrow O-2, O-2 reversible arrow SiO2, O-2 reversible arrow NO, and NO reversible arrow Si O2 have been measured. The oxygen exchange is discussed from the perspectiv e of the reaction occurring on SiO2 during the oxidation of Si. The activat ion energy was the same for the exchange between O-2 molecules catalyzed by SiO2 and oxygen transport in SiO2, and the pressure dependency of the exch ange could explain the pressure dependency of the oxygen transport in SiO2. These two experimental findings indicate that the dissociation of O-2 is t he rate-determining step for oxygen transport. In pure NO the experimental results gave no clear indication, mainly because the exchange rate between NO molecules in the system was too high to be measured and could only be es timated for the lowest pressure (0.1 mbar) and at room temperature. (C) 199 9 The Electrochemical Society. S0013-4651(99)05-016-8. All rights reserved.