Chemical kinetics and thermodynamics of sodium species in oxygen-rich hydrogen flames

Journal Article · Thu Mar 15 04:00:00 EST 1984 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.447052· OSTI ID:5221609

Hynes, A J; Steinberg, M; Schofield, K

Measurements of sodium and OH concentrations in ten oxygen-rich H/sub 2//O/sub 2//N/sub 2/ flames by respective saturated and low-power laser-induced fluorescence techniques have led to a much improved understanding of the complex flame chemistry of sodium in such oxygen-rich media. Previous interpretations have been shown to be largely incomplete or in error. The one-dimensional flame downstream profiles indicate that the amount of free sodium approximately tracks the decay of H atom and as the flame radicals decay sodium becomes increasingly bound in a molecular form. A detailed kinetic model indicates that the sodium is distributed between NaOH, which is dominant, and NaO/sub 2/. Concentrations of NaO are very small and NaH negligible. The actual distribution is controlled by the temperature, the oxygen concentration, and the degree of nonequilibration of the flames' basic free radicals. Na, NaO, NaO/sub 2/, and NaOH are all coupled to one another by fast reactions which can rapidly interconvert one to another as flame conditions vary. NaO/sub 2/ plays an indispensable role in providing alternate efficient channels by which NaOH can be produced. Its contribution becomes increasingly important at lower temperatures where the flux through the NaO/sub 2/ intermediate becomes dominant over that for the direct reaction between Na and H/sub 2/O. As a consequence, the ratio of NaOH to Na can become enhanced by up to two orders of magnitude at lower temperatures over what might have been expected from the Na+H/sub 2/O direct reaction alone. The dissociation energy D/sup 0//sub 0/(Na--O/sub 2/) is established to be 39 +- 5 kcal mol/sup -1/ and the value of the rate constant for the Na+O/sub 2/+M reaction of 2 x 10/sup -28/ T/sup -1/ cm/sup 6/ molecule/sup -2/ s/sup -1/ for the flame gases.

• Research Organization: Quantum Institute, University of California, Santa Barbara, California 93106
• OSTI ID: 5221609
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 80:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKALI METALS
CHEMICAL REACTION KINETICS
COMBUSTION PROPERTIES
ELEMENTS
FLAMES
FLUORESCENCE
HYDROGEN
HYDROXYL RADICALS
KINETICS
LASER SPECTROSCOPY
LUMINESCENCE
METALS
NONMETALS
OXYGEN
RADICALS
REACTION KINETICS
SODIUM
SPECTROSCOPY