High Temperature Oxidation Chemical Kinetics and Thermodynamics of the Alkali Metals

摘要

The present phase of the research to understand the high temperature oxidation chemistry of the alkali metals in flames now has been completed and has successfully explained their behavior. This basic understanding is a fundamental and initial step in resolving their nature as suppressants of gun muzzle flash and rocket afterburning. The flame chemistries of lithium, sodium and potassium now have been completely resolved and those of the two remaining alkalis, rubidium and cesium, require only final analysis but appear to follow the general observed patterns of behavior. This laser induced fluorescence study, using a matrix of about then fuel-lean diatomic hydrogen/oxygen/nitrogen flames of a large variety of stoichiometries and having different flame temperatures with alkali metals of different kinetic and thermochemical properties is a particularly severe test for any analysis. Because of this, there is a significant confidence in the derived values of the dissociation energies of the MOH and MO2 compounds. Moreover, the kinetic rate constants obtained for these high temperatures are consistent with lower temperature literature values in all cases where such data exist. Additionally, the kinetics whereby oxidation is predominantly via reactions with O2 and water, and regeneration is via reactions with flame radicals, principally hydroxyl, provides a kinetic cycle in which the alkali metal can reduce radical concentration levels. Undoubtedly, this is one, if not the principal mechanism explaining the inhibition of gun muzzle flash by these salts and merits further studies but not with larger concentrations of alkali salts.