The kinetics of the B₂H₆/O (³P) system at room temperature

An experimental study of the kinetics of the B₂H₆/O (³P) system at room temperature, is presented. Modeling was based on a multiple‐parameter fitting process to a complex kinetic mechanism. The aim of the study was to propose and evaluate a preferred set of elementary reactions which might be important for the oxidation of boron‐hydrides. In this study, relative concentration‐vs.‐time profiles of the radicals OH and BO₂ were measured in a low pressure flow reactor, by the technique of laser‐induced‐fluorescence. A range of almost two orders of magnitude in the initial fuel to oxygen ratio was covered, while the residence times of the gases in the reactor were up to 1 s. A comprehensive kinetic mechanism was constructed from the available measured and estimated data in literature. After the fitting process and dropping all of the reactions with negligible contribution, a 46 elementary reactions mechanism was obtained. In this mechanism, 27 reactions are not measured and their rate coefficients were used as the adjustable (within reasonable limits deduced from kinetic and thermodynamic considerations) parameters of the fitting process. Good agreement was obtained between all of the measured and calculated profiles. From sensitivity analysis it was found that only a limited group of these reactions highly contributes to the calculated concentrations of OH and BO₂. With only the highly contributing reactions and all the oxygenhydrogen reactions which are measured and relatively well known, a 30 elementary reactions mechanism was obtained. In this mechanism only 13 reactions are not measured and the agreement between the measured and the calculated profiles is still reasonable. To demonstrate the possible usefulness of the proposed mechanism, the rate coefficient of the reaction B₂H₆ + OH → B₂H₅ + H₂O which was not measured before, was directly measured in our experimental set‐up. The rate coefficient that was obtained in the direct measurement is (3.3 ± 1.1) × 10¹¹ cm³mol⁻¹s⁻¹, in excellent agreement with the predicted one by the multiple‐parameter‐fitting process, which was 2 × 10¹¹ cm³mol⁻¹s⁻¹. © 1995 John Wiley & Sons, Inc.