FLAME INHIBITION BY FERROCENE AND BLENDS OF INERT AND CATALYTIC AGENTS

摘要

The production of the fire suppressant CF_3Br has been banned, and finding a replacement with all of its desirable properties is proving difficult. Iron pentacarbonyl has been found to be up to several orders of magnitude more effective than CF_3Br, but it is flammable and highly toxic. Ferrocene [Fe(C_5H_5)_2], which is much less toxic and flammable than Fe(CO)_5, can also be used to introduce iron into a flame. We present the first experimental data and numerical modeling for flame inhibition by ferrocene and find it to behave similarly to Fe(CO)_5. A ferrocene mole fraction of 200 ppm reduced the burning velocity of slightly preheated premixed methane/air flames by a factor of two, and the effectiveness dropped off sharply at higher mole fractions. For air with a higher oxygen mole fraction, the burning velocity reduction was less. We also present experimental data and modeling for flames with ferrocene blended with CO_2 or CF_3H. The combination of the thermally acting agent CO_2 with ferrocene mitigated the loss of effectiveness experienced by ferrocene alone at higher mole fractions. An agent consisting of 1.5% ferrocene in 98.5% CO_2 performed as effectively as CF_3Br in achieving a 50% reduction in burning velocity. Likewise, four times less CO_2 was required to achieve the 50% reduction if 0.35% ferrocene was added to the CO_2. In contrast, addition of 0.35% ferrocene to the hydrofluorocarbon CF_3H reduced the CF_3H required to achieve the 50% reduction in burning velocity by only about 25%. Thermodynamic equilibrium calculations predict that the formation of iron/fluoride compounds can reduce the concentrations of the iron-species oxide and hydroxide intermediates which are believed to be responsible for the catalytic radical recombination cycles.