Gas Phase Thermochemistry of FeOx(OH)y (x+y = 1-3):
Portrait of a Super-Efficient Flame Suppressant

C. Brian Kellogg and Karl K. Irikura
Physical and Chemical Properties Division
Chemical Science and Technology Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899 USA
Building 222, Room A151

In the search for non-ozone depleting Halon (CF3Br) replacements, several metals, including iron, have been identified as super-efficient flame suppressants. Although some thermochemical data exist for the species which are thought to be most important in iron's flame chemistry, a more complete and accurate characterization of the thermochemistry of iron oxides, hydrides and hydroxides is required for the construction of better kinetic flame models. In this investigation predicted heats of formation (Delta Hf), heat capacities (Cp, Cv) and entropies of several FeOxHx species are reported. The hybrid B3LYP density functional method is employed in conjunction with a relativistic effective core potential on the iron center and a valence triple-zeta basis on all atoms. The coupled-cluster method including single and double excitations and a perturbational estimate of triple excitations [CCSD(T)] is also employed in order to refine the relative energetics of the important species. The predicted thermochemical properties are used to predict the heats of reaction (Delta Hrxn) for several of reactions which may contribute to Iron's outstanding performance as a catalytic flame suppressant.

C. Brian Kellogg / (1/12/98)