Thermochemistry of Aluminum Species for Combustion Modeling from Ab Initio Molecular Orbital Calculations

High accuracy ab initio methods for computational thermochemistry have been applied to aluminum compounds expected to be present during combustion of aluminum particles. The computed enthalpies of formation at 298.15 K agree well with experimental values from the literature for AlCl, AlCl3, AlO, AlOAl, linear OAlO, planar Al2O2, AlOH, AlH, and AlN. The agreement is fair for AlCl2. Major revisions to the recommended thermochemistry must be considered for OAlCl, OAlH, OAlOH, and AlC. This is not surprising since the thermodynamic data for OAlCl, OAlH, OAlOH, and AlC are given in the literature as rough estimates. Calculated thermochemical data are also presented for several species never studied experimentally, including AlH2, AlH3, AlOO, cyclic-AlO2, linear AlOAlO, AlHCl, AlHCl2, and others. Based on the performance of the CBS-Q and G2 methods observed in other systems, the calculated enthalpies of formation would be expected to be accurate to within 61 to 2 kcal mol. However, relatively large differences between the results from the CBS-Q and G2 methods for the aluminum oxides indicate that the uncertainties are slightly larger for these compounds. The thermochemistry proposed here is shown to predict substantially different equilibrium composition from the thermochemistry previously available in the literature. © 2000 by The Combustion Institute