Boron and Aluminum Combustion Products

In conjunction with extensive studies of the combustion of boron- and aluminum-based propellant formulations in oxygen/nitrogen/fluorine environments, we have computed the gas phase heats of formation for more than 70 likely products of these processes, as well as AH and AG at 298 K and 2000 K for numerous possible reaction steps [93-97]. Transition states and activation barriers were found for some of these. 

The molecules involved are relatively small, so that CBS procedures were feasible for these calculations. For boron combustion, we initially used both the CBS-Q and the B3PW91 techniques [93], but changed to the superior CBS-QB3 when it became available [94-96], and continuted with it for the aluminum work [97], At this level, the average absolute error in AHf (determined from formation reactions) was less than 2.0 kcal/mole [96,97]. The same accuracy was achieved for AH(298 K), AH(2000 K) and AG(298 K) for the combustion steps examined. It was observed that AH changes very little, by an average of less than 2.0 kcal/mole, in going from 298 K to 2000 K. In contrast, AG(2000 K) can differ quite significantly from AG(298 K), and tends to be less accurate. (Fortunately 

Certain trends can be seen in Tables 1 and 2. A particularly interesting one concerns the effect of substituting the NF2 (difluoramine) 

Calculated gas, liquid and/or solid phase heats of formation and solid phase heat releases.3  

Calculated gas, liquid and/or solid phase heats of formation and solid phase heat releases (continued). a Compound AH/298 Kt. gas AH/298 K). liquid AHfi298 K). solid O-Solid 

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