Transpiration and Mass Spectrometric Studies of Equilibria Involving BOF(g) and (BOF)3(g)

The reaction of BF3(g) with B2O3(l) was studied by the transpiration method in the temperature range 600° to 1100°K. Results indicate the reaction to be BF3(g)+B2O3(l)=(BOF)3(g).ΔH298° was found to be 4.2 kcal, and leads to ΔHf298°=—566.8±1 kcal/mole for (BOF)3(g). The vapor above mixtures of MgF2 and B2O3 contained in a Knudsen cell was analyzed with a mass spectrometer and was found to contain BF3(g), (BOF)3(g), and BOF(g) in the range 980° to 1230°K. From studies of the temperature dependence of appropriate ion intensities the heat of the reaction (BOF)3(g)=3BOF(g)was derived as 131 kcal at 1125°K. Use of low ionizing electron energies was required to avoid fragmentation effects. The heat of formation of BOF(g) at 298°K was calculated to be —144±3 kcal/mole.