ant value, -451.25 ± 0.52 kcal. per mole, was combined with the values for the heat of formation of amorphous B2O3, -300.0 ± 0.7 kcal. per mole (3), and with the heat of formation of Ti02 (rutile) (5, 9) -225.4 ± 0.2 to give -77.4 ± 0.9 kcal. per mole for the heat of formation of TiB2.022 ±o.oo6, as shown in the following equations: Ti02 + 1.011 203-± 2"22+ 2.516 02 + 451.25 ± 0.52 kcal.2.022B + 1.516 02 -1.011 B203-303.3 ± 0.71 kcal.Ti + 02 -> Ti02 -225.4 ± 0.2 kcal.Ti + 2.022B -2 TiB2,o22-77.4 ± 0.9 kcal.This value is somewhat more negative than those reported earlier. If it is assumed that most of the oxygen was present as B2O3 instead of Ti02, both the original formula of the material and the heat of formation lie well within the stated uncertainties.
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