High-temperature vaporization of B2O3(l) under reducing conditions

The vaporization of B(2)O(3) in a reducing environment leads to the formation of both B(2)O(3)(g) and B(2)O(2)(g). Whereas the formation of B(2)O(3)(g) is well understood, many questions about the formation of B(2)O(2)(g) remain. Previous studies using B(s) + B(2)O(3)(l) have led to inconsistent thermodynamic data. In this study, it was found that, after heating, B(s) and B(2)O(3)(l) appeared to separate and variations in contact area likely led to the inconsistent vapor pressures of B(2)O(2)(g). To circumvent this problem, the activity of boron was fixed with a two-phase mixture of FeB and Fe(2)B. Both second- and third-law enthalpies of formation were measured for B(2)O(2)(g) and B(2)O(3)(g). From these values, the enthalpies of formation at 298.15 K were calculated to be -479.9 ± 25.7 kJ/mol for B(2)O(2)(g) and -833.4 ± 13.1 kJ/mol for B(2)O(3)(g). Ab initio calculations to determine the enthalpies of formation of B(2)O(2)(g) and B(2)O(3)(g) were conducted using the W1BD composite method and showed good agreement with the experimental values.