Development of oxide melt solution calorimetry for transition metal diborides

Oxide-Melt Solution Calorimetry (OMSC) has been used to investigate standard enthalpies of formation in transition metal diborides, a first for the technique. Formation enthalpies for the Group IV and Group V transition metal diborides have been measured (TiB 2 : Δ f H ⦵ = −280 ± 11 kJ/mol, ZrB 2 : Δ f H ⦵ = −328 ± 10 kJ/mol, NbB 2 : Δ f H ⦵ = −245 ± 12 kJ/mol, HfB 2 : Δ f H ⦵ = −336 ± 11 kJ/mol, TaB 2 : Δ f H ⦵ = −195 ± 25 kJ/mol) and compared with good agreement to literature values. Multiple thermochemical pathway confirmations are reported. This data is required for the development of robust diboride phase diagrams for ultra-high temperature applications.