Comment
Figure shows only the first heating process. There exists two stages of sulfidation reactions（１）at 400-515℃　（２）515-680℃.　Total reaction enthalpy, ΔHr=639.1J/g.
The enthalpy of formation
　Product is the hexagonal NbS2.
The enthalpy of formation, ΔHf=42.2Kcal/mol.