Experimental studies on NiSO4 by thermal analysis and calorimetry

Abstract This work includes very new experimental studies on pure NiSO4 with Differential Thermal Analysis (DTA), simultaneous Thermo Gravimetry (TG), and Dynamic Scanning Calorimetry (DSC). Literature only describes the decomposition of NiSO4, and all related multi-nary phase diagrams with nickel sulfate as a compound show a lack in data in the NiSO4-rich region. Indeed, our experiments demonstrate that NiSO4 is stable in equilibrium state and melts at 1483±3 K with an enthalpy of melting of, Δ fus H 1483 K = 44 ± 2 kJ mol − 1 . Prior to this, it undergoes a never before observed structure change at 1243±3 K (nominated as ‘dkostruct’) with the transformation energy Δ tr H 1243 K = 3.9 ± 0.2 kJ mol − 1 . The change from this high to low temperature structure (orthorhombic) is probably connected with a volume expansion. The standard heat capacity C p ( 298 K ) 0 = 93 ± 7 J mol − 1 K − 1 , and from the polynomial for C p ( T ) 0 , derived quantities for the enthalpy increment and the entropy could be deduced for the temperature range from 298 to 950 K. From empirical analysis the heat of formation for NiSO4(c) is Δ f H 298 K = − 880 ± 10 kJ mol − 1 .