Experimental studies on NiSO4 by thermal analysis and calorimetry

• First time measurement and report of NiSO4 melting point.
• First time measurement and report of a structure change in NiSO4.
• First time report for experimental data of the heat capacity from 298 to 950 K.
• Polynomial coefficients for the enthalpy increment and entropy.
• Thermodynamic data for heat of formation and heat of reaction.

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, ΔfusH1483K=44±2kJmol−1. Prior to this, it undergoes a never before observed structure change at 1243±3 K (nominated as ‘dkostruct’) with the transformation energy ΔtrH1243K=3.9±0.2kJmol−1. The change from this high to low temperature structure (orthorhombic) is probably connected with a volume expansion. The standard heat capacity Cp(298K)0=93±7Jmol−1K−1, and from the polynomial for Cp(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 ΔfH298K=−880±10kJmol−1.