Thermodynamic investigations of Bi–Ni system – Part I

The Bi–Ni system has two intermetallic compounds, Bi0.75Ni0.25 and Bi0.5Ni0.5, which melt peritectically. Enthalpy increments of these compounds were measured using high temperature calorimeters. The enthalpy increment data near their peritectic temperatures were used for determining enthalpies of their decomposition. The most suitable polynomial equations for least square fit of enthalpy increment data were: Δ298.15KTHmo(Bi0.75Ni0.25)/(J·mol-1)=-8339+29.86(T/K)-0.0104(T/K)2+1.367·10-5(T/K)3,Δ298.15KTHmo(Bi0.5Ni0.5)/(J·mol-1)=-5580+16.04(T/K)+0.0139(T/K)2-130616K/T. The enthalpy of decomposition of Bi0.75Ni0.25 and of Bi0.5Ni0.5 was found to be 3.51 kJ · mol−1 at equilibrium temperature 744 K, and 9.22 kJ · mol−1 at equilibrium temperature 927 K, respectively. The heat capacities of the compounds were determined using heat flow DSC and fitted into the following most suitable, polynomial equations: Cp,mo(Bi0.75Ni0.25)/(J·K-1·mol-1)=28.92-0.0145T/K+3.05·10-5(T/K)2,Cp,mo(Bi0.5Ni0.5)/(J·K-1·mol-1)=20.25+0.0208T/K-57660(K/T)2.

► First time reporting of Cp of Bi3Ni.
► First time reporting of enthalpy increment and enthalpy of decomposition of Bi3Ni.
► First time reporting of enthalpy increment and enthalpy of decomposition of BiNi.
► Enthalpy of magnetic transition of BiNi is reported for the first time.