Thermodynamics of Ni-Mg-O and Ni-Nb-Mg-O Melts in Equilibrium with Solid MgO

Abstract

The deoxidation equilibrium of magnesium in liquid nickel and nickel-niobium alloys has been measured at the temperature ranges from 1873 to 1973 K and 1873 K respectively, by the use of magnesia crucible with a view to understanding the equilibrium between magnesium and oxygen, and the effect of niobium on the activity coefficients of oxygen and magnesium in liquid nickel.
For the deoxidation reaction in pure liquid nickel, i.e. :
MgO(s)=Mg+O
the effect of the temperature on the equilibrium constant, K_Mg(Ni) ( =a_Mg·a_o/a_MgO), was found to be :
log K_Mg(Ni)=-25500/T + 7.78
while the effect of magnesium on the activity coefficient of oxygen in liquid nickel was expressed to be :
logf^Mg_O(Ni) = (-126300/T + 39.0)[%Mg] 0.003<[%Mg]<0.07
The deoxidation equilibrium of magnesium in liquid nickel-niobium alloys with 0.005-0.042 mass% magnesium has been measured up to 8 mass% niobium. The activity coefficients of magnesium and oxygen in liquid nickel-niobium alloys were given by the expression :
logf^Nb_O(Ni) + logf^Nb_Mg(Ni) = -0.12[%Nb] [%Nb]<8