DEOXIDATION EQUILIBRIUM OF SILICON IN LIQUID NICKEL AND NICKEL IRON-ALLOYS

The deoxidation of liquid nickel with silicon has been determined at temperatures between 1 500 and 1 650-degrees-C using quartz crucibles in order to investigate the deoxidation of nickel based alloys. The effect of temperature on the equilibrium constant of the deoxidation reaction: SiO2(s) = Si + 2O was found to be: log K(Si(Ni)) = - 15680/T + 1.83 while the deoxidation product, logK(Si(Ni))' (= [%Si][%O]2), up to 2 mass% of silicon was expressed as follows: logK(Si(Ni))' = log K(Si(Ni)) - 0.06[%Si] The deoxidation of nickel-iron binary with 0.5 mass% silicon has been measured over all the ranges of the binary system including pure iron at temperatures of 1 600 and 1 650-degrees-C. On the nickel basis, the deoxidation product of nickel-iron alloys, which increased by the addition of iron up to 20 mass%, was empirically represented to be: log K(Si(Ni-Fe))' = log K(Si(Ni)) - (288/T - 0.197) [%Fe] The temperature dependence of the equilibrium constants for the deoxidation of iron was given by the expression: log K(Si(Fe)) = - 30 960/T + 11.86 at temperatures between 1 550 and 1 650-degrees-C. On the iron basis, the value of log K(Si(Fe-Ni))' which decreased with the increase of nickel content up to 60 mass%, was calulated as: log K(Si(Fe-Ni))' = log K(Si(Fe)) - 0.01 [%Ni].