Measurement of aluminum or silicon activity in Fe-Ni (< 30 %) alloys using mullite and ZrO₂-based solid electrolyte galvanic cell

Using mullite (3Al₂O₃·2SiO₂)-tube type and ZrO₂ (MgO mole fractions of 9 %)-plug type solid electrolyte, the activities of Al in the Fe-15, 29% Ni-0.002 to 0.84% Al (mass contents in%) alloys were measured at 1873 K in an Al₂O₃ crucible, and those of Si in the Fe-13, 28% Ni Ni-0.13 to 2.3% Si alloys were measured at 1823 K in a mullite crucible with an excess of SiO₂. The interaction coefficients of e_Al^Ni and r_Al^Ni were determined as -0.0173±0.0052 and 0.00021±0.00007, respectively, and those of e_Si^Ni and r_Si^Ni were determined as 0.0094 ±0.0049 and -0.00008±0.00004, respectively. The oxygen activities obtained by the EMF measurements were compared with those obtained from the contents of analyzed oxygen. The oxygen activities in the Fe-Ni-Al alloys were found to be supersaturated. The interaction coefficients of e_O^Ni and r_O^Ni were determined as 0.0027±0.0012 and 0.00012±0.00004, respectively, from the contents of analyzed oxygen in Fe-Ni-Si alloys.