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‐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 and were determined as −0.0173 ± 0.0052 and 0.00021 ± 0.00007, respectively, and those of and 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 and were determined as 0.0027 ± 0.0012 and 0.00012 ± 0.00004, respectively, from the contents of analyzed oxygen in Fe‐Ni‐Si alloys.