Phase equilibria in the system Fe-Ni-S at 500°C and 400°C

Abstract

Phase equilibria in the system Fe-Ni-S were investigated by dry synthesis at 500°C and 400°C using three elements (Fe, Ni and S) and two synthetic sulfides (FeS and NiS). Phase diagrams of this ternary system at these two temperatures were obtained. The extent of the monosulfide solid solution (mss) is complete at 500°C and 400°C. The d(102)-values of the mss are increasing with the increasing Fe/(Fe+Ni) ratio and are decreasing with the increasing sulfur content of the mss. Pentlandite has the solid solution areas ranging from (Fe_0.66Ni_0.34)_9.02S_8.00 to (Fe_0.30Ni_0.70)_9.35S_8.00 at 500°C and from (Fe_0.70Ni_0.30)_9.39S_8.00 to (Fe_0.41Ni_0.59)_9.24S_8.00 at 400°C. Violarite has the solid solution area ranging from (Fe_0.16Ni_0.84)_3.02S_4.00 to (Fe_0.34Ni_0.66)_3.00S_4.00 at 400°C and does not exist at 500°C. Godlevskite is stable at 400°C and it transforms to α-Ni₇S₆ phase at 500°C run. Tie lines of pentlandite to godlevskite at 400°C and pentlandite to α-Ni₇S₆ phase at 500°C are stable. On the Fe-Ni join, two kinds of Fe-Ni alloys (α-iron and γ-phase) and pure nickel are stable. Alfa-iron has a body-centered cubic structure and pure nickel has a face-centered cubic structure. Gamma-phase has a primitive tetragonal structure and the FeNi₃ phase is included in the γ-phase solid solution.