Thermodynamics of the system Fe-Mn-S: Part I. activities in Iron sulfide-manganese Sulfide Solid Solutions in the Temper
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TECHNIQUE
The sulfur potential of the furnace atmosphere was controlled by the use of H2S-H2 mixtures. Two techniques were applied t o determine the relationship between the composition of the sulfide solid solution, coexisting with metallic iron, and the sulfur potential of the gas phase. In the first method sulfide samples of known Fe/Mn ratio were equilibrated with the gas mixture, then quenched t o room temperature, and investigated microscopically t o find whether metallic iron had been precipitated. The experiments were started with a high PH^S/PH r a t i o at • . . Z 2 which no m e t a l h c iron was formed, and were repeated w i t h stepwise decreased PH2S/PH2 till the PH2S/PH2 ratio for incipient precipitation was determined. In the second technique mixtures of about 50 vol pct sulfide
M A N F R E D F I S C H E R a n d K L A U S S C H W E R D T F E G E R are w i t h Max-Planck-Institut f't~r E i s e n f o r s c h u n g , Di~sseldorf, G e r m a n y . M a n u s c r i p t s u b m i t t e d D e c e m b e r 3, 1 9 7 6 . METALLURGICAL
TRANSACTIONS B
and 50 vol pct metallic iron were equilibrated with the gas phase. The composition of the sulfide attained during equilibration was determined after the experiment by p r e c i s e measurement of lattice constants or by microprobe analysis. In o r d e r t o approach the equilibrium from b o t h s i d e s two samples with different starting composition of the sulfide were equilibrated side by side in the same experiment. The starting compositions were chosen in such a way that metallic iron had t o be sulfurized in one of the samples and iron sulfide had t o be reduced in the other sample. Identical final sulfide compositions were established in both samples at sufficiently long r e a c tion t i m e s . Most of the experiments were performed with the second technique because the results were of h i g h e r precision compared to that achieved with the precipitation method. The furnace used was a tube furnace wound with molybdenum w i r e . The reaction tube of 2.5 cm ID was made of recrystallized alumina (Morganite) and was closed gas tight at its ends. The space between reaction tube and heating tube was also closed gas tight and was filled with a r g o n t o ensure additional protection against oxygen entering into the reaction tube. The furnace temperature was controlled e l e c tronically within ±2°C. The gas phase was composed from purified hydrogen and from a starting mixture of hydrogen and hydrogen sulfide (about 4 vol pct H2S) which was purchased commercially. The gas flowed upwards in the reaction tube. Capillary flow m e t e r s were used for mixing. The sulfides were prepared from reagent g r a d e FeC12 • 4H20 and MnC12 • 4 H 2 0 (Merck and Riedel-de H~en). The clorides were proportioned in the des i r e d ratio, carefully m i x e d by grinding in an a g a t e mortar, then dehydrated under a r g o n at 600°C and finally sulfurized at the same temperature with a gas phase of 20 vol pct H2S and 80 vol pct H2. In o r d e r t o achieve further homogenization
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