THE MnO -lMnS PHASL DIAGRAMi H. C. Chao, Y. E. Smith, and L. H. Van Vlaclk The phase relationships for the MnO-MnS system have only been investigated in the eutectic region. Wentru ] reported a eutectic at 1280~C (23450F) with approximately 50 weight percent of each component. More recently, Silvermari2) corrected these figures to 2275100~F (12460~C) with 63 weight percent MnS and 37 percent MnO. Neither Wentrup nor Silverman investigated the solid solution limits in this system. However, Wentrup did suggest with his phase diagram sketch that the maximum solubility of MnS in MnO is 10 weight percent, and the solubility of MnO in MnS"isnearer 20 weight percent. These figures have been utilized..in ss-bse qient manuscripts without further verification. (3) There had been evidence found in this laboratory that the above solid solution figures were high.. - An-;hPetstigation was therefore started using the following procedure. The samples were heated just above the eutectic temperature in a purified nitrogen atmosphere and contained in platinum foil before quenching into distilled water. The MnO had been prepared by calcining reagent grade MnC03 at 12400~C, Only MnO was detected in subsequent x-ray diffraction analyses. The MnS had been prepared by sulfur deoxidation of reagent grade MnS04 according to the reaction: MnSO4 + S2 2 MnS + 2S02

C,,,-l7- /, cot,1,vlk -g

-2The details of the procedure which utilized atmospheric sulfur pressures at 9500~C are discussed elsewhere!4) The sulfur content was determined to be 36.8*0.2 percent which matches the stoichiometric value of 36.9 percent. No evidence of either MnO or MnS104 was detected microscopically or by x-ray diffraction. The revised diagram is presented in Fig. 1. The melting temperature for MnO is that provided by Glasser!(5) The eutectic temperature of 1232t5~C and eutectic composition of 64 weight percent MnS is in close agreement with Silvermants correction of Wentrup's work. The maximum solubility of MnO in MnS was determinedoto be 1.7t 0.2 weight percent. The maximum solubility of MnS in MnO was determined to be 1.8*0.2 weight percent. These figures represent the lower limit for the presence of liquid at 1260~C and are significantly lower than the earlier estimated solid solution figures.

-3REFERENCES 1. H. Wentrup, Die Bildung von Einschl'ssen im Stahl, Techo Mitt. Krupp, 5 (1937) 131, 2. E. N. Silverman, Synthetic Inclusions in FeO-MnO-MnS-Si02 System in Equilibrium with Resulfurized Steel, Trans. AIME, 221 (1961) 512. 3. Co E. Sims, Nonmetallic Inclusions, Basic Open Hearth Steelmaking, New York: AIME, (1951) 465. 4. H, C. Chao, Lo Thomassen, and L. H. Van Vlack, Inclusion Deformation: I. The Mechanism of Fracture and Deformation in MnS. To be submitted for publication~ 5. F. P. Glasser, The System MnO-Si02, Amer. J. Sci,, 256 (1958) 398

1900 800oo 1700 1600 Liquid 1500 cii~~~~~~~~4-,')~~~~~Liquid MnS 1300 1200 11.8 t34. 98.5~ 1400 MnO + MnSLu MnO MnS Percent MnS Fig. 1. The MnO-MnS phase diagram.

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