Thermodynamics of the liquid binary iron-titanium by mass spectrometry
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data on the thermodynamics of the liquid binary iron-titanium are limited. Using Hadley and D e r g e ' s study* of the equilibrium between titanium in liquid iron and titanium oxides, and the Gibbs energies of TiO and TiO2 reported by Kelley and Mah, 2 Chipman s estimated the activity coefficient of titanium at infinite dilution, ~Ti = 0.011, and 8 In 7Ti/aXTi = 9.0, both at 1600~ (1873 K). (XWi denotes the concentration of titanium in atomic fractions.) More recently F r u e han used part of an EMF study 4 of the system F e - T i - O to derive ~ri at 1600"C (1873 K) for four alloys, 0.066 _< XTi _ 0.143, and calculated 7~i = 0.038 and a In ZTi/a(X~e ) = -- 1.4. In the present paper, the results of a study of the entire binary are reported. Nine liquid alloys with 0.10 _< XTi _< 0.90 were measured in the temperature range of 1450 to 1650~ (1723 to 1923 K). The equal a r e a method 5 was used in the evaluation of the excess Gibbs energy GE and of the enthalpy of mixing H M from the experimental ion intensity ratios. EXPERIMENTAL A commercial high-temperature time-of-flight mass spectrometer (Bendix 3012, Knudsen cell attachment 1031) and a disappearing-filament type micro-optical p y r o m e t e r (Leeds and Northrup 8634-C) were used in the present investigation. The pyrometer was calibrated in situ by the 7-5 transition (1392~ 1665 K) and the melting point (1536~ 1809 K) of pure iron (Battelle bar 110 D-I, 20 ppm impurities). Tantalum susceptor cells were heated by electron bombardment from two W-shaped tungsten filaments. Alloy melts, 0.6 to 1.1 g at the start, were contained in ThO~ c r u cibles covered by ThOa lids. The effusion orifices were 1.0 mm long and had 1.1 mm diameter; the comparatively large orifice diameter was chosen to avoid clogging. All alloys wetted the thoria crucible walls and tended to creep through the effusion orifice during the experiment. As a consequence, the ion currents at constant cell temperature were observed to fluctuate and to increase irregularly. A molybdenum " s h i e l d " exactly matching the ThO2 lid was inserted between this lid and the top of the tantalum cell to prevent r e evaporation of material from the outside of the thoria SIGURDWAGNER,formerlyPostdoctoral Fellow, Department of Metallurgical Engineering, Ohio State University, Columbus, Ohio, is now with Bell Telephone Laboratories, Holmdel, N.J. 07733. GEORGE R. ST. PIERREis ArmcoProfessorof Metallurgy, Department of Metallurgical Engineering, Ohio State University, Columbus, Ohio, 43210. Manuscript submitted September 28, 1973. METALLURGICALTRANSACTIONS
lid. With this arrangement the ion currents stayed constant. The ratio of the vapor p r e s s u r e s of the pure components at 1545~ (1818 K) is P~e/P~i ~- 50"8'7 The ions S6Fe* (91.66 pct) and 4STi* (73.94 pct) were monitored. EXPERIMENTAL RESULTS In Fig. 1 the experimental ion intensity ratios are plotted as In (/Wi/IFe) versus 104/T. The values for In (ITi/IFe) and for (/~Ti --/~Fe ) at the average t e m p e r ature of 1545"(2 (1818K) are listed fo
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