Gibbs energies of formation of intermetallic phases in the systems Pt-Mg, Pt-Ca, and Pt-Ba and some applications
- PDF / 553,442 Bytes
- 7 Pages / 603.28 x 783.28 pts Page_size
- 23 Downloads / 192 Views
J/mol
(MgPt3) = - 2 1 7 , 4 0 0 + 1 0 . 7 T ( •
J/mol
AG ~ (CaPts) = - 2 9 7 , 5 0 0 + 13.0T (•
J/mol
AG ~ (Ca2Pt7) = - 5 5 1 , 8 0 0 + 22.3T (---5000)
J/mol
AG ~ (CaPt2) = - 2 4 5 , 4 0 0 +
9.3T(---5000)
J/mol
AG ~ (BaPt5) = - 2 3 8 , 7 0 0 +
8.1T (---4000)
J/mol
AG ~ (BaPt:) = - 1 9 7 , 3 0 0 +
4 . 0 T (•
J/mol
AG ~
where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group IIA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr203 in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and "FeO."
I.
INTRODUCTION
S I N C E the early studies of Abraham e t a l . tl] on the activity of MnO in MnO-SiO: slags, the platinum-slag-gas equilibrium technique has been extensively used for the measurement of activities of FeO, MnO, and Cr:O3 in slags, tg,3,4]At an oxygen potential fixed by the gas phase, the less stable compound, such as MnO, in the slag is partially reduced and forms a solid solution with platinum. If the equilibrium concentration of manganese in platinum is measured, the activity of MnO in the slag can be derived using the standard Gibbs energy of formation of MnO and the known activity-composition relationship in the Pt-Mn system. Because of the absence of activity data in ternary or higher order solid solutions such as Pt-Mn-Fe, the technique has been traditionally limited to slags in which only one component can be easily reduced into platinum. Even some of the more K.T. JACOB, Professor and Chairman, is with the Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India. K.P. ABRAHAM, formerly Professor and Chairman, Department of Metallurgy, Indian Institute of Science, is Consultant, Regional Research Laboratory, Trivandrum 695 019, and Research and Development Centre for Iron and Steel, Steel Authority of India Ltd., Ranchi 834 002, India. S. RAMACHANDRAN, formerly Visiting Scientist, Department of Metallurgy, Indian Institute of Science, is Principal Consultant, Process Analysis Centre for Emerging Technologies, Steel Authority of India Ltd., Madras 600 001, India. Manuscript submitted August 30, 1989. METALLURGICAL TRANSACTIONS B
stable components in slags such as MgO, CaO, and BaO may interact with platinum to form strong intermetallics and thus limit the region of applicability of this technique. The stability of the platinum-rich intermetallics containing alkaline earth metals can be easily and accurately measured at lower temperatures u
Data Loading...
