An investigation of high temperature thermodynamic properties in the Pt-Zr and Pt-Hf systems |
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Authors: | P J Meschter W L Worrell |
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Affiliation: | (1) Department of Chemical and Metallurgical Engineering, University of Tennesee, 37916 Knoxville, TN;(2) Department of Metallurgy and Materials Science, University of Pennsylvania, 19174 Philadelphia, PA |
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Abstract: | High-temperature thermodynamic properties of Pt−Zr alloys containing 2 to 25 at. pct Zr and Pt−Hf alloys containing 20 to
25 at. pct Hf have been measured over the temperature range 1100 to 1400 K by a galvanic cell technique using a thoria-based
electrolyte. Activities of Zr and Hf show large negative deviations from Raoult's Law; at 1300 K and 23 at. pct Zr of Hf,
for instance,a
Zr=6.5×10−16 anda
Hf=7.9×10−17. Correlation of emf results with X-ray phase data enables calculation of standard free energies of formation of the intermetallic
compounds ZrPt5, ZrPt3, and HfPt3. At 1300 K ΔG
f
0
(ZrPt5) =−92,680 cal/mole; ΔG
f
0
(ZrPt3)=−91,740 cal/mole; and ΔG
f
0
(HfPt3)=−97,350 cal/mole. The high stabilities of phases in the Pt−Ti, Pt−Zr, and Pt−Hf systems verify the predictions of the Engel-Brewer
correlation. The large negative entropies of formation of TiPt3, ZrPt3 are discussed. Applications including side reactions in fuel cells and thermocouple systems are mentioned.
P. J. MESCHTER, formerly a Graduate Student at the University of Pennsylvania
This paper is based upon a dissertation submitted by P. J. Meschter in partial fulfillment of the requirements of the degree
of Doctor of Philosophy at the University of Pennsylvania. |
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Keywords: | |
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