Phase stability investigations of the palladium-cadmium system: part i. thermodynamic studies

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Two different isopiestic techniques were employed in the present study. The first technique, used to determine the activity of cadmium in the fl:phase at 1073 K, has been described previously by Chang, Henning, and Naujock. 9 Palladium samples, weighing approximately 1 g, prepared from foil of a thickness 0.025 mm, were equilibrated with vapor from a cadmium reservoir. During the course of each experiment, the temperatures of sample and the reservoir

were kept constant within _-_0.75 K. The experiments were terminated after two to four weeks by quenching the quartz tube, which contained the sample and the reservoir, in cold water. The composition of each sample was calculated from its weight change. The data obtained with this method are designated "Run 1", which is actually a series of five separate experiments with sample temperatures close to 1073 K and reservoir temperatures between 707 and 948 K. The second technique, used to determine the cadmium activity between 33 and 64 at. pct Cd in the temperature interval between 830 and 1350 K, has been described previously by Komarek and co-workers. J~ In any one run, between 15 and 25 samples, which were prepared from the same palladium foil as above, and weighed approximately 200 mg, were enclosed in special graphite crucibles. These samples were brought into equilibrium with vapor from a cadmium reservoir. The evacuated and sealed quartz tube, containing samples and reservoir, was heated in a temperature gradient with the reservoir at the lowest temperature. The temperatures of the samples and the reservoir could be kept constant within --- 1 K; they were measured by raising and lowering a calibrated Pt-Pt 10 Rh thermocouple in a central thermocouple protection tube. ~~ The experimental data obtained by this method is labelled "Run 2" through "Run 6". A feature of the second method is that each experimental run yields a large number of data, whereas the first method yields data of higher accuracy. An application of the two methods together combines the advantages of both and thus enables cross-checking of the data obtained from each method separately.

Y. MAA, formerly Graduate Student, Materials Department, University of Wlsconsln-Mdwaukee, is now with Square D Company, Milwaukee, WI 53201. A. MIKULA is with the lnst~tut for Anorganische Chemie, Universit~it Wien, Vienna, Austria. Y. A. CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, Umversity of Wisconsin-Milwaukee, is now Professor of Metallurgical Engineering, Department of Metallurgical and Mineral Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706. W. SCHUSTER, formerly a Postdoctoral Research Associate, Materials Department, University of Wisconsin-Milwaukee, is now with the Institut for Anorganische Chemle, Universitat Wlen, Vienna, Austria. Manuscript submitted April 23, 1981.

The palladium samples were prepared from 99.99 pct pure Pd (Sandia Laboratory, California), which was rolled to a final thick

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