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VOl. 77
NOTES The Vapor Pressure of Americium Metal
higher pressures, was obtained from observations of the volatilization of americium from a dilute solution in plutonium. It was assumed that the RECEIVED SEPTEMBER 3, 1954 two metals form an ideal solution. Since ameriThe vapor pressure of americium has been meas- cium4 and plutonium6 differ substantially in their ured over the temperature range 1103 to 1453”K., metallic properties, this assumption is open to some by the same method and with the same equipment question. described elsewhere for PUFR and AmF3.‘S2 MeasThis work was performed under the auspices of urements were made independently on two sam- the United States *AtomicEnergy Commission. ples of metal in which extreme care was exercised (4) Edgar F Westrum, Jr., and LeRoy Eyring, THISJ O U R N A 73, L, in the preparation, cleaning and loading of the sam- 33!1G (1031). ples, in an effort to prevent the formation of an im( 5 ) W B. H Lord, .Vatwe, 173, 534 (1951). pervious oxide “skin” which is known to cover mol- RADIATION LABORATORY ASD ten americium metal upon exposure to trace DEPARTMENT OF CHEMISTRY AND amounts of oxygen. Fairly self-consistent data were CHEMICAL ENGINEERING OF CALIFORNIA obtained in the two runs, using about a milligram of UNIVERSITY metal in each case. However, it was not possible BERKELEY, CALIFORNIA to make critical examinations of the contents of the effusion vessels after firing. Owing to the fact that some degree of contamination was inescapable, and Some New Intermetallic Compounds with the “/?-Wolfram” Structure to the somewhat unpredictable behavior of small samples of liquid americium with respect to tantaBY S.GELIER, B. T. MATTHIAS A N D R. GOLDSTEIN lum effusion vessels, the experiments were felt to RECEIVED SOVEMBER 2 , 1954 be insufficiently controlled to regard the results as A recent paper by Hagg and Schonbergl has final. The measurements are presented as preliminary values-the first which have been obtained on shown that “&wolfram” is actually wolfram oxide pure metallic americium-with the expectation w30, with the U’ and 0 atoms randomly distribthat they will be re-examined a t a later date. All uted among the two- and sixfold positions of the data used in our calculations were obtained a t tem- A15 type2 structure. Many intermetallic comperatures above the melting point of the metal, pounds with the ,115 structure are now known. In and therefore refer to vaporization from the liquid all of these the atoms are ordered. Several have been found to be superconducting above l.2°K.3 state. The two runs resulted in two linear curves of V,Si4 has a superconducting transition temperature loglop(,,) vs. 104/T,separated vertically by about between 16.9 and 17.1°K.,which is one of the high10% of the vapor pressure and differing in slope by est known. The compounds to be described in about 1%. Average scattering of the points about this paper were discovered in the search for superconductors with high transition temperatures. One each curve was 7% of the vapor pressure. The equation for the best straight line is: log fi = of these, NbaSn, has the highest transition temper7.563 - 13,102/T. If a AC, of vaporization from ature, 1S.0c5+ O.l°K.,known to date.5 The new compounds with the p-W structure are the liquid of -2 cal. mole-’ deg.-’ is assumed, the best fit is obtained by: log p = 11.092 - 13,7OO/T NbsSn, NbsOs, Nbdr, NbaPt, TaoSn and V3Sn. - log T . The free energy of vaporization equation The superconducting transition temperatures of is: A F = 62,600 - 50.76 T - 2.303(-2)T log T . the niobium compounds are6 18.0,
