The phase diagram of plutonium at pressures up to 75 kbar

SHORT COMMUNICATIONS

292

distances are simply a/l/z, while for the MgQCd type compounds there are two distances, viz. d, between M and X lying on the same plane, and d’, between M and X on different planes. All the straight lines of the graphs were calculated by the least-squares method using the experimental values, and the agreement is satisfactory. The lattice parameter for YbTlQ reported by IANDELLI was a misprint in the original papers; the correct value is a =4.770 A (author’s communication). As can be seen from the graphs, for the MJnQ and MHga compounds, these distances decrease linearly with the rare-earth trivalent ionic radius; the large difference between the two distances, d and d’ for the hexagonal Hg compounds corresponds to an unusually low value of the c/a ratio (from 1,45 for LaHgQ to 1.50 for LuHgQ), compared with c/a= 1.63 for a close-packed structure. For MTls, and slightly more so for the MPba compounds, the distances decrease regularly but not linearly from La to Lu, becoming nearly constant for the last rare earths. This observation is imputed to the greater dimensions of Tl and Pb compared with those of In, which at a certain stage prevent further approach between these atoms. Istituto

A. PALENZONA

0%ckci~nica $.%a,

Uaiversita’

di Gefnoa (Italia)

I A. IANDELLI AND A. PALENZONA, J. Less-Common iWetals, 9 (1965) I. 2 A. IANDELLI, Natl. Phys. Lab. Proc. Symp., 9 (1959) paper 3F. 3 A. IANDELLI AND A. PALENZONA, Atti Accad. Nazi. Lincei, 37 (1964) 105. 4 H. R. KIXCH;~AYR, Acta Phis. A&r., 18 (rg64) 193. 5 H. H. KIKCHIAYR, ~o~atsch., 95 (Ig64) 1667. 6 A. IANDELLI, Alti Accad. Nazi. Lincei, 29 (1960) 62. 7 Yu. B. KUZMA AND V. YA. MARKIV, KristalEograf:‘ya, 9 (1964) 279. 8 Yu. B. KUZMA, R. V. SKOLODZRA AND V. YA. MARKIV, Dopouidi Akad. Nauk. (‘964)

Ukr. S.S.R., 8

1070.

9 A. IANDE~LI, 2. Anorg. Allgem. Chsm., 330 (1964) 221. 10 J. L.MORIAKTY, R. 0. GORDON AND J. E. HUMPHREYS, Acta Cryst.. 19 (rgG5) 285. II I. R. HARRIS AND G. V. RAYNOR, J. Less-Common iWetals, 9 (1965) 7, r2 A. IANDELLI, Calij. Rare E~Fz&~s Res. Co@. Lake Arrowhead, 1960, Paper 111-3.

Received

November

I. Less-Common

27th, 1965

Metals, IO (1966) 290-292

The phase diagram

of plutonium

at pressures up to 75 kbar*

STEPHENS’ has determined the phase diagram of plutonium to about 35 kbar. It was shown that the number of solid state phases is reduced from six at atmospheric pressure to two, the 01- and /?-phase, at pressure of about 27 kbar. Extrapolation of STEPHENS’ work suggested an &-liquid triple point at about 52 kbar and 520%. The objective of the present study was to extend the phase diagram of plutonium to pressures of 75 kbar and melting temperatures. Plutonium specimens, 4.75 mm in diameter and 9.4 mm long, were prepared by rolling in the beta phase at 15o“C, cooling in silicon oil to room temperature, and machining to size. All of the plutonium used in the study was purified by fused salt *

This work was performed under the auspices of the United

f.

Less-Commolz Metals, IO (1966) zgz--294

States Atomic

Energy

Commission.

SHORT COMMUXICATIONS electrorefining”. diagram. melts,

293

Three batches

Equivalent

even though

results

of unalloyed

metal were used to determine

were obtained

differences

with the three

in impurity

different

levels were detected

the phase

consolidation

by chemical

and

spectrographic analyses. Pressures up to 45 kbar were generated in a single-stage piston-cylinder apparatus; a double-stage device was used above this pressure. Details of similar apparatus and general experimental techniques have been published by KENNEDY, NEWTON, JAYARAMAN AND KLEMENT 3~4~5.The sample chambers in the present work utilized talc (lava Grade 1136) as a pressure transmitting heating element; the remainder of the assembly consisted

medium and graphite as a of the specimen encased in

a sleeve of boron nitride. Differential thermal analysis (DTA) by means of two chromel-alumel thermocouples, one close to the specimen and the other slightly displaced from it, was used to detect the phase changes. Heating and cooling rates of 5”C/sec were maintained by programming and controlling instruments. Very strong DTA signals were recorded for all transformations. In fact, the transformation temperature could be determined by noting the thermal arrests on records of the specimen temperature. Corrections for the pressure effects on the chromelLalume1 thermocouple were made in accordance with the suggestions of HANNEXW AND STROXG~. Temperatures are believed to be accurate to & 5OC for single-stage work and + 10% for double-stage techniques. Corrections for friction and expansion of the heated sample chamber were made in a manner similar to that described by KENNEI)Y ANI) NEWTON~. Typical doublevalue friction corrections were 4.6 kbar at 15 kbar, 6.0 at 40, and 8.0 at 65. Pressures are believed accurate to + I kbar for single-stage experiments, and f z kbar for the double-stage apparatus. Bismuth was used as a support medium for the high-pressure piston in the 700

I \

I

I

I

!

I

I

L

PRESSURE,

k bars

Fig. I. J. Less-Common

Metals,

IO (1g6G) zgz-.zg+

SHORT COMMUNICATIONS

294

double-stage device. The pressure in the sample chamber was calculated from the total ram pressure, the area of the bismuth column and the Bi I-+11 transition pressures. Of course, all work was accomplished in a glovebox that enclosed the loading frame of the hydraulic press. Figure I shows the results of this study. A comparison with the data of STEPHENSI to 35 kbar shows reasonably good agreement with only minor discrepancies, well within the experimental accuracies of the studies. The most interesting feature of the diagram is the decrease in slope of the 01~?;8 phase boundary with increase in pressure, particularly at pressures over 30 kbar, to zero slope at about 55 kbar. Above this pressure, the curve appears to have a negative slope, implying that the density of the /?-phase is greater than that of the&-phase. The temperature hysteresis associated with the OLe /3 transformation was observed to be a function of pressure, decreasing from its maximum value of about 55°C at one atmosphere pressure, to about 5°C at 25 kbars. The 0 z y transformation displayed a similar phenomenon. The data for the y z E and E z liquid transformations indicate an increase of temperature hysteresis with pressure, but their magnitudes fall within the limits of accuracy for the experimental measurements. R. G. LIPTAI

Metallurgical Division,

R. J. FRIDDLE

Argonne National Laboratory, Argonne, Ill. (U.S.A.) 1 D. R. STEPHENS, 2 B. BLUMENTHAL

J. Phys. Chem. Solids, 24 (1963) AND M. B. BRODSKY, Plutonium

1197. 1960,

Cleaver-Hume

Press,

London,

1961, p.

3 W. KLEMENT, Jr., A. JAYARAMAN AND G. C. KENNEDY, Phys. Rev.., 129 (1963) 1971. 4 G. C. KENNEDY AND R. C. NEWTON, Solids Under Pressure, McGraw-Hill, New York,

1963, p.

163. 5 A. JAYARAMAN, W. KLEMENT, JR. AND G. C. KENNEDY, Phys. Rev., 131 (1963) 544. 6 R. E. HANNEMAN AND H. M. STRONG, J. Appl. Phys., 36 (1965) 523. Received

December

rgth, 1965

J. Less-Common Metals,

The isothermal

IO (1966) 292-294

compressibility

There are no reports

of uranium

of the compressibility,

monocarbide

either adiabatic

or isothermal,

of

uranium monocarbide in the literature. From the 24°C elastic constant measurements of GRAHAM AND CHANGE on single crystals of uranium monocarbide, one may calculate an adiabatic coefficient of volume compressibility (at atmospheric pressure) of 6.11 x 10-13 cmz/dyne. Thus, the corresponding isothermal coefficient will be somewhat higher than this value. In order to measure the isothermal compressibility, an arc-cast cylinder approximately I cm in diameter and 3 cm long was obtained. Its bulk density was found to be 13.59 g/cm3 at 23°C; this is 99.7% of the calculated X-ray density of stoichiometric UC. The linear compression of the cylinder was measured at Q kbar intervals to 7 kbars on a Harwood 30 kbar unit using a 50-50 (parts by volume) mixture of pentane and isopentane as a pressurizing liquid. All length changes were measured J. Less-Common

Metals, IO (1966) zg4-zg5