Plutonium phase diagram

The main features of the phase diagrams of intra-thorium, -uranium and -plutonium phase diagrams have also been presented in figs. 64-66. The uranium-thorium phase diagram exhibits a miscibility gap in the liquid state. The plutonium-thorium phase diagram is more complex, with the two elements miscible in the liquid state in the A2-solid solution a small miscibility gap is observed, however a compound at composition PuyTha appears at low temperature. 

Fig. 1. Piessuie—volume—tempeiatuie phase diagram of plutonium metal (35). To convert MPa to atm, multiply by 9.9.

Fig. 9. The plutonium—oxygen phase diagram where L = Hquid a, P, y, 5, and S are metal phases and the dashed lines represent uncertain phase...

Present production processes use two stage counter-current extraction to remove americium from molten plutonium with magnesium chloride based salts. Both 35 mole % NaCl - 35 mole % KC1 - 3D mole % MgCl2 and 50 mole % NaCl-26 mole % CaCl2 - 24 mole % Mg Cl 2 are used for americium extraction. Figures 4 and 5 show the ternary phase diagrams for these salt systemsU0). 

Pu-Ga phase diagram, 29 684. See also Plutonium- gallium alloys PULEG (/-Pulegone, /-menthol from, 24 523... 

Figure 5.11. Connected binary phase diagrams of the actinides. The binary phase diagrams (temperature vs. composition) for adjacent actinide metals are connected across the entire series (two-phase regions are in black, uncertain regions in grey). The transition from typical metallic behaviour at thorium to complex behaviour at plutonium and back to typical metallic behaviour past americium can be noticed (adapted from Hecker 2000).

The stability of the fee 8-plutonium, which is malleable and easily shaped, is important because of its uses (in nuclear weapons, etc.). This phase may be retained, either in stable or metastable conditions, down to room temperature by the addition of gallium or aluminium. In a way, the two versions of the phase diagram may now be reconciled. The diagram in Fig 5.16 (a) is adequate for practical applications... 

A system particularly studied from a thermodynamic point of view is the monocarbide (AnCi x) system. A range of stability for carbon deficient compositions in the monocarbides is present in many metal-carbon phase diagrams. Table 6 shows the composition range at room temperature for actinide monocarbides. The non-stoichiometry range is very limited for uranium monocarbide for neptunium and plutonium monocarbides, the stoichiometric AmCj oo composition is not stable. 

We now give a simple application of the present method to Plutonium which is a good test case. Pu lies between light actinides with itinerant 5/ electrons and heavy actinides with localized 5/ electrons. The competition between these two electronic regimes in Pu is responsible for a lot of unusual properties as large values of the linear term in the specific heat coefficient and of the electrical resistivity or a very complex phase diagram. 

Cope, R. G., D. G. Hughes, R. G. Loasby, and D. C. Miller The Plutonium-Ruthenium and Plutonium-Neptunium binary Phase Diagrams. In E. Grison, W. B. H. Lord, and R. D. Fowler (Eds.), Plutonium 1960. Proc. of the 2nd Int. Conf. on Plutonium Metallurgy, Grenoble (1960). London Cleaver-Hume Press Ltd. 1961. 

As Indicated previously, the tentative phase diagram of the Pu-0 system shows plutonium sesquioxide as a line compound from room temperature up to its melting point. During the course of the preparation of for low temperature heat capacity... 

Plutonium. Gardner et al. (26) have made a careful high temperature x-ray diflFraction study of the plutonium-oxygen system in the range from room temperature to 900°C. observing diffraction from oxide samples contained in silica capillaries. They review briefly previous work apropos of phase transformations (i.e., thermal and electrical measurements) and construct a phase diagram as shown in Figure 5. 

Plutonium oxides. The phase diagram of the plutonium-oxygen system is shown in Fig. 9.2. The observed compounds are the stoichiometric PujOj and PUO2 and the nonstoichiometric PuOj.sj and Pui. i. PuO has also been shown to exist, but only under extreme conditions. No oxide of higher oxidation state than PuOs has been formed. 

Figure 9.2 Phase diagram of the plutonium-oxygen system. From Mattys [M4] and Olander [02], by permission.)...

Figure 9.3 Phase diagram of the uranium-plutonium-oxygen system at 20°C (K2, II ].

Cramer, E.M., F.H. Ellinger and C.C. Land, 1960, Plutonium-Zinc Phase Diagram, in Extractive and Physical Metallurgy of Plutonium and its Alloys, ed. W.D. Wilkinson (Interscience Publishers, New York) pp. 169-180. 

Mikheev (1988,1989,1992) has obtained extensive evidence through cocrystallization that almost all the tripositive lanthanide (except for Sm, Eu, Tm and Yb) and actinide ions (U, Np, Pu, Cm, Bk) can be reduced and have (M /M ) in the neighborhood of — 2.5 to — 2.9 V. The lanthanide potentials are not consistent with the experimentally confirmed generalized f electron energetics scheme developed by Nugent (1975). The potentials are not consistent with potentials inferred from pulse-radiolysis studies (Sullivan et al. 1976,1983,1988). If the potentials (M /M ) proposed by Mikheev for uranium, —2.54 V, and plutonium, —2.59 V, at macroscopic concentrations (Mikheev etal. 1991) were correct, phase diagram studies and electrochemistry ih molten salts should have revealed the ions and Pu ", but no evidence other than cocrystallization has been presented. In fact, the crystal chemistry of the reduced uranium halide NaUjCl (Schleid and Meyer 1989) is consistent with ions and metallic electrons. The cocrystallization model (Mikheev and Merts 1990) may not be transferable to aqueous solution and thus Mikheev s (M /M ) potentials are not cited in table 5. 

This system is composed of the following phases plutonium metal with its six crystal forms a zeta phase at PU3C2 PuC with a defective cubic structure another cubic compound at PU2C3 and a tetragonal PUC2 phase at high temperatures. This is summarized in a tentative phase diagram shown in Fig. 71. 

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