Table 2.5. Allotropic Forms of Plutonium Metal(a)

DOE-STD-1128-98

Table 2.5. Allotropic Forms of Plutonium Metal(a)

Phase

Stability Range C

Density g/cm3(b)

Stable below 115

19.86

~115 to 200

17.70

~200 to 310

17.14

310 to 452

15.92

σ'

452 to 480

€

480 to 640

16.51

(a)

Wick, 1967, p. 34.

(b)

Theoretical X-ray density. The actual density is slightly lower due to crystal

lattice imperfection.

Plutonium is an active metal. In moist air or moist argon, the metal oxidizes

rapidly, producing a mixture of oxides and hydrides (Haschke, 1992). If the

metal is exposed long enough, an olive-green powdery surface coating of PuO2

is formed. With this coating, the metal is pyrophoric, so plutonium metal is

usually handled in an inert, dry atmosphere of nitrogen or argon. Oxygen

retards the effects of moisture and acts as a passivating agent (Raynor and

Sackman, 1963). For a description of the storage hazards that the oxidation of

plutonium metal creates, see Section 2.6.3.1, "Oxidation of Plutonium." A

comprehensive treatment of the oxidation of plutonium, the properties of its

oxides, oxide growth, and oxidation kinetics was reviewed by Colmenares

(1975).

Plutonium metal also reacts with most common gases at elevated temperatures.

Plutonium metal is rapidly dissolved by HCl, HBr, 72% HCl04, 85% H3PO4,

concentrated CCl3COOH (trichloroacetic acid), sulfamic acid, and boiling

concentrated HNO3 in the presence of 0.005M HF. The metal reacts slowly

with water, dilute sulfuric acid, and dilute acetic acid. There is no reaction with

the metal in pure HNO3 at any concentration, with concentrated acetic acid, nor

with dilute sodium hydroxide.

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