Plutonium Hexafluoride
Properties
| State | Solid (sublimes to gas above 62 °C) |
| Color | Reddish-brown |
| Solubility | Reacts violently with water; soluble in anhydrous HF at low temperature |
| Melting Point | 51.6 °C (triple point) |
| Boiling Point | 62 °C (sublimes at 1 atm; liquid only under pressure) |
About Plutonium Hexafluoride
Plutonium hexafluoride (PuF6, 357.99 g/mol) is the reddish-brown molecular hexafluoride of Pu(VI), structurally octahedral and analogous to UF6 and NpF6, but unique in pairing a transuranic +6 oxidation state with near-ambient volatility — it sublimes at 62 °C at 1 atm. The standard preparation is fluorination of PuF4 with elemental F2 at 500 °C. Compared with UF6 it is far less thermodynamically robust: heat it above about 100 °C and it walks back to PuF4 + F2 because the Pu(VI)/Pu(IV) reduction potential sits very close to F2's oxidizing power. That instability is what makes the chemistry interesting and the engineering hard. Most of the technical interest in PuF6 has come from fluoride-volatility reprocessing concepts: fluorinate spent oxide fuel wholesale and you get a gas stream of UF6, NpF6, PuF6, and volatile fission-product fluorides (RuF5, MoF6, TcF6) that you separate by fractional sublimation or selective reduction (PuF6 reduces cleanly to non-volatile PuF4 with ClF3 or NOCl). The promise is smaller waste volumes and simpler unit operations than aqueous PUREX. Bench-scale chemistry was worked out at Oak Ridge, Los Alamos, and at Russian and Japanese institutes through the 1960s-80s, but no commercial fluoride-volatility plant for plutonium has ever been built.
Where you'll encounter it
If you've read any of the open-literature reprocessing reports out of ORNL or PNNL, you've seen PuF6 mentioned as the difficult cousin of UF6 — the species that drove engineers to specify Monel-clad reactors, fluoropolymer gaskets, and double-walled containment for actinide gas streams. In a fluorination experiment you can watch the color shift from the pale pink of PuF4 to the dark red-brown of PuF6 as F2 partial pressure is raised, then watch it fade back if the bed temperature drifts above 100 °C and the equilibrium tips. The compound also appears in actinide gas-phase spectroscopy work at LANL and Argonne, where its octahedral vibrational modes have been used to benchmark relativistic DFT calculations on heavy-element fluorides — the same kind of calculation that informs predictions for SgF6 and the heavier transactinide hexafluorides nobody has ever weighed.
Common Uses
- Bench-scale intermediate in fluoride-volatility reprocessing R&D at ORNL, LANL, and Russian/Japanese institutes
- Gas-phase separation of Pu from U and Np by fractional sublimation in fluoride-volatility flowsheets
- Reference compound for actinide hexafluoride vibrational spectroscopy and relativistic DFT benchmarking
- Precursor to Pu(VI) oxo-fluoride coordination complexes in actinide structural chemistry
- Test substrate for materials qualification of Monel, nickel, and fluoropolymer hardware in actinide F2 service
Safety Information
Combines Pu-239 alpha radiotoxicity (DOE inhalation ALI ~30 nCi for soluble Pu) with aggressive fluorination chemistry. Reacts violently with water, organics, and most metals to release HF and disperse alpha-active aerosol. Thermally unstable above ~100 °C, decomposing to PuF4 + F2. Handled only in fluorine-compatible Monel/nickel/PFA systems inside negative-pressure alpha glove boxes with HEPA-filtered exhaust. SPECIAL NUCLEAR MATERIAL under DOE/NRC accountability. GHS: H300 (acute toxicity Cat 1), H314 (corrosive Cat 1A), H350 (carcinogenicity Cat 1A from radioactivity).
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.