Transcript RFSS: Part 3 Lecture 14 Plutonium Chemistry • From: Pu chapter  http://radchem.nevada.edu/c lasses/rdch710/files/plutoniu m.pdf  Nuclear properties and isotope production  Pu in nature  Separation and Purification  Atomic properties  Metallic state  Compounds  Solution chemistry • • Isotopes from.

RFSS: Part 3 Lecture 14 Plutonium Chemistry
•
From: Pu chapter

http://radchem.nevada.edu/c
lasses/rdch710/files/plutoniu
m.pdf

Nuclear properties and
isotope production

Pu in nature

Separation and Purification

Atomic properties

Metallic state

Compounds

Solution chemistry
•
•
Isotopes from 228≤A≤247
Important isotopes
238Pu

 237Np(n,g)238Np
* 238Pu from beta
decay of 238Np
* Separated from
unreacted Np by ion
exchange
 Decay of 242Cm
 0.57 W/g
 Power source for space
exploration
* 83.5 % 238Pu,
chemical form as
dioxide
* Enriched 16O to limit
neutron emission
 6000 n s-1g-1
 0.418 W/g
PuO2
 150 g PuO2 in Ir-0.3 %
W container
14-1
Radiation damage
• Decay rate for 239Pu is sufficient to produce radiation
damage
 Buildup of He and radiation damage within metal
• radiation damage is caused mainly by uranium nuclei
 recoil energy from decay to knock plutonium
atoms from their sites in crystal lattice of metal
 Vacancies are produced
• Effect can produce void swelling
• On microscopic level, vacancies tend to diffuse through
metal and cluster to form voids
• Macroscopic metal swelling observed
14-2
Pu Decay and
Generation of Defects
•
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α particle has a range of about
10 μm through Pu

U recoil nucleus range
is only about 12 nm
Both particles produce
displacement damage

Frenkel pairs
 namely vacancies
and interstitial
atoms

Occurs predominantly
at end of their ranges
Most of damage results from
U nucleus
Distortions due to void
swelling are likely to be larger
than those from heliumbubble formation
14-3
Pu Compounds
•
Original difficulties in producing compounds

Amount of Pu

Purity
• Aided by advances in microsynthesis and increase in amount of available
starting material
• Much early effort in characterization by XRD
Pu Hydrides
• PuHx

x varies from 1.9< x <3.0

Pu + x/2 H2PuHx
 H2 partial pressure used to control exact stoichiometry
 Variations and difficulties rooted in desorption of H2
• Pu hydride crystallizes in a fluorite structure
• Pu hydride oxidation state

PuH2 implies divalent Pu,

measurements show Pu as trivalent and PuH2 is metallic
 Pu(III), 2 H- and 1e- in conduction band

Consistent with electrical conductivity measurements
• Hydride used to prepare metal (basis of Aries process)

Formation of hydride from metal

Heated to 400 °C under vacuum to release hydrogen

Can convert to oxide (with O2) or nitride (N2) gas addition during
heating
14-4
Pu carbides
•
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Four known compounds

Pu3C2, PuC1-x, Pu2C3, and PuC2

PuC exists only as substoichiometric compound
 PuC0.6 to PuC0.92

Compound considered candidate for fuels
Synthesis

At high temperatures elemental C with:
 Pu metal, Pu hydrides, Pu oxides
* Oxygen impurities present with oxide starting material
* High Pu carbides can be used to produce other carbides
 PuC1-x from PuH2 and Pu2C3 at 700 °C

Final product composition dependent upon synthesis temperature, atmosphere (vacuum
or Ar) and time
Chemical properties

PuC1-x oxidizes in air starting at 200 °C

Slower reaction with N2
 Formation of PuN at 1400 °C

All Pu carbides dissolve in HNO3-HF mixtures
Ternary phases prepared

Pu-U-C and Pu-Th-C

Mixed carbide-nitrides, carbide-oxides, and carbide hydrides
14-5
Pu nitride
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•
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Only PuN known with certainty

Narrow composition range

Liquid Pu forms at 1500 °C, PuN melting point not observed
Preparation

Pu hydride with N2 between 500 °C and 1000 °C

Can react metal, but conversion not complete

Formation in liquid ammonia
 PuI3 + NH3 +3 M+ PuN + 3 MI+ 1.5 H2
* Intermediate metal amide MNH2 formation, PuN precipitates
Structure

fcc cubic NaCl structure

Lattice 4.905 Å
 Data variation due to impurities, self-irradiation

Pu-N 2.45 Å

Pu-Pu 3.47 Å
Properties

High melting point (estimated at 2830 °C)

Compatible with steel (up to 600 °C) and Na (890 °C, boiling point)

Reacts with O2 at 200 °C

Dissolves in mineral acids

Moderately delocalized 5f electrons
 Behavior consistent with f5 (Pu3+)
 Supported by correlated spin density calculations
14-6
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•
Pu oxide
Pu storage, fuel, and power
generators
PuO (minor species)
Pu2O3
Forms on PuO2 of d-stabilized
metal when heated to 150-200
°C under vacuum
Metal and dioxide fcc, favors
formation of fcc Pu2O3
Requires heating to 450 °C to
produce hexagonal form
PuO2 with Pu metal, dry H2,
or C
 2PuO2+CPu2O3 + CO
PuO2

fcc, wide composition
range (1.6 <x<2)

Pu metal ignited in air

Calcination of a number of
Pu compounds
 No phosphates
 Rate of heating can
effect composition due
to decomposition and
gas evolution
•
•
•
PuO2 is olive green

Can vary due to particle
size, impurities
Pressed and sintered for heat
sources or fuel
Sol-gel method

Nitrate in acid injected into
dehydrating organic (2ethylcyclohexanol)

Formation of microspheres
 Sphere size effects
color
14-7
Pu oxide preparation
• Hyperstoichiometric sesquioxide (PuO1.6+x)

Requires fast quenching to produce of PuO2 in melt
 Slow cooling resulting in C-Pu2O3 and PuO2-x
 x at 0.02 and 0.03
• Substoichiometric PuO2-x

From PuO1.61 to PuO1.98
 Exact composition depends upon O2 partial pressure

Single phase materials
 Lattice expands with decreasing O
14-8
Pu oxide preparation
•
PuO2+x, PuO3, PuO4

Tetravalent Pu oxides are favored
 Unable to oxidize PuO2
* High pressure O2 at 400 °C
* Ozone

PuO2+x reported in solid phase
 Related to water reaction
* PuO2+xH2OPuO2+x + xH2
* Final product PuO2.3, fcc

PuO3 and PuO4 reported in gas
phase
 From surface reaction with O2
* PuO4 yield decreases with
decreasing O2 partial
pressure
14-9
Mixed Pu oxides
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Perovskites

CaTiO3 structure (ABO3)

Pu(IV, VI, or VII) in octahedral
PuO6n
Cubic lattice
 BO6 octahedra with A cations at
center unit cell
Double perovskites

(Ba,Sr)3PuO6 and
Ba(Mg,Ca,Sr,Mn,Zn)PuO6
M and Pu(VI) occupy alternating
octahedral sites in cubic unit cell
Pu-Ln oxides

PuO2 mixed with LnO1.5

Form solid solutions
 Oxidation of Pu at higher levels
of Ln oxides to compensate for
anion defects

Solid solutions with CeO2 over entire
range
14-10
Pu oxide chemical properties
•
•
Thermodynamic parameter available for Pu oxides
Dissolution

High fired PuO2 difficult to dissolve

Rate of dissolution dependent upon temperature and sample
history
 Irradiated PuO2 has higher dissolution rate with higher
burnup

Dissolution often performed in 16 M HNO3 and 1 M HF
 Can use H2SiF6 or Na2SiF6

KrF2 and O2F2 also examined

Electrochemical oxidation
 HNO3 and Ag(II)

Ce(IV) oxidative dissolution
14-11
Pu fluoride preparation
• Used in preparation of Pu metal
• 2PuO2 + H2 +6 HF 2 PuF3 + 4 H2O at 600 °C
• Pu2(C2O4)3 + 6 HF2 PuF3 + 3 CO + 3 CO2 + 3 H2O at 600 °C

At lower temperature (RT to 150 °C) Pu(OH)2F2 or
Pu(OH)F3 forms
 PuF3 from HF and H2
 PuF4 from HF and O2

Other compounds can replace oxalates (nitrates, peroxides)
• Stronger oxidizing conditions can generate PuF6

PuO2 + 3 F2 PuF6 + O2 at 300 °C

PuF4 + F2  PuF6 at 300 °C
• PuF3
• Insoluble in water
• Prepared from addition of HF to Pu(III) solution

Reduce Pu(IV) with hydroxylamine (NH2OH) or SO2
• Purple crystals

PuF3.0.40H2O
14-12
Pu fluoride preparation
• PuF4
 Insoluble in H2O
 From addition of HF to Pu(IV) solution
* Pale pink PuF4.2.5H2O
* Soluble in nitric acid solutions that form fluoride
species
 Zr, Fe, Al, BO33 Heating under vacuum yields trifluoride
 Formation of PuO2 from reaction with water
* PuF4+2H2OPuO2+4HF
 Reaction of oxide with fluoride
* 3PuF4+2PuO24PuF3+O2
 Net: 4PuF4+2H2O4PuF3+4HF+O2
* High vacuum and temperature favors PuF3
formation
14-13
 Anhydrous forms in stream of HF gas
PuF6 preparation
• Formation from reaction of F2
and PuF4
• Fast rate of formation above 300
°C

Reaction rate
 Log(rate/mg PuF4 cm2hr-1=5.917-2719/T)

Faster reaction at 0.8 F2
partial pressure
• Condensation of product near
formation

Liquid nitrogen in copper
condenser near PuF4
• Can be handled in glass
Fluorination of PuF4 by fluorine diluted with
14-14
He/O2 mixtures to produce PuF6 (Steindler, 1963).
Pu fluoride structures
absorption spectrum of
gaseous PuF6 from
Steindler and Gunther
(1964a)
• PuF4
 Isostructural with An and Ln
tetraflourides
 Pu surrounded by 8 F
 Distorted square antiprism
• PuF6
 Gas phase Oh symmetry
14-15
Pu fluoride properties
• PuF3
 Melting point: 1425 °C
 Boiling point: decomposes at 2000 °C
• PuF4
 Melting point: 1037°C
• PuF6
 Melting point: 52°C
 Boiling point: 62°C
 ΔsublH°=48.65 kJ/mol, ΔfH°=-1861.35 kJ/mol
 IR active in gas phase, bending and stretching
modes
 Isotopic shifts reported for 239 and 242
 Equilibrium constant measured for PuF6PuF4+F2
 ΔG=2.55E4+5.27T
 At 275 °C, ΔG=28.36 kJ/mol
 ΔS=-5.44 J/K mol
 ΔH=25.48 kJ/mol
14-16
Pu halides
• PuF6 decomposition

Alpha decay and temperature
 Exact mechanism unknown

Stored in gas under reduced pressure
• Higher halide preparation

PuCl3 from hydrochlorination
 Pu2(C2O4)3.10H2O+6HCl2PuCl3+3CO2+3CO+13H2O
 Reaction of oxide with phosgene (COCl2) at 500 °C
 Evaporation of Pu(III) in HCl solution

PuCl4
 PuCl3+0.5Cl2PuCl4
* Gas phase
* Identified by peaks in gas phase IR
14-17
Ternary halogenoplutonates
• Pu(III-VI) halides with
ammonia, group 1, group 2,
and some transition metals
• Preparation
 Metal halides and Pu
halide dried in solution
 Metal halides and PuF4 or
dioxide heat 300-600 °C in
HF stream
 PuF4 or dioxide with NH4F
heated in closed vessel at
70-100 °C with repeated
treatment
 PuF6 or PuF4 with group 1
or 2 fluorides
phase diagram of KCl–PuCl3 system
14-18
Pu non-aqueous chemistry
• Very little Pu non-aqueous and organometallic chemistry

Limited resources
• Halides useful starting material

Pu halides insoluble in polar organic solvents

Formation of solvated complexes
 PuI3(THF)x from Pu metal with 1,2-diiodoethane in THF
* Tetrahydrofuran
 Also forms with pyridine, dimethylsulfoxide

Also from reaction of Pu and I2

Solvent molecules displaced to form anhydrous compounds

Single THF NMR environment at room temperature
 Two structures observed at -90 °C
14-19
Pu non-aqueous chemistry
• Borohydrides
 PuF4 + 2Al(BH4)3Pu(BH4)4+ 2Al(BH4)F2
 Separate by condensation of Pu complex in dry
ice
 IR spectroscopy gives pseudo Td
 12 coordinate structure
• Cyclooctatraene (C8H8) complexes
 [NEt4]2PuCl6 + 2K2C8H8 Pu(C8H8)2+4KCl +
2[NEt4]Cl in THF
 Slightly soluble in aromatic and chlorinated
hydrocarbons
 D8h symmetry
 5f-5f and 5f-6d mixing
* Covalent bonding, molar absorptivity
approaching 1000 L mol-1cm-1
14-20
Pu non-aqueous chemistry
• Cyclopentadienyl (C5H5), Cp
 PuCl3 with molten (C5H5)2Be
trisCp Pu
* Reactions also possible with Na, Mg,
and Li Cp
 Cs2PuCl6+ 3Tl(C5H5) in acetonitrile
 Formation of Lewis base species
CpPuCl3L2
* From PuCl4L2 complex
 Characterized by IR and Vis spectroscopy
14-21
Pu electronic structure
•
•
Ionic and covalent bonding models

Ionic non-directional electrostatic
bonds
 Weak and labile in solution
* Core 5f

Covalent bonds are stronger and
exhibit stereochemical orientation

All electron orbitals need to be
considered
 Evidence of a range of
orbital mixing
PuF6

Expect ionic bonding
 Modeling shows this to be
inadequate

Oh symmetry

Sigma and pi bonds
 t2g interacts with 6d
 t2u interacts with 5f or 6p
and 7p for sigma bonding
 t1g non-bonding

Range of mixing found
 3t1u 71% Pu f, 3% Pu p,
26% F p characteristics

Spin-orbital coupling splits 5f state
 Necessary to understand full
MO, simple electron filling
does not describe orbital
* 2 electrons in 5f orbital
 Different
arrangements,
7 f states
14-22
•
PuO2n+ electronic
structure
Linear dioxo

Pu oxygen covalency

Linear regardless of number of valence
5f electrons

D∞h
• Pu oxygen sigma and pi bonds

Sigma from 6pz2 and hybrid 5fz3 with
6pz

Pi 6d and 5f pi orbitals
• Valence electrons include non-bonding
orbital
 d and f higher than pi and sigma in
energetics

5f add to non bonding orbitals
• Weak ionic bonds in equatorial plane
• Spin-orbital calculations shown to lower bond
energy
14-23
Review
• Nuclear properties and isotope production
 Production from 238U
 Fissile and fertile isotopes
• Pu in nature
 Location, levels and how produced
• Separation and Purification
 Role of redox in aqueous and non-aqueous separations
• Metallic state
 Phases, alloys, and reactions with gases
• Compounds
 Preparation and properties
• Solution chemistry
 Oxidation state
 Spectroscopic properties
 Structure and coordination chemistry
14-24
Questions
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Which isotopes of Pu are fissile, why?
How can one produce 238Pu and 239Pu?
How is Pu naturally produced?
How is redox exploited in Pu separation? Describe
Pu separation in Purex and molten salt systems.
What are some alloys of Pu?
How does Pu metal react with oxygen, water, and
hydrogen?
How can different Pu oxidation states in solution
be identified?
Name a stable Pu(VI) compound in solution,
provide its structure.
14-25
Question
• Respond to PDF Quiz 14
• Post comments on the blog
 http://rfssunlv.blogspot.com/
14-26