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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS -1963
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JUN 278.
ORNL - AEC - OFFICIAL
THE PREPARATION AND NATURE OF RARE-EARTH AYDROXIDE SOLS, AND
IMPLICATIONS ON THE PREPARATION OF TRANSPLUTONIUA ELEMENT OXIDES * VIN
:
S. R. Buxton, C. J. Hardy, ** and M. H. Lloyd

RELEASED FOR ANNOUNCEMENT
IN NUCLEAR SCIENCE AXSTRACTS
LEGAL NOTICE
This report mo prepared u w account of Government sponsored work. Neither obe Vallad
Stalos, dor the Commissioa, por say person acting on bebou of the Commission:
A. Makes way wurraty or representa uon, expressed or implied, with rospect to the accu-
racy, completeness, or wofülaoss of the talormation contalood in wis roport, or that the use
of way Information, apparatus, motbod, or process disclosed in this report may not latringo
primitoly owned lihts; or
B. Arrumei aay Habillues with respect to the use of, or for damago rerudag trom ube
un of any information, apparibus, method, or process discloud in this report.
As vand la the above, "persoa acting on behalf of time commission" includes way one
plogo or contractor of the Commisoka, or employee of inch coatractor, to be exlaat about
such employee or contractor of the Commission, or employme of such coalractor preparus,
donemiaates, or provides access to, may taformador purnuant to No oboployment o contract
with the Commission, or his employment with such contractor.
CAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee
Operated by
UNION CARBIDE CORPORATION
for the
V. S. ATOMIC ENERGY COMMISSION
*Research sponsored by the U. S, Atomic Energy Commission under contract with
the Union Carbide Corporation.
**Guest Scientist at the Oak Ridge National Laboratory, 1965-1966, from the
Chemistry Division, Atomic Energy Research Establishment, Harwell, England.
The text of a paper to be presented at the 12th Annual Meeting of the American
Nuclear Society, Denver, Colorado, June 19-23, 1966.
ORNL - AEC - OFFICIAL
Paper sponsored by ANS member, Dr. R. G. Wymer.
CONTENTS AND LIST OF SLIDES
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1. INTRODUCTION
2. PREPARATION OF SOLS AND GELS OF RARE-EARTH HYDROXIDES
Siide 1. Florsheet
Slide 2 Color slide of sols in tubes
Slide 3. Sphere forming column
Slide 4. Color slide of gel spheres
3. ELECTRON MICROSCOPY AND ELECTRON DIFFRACTION F SOLS AND GELS
Slide 5, 'Electron micrograph of Pr sol
Slide 6. Electron diffraction of Pr sol
Slide 7. Electron micrograph of Eu sol
Slide 8, Electron diffraction of Eu sol
Slide 9. Electron micrograph of cross section of Pr gel sphere
4. CONVERSION OF GEL SPHERES TO OXIDE SPHERES
Slide 10. Color slice of Pr gel spheres and oxide spheres
Slide 11. Polished section of oxide spheres
Slide 12. Table of properties
Slide 13. Table of applications
5. IMPLICATIONS ON THE PREPARATION F TRANSPLUTONIUM ELEMENT OXIDES
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1.
INTRODUCTION
4'The sol-gel process has been used (up to the present mainly to prepare oxides
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of thorium, uranium ard plutonium for use in fuel elements. The versatility of
the process has been further demonstrated by our preparation of rare-earth oxides
as dense microspheres and fragments which bave potential applications in
the nuclear field and in industry in general. The knowledge gained 1:3 being
applied to the preparation of oxides of americium and curium in a form suitable
for incorporation into targets in the High Flux Isotope Reactor at Oak Ridge.
This paper will discuss the preparation or the rare earth hydroxide sols
and gels and the details of the size and shape of the colloidal particles 68
determined by electron microscopy. It will also discuss the extension of the
work to the preparation of transplutonium element úxides.
2. PREPARATION OF SOLS AND GELS F RARE-EARTH HYDROXIDES
shown
A flowideet is fiven in SLIDE 1 for the five steges in the complete process.
The rare-earth hydroxide is precipitated by the addition of a 0.2 M solution
of the rare-earth nitrate to a twenty times excess of simonium hydroxide at
25°C. The precipitate is centrifuged and washed 5-6 times with co,-free water
until the ph of the water is about 9. An alternative method is to wash the
precipitate on a sintered-glass filter.
The resulting viscous paste is then heated for 1 hour at 80°C during which
time the apparent pH decreases to about 6.5 and the paste turns into a watery
sol which can be evaporated Irom 0.5 to 2.5 M. Tae mole-ratio of residual
ritrate to metal varies between 0.06 for the heavy rare-earths to 0.26 for the
light rare-earths.
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The sol is formed into microspheres of sel in a column containing a long-
chai.n alcohol which extracts part of the water from the sol.. This column wi.ll
be described in more detail later. The gel microspheres are dried at 120°c
in vacuum, heated to 500°c to decompose the residual nitrate, and then calcined
at 1200-1475°C for 3 hours to form the oxide. The product * microspheres of having
controlled size, high density, low surface area, and good crushing strength.
The appearance of the sols before forming into spheres is €.nown in
SLIDE 2. The apparatus for forming microspheres of gel by dehydration is shown
in SLIDE 3. This has been described in detail by McBride and others in
ORNL report 3874.
The aqueous sol is introduced as fine droplets of controlled size at the top
of a tapered column which contains the alcohol, e.g., 2-ethyl-l-hexanol. The
alcohol is introduced tangertially at the bottom to give & swirling action to
prevent microspheres sliding down the sides of the column at the bottom. The
partially wet alcohol is removed at the top and recirculated, and part of the
flow is taken past the sol injector. This type of column can be operated batch-
vise or continuously, with or without purification of the solvent by dist1llation.
The average residence time of the microspheres is about 30 minutes.
The product at this stage *t microspheres of rare-earth hydroxide gel
shown in SLIDE 4.
3. ELECTRON MICROSCOPY AND ELECTRON DIFFRACTION OF SOLS AND GELS
We have examined the hydroxide sols and gels by electron microscopy to
determine the size and shape of the colloidal particles at the various stages.
SLIDE 5 shows electron micrographs of praseodymium hydroxide particles aged for
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different lengths of time at 25°c. The freshly precipitated material consists
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of amorphous particles of 30-60% diameter, and these sicwly change into roc-
shaped crystals within about an hour. At stage C the viscous paste has become
a watery translucent sol containing rods and bundles of rods 500-1500$ long
by 50-2508 wide. No appreciable further change occurs on aging the sol for
several days.
SLIDE 6 Snows the electron diffraction patterns of selected areas corresponding
to the previous samples. The broad diffuse lines given by the amorphous
precipitate sharpen with time and the finac pattern is characteristic of
hexagonal praseodymium trehydroxide.
SLIDE 7 shows electron micrographs of europium hydroxide sols which require
a longer aging time to form the crystalline rods. The rods and bundles of
rods are also larzer, being 2000-7000$ long and 200-6008 wide. SLIDE 8 shows
very clearly the amorphous nature of the initial precipitate compared with
the crystallinity of the rods. We have found that the cross-sections of the
bundles of rods are roughly square by sectioning a gel microsphere with a
microtome and examining the 2008 thick section by direct transmission electron
microscopy. SLIDE 9 shows the random orientation of bunules in a section of a
praseodymium gel sphere, with several bundles sectioned approximately at
right angles. The well-defined square at the tope has a 1408 side and consists
of an array of about ? x 7 rods, each of 208 diameter. We have not yet been
able to resolve the detailed structure of the 208 rods.
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4. CONVERSION OF GEL SPHERES TO OXIDE SPHERES
..-.
-
The gel microspheres are dried at 120° for several hours, heated to 500°C
and then to a higher temperature to calcine them to oxide. SLIDE 10 shows
the spheres of Proou prepared by heating tue praseodymiwa hydroxida gel spheres
to 1000°C. SLIDE 11 shows polished cross-sections of P7,607and also monoclinic
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Eugo, microspheres. A slight porosity is visible, particularly in the europia
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spheres, and we thirik that this is due to the random packing of the bundles of
crystalline rods, which leaves micropores on sintering. However, the densities
achieved are higher than can be obtained by pressing powdered oxide into pellets
and heating these to 1800°c. Some properties of the oxide microspheres are
shown in SLITE 12.
There are several potential applications of rare-earth oxides in this form
in the nuclear field and in industry in general. SLIDE 13 lista some of these.
5.
IMPLICATIONS ON THE PREPARATION OF TRANSPLUTONIUM ELEMENT OXIDES
Our interest in the preparation of transplutonium element oxides arises
from the need to irradiate americium and curium in the High Flux Isotope Reactor
at Oak Ridge to produce trans-curium isotopes.
The sol-gel methods developed for the trivalent rare-earths have been
applied to the production of sols of trivalent americiuñ-241
which were then formed into gel microspheres and calcined into stable oxide
microspheres at 1150°c. Small differences between americium and rare-earth
behavior suggest that americium is more amenable to sol formation and microsphere
preparation than are the rare-earths. There was less tendency for americium
hydroxide to peptize during the later stages of the washing procedure, and the
sol formed after digestion was quite translucent, which indicates a small size
of the aggregates. A nitrate/americium mole ratio of 0.15 was required for good
sol stability. The sols were concentrated to nearly 2 M by evaporation.
Difficulties may arise with other transplutonium elements, especially highly
in 2--..-.-.
radioactive ones, due to radiolysis. This can cause the sols to foam,
;
. -*..*
decompose the nitrate counter-ion which is considered to stabilize the sols,
a
give gas bubbles in the gel spheres, and cause self-heating with consequent
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e
s
e
premature drying-out of the sols. However, initial results by Bayharz at
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ORNL with the highly active curium-244 on a gram scale have been encouraging
and work is continuing to obtain dense microspheres of both americium and
, curium oxides with remote operation of the various stages in the process.
ANALDIAN.
ORNL - AEC - OFFICIAL
ORNL-DWG 66-3235R
.. WASHING
PRECIPITATION OF HYDROXIDE
ADDITION OF 0.2 M Ln (NOz!?
TO 20X EXCESS OF 8 M NH OH
WITH STIRRING, 25°C
CENTRIFUGATION AND 5-6
WASHES WITH CO.-FREE
WATER UNTIL pH = 9
GEL MICROSPHERES
SOL FORMATION
FORMATION AND DRYING OF SPHERES
WITH LONG-CHAIN ALCOHOL IN
TAPERED COLUMN
HYDROXIDE PASTE HEATED
1 HR, 80°C; EVAPORATED
FROM [M] = 0.5-2.5 M
(NO,/M = 0.05-0.26)
OXIDE MICROSPHERES
CALCINATION
VAC, 120°C, 5-70 HR
VAC, 500°C, 3 HR
AIR 1200-1475°C, 3 HR
50-250 DIAMETER
90-95% DENSITY
0.01-0.05 m/g
SLIDE 1. FLOWSHEET FOR PRODUCTION OF LANTHANIDE HYDROXIDE
SOLS AND OXIDE MICROSPHERES
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UIXOL ASSIFIED
ORNL OWC
TWO-FLUID NOZZLE
AQUEOUS SOL FROM
SYRINGE PUMP
-
.
TO DISTILLATION
SYSTEM +
6-in. DIAM
12. in.
3-in. DIAM —
0-0.2 GPM
III 0-3 GPM III
CENTRIFUGAL
PUMP
40 in.
FROM DISTILLATION SYSTEM
2-in. DIAM
3-in. DIAM
2 in.
ORGANIC SOLVENT ENTERS
COLUMN TANGENTIALLY
6
in.
COLLECT GEL
SPHERES
SLIDE 3. SCHEMATIC FLOW DIAGRAM OF EQUIPMENT
FOR FORMING GEL SPHERES
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SCALE H = 6008
Electron Micrographs of Praseodymium
Hydroxide Sols.
A-FRESHLY PRECIPITATED, AGED 18 min.
B - PRECIPITATE WASHED, AGED 80 min.
Ô - PRECIPITATE WASHED, AGED 140 min.
D - PRECIPITATE WASHED, AGED 6 days
:
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PHOTO 83062
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SLIDE 6
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Electron Diffraction Patterns of
Praseodymium Hydroxide Sols.
A-FRESHLY PRECIPITATED, AGED 18 min.
B - PRECIPITATE WASHED, AGED 80 min.
C - PRECIPITATE WASHED, AGED 140 min.
D - PRECIPITATE WASHED , AGED 6 days
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PHOTO 83061
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Sidek
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ir vim.....
SCALE H=6008
SLIDE 7. Electron Micrographs of Europium
Hydroxide Sols.
A-FRESHLY PRECIPITATED, AGED 20 min.
B- PRECIPITATE WASHED, AGED 80 min.
C-PRECIPITATE WASHED, AGED 25 hrs.
D - PRECIPITATE WASHED, AGED 67 hrs.
ORNL - AEC - OFFICIAL
PHOTO 83063
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SLIDE
.
-
-
Electron Diffraction Patterns of
Europium Hydroxide Sols.
A-FRESHLY PRECIPITATED, AGED 20 min.
B-PRECIPITATE WASHED , AGED 80 min.
C-PRECIPITATE. WASHED , AGED 25 hrs.
D-PRECIPITATE WASHED , AGED 67 hrs.
-
*
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.
SLIDE 9.
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Oils
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OSN-inirnirii,
PHOTO 83245
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Polished Cross-Sections of Microspheres of Picou and Eu, Oz.
SLIDE !!
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URNU-ALL-UrHILIAT
ORNL DWG. 66-1376
PROPERTIES OF Pr6011 AND Eu2O3 MICROSPHERES
Crystallite
Oxide
Maximum
Temp. of
Calcination
(°C)
Crystal
Form
Size
(x-ray)
Density
(toluene)
(% theory)
Surface
Area
(mº/g)
Crushing
Strength
(166 u
diam)
(g)
600
Pr6011
1000
cubic
90-95
200-300
600-700
Eu2O3
1475
monoclinic
90-95
0.01-0.03
300
SLIDE 12.
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APPLICATIONS OF LANTHANIDE OXIDE MICROSPHERES
-2
1. EuZOzGd2O3. Sm2O3 (Y203) as neutron absorbers in reactor control rods,
or as dispersions in oxides (UO.) as burnable poisons or to improve
properties.
.7
2
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2.
Radicactive isotopas of Eu Tm and Pm in the thermo-electric generators or in
artificial heart-pump.
3. Stable isotopes for storage with minimum surface area and ease of dispensing.
4.
Uniform distribution of M,O
in metal oxide catalysts and phosphors.
5. Application of methods to preparation of oxides of Am and Cm for the High
Flux Isotope Reactor.
SLIDE 13.
END
DATE FILMED
7) /29) 166







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