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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
ORNE Ptofa .
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Cont-660524-4
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ACADROS JAN ,50
SOL-GEL PROCESS DEVELOPMENT AND MICROS PHERE PREPARATION*
P. A. Haas
M. H. Lloyd
W. D. Bond
J. P. McBride
Chemical Technology Division

RELEASED FOR ANNOUNCEMENT
IN NUCLEAR SCIENCE ABSTRACTS
For presentation at the Second International Thorium Fuel Cycle
Symposium at Gatlinburg, Tennessee, May 3-6, 1966.
LEGAL NOTICE
This report was prepared as an account of Government sponsored work. Neither the United
statos, nor the Commission, nor any person soting on behalf of the Commission:
A. Makos any warranty or reprosentation, expressed or implied, with respect to the accu-
racy, complotoness, or usefulnors of the information contained in this report, or that the uso
of any information, apparatus, mothod, or procoss disclosed in this report may not infringo
privately owned righto; or
B. Assumes any liabilities with respect to the use of, or for damages rosulung from the
uso of any information, apparatus, method, or proceso disclosed in this report.
As used in the abovo, “porson acting on behalf of the Commission” includes any om-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
such umployee or contractor of the Commission, or employec of such contractor prepares,
disseminatos, or provides access to, any informatiop pursuant to his employment or contract
with the Commission, or his employment with such contractor.
*Research sponsored by the U.S, Atomic Energy Commission under contract
with the Union Carbide Corporation,
OAK RIDGE NATIONAL LABORATORY
operated by
for the
U.S. ATOMIC ENERGY COMMISSION
SOL-GEL PROCESS DEVELOPMENT AND MICROS PHERE PREPARATION*
ORNL - AEC - OFFICIAL
P. A. Haas
M. H. Lloyd
W. D. Bond
J. P. McBride
ABSTRACT
The continued development of the sol-gel process at the Oak Ridge
National Laboratory is presented. The originaı development and application
to preparation of high density thoria-urania fragments for vibratory com-
paction was reported at the 1962 Thorium Fuel Cycle Symposium. Since then,
edir
we have prepared sols of ThO2, UO2, Pu02, and other actinide or rare earth
oxides. These sols can be gelled and fired to give high-strength oxide
particles,
Most of the sols are prepared from nitrate salts and peptized by nitrate
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ion. The thoria sol preparation procedure is unique in that the basic
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colloidal particle is formed by steam denitration at temperature approaching
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500°C. The most completely developed procedure for urania sols is based on
precipitation-dispersion starting with U(IV) nitrate solution. Hydrous
uranium dioxide is precipitated by NH4OH--N2H4 •H20 solution, washed to
incipient peptization, and then heated to 60°C to form a sol. The addition
of formic acid prior to precipitation helps to maintain a high U(IV) content
and simplifies the precipitation step. Plutonia sols may be prepared from
Pu( NO3)4 solution by a precipitation-peptization technique; careful control
of the temperature and other process conditions is necessary. The plutonia :
sols are polymers of hydrated Pu( IV) oxide. Mixed sols were prepared by.
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“Research sponsored by the U.S. Atomic Energy Commission under contract with
the Union Carbide Corporation.
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ORNL - AEC - OFFICIAL
either co-precipitation or by simple mixing of the different sols. Limited
ORNL - AEC - OFFICIAL
amounts of a second component may be adsorbed on the colloidal particles
of a sol; for example, up to about 10 mole per cent uranyl ion can be
adsorbed when Uog or uranyl nitrate is added to a thoria sol.
A process was developed for converting these sols into strong, dense
oxide spheres, 10-1000 microns in diameter. The sols were dispersed into
droplets in an organic liquid that converted them to gel spheres by extracting
water at slow, controlled rates. To suspend the soỉ drops and avoid
coalescence, clustering, and deposition on the wall, the use of surfactants
in the organic liquid and of apparatus having special configurations were
necessary. The spherical gel particles were separated from the organic
liquid, then dried and fired to give the oxide product, Microspheres were
prepared by using 2-ethyl-1-hexanol as the drying solvent, in continuous
column systems that included solvent recovery. Capacities were up to about
1200 g of 'thoria microspheres per hour. Several hundred kg of thoria
microspheres, over 15 kg of urania microspheres and smaller amounts of
were
the other compositions were prepared,
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1. INTRODUCTION
The development of the sol-gel process and its application to the preparation
of the theoretically dense fragments of thoria-urania for vibratory compaction was
reported at the last Thorium Fuel Cycle Symposium.. This paper describes the
continued development of sol-gel processes, especially as adapted to the production
: ORNL - AEC - OFFICIAL
of spherules.
Basically, the sol-gel processes consists of three major operations: (1) pre-
paring an aqueous sol, (2) removing water to give solid gel particles, and (3)
firing at controlled conditions to remove volatiles, sinter to a high density,
and cause any necessary reductions or chemical conversions. The original flowsheet
(Figure 1) was developed for a thoria sol. According to this flowsheet, thorium
nitrate is stean-denitrated to thorium oxide that can be dispersed into a stable
sol by add toiing very dilute nitric acid or uranyl nitrate solution. The thoria (or
thoria-urania) sol is evaporated to form a gel, and then fired to densify.
A particle density of 9.9 g/cc or greater is achieved in 1 hour at 1150°C.
After sizing, the oxide particles are suitable for vibratory packing into fuel tubes.
The development studies have included investigations of sol preparation for most
of the metal oxides that might be used in irradiation specimens or fuel elements.
One purpose is to obtain the same advantages for these metal oxides as are obtained
in the thoria s01-gel process. Another purpose is to be able to prepare mixed-oxide
products by preparing mixed oxide sols or mixing pure sols. The sol preparation..
procedures and the characteristics of the microsphere products for oxides other than
pure thoria are given in Section 2.
Spherules of a high-density oxide or dicarbide are the preferred fuel materials
for many reactor designs. For example, spheres are preferred when pyrolytic carbon
coatings are used since the coating 18 a sma11 "pressure vessel" for fission product
The greater mechanical strength, the controlled void volume, the bulk flow properties,
or the overall uniformity possible with spheres are important advantages for many
applications. Therefore we started studies to modify the sol-gel process to
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small high-density spheres while retaining the important advantages of simplicity
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and relatively low sintering temperature. The microsphere preparation process
is given in Section 3 and replaces the evaporation step in the original sol-gel procesi
A pilot-plant-scale system for preparation of microspheres has been installed and
operated as part of a Coated Particle Development Facility (CPDF) at the Oak Ridge
National Laboratory.
This system has been operated with thoria sols at rates up to
25 cc/min of sol (1200 g Thoz per hour for a 3 M thoria sol). The characteristics of
the over 100 kg of product microspheres have been equal or superior to those prepared
in smaller equipment. This column system is being used to supply microspheres for othe
parts of the fuel-cycle program and to investigate the problems of long-term, remote
operation. This system will be operated with sols other than pure thoria in the
future.
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Acknowledgment - This paper reports developments from several fuel cycle studies
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made by many workers at the Oak Ridge National Laboratory. The literature references
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will serve as an acknowledgment of specific contributions,
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.2. SOL PREPARATION AND CHARACTERISTICS OF THE PRODUCTS
... The feed materials for our sol preparation procedures have been nitrate salts or
solutions because the products of many of the solvent extraction processes are nitrate
salt solutions. Also, any residual nitrate remaining in the sol or gel can be
volatilized during calcination.
Conversion of the nitrate into an oxide sol requires the following four steps,
which may be combined or accomplished in different orders:
A. Reducing or oxidizing to the best valence; U(IV) and Pu(IV) are preferred
for urania or plutonia sols,
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2. Converting the metal nitrate into a hydrated oxide.
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3. Removing excess nitrate and nonvolatile impurities. For instance, NH4NO3 or
NaNO3 must be removed if the hydrous oxides are precipitated/NH4OM or NaOH. 3
OFFICIAL
4. Dispersing the oxide as a stable sol.
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The preparation procedure for thoria sols is unique in that the basic colloidaly
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particle is formed by a steam denitration at temperature approaching 500°C.
8018, the colloidal particle is formed in solutions or wet precipitatęs.
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2.1 Urania Sol and Microsphere Preparation :
Sols for the preparation of UO2 microspheres by the sol-gel technique
were prepared by precipitation of hydrous U(IV) oxide and its subsequent dispersion.
A flowsheet for the laboratory preparation of U(IV) sol is given in Figure 2.
A uranous nitrate solution is prepared by the catalytic reduction with hydrogen
of a uranyl nitrate solution containing excess nitric acid. The solution is
filtered to remove the catalyst. Formic acid is added to the filtered solution.
The hydrous oxide is formed by precipitating U(IV) with an NH4OH solution
containing hydrazine. The precipitated hydrous oxide is collected by filtration
and washed to remove excess electrolyte. The washed filter-cake is then heated
at 69 to 65°C to produce a fluid, stable sol. A blanketing gas (argon) is
used during all stages of the process to protect the material from oxidation
by air. For critically control with enriched uranium, the sol preparations
were carried out batchwise using 300 g of uranium in each preparation. Sol
concentrations of 1.3 to 1.6 M UO2 were achieved (Table 1). Details of the
development of the sol preparation method and microsphere forming, drying,
and firing studies are given in ORNL-38743.
The nitrate/uranium mole ratio and the completeness of uranium reduction
are important to sol formation. During the precipitation step, the addition
of ammonia is controlled to give a pH between 7 and 8. In a typical
preparation, 3.0 M NH4OH--0.5 M N2H4-H20 solution is added at a rate of about .
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125 ml/min to a 0.5 M U(IV)--2.3 M NOZ solution with vigorous stirring,
The addition of formic acid to the v(IV) nitrate solution is necessary to maintain
a high v(IV) content (> 90% of the total uranium) in the precipitated hydrous .
oxide and subsequent urania sol. In the absence of formic acid the U(IV)
content of the hydrous oxide would be down to 80% of the total uranium in
contrast to the > 99% U(IV) content of the original U(IV) nitrate solution. In
addition, the formic acid simplifies pH control in the precipitation step,
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increases the rate of washing of the filter cake, and inhibits oxidation of
the U(IV) during microsphere formation.
The urania sols were formed into gel microspheres by the same procedures
developed for preparation of thoria microspheres (section 3 of chis paper).
Two organic surfactants together, about 0.5 vol % each of Amine O and Span 80y
were necessary to prevent coalescence and clustering of the urania sol drops.
The gel spheres were dried by gas flowing through a bed of spheres on a glas's.
frit. A variety of drying coniitions were tested for effectiveness of removing
the 2-ethyl-1-hexinol and surfactants from the gel microspheres". Steam
stripping by an argon-steam mixture appears to be the most effective method.
Drying with argon alone at 150°C best preserved the U(IV) content of the gel,
but the carbon content was about a factor of 3 higher than when steam was
present. Vacuum drying at 100°C for 74 hr yielded gelled microspheres, still
containing about 5 wt% carbon. In general, the carbon content of the dried
gel spheres was 2 to 7 wt %.
The Uo2 microspheres were fired at 1150-1250°C in high-purity alundum
boats inside a 2 1/2-in.-ID furnace tube of high-purity alundum. Two firing
procedures were used. In one, the spheres were heated in Ha at 300°C/hr to
the firing temperature and held at that temperatura for 4 hr. In the other,
wel
temperature and held for 4 hr.
Table 2 shows firing data for typical products. Microspheres from the
straight Ha firing and the CO2-Hą firing differed in carbon content, crush
strength, and x-ray crystallite size as measured by x-ray diffraction line
broadening. The Ha-fired products contained 2000 to 5000 ppm carbon and had
crush strengths, generally, between 1.3 and 2.3 lb per sphere. The co2-H2
firing effectively lowered the carbon content but decreased the product
strength. The crystallite size from x-ray line broadening obtained on microspheres
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of a typical Ha-fired product was 450 A, while that for a CO2-Hą fired :
product was 2500 A.
The preparation method routinely produces yields of 90% of the calcined
microspheres from a 300-8 batch in the 125- to 177-u-diam size. In this 125
to 1774 fraction about 3/4 of the spheres (by weight) are of 149- to 177-4 size.
Our early microsphere forming experience with urania sols was primarily in
the 50- to 250-u-diam size range, but we have been forming up to 500u spheres.
Figure 3 shows typical urania microspheres. The bright spots are light
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reflections from the surfaces of the spheres. Polished sections of these.
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same spheres are shown in Figure 4. Although it doesn't appear at this
magnification, there is a uniformly distributed microporosity in these spheres
which tends to coalesce to form macropores at about 1700°C.
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2.2. Thoria-Urania Sols and Microspheres
Sol-gel technology is being extended 'co include mixtures of thoria and ...
urania in all ratios. We are concentrating our efforts on an approach where
sols are mixed in the desired ratio, since this would be the most convenient
approach to use with a variety of fuel compositions. In the original sol-gel.
process, uranyl nitrate or uog' is added to a thoria sol and U(VT) is adsorbed
on the surface of the thoria particles. This technique is limited to U/Th ratios.
of less than 0.1.
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In the present, mixed sol approach, a thoria sol is mixed directly with a
urania sol. Other possible methods for preparing mixed sols, such as solvent
extraction of nitrate ion from mixed thorium nitrate-uranyl nitrate solutions,
dispersal of. precipitated thorium hydroxide with uranyl nitrate, and co-precipitation
of uranium and thorium hydroxides followed by peptization in nitric acid are also
being investigated. The level of preparation of all of the approaches is
laboratory-scale. We are concentrating our efforts on sols that have a Th/U
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atom ratio of about 3.5 since this appears to be one composition of interest for
reactor uels.
We have prepared UO2-Th02 sols on a laboratory scale by the following
specific methods:
1. Blending together of UO2 sols with Th02 sols.
2. Dispersion of a 95% 102--5% Thoz filter cake in the Th02 sols.
3. Dispersion of coprecipitated thorium hydroxide with uranyl nitrate,
4. Dispersion of thorium hydroxide with uranyl nitrate.
· Sols can be prepared which are both fluid and stable by all of these methods.
are not the first two methods have been used to prepare 300-g lots of calcined
microspheres of near-theoretical density and Th/U atom ratios up to 3.5 (Figure 5).
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The last two methods have not been as thoroughly investigated and will not be
discussed further.
The preparation of stable, fluid 102-Th02 sols iras been successfully
demonstrated by mixing our standard 102 sols with our standard Th02 sols. Using
these sols, we have prepared 300-g lots of 200-300-u-diam calcined mic::ospheres
with Th/U atom ratios up to 3.5. The upper limit of concentration of (Th + U)
appears to be about 1.6 M for fluid sols at Th/U«3. Above this concentration,
che sols are too thick for microsphere formation. The chemical composition
and crystallite sizes typical of this sol is shown in preparation CP-6
(Table 3). This CP-6 sol was formed into about 300 g of approximately 350-4-diam
gel microspheres using 2-ethyl-1-hexanol containing 0.3% Span 80 and 0.5% Ethomeen
S/15 surfactants. Excellent gel microspheres were produced which had shiny surfaces
and no evidence of, pitting. These spheres were dried to 125°C in argon with no :
evidence of cracking or deleterious pitting of the surface. After calcination
at 1200°C, these spheres wete had nearly theor tical density, excellent
crushing strength, and low-carbon contents (Table 4). The residual porosity
remaining in the microspheres was shown to be less than 200 .A by mercury.)
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The second method in principle is the same as the first mixed sol
method except that a small fraction of the total thorium is present as
precipitated thoria. Precipitated thoria has a crystallite size of 30 A,
whereas the thoria prepared by steam denitration of thorium nitrate has a
crystallite size of 65-80 A. We plant to prepare sols with a pure UO2
filter cake to note if the presence of the precipitated thoria has any
effect. In this method of preparation, a 95% VO2--5% Thoz filter cake
is blended with a standard thoria sol. The 95% 102--5% Thoz filter cake
is prepared by precipitating the hydrous oxides from a solution containing
uranium (IV) nitrate and thorium nitrate (Th/U atom ratio 19/1) with
ammonium hydroxide, filtering to form the filter cake, and then washing
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the filter cake until the filtrate is nitrate-free. This UO2-Thoz filter
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cake can then be blended with thoria sols to obtain higher compositions
of Th02. Typical chemical compositions and crystallite size of dispersed
particles are shown for preparations CP-12 and CP-13 (Table 3). For the
sols having a Th/U atom ratio of 3.5, the upper limit of concentration for
fluid sols appears to be about 2 m (Th + U).
The sol preparations, CP-12 and CP-13, were formed into gel microspheres
using 2-ethyl-1-hexanol containing 0.3% Span 80 and 0.5% Ethomeen 5/15
surfactants. About 200 g of 250-300-u-diam gel microspheres were formed with
CP-12, and approximately 250 g of 300-350-u-dlam gel microspheres was formed
with CP-13. The spheres were dried in argon at 125°C without any observable
cracking of the gel.
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ORNL - AEC - OFFICIAL
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An oxidizing atmosphere during part of the calcination cycle was necessary
to obtain a product of near theoretical density and low carbon content
(Table 4). Firing in completely reducing conditions produced spheres of
low-density, high-carbon content, and low crushing strengths. The
attainment of high density does not appear to depend on removing the carbon;
the
rather, it seems to depend on degree of oxidation of the VO2. For
example, exposing the spheres to air at room temperature for 1 day prior
was
to firing in a reducing atmosphere produced a product containing only 200 ppm
of carbon but the density was only 90% theoretical. We have not as yet
discovered the optimum calcination conditions. However, it appears that
oxidation by air to 1200°C or by coa from 850 to 1100°C prior to reductions
of the U02 yields products that have properties which are acceptable.
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2.3 Puo2, PuO2-U02, and Pu02-Tho2 Sols
A sol-gel process for the preparation of dense oxide forms of PuOz was
developed and tested on a laboratory scale. The plutonia sols are compatible
with thoria sols and urania sols which have been produced at the Oak Ridge
National Laboratory. Although continued development of this process will be
required before large scale production is feasible, the ability to produce .
dense plutonia as well as homogeneous plutonia-urania or plutonia-thoria
at any desired ratio has been demonstrated. Plutonia sols and mixed sols
have been calcined to oxide fragments which are suitable for vi ratory compaction
and formed into gel microspheres which calcine to uniform, dense oxide spheres.
The sol-gel process for plutonia utilizes the polymerization behavior
of tetravalent plutonium to produce crystallites of collodial size and to
maintain valence stability. The procedure corisists of three steps; namely,
precipitation, peptization, and denitration. The final sols are essentially
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colloidal plutonium dioxide, which vary from 1 to 3 M in plutonium and have
N03/Pu mole ratios of 0.1 to 0.3. The sols are stable for several months
and may be stored without difficulty.
The flowsheet for this process is shown in Figure 6. Dilute plutonium
nitrate solution (10 to 20 g/liter), which contains 1 to 2 M excess
HNO3, is precipitated by slow addition of the plutonium solution into a
100% excess of 2 M NH4OH with rapid agitation. Essentially complete removal
of contaminant nitrate and ammonium ions is readily accomplished by water
washing. After filtration of the plutonium precipitate, the filter cake is
resuspended in water and filtered. Three washings are usually sufficient
· to reduce the pH of the filtrate to less than 8.0 which indicates satisfactory.
removal of contaminant ion.
Freshly precipitated plutonium is peptized by digestion at 50-80°C
with dilute HNO3. Complete peptization is characterized by a color change
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from light green to a nearly transparent dark green. The minimum nitrate
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concentration necessary for complete peptization is one mole of HNO3 per mole
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per mole
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of plutonium. At this concentration, a digestion time of about 4 hr at
80°C is required, Higher nitrate concentrations can also be used, and, at
N03"/Pu mole ratios of 2 or more, the digestion time. is 10 to 15 min.
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The plutonium sol produced during digestion is a stable colloidal
dispersion; horever, this material is not suitable for fuel particle preparation
until the nitrate concentration has been reduced. This is accomplished
by evaporating the sol to dryness and baking the dried gel, Nitrate removal
is a function of both time and temperature, and excessive baking will result
in material which cannot be redispersed. A baking time of 6 to 8 hr at 200°C
.
is generally required to produce sols in which the nitrate concentration has
been reduced to mole ratios of 0.1 to 0.3.
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The final sol is prepared by resuspending the baked gel in excess water,
followed by evaporation to the desired plutonium concentration. Plutonium
concentrations in excess of 3 M can be achieved. These plutonium sols can be
dried and calcined to dense hard fragments, and they can be formed into
microspheres which calcine to dense oxide spheres at 1150°C. Plutonia sols
can also be mixed with thoria or urania sols and formed into microspheres
or fragments.
Laboratory-Scale Preparation. - Numerous small scale batches of plutonia sol
were prepared using laboratory equipment and conventional glove box and
alpha-handling equipment. Batch sizes have varied from 5 to 30 g of plutonium.
Plutonium feed solutions were purified by HNO3 anion exchange, and
plutonium valence was determined by spectral analysis with a Cary recording
spectrophotometer prior to sol preparation. When detectable amounts of hexa-
valent plutonium were found, the valence was adjusted to the tetravalent state
with nitric oxide. Product from the isn'exchange column provided excellent
feed for preparation of sol.
The plutonium concentration averaged about
20 g/liter, and the HNO3 concentration varied from 1 to 2 M. Storage of
such solutions for several weeks at room temperature was possible before
valence adjustment became necessary.
Plutonium was precipitated by adding the stock solution at the rate of
approximately 30 ml per. min to rapidly stirred NH4OH. The precipitate was
vacuum filtered on a medium frit sintered glass funnel. After washing, the
precipitate was transferred to a round bottom flask for digestion and
CUNI
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concentration. The plutonium concentration was adjusted to 0.1 M and sufficient
HNO3 was added to provide a concentration of 0.1 M. At this acid concentration,
complete peptization of the precipitate occurs in about 4 hr at 50°C. The
resulting sol is evaporated to dryness under vacuum at 80°C. While evaporation
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under vacuum is not mandatory, concentration can be effected more rapidly. For
ease of transfer, the concentrated sol can be transferred to a beaker for :
baking just prior to going to dryness. The sol is dried and baked to remove
nitrate at 200°C on a hot plate or in an oven. The solids are baked until all
but a sma11 fraction can be redispersed. This is taken as the minimum nitrate
obtainable for a given sol preparation, since continued baking will result in
totally nondispersible solids. The final sol is prepared by dispersing the
baked gel in excess water and evaporating to the desired concentration.
Typical plutonium sols prepared in this manner are stable colloids with
NO3"/Pu mole ratios of 0.1 to 0.3. Sols with plutonium concentrations in excess
of 3 M can be prepared.
Microsphere Preparation. - The final plutonium sols can be formed into gel
microspheres and calcined to dense, strong oxide spheres using the procedures
developed for thoria microspheres. This process is reported as the final
section of our paper. Microspheres of about 200 diameter after calcination
were prepared from pure plutonia sol (Figure 7), a mixed sol of 75% urania-,
25% plutonia (Figure 8) and a mixed sol of 50% thoria--50% plutonia (Figure 9).
Most of the microsphere preparations were with about 0.5 vol % each of Span.80
and Ethomeen S/15 as the surfactants in the 2-ethylhexanol solvent,
Microspheres have been prepared on a laboratory scale from mixed PuOz-Thoa
sols at Pula concentrations of 2, 10, 30, 50, and 80 wt% and from mixed
PuO2-U02 sols at PuO2 concentrations of 15, 25, and 50 wt %. The density of
these products after calcination at 1150°C varied from 95 to 99% of
theoretical. (The theoretical density of mixed oxides was taken as the wt .
average of the components.)
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3.0 MICROS PHERE PREPARATION
In the microsphere preparation process, drops of sol are gelled by
extracting the water into an organic liquid, such as 2-ethylhexanol, called
the "solvent". This operation replaces the gellation by evaporation of
water in the original flowsheet.
The process for conversing a sol into a calcined microsphere includes
the following six operations:
1. Dispersion of sol into drops.
2. Suspension in solvent and extraction of water to cause gellation.
3. Separation of gel microspheres from the organic liquid.
4. Recovery of solvent for reuse.
5. Drying of gel microspheres.
reuse
6. Calcination and sintering.
The size of the product microsphere is deter:ined in the first step. In the
second step, the extraction of water causes gellation and thus converts
the drop of sol into a solid sphere. This is the key process step. The
interfacial tension holds the drop in a spherical shape. This limits the
maximum microsphere size since very large drops will distort. The slow
extraction of water is essential to obtaining a microsphere with a high
density and high strength. If the water is extracted too rapidly, the drop
breaks into fragments or forms a hollow particle. The remaining four operations
are simple in principle. However, the densification during sintering and the
amounts of carbon and gases in the calcined product can vary greatly depending
on the conditions used.
The first four process operations may be done in a continuous column
system (Figure 10). The sol is dispersed into drops which are released into the
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enlarged top of a tapered column. These drops are suspended or' fluidized by
a circulating upflowing streari of the organic liquid. As the water is.
extracted and the drops gel into solid microspheres, the settling velocity
increases. Tive column configuration and the fluidizing flow rates were
se? :cted to permit the gelled particles to drop out continuously while sol drops
are farmed in the top of the column. The separation of the gel spheres from
the organic liquid is completed by discharging them onto a fritted-glass
filter and draining the liquid through the fritted glass. The spheres are
dried and calcined. Fresh or purified solvent is continuously added to the
column and displaces a stream of wet solvent to a recovery system. Water is
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removed from the solvent by distillation.
Other types of equipment have been used for the same process step. The
columns may be operated batchwise without removal of product or recovery
of solvent. Agitation in baffled vessels has also been used for dispersion and
suspension of the sol drops when microspheres of less than 100 u diameter
were prepared. A mixer-settler type systein would be a simple and efficient.
microsphere preparation system if the relatively non-uniform product and a
mean diameter of 80 u or less are acceptable.
3.1 Dispersion of Sols
A major part of the microsphere preparation studies has been the development
of sol dispersers. None of the dispersers tested were optimum in all respects,
but the important requirements can be met.
Two-fluid nozzles (Figure lla) were used for most of the studies reported
here. These devices were excellent for obtaining uniform and controllable
wrop diameters at sol feed rates of 0.5 to 10 cc/min. The sol is introduced in
the center of a flowing organic stream, which acts as the drive fluid. The
continuous flow of sol is accelerated to the velocity of the drive fluic; thus
R
.
js
f
TE
-14-
the diameter of the sol stream which results is independent of the diameter
of the sol entry tube. The sol stream breaks up by a varicose mechanism to
give sol droplets with diameters that are 2 to 2.5 times the diameter of the
sol stream. This type of breakup was predicted theoretically and observed
experimentally.4 The breakup of a 3 M thoria sol in a two fluid nozzle
(glass) was photographed (Figure 12). The organic flow was proportional
to the sol flow; thus droplets of the same size were formed at the three
va
e
wa
eie
different sol flow rates. The diameter of the sol drops can be predicted by
the following equation:
where
D = the sol drop diameter,
f = the sol flow rate,
V
V = the drive fluid velocity where the sol stream is introduced,
k = a dimensionless constant of 2.0 Betsel 2.5.
In order to produce uniformly sized droplets with a two-fluid nozzle, the
flow of the drive fluid must be laminar. Therefore, the nozzle should be
designed to minimize turbulence and give iaminar flow. Thus, the value
of V and the sol flow rate, f, are limited.
Sol drops may be formed from a larger mass of sol by application of one
or more forces such as gravity, centrifugal fields, shear, inertia, interfacial
tension, and electrostatic repulsion. In order to obtain uniform drops and
controlled diameters, both the force and the configuration of the sol must be
uniform and one or both must be controllable. In all the dispersers used for
·
I Mass
+....
.
-.
.
..
.
.
.
.
.
-15-
microsphere column operation, the uniform sol configuration is obtained by
feeding the sol through small (0.004 to 0.030-in.-diam) orifices.
The two sol dispersion mechanisms which gave the most uniform drops
during our development tests each have an important limitation. Small orifices.
immersed in the 2-ethylhexanol are a practical and simple means of forming
1200-2000 u sol drops by the falling drop mechanism. But the orifice size
necessary to produce sol drops smaller than 1000 u is too small to be
practical. The two-fluid nozzles (Figure 1la) give excellent uniformity
and simple, easy control of the drop size over a wide range. However, the
maximum capacity .per two-fluid nozzle (1 to 10 cc/min depending on the drop
size) and the need for non-pulsating and accurately controlled flows are
important limitations for remote, large-scale operation.
A promising method for uniform dispersion of a sol on a large scale is to
shear the sol :stream emerging from an orifice by maintaining a velocity
gradient in the 2EH at the orifice. This method was tested with rotary
feeders (Figure 11b) immersed in the top of the column. The sol stream
leaving small orifices (0.010 or 0.016 in diameter) in' the feeders are sheared
off with most of the force from the velocity gradient in the relatively
stagnant 2h. In other devices (Figure 11c), the orifices are stationary
and the 2EH is pumped past the orifice through a confined flow channel.
An electrostatic sol disperser was developed on a laboratory scale and
tested in the microsphere column.5 This device has fifteen No. 24 hypodermic
needles at a controlled positive potential with a copper ring at ground potential
around each needle. The mode of dispersion varies with voltage with distinct
7.
.
.
'
L
'
4n
;
.
.
'
.
*"
transitions. As the voltage is increased, there is first an operating region
with little effect, then a region of a single stream of very uniform drops, and then
a fan-like spray of nonuniform drops. For the intermediate region of uniform
.
1
A
*,
R
.
-
-16-
.
.
drops, the soļ drop size is a function of voltage, sol flow rate, and sol
concentration. Using the electrostatic, multiple-nozzle disperser, the
calcined product size distributions for a 3 M thoria sol and a limited
range of mean sizes (200 to 350 u) were as good as for a two-fluid nozzle.
3.2 Column Design
Tapered columns (glass) were the most successful of several column
configurations tested. Continuous addition of sol drops and removal of gel
microspheres was possible for columns up to 1/2 in. minimum inner diameter
by simply using smooth, gradual tapers and axial upflow of solvent.
When the tapered columns are scaled up to larger than 1/2 in. minimum
inner diameter, the suspension of the sol drops and gel spheres become s
unsatisfactory in several ways due to the laminar flow and parabolic velocity
distribution. The problems with maintaining fluidization in the larger
columus were eliminated by introducing a solvent tangentially at the bottom
CONS
.
of the column below the point of minimum inner diameter (Figure 10). This
tangential stream produces a swirl that extends with decreasing intensity
from 1 to 3 ft up the column. The mixing of the swirl prevents the
accumulation of particles on one side of the column. By controlling
ne
NS
OS
tangential and axial flows separately, the velocity profile across a diameter
can be flattened, or the upflow at the center may even by a minimum, with a
maximum between the center and the wall. The flattening of the velocity
profile by the swirl reduced the amour.t of axial mixing so that the wet sol
drops remained in the upper half of the column.
.:
3.3 Drying and Calcining Conditions
· Drying and calcining are necessary to remove volatile matter and to
sinter the spheres to a high density. The temperature and the atmosphere
are controlled according to a program in which the gel spheres as removed
i
.
•
-17-
OR
from the column are heated to about 1200°c and then cooled to room
temperature. The voq spheres must be protected from oxygen. The overall
drying-calcining operation is conveniently done in two steps in two separate
pieces of equipment. Drying was done with the spheres supported by a fritted
glass disk in a Pyrex vessel (Figure 13). The 2H was drained off through
the frit. The entire vessel was heated by a mantle and heated gas was
passed up through the disk. The dried spheres were calcined in alumina
crucibles inside laboratory muffle furnaces.
For thoria microspheres, the preferred conditions are:
Drying
Ar
25 to 110°C in 1 hour
.
.
.
-,_
,
.
.
a
m
am
.i.
in
.
--.
17
ce
Ar + steam 110 to 200°C in 6 hours
Firing
Air
From 100°C to 500°C at 100°C/hr
From 500°C to 1150°C at 300°c/hr
At 1150°C for 4 hours
For thoria-urania sols made with voz (NO3)2 or voz (limited to 10% urania),
the urania is reduced to Uo2 by Ar-4% Hą for four hours and then is protected
by an Ar atmosphere during cooldown. If carbon black is added to the sol,
carbide microspheres may be formed by the reaction of the carbon with the
oxides at temperatures of ~1700°C in an inert atmosphere or vacuum.
The rates of temperature rise listed for the thoria microspheres were
slow enough to be safe for any of the sols which we used. Much faster rates
of temperature rise during either drying or calcination sometimes resulted in
fractured particles, or in the presence of more porosity, larger surface
e
areas, and lower particle crush strengths.
.
-18-
.
3.4. Solvents and Surfactants.
.
. -.
.:ri
or
in
The eight-carbon alcohol, 2-ethylhexanol (2EH), was the organic liquid
for all the microsphere-preparation studies reported here. In general,
the long-chain alcohols are the most satisfactory solvents. Halogenated
solvents were avoided because of possible halogen contamination of the
product. Considering the many excellent properties of 2EH for this use, we
are unlikely to find anything significantly better.
A surfactant must be dissolved in the solvent to prevent coalescence :
of the sol drops with each other, coalescence of the sol drops on the column
walls, and/or clustering together of partially dried drops. Surfactants
also lower the interfacial tension between the soi and the 2EH; the inter-
facial tension must be high enough to keep the drops spherical.
The
vere
concentrations of surfactant used were 0.1 1:0 1 vol %. Span 80 (an Atlas
Powder Co. ester) was most effective for preventing coalescence and clustering,
but it also gave a low interfacial tension and permitted distortion of the larger
drops of sol. Ehtomeen S/15 and Amine O were successful for forming thoria
spheres in all sizes. For sols other than pure thoria, Span 80, and Ethomeen
S/15 were generally used together with 0.5 vol % of each as the most common
WE
S
.
concentrations.
?
VS
sy
3.5 Solvent Recycle
The solvent that overflows from the microsphere column to the wet solvent
tank is purified before it is returned to the column. The water content is
efficiently reduced by a simple, single-stage distillation. The boiling
point of the 2EH changes rapidly with water content: from 183°C for pure
2EH to 150°C for 0.62% H20 and 98°C for the azetrope when an aqueous phase
is present. The solubilities at room temperature are 2.55 wt% for water in
INT
.
.T-
tul
L.
CR7
*
2EH, and 0.1 wt% for 24 in water. Operatir.g conditions are usually selected
.
-19
-19-
ORNI - AEC - OFFICIAL
..
to give a 0.5 to 1.0 wt% difference in water content for the dry and wet
solvent.
...
T
..
.
.
Use of the steam heated still with 90-psig steam, heat exchangers and a
phase separator give very simple and efficient operation. Only a smali
fraction of the liquid is vaporized. Most of the heat required is sensible
heat, and a good heat exchanger minimizes the heating and cooling load. As
water and 2EH are vaporized, the water content of the liquid decreases until
the boiling point approaches the condensation temperature of 90-psig stean
(165°C). Thus, the amount of boilup is automatically controlled and no
measurement or control devices are needed. After the vapors are condensed,
the aqueous and 2EH phases separate by gravity and are discharged through
jacklegs. This single stage distillation with separation of the condensed
liquids requires less heat than using reflux in multiple stage column.
Gradual color changes of the solvents indicate the accumulation of
surfactant or solvent degradation products. The accumulation of these impurities
did not cause any apparent deleterious effects during the longest runs
(over 100 hr) which we have made. If these impurities do limit the recycle
of solvent, the costs of solvent treatment versus replacement will have to
be considered,
3.6
Product Characteristics
SY
The product characteristics of principal importance were: particle shape,
size, chemical composition, density, strength, amount and type of porosity
"TYY
present, and irradiation behavior. Generally, nearly 100% of the particles
in the product size range were spheres (Figures 7, 8, and 14). Some of the
nonstandard sol preparations and/or column conditions can result in clustering or crac
into fragments and thus can result in nonspherical particles. About 750 u diameter
thoria microspheras were about the largest possible for the conditions used as
ORNL - AEC OFFICIAL
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ORNL - AEC - OFFICIAL
shown by the fact that the largest gel particles were slightly distorted.
were
(The interfacial tension cannot maintain the spherical shape when the sol
drop becomes very large since the distorting forces become relatively larger.)
Omes
The lower size limit is determined by the practicality of dispersing the
sol into very small drops ard collecting the product.
The chemical compositions of the products are of importance with
respect to the impurities present and to the practicality of preparing
products that are mixtures. The only impurity problem is the presence
of 2000 to 5000 ppm of carbon in calcined urania microspheres. This carbon
ami
is from the 2EH and/or the surfactants. The nitrate, ammonia, formate, and
hydrazine are completely volatilized. The 2EH and surfactants leave no
residues other than carbon and the carbon can be completely oxidized during
calcination if an oxidizing atmosphere is acceptable. The concentrations of
other impurities are the same as or less than those in the nitrate salts from
which the sols are prepared. The sol-preparation, sphere-forming, and sphere-
drying' operations are not corrosive to stainless steel or glass apparatus, and
the microspheres are inert to alumina at 1200°C,
Most of our gel microsphere:3 sinter to strong particles of nearly theoretical
density at 1150°C. The porosity remaining at this temperature will be fine
and uniformly distributed.
The results for pyrolytic carbon coating and
irradiation of sol-gel microspheres are good; these will be reported in
es
detail in other papers.
ORNL - AEC - OFFICIA!
-22-
REFERENCES
1. 0. C. Dean, et al., "The Sol-Gel Process for Preparation of Thoria
Base Fuels", TID-7650, p 519-42 ( 1962).
2. A. L. Lott, et al., "The Oak Ridge National Laboratory Kilorod .
.
,
PS
J. P. McBride, Preparation of UO2 Microspheres by a Sol-Gel Technique,
ORNL-3874 (Feb. 1956).
* 1997
.
A. C. Merrington and E. G. Richardson, "The Break-up of Liquid Jets", .
Proc. of Physical Soc. (London), 59, (331) 1-13, (1947).
D, M. Helton, "Dispersion of a Liquid Stream by an Electrical
Potential: Applications to the Preparation of Thoria Microspheres",
ORNL-TM-1395, (1966).
6. J. L. Kelly, et al., "Sol-Gel Process for Preparing Spheroidal Particles
of the Dicarbides of Thorium and Thorium-Uranium Mixtures", Ind. Engr. Chem.
4, 212-216, (April 1965).
I'4
''
.
-
-
-
- -
-
-
-
.
.
*
.
*.
.
4,
P
.
1
-;-
.
Table 1 . Properties of Typical Urania Sols
Specific
Gravity
(g/cc)
Uranium
Conc.
(M)
U(IV)
Content :
s of U).
NO,
Ratio
HCOO /
Ratio
-1.317
1.23
0.13
0.44
1.319
1.319
.
.. 1.27
0.07
0.38
1.369
1:369
. 1.48
86
1.48
1.373
1.49
0.14
0.45
0.45
0.31
1.404
1.61
0.11
1.405
1.405
1.62
1.62
87
0.11
Table 2 • Firing Data for 125- to 177---Diameter UO, Microspheres :
Sintered in H, at indicated temperature for 4 hr
·
.
• Heat-up
Schedule
Sintering; Wt Loss on
Temp.: Sintering Gel
(°C). (W+ %)..
Wt. Req'd
,to Crush
. (g)
Carbon
Content
(opm)
Product
Density
(% of theor.)
a...
:
6.9
871 ...
4600, :
97.8
..
1150
1250
.
.
.
. 1050
....
4900
97.6
1150
10.2
:
:
354
.
:
.: 460
.
-100
.
..
1250
.
..
313
*.35:1
200
<100
: ~100.
.
b.
• ~100
a. Hy to firing temperature at 300°C/hr
b. CO, to 450°C at 50°C/hr; CO2 to 600°C at 25°C/7r; Co, to 950°C at 50°C/hr;
Hy to firing temperature at 300°C/hr.
*-
,
Table 3. Preparations of UO2-Th02 Sols
Preparations Scale: ~ 300 g of combined oxides
Th/U
Mole Ratio
(Th + U)
Preparation Code
NO3/(Th + U)
Mole Ratio
U(IV)
% of u
X-ray Crystallite Size, A
lll
311
Oto
0.11
CP-6
CP-12
CP-13
3.45
3.75
3.69
1.58
1.64
2.03
-
65
52.6
63.5
65
67
72
64
62
68
65
0.13
0.13
.
65
62
.
condos - prepared by blending a urania sol (1.32 M U, 88% U(IV), and NOZ/U = 0.16 with GS-26 thoria sol
(3.07 M Th, NO3/Th = 0.099) prepared from steam denitrated thoria.
CP-12 and CP-13 prepared by mixing a thoria paste filter cake made from water, HNO3, and steam denitrated
thoria which contained excess nitrate with a near-nitrate-free 5% Th02--95% 102 filter cake prepared by
coprecipitation from a U(NO3)4-Th(NO3)4 nitrate solution. Dilution with H20 from 2.7 M (Th + U) was required
for fluidity.
.
.
.
- -
- . .
.
.
.
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.
.
.
.
.
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Table 4. Firing Conditions and Properties of Fired UO2-Th02 Microspheres
Conditions:
15-25 g of gel microspheres per firing; samples
were cooled to room temperature under argon atmosphere
Soaking Conditions
Heating Conditions
Temperature
Rise Rate Range
Atm oc/tır
Firing
No
Sol Prepa
Product Analyses
Crushing
Strength
0/1 ratio (8)
B.E.T.
Surface Area
Temp Time Carbon
(°c) (hr) (ppm)
Density”
(g/cm3)
(°c)
O
Atm
(m2/8)
CP-12
1
400
300
200
50
10.14
2.006
581
air
air
air
Ar-4% H2
Az-4% Ha
0.005
2
25-1000
1000-1200 - Ar-4% Hz
25-200 air
air
200-1000
1000-1200. Ar-4% H2
1200 3.5
2001
1200 5.5
'
400
-
300
.
30.
10.13
2.009
532
0.017
.V
.
3
CO2
25-1000
1000-1200
.
Ar-4% H2
400
300
400
300
1200 3.5
150
10.35
4
2.011
585
0.005
.
4
.
Ar-4% H2
Ar-4% H2
25-1000
1000-1200
25-1200
393
10.1
CP-13
Ar-4% H2
Ar-4% Hz
air
Ar-4%
6400
100
1200 3.5
1200 4
25
1200 4
8.02
10.1
air
2.081
2.00?
300
..1305
0.006
Ar-4% H2
Ar-4% Hg
atti
200
10.1
2.061
1393
4.08
3
COZ
300
300
300
300
300
25-1000
25-850
850-1100
25-850
850-1100
Ar-4% Hz
1100 .4
<100
10.2.
2.026
1518
0.005
4
Ar-4% Hz
air
:
Ar-4% H2
1100 4.
<100
9.81
2.015
1884
0.173
asee Table 1.
"By Hg porosimetry: Theoretical density is 10.25 g/cc.
CAve. of 10 microspheres; size tested was 250 diameter except 1504 with CP-12, .
ORNL - AEC - OFFICIAL
ORNL - AEC - OFFIGIAL

ORNL DWG. 65.437
H20
VO2(NO3)2
NHZ SOLUTION
(0.2 M)
SOL PREPARATION
THORIUM NITRATE
SOLUTION
STEAM
DENITRATION
185-475°C 1
BLENDIN
..(~2 M)
Tho,
| NO 5 = 0.077 ML2 = 0.017
Voz-Tho2
SOL
HjO
STEAM.
350-450°C
GELATION :
EVAPORATION!
80-85°C
DENSE UO,-Tho2
TO SIZING AND
VIBRATORY
COMPACTION
CALCINATION
AIR, 300°C/hr TO 1150°C
1150°C, 1 hr
REDUCTION
ARGON-4% HYDROGEN
1150°C, 4 hr
ARGON - COOL TO 100°C
Uog-Thoz
GEL
(DENSITY: ~7 kg/liter)
Fig. 1
Original Sol-Gel Process Flowsheet.
.
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0.5 M UO,(NO3)2 -2.3 M HNOZ
0.26 M UREA
;' 30-60 mg PT CATALYST
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FILTRATION
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.
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UINO, SOLUTION
.
CONC. FORMIC ACID

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.
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FORMIC ACID ADDITION
| SOLUTION MADE 0.3 M IN FORMIC ACID
PRECIPITATION
3.0 M NH, OH
0.5 M N HAH20
.
-
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U(IV) HYDROUS OXIDE
SUSPENSION
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9 LITERS H2O

..
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FILTRATION AND WASHING
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WITH NO. 42 WHATMAN PAPER
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HEAT AT 60-65°C AND STIR
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Fig. 2
Flowsheet for the Laboratory Preparation of Urania Sol.
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Fig. 3 typical U02 Microspheres (Diam - 125 to 177 p).
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Fig. 4
Sections of UO2 Microspheres; Density: 96% of. Theoretical;
Carbon: < 100 ppm; Crush strength: 550 g.
ORNL DWG 61-111
ORNL - AEC - OFFICIAL

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Ratio of 3.5, Density by Hg Porosimetry of 99%, 30 ppm C, and O/U
... Mole Ratio of 2.016.
.
ORNL - AEC - OFFICIAL
WOWA
Fig. 5. Calcined ThO2-00, Microspheres Prepared by Mixing Thoria
and Urania Sols.
KITA
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PRECIPITATION
100% EXCESS OF
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-
.: WASHING
WATER WASHING TO
FILTRATE PH of 7-8
PEPTIZATION :
DIGESTION AT 80°C -
TO COLOR END POINT
(LIGHT GREEN TO VERY
: DARK GREEN)
..
:.
:::
:
..
.
...
.
RESUSPENSION
WATER ADDITION
1. WITH AGITATION
NO, REMOVAL
HEAT TO DRY NESS;
BAKE AT 120-200°C
$
:.:.:.
:.
:: PLUTONIUM SOL
Pu CONC. 1-3 M
.
.
1

(NO3. CONC. 0.1-0.4 MOLES NOZ/MOLE PU)
....
D
•
Flowsheet for Plutonia Sol Preparation.
.
PHOTO 81177
-
C
.
10
ULT
-
re
X
*
.
1
.
.
UNCALCINED
CALCINED
Fig. 7. Plutonia Gel and 1150°C Sintered Microspheres. Average Diam: 130 M; Density: 96% of Theoretical.





.
IS
win
!
The
7
PHOTO 81179
MUS
1.
7
-
.
X
I
me.
."
********
.
.
Sibirisinden
min.
.
i
&
.:
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:
.
mtotine
demien
::
die
ܗ ܚܕܪ--
die
.
.
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..
"
;.***.**. There
erot
siciliani
to the games
hatimator
s
?
"
mere
UNCALCINED
CALCINED AT 11:50°C
IN HMDROGEN
,
Fiq. 8.
75% Urania--25% Plutonia Before and After Calcining. .

sinuniladiti
.:.

... حمد ۰۸
۰۰۰۰
به
م،
د... ۱۰
همت
:
50% Thoria--50% Plutonia Before and After Calcining.

.
من له مسمن
حمد
::...
: همه نه دمعه
ا
وه .
و .وFi
,مه و همه به
سه
ر
متنه نننعنننمندیشمممممننعهنعنننممست مسلمتين يمنييننننننننننننننننننننننننننن
CRNL-DWG 65-913
- ARGON
SOL FEED
TANK
TWO-FLUID
NOZZLE
SOL METERING!
PUMP
ARGON
COOLING WATER
PHASE
SEPARATOR
90 psig STEAM
STILL
POT
FLUIDIZED
MICRO-
SPHERES
WASTE WATER
ARGON
ARGON
.
CONDENSATE
ET-FILTER
-25- .
M
WET
SOLVENT
TANK
ION
EXCHANGE
RESIN
.
HEAT
EXCHANGER
DRY
SOLVENT
TANK
COOLING
WATER
.
.
E

PRODUCT
COLLECTIC
mopean
&
FILTER
FILTER
@
Fig. 10 Sol-Gel Microsphere Column and Solvent Recovery System.
ORNL DWG 65-6193
..
k
Aqueous
7
Aqueous
Sol -
Aqueous Sol –
WILMIN
Organic
Drive-Fluid
leinen
Organic
Drive-Fluid
Three, Spacing
Fins
-
0.010" 10
0.020" OD
0.125" ID : :
Eight, Equally
Spacod Holes
0.010" D
Eight, Equally
Spaced Holos
0.010" 0
>
?
1/4
A
-1.1/4"D-
3/4" 10
7 1/4" OD
c. Shear Disperser


a. Two Fluid Nozzle
b. Rotary Dispers er
. Fig. 11
Sol Dispersion Devices.

PHOTO 66462
Lahteet.
..
ir var v. *) un
B
.
0.5 cc OF SOL/min
12 inch
-42-

1.2 cc OF SOL/min
n
a
www
.
rumah
min
..
.
..
dito
ugo
n.,
...
...
-
- -
.
...
.
.
-
..'
.
het nie
vinner
.
.
Di
.
DO O No 0 00:0
mit einem anderen
vers
:
YA
2.5 cc OF SOL/min
Fig. 12 Breakup of a 3 M Thoria Sol into Drops.
tit
.
--
_
:'
.
::
.
-
...
9
2.
-


-28-
ORNL Dwg. 65-3826
GAS EXIT

.
uit!
01
IIII
10.III.I
! ! ! ! ! !
!
!
!
30-45°
3/4"
90-120°
. 1. C. WELL - 3 mm ID
.
.
.
.......
...
..
..
.
.
...
..
.
.
..
GEL MICROSPHERESSE
Vi
a
h
Nivet
COARSE FRITTED DISK
3/4"
I
III..
1
19-38
Wiki
....ii...III
GAS ENTRY
Fig. 13 Pyrex Vessel for Drying Microspheres.
ATWA
UN

.
سنة مدنبند صممتعففهمت
.
:
1
D
2
.
1
b están conected
am
.
patah
50 MICRONS
250 MICRONS
500 MICRONS
750 MICRONS
i
Fig. 14
:
Thoria Spheres Calcined at 1150°C.
I
.
contramos
la historia
.
i
.
..-
1;
-
M
A
*
.
.
m
.....
.
.
ultidis:
.
.
its.."
:
..
...
:
.,


2
A
.
END

DATE FILMED
7 / 28 /66
VA
V
.
,
.
.
.
-
--
-