Note: Descriptions are shown in the official language in which they were submitted.
~L274855
INTRODUCTION
Methods for the preparation of metal oxide microspheres
via sol-gel routes are well known in the art. For example, a
metal oxide aquasol may be injected into a dehydrating solvent
which forms the aquasol into spherical droplets by surface
tension forces and extracts water from the droplets to produce
solid microspheres. Alternatively, the aquasol droplets may be
dehydrated by contacting them ~ith a heated solvent in which
water has a minimal miscibility. Such methods have been
described in U.S. 3,312,632 and in U.S. 4,349,456.
By another known method, a salt or aquasol is mixed with
an ammonia releasing agent and then introduced as a droplet into
a liquid maintained at a temperature sufficient to thermally
degrade the ammonia-releasing agent and cause ammonia release
which results in gellation of the droplets into firm metal oxide
microspheres. Variations of these methods are discussed in U.S.
Pat. No. 2,620,314 and in U.S. Pat. No. 3,312,632.
The methods described above result in metal oxide
microspheres which are large, often hundreds of micrometers in
diameter. These methods are generally not suitable for preparing
submicron particles.
Microspherical metal oxide particles may be prepared by
the controlled hydrolysis of the corresponding metal alkoxide
compound in dilute solution. The microspherical particles
produced by this method are of high purity and are very uniform
in size with average diameters ranging from less than 0.05
micrometers to several micrometers. This method, which is
discussed by W. Stober, A. Fink and E. Bohn in Journal of Colloid
and Interface Science, Vol. 26, 1968, pp. 62-69, and by E.
Barringer and H. K. Bowen in Journal of the American Ceramic
Society, Vol. 65, 1982, pp. C199-201, involves the use of
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expensive and reactive organometallic compounds which must be
handled ln an air- and water-free environment. These
requirements are prohibitive to large-scale implementation o~ the
method and restrict its practice to the laboratory.
The use of emulsion techniques in the preparation of
metal oxide microspheres by sol-gel routes is known in the art.
Aquasols of metal oxides may be dispersed into lmmiscible organic
solvents, often with the aid of surface active agents, and gelled
to form spherical particles by the addition of a gellation agent
such as ammonia gas or compounds such as amines which are capable
of extracting stabilizing ions from the aquasol. Such procedures
which are discussed in G.B. 1,412,937 and G.B. 2,116,959A involve
several processing steps and produce particles which are
generally larger than 1 micrometer.
The method of U.S. Pat. No. 35848,059 comprises the
combination of two separate water-in-oil emulsions, each
containing a different inorganic salt, to form a
spheroidal-shaped particle of an insoluble metathesis product
with average particle sizes in the range of û.l to 5.û
micrometers. The distribution of particle sizes is unspecified.
In order to remove the water-soluble salt by-product, it is
necessary to filter and extensively wash the insoluble
microsphere product.
In U.S. Pat. Nos. 4,011,096 and 4,132,560, methods are
described for the preparation of reticulated and pigmented silica
microspheres, respectively. The pigmented microspheres (2 to 100
micrometer average diameter) are made by acidiFying a
water-in~oil emulsion containing a silaceous aqueous phase
whereas the vesiculated microspheres (0.5 to 5û micrometer
average diameter) are made by acidifying an oil-in-water-in-oil
lZ'7~5~; ~
emulsion prepared by a double-emulsion technique. 30th of these
methods involve numerous processing steps such as extensive
washing and centrifugation of the silica microspheres and they
require the use of undesirably large quantities of surfactants.
These disadvantages render the methods commercially unattractive
from a practical and an economic point of view, as stated in U.S.
Pat. No. 4,173,491.
U.S. Pat. No. 3,857,924 describes another emulsion route
to spherical silica particles. An alkali silicate solution is
treated sequentially with cation and anion exchange materials in
order to remove cations and mineral acids, respectively, to give
a polysilicious acid solution which is unstable toward
gellation. This solution is emulsified in a water-immiscible
solvent wherein it gels within 60 minutes to form silica spheres
with sizes in the range of l micrometer to 3mm. A problem
inherent in this method is that the rapid gellation time requires
that the emulsification step be executed soon after the ion
exchange steps. This restriction would be disadvantageous in
practice. Furthermore, the method does not lend itself to
continuous processing.
It can be seen, then, that the methods currently
available for the preparation of submicron metal oxide
microspheres are unsatisfactory for one or more of the following
reasons:
l. The microspheres obtained are too large.
2. The methods entail complicated, multistep procedures
which would be impractical and expensive to implement on a large
scale.
3. The methods are inherently limited to specific
materials.
-
The direct evaporation in vacuo of water-in-oil
emulsions containing mixed salt aqueous solution to produce
intimately mixed salt particles of unspecified size and shape is
described in ~The Use of Emulsions in the Preparation of Ceramic
Powders" by P. Reynen, H. Bastius and M. Fiedler in Ceramic
Powders, ed. P. Vincenzini, Elsevier Scientific Publishing
Company, Ansterdam, 1983. It has, however, never been suggested
to apply this method to a water-in-oil emulsion containing an
aquasol or dispersion of a metal oxide in order to prepare
micron- and submicron-sized metal oxide microspheres.
The method of the present invention provides for the
preparation of metal oxide microspheres with submicron diameters,
preferably in the approximate range of 0.05 to 5 micrometers, by
a simple method which does not entail numerous processing steps.
THE INVEN T ION
In its broadest aspect, the invention comprises a method
for the preparation of metal oxide microspheres which comprises
evaporating to substantial dryness a water-in-oil emulsion having
as its internal phase an aqueous colloidal dispersion of a metal
oxide whereby there is produced microspherical particles of the
metal oxide having an average particle size diameter within the
range of 0.05 - 5 microns.
This invention specifically provides a process for
producing micron- and submicron-sized spherical metal oxide gel
particles by the steps of:
(i) forming of water-in-oil emulsion composed of fine
droplets of a colloidal dispersion of a metal
oxide in a water-immiscible organic liquid
containing one or more emulsifiers;
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(ii) evaporation of the water-in-oil emulsion of step
(i) to remove the oil and water to form a cake or
free-flowing powder composed of metal oxide
microspheres, and optionally;
(iii) calcining the particles to produce dehydrated
metal oxide microspheres which are free of
organic contaminants.
The Colloidal Dispersion of the Metal Oxide
The aqueous or internal phase of the water-in-oil
emulsion of the above step may contain either a true metal oxide
aquasol in which the typical particle size is on the order of
several millimicrons or a dispersion of the metal oxide composed
of larger yet still colloidal particles. The pH of this phase
may be either acidic, neutral, or alkaline.
The colloidal dispersions of the metal oxides used to
prepare the internal phase of the water-in-oil emulsions contain
those metal oxides which are substantially water-insoluble and
are capable of forming aquasols. Such metal oxides comprise the
oxides of those metals found in Group III-~ through Group IV-A of
the Periodic Table. Included in this group of metals are the
colloidal oxides of silicon which, for purposes of this
invention, are considered to be within the definition of metal
oxides. In certain instances mixed or coated metal o~ide
dispersions may be used.
Typical of the metal oxides that may be formed into
microspherical particles by following the teachings of this
invention are the oxides of silicon, aluminum, iron, chromium,
cerium, tin, zirconium, titanium, zinc, and the like. These are
only considered to be illustrative of the many microspherical
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metal oxides that can be prepared. Also, mixtures of these
oxides may be used.
As indicated, these metal oxides or mixtures thereof are
employed in the form of aqueous colloidal dispersions. These
dispersions contain the metal oxide in a form such that one
dimension thereof is within the average particle size range of
between 1 up to about 20û millimicrons.
The particle size of the metal oxides in the starting
colloidal dispersion will vary depending upon the particular
metal oxide used and its method of preparation. Many colloidal
dispersions of metal oxides of the type described are available
commercially and are of a relatively high degree of purity.
Also, the concentration of the metal oxide in the colloidal
dispersion will vary; usually a minimum amount in the starting
colloidal dispersion will be about 2% and it may be as high as
50%.
In the case of aqueous colloidal silica sols, typical
starting sols that may be used are sold under the tradename,
NALCûA ~. These come in a variety of particle sizes and
concentrations. Illustrative of such starting aqueous silica
sols are those set forth in Table I below.
7~
l ~ o~o o
_, _, o o
~j N N
O O O ~
Is~ ~ ~
_I ~ N
,-~ O
l u~ o o o
O a~
O O O
~ Il~--1
O O O L~ o
~ 1~ N 1`~0
O O~
_~ I~ I O
N
Ir~ u-\ ~) N O ll~
~ r~
O a) I ~ N
_I ~O ' I O
~ cC ~--I N O
I,LJ ~ ~ N C~
~ O ~O I . .
m _~ ~ -I o
O O N ~O O ~ ~t
. ~ 0
O O I N N O
O
O~
N O
O
E E~
t~ _I h
~ ~
~U E E O
"~
.,, ~ ta
U) ~
U~ ~ ~
a~ >.
O ~ ~ > ~
n~ c
a~
o ~ c
t~ ~ C
c~ ~ ~ a~ Q.
c: ~ C ~ cn ~
o ~ ~n
C.~ ur) ~ h C~ O Ul
J ~ ~ a) ~ o N a
c~ a) ~I ~ >CL .~a
Z Q QQ 5 c~ Z r-~
In the case o~ silica sols of the type described above,
there average particle size ranges between about 5 millimicrons
up to about 150 millimicrons. A preferre~ particle size range is
within the range of about 10-60 millimicrons.
Another useful starting colloidal dispersion of the
metal oxides of the type described above are the alumina sols
described in detail in U.S. 3,141,786. These materials are
described as an aqueous sol composed of alumina fiburles having
a surface area of 200-400 square meter per gram and an average
length of 25-1500 millimicrons.
In addition to the specific silica and alumina sols of
the type described above, there are listed below properties and
characteristics of other commercially available colloidal
dispersions of metal oxides that may be used as a starting
material in the practice of the invention:
Alumina Sol
Typical Physical Properties
Surface Area (BET) 320 m /gm.
Particle Size
Powder - by sieving
greater than 45 microns 15%
less than 45 microns 85%
Dispersion - by X-ray diffraction .0048 micron
Loose Bulk Density 45 lbs./ft.3
Packed Bulk Density 50 lbs./ft.3
g_
~ ~27qL~5~
Cerium Oxide Sol
Typical Properties
Formula CeO2
Wt. % 18
Particle Size, millimicrons 10-20
pH 2.7
Specific Gravity 1.19
Viscosity, cps 10
r~
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r~
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>- ~ N ~ ~ --~
a~ ~~o
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C t.)
O ~
O N O ~
O ~ O N
h O ~
I`J ~ N
O Oz ~
O N O 0 I C`~
h O
.,_1 h O
~I N ~ O
O
c ~ z
h f^l ~ O ~ ~
I~J 1~1 N --I O --I ~ I`
h
Q
h Ir~ ~1
O x 0 ' a7
C O~ r`_, O
N Q
~ O
.,1N N O N
h O I -t NIt~ N
tL)~ O O O
C~ ~ --I O
~1 O ~:
._~~ ~ O C~l
~-1 O I I ~ O N
U)~D O O ~ O
O ON --I O ~ ~
a~ h Q
N ~
.~ ,c c
~n o o
.) OO O ~7
E O
V ~)C ~ ,
~1 ~h
o~ ~a ~ta o o I ' '-I
h. Z ~ E C_ O E Q ~ ~
Aquasols of alumina and titania sold under the
tradename, NALCO; aquasols of zirconia and iron oxide sold under
the tradenames, Nyaco ~ and P ~; and dispersible alumina sold
as Disperal~ are particularly useful in this invention.
While the colloidal dispersions of the metal oxides have
been described as being finely divided particles in water7 it is
understood that instead of water, there may be substituted
therefor highly polar liquids such as the water-soluble liquids,
ethanol, isopropanol, water-soluble or immiscible glycol such as
ethylene or propylene glycol, and the like. Such colloidal
dispersions are considered equivalent to the aqueous colloidal
dispersions of the metal oxides.
The Water Immiscible Organic Liquids
The preferred water-immiscible organic liquids which
constitute the oil phase of the water-in-oil emulsion of step (i)
above are sufficiently volatile to evaporate at temperatures
below that which will cause de-emulsification of the emulsion,
yet it is not so volatile as to evaporate at a rate much greater
than water. Commonly available commercial hydrocar~on mixtures
such as those sold under the trade names, Napthol Spirits and Low
ûdor Paraffin Solvent, for example, are useful in this
invention. The amount of organic liquid used in relation to
water may be varied.
While it is preferred to use hydrocarbon liquids of the
type described above, it is understood that other organic liquids
may be also used. Such organic liquids must be hydrophobic and
be sufficiently free of polar groups such that they would either
not be capable of forming the water-in oil emulsions or would
cause extractive dehydration of the colloidal dispersion Qf the
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hydrous metal oxide to occur. Thus, certain chlorinated liquids
such as perchloro ethylene, vegetable oils, and the like may be
used.
Preferred emulsions are prepared with water-to-oil
ratios of l:l to 1:2. The ratios are illustrative of emulsions
that can be prepared, although it should be understood that the
invention is not limited thereby.
The Water-in-Oil Emulsifier
._
Suitable emulsifying systems useful in producing the
water in-oil emulsions of step (i) above are obtained by choosing
a so-called low ~LB material or by combining a low HLa material
¦with a higher HLB material in ratios such that the resultant HLB
¦of the combined materials is su~ficiently low to form a
¦water-in-oil emulsion with fine aqueous droplet size. Although
¦these emulsifying systems are useful in producing good
¦water-in-oil emulsions, other emulsifiers may be used as long as
¦they produce the desired oil-in-water emulsions. The HLB
¦classifications of various emulsifiers are summarized in The HLB
System, ICI Americas, Inc., Wilmington, DE, 1976, and in
McCutcheon's Detergents and Emulsions, 1983 North American
Edition, McCutcheon Div., MC Publishing Co., Glen Rock, NJ.
Also, see Surfactants and Interfacial Phenomena, by Milton J.
Rosen, John Wiley & Sons, NY, 1978, Chapter 8.
As a general rule, the HLB of the emulsifier or
emulsifier system will be below 8 and is preferably within the
range of 4-6.
Typical water-in-oil emulsifiers that have been used
successfully in the invention are the well known commercial
emulsifiers:
~ lZ7~85~i 1
Span 8 O Sorbitan Monooleate
Tween 6 ~ Sorbitan Monostearate Rx 4 moles E~
Ethoduomeen T/13~ N,Tallow 1,3-propylene diamine Rx
3 moles E0
the combination of Span 8 ~ with Tween 6 ~, Tween
61~ or Ethoduomeer~ T/13 form useful emulsifying systems for
the present invention. It is generally desirable to minimize the
amount of emulsifier used. The preferred total emulsifier level
is usually less than 10% of the oil phase by weight. It may
range, however, between 0.5 - 20% of the oil phase.
The emulsions of step (i) may be prepared by any of a
number of techniques known to those skilled in the art. For
example, the emulsions may be prepared by using high-speed
agitation to disperse the aqueous phase into the oil phase
containing the emulsifier or emulsifiers.
Dehydration of the Emulsion
The emulsion is then subjected to temperatures and
pressures which are sufficient to achieve evaporation of both the
water and the oil phases at approximately similar rates. The
temperature to which the emulsion is subjected must not be so
high as to disrupt or break the aqueous droplets within the oil
phase. When the emulsion is properly formulated~ the rate of
evaporation is not critical and whereas it is convenient to
rapidly evaporate the emulsion, it is possible to prolong the
evaporation or even interrupt the evaporation at some
intermediate stage and continue it at a later time.
The evaporation of the emulsion may be conducted in any
device which will accomplish vacuum or atmospheric drying of
solids or distillation of liquids. In the pr~ferred methods for
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preparation of the microspheres of this inventiont evaporation of
the emulsion may be accomplished in thin-fllm dryers and in
thin-film evaporators, each of which may be o~ the mechanically
agitated or non-agitated type, or in stills, dryers or
evaporators of the wiped-film type. For example, the emulsion
may be evaporated in a rotary evaporator. Other methods of
evaporating the emulsion may be employed, however, it should be
understood that the invention is not limited thereby.
The removal of the water and oil phases by evaporation
affords a solid composed of metal oxide microspheres which are
coated with the emulsifiers. If the oil phase contains a
high-boiling component, the microspheres which form upon
evaporation of the free water will be fully or partly suspended
in the high-boiling component and may be recovered by settling,
centrifugation or filtration. Since high boiling organic liquids
are often used, vacuum evaporation is preferred since it allows
low temperatures to be used.
The particular temperature required to dehydrate the
emulsion cannot be described with certainty since as indicated
above, it would be dependent upon the nature of the emulsion
being evaporated, the liquids present in the emulsion, and the
like. It may be said, however, that the temperature should be
below that temperature which would cause breaking of the emulsion
during the dehydration step.
~ y stopping the dehydration step prior to producing
substantially dry metal oxide particles, it is possible to
produce a dispersion which has as its continuous phase the
organic liquid and having dispersed therethroughout the fine
metal oxide microspheres.
Expressed in another fashion, this aspect of the
invention comprises a method for the preparation of metal oxide
microspheres suspended in a water immiscible organic liquid which
comprises evaporating the water and a small amount of the organic
liquid from a water-in-oil emulsion having as its external phase
a water immiscible organic liquid and as its internal phase an
aqueous dispersion of a metal oxide whereby there is produced
microspherical particles of the metal oxide having an average
particle size diameter within the range of 0.05 - 5 microns.
The Microspheres Produced by the
Process of the Invention
The microspheres which are produced by the method of
this invention are observed by electron microscopy to be discrete
and entirely round in shape. The average particle diameter and
size distribution is determined by the size of the aqueous
droplets in the emulsion which, in turn, is controlled largely by
the method of dispersion employed to prepare the emulsion and by
the emulsion formulation. By the method of the present
invention, it is possible to prepare spherical partlcles with an
average diameter in the range of 0.05 to 5 micrometers and,
preferably, 0.1 - 3 micrometers. The ratio of the diameter of
the largest sphere to that of the smallest sphere is equal to
less than approximately 5. Preferably it is less than 20.
Since the method of the present invention does not
involve treatment of the emulsified metal oxide aquasol or
dispersion with a precipitant or gellation agent which could
contribute contaminating ions to the metal oxide microspheres,
the purity of the microspheres is dependent largely upon the
composition of the metal oxide aquasol or dispersion. It is,
-
therefore, preferable to employ a metal oxide aquasol or
dispersion containing stabilizing ions such as nitrate or acetate
which may be decomposed upon calcination. Additionally, it is
highly desirable to employ emulsifiers which are substantially
free o~ metal const~tuents or contaminantsS
The microspheres of the present invention may be
directly calcined to remove residual emulsifiers, oil phase and
water. The temperature and duration of calcination will be
dependent on the particular precursor materials usçd and on the
particular final properties desired. The microspheres may, in
some cases, be washed with certain organic solvents possessing
sufficient polarity to remove residual emulsifiers, oil phase and
water. for example, methyl ethyl ketone or diethyl ether may be
employed to wash residue from the microspheres. The microspheres
may then be dried and calcined if desired.
The temperature at which the calcination is performed
will vary depending upon the particular microspherical metal
oxide particle being treated. Generally the minimum temperature
will be about 300F. but may range as high as 2300F.
It is understood that the temperature will depend upon
the end use to which the calcined metal oxide particles will be
employed. for example, hydrous alumina microspheres must be
calcined above 2000F to convert them to microspheres o~
alpha-aluminum oxide or ceramic alumina. Partially hydrated
alumina phases like gamma alumina are obtained when the
microspheres are calcined below 2000F. Hydrous iron oxide
microspheres may be converted to the hematite phase by
calcination at approximately 1000F.
-
In summary, calcination temperature ranges for common
oxide particles are:
A1203 600 -- 2300F.
SiO2 600 -- 15û0F.
Fe203 600 -- lû00F.
FeOOH 600 -- 1000F.
In the case of silica, the temperature rangP can vary
widely, e.g. rather low temperatures when simple uses such as
fillers or binders are contemplated up to approximately 1500F.
when it is sought to produce a fused silica microsphere.
One of the interesting phenomena of the invention is
that when the emulsions are evaporated to dryness as described
above, the particle size of the produced microspheres is less
than or equal to about 80% of the size of the particles in the
internal phase. The degree of shrinkage upon evaporation
increases with increasing dilution of the metal oxide dispersion
prior to emulsification. The term, "evaporating," or "evaporated
to substantial dryness," is meant to include those products which
have been treated to produce microspheres which are substantially
free of both the internal and external phase of the starting
water-in-oil emulsion. It also includes cases where only the
water has been removed from the starting emulsion and the
colloidal dispersions of the metal oxides are suspended in the
external phase of the emulsion.
Uses
The microspherical particles of the invention can be
employed in a variety of uses. The calcined alumina particles
can be used in the preparation of catalysts. The silica
particles may be used as refractory binders, o'pacifying agents,
and the like. The iron particles can be used in the preparation
of magnetic tapes and the like.
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I Another feature of the invention is that prior to
¦calcination, the particles contain, in most instances, a thin
¦coating of the low HLB emulsifier which allows them to be readily
¦blended into organic systems such as plastics and the like,
¦thereby making many of the particles excellent inorganic fillers
¦and components of finished plastic materials and products.
Evaluation of the Invention
To illustrate the invention, the following are given by
way of example:
¦ Example 1
Two hundred 9. of a dispersion containing 22%
¦Dispera ~ Alumina were added to 210 9. of Napthol Spirits, 5 9.
¦of Span 8 ~ and 5 9. of Tween 61~. The mixture was
¦mechanically agitated in a blender to produce a water-in-oil
¦emulsion. The emulsion was evaporated on a rotary evaporator at
la vacuum of 50mm Hg and at a bath temperature of 8û-90C. A
¦free-flowing powder composed of microspherical alumina gel
¦particles was obtained in approximately 10 minutes. The powder
¦was then stirred in an excess of methyl ethyl ketone to remove
¦residual emulsifiers, solvent and water. After allowing the
alumina to settle, the methyl ethyl ketone was siphoned and the
alumina is first air-dried and then calcined in air at 500C
for 60 minutes. The powder is composed of spherical particles
with a mean diameter of û.5 micrometers and a standard deviation
¦of 0.2 micrometers. The surface area of the sample is 233 M2/g
¦and the total pore volume is 0.4 CC/9.
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¦ Example 2
I
l One hundred 9. of Nalco silica sol containing 30% SiO2
¦were added to an oil phase composed of 100 g. Napthol SpiritsJ
¦1.8 9. Span 8dE~ and 3.2 9. Ethoduomeer~ T/13. The mixture
¦was agitated in a blender to form a water-in-oil ernulsion. The
¦emulsion was then evaporated on a rotary evaporator at a vacuum
¦of 50mm Hg and at a bath temperature of 95C, resulting in a
solid composed of spherical particles with a mean diameter of
0.15 micrometers and a standard deviation of 0.04 micrometers.
Calcination at 800F to remove organic residue affords a
microspherical powder with a surface area of 177 M2/g and a
pore volume of 0.3 cc/g.
¦ Example 3
¦ Fifty 9. of Nyacol~) iron oxide sol containing 7.5 wt.%
¦Fe203 were added to an oil phase composed of 100 9. Napthol
¦Spirits, 3.75 9. Span 8~, 3.75 9. Tween 61~ and 2.50 9. of
Rapisol B246~ polymeric surfactant from ICI Americas Inc. The
mixture was agitated with a laboratory disperser until a
water-in-oil emulsion containing droplets of the desired size was
formed. The emulsion was evaporated on a rotary evaporator at a
vacuum of 50mm Hg and at a bath temperature of 85C. The wet
¦residue which was produced was treated with excess methyl ethyl
¦ketone and allowed to settle. After removal of the supernatant
liquids9 the wet solids were allowed to dry. The resulting
rust-orange powder was shown by electron microscopy to contain
spherical particles with diameters in the range of û.5 to 4
micrometers. The powder was calcined at 8ûûF to afford a
powder with a surface area of 21 M2/g and a pore volume of
l û.l cc/g.
--
Example 4
One hundred 9. of a Nyaco ~ ~irconia sol containing
20~ ZrO2 were added to an oil phase composed of lOO 9. of
Napthol Spirits 7 0 .ao g~ Tween 6 ~, 1.70 9. Span 8 ~. The
mixture was agitated in a blender to afford a ~ater-in-oil
emulsion. The emulsion was then evaporated at a vacuum of 50mm
Hg and at a bath temperature of 85 to 90C for 10 minutes,
resulting in a free-flowing solid. Examination of the solid with
an electron microscope reveals it to be composed of spheres with
a mean diameter of 0.52 micrometers and a standard deviation of
0.25 micrometersL The sample was calcined for 1.5 hours at
800F and ground to afford a powder composed of discrete
microspheres with a surface area of 7 MZ/g and a pore volume o~
0.02 cc/g.
Example 5
Twenty-five g. of cerium dioxide sol from Rhone-Poulenc
containing 18% CeO2 were added to 50 9. of Span 8 ~ and 0.40
9. of Tween 61~. The mixture was agitated in a blender to form
a water-in-oil emulsion. The emulsion was evaporated on a rotary
evaporator at 50mm Hg vacuum and at a bath temperature of
80-85C. After the free water was evaporated and no further
oil phase evaporated, the CeO2 microspheres were recovered from
the unevaporated oil phase by centrifugation. The diameters of
the microspheres were observed by scanning electron microscopy to
be in the range 0.1 to 0.5 microns.
Example 6
Fifty g. Nalco titania sol containing 12% TiO2 were
added to an oil phase composed of lûO 9. Low Odor Paraffin
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Solvent, 5 9. Span 8 ~ and 5 9. Tween 6 ~. The mixture was
agitated in a blender to form a water-in-oil emulsion which was
subsequently evaporated on a rotary evaporator at 50mm Hg. A
solid composed of spherical titania particles with diameters of
approximately 2 micrometers was obtained.
Example 7
An emulsion of colloidal alumina was prepared according
to the method described in Example 1. This emulsion was then
evaporated in an agitated thin-film evaporator at 61mm Hg
pressure and elevated temperature to afford a slurry of alumina
microspheres in the organic liquid. The average diameter of
these microspheres as measured on a Leeds and Northrup
MICROTRA ~ Particle Size Analyzer is 1.25 micrometers and the
relative standard deviation o~ the size distribution is 45%.
Example 8
Thirty 9. of alumina sol containing lû% A12O3 were
added to an oil phase composed of lOO 9. Napthol Spirits, 2.5 9.
Span 8 ~ and 2.5 9. Tween 61~ The mixture was agitated with
a disperser to form a water-in-oil emulsion. The emulsion ~as
evaporated on a rotary evaporator at 30mm ~9 and at elevated
temperature to form a wet cake which was washea with methyl ethyl
ketone and acetone and dried. The resulting white powder was
found by scanning electron microscopy to be composed of discrete
spheres with diameters ranging from about O.l micrometers to 2
micrometers.
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Example 9
Twenty-five 9. of a 22% colloidal alumina dispersion
were combined with 75 9. of a 7.5~ colloidal iron oxide
dispersion and added to an oil phase composed of 100 g. Napthol
Spirits, 2.5 9. Span 8 ~ and 2.5 9. Tween 6 ~. The mixture
was agitated in a blender to form a water-in oil emulsion. This
was evaporated in a rotary evaporator at 50mm Hg and at elevated
temperature to afford a slurry of mixed-metal oxide microspheres
in the organic liquid. The microspheres were observed by
scanning electron microscopy to have diameters ranging from about
0.1 micrometer to about 1.5 micrometers.
-
~27~
G L O S S A R Y
Tradename
Nyacol Philadelphia Quartz
PQ Philadelphia Quartz
Disperal Remet Chemical Corp.
Span 80 ICI America Sorbitan monooleate, N.F.
(water-in-oil emulsifier)
Tween 60 ICI America POE(20 sorbitan monostearate
(polysorbate 60) -- emulsifier
Tween 61 ICI America POE(4) sorbitan monostearate
-- emulsifier
Ethoduomeen Tl3 Armak Ethylene oxide condensation
product of Duomeen T.
Duomeen T Armak N-tallow trimethylene diamine
-- corrosion inhibitor
Nalcoag Nalco Chemical Co. See Table I
Rapisol B246 ICI America Polymeric surfactant
-24-
