Note: Descriptions are shown in the official language in which they were submitted.
l~G~366
NON-VITREOUS CERAMIC METAL OXIDE MICROCAPSVLES
This invention relates to non-vitreous ceramic microcapsules
and a non-melt process for their preparation. In another aspect, it relates
to shaped and fired, spherical, non-vitreous ceramic microcapsules of metal
oxide, such as titania, preferably transparent microcapsules of poly-
crystalline ceramic metal oxide, which microcapsules can be porous or
impermeable, filled or evacuated. In another aspect, it relates to a
process for making said microcapsules by sol-gel techniques involving
steps of liquid-liquid extraction, drying and firing. In a further aspect,
it relates to composites containing said microcapsules. 'r
In accordance with the present invention, there are provided
spherical, free-flowing, discrete microcapsules, the peripheral wall or
shell of each which encloses the single hollow within the interior thereof
being uniformly thick, homogeneous, impermeable or porous and transparent,
and made of ceramic consisting essentially of polycrystalline metal oxide
or amorphous metal oxide convertible to polycrystalline metal oxide upon
firing.
In another aspect, the invention provides a process for making
spherical microcapsules comprising the steps of adding precursor material
comprising an aqueous solution, dispersion or sol of one or more metal
oxides (or compounds calcinable to metal oxide) to a liquid body of a
dehydrating agent comprising an organic dehydrating liquid, agitating said
liquid body to maintain the resulting droplets of said precursor material
in suspension, to maintain relatively anhydrous dehydrating liquid in
contact with the surface of said droplets as they are dehydrated, and to
rapidly extract at ambient temperatures of 20 to 40C the major amount of
water from said droplets and form gelled microparticles therefrom, the
predominant amount of said gelled microparticles being in the form of spher-
ical, gelled, porous, liqu.d-filled microcapsules, recovering said liquid-
filled microcapsules, drying the resulting recovered microcapsules at
temperatures and pressures adjusted to minimi~e fracture and bursting the
same and remove liquid from within the recovered microcapsules, and firing
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~06~366
the resulting dried microcapsules to form spherical ceramic microcapsules
the peripheral wall or shell of each which encloses the single hollow
within ~he interior thereof being porous and heat-sealable, homogeneous,
and made of non-vitreous ceramic comprising polycrystalline metal oxide
or amorphous metal oxide convertible to polycrystalline metal oxide upon
firing at higher temperature.
The microcapsules of the present invention may be shaped and
fired, non-blown or non-expanded, spherical, smooth-surfaced, free-flowing,
discrete, rigid, and crushable, the wall or shell of each being of uniform
thickness, porous, and preferably heat-sealable, or impermeable, preferably
transparent and clear, and made of homogeneous, non-vitreous ceramic poly-
crystalline metal oxide or amorphous metal oxide convertible to poly-
crystalline metal oxide upon direct firing at elevated temperature. The
hollow, central void or interior within these microcapsules (thus accounting
for their relative light weight or.low density) can be filled with selected
solid, liquid, air or other gas, or can be evacuated. These microcapsules
are made by a non-melt process comprising steps of liquid-liquid extraction,
drying, and firing, without requiring coating, leaching, or a gas-blowing or
expanding means to form the void therein.
.~ l - la -
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As used in this application, the term l'microcapsule9'
means a unicellulara hollow particle~ that isg a particle
having a peripheral wall or shell encl.osing or surrounding .~.
a single hollow~ cavity, space or void within the interior
of the particle which, unless otherwise noted, may be
evacuated or filled with a gas, liquid or solid, such
particle being so small as to require means such as an
optical microscope for purposes of measuring the dimensions
thereo~ A microcapsule charac~erized herein as "spherical"
is one which has the shape of a true sphere or spheroid,
that iS3 like a sphere, e.gO~ oblate or prolate. A micro-
capsule characterized herein as '1porous'l i.s one whose wall
has interconnected submicroscopic pores or pass~ges and
is permeable to liquid and/or gas, whe:reas an "impermeable"
microcapsule is one whose wall is seal.ed, non-porous or
closed`such as to maintain the contents within the interior
void of the microcapsuleO A microcapsule whose wal~ is
"homogeneous1' is one whose wal7 under optical microscopic
examination (e.gO at 140X) is completely or essentially
free of extraneous inhomo~enities~ such as pores, VOidSg
occlusions, inclusionsg or dispersionsO A "transparent"
mic.rocapsule is one whose wa~l will transmit; visible
light such that the oukli.ne, periphery or edges o~ bodies
beneath and in contact with fragments o~ the microcapsules
~5 ~;ill be sharply discernible under an optical microscope
~eOg~ at 140X)o A ~polycrystalline~l me~.al oxide is one
with a sufficient degree of crystallinity or m~..croc:rys+~al-
l.ini.gy such that the crystalline species thereof can be
re~dil~ discernibl.e or ident;i:fied by conventional ~-ray
3o or e~.ectron diffractiong whereas an amorphous~' metal
--2--
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~L06~366 , `
oxide or phase is one whose X-ray diffraction pattern is
free of distinguishable lines and thus can be considered :
as noncrystallineO ~ "vitreous" material (in addition
to being like an amorphous material) is one which is
derived from a melt3 while a "non-vitreous" material is notO :
The liquid-liquid extraction step of the process .
o~ this invention can be and preferably is carried out .
. . .
at ambient temperatures (iOeOg without heating) and with ~;
agitationO In this extraction step~ aqueous precursor
materi.al comprising a solution, dispérsion or sol of one ...
or more metal oxides, or one or more metal compounds `.;
calcinable to metal oxides, is mixed with a dehydrating
agent comprising an organic dehydrating liquid capable of . ... ~ :
rapldly extracting at ambient room temperature (23Co) ~;
a suf~lcient,ma~or amout o~ the water (eOgO at least 75~ .
or even as high as 85-95~ or higher) from the resulting
droplets of said precursor material in less than 30
seconds, preferably in less than 15 seconds~ to dehy- ;
dratively gel substantially all o~ the said droplets
and form gelled microparticlesO The bulk of these or
predominant amount of these gelled mlcroparticles are
~iguid-filled, porous~ spherica~ preferably transparent~
mlcrocapsulesO The wall o~ these microcapsule~ comprises
said gelled precursor material and the liquid contained `. .
~5 within the microcapsules comprises water and said dehy~
dratlng l.iquidO The gelled,liquid-filled microcapsules are
recovered and dried in a suitable atmosphare, eOgO air9 .. ~: :
and then fired, for example in air at 300-500~Co~ to .~
remove fugitive materialg e O g~ organic materia~ and wa~er~ . .
and form porous~ non;~vitreous ceramic metal oxide micro- ;~
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~06136~;
~apsules, the liquid formerly within the gelled microcapsules
being replaced with the atmosphere used in said drying
operation, Upon firing the microcapsules at higher tempera- ;
ture, e.g. at 500-1000C. or higher, in a suitable atmosphere,
e,g. air or nltrogen3 or vacuum, the ceramic walls of the
microcapsules may be impermeable with the atmosphere or
vacuum used in this firing step being sealed or entrapped
within the microcapsules. Said firing of the microcapsules
at a temperature in the range 500-1000C.or higher promotes
densification and crystallite growth to the extent that
polycrystalllne metal oxlde is discernible or identifiable
by X-ray or electron diffraction techniques~
In the accompanying drawing, the varlous flgures
are pen-and-ink sketches of photomicrographs taken with a
light microscope at 150X using transmitted light, the
sketches being drawn to the same scale as the photomicro-
graphs.
FIG~ 1 represents shaded sketches of ceramic,
porous, transparent~ spherical microcapsules of this inven-
tion obtained as described hereinafter in Example 8 by
firing in air dried, gelled, porous, spherical microcapsules
to 460Co~ the walls of the fired microcapsules consisting
of polycrystalline anatase titania, TiO2.
FIG'o 2 represents fragments of the same batch
f fired microcapsules represented in FIG~ 1 which have
been broken by crushing between glass microscope slides
to show the transparency and thickness of the walls of
the microcapsules. The transparency (as in glass microbubbles)
is clearly manifested by the discernibility of the undis-
3~ torted, sharp edges, some of which are denoted by reference
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~(~6~366
number 5~ of fragments when observed through overlying -
fragments con~iguous therewithO The relatively uniform
thin wall (about 7-10 microns in thickness in this instance) : .
of each microcapsule is clearly shown by referen~e number
~ .
The aqueous precursor material used to form the
mi.crocapsules of this invention comprises an aqueous
solution, dispersion or sol of one or more metal oxides .
or metal compounds calcinable to metal oxides, or mlxtures
of said forms of precursor materialsO The precursor
material should be pourable and stable, that is, non-gelled,
non-flocculated or non-precipitated~ The equivalen~ con-
centration of the metal oxide in the precursor material .
can vary widely, e~g.~a few tenths o~ one weight ~ to 40 or :.
5 weight %, and the particular concentration chosen will ~ s
be dependent on the particular form of the precursor metal
oxide and dehydrating liquid used and the desired dimensions . .
and proposed utility of the microcapsulesu Generally9 this
concentration will be that sufficient to promote rapid for- :~
mation of droplets in the dehydrating liquid and, generallyg .-
the lower the equiva~ent concentration of metal oxide in
the precursor materials, the thinner the walls and the ~:
smaller the diameters of the microcapsulesO ~ .
The aqueous precursor can be a dispersion or
sol of one or more (e~gO 1 to 53 or more~ ceramlc metal
oxidesg iOeO metal oxides which c~n.be fired into a rigid
or se-lf-supporting po~ycrystalline form and ar~ s~`able in
a normal air environment9 eOg. 9 23Co and 50~ rel.ative
humidityO Useful representative ceramic metal o~ides
include TiO2g Cr203g W03g ThO2a Fe203~ M~Og Y~039 Z~~s
J
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1061366
HfO29 V205g Nb205, UO2, BeO, CoO, NiOg CuO, ZnO, In2Q3, Sb203~ ,~
Al.2039 SnO2, and mixtures thereof such as ZnO-TiO2, Ti-02-Fe2033
SnO2~TiO2, Nd203 TiO29 A1203-Cr203, MgO-A1203, Mg-Ti2, ,
Mgo-zro2~ Th2~U2~ ThO2-CeO2, Bi2O3-TiO2, BeO A1203, 2 "
~e23-A123~ A1203-Cr23-Fe23~ Pbo-zro2-Ti~2~ zno-Al2o3- Cr203g
Al2o3-cr2o3-Fe2o3-Tio2~ and Tho2-Al2o3-cr2o3-Fe2o3-Tio2~
It is also within the scope of this invention to use dis- ~'
persion or sols of said ceramic metal oxides in combination
or admixture with dispersions or sols of one or more metal
oxides which are unstable in normal air environment (such
as Li20, Na20, K20, CaO, SrO, and BaO) and/or ceramic non-
metal oxides having an atomic number of 14 or greater (such
as SiO2, As203, and P205), representative combinations
~ncluding A123-~i2~ TiO2-K2o, ZrO2-Cao, Zro2_A12o3_caO
~,5 ZrO2-SrO, TiO2-BaO, TiO2-ZrO2-BaO, A1203-Na20, MgO-S102~Fe203-BaO,
2 29 A123 As203~ zro2-p2os~ A1203-sio2, A1203-
B203_SLO2, A1203-Cr203-SiO2. Thus, ~he ceramic micr~capsules
of this invention conaist, ~onsist essentially Ofg or com-
prise polycrystaYlin~ Ceramic metal oxide (or amorphous
ceramic metal oxide convertible thereto by ~irin~lthe "ceramlc metal
oxide":in¢luding systems of said oxides in free or combined formsO
, A number of the above-described oxides useful
, i,n ~his inven-tion are commercially available ln the ~orm
:, o~ a~ueous sols or dry powders which can be readily dis-
~5 persed in water to ~orm sols9 such as Al2039 Cr~03 and
Fe203 sols sold under the trademark Y7Nalco"g silica sols
sold under the trademarks 1INalcog" Y'~Ludoxg!' Syton" and
YNyaco~g" and A'1203 co~loidal. powder sold under t;he
trademark "Di.spalQ"
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Instead of using the precursor material in the ;
form of dispersion or sols of said oxides, it is within
the scope of this invention to use the precursor material
in the form of water soluble or dispersible inorganic or
5 organic compounds which are calcinable to the correspond-
ing oxide. These compounds representativel~ include
many carboxylates and alcoholates, eOg. acetates,
formates~ oxalates, lactates, propylates, citrates,
and acetylacetonates, and salts of mineral acids, e.g ,
lO bromides, chlorides, chlorates, nitrates, sulfates,
and phosphates, selection o~ the particular precursor
compound being dictated by availability and ease of
handling. Representative precursor compounds useful in
this invention include ferric chloride or nitrate, chromium
15 chloride, cobalt nitrate, nickel chloride, copper nitrate,
zinc chloride or carbonate, lithium prop~late, sodium
carbonate or oxalate, potassium chloride, beryllium
chloride, magnesium acetate, calclum lactate, strontium
nitrate, barium acetate, yttrium bromide, zirconium
20 acetate, hafnium oxychloride, vanadium chloride, ammonium
tungstate, aluminum chloride3 indium iodide, titanium
acetylacetonate, stannic sul~ate~ lead ~ormate, antimony
l chloride, bismu~h nitrate, neodymium chloride, phosphoric
i acid, cerium nitrate, uranium nitrate, and thorium nitrateO
~l 25 The preferred form of the precursor materials
used in making microcapsules composed of a single metal
oxide composition is an aqueous sol of the metal oxide.
Where the microcapsules are composed of two oxides, the
precursor material can be a mixture of an aqueous sol of
each oxide or an aqueous solution of one oxide or its
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9,i~6136~ ::
precursor with an aqueous sol of the other oxide precursor.
Where microcapsules composed of a ma~or amount of one
oxide and a minor amount of ano~her oxide are desired,
the precursor of the ma~or oxide is generally preferably
in the form of an aqueous sol. In general, the form of
the particular precursor to be used will be dictated by
its availabiliky and ease of handling. For example, ii
the precursors of a]umina, titania, chromia~ silica are
preferably in the form of aqueous oxide sols; and the
precursors of lithia, calcia, magnesla and baria are
preferably aqjueous solutions of their soluble salts.
The preparation of dispersions, sols and solutions
useful in the practice of this invention will be omltted
in the interest of brevity since it wlll be withln the
sklll of the art to prepare such materials, representative
teaching in the art for this purpose being U.S/ Patent
3,709,706 and UOS. Patent 3~795,524. It may be desirable
to filter the aqueous precursor material before use in order
to remove artifact, large colloids, or extraneous matter.
Where microcapsules composed of two or more
oxldes are to be made, e.g., binary, ternary, and quater-
nary oxide compositions, the overall precursor material
will contaln sufficient amounts of the individual pre-
cursors to impart desired properties to the microcapsules.
For e~ample, where microcapsules are deslred having a
certain degree o~ magnetism lower than that obtained
rom microcapsules composed only of iron oxide, the
prPcursor material will comprise aqueous ferric n~trate
admixed with a su~icient amount of titania, alumina or
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silica aqueous sol to obtain the desired lower degree of
magnetism~ As another example, where colored tltania
microcapsules are desiredg eOg~, as ~illers for polyester
coating resins, the precursor material can be an aqueous ~-
titania sol admixed with a sufficient amount of aqueous
ferric nitrate, 500CO-fired microcapsules of 95 weight
~ TiO2 and 5 weight % Fe203 having a gold color and 500Co~
fired microcapsules of 90 weight % TiO2 and 10 weight
Fe203 having a bronze color.
The dehydrating liquid used to dehydrativel~ gel .
the precursor material is preferably a liquid in which r~
water has a limited solubility and in which water is mis- .
cible to a limited extentO Such a dehydrating liquid
will practically instaneously cause formation of llquid ; .~ .
droplets oP the precursor material and rapidly ex-tract .
the major amount of the water from the droplets to form
discrete, dispersed~ liquid-filled microcapsules having
a'porous gelled wall or shellg the ph~sical integrity of
whi.ch is m~intained in the body of dehydratlng liquid~
The .formation of a substantial~y quantitative yield of
gelled microcapsules is compl.ete within 30 secondsO
Furtherg this formatlon does not require he&ting (iOeOg
it can be accomplished at ambient room temperature, eOg.,
23Co ) nor does it require use of a barrier liquidO Though : -
a small amount of solid beads may also be formedg the
predominant amountg io e~ 9 at least 85-95 ~ or higherg o~ -
the microparticl.es formed will be in the form of micro- :~
~ capsu~esO lf the liquid~liquid extraction is carried
t out in a batch operationg there may be a tandency to form
said small amount of solid beads (or rel.ati.vely thicker-
,
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~06;~366
walled microcapsules) toward the end of the extraction
due to the progressively decreasing dehydrating ability
of the dehydrating liquid as it extracts the water from
the precursor material
Generally, dehydrating liguids useful in the
practice of this invention preferably will have a limited
solubility of about 3 to 50 weight %~ preferably 15 to 40
weight ~ for water ~based on the weight of the dehydrating
liquid) at. 23Co Representative organic dehydrating
liquids useful in this invention are alcohols9 such as
alkanols with 3-6 carbon atoms, eOgO n-butanol, sec~
butanol, l-pentanol, 2-pentanol, 3-methyl-2-butanol,
2-methyl-2-butanol, 3-methyl-3-pentanol, 2-methyl-1-
propanol~ 2~3-dimethyl-2-butanol and 2-methyl~2-pentanol,
cyclohexanol, ketones such as methyl ethyl ketone, amines
such as dipropylamine, and esters such as methylacetate,
and mixtures thereofO Some o~ these dehydrating liquids~
eOg. n-butanol, when used to form microcapsules with
relatively large diameters, eOg~ 100-500 microns or
larger, may have a tendency to cause micro~cracks in. the
walls of the microcapsulesO Such micro-eracks can be
prevented or minimized when such deh.ydrating liqu-Lds are
used to ~orm large microcapsules by adding a small amount
of water to such dehydrating liquids9 eOgO 5 to 10 % by
weight of the dehydrating liquidO However~ the res~lti.ng
water-dehydrating liquid mixture still. has ~aid imited solu~
bility for water, pre~erably at least 15 weight %~ . ;
If a dehydrating liquid with a water ~olubility ..
of less than about 3 weight ~0 is used, such as 2~ethyl~
3Q l-hexanol per se, the rate o~ extraction ~rom the droplets
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1~61366 7. ~1 '
o~ precursor material will be relatively slow~ eOg. complete
extraction will be longer than one minute, and even as long
as 10 minutes or more, and the gelled precursor will be in
the form o~ solLd microspheres (or beads)O ~Iowever, de-
hydrating liquids with said low water solubility, eOg. -
2-ethyl~l-hexanol,can be used in combination wlth those
aforementioned dehydrating liquids h~ving greater water
solubility,e.g. 15 to 50 weight ~, to form the microcap~
sules of this inventionO For example, 2 ethyl-l-hexanol
has a relatively higher boiling point than n-butanol and
when a mixture of 5-20 weight % o~ the former and 80-95
weight % of the latter is used, the economics o~ the `~
extraction operation are improved in that losses o~ the
alcohols due to volatilization are decreased~ Although
the precursor material can be ~irst in~ected into 2-ethgl-
l-hexanol to ~orm droplets and then a small amount of a
completely water miscible solvent such as methanol added,
the bulk of the gelled microparticles formed wll~ be
solid beads with a low yield o~ porous, liquid-~ille~
microcapsules. A good yield o~ porous~ liquid-filled
microcapsules can be formed by mixing the precursor
material with a small amount of a completely water mis-
cible liquid, such as methanol~ and then in~ecting the
mixture into a liquid with low water solubility, such as
2-ethyl-1-hexanol.
If a dehydrating liquid is used which has un~
limited solubility in water and is completely mlscible
therewith, as in the case of methanol or ethanol~ neither
microcapsules nor solid beads are ~ormed and in mCJSt cases
the precursor material in effect is merelg dill~ed or further
3~i6
dispersed by such dehydrating liquid~
The liquid-liquid extraction step of this invention
can be carried out at ambient temperatures, e.gO 20 to 40Co g -
- higher temperatures~ e.g. 60~Co and higher~ cause fragmen-
tation of the gelled microcapsules. Excellent, substantial
quantitative yields, e.g~ 95~ and higher, of gelled micro-
capsules, based on the equivalent oxide solids conten'~ o~
the precux~or materia~ can be conveniently achieved at
room temperature (23Co ) o In order to quickly and eff
ciently dehydratively gel the droplets of the precuLrsor
material in a batch operation, the body of deh~drating
liquid is preferably subjected to externally applied
agitation (e.g. by swirling the body of deh~dra~ing liquid
or by inserting a stirrer therein) when the precursor
~5 material is added thereto, and said agitation is continue~
during the course of dehydration of the resultant drcplets
of precursor materialO This agitation maintains the
droplets in suspension (and thereby preven~s agglomeration
and settling of the droplets) and ensures maintenance of
relatively anhydrous dehydrating liquid in contact with
the surface of the droplets as they are dehydratedO In
a continuous liquid-liquid extractlon operatlon~ equiva-
lent agitation can be accomplished by adding the pxecursor
material at a point to a stream of the dehydrating ;iq~id
flowing at a sufficient rate to maintain the droplets in
suspension in the course of their dehydration
The dehydration of the droplets to foxm the
gelled microcapsules will be sufficiently complete wlthin
30 seconds, and usually in less than 15 seconds, from
~0 the time of addition of the precursor materiaY a that
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addition being in the form of drops, flowing streamg or
by bulk,
The size of the droplets, and consequently the
size of the resultant gelled and fired microcapsules,
will be affected by the degree or type of agitation of
the dehydrating liquid as the precursor material is added
thereto. For example, with high shear agitation, e~g~ `~
that obtained with a Waring Blendor, relatively tiny
droplets (and gelled microcapsules) can be formed, eOg.
with diameters less than 20 micronsO In general, gelled
microcapsules with diameters in the range of about 1 to
1000 microns can be produced in accordance with this
invention.
The gelled, porous, transparent, liquid-filled
microcapsules can be separated and recovered from the
dehydratlng liquld in any suitable manner, e~g. by fil-
tration, screening, decanting, and centrifugingg such
separation being preferably performed soon after completion
of the extraction stepO Where the gelled microcapsules
are recovered by filtration, filter cake comprising said
microcapsules and residual dehydrating liquid i9 obtained~ ;
In any event, the recovered mass of gelled microcapsules
are then sufficiently dried to remove the residual deh~-
drating liquid and the liquid within the microcapsules~
the resultant dried, gelled microcapsules being conveniently
referred to herein as green microcapsules~ iOeO dried and
unfired. Said drying can be accomplished in any suitable
manner, care being exercised to prevent too rapid an
evaporation in order to minimize fracturing or bursting
of the microcapsules. This drying can be carried out in
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1061366
ambient air and pressure in a partially enclo~ed vessel
at temperatures, for exampleg of ~0-25aCo Hlgher or
lower drying temperatures can be used with commensurate .
adjustment o~ pressure if necessary to prevent fracture
of the wall o~ the microcapsules. Durin.g the course
of drying, the liquid within the microcapsules diffuses
through the shell or wall of the microc:apsulesg as
evidenced by microscopic observation of the retre~ting
upper surface or miniscus of the liquid within th9
transparent microcapsules, thus attesting to t.he porous
nature of the gelled microcapsules. The larger the dried
microcapsules are, the more free~flowing the~ are~ The
dried microcapsules have sufficient strength to perm~t
subsequent handling. It may be desired to screen classif~
them to obtain desired size fractionsO
The dried microcapsules are then fi.red to convert
them to spherical, smooth-surfacedg light weight or low :.
density, rigid, crushable, microcaps~lesg t;he shell or
wall of which is non-vitreousg syntheticg cerami~ homo~
geneous~ preferably transparent and clearg and comprises
metal oxide which is polycrystalline or is amorphous
metal oxide convertible to pol.ycrystal.line metal oxide
upon firing at higher temperat,ureO Depending on the ..
particular oxide precursor material and firing temperat;ure
used, the walls of the fired mlcrocapsules will be porous . ~:
and heat-sealable or impermeab`ie9 the met;a-L oxide in the ~:
wa~ls being present in whole or in part in the pol~cr~s~
line state or in an amorphous s~ate capable of con.vsr~ion .. :
upon further firing to the poly~rystalline stateO ~or
example9 dried~ gelled microcapsules made from A1~03~:B 03-SiO2
~ . .
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~061366 ~
precursor material can be prefired at 500~Co to produce
porous, transparent, ceramic microcapsules comprising ''
amorphous Al2o3-B~o3-sio2~ which can be further fired at
1000C~ to form impermeable, transparent, ceramic micro~ .
capsules comprising polycrystalline alum'Lnum borosilicate
and an amorphous phase. As another example, driedg gelled
microcapsules made from TiO2 precursor material can be '
prefired at 250-450C. to produce porous, transparent9
ceramic microcapsules consisting of polycrystalline ''
anatase TiO2, and these microcapsules can bs further
~ired to or at 650C to form impermeable, transparent9
ceramic microcapsules consisting of anatase titania~
TiO2, and even ~urther ~ired at 800C~ to form imperme- :
able, ceramic microcapsules conslsting o~ polycrystalline
rutile TiO2. The dried, gelled microcapsules can be fired
in one step directly to impermeable microcapsul.es
In most instances, the crystallites in the poly-
crystalline metal oxide are less than 2000 Angstroms and
usually (and preferably for purposes of transparency~
~o less than 1000 AngstromsO However, crystallites up to
20,000 Angstroms or higherg for exampleg can be obtained
in the same precursor materi.als, eOgO ~e2039 microcapsules ::
with such large crystallites appearing grainy under
a microscope ~eOgO 140X)o
In generalg the particu'lar firi.ng temperature .'
used to convsrt dried and gelled (or 97green99) microcap~
sules into ceramic microcaps~les will be dependent on
the particular precursor material used and the p~rtlcular
physical and compositional properties desi.red in the
~0 ceramic mlcrocapsules and the intended u~ility thereof~
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Generally, the firing temperature se~ected for these
purposes will be 250 to 1300Co
Although firing of the microcapsules to the
impermeable state results in some densification of the .
walls, accompanied by some shrinkage ancl a s~ight decrease
in diameter, the size or size distribution of the fired
microcapsules is controlled as a practical manner in the
extraction operation as discussed above andg thusg the
diameters of the fired microcapsules will be in the range
of about l to 1000 micronsO The wall of the fired micro~
capsule will be u~iformly thick and in the range generall.y `:.
of 0.1 to 100 microns O The fired microcapsules can also
be separated into desired size fractions by screen or
air classification, elutriation, etc., and an~ solid
mlcroparticles, beads and fragments of broken micro-
capsules can be separated by flotation or winnowing
techniques O ~ '
The firing step can be carried out in an at~
mosphere that will not be detrimental to the conversion .
of the gelled microcapsules to the desired ceramlc micro~
capsulesO An air atmosphere wil~. generally be useful0
A hydrogen or other reducing atmosphere can be used
where desired to form ceramic microcapsules compr~sing
reduced metal o~ides, e~gO ~e030r metalsg eOg~ FeO
Inert atmospheresg eOg0 argon3 nitrogen9 xenon9 neon9
or helium, can be used, particularly where it is desired
to form ceramic microcapsules with such inert atmosp~eres
~illed and heat-sea~ed therewithO Generally~ where it ls `;
i desired to form sealed ceramic microcapsules wlth a
~ 30 vacuum or select gas (other than air) encapsulated
~, :
-16-
'~
366 ~
therein, it will be convenient t.o use an air atmosphere
to convert the dried9 gelled microcapsu~es to porous
ceramic microcapsules and then heat-seal the lat.ter '.
in a vacuum or an atmosphere of the select gas
The pressure within the sealed microcapsul.es
will be dependent u-pon the temperature at which sealing
is accomplished and the pressure of the select gas at
that temperature~ ThUS3 the pressure within the sealed
microcapsules can be varied over a wide range, from .
sub-atmospheric to super-atmospheric and predetermined
and calculated according to the gas l.awsO This process '
allows the encapsulation of very pure gases and preselected
mixtures of gases. ~.
In ~irin~ the dried, gelled microcapsules, care
should be exercised to avoid ignition of combustibl.e ma-
terial in or evolved from the green microcapsulesO Said ' .
ignition may cause localized or general overheating which
may cause rupture of the microcapsules or ~ndesirabl.e
changes in the properties of the microcapsule such as
loss of transparency and strengt.hO For example~ igni~ion
can be avoided by starting the firing at a low temperature
and then elevating the temperature at a s~.ow rateO rt
may 'be necessary to faci~ ake removal of combusti'b''e
material by limiting the depth of the bed of mierocapsuF.es
and/or by maintalning a gent~.a air flow over or throu.~h
the bedO
Because of thei.r high temperature s~aY~ .t~ or
refractorines~3 the ceramic microcapsules o~ t~li.3 invention
are useful in app~ications w~Lere hi~h temperatu~es are
encountered~ for example~ up to lOOO~Go or even 2000~Co
~IL06~3~i6 ~
or higher. And they are useful. in low or moderate temperature
applications where their chemical stability or inertness
and physical properties such as strength~ imperviousnessg
and microscopic dimensions and shape lend themselves to
advantage. For example, a mass or layer of the micro~ `
capsules sealed with air or other gas can be used as `:
insu~ation for kilns or cryogenic f~.~L tanks~ Other uses
for the microcapsules are as catalyst support or as the catalyst .-:
per se in petrochemical operations such as crackings,
oxidization~ hydrogenationg etcO The particular appli~
cation or utility of the ceramic microcapsules will be ~ :
dependent upon their composition and form~ eOgD, empty
(i,eO evacuated), filled, porous or sealedO The micro- .
cap9ules can be employed alone or per se in various
applications in the form in whlch they are obtained as ::
flred, or their physical ~orm can be modified after firing ~:
and they can be used in combination with other materials
One area of u~ility for the porous o.r sealed
evacuated or gas-filled microcaps~es of this inventi.on
is that of ~illers or reinforcement for structural plastic~
elastomeric, metallic, or ceramic composites9 especial~.y
those composites used ln high temperature environments
or even hyperthermal environments ~ound in the aerospace
industry and in ablative environments or because of their .:
light weight or buoyancy those composites used in marine
environments~ Technlques used in forming composites where ..
the microcapsules of this i~vention find uti~ity are dis- :
c~osedg for example~ in ~'Modern Composite Materials~
edited~by Brantman and Krockg Addi.son Wes~ey Pubo COD
Teading3 MassD (1967) and g9Handbook of Reinforced Plas~ics
-18-
.
366
by 01eesky and Mohr, Reinho~d Pubq CorpO, NoY~ ~1964) o
In general, the microcapsules of this invention will find
the same utility as fillers as that known for glass micro-
bubbles or microballons (eOgO see UO SO Patent 3~5859157
and 3~365~315~ Bulletins GBIF-1(8201)R~ June 12~ 1972
and L-GBPBC-2(110.2)R, December 1~ 1970 of the 3M Company, .and SPE Journal, Vol~ 25, ~oO 1~, pO 83-87~ April, 1969)o
Suitable representative plastic, rnetalg elastomeric and
ceramic materials which can be used as the matrices for ;:
such composites are described in WO SO Patent 3~709~706~ ;
issued January 9, 1973 to Ho Go SowmanO
The capability o~ the microcapsules to be sealed
lends itsel~ to diverse applications of` the microcapsules
in their evacuate~or~ill.ed formO The evacuated micro-
capsules can be used per se or in composites in thermal
insulation applicationsO The f'illed microcapsules can
be used to store and transport the fill materialg -the
release of which can be accomplished if and when desired
by mechanical fracture of the fil.led microcapsulesO For
example, microcapsules can be filled and sealed with .~:
inert gases, such as nitrogen, argon~ neon, xenon9 helium
and krypton~ radioactive gases such as krypton 85~ re- .
active gases such as oxygen3 hydrogen9 carbon dioxide~
nitrogen oxide~ sulfur dioxide9 bromineg iodine3 chlorine
and other gasesO Batches of microcapsules filled wi~h
dif'ferent gases can be mixed together in desired ratios
and the mixture crushed or f'rac~ured when deslred to
release the gases9 ~or examp~e~ to permit the reactl.on
thereof. And, for example~ the microeaps~les can ~e
fil~ed with liquids~ such as acetic acid9 and sealed~
:
~, ;.
.. -19-
: ~ . . ,:
~L06~366
the release of which can be used in a system to control : ~ :
its p~.
Where it is desired to fill the microcapsules .
with a liquid, e.g. for purposes of storing said liquld
and releasing the same if and when desired, the fired, .
porous microcapsules can be first evacuated in a suita~
ble evacuation chamber to which then the liquid is .
introduced to fill the microcapsules, pressurization ~.:
being used if necessaryO The liquid-filled mlcrocapsules .
can be separated ~rom any excess of the liquid, e.g~ by
filtration, and the filled microcapsules then sealed~
One technique which can be used to seal the liquid- . :
filled microcapsules is by coating them with a suitable .:-:
coating material, such as a polymeric coating dissolved ;~ -
in a solvent which is thereafter evaporated, leaving a
thin, impervious, seal.ing film o~ the polymeric material
on the exterior of the filled microcapsules~ eOg~ as . :
disclosed in U. S. Patent 3~117~027g issued Janu~ry 7,
1364 to JO A. Lindlof and Do Eo Wurster or UO SO Patent .:
3,196,827, issued July 27, 1965 to Do E~ Wurster et alO
. : ~ The porous fired microcapsules (depending
on the size o~ the pores) can be partial~y or substantially
fllled with various select solidsO For exampleg a low . ;
melting solid can be heated to its melting point (eOg~
acetamide) and the resulting liquid pressurized into
evacuated porous fired microc~psules~ Af~er coolingg . .
the excess solid can be removed from the exterlor of
the microcapsules by washing with a sol.ventO Subse~uently~ .
I the filled microcapsules can be seal.ed if desired b~ the :.
¦ ~o coating technique described above~
-20-
~IL06~366 ~
Alternatively~ the porous fired microcapsu3.es
can be evacuated and gaseous subl.lmatlon product (e~gO o~
camphor) can be equilibrated in the evacuation chamber
Upon cooling, the sublimation product can condense o~
the interior walls to form a partial.Ly ~i~led microcapsuleO :-
The product on the exterior walls can be removed with
solvent. Additional~y~ the filled microcapsule can be
subsequently sealed if desired by coatingO
Another alternative would utili~e a solutlon of
a salt or compound (e~gO CoC~2-water soLu~ion) which
deposits solidmaterials wi~hin the microcapsule upon
evaporation of the solventO Repeating this c~cl.e adds
additional quantities to the interio:r o~ the mlcrocap-
sule. Again, the microcapsule can be sealed if desiredO
An addltional method of ~i.lling a porous ~ired
microcapsule involves metathesis or precipitation reactions~ ; ;.
Microcapsules can be partially ~i~.led with a solvent con-
taining a s~lt (eOgO aqueous Cd~N03)2)3fol~.owed by furkher
fil~ing of ~he capsule with a ga~eous react~nt ~eOgO H~S)
which contains ions required to precipltate the desired
compound (e~gO CdS)o
The transparent quality of ceramic microcapsules
of this inventlan is indicative of their ~reedom from gross
inhomogeneities and is a properky coincident with other de-
sirable properties3 such as uniformity of composition and
microstructure and heat sealabilltyO This transparent prop
erty makes the ceramic micracapsules useful9 for example,
as pigments for coloring plastic composites~
The following examples illustrate the inventlon~
.
-21-
,. -. ,
6~366
..
A fresh titanium dioxide sol was made by addlng
5 parts tetraisopropyl titanate to 1 part concentrated
hydrochloric acid (37%)O The resulting sol was dried
on standing in ambient air at room tempe~rature~ forming
a gel which contained approximately 63% Ti02o A portion :~
of the dried gel was regenerated to an qleous sol by .
dispersing with agitation 12O5 gO of the dry g~l in 50 gO
of waterO The resulting regenerated sol was poured into ;
100 gO of swirling n-butyl alcoholg followed immediately by
the addition of further n-butyl alcohol (300 gO) to the :~:
swirling mixture, and swirling of the resultant dispersion ~:
of microparticles continued for about 5 minO The dispersion .:
was filtered through NoO 54 Whatman filter paper.
The reCovered microparticles were found to be
predominantly liquid-~illed~ transparent, spherical micro- :
capsulesO This microcapsule product was allowed to dry on : :
standing in ambient air at room temperature for several ~
hours to remove the liquid within the mlcrocapsules and the .
, 20 resulting driedg porous9 clear~ transparent9 spherlcal9 green .
mlcrocapsules were fired from room temperature to 550 CO
in 1 hrO in an air atmosphere to form rigld, crushable 9
, free-flowingJ smooth-surfaced, homogeneous D clear9 trans-
J, parent9 spherical, sealed~ ai~filled9 ceramic microcapsulesO
X-ray diffr~ction analysis confirmed that the ceramic
microcapsules were polycrystalline anatase Ti02o The
ceramic microcapsules had substantially uniform wall
~3 thicknesses 9 which were predominantly less than 10 microns 9
~, averaging about 7~8 microns 9 and had diameters which ranged
.~
.
30 from about 40 to 170 microns 9 the average diameter being ~ -
approximately 100 micronsO
.
-22-
61366
~xample 2
A titania sol was made by dispersing with agita-
tion 1O6 gO of another portion of the Ti02 gel o~ Example
1 in 30 gO of water3 followed by the adclition of oO6 gD of
Fe(N03)3o9H20O One half of the resulting mixture was in~ .
jected with a hypodermic syringe into an aqueous alcohol
solution of 300 gO n~butyl alcohol and 30 gO water in a
1000 mlO round-bottom flask3 the contents being swirled
by hand, to form a dispersion of microparticlesO The ~. .
10 swirling action was continued for 1 minO to prevent particle -~
settling and agglomeratlonO
The microparticles were recovered by filtering
the dispersion through NoO 54 Whatman ~ilter paper and were
~ound to be predominantly liquid-filled~ transparent,
spherical microcapsulesO A~ter drying the microcapsules
in ambient air, the resulting dried, porous, clear, trans-
parent~ sphericalD green microcapsules were fired in air to
500 C in about 1 hrO The resul.ting ceramic microcapsules
were rigid, crushable9 free~flowing~ smooth~surfaced9 homo
geneous~ polycrystalline~ clear9 transparent, gold in color9
spherical and had wall thicknesses of about 10 micron~ cr
less 9 the dlameters in the range o~ 30 to 300 micronsO :
A portion of the ceramic microcap~ules were then
heated in a hydrogen atmo~phere to 600 C~ over several
hours, allowed to cool to 250~ CO ln hydrogenj and then
cooled to room temperature in a nitrogen atmosphereO The
resultant microcapsules were shiny and black in appearance
and were attracted to a permanent magnet~ apparently due to
the reduction of the Fe2O3 componentO
3 Exam ~
A solutlon was made by dripping 504 gO titanlum
tetrachloride into 500 gO o~ agitated water maintained at
-23-
~06~366
approximately 20 C Care was taken to prevent boiling and : .
e~ection of the acidic solution due to the ensuing exothermic
reactionO A clear, yellow solution resu:LtedO To 831 g~ of
this solution3 350 mlO of ammonium hydroxide (28%) were ~: ;
added with constant agitation 3 forming a thick white flocO
The reaction mixture was filtered and washed thoroughly to
remove excess NH40H~ and 25 gO of the wh.Lte floc were re~
dispersed in 405 g. hydrochloric acid (37~) 9 providing a
sol with 806% TiO2 (2054 gO TiO2)o An additional 5 gO of
water were addedO One-half of the resulting sol was poured
all at once into an agitated solution of 300 gO n~butyl i~
alcohol and 15 gO waterO Predominantly liquid-filled~ .
transparent, spherical microcapsules were formed within
30 secondsO :
The microcapsules were recovered by filtration
through NOD 54 Whatman filter paper and dried overnight at
95 CO The resultant dried~ porous, clear3 transparent9 .
green microcapsules were fir~d from room temperature to
500 C~ over about 1 hr9 yielding rigid~ crushable~ ~ree .:
20 flowing9 smooth-surfacedg homogeneous, clear9 transparent, .:
polycrystalline anatase TiO2 ceramic microcapsules
~ '
A sol was made by adding 2 gO of SnC12o2H20 to
1105 gO water and then dispersing therein 1015 g~ T102 gel
25 (prepared as in Example 1 and assayed at 6105% TiO2)~ The ~ .
resultant clear, yellow aquasol was filtered through NoO 50
Whatman filter paperO
The flltered aquasol was added to a gently stirred
aqueous alcohol solution containing 300 gO n~butyl alcohol .
30 and 22 5 gO water to form a dispersion of microparticlesO
The dispersion was filtered through a NoO 54 Whatman filter .
paperO The recovered microparticles were predominantly
., .
-24-- :,
~06 366
liquid--filled9 transparent 9 spherical microcapsules
They ranged in diameter from 20 to 250 micronsg the
average diameter being about 150 microns 9 and they had
uniform wall thicknesses of about 10 micronsO The .
microcapsules were allowed to dry in ambient air for
several days, the dried microcapsules being porous
clear, transparent 9 and sphericalO -
The dried microcapsules were fired in air
~rom room temperature ~o 500 CO in about 1 hrO and
cooled to room temperatureO The resulting ceramic
microcapsules were rigid, crushable, free-flowing,
smooth surfaced, homogeneous and spherical and had
diameters up to about 200 microns and uniform wall
thicknesses of approximately 10 micronsO Most of the
ceramic microcapsules were transparent, with some o~
the microcapsules being slightly translucentO The ..
transparent microcapsules were clear and colorless
X;ray diffraction analysis of the ceramic
microcapsules indicated the crystalline species to be
similar to anatase titania; however, khe lattice
dimensions were larger than is commor in anatase titaniaO
The crystallite sizes estimated from line broadening -
of X-ray d~ffraction patterns of the microcapsules
were less than 1000 An~ tromsu
A portlon of the ceramic microcapsules were
refired in air from room temperature to 950 CO in 2O5
hrsO and held at 950 CO for approximately 15 minO The
resulting polycrystalline mlcrocapsules were a mixture
o~ transparent 9 translucent and opaque microcapsulesO
X~ray diffraction analysis of them showed them to be
-25-
- . ' ~ ` ~: ''. ,.
~:)6~366 ~
rutlle TiO2 and SnO29 the TiO2~SnO2 ratio of peak in~
tensities being 100~5~ The rutile phase o~ the TiO2 ..
showed a shift toward a larger lattice dlmension ~rom `.
that of normal pure TiO2 rutlle materlal~ indicating ~;
partial solid solution~
~ 1`.,~
A Sol was prepared by mixing together 5O64 gO
aqueous solution of zirconlum acetate ~22% ~rO2 equivalent)9
2 gO aqueous silica sol (Ludox~ LS9 30% SiO~ equivalent), . .
10 four drops of glacial acetic acid and 5 gO waterO . . .
The resulting sol was added to an agitated ~
aqueous alcohol solution of 200 gO n~butyl alcohol and
10 gO of waterO After 1 minO; the liquld-~illed9 trans :
parent 9 spherical microcapsules were recovered by filtering
the resultant dispers.lon through a NoO 54 Whatman filterO
The recovered microcapsules were drled in air at 95 CO
for 0O5 hrO9 the dried microcap~ules being clear~ ~rans~ :
parent9 porous~ and sphericalO The drled mlcrocapsules ~:
were then fired in alr from room temperature to 500 CO
over a 1 hrO periodO The resu~t~ng ceramlc microcapsules
were rigld/ crushable~ smooth~urfaced9 homogeneous~ clear~
transparent9 and ~pherical wi.th diameter of 100~200
mlcrons and a uni~orm wall thickness of about 5 micronsO
A portlon of the ceramlc mlcrocapsules were
refired in air from room temperature to 950 C~ in 2O5
hrsO and held at 950~ CO ~or approxlmately 15 minO 9 ,
the resultant 9509 CO fired microcapsules being rigid9
crushable~ sealed~ alr~filled and having the ~ame
appearance as the 500~ CO fire microcapsules~ X ray
dlffraction a.nalysls of the 500~ C~ ~red microcapsules
.,
-26-
~;~
~ 6~3~6
gave a pattern wh~ch appeared to ind.icate tetragonal f
Zr2 whereas the 950 CO fired capsules provlded de~inite
indication of tetragonal Zr02O In each case9 zirconla
was the only crystalllne species revealed by X~ray
5 diffraction analysisO
Example 6
A sol was prepared by mlx~ng together 5 gO
of Ti02 ~el (prepared as ln Example 1~9 2O5 gO ZnC12
(60% ZnO equivalent~9 and 40 gu waterO The sol was
10 added to a 1 liter flaek containing a swir11ng solutlon
of 400 gO n butanol and 20 gO waterO After 1 minO of ~ :
swirlingD the microparticles were recovered b~ filter~
ing the disperslon through a NoO ~4 Whatman filterO The ~-
re~ultlng recovered liquid~fllled~ transpa.rent 3 spherical
; 15 microcapsules were dried in alr at 95 CO for 0~5 hrO 9
the drled microcapsules being clear~ transparent~
porous and sphericalO :
The dried mi.crocapsules were placed in an air
atmosphere3 240 CO kiln and the temperatu~e raised to
20 550~ CO in about 45 minO The fired microcapsules were
810wly cooled ln the kilnO The cooled ceramic micro~
capsules were rigidD crusha~le~ free~flowing9 smooth~
sur.faced~ homogeneous3and spherical and most of them
were clear3 transparent9 and colorless~
X~ray dlffraction analysis of the ceramic
microcapsules showed them to contain anatase titania3
Ti02 After further f~ring to 950~ CO in ai~ from room -.
temperature over 20 5 hr~O and holding at 950~ CO for 15
.. minO9 the X~ray diffractiorl analysis showed rutile Ti02
and the presenoe o~ a very low intens~ty peak ind1cated a
small amount zinc titanate~ .
'
.
~i -27-
, .,. : . , .i. . . :
,,
.~ : . , , , " .. , ~: :
36;6
X-ray fluorescent examination of the 950 C~ ;
fired microcapsules showed only about 3-5% ZnO to be
present~ :
Exam~le 7
~ . .
A titania sol was made by dispersing 5 gO o~
a gel (63% TiO2, made as in Example 1) in 50 gO waterO
The resulting sol was slowly poured into a stirred
solution of 1200 g. n-butyl alcohol and 60 gO water~ .
and stirring was continued for about 1 minO The dispersion
10 of liquid-filled, transparent, spherical microcapsules : ~ ~
. .
was filtered using No. 54 Whatman paper~
The recovered microcapsules were dried in air
at room temperature for 1 hrO, then further dried in air .:~
at 95 C~ for 2 hrs. The dried microcapsules were porous 3
15 clear, transparent and spherical with dlameters up to .
300 microns and walls which were generally less than 10 .
microns thicko The microcapsules were fired in air from
room temperature to 400 CO in about 0O5 hr~ 5 held at
400 CO for 1 hrO in an air atmosphere~ permitted to :
20 cool in the Purnace to 200 C~, and then wlthdrawn and .
cooled to room temperature within a few mlnutes~ The ~
resulting ceramic microcapsules were rigid, crushable9 i -
~ree-flowlng, smooth-surfaced, homogeneous~ clear9 .. ~. .
transparent, porous, and sphericalO i
Samples of the ceramic mlcrocapsules loaded ~ ~.
~':
in alumina combustion boats were placed in an electri-
cally heated tube furnace having a 75 mmO diameter tube
of Vycor~ which was then s~aled with gas-tight caps on
each endO The sealed tube was evacuated to a pressure -
of 5 Torr to remove air from the porous microcapsulesO
-2~-
~6~31~6
The evacuated tube was heated to about 300 CO over 105
hrsO and then argon was slowly introduced to the evacu~
ated tube until.a pressure of 1 atmosphere was reached~
The temperature was then raised to about 600 CO in
about 1 hra and held at 600 CO for 1 hrO to heat seal
the microcapsules and entrap argon therein~ the tube
being continuously flushed (during the sealing) with
argon at a rate Or 1~5 llters/hrO and with a pressure
just slightly above 1 atmosphereO The resulting argon-
filled, sealed microcapsules were cooled in the furnaceunder argon to room temperatureO ~:
Samples of the argon-filled microcapsules were
analyz~d qualitatlvely for gas composition by breaking
the microcapsules in a sealed evacuated tube and analyzing
the gas in the tube with a mass spectrometerO One of
these samples contained predominantly argon with small
amounts Or C02 and N2; another sample contained C02 with
some argon and N20 A~ter s~x months storage3 another
sample of filled microcapsules was analyzed as above
0 and found to contain predominantly argonO
Example 8
A titania sol was made by dispersing 2 gO TiO2
~el (made as in Example 1) in 30 gO waterO The resulti.ng
sol was poured into a swirling solution of 400 gO n-
butanol and 40 gO water~ The resulting mixture wasswirled for about ~05 minO and the resulting dispersed
spherical microparticles were separated by filter~ng the
mixture through a NoO 54 Whatman paperO ~.
The recovered predominantly liquid~filled 9
transparent9 spherical microcapsules were dried in air
-29-
,. , .. . . . :, ,
~061366
at room temperature for several hoursO The dry, porous a
green microparticles were stirred into a Fluorinert~ .
77 fluorocarbor (an inert fluorocarbon mixture of
compound. corresponding to the empirical ~ormulas~
C8F18, C~Fl69 and C7F15 ); the microcapsules ~loated
to the surface of the fluorocarbon and a small amount of
solid microparticles and broken or thick~walled micro-
capsules sank to the bottom of the fluorocarbonO The
floating microcapsules, which had diameters up to 300
microns and wall thicknesses of less than 10 microns 9
were recovered by decantation and filtrationO The
residual fluorocarbon liquid vaporized at room tempera-
ture from the recovered microcapsulesO
The microcapsules were then placed in an air
15 atmo~phere furnace at 200 CO The temperature waa
elevated to 460 CO in 0O5 hru, held for 5 minO and the
~ired microcapsules were slowly withdrawn from the
kiln over a 10 minO periodO The rired microcapsules ~ -
were rigid, crushable, free ~lowing, smooth-surfaced9
homogeneous, clear9 transparentl porous, and sphericalO
A sample of the flred micorcapsules were loaded
in a ceramic boat and the loaded boat was placed in a
250 Cu furnace disposed in a chamber capable of being
evacuated, and the furnace was held at 250 CO under
atmospheric pressure for about 0O5 hrO The chamber9
including furnace and loaded boat 9 was then evacuated to .
. a pressure of 5 x 10 6 Torr and the temperature raised
to about 450 CO in about 5 minO and held at 450 CO for
1 3/4 hrsO During the latter heating operation9 the
pressure in the chamber decreased to about 2 x 1.0 6 TorrO
, .
', .
,: .
' ' ' ,; ',. '. ', ' . :.
~06~366
The temperature was then raised to 650 CO over a period
of about 10 minO, held at 650 CO for about 1 hrO and
the furnace cooled within a few minutes~ timeO The loaded
boat of heat sealed9 evacuated microcapsules was then re
moved from the furnace and chamberO
Another sample of the 460 CD air-fired micro-
capsules was loaded in a ceramic boat, the boat placed
in a furnace diæposed in a chamber, a small air flow
maintained through the chamber while the furnace was
raised to 450 CO~ and the furnace then evacuated to about
10 6 Tor~ when 450 CO was attainedO The furnace was
held for 1 1/2 hrsD at 450 CO under the vacuumO The
temperature was then raised to 650 CO ~ver a period
of about 10 minO~ held at 650 C~ ~or about 1 hrO, an~
the furnace cooled within a few minutes ? timeO The
loaded boat o~ heat sealed, evacuated mlcrocapsules was
- then removed from the furnace and chamberO
After standlng at room temperature for two
months~ tlme 9 each of the two 650 CO fired samples was
placed in a vacuum glass chamber (connected to a mass
spectrometer) and the chamber evacuated to a pressure
of about 10 6 TorrO The microcapsules ln the evacuated
chamber were then mechanically broken by dropping a steel
ball (which had been held above the microcapsules with
an external magnet) and allowing the ball to fall onto
the microcapsules to break themO The breaking o~ the
microcapsules resulted in partial pressure changes ln the
evacuated chamber~ this change being immediately regis-
tered and measured by the mass spectrometerO The partial
-31- ~
. . . . . .. . . . : .. . . . .. . ..
\\
1~16~366
pressure changes indicat~dthat the 650 CO fired micro-
capsules had been sealed with a substa~tial vacuum insideO
Exam~le 9
A sol was made by disperslng with agitation 3
gO Ti02 gel (made as in Example 1~ ln 30 g~ waterO The
resulting 901 was ~iltered through a 1O5 micron Millipore~
filter and the filtered sol poured into a swirLing solu- ~
tion of 600 gO n~butanol and 45 gO water to form gelled -:
mlcroparticlesO The swirling was continued for about 1
minO and the resulting microparticles were recovered by
filtration through a 45 micron screenO The recovered
microparticles were predominantly liquid filled9 trans~
parent3spherical microcapsules and they were dried in air
at room temperature for about 20 hrsO The drled micro~
particles were almost all porous, transparent, spherical
microcapsules with diameters generally about 60 to 300
; microns and wall thicknesses below 10 micronsO :
The dried microcapsules were fired in air ~rom ~:
room temperature to 460 CO over a period of 1 1/3 hru
~, 20 and held at 460 CO for 20 minO The fired microcapsules
~ were gradually removed from the furnaceO The fired mlcro-
.l capsules were separated from a small amount o~ solid
part.icles and broken microcapsules by the ~loatation
~ technlque of Example 80 The recovered rigidc crushable9
.', .
smooth surfacedD homogeneous~ porous9 transparent9 clear9
spherical microcapsules were placed in a vitreous silica
tube located in an electrlc furnace~ the ends o~ the tube
sealed~ the tube evacuated to 6 x 10 6 Torr~ and the
tube heated to 450 CO :~n about 14 minO and held at 450
i 30 CO for 3 hr~O ~n the vacuumO The pressure after 3 hrsO
., ~
! .
., .
.' '
~ .
10~36~
was 5 x 10 6 TorrO The valve to the vacuum system was
closed off and neon gas was permitted to enter the
vitreous tube at a slow rate~ the pressure being gradc
ually raised to about 1 atmosphere of rleon over 5 minO
time and the temperature maintàined at 1150 CO for about
1 hrO The tube was heated to 650 CO in about 10 minO
and held at temperature under a neon atmosphere for
about 15 hrO The system was allowed to cool for 20
minO under the neon atmosphere and the"sealed, neon filled9
microcapsules were removed from the tubeO C~nfirmation
that the recovered mlcrocapsules contained gas that was
predominantly neon (about 2/3 atmosphere) was obtained
by the mass spectrometer technique of Example 7O
~ i
Forty gO of aquasol containing lOo 5% A1203
(Nalcoag~ LN-1331-256) were poured into a 1 llter flask
containing 400 gO of swirling n~butanolO The sol~alcohol
mixture was swirled for 1 min0~then rapldly filtered
through a Whatman NoO 54 paperO The microcapsules
20 obtained were predominantly porous, transparent 9 liquld '
filled3 and spherical9 with diameters up to 300 microns
and substantlally uniform wall thlckness of about 5 to
25 micronsO
The recovered microcapsules were air~dried for
about 24 hrO at room temperature to porous 9 transparent 9
clear~ spherical microcapsules which were then fired ~rom
room temperature to 600 CO in about 1 1/2 hrO to form
rigid9 crushable3 smooth~surfaced~ free~flowingg homo
geneous9 porous3 transparent3 spherical microcapsules
of polycrystalline A1203O
-33~ .
13~6
Example 11
-A titania sol was made by dispersing 2 gO Ti02
gel (made as in Example 1) in 20 gO waterO The dispersion
was poured into 200 gO swirling sec~butyl alcohol to
formed gelled microparticles3 and swirling continued for
1 minO The dispersion was filtered through No. 54 Whak ~ .
man filter paperO The recovered particles were predom ~ ~ -
inantly clear, transparent, yellow in color, spherical
liquid-filled microcapsules and generally ranged in
diameter from about 10 to 200 microns with a uniform wall
thickness of about 3 microns or lessO The recovered .
microcapsules were slowly dried in ambient air at room
temperature, resultlng in clear, transparent~ porous~
spherical microcapsules in a green stateO When fired in . .
air, e~gO 400 CO for about 1 hrO, they will be rigid,
crushable, clear, transparent, homogeneous 9 smooth~ :
surfaced, free-flowing3 porous, spherical microcapsul~s :.
of polycrystalline anatase TiO2 and can be further fired
eOgO 650 Cu for about 1 hrO D to form sealed microcapsules
filled with selected materialsO
., .
Twenty gO of alumina sol (Nalcoag~ LN 1331-256
having 10o 5% A1203) were poured into 200 gO of swirling
sec-butyl alcohol to form gelled microparticlesO After
swirling 1 minO3 the dispersion was filtered through a
NoO 54 Whatman filter paperO The recovered microparticles -
were predominantly clearg transparent 9 colorless~ porous 9
liquid filled3 spherical microcapsules having diameters
up to 300 microns and wall thicknesses generally less
than 10 microns~ After lowly drying in ambient air3
.,
-34-
'''; . ~ . ' ' ' ' ', ''... ~` ' ', `~ '' '
" . . . . . . .. ~ . , .. , :
, . . ... .. .. . ,, . ~ .. .
~06~L36~
the dried microcapsules were porous9 clear, colorless~
transparent, and sphericalO The dried microcapsules could
be fired in air (eDgO 600 CO for about 1 hrO) to form
rigid, crushable, pprous 3 smooth-surfac:ed 9 free-flowingj
homogeneous, clear, transparent, spherical microcapsules
f polycrystalline A1203 which could be sealed with a
selected material filled therewithinO
Example 13
Forty gO of sol (Nalco~ LN 1331-273` containing
the equivalent of 5O~6% Fe203 were poured into 400 gO of
gently Swirling n-butanol in a l-liter flask to form
gelled microparticlesO Swirling was continued f`or 0O5
minO and the dispersion filtered through No~ 54 Whatman
filter paper. The recovered microparticles were predom-
inantly liquid-filled, transparent, porous, spherical
microcapsules; they were slowly dried for several days
at room temperature to permit tlle liquid within the
porous mi¢rocapsules to evaporateO The resulting clear~
shiny, dry, transparent~ porous, spherical microcapsules
werè predominantly between 100 and 200 microns in diameter~
had uniform wall thicknesses averaging betwèen 5 and ln
microns, and were amber in color~ :
A portion of the dried microcapsules were placed
in-an-alumina boat9 fired in air from room temperature to
600 CO ove~ one-hour~s time,and cooled to room tempera~
tureO The fired microcapsules were rigid~ crushable,
smooth-surfaced, free flowing, transparent~ spherlcal9 ~
. and of polycrystalline iron oxldeO The color of the .~ :
'. fired microcapsules ranged from red to black as observ~d
. 30 by the unaided eyeO Under the microscope at 140Xa the
' ~.
-35-
~ :' '
.,
',, '.,: ' ' : ~' ' '. ' :', . `', ,- '.'` ' .. ,'. ''
'1~6~3ti6
red microcapsules appeared to be grainy but smooth~ and
said black microcapsules were red9 shiny9 and very clear,
many of the latter clear microcapsules were attracted to
a magnetu ; :
Exam~le 14
Twenty g~ of a sol (Nalco~ LN-1331-270) con~
taining the equivalent of 6016% Cr203 were poured into ~ :
a solution of 300 gn n;butanol and 15 go water being
gently stirred by a laboratory stirrerO ~t T rring con-
tinued for 1 minO and the dispersion was filtered to
recover the resulting porous9 liquid filled9 transparent3
spherical, gelled microcapsulesO
After drying in the air at room temperature the
resulting porous microcapsules (green in color) were
examined under a microscope at 140X and observed to be
spherical with transparent wallsO The dried product was
fired in the air from room temperature to 500 CO in 45
minO and held at 500~ CO for 2 hrO The fired microcapsules
were rigid 3 crushable, smooth-surfaced~ free~flowing a
homogeneous~ spherical9 opaqueD green in colorg grainy,
and very shlny and of polycrystalline Cr203O
~ e 15
-- .
Twenty gO of A1203 sol havingl0O5~1203 and
two drops of Cr203 sol having6O16 ~ Cr203 were blended
together and microcapsules made as ln Example 140 The
microcapsules were recoverd~ dried and fired from room
temperature to 1250 CO in 2 hrO and held at 1250 CO
for 24 hrO The fired microcapsules were r-lgld9 crushable a
smooth surfacedg free~flowlng~ homogeneous a spherical
-36-
. : : ,
1~6~3~6
polycrystalline and were opaque and pink indicat.ing a
coloration of the alumina by the Cr203 as in rubyO
A titania sol was obtained by dispersing 2 1/2
gO TiO2 gel (made as in Example 1 containing the
equivalent of 6107% by weight TiO2) in 20 gO waterO
Secondary butanol (200 g~) was agitated in a Waring
Blender rapidly~ but controlled to cause rapid swirling
without frothingO The titania sol was poured into the
alcohol and agitation continued for about 3 secu The
resulting dispersion of micropartlcles was filtered
through a NoO 54 Whatman filter paperO After drying in
the air at room temperature to remove the solvent from :~
the recovered particles, the resulting dry ge:l agglomerates
o~ microcap3ules were shaken in Fluorinert~ FC~77 fluoro~
carbon to aid in separation of the individual tlny micro-
capsules9 ~iltered9 and dried at room temperature for
2 hrO then at 90 CO for 1 1/2 hrO The recovered spherical
microcapsules were predominantly clear9 transparent 9
porous and very small and were screened through 30 and
20 micron sieves and fired in air from room temperature to
400~ CO over 3~4 hr~ Microcapsules of 5 microns diameter :
....
and smaller were observed microscopicallyO The per~ent ~: .
by weight of fired microcapsules ln the vari.ous size
ranges waso
Fraction~ _icrons % by_Wei~ht
' +3 tmaxO 50~ 15
~30 ~20 180 4 ~:~
-20 66o6
, 30 lOOo
.. `. ~, .
-37-
~ ' '
~ j
i1366
.. ~
E~am~le 17
A solutl.on was made by dissolvlng 28Ol gO basic : :
aluminum acetate9 A1~0H~2(00CH3)ol/3 H3B03 ~Niaproo ~ 9 '- .
in 171 gO waterO Twenty gO o~ silica sol ~Ludo ~ LS9
5- 30~ SiO2~ which had been preacidified with three drops
of concentrated hydrochlor~c acid (37%) was stirred in ..
the solutionO Twenty mlO o~ the result.ing sol was
poured into a swirling body of 200 gO sec~butanol in a
500 mlO flaskO Sw~.rl~ng was continued for 1 minO and
the micropartlcles were recovered by filtering through
a NoO 54 Whatman filter paper~ The filtered micropartlcles
were slowly drled ln air at room temperatureO The dried
microparticles were examlned under a steroscopic micro
scope and all were found to be`spherical with at least
90% of the particles in the form of porous microcapsules
with diameters ranging from about 10 to 500 microns9 the -~
average diameter bei.ng about 100 micronsO Wall thi.cknesses ..
of these mlcrocapsules were uni~orm w~thln each mlcro~ :
capsule and varied between partlcles ~rom about 4 to 20
20 micronsDwith the average thickness being about 10 mlcronsO .,
Practlcally all of the mlcrocapsules were transparent
and clear ~a minor amount were hazy but still transparent9
and a minor amount were opaque and had relatively thick
walls~O A port~on o~ the dried mlcrocapsules were flred
from room temperature to 500~ C~ over a 2 hrO per~od and
then cooled ln room temperature airO The flred micro~
capsules were rigid9 crushable9 transparent9 smooth~
surfaceda free~flcwingg homogeneousg and sphericalO The
appearance as obser~ed under a stereoscopic mlcroscope
at 140X was essentially the same as that o~ un~lred micro-
- -3~- ;
, .
1~63L366
capsulesO A small quankity of the fired microcapsules
were stirred in a drop of lndex oil. ~1058) on a g`lass
sllde and the microcapsule wall~ were determined to be
porous by observing the penetrat~on of index oil through
the walls
Example 18
A measure o~ the time to form microcapsule~
was made in a series of runs wherein standard condltlorls
were ma~.ntained with the except~on of the length of time
10 that a sol was swirled in dehydrating liqu~`do The results :
show that mlcrocapsules can be formed withln a ~ew seconds
and a substantial yield produced wlthln about 15 se¢onds~
The results are tabulated in th~ table below~
The sol used in the runs was prepared as ln Example 1
from l part of T~.02 gel (61% Ti02~ and 10 parts of wateru
In-each run~ the sol ~20~0 gO) was added al:l at once lnto
200 gO of n~butanol being swirled by handO The swirling :
was continued for a certaln time immed.~ately after addl~
tisn and then the contents were poured all at o~ce onto : -.~
20 a NoO 54 Whatman ~ilter paper on a Buchner funnel (1002 ~::
cmO dlameter~ fitted on a water asplrated fla~kO The
ti.me requ.ired to ~ilter the contents wa~ notedO The .:
~ilter pape.r loaded w.~.th the f.il.tered~ l.iqul.d~filled .:
microcapsule product was air drled at room temperature
25 for 2 hrsO 9 and then dried at 90~ CO for 1i2 hr~ The `.
product was removed from the filter paper b~ tapping and
welghed to give a dry welght 0~ microcapsulesO The dr~ed .
microcapsules were flred ~rom ro3m temper~ture to 500~ :
C~ over a period of 1~ hrO The result~.ng f~.red micro~ ..
capæule~ were we~.ghedO The final f~red rlgld~ crushable9
:, .
', ' ';'
-39- ; .:
`"''' '
,, ~ .. . .... .... . . . ... . . .
~n~366
smooth-surfaced product was clear, transparent3 homogeneous9
spherical microcapsules with diameters up to 300 microns~
Swirl Filtration
time, time3 Dry weight ofFired weight of
5 secO* sec.** ~ e__le~ microcapsul~
200 (filter 0O40(m~crocap~ 0029
paper was sules adhered `.
coated with to filter paper) ',:
sticky gel~
1020 (slight 0087
amount of micro-
capsules could
not be tapped i~
from filter j~ ~
paper)
1O40 1O02
18-20 1044 loOO
18~20 1~41 1O02
* Time from moment of 801 addltion to moment of pouring
dlspersion on filterO ..
** Time from pouring dispersion on ~ilter to moment :
filter cake appeared du119 indicating dehydrating .
liquid has passed through filterO
'. ' ' ' '
The above data show that at 5 seconds swirl
25 time D some o~ the sol had gelled to ~orm microcapsules 3 '' .:~. '
but much of it was not sufficlently dehydratively gelleda
hence the f~ltration was slow and the yield was low~ By
' 10 seconds swirl time, the formation of microcapsules was :
I almost complete9 and the difference in results between the
15, 30~ and 60 seconds runs was vlrtually indistinguish~ . -
ableO These data show that substantially quantitative
yields of gelled microcapsules can be obtained in accordance
with this invention within30 secondsO
Exam~le 19
3~ Dried titania microcapsules were prepared as
described in Example 9 and ~ired from room temperature to
f
:
, . ,
361~
460 CO over a period o~ 1 1/3 hrsO and held at 460 C4 "'
for 20 minO The resulting rigid~ crushable., smooth
surfaced, free flowing3 homog~neous, porous9 transparent
spherical microcapsules of polycrystalline anatase T~02
were utilized in preparing a number o~ composites as
described belowO
A quantity of the fired microcapsules prepared
as described above were placed in a 2~5 cmO diam~ter steel ;
.mold together ~ith small pieces of Woods metalO The .
10 mold was heated to 115 CO and a plunger was lnserted i:
into the moldO Gentle, firm pressure was applied to the
plunger to pack the moldO The mold was cooled to 40 CO .
and the microcapsule-Woods metal composite (0031 cmO ::
thick) was extracted there~rom~ A~ter cooling the com~ .
posite to room temperature, it was broken and examlned
microscopically at 60X and 140Xo A well-packed dispersion
of intact, microcapsules in the metal matrix was observed~ .
the microcapsules being the major component by volumeO . ~.
Fired microcapsules prepared as described :
above were ~urther heated from about 450 CO to 600~ CO
over a period o~ about 2 hrsO The microcapsules were
cooled and when examined with a stereoscopic mlcrGscope
(140X) were observed to be transparent, spherical~ and
impermeable to ir,dex oilO A portion of theæe mlcrocapsules
was mixed into a viscous solution of polymethylmet~
acrylate dissolved in acetone~ The res~l~lng mixture ::
was ca~t into a sheet about 0031 cmO thick and the solvent .. ; :
was allowed to evaporate from khe mixtureO A solid sheet
was obtained and under microscopic examlnation ~he micro~
capsules were observed intact and dispersed withln the
composite~
,
.,
-41-
. ' ' :
3166
A portion (1 gO) of the above~described micro~
capsules (fired to 600 CO) was mixed with 5 gO of powdered
bottle glassO The mixture was placed in an alum~na
crucible and placed in a furnace preheated to 1080 CO
and held at that temperature for a time sufficient to
melt the glass, at which point the microcapsules floated
to the top of the meltO The crucible was withdrawn from
the furnace and cooled in air to room tem~eratureO The
glass-mi~rocapsule composite was removed from the
crucible by fracturing the crucibleO Microscopic exam
ination (140X) of fractured pieces of the composite .
showed that the microcapsules concentrated at the top
region of the composite where they were ~lrmly embedded
as intact,discreet, dispersed microcapsules in the clear
glas~ matrixu
Exam~le_20 ' :
An alumina crucible tl~9 cmO dlameter~ 205 cmO .
he:Lght~ was loaded about 3/4 full with the fired micro-
capsules (fired to 600 Cu) prepared as described in
Example l9o The loaded crucible was placed in a ~urnace
wlth an alr atmosphere and the temperature ralsed ~rom
room temperature to 1200 C~ over a 2 hrO pe~iodO The~
the temperature was raised to 1475~ CO over a 5 hrO perlodO . .
The crucible and contents were permitted to cool overnight .
ln the furnace and an integral mass was extracted from
the crucibleO Microscopic examlnation (140X) showed
considerable crystal growth o~ the tltania in the micro~
capsules walle 9 but the microcapsules were still hollow
and sphericalu The microcapsules had sintered together
at points of contactO
-~12-
. l;. .. ~
