CA1292106C - Hollow microspheres made from dispersed particle compositions - Google Patents

Abstract

ABSTRACT

Hollow porous and non-porous microspheres are made from dispersed particle film forming compositions comprising dispersed particles, a binder, a film stabilizing agent, a dispersing agent and a continuous liquid phase. The hollow porous microspheres have walls with voids which are interconnected to each other and to the inner and outer wall surfaces. The microspheres can be made from dispersed particles of ceramic, glass, metal, metal glass, plastic, and mixtures thereof. The microspheres can be used as filler materials and as supports and enclosures for catalysts. The hollow microspheres are made by feeding the dispersed particle composition and a blowing gas to a coaxial blowing nozzle having an inner coaxial nozzle for the blowing gas and an outer coaxial nozzle for the dispersed particle composition. The blowing gas is fed to the inner nozzle and the dispersed particle composition is fed to the outer nozzle to blow and form, in the region of the coaxial blowing nozzle orifice, hollow dispersed particle composition microspheres. The hollow microspheres are removed from the region of the orifice and treated to bring the dispersed particles into point to point contact and to harden them to obtain hollow green microspheres, which are subjected to a sufficiently high temperature to remove the continuous liquid phase from the hollow green microspheres and to sinter the dispersed particles to obtain hollow porous microspheres. The hollow porous microspheres can be treated with semipermeable membrane forming materials to make them non-porous and suitable for use in selective separation processes and in biotech processes.

Description

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This application is a divisi.on of Application No. 488,123 filed ~ugust 6, 1985.
The present inventîon rel~tes to hollow microspheres made from clispersed p~rticle film forming compositions comprising dîspersed particles, binder, film stabilizing agent, dispersing agent and cc~ntinuous liquid phase.
The present invention particul~rly rel~tes to hollow green microspheres a~ade from dispersed particle film forming compositions comprising dispersed solid particles, P binder material, a ~llm st~bilizing ~gent, a dispersing agent for the sdid partieles ~nd a continuous aqueous or non-uqueous liquid phase.
The present invention particularly relates to holl~w green microspheres made from dispersed particle film forming compositions which hollow green microspheres are substantially spherical, have substantially uniform diameters and hsve subst~ntially uniform wall thiclcness. The hollow green microspheres llre free o~ latellt so1id or liquid blowing gas materials, and the wulls of ehe hollow green microspheres are substantially free of holes, relatively thinned wall portions or sections and bubbles.
The present invention particularly rel~tes to rigid hollow porous microspheres which are subs~antially spherical, have substantially uniform diameters, und have substanti~lly uniiEorm wall thickness and the walls have uniform void content and void distribution and voids which Qre connected to each vther and to the inner Qnd outer microsphere w~l surf~ces. The w~ls of the holls~w porous microspheres are free of l~tent solid or liquid blowing gas msteri~ls, ~nd ~are substantially free of relatively thismed w~ll portions or sectIons and bubbles.
The hollow green microspheres can be made from ceramic, ~lass, met~l, metsl glus5 und plsstic particles, and mixtures Shereof.

t :~9Z:~6 The present in~rention relates to a method and npparatus for using a c~xial blowing nozzle and a blowing gas to blow hollow microspheres from a dispersed particle film forming composition comprising feeding the blowing g~s to an inner coax~al noz~le, feedin~ the dispersed particle ~llm forming eompositioll to s~i outer coaxial nozzle, ~orming sphencally shaped hollow microspheres in the r~gion of the or~ ce of the cc~axial blowing nozzle ~nd removing the hollow microspheres from the region of the ori~lce of the coa~aal blowing nozzle.
The present invention more particularly rel~tes to a method and appar~tus for using a co~a~l blowing nozzle and an external fluctuating pressure field, e.g., a transverse iet entraisling fluid and a blowing gas to blow hollow microspheres from a dispersed particle film forming composition comprising applying the blowing gas to the inner surface of the film formir~g composition to continuously blow individual spherically shaped hollow microspheres and using the transverse jet entraining tluid to assis~ in the mi¢rosphere formation and the detaching of the hollow microspheres from the blowing nozzle.
The continuous liquid phase of the dispersed particle Slm forming composition allows the hollow microspheres to be blown by forming a stable ~llm to eontain the blowing g~s while the hollow microsphere is being blown and formed.
The dispersed p~rticles in the dispersed particle composition, as the dispersed particle composition is orn~ing the hollow microsphere and after the microsphere is formed, linX up with each other to form a rig~d or relatively rigid lattice work of dispersed particles which dispersed particle lattice work with the binder and continuous liquid phase comprise the hollow green microspheres.
The hollow microspheres after they are formed can be hardened ~n ~mbient ~tmosphere or by heatîng and removing a portion of the continuous phase or by cooling where a thermoplastic binder is used.
Where a photo or ionizing radiation polymerizable binder is used, the hollow microspheres can be subjected to ultraviolet light or ioni~ing radiation ~o rapidly polymerize the binder and harden the microspheres.
The hardened hollow green microspheres have sufficient strer~gth for handling and further treatment without significant breaking or de.~orming of the m;crospheres.
The ~ardened green microspheres are treated at elevated temperatures to remove the rem~inder of the continuous liquid phase and volatile materials such as binder, film stabilizing agent and dispersing agent. The treatment at elevated temperatures sinters and coalesces the dispersed solid particles to form rigid hollow porous microspheres that are substantially spherical in shape, have substantially uniform diameters and ha~e substantially uniform w~ll thickness. The heating at elevated temperatures, in removing the continuous phase ~nd added materi~ls, creates interconnecting v~ids in the walls of the microspheres which result in the porous characteristics of the n~crospheres. The sintering and coalescDng of the dispersed solid particles, depending on the time and temperature of the heatulg step can cause a small degree of compaction of the di~persed particles and can cause the coalescing of the particles at the points in which they are in contact to form rigid, uniform size and shaped n~icrospheres of uniform w~ll thickness, uniform ~oid content and uniform distribution of voids in the walls and high strength. Because the porosity is a result of the removal of the continuous phass from uniformally dispersed solid particles, the pores are continuous from the outer w~l~ surface OI the microsphere to the inner w~ll surface of the microsphere and the w~lls of the microspheres ha re substantially urLiform roid content and uniform distribution of the voids that are created.

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The rigid hollow porous microspheres of the present invention can be treated to impregnate the pores or place within the pores semipermeable membranes and the thus treated microspheres can be used in selective ~as or selective liquid separation . processes. The porous microspheres may also be treated to act as a substrate for or to cont~in a catalyst and be used for cerrying out chemical processes.
The rigid hollow porous microspheres of the present invention can be treated to encapsulate within the microspheres genetically en~ineered or natural living microor~anisms. The microspheres containing the living organisms can be treated w~th nontoxic semipermeable membranes to seal the microsphere pores. The semipermeable membrane can selectively allow passage of nutrients and oxygen into the hollow microspheres and allow passage of biologically produced products and/or waste products out OI the hollow mic~spheres. The hollow porous microspheres m~
accordingly be used in conjunction with genetically en~neered bacteria or other living microorganisms, antibiotics or enzymes in processes to produce or separate and purify pharmaceutical or chemical products.
The rigid hollow poroals microspheres of the present invention can be employed to encapsulate liquids or gels which are caused to be deposi~ed in~o the internal hollow cavity of the microspheres by hydrostatic pressure or by centr~fugal force. The liquids or gels can subsequently be used as adsorbents, absorbents Qr catalysts, or as slow release chemical agents. An outer membrane film may be added to control the seleceivity of the process and thereby,- for example. combine the processes . of membrane separation and adsorption . absorption or affinity chromatography. The outer membrsne can also be used to protect a catalyst from contamination.

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BACKGROUND OF THE INVENTION
In recent years, there have developed many uses for hollow microspheres of uniform diameter, uniform wall thickness ~nd uniform strength. Hollow microspheres have found industrial uses as filler materials ~nd as proppants to increase gas recovery from gas wells.
Though there are known methods for producing hollorN microspheres the known methods suffer one or more shortcomings including production of very small microspheres, microspheres of random size distribution, microspheres which contain latent liquid, solid or gas blowing agents, and microspheres which have thin wall sections or walls having sn1all gas bubbles dissolved or trapped in the walls . See ~ for example, Sowman U.S.P. 4,349,456 (sol gel process), and De Vos et~ al. U.S.P. 4,059,423 (latent blowing gas process). Other methods that avoid these shortcomings generally involve c~rying out the microsphere forming step at high or relatively high temperatures. See, for example, L.B. Torobin U.S.P. 4,303,431 (glass), U.S.P. ~,303.603 (plastic), and U.S.P.
4,415,512 (metal) Prior to the time applicant made the present invention there was no known simple economieal method of producing rel~tively large hollow microspheres or hollow porous microsphereswhereby- the microspheres were substantially spherical, of substantially uniform diameter, uniform w~ll thic3cness, uni~orm void content and uniform void distribution and intercommunication of the voids in the walls and uniform strength and where the microspheres could be produced at about ambient temperatures.
Further, the recently developed processes which use a multiplicity of hollow porous glass or porous plastic tubes coated with semipermeable membranes for c~rrying out selective gas or liquid separstiQ-l processes suffer from sevcral shortcomings. The porous glass nn~l plastic t~lbes are ,: .

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joined by headers which are dificult to manufacture and se~l, and the glass tubes in use frequently break. The processes using plastic tubes are limited in operating temperatures and pressures due to the tendency of the tubes to creep and/or buckle with increasing temperature~. Also, attempts to make hollow gl~ss tubes with interconnected voids in the tube walls by acid etching of a separated gluss phase has resulted in exce~sively weak glass tube walls.
In addition, the recently developed use of bioengineered microbacteria to produce pharmaceutical and chemical products has been hampered by the abserlce of a lRrge scal2 process in which a self-sustaining sterile growth environment for the bacteria coulcl be maintained, which at the same time allowed selective permeation of o~cygen and nutrients to the bacteria, and selective removal of the w~ste products and/or bio produced products from the sterile environment.
Though numerous pharmaceutical and chemical products have been produced in the l~boratory or by sm~ll scale in vivo processes there has not been an economical means developed which would allow general large sc~le handling and processing of the bacteria and sterile environment snd the effi~ient separation and purific~tion of bioproducts produced.

OB3ECTS OF THE INlVENTION
It is an object of the present invention to provide a process and apparatus for making hollow microsplleres from a dispersed particle film ~orming compositio~ ~t about ambiellt or rel~tively low temperatures using a co~a~l blowing nozzle ~nd a blowing gas.
It is another o~ject of the present invention to m~lce hollow green microspheres ~rom a dispersed particle fflm forming composîtion comprising dispersed solid p~rticles, a binder material, a ~llm s~abilizing ~25~

agent, a dispersing agent for the solid particles and a continuous aqueous or non-aqueous liquid phnse.
It is arlother object of the present invention to make hollow green microspheres from a dispersed particle film forming composition comprising dispersed ceramic particles, glass particles, metsl particles, metul glass particles or plastic particles, and mixtures thereof.
It is another object of the present invention to use a coaxial blowing nozzle to bIow a dispersed particle film forming composition to form hollow green microspheres which are sphericPl in shape, have uniform di~meters and uniform thin walls, which walls are substantially free of trapped gas bubbles or dissolved latent blowin~ gases which can rorm bubbles and/or escape to form holes.
It is still another object of the present invention to produce f~om dispersed particle CQmpoSitionS în an economical simple m~nner hollow porous microspheres which are substantially spherical in shape, ur~form in size, wall thickness and have uniform and prescribed void content and uniform void distribut;on in the walls and which have subst~ntially uniform strength.
It is still ~nother obJect of the present invention to produce from dispersed particle compositions hollow microspheres which have been tre~ted to seal the pores or to fuse the dispersed particles to subst~ntially close off the pores and remove the voids.
It is another object of the present invention to make rigid hdlow porous and rigid non-porous rnicrospheres for use as filler materials and prop pants .
It is another object of the present invention to malce rig;id hollow porous microspheres suitable for use as substrates for semipermeable membranes in proeesses for earryirlg out gas und llqui~ separ~tions and for use a~ substrates for cfltalyst and enzymes.

It is another ob3ect of the present invention to rnuke rigid hollow porous microspheres ~uitable for use as substrates for semipermeable membranes in processes for the manufacture snd purification of pharmaceutical or chemical products using or derive~d from geneticslly engineered bacteria, natural living microorganisms and enzymes.
It is another object of the present invention to make rigid hollow porous microspheres suitable as containers for liquids, adsorbents, absorbents or catalyst, or as conta~ners for chemical agents whose release is subject to predetermined control , e. g., controlled slow release .

BRIEF DESCRIPTION OF THE DRAWlNGS
The attached drawings and photographs illustrate exemplary forms of the method and ~ppsratus of the present invention for malcing hollow n~icrospheres from a disperse particle film forming composition and illustrate some of the hollow microspheres that sre obtsined.
The Figure 1 of the drawings shows in cross-section an apparatus having a co~xial blowing nozzle means for supplyin~ the dispersed particle composition material from which the hollow porous microspheres are formed and for supplying the gaseous materl~l for blowing the hollow rucrospheres .
The Figure 2 of the drawings is 8 detailed cross-section of a coaxial nozzle construction and shows the formation of fi~amented hollow microspheres .
The Eigure 3A of the drawings is a cross-section of a modified coaxial nozzle construction and shows the formation of filamented hollow microæpheres ~
Figure 3B oî the drawings is a cross-section of ~ coaxial nozzle construction ~nd shows an embodiment of the invention in which smnll gas bubbles are formed in the continuous liquid phase prior to blowing the hollow microspheres.
The Figure ~ of the rlrawings is a cross-section of a coaxial nozzle construction o Figure 2 used in conjunction .with a tr~nsverse je~ ~o assist in the formaffon and detachment of the hollow micr~spheres from the coaxial nozzle and shows the formation of filamented microspheres and the breaking away of the ~llaments from the microspheres caused by the lateral fluctuations of the filaments induced by the transverse jet entraining fluid.
The Figure 5A of the dr~wings is ~n enlarged cross-sect.ion of a hollow porous microsphere made from the dispersed particle comlpositions of the present invention and showing the interconnecting lroids.
The Figure 5B of the drawings is an enlarged cross-section o~ a hollow porous microsphere of the present invention showing l~rge or macro pores whic:h extend through the walls and which are evenly distributed in the w~lls of the n~icrosphere.
The Figure 5C is a cross-section of the mïcrosphere section illustrated in Figure 5A in which the inner volume of the hollow microsphere has been filled with a catQlyst material, or a liquid adsorbent or absorbent material.
The Figure 5D is ~ cross-section ~ the microsphere section illustrated in Figure SB in which the inner volume of the hollow microsphere has been filled with living cell microorganisms in a nutrient broth Rnd the macro pores sealed wi~h a semipermeable membrane.
The Figure 6A is an enlarged cross-section of a hollow microsphere made fr~m the dispersed parti~le compositions of the present invention wllich has been heated at elevated temperature to remove the b~nder ~nd continuous phase a~d sinter the dispersed particles.

~;2 9~:~06 The Figure 6B is another cross~section of the microsphere section illustrRted in Figure 6A which has been treated with a sol composition and ag~in heated at eleYated temperature to deposit solid p~rticles from tlle sol composition which fi~rm a lattice work ~f the particles in the microsphere wall pores to reduce the pore size, i. e ., to produce micro pores, which micro pores can provide support for a semipermeable membrane to be cleposited on, impregnated or pl~ced in the micro pores.
The ~igure 6C is another cross-section of the microsphere seetion illustr~ted in Figure 6A in which the ps~res in the w~ll of the hollow microsphere have been sealèd with a semipermeable polymeric or immobilized liquid membrane.
The Figure 7A is a photograph of an embodiment of the invention illustrated in Figure 4 in which substantially spherical hollow green microspheres are obtained using a transverse jet entraining nuid and shows the breaking aw~y oP the filaments connecting the microspheres.
The Figure 7B is a photograph of an embodiment of the invention illustrated in Figure 2 in which fi~amented hollow green microspheres are obtained.
The Figure 7C is a photograph of another embodiment of the invention illustr~ted in Pigure 2 in which non-filamented hollow green microspheres are obt0ined.

THE AI)YANTAGES
, The present invention overcomes many of the problems associated with prior attempts to produce hollow green microspheres and to produce hollow porous microspheres from dispersed partide compositionsv The proeess and ~pparatus of the present invention ~llows the production of hollow green n~icrospheres an~ Figid hollow porous microspheres having prede~ermined char~cteristic~ of uniform di~meter, uniform wall ~L2923L0~

thickness and uniform void content, uni~orm void distribution snd void intercommunication in the walls and high strength such that hollow porous microspheres can be designed, manufactured and tQilor made to suit a particular desired use. The diameter., wall thickness D void content, void distribution and void intercQmmunieation in the walls, strength Qnd chemical properties of the hollow porous microspheres can be determined by carefully selécting the constituents of the dispersed particle composition, particularly the dispersed solid particles, the si~e of the dispersed solid porticles and the volume percent solid~ of the dispersed particle, i.e., liquid/solids, C00 pOSitiOII, and the elevated temperature at which the hollow green microspheres sre fired and æintered to remove the continuous phase.
The diameter and wall thickness of the hollow microspheres are determined prima~ly by the geometry of ~he nozzle components and by the viscosity of the dispersed particle composition, the blowing gas pressure, and where used the linear velo~t~ of the trans~rerse jet entrQining fluid, The porosity and degree of intercommunication of the voids in the microspheres walls is determined primarily by the volume percent solid particles in the dispersed particle composition ~nd the degree of sinterulg. The process and apparatus of the present invention allow a wide ran~e of setection of dispersed particles to form the composition Dnd a wide range of selection of the blowing gas to blow the hollow microspheres.
` The process and apparatus of the present invention provide a pr~cti~:al and economical means by which hollow green microspheres and hollow porous microspheres having uniform cZiameters and uniform thin ~alls of high strength can be produced. The process and apparatus of the present invention provide ~r the produ~tion of hdlow gre~n microspheres ~nd hollow porous microspheres nt economic prices and in large quantities.
The process and apparatus of the present in~ention, as compared to the prior art prooess (De Vos U.S.P. 4,059~23~.using a latent liguid or solid blowing agent, produces unifor ;l size spheres as compared to spheres of rRndom size distributian, and produces spheres the walls of which are of uniform thickness, are free of thin wDlled portions, trupped bubbles or gases, or trapped latent ~lowing agents which weaken the wal~8, or which may subsequently escape and leave holes in the walls.
The process and apparntus of the present invention, as compared to the prior art sol gel microcapsule process (Sowman U.S.P. 4,349,456~, produces large uniform size spheres with uniform thin walls. The Sowmnn sol gel process produces - small spheres of random size distribution and spheres which have thin and weakened wall portions.

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D~SCUSSION OF THE INY~NTION
-The invention will be described with reference to the accompanying Eigures of the drawings wherein like numbers designate like parts throughout ~he several views. . -E~eferring ~o Figures 1 and 2 of the drawings there is illustrated avessel 1, made oî suitable non-corrosiYe material capable of being heated, by means not shown, and containing stirring or mixing means, also not shown, cap~ble of m~intaining the solid particles in the disper~ed particle film forming composition 2 evenly dispersed throughout the continuous liquid phase of the composition in vessel 1.
The vessel 1 cont~ins a removable lid 3 which may be removed to fill vessel 1 with a charge of dispersed particle composition 2. The lid 3 contains a centered opening 4 through which a vertically moveable upper portion Sa of hollow tube 5 passes. The lower portion of hollow tube 5 forms the inner concentFiC blowing nozzle Sb for the blowing gas 6. The inner concentric blowing nozzle 5b, passes through and is eentered by cente~ng means 7.
The lower portion of inner coaxial nozzle 5b of the hollow tube 5 can have removeably connected thereto ~ calibrated nozzle 8 such that inner ~oncentric nozzle 5b may have the inside diameter of orifice opening 9 changed to 9a.
The bottom flot>r 10 of vessel 1 cont~ins verticQlly disposed outer coaxinl nozzle 11, which communicates with the inside of vessel I through.
opening 10a in the floor 10 of vessel 1.
The centering means 7 is connected to the inner wall surface of outer coa~nfll nozæle 11 and serves to center the inner eoax~al nozzle 5b in outer coa~aal nozzle 11.
The lower portion of outer no2zle coa~dal 11 can have removealbly connected thereto a c~libr~ted nozzle 12 such th~t o~ter coaxial nozzle 11 may have the inside diameter of oriffce opening 13 change~ to ~3a~

The blowing gas 6 is fed to vessel 1 through hollow tube 5. a positive pressure can be applied to dispersed particle composition 2 by feeding a pressurizing gas 14 through conduit 15 into vessel 1 in the area 16 above dispersed particle composition 2. The outer coaxial nozzle 11 c~n be îormed by a downw{lrd extension of the bottom 10 of vessel 1 or can be formed sep~rately, as shown in Figure 3A ~ and suitably connected to the bottom of vessel 1.
The blowing nozzle lOb consists of an inner nozzle 5b having an orifice 9 or 9~9 for a blowing gas, and an outer nozzle 11 having an orifice 13 or 13a for the dispersed particle composition. The inner nozzle Sb is disposed and centered within and coaxial to outer nozzle 11 to form annular space 17 between nozzles 5~ and 11, which annular space provides a nOw p~th for dispersed particle composition 2.
The orifice 9 or 9a can terminate a short distance above the plan of orifice 13 or 13a, respectîvely of outer nozzle 11. The cross sectîon OI
annular space 17 of coaxiRl nozzle lOb îs sufficiently large such that the particles irl dîspersed partîcle composition 2 flow freely through the annul~r space 17 wîthout agglomeratîng or piugging.
The dîspersed par~îcle composition 2, at about atmospheric pressure or at an eleva~ed pressure applied by introducing gas 14 to area 16 above dîspersed particle composition 2 în vessel 1, ~ows downwardly through annular sp~ce 17 Qnd fills the area betweera orifîce 9 and 13, or 9a and 13a. The surface tens~on forces in the dispersed partic~e cos~posîtion foim ~ thîn liquid film ~8 across orifice 9 and 13 or 9a and 13a.
A blowing gas 6 at ~bout th~ temperature of the disperse~l particle composîtion 2 ~nd at a pressure slightly above the dispersed particle composition pressure at the blowin~ nozzle, îs fed th~ou~h hollow tulbe 5 and inner e~aaQal nozzle 5b and brought into cont~ct with the inner ~Z9~06 surface of the ilm 18 of dispersed particle composition 2. The blowing gas 6 exerts a positive pressure on the disp~rsed particle composition film to blow and distend the film outwardly to form an elongated cylinder shaped liquid film 19 of dispersed particle composition filled with the blowing gas 6.
The elongated cylinder initially is closed at its outer end and is connected at its inner end to outer nozzle 11 or 12, ~t the peripheral edge of orifice 13 or 13a.
The continued feeding of dispersed particle composition 2 and blowing gas 6 to the coaxial nozzle lOb forms alternatively fillamehts 20, 22 and 24 and microspheres 21 and 23, respectively.
A balancing pressure of a gas, i.e., a slightly lower pressure, is provided in the area of the blowing nozzle lOb into which the elongated cylinder shaped 19 dispersed particle composition liquid f~m is blown.
The illustrated coax~l nozzle c~n be used to produce hollow microspheres having diameters up to three to ~lve times the size of the inside di~meter of orifice 13 or 13a.
The tapered nozzle ~pparatus illustrated in Figures 1, 2, 3A and 4 allows the use of larger inner diameters of outer nozzle ll and larger inner diameters of inner nozzle Sa, both of which reduce the possibility of plugg~ng of the coaxial nozzle lOb wherl in use. The use of a larger inner diameter of outer nozzle 11 is of particular advantage when the dispersed particle composition ccm~ains rela~iYely large dispersed solid particles and/or when the dispersed particle composition has a rel~tiYely high or high viscosity. ~
Eigure 3A illustrRtes an embodiment of the invention in whlch outer coaxial no2zle 11 is removeably connected to the floor lO of vessel 1 such that orifice 13 m~y be in the form of ~ circular die and dies of various diameters may be ~nterchangcd and used. The inner hollow tube S, the ~ Z~06 lower portion o which forms inner coa~a~l nozzle 5a is moveable vertically and is remov~ble and hollow tubes 5 having different inside diameters of orifice 9 and different outside diameters may be used. The inner coaxial noz~le 5a, as before is centered.~y centering means 7.
The Figure 3A embodiment also prs)vides a means b~y which the cross section area of annual space 17 mEly be increased or decreased independently of the size of orifice 13 in outer nozzle 11. In Figure 3A
the dispersed p~rticle composition 2 is fed through an:nular space 17 ~nd blown by blowing gas 6 to form elongated cylinder 19, Çorming microsphere 21 and microsphere 23, respectively.
The ~igure 3A embodiment provides an apparatus in which the plane of the oFifice 9 of inner nozzle Su can be adjusted to be above, at the same level or below the plane of the orifice 13 of outer nozzle 11. By the selection of a desired outer diameter of inner nozzle Sa and an inner di~meter of ori~lce 13 the gap , i. e ., the distance between the outer diameter of the nozzle Sa and the inner dif~meter of the inner nozz~e 11, through which the dispersed particle composition 2 flows can be preselected. The gap in this case c~n ~e used to determine the forming microsphere , i . e ., the elongated cylinder 19 , film thickness ~nd tlhe microsphere wall thickness.
Figure 3B illustr~tes an embodiment of the apparatus of the invention in which the plsne of the orifice 9 of inner ~iozzle Sa can be adjusted to b~ sulbstanti~lly ~bove the plane of the orifice 13 of outer nozzle 11. The disp~rsed parti~le composition 2 is ~s before fed and moves downwardly through annul~r space 1~.
By p~rti~lly restrict~ng the size of orifice 13, controlling the vnscosity of dispersed particle co~position 2 and by maintaining u positi~re pressure on the dispersed pllrticle composition 2 and maintain~ng a slightly higher positive pressure on blowing gas 6 ~mal1 evenly sp~ced ~L2~2~L0~

apart gas ~lled bubbles 19a can be formed in the continuous liquid phase of dispersed particle composition 2 in the outer coaxial nozzle 11.
The bubbles 19a as they leave ori~ice 13 are carried downw~rdly by the downwardly moving dispersed p~rticle composition 2. BecRuse the gas bubbles lga are un~er positive pressure while withirl outer coaxial nozzle 11, the bubbles at l9b and 19c expand as they leave orifice 13 until the internal gas pressure in the bubbles reach equilibrium with the ambient atmosphere pressure as shown at microspheres 21 and 23. The expanding bubbles l9b and 19c are connected by filament 2D and expanding bubble l9c is connected to hollow microsphere 21 by filament 22, and microspheres 21 and 23 are connected by filament 2~.
Figure 4 of the drawings illustrates another embodiment of the invention in which a transverse jet 31 is used to direct an inert entr~ining fluid 32 which is at about the same temperature as the dispersed particle composi~ion 2. The entraining fluid 32 is ed through transverse jet 31 and directed at the coaxial blowing nozzle 10b. The transverse jet 31 is aligned to direct the flow of entraining fluid 32 over and around the blowing nozzle IQb in the microsphere forming region at and behind orifice 13a. The entraining fluid 32 as it passes over and around blowing nozzle lOb fluid dyn~mically induces a pulsating or fluctuating pressure field in the entraining fluid 32 a~ the opposite or lee side of blowing zzle lOb in its wake or shadow. The f~uctuating pressure ~leld induces regul~r periodic later~l oscillations of the cylinder and connecting filaments similar to those of a ~lag flapping in a breeze.
The entra~ng f~uid 32 es~velops and acts on the elongated cylinder 19 during its formation in ~ch a manner as to cause the cylinder 19 to flap, ~old, pinch a~sd close off at its imler end at point 26 proximal to the oriflce 13a of outer no~zle 11. The continued mo~ement of the entra~ning flu~d 32 over the elongated cylinder 1~ produces fluid drag ~ ~2~0~

forces on the cylinder 19 and detaches it Irom the orifice 13a of the outer nozzle 12 to allow the cylinder to be entrained and transported away from outer noz~le 12. The surface tension forces of the dispersed particle composition 2 act on the entr~ined falling el~ngated cylinder 19 and cause the cylinder $o seek a minimum surface area and to as the spheres move away frorn outer coaxial nozzle 12 to become more and more spherieally shaped hollow dispersed particle composition microspheres ~1 and 23. The lateral fluctuations of the connecting f~laments induced by transverse iet entraining fluid act on the ~llaments to cause the filaments to break up.
The microspheres 21 and 23 as they are formed rapidly harden to form hollow green microspheres. The filaments 20 and 22 ~Iso rapidly harden and due to the induced QuctuRting pressure field can be broken aw~y from the microspheres 21 and 23 as illustrated in Eigure 4 and Figure 7.
ln the Fi~ures 1 to ~ embodiments of the invention heating means (not shown) for removing a portion of the continuous phase or eooling means ~not shown~ where a thermoset~ing binder phase is used can be disposed below the coaxial blowing nozzle IQb to rapidly heat, remove continuous lic~uid phase and harden or to eool nnd harden the hollow rnicrospheres. The hollow green microspheres c~n then be heated and fired at elevated temper~tures to remove the continuous liquid phase and added binder, ~ilm stabilizing agent and dispersing agent and sinter th~
dispereed solid particles at the dispersed particles points of contact to form high strength, uniform diameter hollow microspheres of uniform wall thickness and uniform voicl content ~nd uniform ~toid distribution in the w~lls of the microsphs3res.

~9~ 6 The dispersed sintered particles de~me interconnecting voids in the hollow microsphere w~lls which are continuous and extend from the outer wall.surface to the inner wall surface of the hollow microsphere.
Additional cooling time or heating time, if necessary or desirable, can be provided by using ~ shot type tower, fluidized bed, an air cushion, a cushion of finely divided fluidized particles, liquid carrier or belt earrier system or con~binations thereof for the hollow green microspheres to further harden the n)icrospheres to make them easier to handle.
In the Figures 2 to 4 of the drawings the hollow microspheres a;re connected to each other by thin filaments. As can be seen in the drawings, as the microspheres progress uway from coaxial nozzle lOb surface tension forces act on the forming hollow microspheres to effect the. gradual change of the elongated shaped forming mierosphere into the generally spherical shape microsphere 21 and more spherically shaped micrs7sphere 23.
The same surface tension forces also o~use a gradual reduction in the di~meter of the connecting filaments 2û, 22 and 24, as the distance between the microspheres and the blowing nozzle 10b ir~CreQses. l`he hollow n)icrospheres 21 nnd 23 are connected by thin filaments 20 and 22 s~hich, as they progresæ away from the blot~nng nozzle 10b, become of substantially equal length ~d are ~OntislUOUS with the microsE2heres.
In the Ngures 2, 3 and 3A embodiments.the filaments are or can be broken away from the microspheres by use of external fluid jets or at such time as the microspheres are collected , e . g ., on a fluidized ~ed or solid support.
Figure 5A of the dra~vings is an enlarged cross sect}on of a hollow porous microsphere 41 made in accordance with the present invention.

~Z~2~6 The microsphere illustrated is shown after ~iring ut elevated temperature and shows dispersed particles 42 ~d the intercc~nnecting voids 46.
The Figure 5B of the drawings is an enlarged cross section of a hollow porous microspheres 41 made in accordance wit11 an embodiment of the invention showing dispersed particles 42 and interconnecting voids 46 and large uniform macro size pores 44 of a predet,ermined si~e. In order to obtain the desired size macro pores 44 there is added to the dispersed particle composition and distributed throughl3ut the composition a small props)rtion of combustible, vaporizable or meltable macro particles. The combustible, vaporizable or meltable particles are selected so that they are burned, vaporize or melt at temperatures below the melting temperatures of the dispersed solid particles, but at temperatures above the blowing temperatures. The size of the combusti~le, vaporizable or meltable macro particles is selected such that they are about ~he same size or slightly larger in size than the wall thickness of the hollow microsphere being blown. In this embodiment when the hollow green microspheres are heated and fired ~t elev~ted temper~tures to sinter the dispersed particles, the macro pores 44 are obtuned which extend completely through the walls of the hollow microspheres.
The Eqgure SC is a cross-sectis)n of the microsphere section illustr~ted in Figure SA in which the inner volume of the hollow microsphere is filled with a catalyst material, or a liquid adsorbent or absorbent mater~ 52.
The Figure SD is a cross-section of the microsphere section illustrated in Figure SB in which the inner volume of the hollow microsphere is fllled with living cell microorganisms 54 in a nutrient broth 55 and the macro pores 44 are se~ed with a semipermeable membra~e S3.

2~6 The Figures 6A, B and C show an enlarged detailed cross section 45 of a hollow porous microsphere after it has been ~ired at an elevated temperature and after the continuous liquid phase has been remo~ted.
The firing is carried out ~t elev~ted temperature, but below the me~ting temperature of the dispersed particles 42 which become sintered together at their points of eontact to form strong bonds ~nd a strong uniformly thick microsphere wall. In ~l~qng at elsvated temperatures the remailling continuous liquid phase and additive materials or agents are vapori zed and leave pores 47 at the outer surface of the microsphere wall which pores extend by interconnecting voids ~6 through the wall 45 of the microsphere to the inner wall surface pore 48 of the microsphere.
The Figure 6B shows a detailed cross section of the wull of the hollow microsphere of EYgure 6A where the microsphere is treated with a sol or st)l gel , e . g., silica sol gel , or other dispersions of colloidal p~rticles and again fired at elevated temperature to deposit in the interconnecting voids ~nd on the surfaces of the particles that form the interconnec~ing voids of the microsphere wal~ small solid p~rticles 49, e. g., silica particles . The sol or sol gel composition can be deposited in a layer in the outer portion of the microsphere wall, in the center portion, in the inner portion of the microsphere wull or throughout the microsphere wall. The solid particles from the sol or sol gel are deposited ~and adhere to ~he surfaees of the particles that form the interconnecting ~oids 46, and the solid particles link-up and form in the interconnecting voids a porous lattice work of linked up deposited sol or sol gel p~rticles.
The porous lattice work of solid particles from, e.g., the sol or sol gel deposite~ in the intercvnnecting voids and on the surPace of the purticles th~t form the voids 46 serves to reduce the vo~d content, i.e., the volume percent voids and the pore size of the voids in the ~29Z~

microsphere wall, i.e., îorm micro pores, when a controlled smaller pore size is desired. The reduction of the pore size and the void cnntent at the same eime increase the surface area of support in the pores in those embodiments in :vhich it is desired to deposit, impregnate or otherYrise place a semipermeable membr~ne in the interconnecting voids and~or on the outer por~ area of the microsphere wall. In Q pr,eferred embodiment of the invention, the membranes are impregnated or deposited within the microsphere wall to strengthen the adhesion of the membrane to the hollow microsphere wall and avoid lif~ing off of the membrane dui[ing depressuring in processes which employ pressuring and depressuring cycles.
The Eigure 6C of the drawings shows a detailed cross section of the thin wall of the hollow microsphere of Figure 6A in which the pores in the wall of the hollow microsphere are trested and impregnated and sealed with a semipermeable membrane 50. The semipermeable raembrane is impregnated, deposited or otherwise placed in the microsphere wall through surface pores 47 Rnd into voids or interconnecting channels 46, closing pores 47 and forming a discontinuous thin film 50 in the wall of the hollow microsphere.
The Figure 7A is a photograph of an embodiment of the invention illustrated in Figure 4 and generally following the procedure described in Example 1 in which hollow green n~icrospheres are made - using a transverse jet entraining fluid and shows the breakirig away of the filaments connecting the microspheres. The hollow green microspheres obtained are substantially spherical in shape and have substantially uniform di~neters and substan~ially ~:u~iform wall thickness~ The h~llow green microsphere shown in the photograph ~Figure 7A~ has an about 2000 micron diameter and an a~out 20 micron wall thlckness~

~z9~o~

The Figure 7B is a photograph of an embodiment of the in~rention illustrated in Figure 2 and generally following the procedure described in Example 2 in which filameneed hollow green microsphleres were obtained.
The hollow green microspheres shown in the photograph (F~gure 7B~
have an Rbout 4000 micron diumeter and an ~bout 40 rnicron wall thickness. The diameter and wsll thickness are measured from a section taken through the center of the microsphere and perpendieular to a line dr~wn through the microsphere connecting the points at whieh the filaments are att~ched to the microsphere.
The Figure 7C is a photograph of another embodiment of the invention illustrated in Figure 2 in which non-filamented hollow green microspheres were obtained. The hollow green microspheres shown in the photograph (Figure 7C) has an about 3000 micron diEImeter and arl about 40 micron wall thicknes~. The diameter and w~ll thickness ~qre measured from ~ section ~aleen through the center of the microsphere and perpendicular to a line drawn through the microsphere connecting the points at which the filaments are attRched to the microsphere.

APPAR TUS
Referring to Figure 1 of the drawings, ~he vessel 1 is constructed to be heated or cooled, by means not shown, and is provided with stirring me~ns, not shown, which stirring n~eans mairltains the particles in the dispersed particle composition 2 evenly dispersed throu~hout the composition 2. The coaxial blowing nozzle 10b consïsts of an inner nozzle 5b and ~n outer nozzle 11. The inner nozzle 5b and outer noz2le 11 form annular space 17. The dis~ance between the inner w~ll of nozzle 11 and the outer wall of nozzle 5b can be 0.050 to O.û04 (1270 to 102), preferably 0.030 to O.OU5 (762 to 127) and more preferably 0.015 to 0.008 inch (381 to 203 microns). The distance betw~en the inner wall of nozzle 11 v.nd the outer wall of no~:~.le 51b is ~elect&d ~uch that it is l~rge enough to pre~ent plugging of the nozzle and to prevent any signi~icant compaction of the dispersed solid p~rticles, such that the viscosity of the dispersed p~rticle composition is not significantly changed in passing through coa~Qal nozzle lOa.
The inside diameter of orifice 9 of the inner blowing nozzle 5b can be 0.32 to 0.010 (8130 to 254), preferable 0.20 to 0.015 (5080 to 381) and more preferably 0 .100 to 0 . 020 inch ( 2540 to 508 microns) . The inside diameter of orifice 13 of outer noz~le 11 can be 0.420 to 0.020 (10668 to 508), preferably 0.260 to 0,û25 ~66Q4 to 635~ and ms~re preferably 0.130 to 0.030 inch (3302 to 762 microns).
The dispersed particle composition is extruded through a gap formed between the outer edge of orifice 9 of inner nozzle 5b and the inner surface of the inner wall of outer nozzle 11, or the inner edge of o~fice 13 of outer nozzle 11 (Figure 4) whichever is smallest. The gap, i . e ., smallest annular area , through which the dispersed partiele composition 2 is extruded c~n be 0.050 to 0.004 (1270 to 102~, preferably O.D30 to 0.005 (~62 to 127) and more preferably 0.015 to 0.008 inch (381 to 2û3 microns~. The minimum size of the gap is determined to some extent by the size of the dispersed solid particles, and is set large enough to pre~vent plugging of the nozzle. The size of the gap is set such that the desired wsll thic}~ness of the mierospheres being blown and the desired diameter of the microspheres being blown is obtained.
~ n Figures 1, 2, 3A and 4 the orifice 9 of inner noz~le 5b c~
terminate at about the plane or a short distance above the plane of orifice 13 of outer nozzle 11. The orifice 9 can be spaced above the plane of ori~lce 13 at a distance of 0.001 to O.la5 1~25.4 to 3175~, preferably 0.002 to 0.050 (Sl to 1270) and. more preferably 0.003 to 0.025 inch (76 to 635 microns).

10~

~ n the Fggure 3B embodiment the o~ice 9 of inn2r nozzle 5b can be spaced a distance of 0.050 to 0.400 inch (1270 to 10160 microns) above the plane of orifice 13 of outer noz~le 11.
In the Figures 2, 3A and 3B embodiments relatively lower viscosities and relatively higher blowing gas feed rates tend to produce non-filamented microspheres, see Figure 7, and relatively higher viscosities and relatively lower blowing gas feed rates tend to produce filamented microspheres.
The outside di~meter of coaxi~l nozzle lOa is not important, exc,ept in the Figure 4 embodiment which utilizes a transverse jet. in the ~igure 4 embocUment the outside diameter of the coaxial nozzle lOa can be 0.520 to 0.030 (132û8 to 762), prefernbly 0.360 to 0.035 (9144 to 889) lmd more preferably 0.140 to 0.040 inch (3556 to 1016 microns~. The transverse jet Figure 4 embodiment has distinct process advant~ges over the use of a simp~e coaxial blowing nozzle. The transverse jet provides a controlled means ~or individually sealing off each microsphere ~t the nozzle orifice when the microsphere formation is complete. The transverse jet also provides a eontrolled me~ns for rapidly removing and transporting the formed microsphere away from the nozzle orifice which allows reduction of the mass of the connect;ng filaments and subst~ntial removal or prevention of thickened wall portions at the pOilles of connection of the f;l~ments. The transverse jet also provides controlled means, depending on the viscosity of the d;spersed p~Lrticle composition, e. g., low viscosities, and the linear velocity of the transverse jet entraining fluid in the ares of microsphere form~tion, e. g., high line~r velocity, for the elimination of the connecting filaments, i. e ., the ~ll~nents ~re rapidly thinned ~nd bro~en and the remaining portions of the filaments by surface tension forces are c~used to flow back into the formed microsphere and be evenly distributed in the wall of` the mic~ospheres.

2~0~

Further 9 where the other operating conditions rem~ the same ~
increasing the transverse jet velocity provides a reduction in microsphere ~iameter and decreasing the transverse jet velocity provides an increase in microsphere ~iameter.
The coaxial nozzle 10b, i.e., inner nozzle 5b and outer nozzle 11, can be made from stainless steel, plstinum ~lloys, glass or fused alumina. Stainless steel, however, is a preferrecl material.
In the Figure 4 embodiment, the transverse jet 31 is aligned to direct the flow of entraining fluid 32 over and ~round outer nozzle 11 in the microsphere forming region of orifiee 13a on the lee side of outer nozzle 11 (coaxial nozzle 10b). The center axis of transverse jet 31 is aligned at an angle of 15 to 85, preferably 25 to 75 and more preferably 35 to 55 relative to the center axis of the coaxiDl blowing nozzle 10~.
In Figures 1 to 4, ~he inner diameter of ;)ri~lce 9 (9a) can be 0.10 to 1. 5 times, preferably 0 . 20 to 1.1 times and more preferably 0 . 25 to û.80 times the inner diameter of o~ifllce 13 (13a).
In Figures 1, 2, 3A, 33 and 4 the proper g~p between the outer edge of orifice 9 and the inner edge of ori~lce 13 can best be determined for a p~r~icular dispersed particle composition by extending downward the inner nozzle 5b a suf~lcient distance ~nd/or with sufficien~- pressure to completely block-off the flow of dispersed particle composition, and to then while feeding blowing gas through inner nozzle 5b, Yery slowly raise the inner nozzle Sb uneil a stable system is obtained, i.e., -unt~l the hollow microspheres are being formed.

o~

PROCESS CONDITIONS
__ ~
The dispersed particle compositions of the present invention can be blown into hollow microspheres at temperatures of about 10C to 300C, pre~erably 18C to 200C and more prefersbly 18C to 100C.
For example, the dispersed particle compositions of the present invention can be blown into microspheres at about ambient temperatures, e.g., 18 to 28C. In order to assist in drying, i.eO, parti~l removal o continuous liquid phase from the microspheres, the composition can, prior to blowing the microspheres, be heated to temperatures of 30 to 150C and preferably 50 to 125C . At temperatures above 100C, e. g., when the continuous liquid phase is water, the vessel 1 and the area into which the microspheres are blown can be pressurized.
To assist in hardening the microspheres, thermoplastic binders may be used. When thermoplastic binders are used the dispersed particle compositions can, prior to blow;ng the microspheres, be heated to temperatures 30 to 300C, preferably 5û to 200C, and more preferably 75 to 150C.
The dispersed particle compositions are maintained in a liquid, fluid form at the desired blowing temperature during the blowing operation.
The dispersed particle compositions at the blowing temperature are ~luid and flow easily. The dispersed particle com~osition just prior to the blowing oper~ion can have a viscosity of 10 to 600 polses, preferably 20 to 350 and more preferably 3n to 200 poises.
Where the proeess is used to make non-~llamented microspheres, e. g., using the transverse jet embodiment, the dispersed particle composition just prior ~o the blowing operation can have ~ viscosity of 10 to 200 poises, preIerably 20 to 10û poises, and more preferably 25 to 75 poises.

~Z92~

Where the process is used to make ~llamented microspheres 9 the dispersed particle composition just prior to the blowing operation can have a viscos;ty of 50 to 600 poises, preferably 100 to 400 poises, and more preferably 150 to 300 poises.
The dispersed p~rticle compositions fed to the blowing nozzle can be at about ambient pressure or can be at slightly elevated pressures sufficient to provide an adequate amount of Idispersed particle eomposition at the coaxial blowing nozzle to blow the microspheres.
The dispersed particle composition is oontinu~usly fed to the coaxial blowing nozzle during the blowing of the microsphere to prevent premature breaking and detaching of the elongated cylinder shaped dispersed particle composition liquid film as the microsphere is being formed by the blowing gas.
The blowing gas can be at about the same temperature as the dispersed p~rticle cornposition being blown. The blvwing gas temperature can, however, Ibe at a higher temperatllre than t}~e dispersed particle composition to assist in maintaining the fluidity of the dispersed particle oomposition during the blowing operation or can be at ~ lower temperature than the dispersed particle composition, e. g., when using thermoplastic binder material, to assist in the solidification and hardening of the hollow dispersed particle composition microsphere as it is formed~ The pressure of the b~owing gas is sufficient to ~low the nucrosphere and will be slightly above the pressure of the dispersed particle composition at the orifice 13 of the outer nozzle 11. The blowing gas pressure will also depend on and be siightl~ above the ambient pressure external to the blowing nozzle.
The ~mbient pressure external to the blowing nozzle ca~ be at about ~tmospheric pressure or c~n be at slightly elevated p~essures.

Where it is desired to blow , e . g ., an aqueous disperseti par ticle ~2~2~

composition at above ambient temperatures, or a dispersed particle composition comprising a volatile solvent at above ambient temperatures, the ambient pressure can be increased above atmosE~heric pressure to prevent excessive flash evaporution of the aqueous phase or of the volatile solvent phase. The ambient pressure e~terrlal to the blowing nozzle will, in any event, be such that it substantially balances, but is slightly less than the blowing gas pressure.
In the embodiment of the invention illustrated in Figure 4 of the drawings, the transverse jet inert entraining flu;d which is directed over and around the coaxi~l blowing nozzle to assist in the formation and detaching of the hollow dispersed psrticle composition microspheres from the coaxial blowing nozzle can be at about the temperuture of the dispersed particle composition being blown. The entraining fluid can, however, be at a higher temperature than the dispersed particle composition to assist in m~intsining the fluidity of the hollow dispersed particle composition microsphere where a thermoplastic binder is use~ or to assist in drying, e.g., partial removal of the continuous liquid phase during the blowing operation. The entraining fluid can alternaffvely be at a lower temperature than the dispersed particle composition to assist in the stabilization of the ~orming ~llm and the solidification and hardening of the hollow dispersed particle composition microsphere as it is ~ormed where the binder is a thermoplastic material.
The transverse jet entraining fluid which is directed oYer and around the coaxial blowing noz~le to assist in the formation and detaching of the hollow dispersed particle composition microsphere from the co~cial blowing nozzle can have a linear velocity in the region of microsphere formation of 1 to 1~û f~/sec (0.3 to 3.0 m/sec), preferably 5 to BO ftlsec (1.5 to 24 m/sec~ and more preferably 10 to ~0 fttsec (3.0 to 18 m/sec).

~;~9;~ 6 --3~--~ Yhere the process is used to make non-fflamented microspheres, the linear veloci~y of the ~ransverse jet entraining fluid in the region of microsphere ormation can be 30 to 120 ftlsec (12 to 37 mlsec), preferably ~0 to 100 ftlsec ~12 to 30 m/sec~ ~ and more preferably S0 to 80 ft/sec (15 to 24 m/sec).
Where the process is used to make 911amented microspheres, the linear velocity of the transverse jet entraining fluid in the region of microsphere formation can be 1 to 50 ft/sec (0.3 to 15 m/sec), preferably S to 40 ft/sec (1.S ts~ 12 m/sec) and more preferably 10 to 30 ftlsec ~3.0 to 9.0 m/sec).
The distance between the filamented microspheres depends to some extent on the viscosity of the dispersed particle composiffon and the linear velocity of the transverse jet entraining fluid.
The hollow dispersed parffcle composition microspheres after formation may be contacted with heated ~mbient air to assist in removal of continuous liquid phase and drying and hardening the microspheres, e. g., when an aqueous or volatile sol-rent continuous phase is used.
The microspheres aPter they are formed to assist in removal of continuous liquid phase can be dropped throu~h a heated "shot tower"
and collected at the bottom of the tower in a liquid bath or on an air cushion.
The hollow microspheres after formation may be contacted with a quench f}uid , e. g., cooled ambient air or an immiscible liquid spray to assist in hardening the microspheres , e . g., when a thermoplastic binder is used. The hardened microspheres can be collected on an air eushion, moving belt or in a fluidized bed. The cooling or quench fluid should be at a cold enough temperature to rapidly coc)l and harden the microspheres, such ehat they are ns)t significantly deformed in subsequerlt handling.

LO~

The hollow green microspheres can optionally be treated by additional drying ~t slightly elevated temperatures to cure, further harden and further strengthen the bindler~
Where an ~queous or volatile solvent continuous liquid phase is used the further treatment can be carried out at a tempersture of 40 to 200C, for 0 . 5 to 10 minutes, preferably 60 to 140C, for 1. 0 to 8 . 0 minuteæ and more prefersbly at a temperature of 80 to 120C ~or 2 . O tv 6.0 minutes.
The hardened hollow green microspheres are then treated or fired at substantially elevated temperatures to remove the continuous liquid phase and volatile materials from the hdlow microspheres.
The firing at elevated temperat1~res removes, for ex~mple ~ the binder, surface active agent, dispersing agent and remaining continuous liquid phase from the interstices between the dispersed solid particles in the dispersed particle composition Irom which the microspheres were formed and creates the porous characteristics of the hollow microspheresO
Because continuous phase and ~or example the binder fill the interstices between the particles in the dispersed particle composition the removal of the continuous phase and binder result in obtaining interconnecting voids in the walls of the hollow microspheres which are continuous f~om the outer wall surface of the hollow microspheres through and extending to the inner wall surface of: the hol~ow microspheres.
The firing of the microspheres also causes the particles OI the dispersed par~icle composition to sinter at the points of contact of the particles with each other such that the p~rticles coalesce to ~orm a strong rigid lutticework hollclw microsphere wall.
The ~emperature at which the treatmerlt or firing at elevated temper~ture is carried out depends on the particular m~terial ccmprising the dispersed solid particles. The treatment or firing tempernture is below the melting and softening temperature of the material comprising the dispersed solid particles and below the temperature that would cause collapse of the hollow microspheres. Where glass or m,etal glass particles are used to form the dispersed particle composition, the firing temperature is below the melting temperature of the glass and below the devitri~lcatiorl tempera~ure OI the metal glass particles.
The time-temperature rel~tionship of the firing step is such that the continuous phase and binder are heated and removed while at the same time the microsphere is gainin~ strength from the dispersed particles sintering and becoming adhered together at their points of contact.
The time-temperature relationship of the firing and sintering step will also depend to some extent on the wall thickness of the microspheres and the weight percent or volume percent so}ids of the dispersed solid particles in the continuous liquid phase.
The microspheres ~re he~ed at 8 r~e such as to allow time for the permeation and remo~l of the vol~tile constituents of the continuous phase and the binder material through the pores of the walls of the microspheres without cracking or breaking the walls of the microspheres, or trapping any bubbles in the walls of the microspheres.
In the dispersed particle compositions where ceramic materials complqse the dispersed particles, the firing step can, for example, be carried out at temperatllres of 800 to 2000C, for û.5 to 180 min~tes.
In the dispersed particle compositions where glass particles comprise the dispersed particles, ~he firing step can, for example, be carried out at temperatures of 600 to 1600C, for 0.5 to 120 minutes.
In the dispersed psrticle compositions where metal particles comprise the dispersed particles, the fi~ng step can, ~or example, be carried out ~t temperatures of 150 to 1600C, i~or O.S to 120 minutes.

~2~

In the dispersed particle compositions where metal glass particles comprise the dispersed particles, the ~iring step can, f~r example, be c~rried out at temperatures of 150 to 12~0C, fvr ~.5 to 60 minutes.
In the dispersed particle COmpositiQnS where plastic particles comprise the dispersed particle composition, the firing step is carried out at temperatures below the melting and decomposition temperatures of the plastic particles. The firing step can, for example, be carried out at temperatures of 60 to 300C, for 0.5 to 60 minutes.
The dispersed particle con~position microspheres are formed at a rate of 5 to 1500, preferably 10 to 800 and more preferably 20 to 400 per second.
The above mentioned firing temperatures and firing times for the v~rious mentioned dispersed particles are given only as illustrative and higher or lower temperatures and longer or shorter fi~ing times can be used as req~ired.
An important feature of the process of the present invention is that under a specified set OI opera~ing conditions each microsphere as it is ~ormed is OI substantially the same size, shape and wall thiclcness and the same porosity, i.e., void content and void distribution as the preceding and following microspheres.

BLOWING GAS
The ho!low dispersed particle composition microspheres can be blown with a reictant gas or an iner~ gas. Suitable blowing gases are argon, xenon, carbon dioxide, oxygen, hydrogen, nitrogen and air. The blowing gases are preferably dried before use.
The blowing gas can be selected to react with the continuous liqui(l Rhase, the bin~er or dispersed psrticles~ The blowing gas can be selected to ~ssist in the hardening of the dispersed particle composit,ion, ~Z9~6 for example, by dehydrating the blowing gas to assist in dryîng. The blowing gas can be heated to assist in drying the hollow microspheres.
The blowing gas can be selected to react with the binder material to increase the r~te of hardening and strengthen~ng of the binder muterialO
The blowing gas can also act as or can contain a cat~yst to assist in the hardening and/or curing of the binder materi~.

DISPERSED PARTICL~S CO~POSITION
The dispersed particle ~llm forming compositions of the present invention can comprise dispersed particles, a binder, a film stabilizing agent, a dispersing agent and Q continuous liquid phase.
The dispersed purticles may be partiolly dissolved in the continuous liquid phase and partially solid, or can be substantially solid in the continuous liquid phase.
The continuous liquid phase can be aqueous or non-aqueous and may act as a solvent for the binder material, film st~bilizing.agent and dispersing agent. Aqueous continuous liqui~s include water and non-aqueous continuous liquids include conventional organic solvents.
The disperse particle composition can contain constituents :vhich naturally form a stable thin film and stable thin film wall hollow microsphere. However, if sueh is not the case a fillm stabilizing agent is added. The conventional foam stabilizîng agents can be used as film stabilizing agents.
The dispersed particle composition may naturolly form a stable dispersions of particies. Whether or not this occurs depends to some extent on the dispersed particle size and ~he af~mity of the dispersed particles for the continuous liq~id phase and the presence of residual charges on the particles' surfaces. Usually a dispersing agent is added, ~Z~2~)6 particularly where the particles are rel~tively large, e. g., above 0. 10 micron .
The dispersed particles csn be ceramic particles" gl~ss particles, metal particles, metal glass p~rticles and plastic particles. The dispersed particle composition can also have added thereto combustible, vaporizable or meltable macro particles. The addition of ~he macro particles allows creating in the microsphere wall, uniform size and uniformly distributed macro pores of a predetermined and preselected sizeO The macro particles ure subsequeJItly removed to obtain controlled size macro pores in the walls of the hollow microspheres.
Grain growth inhibitors, such as MgO can optionally be added to the dispersed purticle composition where desired to control the growth of the grain size of the dispersed particles during the firing and sintering step.
Plasticizers, such as those described in the Mistler U . S . Patent 3, 652, 378, can optionally be added, for example to the binder material, to improve the plasticity of the dispersed particle composition and the flex~bility and h~ndling properties of the hollow green microspheres.

DISPERSED PARTICL S
The idispersed particles can be selected from a wide variety of materisls and can include ceramic mateFials (inclu~ing graphite and metal oxides~, glasses, metals, met~l glasses and plastics, and mixtures thereof .
The dispersed particles can be 0 . 005 to 60 microns in size, preferably, O . 05 to 20 and more preferably 0 .1 to 10 microns in size .
Gener~lly a relatively narrow particle size distri~ution of particles are used. The sm~ller particles, e.g., û.005 to 0.1 micron range size are referred to as colloidlal size particles and particles in this size ~ar~ge are Q~

--3~--available in the form of sols or sol gels or sol or sol gel precursor m~terials, or colloidol porrders. Dispersed particle compositions ma-1e from sol or sol gel materials, depending on the affinity of the colloidal size p~rticle for the continuous liquid phase an~ the particles having a charged surface can form a stabte dispersion without an added dispersing agent. ~urther9 where the sol or sol gel materials are used for the dispersed particle composition on îorming the hollow microsphere and remov01 of a portion of the continuo-ls liquid phase, the particles can link up into a rigid or relatively rigid latticework, without the addition of separate binder material, to forn~ a hollow green microsphere, e. g., a gel. The gel structure in this instance acts as the binder material. However, under usual conditions and for ease of handling the hollow green microspheres a binder material is added to the dispersed particle composition.
Sol gel materials c~n be used to make hollow microspheres by reversibly converting the gel before the blowing step to a sol by applying vibration, stir~ g or subjecting the gel to ~ high sheer force, for example, by causing it to flow under pressure through the coaxial nozzle. On issuing ~rom the orifice of the coaxial nozzle the sol forms the hollow microsphere and subsequerltly due to the absence of the applied v~bration, stirring or sheer ~orces rapidly reverts to the gel to form a hollow green microsphere.
The colloidal size particles when used as the dispersed particles can be purchased as sol dispersions or gels or as colloidal pow~ers or can by convenSion~l me!ans be formed in situ JUSt before or just ~fter blowing the hollow microspheres, ~or example by chemical mean~ from sol or sol gel precursor materisls.

~z~

The dispersed par~icle compositions can comprise the following in~redients an weight pereent based on total composition. The dispersed solids and macro particles are also gi-ren in rolume pe:rcealt.

TABLE I
Weight Perceng Broad Preferred More PreIerred Dispersed Solids 20 to 90 40 to 90 70 to 90 Dispersed Solids (Vol.%) (20 to 80)(30 to 703 (40 to 60 Macro Particles (Vol.96 Solids)(0.5 to 2û~~1 to 10) (2 to 6) Continuous Liquid Phase10 to 5010 to 30 10 to 2û
Binder Material 0 to 15 0.1 to 10 0.1 to 6 Eilm Stabilizing Agent0 to 2.00.05 to 1.50.1 to 1.0 Diæpersing Agent 0 to 2.0 0.05 to 1.50.1 to ~.0 The volume percent solids in the dispersed particle composition is an important parlmeter of the composition. Where uniform size spherical particles sre ideally packed the maximum theoretical solids content is 74%. Where substantially uniform size spherical particles are used in a "random" packing the maximum solids loading is about 60 volume percent.
In carrying out the process of the present invention using generalb regular shaped particles and reasonably narrow particle size distribution, for example, in the seventy to eighty weight percent fraction of the partic~es, the largest particle is about 5 to 10 times larger than the smallest particle an the seventy to eighty percent fraction. Due to the marlner in which the particles are obtained th~re are usually present a sm~ll percentage, e. g., twenty to thirty weight percent, of very small particles.
When the dispersed particles are smaller than about 0. 005 micron the p~rticles begin to assume the properties of a trl~e solution. When the particles are larger than about 0.1 micron there is a strong tendency for the particles tv separate out o the continuous liqu~d pha3e.

The addition of a dispersing agent andlor continuous stirring or agitation of the dispersed particle composition will fnaint~in the particles uniformly dispersed in the dispersed p~rticle composition.
When colloid~l si~e particles comprise the disper sed particles, the particles can be formed in situ either before or after the microsphere blowing step.
A readily available source of colloidaI size particles are the eommercial~y available sol gel materi~ls, colloid~l powders, the bQll clays and the bentonite clRys.
Further, there ~re now avn~lable in concentrations of 10 to 50 weight percent solids, silica sols and metal oxide sols from the Nalco Company located in Oakbrook, Illinois.
Where relatively narrow particle size distribution of p~rticles are used, though strong hollow microspheres and hollow porous microspheres can be obt~ined, it h~s been difficult to obtsin unif;3rm size openings or pore openings on the outer and inner microsphere wall surfaces. In accordance with a preferred embodiment of applif~ant's invention macro pore openings of predetermined uniform and precise size can be obtained. This is done by uni~ormly mix~ng with the dispersed particle composition uniform size m~cro particles which consist of combustible, vaporizable or meltable materisls that will burn or decompose and vaporize or melt at temperatures - abo~e the blowing temperatures and below the temperatures at which the hollow green microspheres are fired and sintered.
The macro particle size is selected to be about the same or slightly larger ~n size than the thickness of the wall of the microsphere in which it is to create uni~orm - ~ze m~c~ por~s. Thus in microspheres having wall ffiidmess of for exa~le 5 b4 400 microns or l0 ~ 200 micre2ns~
the ma~ro particles w~uld be a~ou~ 50 to 400 m~ns or l0 to 200 micn:~ns in size, r~spec~ly, e.g., slightly l}~rger ~an th~

12~Z~ )6 w~ll thickness. The diameter of the macro pore can of course be made larger than the thickness of the microsphere w~ll if such is desired.
The m~cro particles can be abou~ 0 . 8 to 4 . O times the thickness of the microsphere wall, pre~erably the macro particles are 1.1 to 2.0 times the thickness of the microsphere w~ll, and mcre pre!ferably the macro particles are 1.1 to 1. 5 times the thickness of the microsphere wall.
The macro particles may be added to the dispersed particle composition in an amount of about û.50 to 20%, preferably 1 to 10% and more preferably 2 to 6% of the dispersed particles plus maelo particles volume.
The macro pores can be obtained without significant weakening of the microsphere wall. Where the m~cro particles are smaller, e.g., 0.8 times the wall thickness, when fired at elevated temperatures, the vaporization of the macro particles blows through the wall.
This embodiment allows the creation in the microsphere w~ll of macro pores of a prede~ermined size such th~t materials, such as living microorganisms that are of a size of, for example, S to 100 microns, can be given an access path in~o the interior of the microsphere without injury to the living microorganisms.

CONTINUOUS LIQUID PHASE
The continuous liquid ph~se can be nqueous or non-~queous. The continuous liquid phase can act as a solvent for one or more of the active ingredientæ, for example, the binder material, the surface active -: agent and dispersing agent.
The aqueous continuous liquid phase can comprîse ~ater and/or water and water soluble solvents. The aqueous coaltinuous liquid phase composition can comprise binder materials which include acrylic polymers, acryl~ polymer emulsions, ethylene oxide polymer~ hydroxethyl cellulose ~LZ~Z~06 methyl cellulose, polyvinyl alcohol and xanthan gum. (See, for example, binders disclosed in Callahan, et. al. U.S.P. 3,588,571.) The non aqueous con~inuous liquid phase can comprise org~nic solvents such as acetone, ethyl ~lcohol, benze~e, bromochloromethane, butanol, diacetone, ethanol, isopropanol, methyl isobutyl ketone, toluene 9 trichloroethylene and xylene .
The non-aqueous continllous liquid phase can comprise binder materials which include cellulose ucetate, butyrate resin, nitro cellulose, petroleum resins, polyethylene, polyacrylate esters, polymethyl methacrylate, polyvinyl alcohol, polyvinyl butyral resins, and polyvinyl chloride. (See, for example, binder materials disclose~ in Park U.S.P.
2,966.719; Pauley, et. al. U.S.P. 3,324,212; and Kappes, et. al. U.S.P.
3,740,234.) Thermoplastic organic binder materials that can be used are polyvinyl resins, e . g., polylfinyl alcohol ~ water- or organis:
solvent-solu~le), polyvinyl chloride , copolymers of vinyl chloride and vinyl aceta~e, polyvinyl butyral, polystyrene, polyvinylidene chloride, acrylic resins such as polymethyl methacrylate, pvlyallyl, polyethylene, and polyamide (nylon) resins.
Thermosetting resin organic binder materials that can be used are those in the thermoplastic wate~ or organie solvent-soluble stage of partial polymerization, the resins being converted after or during formation of the microspheres into a more or less fully polymerized solvent-msoluble stage. Other useful resins are alkyd, polysiloxane, phenol-~orm~ldehyde, urea-formaldehyde and melamine-formaldehyde ~esins.
In addition the photopolymerizable organic polymeric binder materials that can be used are disclosed in C . G . Raffey, "Photopolymerization of Surface Coatings", Wiley, 1982.

~.~9Z~06 The selection of a particular thermoplastic, thermosetthlg or photopolymerizable binder material will depend to some extent on the solubili ty or dispersibility of the particular binder material in the aqueous or non-aqueous continuous phase that i~ to be used. ~urther, certain binder materials, e. g., methyl cellulose c~n function us a ~llm stabilizing agent.

FILM STABILIZINC AGENTS
The dispersed particle composition may contain a natural film stabilizing agent, e. g., a surface active film stabilizing agent, or where the composition exhibits insufficient microsphere wall film stability, a film stabilizing agent can be added. The conventionally used foam stabilizing agents can be used as Slm st~bilizing agents.
A sufficient amount of film stabilizing agent is added such that when the dispersed particle composition is lblown to form the microsphere a thin stable film is formed which allows the blowing and stretching of the film without bre~king and the formation and detaching of the hollow micr~sphere. The film stabilizing ag~nt allows su~ffcient time for the surface tension properties of the continuous phase of the dispersed particle composition to c~use the microspheres to seek the smallest surface area, i.e., to form a spheric~l shape.
Film stabilizing agents such as eolloid~l particles of insoluble substances and viscosity stabilizers can be added to the dispersed particle composition. These types of additives can effect the viscosity of the surface ~lm of the wall of the microsphere to stabilize the fïlm durirl~ microspher~ film w~ll formatioll. A surfaee active film stabilizing agent suitable for use in an aqueous continuous phase composition is lauramide clieth~ol~mine. Anionic sur~ce active agents such as laur~rl sulfate, sodium lauryl sul&te, and ~mmollium la~lryl sulfate can also be used. Other fflm stabilizing agents th~t casl be used are diethanolamide, dihydroxy ethyl lauramide and lauric diethanol~mide. The film stabilizing agent can in certMn compositions also function as a clispersing ~gent.

DISPERSING AGENTS
Where dispersed particles are in the cdloid~1 size rsnge of O . 005 to 0.1 microns in size and they have an ~f~mity for the continuous liquid phase or if they hAve like surface charges, they C811 naturally form a stable dispersion and ~n added dispersing agent may not be needed.
Also, when the dispersed particles are formed in situ just before or just after the microsphere blowing step an added dispersing sgent m~y not be needed. However, for ease of handling and for m~intaining the dispersed p~rticles, particularly particles abo-re 0.1 to 1. 0 microns in size, in a stable dispersion a dispersin~ agent is usually added.
When the dispersed parffcles are small~r than about O . 005 microns the particles begin to assume the properties of a true solution. When the pareicles are greater than 0.1 micron there is a natural tendency for the partic~es to separ~te out of the contLnuous phase and a dispersing agent and/or continuous stirFing of the dispersed particle composition is or are required up until just be~ore the blowing of the hollow microspheres is carried out.
A sufficient amount ~ dispersing dgent is added such that the dispersed p~lrticles form a stable dispersion or a per~od long enough to blow the microspheres and for the microspheres to form hardened hollow green microspheres.
Dispersing agents that are sult6lble for use wieh ac~ueous continuous liquid phase composition~ are the commercially available sodium a1kyl and sodium aryl sulfunic acids. Ans)ther dispersin~F agent that can be used is sold under the trade Itark DarvRn-7 which is a sodium polyelectr<)lyte, and is available from R ~ T o Vanderbilt Co., 230 P~rk Avenue , New York , New Yor3c 10017. Organic c~rboxylic acids nnd organic polyc~rboxylic ~cids , e . g., citric ~cid , can be added to maintain a desired pH , and function as dispersing agents.
Dispersing agents t~t are suitable for use with non-aqueous, eOg., or~anic solvent, continuous liquid phase sompositions are generally those used in the ceramic industry, e. g., fatty acids (glyceryl tri-oleate), Menhaden Fish Oil ( Type Z-3, sold by Jesse Young, 5O . ) and the commercially a~railable benzene sulfonic scid ~urfactants.
The dispersing agents can also in some cases, depending on the constituents of the dispersed particle composition, function as the film stabilizing a~ent.

CERAMIC MATERIALS
The ceramic m~teriul from which the dispersed particle compositions of the present invention can be made are gener~lly those that are presently kno~vn and used in the ceramic industry. Other eeramic materials, including metal oxides, that cfln be used as starting mater1als for the present invention are disclosed in Sowman U.S.P. 4,349,~56.
The selection of ~ p~rtieulRr ceramic material will depend on the desired properties of the hollow microspheres, the ease of processing and the avnilability and cost of thè ceramic material or metal oxide material. For certain uses graphite particles can be used as the dispersed particie cer~mic material.
The con-rentional1y used ceramic muterials such ns Alumina ~Al2O3), Mullite (3Al2O3-S1O2), Cordierite ~2MgO-2Al2o3-ssi~)2)~ Zircon ~Zr2 SiO2), und Zirconia (~rO23 can be used. Naturally o~urring clQy matelqals such as ltaolinite, montmorillon}te, illite und beneonite can also be used. The ~)ull cl~y materi~ls can ulso be used.
*Trade ~arlc ~2~06 Where appropriate the ceramic materials can be ground or otherwise treated to obtain a desired particle size.
A preferred mateFial is a~umina (Al2O3) sold by Alcoa Aluminum Co.
under the trade name of "A-16" and "A-17". The A--16 and A-17 trade names designate two grades of alumina differing slightly in purity and particle size.
The particle size and particle distFibution of a commercially av~ilable alumina suitable for use as dispersed particle materisls is as follows:

Size Range Fraction Within Effective Size ~microns) Size _ (microns) 0-0. 1 0, 0~ -0.3 0.28 0.20 0.30-0.6 û.43 0.45 0.6-1.0 0.15 0.80 1.0-1.5 0.05 1.25 1.5-3.0 0.03 2.0 The heating to fire nnd sinter the cerumic particles is carried out at elevated temperatures sufficient to cause the particles to sinter together at their points of contact and will depend on the properties of the particular ceramic materials treated. 5'~here materials such as graphite are ffred they are fired in a reducing atmosphere, or a non-cxidizing atmosphere and at a eemperature at which the graphite particles at the points in which they are in contact sinter together.

GLASS MATERIALS
The constituents of the glass ma terial from which the dispersed particle compositions of the present invention are m~de can be widely varied to obtain the desired physicul characteristics of the hollo~v glass microspheres. The constituents of the glass compositions can be selected to form hard hollow porous microspheres which are capable of contacting adjacent micrsspheres without significant wear or deterioration nt the points of contact. The constituents of the glass particles, depending on their intended use ~ can be synthetically produced glasses or natural2y occurring glasses. The eonstituents of the glass can be selected and blended to h~ve sufficient strength when hardened and solidîfied to support a sibstanti~l ~mount of weight.
~ laturally occurring glass materi~ls such as bassltic mineral comps>sitions ean also be used. The use OI these naturally occurring glass materials can in some cases substuntially reduce the cost of the raw materials used . The glass materials disclosed in applicant's U . S . P.
4,303,431 can be used as starting materials.
For low cost production it i5 advantageous to use waste glass, e. g., cullet or glass derived from refuse . In certain embodiments, use is made of high silica gl~ss, such as ordinary soda-lime glass. ln other embodiments, an ordinary silicate glass is used. The psrticular glass selected, however, wi~l be largely determined ~y the proposed end use of the hollow gl8ss microsphere. For ex~mple, where the glass microspheres are to be used as filler m~teri~ls, then the low cost glass, such as s~aste glass can be used.
The glass materials disclosed in the De Vos U.S.P. 4,059,423 can also be used in the present invention. Where appropriate the glass materials can be ground or otherwise reduced in size to obtain a desired particle size.
The heating to filre and sinter the g~ass particles is carried out at elevated temper~tures sufficient to cause tlle particles to sinter together at their points of contact and will depend OTI the properties of the particular glass materi~ls treated.
Mixtures of rellltively low temperature melting glass and rel~tively high temperature melting glass particles can be used to sdYant~ge. The low melting glass during sintering dissolves partially into the high melffng glass particles, thereby allowing their fusion at the contact points ~t temperatures lower than the softening temperature of the high melting glass.
METAL MATERIALS
The process of the present invention can be used to îorm hollow microspheres from dispersed metal particles such 8S iron, steel, nickel, gold, copper7 zinc, tin, tungsten, lead, aluminum and msgnesium and the like, and mixtures thereof. The metals disclosed in the Schmitt U.S.P. 3,264,073 and in Farnand U.S.P. 3,674,461 can be used as starting materials in the present invention.
Where appropriate the metals can be ground or otherwise reducecl in size to obtain a desired particle size.
The heating to fire and sinter the met~l particles is carried out at elevated temperatures sufficient to cause the particles to sinter together at their points of contact and will depend on ~he properties of the particular metals treated. Where certain metsl mate~als are used as the dispersed particles the firing and sintering step c~n be carried out in ~
redueing or non-oxidizing atmosphere.

rlETAL GLASS MATERIALS
The term metal glassSes) as used herein is intended to mean the metai ~lloy materi~ls snd compositions which on rapid cooling from a temperature above their liql~idus temperature to a temperature below their glass témperaturé can form amorphous solids.
The term liquidus temperature as used herein is de~ined as the temper~ture at which the liquid ~nd crystal phases of a metal alloy composition can exist in equilibrium, that is the temperature at which the crystalline phase can first,appear when the liquid is ~oled.

2~)6 The term glass temperature as used herein is defined as the temperature at which the con~lguratioll of the metal alloy atoms become frozen in an amorphous solid state.
Many of the known metal glass alloy compositions have liquidus temperatures within the range of 900C to 1200C and glass temperatures within ~he range of 300C to 500C depending on the constituents of the compositions .
There are a wide variety of melal glass alloy compositions Y.rhich can be used in accordance with the process o~ the present in~ention to make hollow porous metal gl~ss microspheres. The metal ~glass alloys compositions have been broadly described as (1) metal-metalloid alk~ys, (2) transition metal alloys and (3) simple metal alloys. The known metal glass alloy compositions include precious metal alloys, alkaline earth metal alloys, rare e~rth me~al alloys and actinide metal ~lloys.
~ he dispersed metal glas~ particles can be made from the metal glass alloy ma~erisls disclosed in the applicant's U.S.P. 4,415,512.
Where appropriate the metal glass materials can be grolmd or otherwise reduced in size to obtain the desired particle size.
The hardened hollow green microspheres obts~ned from the blowing step are subsequently hested to a temperature sufficiently high to ~lre and sinter the metal glass particles together. The temperature used, however, is not high enough to melt or high enough to dev~t~fy the metal glass particles and will depend on the properties o~ the metal glass material treated.
In addition low melting temperature non-metal glass particles may be added to dissolve into and thereby partially ~use the metal glass particles to pr~duce a matrix Rt ~emperatures below the glass transition temperatures.

- so -The met~l gl~ss microspheres can, ~or exarnple, be rapidly heated to temperatures to fire and sinter the particles, followed by rapid quenching in a manner which a~roids devitri~ication. The heating step, however, is carried out in a manner such that the conltinuous phase and binder are allowed to per~neate out of the w111s of the hollow green microspheres without cracking the w011s or lea~ring any bubbles trapped in the walls.

PLASTIC MATERIALS
The plastic materials that can be used are those disclosed in applicant's U.S.P. 4,303,603. Other plastic materials that can be used are nylon, latex particles and aqueous dispersions of TEFLON (PTFE).
Plastic pareicles o~ the desired particle si2e can, for example, be obtained by comminuttillg the plastic materiat or otherwise tre~ting the plastic m~teri11 to reduce its size.
The heating to ~Ire and sinter the plastic particles is carried Oue a~
temperatures below the decomposition temperatures of the plastic particles and is carried out at elevated temperatures suficient to cause the partides to sinter toge~her at their points of contact and will depend on the properties of the plastic materials treated.

MACRO PARTICLES
The macro particles are selected to be-of uniform size and generQlly sphericQlly or spheroid in shape with preferably smooth w~1 surfaces.
The particles are generally solid and made from combustible, decomposable, vaporizable or meltable mlterials. The meltable materials when lleated will melt and spread to ~he adjacent particles. The macro p~rticle material is setected such that it remains solid at the blowing and microsphere hardening temperatures and is removed at temperatures *Trade ~lar~c below the temperatures at which the firing and sintering step is carried out. Suitable materials ~or use as macro p~rticles are carbon, naphthalene, ~nthracene, camphor, polyformaldehyde resins ~ and polyetbylene, polypropylene and nylon beads or pellets. Various organic polymeric materials that meet the above criteria can also be used. In addition, relati~rely low melting temperature metals and glasses can be used as the macro particles.
The macro particles c~n comprise 11. 50 to 20 percent by volume, preferrably 1 to lG percent by volume, and more preferrably 2 to 6 percent by volume of the volume of dispersed solid particles plus macro particles.

DESCRIPTION OF THE HC)LLOW MIC~OSPHERES
The hollow green microspheres and hollow porous microspheres made in accordance with ~he present invention can be made from a wide variety of film forming dispersed particle compositions. particularly dispersed cer~mic, glass, metal, met~l glass and plastic particle compositions and mixtures thereof. The dispersed particle compositions compr~se an aqueous or non-a~ueous continuous liquid phase and have the necessary viscosities when being blown to form stable films. The hollow microsphere stable film wall after the microsphere is formed rapidly changes from liquid to solid to form hollow green microspheres.
The hdlow green microspheres can be substanti~ly spherical in shape and can be substantially uniform in diameter and wall thickness. -The hollow green microspheres as they ~re being formed and/orafter they are ~ormed can have 8 portion of the continuous liquid phase removed ~rom the disp0rsed particle composition from which the microspheres were formed. The removal of s~ontînuous liquid ph~se can act to bring the dispersed p~rticles closer together and into point to ~92~

point contact with each other. The dispersed particles can then link up with each other to form a rigid or relatively rigid lattice work of dispersed particles which particles lattice worlc with the binder (if one is used) and eontinuous l;quid phase (that remains~ comprise the hollow green microspheres.
The hollow green microspheres are free of any latent solid or liquid blowing gas materials or latent blowing gases. The walls of the hollow green micr<~spheres are free or substantial ly free of any holes, relatively thinned wall portions or sections, trapped gas bubbles, or suf~icient amounts of dissolved gases to form bubbles.
The term "latent`' as applied to latent solid or liquid blowing gas materials or latent blowing gases is a recognized term of art. The term latent in this context refers to blowing agents ~hat ~re present in or added to glass, metal and plastic particles. In the prior art processes the glass, metDl and plastic pnrticles containing the "latent blowing agent" are subsequen~ly heated to vaporize and/or expand the latent blowing agent to blow or "puffn the gl~ss, metal or plastic particles to form rnicrospheres.
In applicant's invention the hollow green microspheres, because the walls are substantially free of any holes, thinned sections, trapped gas bubbles, and/or suîficient amounts of dissolved gases to form trapped bubbles, are substantially stronger than ~he hollow green microspheres heretofore prodllced.
The hollow green and hollow pQrOUS microspheres contain R single central cavity, i.e., the single cavi~y is free of multiple w~ll or cellular structures. The walls of the hollow green and hollow porous microspheres are ~ree of bubbles, e.g., foam sections.
The hollow green and hollow porous micr~spheres can be mac!le in various diameters and wall thickness, depending upon the desired end use of the microspheres. The microspheres can have an outer diameter of 200 to 1û, 000 microns, preferably 500 to 6000 microns and more preferably 1000 to 4000 microns. The microspheres can have a wall thickness of 1. 0 to 1000 microns, pre~erably 5 . O to ~00 microns and more preferably 10 to 100 microns.
When the dispersed particles are sintered, the smaller particles can be dissolved into the larger particles. Th~ sintered particles in the hollow porous microspheres can be generally regular in shape and have a size of 0 .1 to 60 microns, preferrably 0 . 5 to 20 microns, and more preferrably 1 to 10 microns.
The porous microspheres depending on their use, for example, RS a substrate for catalyst or separation or biotech membranes, can have diameters of 1200 to 6000 microns and wall thicknesses of lû to 200 n~crons, and preferably diameters of 2000 to 4000 microns and wsll thicknesses oî 20 to 100 microns.
The hollow green microspheres can, depending on the volume percent of dispersed solids used in forming the dispsrsed particle composition can shrink a small degree during the high tempersture firing step. Shrinkage, hoYIrever, is primarily in wall thicknes~ rather th~n diameter. The shrinkage is more evident when relatively low volume percent dispersed particle compositions are used to ~rm the hollow microspheres.
The porosity, di~neter and wall thickness of the hollow porous microspheres w~ll effect the average bulk density oi~ the microspheres.
The porous ceramic, glass, metal, metal gless and plastic microspheres prepared in accordance with the invention will have an average bulk density of 1 to 150 lblft3, (0.020 to 2.4 gm/cc), preferably 2.0 to 60 Ib/ft3, ~0.030 to 0.95 gmlcc), and more preferably 4 to 20 lb/ftl, (0.060 to 0.32 gmlcc~.

Z~06 Where the microspheres ~re formed in a manner such thnt they are connected ~y continuous thin ~itaments, that is they are made in the form of filamented microspheres, the length of the connecting ~ ments can be 1 to 40 ~ usually 2 to 20 and more usually 3 to 15 times the diameter of the microspheres. The diameter, that is the thickness of the connecting filaments, can be 1/5000 to 1/10, usu~lly 112500 to 1/20 and more usu&lly 1/100 to 1/30 of the diameter of the microspheres.
~ n certain embodiments of the invention, the ratio of the diameter to the wall thickness, snd the conditions of firing and sintering the hollow microspheres can be selected such th~t the microspheres ~re flexible, i.e., can be deformed a slight degree under pressure without breaking.
The preferred embodiment of the invention, particularly with the ceramic materials, is to select the ratio of the diameter to wall thickness and the conditions of firing and sintering the hollow porous microspheres such that rigid hollow porous microspheres are obtained.
The fired hollow porous microspheres of the present invention can have ~ distinct lldv~ntage of being rigid, strong and capable of supporting a substantial amount of weight. They can thus be used to make simple inexpensive self-supporting or load bearing structural systems for carrying out gas or liquid separation or pharmaceutical and chemical processes.
Other uses of the hollow porous or non-porous microspheres are as filler materials and proppants.
The porosity or voids - content of the walls of the hollow mierospileres is dependent upon the volume percent of dispersed solids of the entire dispersed partide composition and the firing and sintelqng temperature.

~Z~6 The porosity of the walls , i. e., the void content , of the hollow fired microspheres can be 5~ to 45% p preferably 15% to 35g6 and more preferably 20% to 30% by volume OI the microsphere walll.
~ n applicetions in which a porous hollow microsphere is not needed or wanted the firing step can be carried out at suf~iciently high temperatures snd firing times to close off and seal the interconnecting void structure in the microsphere wall. This treatment step can be carried out in R manner so that it does not collapse the microsphere wsll interconnecting void structure, sueh that the microspheres retain their size, shape und low density.
The hollow microspheres produced using the transverse jet embodiment of the invention are substantially sphe~icPl and have substantially uniform diameters and wall thiclcness.
The hollow microspheres that are produced without the use of an external fluctuating pressllre ~leld, e.g., without the use of the trsnsverse jet entraining fluid, can be substantiaIly spheri¢al and can have s- bstantially uniorm di~neter~ or they can have thickened wall portions on opposite sides of the microspheres et the points at which the filaments are connected. The thickness of the thickened portions depends in part on the viscosity of the dispersed particle CQmpOsitiOn, the rate of hardening, the distance away from the coaxial blowing noz~le when they harden and the ability of the surface tensiorl properties of the dispersed particle composition to absorb and distribute in the wall of the microsphere the portions of the dispersed particle composition that form the filaments.
The preferred hollow microspheres are- the subst~ntially sphericsl microspheres. However, in some applications the hollow microspheres with the thickened wall portions c~n also be used. The thickened wDII
portion~, in the area of the points nt which the filaments are attached, 2~

can be 1. al to 2 . O times the microsphere wsll thickness; can be 1.1 to 1. 5 times the microsphere wall thickness; and can be 1. 2 to 1. 3 times the microsphere wall thic}cness. The cross section of the microsphere other than the thickened wall portion section is substantially spheric~
and of substantially uniform w~ll thickness. All the microspheres produced under a given set of operating conditions and dispersed particle composition constituents are substantially the same in sphericity, wall thickness, void content and void distribution. A specific advantage of the process of the present invention is that in the production of hollow microspheres, the preceeding and the ~ollowing microspher~s that are produced are substantially the same.
The lower viscosity dispersed particle compositions tend to produce the more spherical microspheres and the higher viscosity dispersed particle compositions tend to produce microspheres with thickened wall portions at opposite ends of the hollow microspheres.
The hollow porous microspheres produced in sccordance with the present invention, depending in part on the dispersed p~rticle size, e . ~., O .1 to 3 . O microns ~ and dispersed particle size distrqbution, volume percent solids used and firing temperatures, can contain interconnecting voids or channels between the sintered particles in which the distance between particles, can be, for example, 1 to 5 microns. In order to obtain a more controlled and more uniform pore size the hollow porous microspheres can be treated to fill or partially fill and seal the interconnecting voids in the walls of the- microspheres with a sol gel, i. e ., a dispersed particle composition of colloidal size p~rticles dispersed in a lic~uid phase. The hvllow microspheres are again fired to sinter the colloidsl size p~rticles in the interconnecting voids. The ~lloidal size particles on firing link up to form a rigif~ latticework of particles across the interconnecting voids, sinter to the surface of the particles forming ~az~32~06 the interconnecting voids and the ~iring remo~es the liquid phase from the colloidal dispersed particles.
The forming of a porous rigid latticeYvork of sintered colloidal size particles in the interconnecting voids changes the relatively large irregular pore size of the interconnecting ~roids to reiatively uniform size micro pores of the sintered colloidal size particles. This embodiment o~
the invention allows the selection of a particular material Qnd particle size to form the hollow microsphere and the selection of a different particle material ~collo~dal particle) and particle size to form the controlled small micro pores. In this manner the strength of the microspheres can be maximized (lsrge particles) and at the same time the desired size of the small micro pores can be obtained (small p~rticles).
The hollow porous microspheres can be treated with the dispersed particle compos;tion of colloidai size partides to fill the interconnecting voids in the walls to the complete thickness of the walls, to only the top portion of the s~lalls , e . g ., the top third , the mid~le portion of the walls, e . g., the middle third, or the inner portion of the walls 9 e . g., the inner third of the thickness of the wall of the microsphere.
The micro pore structure provides a surface on or in which semipermeable membranes, en~ymes. Iiquid membranes and catalysts can be plaeed or deposited.
In another application where it is desired to have maximum wall strength the heating at elevated temperatures can be carried out at temperatures high enough to melt the dispersed particles, to fuse 1 he pores closed, to fuse the in~erconnecting voids closed and to remove substasltially all of the intereonnecting void structure from the walls of the hollow microspheres. The heating at elevated temperatures is carri~d out at temperatures high enough for the ~ir or other gas in the intercorlnecting ~oids to ~issolve in the fused dispersed pareicles or to o~

~orm bubbles ~nd migrate to the surfaces of the microspheres and out of the walls of the microspheres.
Alternatively, microspheres may be treated to hsYe the interconnecting voids filled and sealed with a dispersion of colloidal size particles that have a lower melting temperature than the dispersed particles in the hollow porous microspheres and the dispersion of colloidal size particles, then heated and fused to seal the interconnecting voids.
Without intending to be limiting but r~ther to be used as a point of reference the Table II below provides exemplary relationships between the outer diameters of the microspheres, microsphere wall thickness, dispersed particle size, and ratio of the microsphere wall thickness to the outside dhmeter of the microsphere.

TAB LE I I
Broad PreferredMore Preferred Diameter (microns)200 to 10000500 to 60001000 to 4000 W~ll thickness (microns) 1.0 to 10005.0 to 400 10 to 100 Dispersed particles (microns)0.005 to 600.05 to 20 0.1 ~o 10 n~lacro particles (microns) lo~) to 10005.0 to 400 10 to 100 R~tio of wall ~hickness to outside microsphere di~neter1:4 to 1:5001:10 to 1:300 1:20 to 1:200 - .
ln certain embodiments of the invention, for example, where the hollow microspheres are used as catalyst supports or to contain catalyst, in biotech processes, in chemical separation processes ~nsl as iller materi~ls, the hollow microsp~eres can have the ~imensions shown belour in Table III.

- ~9 -TABLE III
Preferred More Pre~rred Diameter (microns~1200 l~o 6000 20ao to 4000 W~ll thick~ess (microns310 to 2IDO 20 to 1ûO
Dispersed particles (microns) 0.05 to 10 0.1 to 5 Macro particles ~microns)lû to 200 20 to 1ûO

Ratio of wall thickness to outside microsphere diameter 1:10 to 1:30~ 1:50 t<~ 1:2û0 Dispersed particles ~Vol.%) 20 to 70 40 to 60 Macro particles (Vol.% dispersed particles~ 1 to 10 2 to 6 When use as proppsnts the hollow microspheres cnn advantageously have diameters of 500 to 2000 microns and wall thickness of 50 to 800 microns and pre~errably can have diameters of 600 to lOOû microns and wall thickness of 100 to 300 microns, respectively.
~ n a preferred embodiment of the invention alumina (A1203) hQ~ring a particle size of 0 .1 to 3 . O microns is the dispersed p~rtiele . Illustrative aqueous alumina dispersed particle compositions are given below .
TABLE IV
~7ate ul Function eight Percent Alumina ~0.1 to 3.0 microns~ Dispersed Particle 70-90 (Alumin~ ~Volume %) ~40-~0 Water Continuous Phase 10-20 D~rvan-7 Dispersing Agent 0.1-1.0 Methyl Cellulose Binder 0.1-~.0 Lauramide Diethanol~mineEilm Sta~ilizing Agent 0.1-1.3 The ~ollowing cxamples illustrate the preparation of hollow clispersed particle composition microspheres in accordance with the present in~ention which microspheres have substantially uniform poroslty , i . e ., void content, and uniform void distribution.

Example 1 An a~ueo~s dispersed particle composition is prepared having the following constituents in the amounts indicated:

Weight Percent Al2O3 (0.10 to 3.0 microns) 85.3 (Volume Percent Al2O3) ~ (59.0) Kelzan(1) (Xanthane Gum) (Binder) 0.16 D~rvan-7(2) (Dis:persing Agent) 0.30 Citric Acid (Dispers~ng Agent) 0.04 Laur~mide Diethanolamine (Film Stabilizing Agent) 0.10 Water 14 . 7 ~1) Sold by Kelco Company, 20 N. Wicker Drive, S:~hicago, Illinois.
(23 Sold by R.T. Vanderbilt Co., 30 Winfield Street, Norwalk, Connecticut.

The dispersed particle compositions are prepared by weighing 11 gr~of Kelzan,* 22 grams of Darvan-7, 2~S grams of citric acid and mixing them toge~her with 1, ûO0 grams of wnter in a polyethylene jar .
There is then added to the mixture 6,000 grams of A1203. The dispersion is mixed by rolling in thQ ja.r on 8 ball mill r~ck at low speeds (circumferential speed 2û cmlsec.) ~or two to three hours. The *q~ Mark , C)6 dispersion is then allowed to sit until any entrapped air is removed. To provide the film stnbilizing agent required for microsphere film stabili3ation during microsphere formation, O.1 weight percent of l~uramide diethanolamine is added to the dispersion. The dispersion nnd the ~llm stabilizing agent are mixed b~ rolling in the jar at slow speed, to avoid air entrainment and oam formation, for approximately one hour.
The viscosity of the nqueous dispersion is measured just prior to introducing the composition to the embodiment of the invention illustrated in Figure 4 of the dral,vings and is adjusted to about 75 to 100 poises.
The viscosity is measured by a Brookffeld rotating cylinàer viscosimeter.
The apparatus used is equipped with a coaxial nozzle of 0 . 086in .
(2184 microns) ID for the outer nozzle and 0 . 060in . OD ( 1524 microns) for the inner nozzle. Initial prep~ration consists of establishing 100cc/min. of dry M2 flow through the inner nozzle, loading the app~ratus with 200ce of the dispersed particle composition and having the inner no~zle fully downwardly extended. The apparatus is closed and pressurized to S to 6 psi (~igure 1~. The microsphere blowing is initiated by slowly re~racting the inner no~zle until the composition filows at an even flow rate through the coaxial nozzle and by slowing the blowing gas flow rate to S0 to 60 ccfmin.
The transverse jet linear gas velocity ( Figure 4 ) in the area of microsphere production is ~naintained at a rate of 2 to 10 feet per second (0.6 ~o 3~.0 mlsec).
The microspheres are fi1Qmerited, i.e.-, eonnected by continuous fil~ments. As the distance of the microsphere from the coaxial nozzle increases the sphere becomes more rounded and the diameter of the connecting filament is reduced to about 1110 to 1/20 of the microsphere diameter. The microspheres are at this point ~ uniform distnnce npart of )6 --~2--approximately 4 to 10 microsphere diameters. Durirlg the blowing of the microspheres, the connecting filaments are broken away by the later~l fluctuations of the filaments induced by the flow of the transverse jet entraining nuid. The filaments break away from the microspheres at the points of conneetion to form free falling microspheres interspaced with broken away filament pieces.
The downward f~lling microspheres are p~rtially dried and hardened to form hollow green microspheres. In this example to facilitate collection OI a sample of the hollow green mierospheres some are collected on a rotating disc or moving belt placed a short distance (e . g., 3 to 12 inches ) below the outer orifice of the coa~aal nozzle . The microspheres walls, because of the short distance they are allowed to fall, are slightly flattened at the initial point of contact with the rotating disc or moving belt. In order to obtain substantially spherical microspheres additional drying time can be provided by allowin~ them to drop in a drying tower R sufficient distance, e. g., 6 to 16 feet, for ~hen~ to become sufficiently hardened such that they are not deformed on contact. The hollow green microspheres can also be collected in water, on an Qir cushion or nuidized bed ~ and can be heated and dried to further strengthen them prior to processing them to the firing step.
The hollow green microspheres are fired and sintered at a temperatur~ OI about 1550 to 1650C for about one to three hours under conditions such that the continuous liquid phase and binder are removed without cracking thé wslls of- the microspheres. The ~red microspheres are examined and are found to have substanti~lly uniIorm diameters of about 2, 000 to 4, 000 microns, and to have thin walls that are o substantially uniform thickness of about 2û to 30 microns. The sphere walls ha~re a porosity of about 25 to 30% and uni~orm void content and uniform distribution of the interconnecting voids in the walls.

The surface of the microspheres ~ppear smooth and of relatively high strellgth requiring in excess of 400 psi at point to point contact to break the fired rnicrospheres.

E~c~mple 2 The procedure of Example 1 is ~ollowed with the exception that the transverse jet of the Figure 4 embodiment is not used and the inner coaxial nozzle N~ gas flow is mahltained at about 20 to 30 cc/minute.
Hollow ~reen microspheres are formed as shown in E~igure 2 which at a distance of two to three feet below the blosqing nozzle are evenly spaced apart. The fil~mented microspheres as before are produced, but the filaments do not break away during their format.on. The filaments are, however, broken away when the microspheres are collected. As ~efore samples are collected on a rotating disc or mo~ring belt placed a short distance (e. g., 3 to 12 inches) inches below the outer ori~ice of the coaxial blowin~ nozzle.
The microspheres are collected and sepsrated from the broken away ~llsments and are ~Ired and sintered at about 1550 to 1650C for about one to three hours. . The ~Ired microspheres have a diameter of about 2500 to 4000 microns and have thin walls of about 30-40 microns. The microsphere walls have ~ porosity of about lS to 20g6 and uniform void content and void distribution.
The microspheres collscted on the rotating disc are found to have slightly thiclcened w~ll portions at 1:he pc ints of connection of the ~llaments. It is found that the drying and hardening time provided by a six to twelve foot ~11, awQy from the co~aal nozzle, allow sufficient time for the microspheres to become substantially spherical in shape and subst~ntialay uniform in ~iiameter, î.e., distribute thc thickened wall portions to the rest of the microsphere wall.

~2~0~ii The microspheres are checked or crush strength and it is found th~t strong microsphere~ are obtained.

Example 3 An aqueous dispersed particle composition is prepared having the following constituents in the amounts indicatsd:

Weight Percent A12O3 (0.1 to 3.0 microns) 84.4 ~Volume Percent A12O3) ~58~
M~thocel~ (Binder) 0.60 Darvan 7 (Dispersing Agent) 0.30 Citric Acid (Dispersing Agent) 0.04 (Film Stabilizing Agent)(2) --Water 14 . 7 (13 Methoeel (A-15LZ), methylcellulose sold by Dow Chemical Co., Midland Michigan.
(2) The Methocel also functions in this example as the film stabilizing agent .

The dispersed particle cornpositïon was prepared in accordance with the procedure oi Example 2, modified by adding 45 grams of Methocel binder ~nd 5750 grams of AlaO3 and by pressurizing the apparatus to 15 to 20 psi. The microspheres are collected on a rotating disc or moving belt placed a short distance below the cs~ l nozzle. Hollow green microspherss which ha~e slightly ~hickened wall portions at the points ~t which the filaments sre attached are recovered.

The hollow green mic~Dspheres are collected ~nd fired at a temE~erature of 1500 to 170ûC for 1 to 3 hours. The fired microspheres walls are exDmined and are found to have substantially uniform porosity 2~

of 25 to 30% and substantially uniform void content and roid distribution.
The ~ired microspheres are about 2500 to 3000 rnicrons in diameter and have an approximate 20 to 25 micron wall thiclcness.
A section of the microspheres taken at a right angle to a line drawn along the ~is of the points at whi~h the Slamellts are attached shows that the microsphere walls are OI substarltially uniform diameter and substantially uniform wall thickness. A sample of the fired microspheres are checked and strong hollow porous microspheres are obtained.

Example 4 The procedure of Example 3 is repeated, except that about ~ to 4%
by volume of the A12O3 particles ~re replaced with macro nylon particles. The macro nylon particles are smooth and are substantially spherical in shape, smooth surf~ced and about 25 microns in diameter.
DuF~g ~he mixing step the macro particles are distributed ir3 the dispersed particle composition. The dispersed particle composition is as in Ex~mple 3 blown to obtain hollow green microspheres. The green macrospheres are collected and it is noted that there is distribute~ in the thin wall of the microspheres the nylon particles, i . e ., the nylon particles show through the outer wsll surface OI the microspheres.
The hollow green microspheres ~re slowly heated to a temperature of 1500 to 1650C to ~lre and sînter the dispersed alumina p~rticles.
During the ffring step the binder ma~erial and continuous phase and the nylon macro partîcles are removed. Hollow porous microspheres about 2500 microns in ~iameter having thin walls of about 20 microns are obtQined .

The wall8 of the hollow porous microspheres have uniform void content ~nd have uniformly distribute~ voids. The walls of the ~9;~ 6 microspheres also have distributed therein macro pores which extend through the walls and are about 25 microns in size.

Exa~ S
An aqueous dispersed particle composition is prepared in accordance the procedure of Exarnple 3 with a difference that finely divided glass particles are substituted for the alumina ~A1203). The glass particles have a particle size distribution of 1 to 10 microns with the averagé
particle size being 5 microns. The constituents of the composition of the glass particles, in percentages by weight are SiO~--65 to 75~6, Na~O--11 to 14%, CaO--11 to 13%, MgO--l to 2%, A1203--1.5 to 3.596. The glass particles are added to the binder and continuous phase of the dispersed particle composition in an amount to obtain approximately 70 to 80 weight percent of glass particles in the dispersion, which is about 40 eO 55 volume percent of glass particles in the composition. The dispersion is mixed by rolling the jar on a ball mill racl; st low speed (circumferential speed 20cm/sec) for three hours. The composition is allowed to sit and deair.
The water content of the dispersion is adjusted with continued mixing to obtain a viscosity of about 75 to 150 poises. The microsphere blowing is Iz~i~iated as before by slowly retracting the inner nozzle until the composition ~ows at an eYen rate through the coaxi~ noz~le while maintaining the blowing gas flow rate at 50 to 60 cc/minute. The gas : , pressure above the composition in the apparatus is maintained at about 10 to lS psi. r~licrospheres of uni~rm diameter are continuously produced and at distances of about 2 to 3 feet from the coa~ nozæle are u~formly spaced ap~rt. These microspheres as they are blown and formed are rapidly dried by contacting them with heated ~ir at 90~C in a 2~6 tower 14 feet in height and ~bout 6 to 12 inches in diameter. The hollow green microspheres are, collected ~t the bottom of the tower on an sir cushion, transported to a fluidized bed and filrther dried at a temperature of 120 to 160C to obtain hollow green mic~rospheres that are substantially spherical and of substantially uniform diameter and high strength. The dried hollow green microsl?heres are then fired at a temperature of 600 to 800C for sufficient time to sinter the particles.
The fi~ng temperature is selected to be belc~ ~e sof t~aing te[~erat~re of the glass partioles and the glass particles sinter and co~lesoe into a hollow porous vitrious microsphere without any signiIicant change in the sphericity of the microsphere or its diameter. l)uring the firing step the binder ma~erial and continuous phase are removed leaving hollow porous glass microspheres of about 3000 to 4000 microns diameter, having thin uniform walls of about 25 to 35 microns~ The microspheres on cooling are found to be of rel~tively high strength, to have about 25 to 35% porosity and uniform void content and void distribution, and appear to have a smooth, glassy appear~nce.

Example 6 The hollow porous fired microspheres containing the 25 micron macro pores obtained in Example 4 are cleaned, sterilized and dried.
The cle~ned, gterilized - and dried microspheres are rigid and are loaded ir~to a cen~rifuge and maintained in the outer area of the centrifuge.
There i~s then added to the centrifuge living cells or other biologie~lly active materials suspended in a nutrient broth.
The c nt~rifuge is turned on and operated at a suffilciently low rpm such th~t the cells ~re substanffally unhRrmed. The living cells have an effective size of three to fifteen mis:r~ns. The centrifugsl force exerted ~2~6 on the nutrient ~roth causes the nutrient broth and cells to pass through the macro pores and to enter the central cavity of the hollow microspheres. Where iarger si~e cells are used, larger macro pores are provided.
The hollow microspheres containing the living cells are removed from the centrifuge and tre~ted with a nontoxic protective gel to impregnate ~nd seal the macro pores and smaller pores.
The proteotive gel, sealed microspheres are washed and are treated with a solution which causes a selective semipermeable membrane to be deposited on the sur~face of the protective gel.
~ he microspheres containing the encapsulated cells are self-supporting and are placed in a column and maint~ined under conditions which allow for the growth of the enclosed cell colonies and subsequently allow for the production of biological products by the living c~lls .

Example 7 The hollow porous microspheres made in Example 3 are further treated as described below to obtain hollow porous microspheres wit~
controlled micro pores.
The hollow porous microspheres obtained in Example 3 have pore openings, i.e., distances between the sintered dispersed particles that form the inters~oQnecting voids of about 1 to 3 miorons.

~ .
The microspheres are s:ollected ~n~ are contacted with a stable SO
weight pereent colloidal partiele size silica sol dispersion in water. The silica p~rticles are about 0.05 to 0.1 microns in si~e and comprise about 25 to 35 volume percent of the sol. A positive pressure is applied ~bove the liquid level of the silica sol to force the silica sol into the intercolmes:ting voids in the walls of the hollow porous microspheres to 2~0~i form a layer of 801 dispersion to a deptil of about one third of th~
thickness of the microspheres w~lls (see Figure 6B).
The microspheres are then cleaned, dried and fired at temperature of about 1000 to 1200C, i.e.9 below the melting temperature of the silica particles, for suf~icient time to sinter the silicu particles and to remove the water from the silica particles. The sintered silica particles form a rigid l~tticework of particles in the interconnecting voids in the microsphere sv~lls to about the depth the sol penetrated into the microsphere wa~l. The remov~l of the continuous liquid phase and the firing and sintering of the sol dispersion results in a slight shrinkage in the thickness of the layer of the sol dispersion in the microsphere wall.
The ~ilic~ partides at the points at which they are in contact with the alumina particles that form the surfaces of the interconnecting ~oids are partially ~issolved into or sintered to the silica particles.
The sintered silica particles comprise a strong lattice work of porous silica particles with pores of n controlled 0 .10 to 0 . 50 micron size, i.e., w~th micro pores. Particles of colloidal size; other than silica particles, for example alumina particles can be used in the manner described to form the micro pores.

Example %
a collo~dal ~table silica sol dispersion containing about 50 weight percent silica particles in water, e.g., about 25 to 35 volume percent, ~s used to make hollow porous silica microspheres. The dispersed silica partiales are about 0.0S to û.l miaron in size. There is added to the sol about 0 ~ 60 weight percent methyl cellulose binder and about û .1 weight percent lauram~de diethanolamine film stabili2ing agent. About 2û0cc of the 801 dispersion is charge~ to the appara~us of EFample 1.

~2~ )6 --~o--The hollow silica microspheres are blown generally following the procedure of Example 1.
Hollow green silic~ particle microspheres are obt~ined. The hollow green microspheres llre fire~d at a te-nperature of about 1080 to 1200C to remove the continuous phase fr~n the hollaw gre~ s:ilica particle nLicr~sp~eres and for sufficient time to sinter the particles together. Hollow porous silica particle microspheres of about 1500 to 2000 microns dismeter and 20 to 25 microns wall thickness are obtsined. The microsphere ~qalts are found to have a uniform porosity of about 3Q to 35% and uniform void content and void distribution.

Example 9 .

Hollow fused porcel~in microspheres ~re prepared from a dispersed particle composition having the following constituents in the amounts indicated:
Crams Feldsp~r (1) 1212 Ksolin ~2~ 1212 Al O (3) 606 Kelzan (Xanthan Gum~ 5.0 Darvan-7 15 . 6 Citric Acid - 2 . 5 Water . . 1000 " - = , ~1~ The Feldsp~r is sold under the trad~nar~c Felex 100 Feldspar*by the Feldspar Corporation, Spruce: Run, North Car~lina 2277~.
(2~ The Kaolin is sold under the tradeneL~c Velvacas1~by ~he aeorgia Kaolin Clsmpany~ P.O. ~ox 490, Dry Branch, Georgi~ 31021.
(3) The Al2O3 is sold under the t~c ~Alco~*A-lq by the Aluminum Company of Ame~ea, Pittsburgh, Pennsylvania.

The dispersed particle composition is ~ormulated following the procedure of Example 1, except that the Feldspar, Kaolin an Alumina are premixed prior to adding them to the liquid phase.
The microspheres are blown also ~ollowing the procedure of E;xample 1 to obtain hollow green microspheres about 2000 1:o 2500 microns in diameter and having a wall thickness of about 40 micrans.
The hollow green microspheres are fired at a temperature of 1180 to 1275C for a sufficient period of time to remove the continuous liquid phase to form interconnecting voids and then fuse the interconnecting voids closed, fuse the dispersed solid particles, have the interconnecting voids form bubbles and have the bubbles migrate to the microspheres wall surfaces and out of the microspheres walls.
On cooling it is found that hollow fused wall porcelain microspheres of uni~orm diameter of 2000 to 2500 microns and uniform wall th;ckness are obtained. The w~ls of the microspheres are examined and are found to be about 20 microns thick , i. e ., the walls have become about 50~6 thinner due to the fusi~n and removal of the interconnes~ting voids. The walls of the microspheres are found to be substantially free of interconnecting voids and trapped buhbles and the microspheres are found to be strong, Hollow green microspheres, hollow porous and hollow -fused microspheres can be made from ceramic, metal, n: etal Klass and plastic particles using the methods illustrated in the foregoing examples. The particular binder materials, film stabilizing agents and dispersing agents can be varied depending on lthe particles used, particle size, and the use of an aqueous or non-aqueous continuous phase.

-72- ~ 6 UTlLITY
The hvllow porous microspheres made in acoordance wlth the present invention have many uses, including the use as membrane substrates in the manu~acture of systems using selective semipermeable material membranes, polymeric membranes, metal membranes and immob,ilized liquicl membranes in selective gas and liquid separation processes.
The hollow porous microspheres can be made to contain macro pores or miero pores. The hollow microspheres with the macro pores can be treated to encapsulate within the microspheres living microorganisms, virus or enzymesO The hollow microspheres with the micro pores can be treated to place in the walls semipermeable, polymeric, metal or liquid materi~l membranes and can be used to carry out chemicel processes and chemical sepuration processes.
The hollow porous microspheres can suitably be treated with catalyst materials, adsorbents, or absorbents and used to carry out petroleum and chemicel processes which processes involve the use of a catalytic material, adsorbents or absorbents, either individually or in combination with selective solid or liquid membranes.
The hollow porous microspheres and microspheres that have had the pores sealed by sinterlng the pores closed, or by filling the pores with an organic or inorganic sealing snaterial can be used as proppants in gas recovery processes. as filler materials or aggregates in cement, plaster, asphalt and construction board materials.
The h<~llow microspheres can be bonded together by sintering or suitable resin adhesives vr bonded together by suitable fusable mate~ials and molded into sheets or other ~orms and used to make new light weight construction materi~ls for use in new construction, including homes, fe.ctori~s and office buildings.

~2~L0Çi --~3--The hollow microspheres may ~e adhered together with known adhesilres or binders to produce semi- or rigid cellular type materials for use in manufacturing various products or in construction. The hollow microspheres when used in manu:~acture of construction materials can ~dvantageously be used alone or in eombination with styrofoam, polyureth~ne foam, phenol-formaldehyde foam, orgnnic and inorganic binders and the like.
The process and apparatus of the present invention as mentioned above can be used to blow hollow green microspheres from suitable film forming dispersed particle compositions having sufficient viscosity at the temperature at which the microspheres ~re blown to form a stable elongated cylinder shape of the dispersed particle composition being blown and to subsequently be detached to form the spherical shaped hollow microspheres and form hardened hollow green microspheres.
In carrying out the pr~cess of the present invention, the continuous liquid phase and the dispersed ceramic, ~lass, metal, metal glass and plastic particles, ~nd mixtures thereof to be used to form the dispersed pareicle compoa~ion sre selec~ed ~nd treated and/or mixed with a binder, dispersing agent and film stabi~izing agent to adjust the viscosity and surface tension characteristics of the dispersed particle composition such that at the desired blowing temperatures the compositions ~re capable of forming hollow green microspheres of the desired diameter and wall thickness and sufficient hardness that the microspheres can be handled and collectedl without substantial breakage or sieformation.
These and o~her uses of the present illvention will become apparent to those skilled in the art from the foregoi3lg description and the appended claims.

o~

lt will be understood that various changes and modifications may be made Ul the invention, and that the scope thereof is not to be L;mited except as set forth in the following claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Hollow porous microspheres of substantially uniform diameter of 200 to 10,000 microns wherein the walls are of substantially uniform wall thickness of 1.0 to 1000 microns, the walls of said hollow microspheres comprise sintered together particles which define interconnecting voids within the walls and a single central cavity in the interior of the microspheres and inner and outer microsphere wall surfaces, said interconnecting voids are continuous and extend from the outer wall surface to the inner wall surface, said walls have substantially uniform void content and said interconnecting voids are substantially uniformly distributed in the walls of the hollow microspheres, and the walls of said hollow microspheres are free of latent solid or liquid blowing gas materials and are substantially free of relatively thinned wall portions and bubbles.

2. The hollow porous microspheres of claim 1 wherein the microspheres are of substantially uniform diameter of 500 to 6000 microns and of substantially uniform wall thickness of 5 to 400 microns.

3. The hollow porous microspheres of claim 1 wherein the microspheres are of substantially uniform diameter of 1200 to 6000 microns and of substantially uniform wall thickness of 10 to 200 microns.

4. The hollow porous microspheres of claim 1 wherein the microspheres have a diameter of 2000 to 4000 microns and have a wall thickness of 20 to 100 microns.

5. Hollow microspheres which consist of the hollow porous microspheres of claim 1, 2 or 3 wherein the interconnecting voids defined by the sintered together particles have been closed and sealed.

6. Hollow microspheres which consist of the hollow porous microspheres of claim 1, 2 or 3 wherein the sintered together particles defining the interconnecting voids have been sintered or fused to close and seal the interconnecting voids.

7. The hollow porous microspheres of claim 1, 2 or 3 wherein the microspheres are substantially spherical in shape.

8. The hollow porous microspheres of claim 1, 2 or 3 wherein the sintered particles have a particle size of 0.5 to 20 microns.

9. The hollow porous microspheres of claim 1, 2 or 3 wherein the sintered particles have a particle size of 1 to 10 microns.

10. The hollow porous microspheres of claim 1, 2 or 3 wherein the ratio of the microsphere wall thickness to the microsphere outside diameter is 1:10 to 1:300.

11. The hollow porous microspheres of claim 1, 2 or 3 wherein the void content of the walls of the microspheres comprises 5 to 45 percent by volume of the hollow microsphere wall.

12. The hollow porous microspheres of claim 1 containing distributed in the walls of said microspheres macropores which are 1.0 to 1000 microns in size and which extend through the microspheres walls.

13. The hollow porous microspheres of claim 2 containing distributed in the walls of said microspheres macropores which are 5 to 400 microns in size and which extend through the microspheres walls.

14. The hollow porous microspheres of claim 3 containing distributed in the walls of said microspheres macropores which are 10 to 200 microns in size and which extend through the microspheres walls.

15. The hollow porous microspheres of claim 4 containing distributed in the walls of said microspheres macropores which are 20 to 100 microns in size and which extend through the microspheres walls.

16. The hollow microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together inorganic particles.

17. The hollow microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together ceramic particles.

18. The hollow microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together alumina particles.

19. The hollow porous microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together the glass particles.

20. The hollow porous microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together metal particles.

21. The hollow porous microspheres of claim 1, 2 or 3 wherein the walls of said microspheres comprise sintered together plastic particles.

22. The hollow porous microspheres of claim 1, 2 or 3 having placed in the interconnecting voids in the walls of each microsphere a selective semipermeable membrane such that the interior of the hollow microsphere is closed off from the exterior of the hollow microsphere.

23. The hollow porous microspheres of claim 13, 14 or 15 having placed in the interconnecting voids and in the macropores in the walls of each microsphere a selective semipermeable membrane such that the interior of the hollow microspheres is closed off from the exterior of the hollow microspheres.

24. A method for making hollow porous microspheres of 200 to 10,000 micron diameter and of 1 to 1000 microns wall thickness from a stable dispersion of a dispersed particle film forming composition, said composition comprising dispersed particles in a continuous liquid phase, said method comprising feeding said dispersed particle composition and a blowing gas to a coaxial blowing nozzle, said coaxial blowing nozzle having an inner coaxial nozzle for said blowing gas and an outer coaxial nozzle for said dispersed particle composition and a coaxial blowing nozzle orifice, feeding said blowing gas to said inner nozzle, feeding said dispersed particle composition to said outer nozzle to blow and form, in the region of said coaxial blowing nozzle orifice, hollow dispersed particle composition microspheres having stable film walls, removing said hollow microspheres from the region of said coaxial blowing nozzle orifice, surface tension forces acting on said hollow microspheres to cause said hollow microspheres to form a spherical shape, treating said removed hollow microspheres to bring the dispersed particles into point to point contact and to harden them to obtain hollow green microspheres; and subjecting said hollow green microspheres to a sufficiently high temperature for a sufficient period of time to remove the continuous liquid phase from the hollow green microspheres and to sinter the dispersed particles at their points of contact and to form within the walls of said hollow microspheres interconnecting voids that are continuous from the outer wall surface to the inner wall surface of the hollow microspheres, and to obtain hollow porous microspheres having substantially uniform void content and substantially uniform distribution of the voids in the walls of the microspheres.

25. The method of claim 24 for making hollow microspheres 500 to 6000 microns in diameter and 5 to 400 microns wall thickness.

26. The method of claim 24 or 25 wherein an external pulsating or fluctuating pressure field having periodic oscillations is applied to the orifice region of said coaxial blowing nozzle during formation of said hollow microspheres, said fields acting to assist in formation of said microspheres and to assist in detaching the microspheres from said coaxial blowing nozzle orifice.

27. The method of claim 25 for making hollow microspheres wherein the hollow microspheres are formed at said coaxial blowing nozzle orifice, the dispersed particle composition is continuously fed to said outer coaxial nozzle while said microspheres are being formed, an entraining fluid is directed at said coaxial nozzle at an angle relative to a line drawn through the center axis of said coaxial blowing nozzle, said entraining fluid passing over and around said coaxial blowing nozzle to fluid dynamically induce a pulsating or fluctuating pressure field having periodic oscillations at the opposite or lee side of the blowing nozzle in the wake or shadow of said blowing nozzle, said entraining fluid acting on the microspheres to pinch and close-off the microspheres at a point proximate to the coaxial blowing nozzle and said entraining fluid acting to detach the microspheres from the coaxial blowing nozzle and move the microspheres away from the coaxial nozzle, surface tension forces acting on said hollow microspheres to cause said hollow microspheres to form a spherical shape, and to obtain hollow microspheres that are substantially spherical, having substantially uniform diameters, substantially uniform wall thickness and substantially uniform distribution of interconnecting voids in the walls of the microspheres.

28. The method of claim 24, 25, 26 or 27 wherein the lower portion of the outer coaxial nozzle is tapered inwardly to form with the outer edge of the inner nozzle a fine gap and the dispersed particle composition is fed under pressure through said gap to form a stable thin film of film forming dispersed particle composition across the orifice of the coaxial blowing nozzle.

29. The method of claim 24, 25, 26 or 27 for making hollow sealed pore microspheres which comprises continuing to heat said hollow porous microspheres for a sufficient period of time to close and seal said interconnecting voids to obtain hollow microspheres in which the interconnecting voids have been closed and sealed.

30. The method of claim 24, 25 or 27 wherein the dispersed particles comprise inorganic particles.

31. The method of claim 24, 25, 26 or 27 wherein the dispersed particles comprise ceramic particles.

32. The method of claim 24, 25, 26 or 27 wherein the dispersed particles comprise alumina particles.

33. The method of claim 24, 25, 26 or 27 wherein the dispersed particles comprise metal particles.

34. The method of claim 24, 25, 26 or 27 wherein the dispersed particles comprise glass particles.

35. The method of claim 24, 25, 26 or 27 wherein the dispersed particles comprise plastic particles.

36. The method of claim 24, 25, 26 or 27 wherein the dispersed particle composition comprises an aqueous continuous liquid phase.

37. The method of claim 24, 25, 26 or 27 wherein the dispersed particle composition comprises an nonaqueous continuous liquid phase.

38. The method of claim 24, 25 or 27 wherein the dispersed particle composition has a viscosity of 10 to 200 poises.

39. The method of claim 24, 25 or 27 wherein the dispersed particle composition comprises one or more of 0.1 to 10 weight percent binder, 0.05 to 1.5 weight percent film stabilizing agent and 0.05 to 1.5 weight percent dispersing agent.

40. The method of claim 24, 25 or 27 wherein binder comprises 0.1 to 10 percent by weight of the dispersed particle composition.

41. The method of claim 24, 25 or 27 wherein dispersing agent comprises 0.05 to 1.5 weight percent of the dispersed particle composition.

42. The method of claim 24, 25 or 27 wherein the dispersed particles comprise 30 to 70 volume percent of the dispersed particle composition.

43. The method of claim 24, 25 or 27 wherein the dispersed particles comprise 40 to 60 volume percent of the dispersed particle composition.

44. The method of claim 24, 25 or 27 wherein the dispersed particles have a particle size in the range of 0.10 to 10 microns.

45. The method of claim 24, 25 or 27 wherein the dispersed particle composition has a viscosity of 10 to 200 poises, the dispersed particle composition comprises one or more of 0.1 to 10 weight percent binder, 0.05 to 1.5 weight percent film stabilizing agent and 0.05 to 1.5 weight percent dispersing agent, said dispersed particles comprise 40 to 60 volume percent of the dispersed particle composition and said dispersed particles have a particle size of 0.10 to 10 microns.

46. The method of claim 24 or 27 wherein the hollow porous microspheres obtained contain macropores 1 to 1000 microns in size distributed in and extending through the walls of said microspheres.

47. The method of claim 25 or 27 wherein the hollow porous microspheres obtained contain macropores 5 to 400 microns in size distributed in and extending through the walls of said hollow porous microspheres.

48. The method of claim 24, 25 or 27 wherein the sintered hollow porous microspheres are treated with a sol dispersion comprising small solid particles dispersed in a liquid to place the sol dispersion in the interconnecting voids in the walls of the hollow microspheres, the thus treated hollow microspheres are heated at elevated temperature to have the small solid particles from the sol dispersion link up and form a rigid porous latticework of the small solid particles in the interconnecting voids and to remove the liquid in the sol dispersion from the microspheres wall voids.