CA2026559A1

CA2026559A1 - Process for making a lightweight cellular inorganic material

Info

Publication number: CA2026559A1
Application number: CA002026559A
Authority: CA
Inventors: Gary L. Messing; Takamitsu Fujiu
Original assignee: Research Corp Technologies Inc
Current assignee: Research Corp Technologies Inc
Priority date: 1989-09-29
Filing date: 1990-09-28
Publication date: 1991-03-30
Also published as: AU6522290A; WO1991004951A1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for making a cellular inorganic material is disclosed. In this process a sol is formed by dispersing inorganic particles having a size of less than 1000 .ANG. in a dispersant liquid. A liquid, immiscible in the dispersant liquid, is added to the sol. A stabilizing effective amount of surfactant is added to the sol prior to, concurrently with or subsequent to the introduction of the immiscible liquid.
The stabilized sol is converted into a gel by increasing the viscosity of the sol. The gel is next treated such that the immiscible liquid is dispersed into a plurality of droplets or vaporized into an interconnected gaseous network wherein the gel becomes cellular. The dispersant liquid and the immiscible liquid are removed from the cellular gel followed by removal of the surfactant and sintering to form the cellular inorganic material. The above process may be supplemented by the additional inclusion of an inorganic material selected from the group consisting of inorganic whiskers and inorganic fibers introduced into the dispersant liquid along with the inorganic particles.

Description

r 7454 ~. 2026~9 ~ ~, ' .
The importancc o~htwA~qht, inorganic ~a~erial~
ha~ b~n rQcognized in recent year6 ~hat with it~ ~rowlng use as an aaoustic and tn~rm~l insul~tor, a cat~ly~t upport, an el~atronic ~ub~trate ~nd the lik~ Th~e application~ derlve 10 ~xom the unlgue phy~iaal properties of l~htweigh~ inorgan~c materlal~ w~ch inalud~ low thermal conduativity, low do~ Y
and low dlelea~ric con8tant. Fur~h~rmor~ b~lk pro~tles, which accrua from it~ ~ize, ~hA~e and number of pores, a~o co~tri~ute to ~ts u-~ ~n these and othex 15 ~pplica~ion~.
Ther~ are two general c~a~ses of l~ghtwei~ht, inorganic material~. m~ ~r~t clas~ are those fab~cnt~d ~:
from fib~r~, ~h3t i~, ~haped ~as~ of fi~rs or w~i~ker5, O~
: wh~ch fibergla~ a prim~ exampl~. ~lthough thos~
20 lightweigh~ mat~rial~ h~ all th~ advantages as~oo$ate~ w~th l~ghtw~gh~ ~norganic materi~, th~ Juffer from a majo~
dl~advan~age. That i~, wben fo~m~d ~olely ~rom fiber8, the phy~a~ prop~rties of the abricated produ~t ~r~
ani~otropi~
~hb a~oon~ ola~ oS l~ghtweight i~org~nic matex~al~ :
ar~ those mat~rl~l# whloh po~e~ pO~8~ n oth~rw~e den~e inosgBnlc m~trlx. Ex~mplc8 o~ thi~ ~yp~ o ma~er~al l~clude gh~weigh~ ~ement~, fo~ed qla~, repllcat~ ~oam6 and intered hollov ~ph~r~8. ~qh~weigh~ oement~ are mad~ by 30 otlrr~ng ~ cbmpu~tion of ~ #urfa~tant and a aement~ ~he bubbles created by th~ ~t~,rr~ ng action arei ~t~lized by the ', ~ 35 ~' ' , . ' ~ . ~ '': .~; ` "

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i:;

~ 2~2~9 surfac1~ant unt~ 1 the cement har~en3 ~ Foamed glasses are 1 formed by addinS1 a decomposable coml?ound to a gla~ powd~r whi~h is heated. The compeund decc~mpo~es w$th the re~ultan~
forrQation of a gaq whil~3 the gla89 E~of~sns ~nd mal~ he ~ubb~es created by ~he ga~; in ~hQ viscou~ mo~ten gla9~ are 5 ~tabill2~d ana p~e~ervad ~y ~ooling~ R~plicatecl foams ar~
prepared by adding a 61urry o~ a powd~x lnto a polymeric foam. The thus in~iltrated ~oam iS dried ~hen hcate~ to d~c:ampo$e the polym~$ ahd sinter the ~owder.
The ligh~weigh~ inorganic mater~ Al~ of the prior 10 art, charact~rized ~y interspersed p~xes, lika lightwe~ht materials ~abricated solely from fi~rs, ~uffer fro~
impo~tant disadvanta~e~. These p~ior art m~t~ri~l~ are usually characterized by r~lati~ely large pore 8ize~ .
Gener~lly, lightweight cements, fo~me~ glas~, replicated 15 ~oams and ~int~r~d hollow sphere~ all in~lud~ pore~ ~reat~r than one millimeter in diameter. The lightweight~
po~e-oontaining mater~al~ of th~ prior art al~o are lim$t~d by the numbe~ of ~at~rial sy~tems ~hat could b~ used in ~h~ir formation . O~tes~imes, a glass ~ ~ ç~n~nt or tho like i~ not 20 des~red. E~owever, the~ te~ch$ng of the prior art doe~ not di~clo~ porou~ inorganic mat~rial~ other than porous gla~
or cement. MorQo~ror, ~h~re are a number of d~ect~ ~ecifio to ~ach cla~ of inter~persed porou~ material. Fo~ in~ance, replicated ~OZ111~5 arQ characterized ~y ~ollow ~truts ~3~a~
25 lower ~ir m~ahanlaal ~treng~h.
~ he abo~r~ r~mark~ ~ugge~t th~ general ch~rac~Qr-i~ti¢~ o a proo~ needed to ~Id~r~nce the art of lightwe~ght cellular i~organic m~teri~ or~ation. P. new proces~ for mak~ng a lightwe~gh~, ~norgar~ic material ~hould pe~nit 3 t~iloring of the of ~e mat~rial's micro~tructur~ and properties. ~or example~ de~ir~d pore ~ize, bulk d~n~ity ~tr~ngth properti~ lectr~cal proPart~e~s ana the l~ke ~hould be obtainable within n~rrow li~nit~.

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2 202~9 ,, Th~ proce~e~ of the prior art re~ulting in the ~ormation o~
porou~, lightwe~gh~ inorganic m~terial~ do not mee~ this re~uixement.

The prior art include~ A plural~ty of teach~ng~
directed ~o oRllular inorgania material~ relevant to the desired produat d~scus~ed above. That i~, t~ identifi~d prior art is dir~ct~d to proces~o whlch prod~ca lnorganic cellular mater~als who~e por~s are ~ormed from a ga~
10 generat~ng agent.
U,S. Patent 3,136,645 to De~ and U.S. ~a~e~t 3,igo,g88 to ~es~ et a~. de~ine a prooe~ wh~rein silioA, s~llcon, an aqueou~ ~odium ~ilic~t~ ~olution, ~odium fluorc~iliaate and a ~uatexna~y ammonium halide 8urface ~5 aoti~e agent are ~ntimately mixed with the re~ultant generation of a gas f~om the react~on o~ 5~1icon and ~od~um ~luoro~ilicate. A mineral ~oam i~ form~d fro~ the ~o~m~d product of thi~ reaction. -~
U.S. Pi~ent 4,112,032 to Bla~zyk et al~ desoribe~ a 20 proce~ ~or mak~ng a porous ~llioa-contaln~ng article. In ~hi~ p~oo~ a collo~dal 5ilic~ ~olution i8 reacted with an org~inio ocmpound selected f~om the group con8~ting of for~aldehyd~, paraformaldehyde, fo~miamide, glyOXd methyl formate, ~thyl fo~m~t-~, m~thy~ ac~t~th ~ ethyl ace~tatÇ
25 and mixtures thereo~ at a temper~ur~ con~i~tent w~th ~he -~
mal~tenanc~ of t~e liquid solution for a tim~ ~iu~ ient to gel th~ porou8 product of this re~ction~ ~ :
A ceramic ~oam materi~ formed in a proces~
di~closed in U.S. Patent 4,6~0,832 to ~rocbmeyer~ The ~832 .~ ` ; .~
2 ~ 9 patent involves a prooess in which an organic polymer ~oam, 1 preferably polyurethane foam, is impr~gnated with an ~q~eo~
~lurry of a thix~txopic cer~mia compo~ition, prQerably a gRlled alumina hydrate. A colloidal di~persion of the gellod alumina hydrate i-~ formed by adding ~ id to a ~lu~y o~
5 ~e alumina ln water~ The polym~ric ~oam, imp~gnnt~a with the collotdal dispersion, i8 fired ~t ~ tem~erature of a~
least 2,000F fo~ a period of time ~uffi~ien~ to Yol~lizo the orgdnic constituent~ and ~int-r the r~raotor~ material r~ulting ~n the formation of the c~ramic foamed produc~.
Se~al addit~onal r~f~r~n~e~ di~clo~o th~ ~ddition ~f organi~ ~o~m~ng agent~ to a~ramlc ~olloid~, ~lurrie~. and th~liXa. The~e ` fouming agents ge~erate gases which c~u~e ~oaming. ~n ~ddition, other foaming m~t~rial~ ~r~ added to ceramic sol~, solution-~, oolloida and the like wherein the 1~ reaction product i8 a foxm qenex~ting ga~ In ~h~ ca~e~
inorganic materi~ls ar~ reac~ed witb reactiv~ compon~nt~ of a cer~m~c solution, especially alkali ~e~al ~ilica~e~. The~
~ach~ng~ re~ult in the formation o~ iarge pore BiZ~ foamed Lnorganic ceramic matarial~. TheYe product~, although having 20 high str~ngth to weight ratios, do not po~ess ~uf~ici~nt ~trength ~o be u~eful i~ high ~trength applications.

A n~w proae~s has now b~n d~covered wn~-ch allow~
~5 tailorinq of ~h~ propertie~ of l~ghtweight ~llular ino~gani¢
material~. ~hi~ prOC~B~ p~rmit~ formation of lightw~ight aellular inorganio mater~al~ having de~lred p~yc~cal gtructure and propertie~. For ~x~mple, an $norgan~o a~llular material oh~ractariz~d by poreY w~iah are oon~dera~ly 3 ~maller than ~he cellular product~ formQd ~r this ~nown prior art proce~B for ~king cellular inorganic ~at~ials ~ can be produced. ~ such, tha proce~ o~ ~he prese~
in~ention i~ far more fl~xiblo ~n produçing desirable ~ .~. . . .
". . :, ~ ... -.~ .: .

202~9 ~norgani~ cellular materials tha~ a~ ~he proce~s~ f~r 1 making cellular inorganic produc~s produc~d ~ th~ proo~es o~ the ~ior ~rt~
In accordAnce with the ~re~ent inven~ion, a pr~c~
for maki~g a cellular inorganic m~texial i~ di~clos~d~ I~
5 th~s proce~s finely divided particl~s, having a ~ize o~ les~
~han about 1,000 An~trom~, of an inorganic ma~erial ar~
di~po~Rd in a dispersant material, a liquid having ~hQ
s~ructural fo~mula ROH, where R i8 hydrogen or lower al~yl.
An org~nic ma~erisl in th~ uid ~t~t~, ~mmiscibl~ ~n said 10 ~ol, i~ then introduced into said 801. A ~tabilizing ~f~ecti~ amount of ~ surf~atant i~ added to the ~ol p~ior to,^~concurrently with or ~ubsequ~nt to th~ introduction of the immiscible organic liquid. The v~co~ty o~ the so-tre~ted ~o} is incr~ased ~uch tha~ ~ ~el i9 fo~ed. Th~
15 g~ treated t~ diaper~e the immi~oible organic material into a plux~l~ty of droplets or vapor~zed into a~
int~r~onnected ga~eous n~twork wherein ~h~ gel become~ .
c~llular, ~he cellular gel ~s n~xt ~reated ~o r~move the di~per~nt mate~ial and th~ imm~cible orqania material. The ~ su~faotant i~ then r~moved. Fi~al~y, th~ cellular ~el i~
6in~ered to form th~ a~l~ular ino~gan~c matexial~ :
~n further Qccordanc~ w~h the p~ent in~antion, a proe~a i~ provided whiah ~nclud~ th~ ~tep~ of ~he pxoce~ :
rec~ted abov~ w~h thc ad~itiona~ ~Qp 0~ including, in 25 ~ddition to the i~organic particl~a, an inorganic material ~elected ~om th~ group con~i~ting of inorganic whis~er~ and inory~nio iber-. The inorgAnia material i~ p~ent in a ~: -con~ntr~t~ on uch that the inorgAnic material compri~a~ ~:
b~tw~en about 1% to about 50~ by volume on a dry volw~e 3 bA~{ 5 , ~ :,. ' , . .'" ` " :.',:

. -6-r 2 0 2 6 ~ 5 9 . .
1 The pr~ce~s o~ the pres~nt Lnvention ~nvolves the formation o~ a cellular inorqanic mat~x~l. In ~his p~oceB
a ~inely di~ided in~rt i~organic ma~erial ha~ng a par~icle ~ize of les~ than about 1,000 ~ ig di~posea in ~ uid.
Those skilled in the art are ~wa~e that such inorganlc oxides as ailica, alu~ina, zirco~ia, magnesia, b~ryll~s, ~itania and mixtuxes thereof ara within the cont~mplation o~ thi~
Lnorganic ~nu~. However, theoe inorganic ~xide~ are only ~llustx~tive of pr~fer~d specie~ ~thin thi~ generic ~1~SR
10 and any inorganl~ material having a particle 5iZ~ 0~ le~B
than abou~ 1000 A may ~e emplo~d. In addition, mixtur~ of the~se materials, wheth~r natural ores or ~ormulat~
compoun~, can be utilLzed in thi~ application. For ex~mple, mull~t~, a natural m~neral, a co~pound ha~ing the ~tructural 15 form~la 3A1203.2SiO2, a~ may formulat~d com~ounds such A~
f~rrite, barium tit~n~te, BaTiO3, the comp~ex oxlde, Pb(Zr,Ti)03 an~ ~he siltcon nlt~iae, 6~3~4, can be used alone, with each other or w~th o~e o~ more of the aforementioned inorganic oxide~.
The di~per~ant material into whi~h the ~incly di~ided inorganic p~rticles are digpo~d i~, ln ono preferred embodiment, a llquia having th~ a~ructural formul~ RO~, whe~e R is hydrogQn or lower alkyl. An obviouo preferr~a ~ embodi~ent o~ t~is ol~aa of liquid~ $- water. ~owever, ~ower : 25 alkanols ~u~h ~ m~thanol, ~thanol, n-p~opanol, isopropanol, : n-butano}, i~obutanol, t~rtiary bu~anol and ~he l~ke may al~o be utili~d ~a the di~per~ant liqui~.
To thio oal o~ h~aro~ol i~ ~ded a liquid, an organic material immiscabl~ in the liguid di~persant, Any ~' 3 org~nic m~ter~al in the li~uid atate immi~oible in the , ., ,.. . . ,, ... -. . ~ . . . ... ~ ~

r 2 ~3 2 ~

di~per~nt liquid, a liquid having ~h~ ~tructural formulA
~OH, wh~th~r h~ing a higher or lower boilin~ point than the liquid di~pe~ant ma~ b~ employed~
Recause immi~cibillt~ ritical, the organlc li~uid, in ~his preferred embodiment, i~ u~ually non-polar in that the dispersant liquid, a liquid having the structural fo~mula RO~ pol~r. Those s~ d in the art are a~are that polar and non-polar liquids ~re oft~ntime~ immi~cible in each other~
Among the non~pola~ o~gan~c li~uids w~thin the contemplation of th~ immi~aible material of thi~ inYention are ~aturated and unsaturated hydrocarboDs ~ub~titut~d or un~ùbstitu~ed with halog~n which ~r~ uid at ambient conditions. Of th~e, h210gen sub~tituted alk~ne6 are prefe~red~ For ~xample, fluoro-chloroalkanss, particulArly fluoro~hlorom~than~ an~ fluorochloro~than~, find utility in thi~ applioation. Thus, trichlorofluoromothane, difluoro-dichloromethane, trif l~lo~ochlorom~th~ne and other ~luoro-chloro-~ tituted ~ethane~ ~re o~entim~ used iJ~ thiff application. Other immiscible hydrocarbons th~t ~ay b~ u~ed ~O in thi~ proc~ inalud~ ~kan~s, ~uah as butan~, pentane, hexane and thd like, alken~, which includ~ penten~s ~nd h~n~s, a~d aryl halides such ~ chlo~ nz~no and chloro~oluene~ among other~.
nother pre~erred embodiment o~ tho p~8~nt 25 invention th~ di~persant and the inuniscible organic liquias : are rever~e~. That i~, th~ diaper~ant material i~ ~
:~ non-pol~x orgA~lc l$Quld ant he $mmi8ci~1~ m~t~rial ~s a polar li~uid. In this ~mbodim~nt th~ preferred ~nd more pr~f~r~od ombodiments of the polar liquid used a- the 3 di~p~rsan~ liguld in the ~mbod~mont de~rib~d above are utiliz~d a8 th~ preferred and mnre pr~f~rred embodiment~ o~
~he immi~bl~ liquid. Thus, the immi~aible liq~id i~
pref~rably ch~raatorizod b~ tho ~ructural for~ula ROH, where R is hydrogen or lower alkyl, with ~ater being part~ularl~
pref~red~ Sim~ the pre~e~red And more ~xeferred ~mbodlment~ of the di~p~r~ant li~uid correspond to th~

~, ,"~

2026~9 preferr~d ~nd more preferr~d embodiment~ of the materi~l~
1 utilized a~ the imml~cible organ~ uid in the first reci~ed preferred embodimen~. Th~refore, the dispex~an~
l$~uid is preferably a sa~uxated o~ uns~turated hydrocarbon whi¢h may be halegen su~stituted.
~o aid in the la~er gel~tion o ~he finely divided par~icl~ di~persed in the disper~ant ~iquid, oft~n r~f~red to as a sol, or a hydrosol when the di~pexsant liquid ia water, a gela~ion aiding ~gent i~ optionally added to the ~1 or hydrosol. The gQlatiOn aiding agent i~ added to the sol 10 or h~drosol for th~ ob~iou~ p~po~e o~ iner~a~ing th~ rate o~
qelation formation. Those skillod in the ar~ are aware, for ex~ple, that hydro~ols axe ~lkaline, characteri~ed by ~ pH
in exc~ of 7. Reduction of hydrosoi alkalinity to a pH
hclo~ 7, that ~B, acidiying the h~drosol, re~ults in more 15 rapid gelation. Thus, in a praf~rr~d embodim~nt, the ~ptional ~tep of int~oduc~ng a gela~ion aiding agent involve~
th~ ~dition of an ~d t~ the sol. Prefera~ly, th~ acid uti~ized i~ a mineral acid. Among th~ pref~rred min~r~l acids for use in thi~ app1ication Are hydrochloric acid, 20 sulfuric ~cid and nitric acid. Of the~e, ~ulfuric acid i~
particularly prefa~red.
In other sol~ the yelation aiding agent may b~
alkaline. In summary, th~r~or~, th~ g~l~ting aidlng agent ~s ju~t th~t, ~n ~gent ~hat a~ds in gelling th~ 601. In 25 certa~n ~ol ~yst~m~ the chemistry i~ such that hiqher ~H
enhance~ gelation. Thus, an ~lkalinating ~ent ~uch a~ ~aOH, RO~ 3 ~nd the like may b~ ~mployed in t~i~ application.
In order to form a aellular ~ateri~l it i~ r~qu~ad th~t the ~mi~cib~e liq~id be uniformly disper~ed in ~he 3 di~persant liquid. To accompli~h this a ~tabilizing effective amount o~ ~ur~ac~ant i~ add~d to the ~ol of finely dividod p~rticle~ ~n tho di~pe~s~t liquid. ~h~ ~ur~ct~nt may be add~d to the ~ol prio~ to, concur~ntly w~th or ~ubseguent ~o the introduction of the immi~ci~le ~rgani~
35 li~uid. Altern~ively, the ~urfactant may ~e ~dded ~n part.
Tha~ is, the ~ur~c~ant is partially added ~t two or all three of the-e pointg in the proceas of thi~ invention.

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~: - 202~9 Any s~rfactant which disper~e~ the immi~clblfl 1 liqu~d ~n the di~persant li~uid may be uti~ized. ~hu~, the ~urfac~ant may b~ cationic, anlonic, non-ion~c or amphoteric.
of the$~, anion~ ~nd ca~ionic ~rfactant~ h~ve be~n found ~o be especially eff~ctive. An~oni~ surf~otant~ u~e~ul in this 5 application ~nclude ~odium dodecyl sulfate (SDS) ~
polyalkoxycarbox~l~tes and th~ likQ~ ~S i~ p~ticulArly preferr~d. Among the cationic ~urfAc~ants within the con~mplat~on of ~e present invention ~r~ ~liphatic mono-, di- and polyamine~, amine oxide~, alkyl~mine al~oxylates, 10 espec~ally alkylamine ~thoxylates, qu~t~rn~ry ~mmonium ~a~t~
and the like. Fo~ exampl~, cetyltrimethylammonium ~ro~ide ~hB) ~s particul~rly prearr~a ~or Use B~ a cationie ~urfactant.
An optio~al additional at~p may be included in the ~5 proc~s~ of the present inventio~. ~n this S~Qp ~
co-~urfactant, diff~r~n~ from th~ suractant, ~s added to the ~ol or hydr~ol. A co-~urf~ctant, for ex~mpl~ employed to better emulslfy th~ pr~f~rred embodiment wh~rein ~n immisc~bl~ organic liqu~d ~ s add~d to a polar di~per~ant 20 li~uld to Aid in th~ ~tabilization of ga~ bubblas th~ m~y ~ub~ u~ntly form in '~hi~ proces~ ~ That is, the oo-~urfactant ~upplem~nt~ th~ ac~lvity of the surfactant~
~: Th~ u~e o~ a co-surfact~nt i5 p~rti¢ularly ad~lsa~le in tho~ ca~o~ where, although the ~ur~act~nt 25 ~d~q~ely dl~per~e~ th~ org~nic immi~c~l8 li~u~d ~n the dl-per~ant l~quia, ~h~ ~urfac~nt does nc~t pro~riae ~dequ~t~
bilization of the imm$scible org~nia liqui~. ~.or ~xampl~, in th~ pr~ferr~d ombod~nent where~n a halogen~ted ~lkane i~
emp~oy~d a~ ~he imm~-~aibl~ or~anic liquid it i~ known that 3~ al~anol~ aid in ~t~ disper~ion. Thi~ iB e6peci~11y the case wh~n the ~isper~ant liqu~d is water. 0~ oour~e, if an alkanol 1~ util~zed ~6 ~h~ di~pers~nt ligu~d, it i~ obviou~
that the alkano~ uged a~ the co-sur~aCtant ls not identical to th~ alka~ol employed as the d~p~r~ant liquid.

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~`''',.~ ;~'', . ' 2~2~9 In the partiaular1y pre~erred ~bod~ment wharein a fluorochlorocarbon i~ utilized a~ the imm~oible orgAnic li~uid in the disp~xs~nt liquid water, and wh~rein the ~urfactant i~ an ~nionic or cationic RurfAc~Ant, it i8 particularly desirable to u~e an alkanol as a eo-~ur~ot~nt.
5 Of the alkanols, meth~nol i~ p~rticularly pxe~erred. ~he u~
of methanol a~ ~ co-~urfactant qig~iic~ntly improYes ~h~
emul~ catlon of th~ ~luoroahlorocar~on ~n the 801. Thi~, 1n turn, increas~ the cellular ~niform~ty of th~ fi~al produo~.
i ~he optional step o~ adding a co-~urf~ctan~ to the ~ol or hydro~ol pref~ably occurs simultaneou~ly with the add~tion of the ~urfactant. ~hus, ~he ~o-~ur~ao~ is ad~ed pr~o~ to the intxoduction of, simult~n~ously w~th o~
subsequ~nt to the addition of the immi~aible organlc liqui~.
5 ~$ternatiYely, the co-surfactant may be introduced lnto the ~ol in pa~t, that i~, ~n two or ~n ~11 three point~ wh~re the ~o-surfaatant may be added.
The thu~ treated sol or hydro~ol i~ n~xt con~e~ted lnto a gel. In thi~ ~tep the visco~it~ of t~e 501 or 2~ hydro~ol ls increased to ~ 1 æt which sol b~come~ a qel.
In a pre~erre~ ~mb~diment thi~ ocaur~ by increa~ing th~
v~C08ity o:E the ~ol to ~btween a~;out 8~ ep hnd ~out 1500 cp. To Accompli~h gelation, a~ th08e ~k~ d in ~he ~rt ~re aware, the sol may b~ ag~d, that i8, the ~ol i~ owad ~5 to r~main untraa~ed ~or a period of time. ~ow~Yer, ge}ation by aglng may tak~ an unacceptably long pariod of tim~, ~hereforQ, ~o aace1era~e th~ procedure, the ~ol may be h~ated, it~ p~ chanqed or both~
Cell g~neration i~ initiatd immediately sub~eguent 3 to gelation~ ~ell generation to ~on~rt th~ thu~ for~d qel ~o a ohllular gal occur- by t~atm~nt o~ the gel. In one pxeferred ~mbodiment, thi~ treatment involve~ heating thQ gel ' ~02~59 ~o a temperature ~low the ~oiling point of the di~per~ant d. ~his ei~her results in the formation of disper~d liqui~ droplet~ or of a gaseous ne~wor~ o~ tha immi~cible organic ~n th~ dispers~nt llquid.
I~ another pre~erred embodimant, c~ nera~ion, 5 result~ng fr~m disp~r~ed liquid droplets or a vapori~d ga~eou~ network of the immi~a~ m~teria~, can be effe~uated by cha~ge in pres~ure. That i~, th~ pr~sur~ c~n be reduc~d t~ a l~v~l whioh produce~ the same re~lt a~ that provided by temperature increase.
Wheth~r c~llular fo~mation r~lt~ in an open-celled network or a clos~d-cell~d st~ucture can depend on wh~th~ the above di~cu~sed ste~ re~ults in the for~ation of liqu$d droplets or a gaseous ~etwork. Thi~, in turn, depend~
upon whe~her ~he i~mi~cible liyuid or ~he dispersant li~uid 15 has the hi~h~r vapor pressure. Tho~ ~killed ~n ~he art will appreciate that ~or~ation of a ~ultipli~i~y Df droplet~ of lmmi~oibl~ liq~id can r~sul~ in a clo~ed cellul~r product, w~tle the ~ormation of int~rconn~ot~d ga~eou~ network u~ually ~f f~ots the foxm~tion of an o~en celled product. Tho~e 20 skilled in the art will und~r~tand, of ~our~Q, that ~v~n i~
th~ immi~cible l~qu~d has a higher ~apox pre~ure than the di~per~ant liquid a su~ficiently high ooncentr~tion of di~persed l~qu~d dropl~t~ will re~u7t in int~rconnection o~
the~ droplet~ cAu~inq the formation of an intexc~nnected -25 open- cel~-ed network. Similarly, a small en~ugh conc~ntration of vaporized immi~ciblo mat~rial ~ill not prov~de enough pathWAyB to in~ure an op~n~ d ~truature.
Th~ abov~ re~ark~ sugge~t th~ preferred embo~iment of ~he pre~ent proc~ wh~r~in tha ~te~ of gelation and 3 a~llul~x *ormat~on ocaur ~ub~tantially ~multaneou~Ly. In thi8 combined st~p, the ~ol i~ eith~r heated to a t~mperature below the boiling ~mp~rat~ of the disperh~nt l~quid ~t atmosph~ric pre~ure or th~ ~emperaturo of the ~ol ~
maint~ined con~t~nt whil~ th~ p~ ure is reduced ~o a 3~ pro~ur~ abvve the vapor pres~ure of the dispor-ant liquid at ambiont tomp~r~ure. Th~ not only incxQase- the vi8c08ity '~

1~
2~2~9 ~f the ~ol, preferably to be~ween about gO ~p and ab~t 150~
l cp, and thus effects gelation, ~t, ~n addition, disper~e~ er vnpor~zes ~he immiscible organi~ u~d to form a ~losed or open celle~ g~l, respectivel~.
The s~ep o~ c~llular ormhtion i~ coin~ident with 5 the step o~ im~iscible organic liquid remov~l in the pr~ferred ~mbodL~ent wherein ths im~iscible ~i~ui~ h~ a lower vapor pressure than the di~per~ant liqu~d. That is, the vaporized Lmmi~cible org~nic material escap~A through the interconnected networ~. Pre~erably, the colncide~ ~tep o~
cellular fo~mation and immi~cible or~anic compound rQmoval occurs at a temp~rature in tho r~nge o~ ambient and about 20~, more preferably, betwRen ~mbient and ~bou~ 150~ ~nd most pr~ferably, between ambient and ~bo~t 100C.
The thu~ formed cellula~ gel ~ next tre~ted to 15 r~mo~e the disper~a~ liguid. Thi~ stap is accompli~hed, in one preferr~d ~mbodim~nt, ~t atmospheric pre~sure by ~xpo~ing the ~ellular gel containing di~per~nt to a temperat~re in the range of betw~n about 20aC and about 100C. Preferably, this etep occurs at a ~emperatur~ of between about 25C and 20 ~bou~ 75C. ~or~ p~exably, the dis~?er~ant-containing cell~llar gel i~ exposed to a temper~ure in the r~nSro of between about 35 ~: and about 50 C . This procedure occurs over a per~od of ~tw~en about 1 day and ~bout 1 ~k.
Prefer~ly, the time period ove~ whiah drying o~cur~ ~o 25 between about a days and about 3 d~s.
In anothe~ preferred embodiment, the d~per~ant-¢~nt~ining cellular g~1 ls expo~od ~o a reduced pre~sure envlronment wher~in ~he same dispersant removal re~ult i-obtained as in the above-d$~cu~sed embodiment.
3 In the preerred embod~ment wherein ~h~ V~pOr pree~ur~ of ~e ~mmisoible organic liquid i6 grea ~r t~an that o~ the di~persant li~auid the st~p ~ equent to cellular : ~ -gel fo~m~tion i~ the remo~al of th~ di6per~nt liquid. Th~

;~. . . . . ~; ~ ~

202~9 removal of the dispersant llguid i~ su~stantially identical 1 w~th the JtCp of di~persant li~id remo~ n the pr~ferred embodiment wherein the dispersant li~uid has ~ hi0her v~por pr~ssure than the immisciblç liguid. Thu~, the pr~f~xred procedures mentioned therein appl~ to ~hi~ em~odiment.
The following step, in ~hi~ embodiment whe~ein the immiscibl~ organic liquid ha~ a hig~er ~apor pre~ure than the dispersant l~uid, occurs und~r condition~ very ~imilar ~o the removal of the di~persant liquid. T~at i~, it oc~urs a~ ~ temperature ~n the range o~ b~w~cn ~bout 20C and about 10 100C. Preferred embodimen~s generally in ~aaord~nce with the pr~fQ~x~d pro~eaures utilized in the dispersant re~oval ~t~ albelt, in m~ny c~es, a~ sltqhtly high~r t~mperature~
or slightly lower pres~ureg over ~lightly longer periods of time ~re used ~n thig ~mmiscible mate~ial r~mov~l step.
The aellular gel, frce of di~per~ant liquid, whether open or clo~a oell, is next treated to remove tha ~ur~tant con~tituent ~herefrom, thu~ converting th~
c~llular gel to ~ celltllar inorganic ~el. qlhis step o~
removing th~3 ~urfactant i~volv~ thermodynamic treahnent of 20 ~h~ foamed gel. In a preferr~d ~mbodiment, the cellular ~l heat~d to ~ tempera~ure in th~ r~ng~ of ~etweerl ~bout 300 C and about 500 C over a pRriod of about 1 day to ~bout 3 day~. Nore pr~r~bly, the ~urfactant removal ~tep lnvolve~
expos~ng the ~oamed gel ~o a temp~r~ture in the rang~ o between about 3~0C and about 450C for a period ~n the ranqe of about 13 ~o 2~ day~. More pr~~ra~1y, th~ ~urfacant re val ~t~p in~ol~e~ heatin~ the foamed gel at a temperature ..
in the ~ange of b~een about 375aC and about 425C for about 2 day~.
3 Thi~ t~ermodynamic treatment which constitutes the surf~ot~nt removal ~tep i~ believed to ~f~ect A chemical reaction of ~h~ org~nic aompound whioh ~er~s a~ th~
~urfactant, w~th oxygen to ~orm the carbon oxide~, carbon monoxiae and/o~ carbon diox~d~. Thi~ g~saou~ ~rbon oxide8 . ,. i . ,~ , , :

- 2 0 2 S ~ ~ 9 produ~t easily e~cape~ from the gel l~hving a ~ur~actant-1 free, i.e./ organic-fxee gel Of cour~e, t~i3 ~heory explaining ~urfactant removal 1~ ~ust tha~ and the inv~ntio~
is lndependent of any theory explaining ~ts opcrability.
The cellular, organic-~rce gel resul~ing from ~he 5 organic constituent removal step i~, in a la~t step, ~int~red to pxoduce the ~inal ~ellular inorganic product. The 8~ ntering ~tep inYolv~ heatlng th~ orgRnic-free gel at a sintering e~rective te~perature. A~ tho~ skilled i~ the art are aware, a ~int~rin~ effectiv~ temperature i~ on~ a~ which 10 densif lcation of the ma~erial being 8~ nt~red begin~ In a prefer~ed ~mbod~en~, where th~ inorganic ~rticle~ are s~l~ca, the s~ntering s~ep ocaurs at a temperature ln the range of between about 900C ~nd about ~200C. Hore preferabl~, slnt~rin~ accur~ at a temperature in the range of 15 b~twe~n about 1000C and ~bout 1100C to produc~ th~ cellul~r inorgan~c product of the pre~ent invention.
In anath~r pr~f~rr~ ~mbo~im~nt, whffrein th~
inorg~nic partl~le~ are sil~con nitride, sinter~ng occurs ~t a t~mperatur~ ~n tho rang~ of b~tw~n about 1800~C and a~out 20 2200OC, more pr~f~r~bly, betwe~n ~bout 1900C and about 2lua~c.
In ~till anothcr preerr~d e~bodiment, the pref~rred embodiment wherein the lnorgan~c particle~ a~e ~lumin~, th~
~inte~ing ~ff~cti~e temper~ture i~ in t~ r~nqe of between 25 a~ut 1200C and about lB00C, more preferably, betw~en about 1400C ~nd abo~t 1600.
The above diBoUBBion 0~ ~intering ~empex~ture ~:
empha~iz~ that sint~ring preferably ocaur~ at a temperature in the range of betwe~n abou~ 900C and about 2200C With the 3 above sp~ai~a range~ preferred dep~nd~ng upon the identity of the inorganic particle8. ~ :
Sinterlng occur~ over a poriod of about 0.5 hour to ab~ut 4 hour~. Mor~ pr~ferably, the term ~r which sinterinq occurs ~ in the range of b~t~n a~out 0.75 hour 35 ~nd ~bout 2 hou~. Mo~t preferably, 6intering occur~ over a :~
.perlod of b-~ween about 0.8 hour and about 1.5 hours~

t.',. ' ' ', " ' . . . ' " ' .~ '` ~' : " , . ' ' ' ~ ' . . ', ' :

~2~9 T~e sintering step can occur in ~ny en~ironment.
1 That is, sintering can be conducted in a ~cuum or in the presence of a ga~ which may ~e r~activ~ or in~rt. ~ong th~
reaetive en~ironments, the most aommonly u~llz~d i~ air. Of the lnert ~a5~8, ~inter~ng in nitrogRn i~ mo~ pre~erred, although An atmosphere of argon i8 al~o o~ten ~mploy~d. 0~
all thes~ po~slbilitiee, ~in~ering in air i8 most pr~f~rr~d.
The above detailed description ls ~pplic~ble to anothex preferred embodiment of th~ pre~nt lnv~ntion. This pre~rred proc~ i8 identical with the pro~ses de~lne~
1~ abovQ with the a~d~tio~ nc}usion o~ an i~organic material in the ~i~pers~nt li~uid alonq ~ith the i-horgan~c p~rtlcle~.
The~incluaion of ~n inorganic materi~l, in ~ddition ~o inorganic p~r~cles, allows fox refinement and t~iloring of prop~r~ie~ o~ ~he re~ult~t cellular product to m~t requir~ents partiaular to spec~fic applicatton~ lncluding those requiring hlgher ~en~ and/or compressive strength, improved duct~lity and toughne~ and neces~ary di~l~c~ric prop~rties ~
~he inorganic material, ~elected from the group consisting of ~norganic whi~era and inarganic fi~er6, i-add~d to the d~spersant liqu~d along w~th th~ inorganic : p~rticles ~n ~ ~oncentrat~on ~uch that the organic material : repre~nts betwe~n 1~ and about 50~ by volume on a dry vo~ume b~si~. ~hat i~, the inorganic mat~r~al ~pr~nts b~tween ~5 ~bout 1% and ab~ut 50~ ~y volume b~sea on th~ total volume of tho ino~ganic p~r~ic}eY and ~he inorg~ni~ m~t~rial.
Preferably, the ~norqaniC material i~ ~re~-n~ ~n a ooncentration ~pre~entativ~ of a concentr~tion of between about 5~ and about 50~ by volum~ on a dry volum~ b~ . More 3 prefer~bl~, the inor~nic material con~titutes between ~bou~
10% ~nd abou~ 40% by volume on a dry volume ba~ till ~or~ p~eferably, the inorganic materlal i~ found in a concentration in th~ range of between about 15~ ~nd about 30 by volu~e on ~ dry v~lu~e b~ig. It i~ particularl~
pr~ able that the inorganic material re~re~e~ts about 20 ` by volum~ on A ~y ~olume baOEi~.

, ". . , . ~ ~.

,, ` : :
,i;, . . .

~ 0 ~ 9 ThR inorganic material, as s~ated ~bove, iB
1 ~elect~3d from t~e group consisting of inor~ania whi81~r8 and inor~anic fiber~. Wh~th~r ~hi~ker0 ~r ~iber~, th~ inorganic material is preferab~y ohar~cterized by An aspect r~tio, i.e., a l~ngth to w~d~h ratio, of at least more than a~out 5 5~ hos~ skilled in the art ~re aware th~ whisk~r~ are defin~d a~ mono-cxystalline mat~rial~ wher~as 1bers ax~
polyorystalline, Inerganic mate~ial~ within the cont~plation of th~ present invontion in~lud~ inorganc wh~ker~ and ~norganio fiber~ form~d fr~m sillcon caxbide, 10 ~}~con n~txide, alumina ~nd mullit~, among others~ ~f th~-preferr~d compounds and na~ural oco~rxing o~, the use o~
si ncon anr~ide, especially silicon carb~de whisXers, is par~icularly ~pplicable for uq~ in ~ preferred embo~im~nt of the pressnt inv~ntion.
~t ~hould be appr~ciated that the proce~ o~
prepar~ng ~norg~nic aell~lar product~ which ~ncludes an ~norgan~c material, compri~es all the step~ reaited here~nbefore except for th~ inclu~ion of the add~tlonal ~t~p of adding the inorganic m~t~rial ~o th~ dispersant liquid ~ -~
20 prior to, simult~neou~ly with or 5ub8equ~nt to t~e introdu~ion o~ the inorganlc particles to the di~p~rsant l~gufid. ::
The pre~ent inve~ion not only oont~mplate~ the ~ :
proces~o~ d~scr~bed abov~ but alBo the product~ produced i~ :
25 these proao~es. That i~, ~h~ cellular inorg~nic ma~erials produced in accordance with th~ above-dein~d proce~ r~
within t~e cont~mplation of th~ pra6~nt inv~ntion.
The ~ollowin~ ex~mples are qiven to illuotr~te the 8COp~ of th~ pre~ent ~nv~ntion~ B~cause these sxamples are 3 g~ven for illustrative purpo~e6 only, the procea~ of th~
present in~e~tion sho~ld not be l~mi~ed thereto. -~
,:

, .: ~

;~;., , . ,. . -.. ~ ,, ., , , , . ~

202~9 EX~PLI: 1 PrePar~tion o~ a Cellul~r Material from ~ Sol A silica sol compri~ing 40~ by w~iqht ~ilica in 5 water, s~abilizRd with 0.41~ ~y weight sodium oxid~, W~8 utiliz~d. ~lthough the silicR ~ol cou7d have bee~ prod~ce~
by addin~ fi~ely divided sil~ca to ~ater, a c~mmercially a~ail~bl~ silica ~o~ ormulati~n, Ludox ~trademar~l HS~40, wa~ ~mploy~d~ To this 8 i 1~ ca sol was add~d ~ulfuric acld in 10 a concentr~tion ~ufficient to reduce the or~ginal p~ of the silica 801, g.7, to a p~ of 5.25. The ~ol W~5 allowed to ~nc~bate for a period of 30 minutes.
The increase ~n acidity of the 3ilic~ to a pH o~
5.25 and incub~tion for 30 minute~ resulted in a 15 corre~ponding incr~a~ in the viscosity of the sol to 8~ cp.
A surfa~t~nt, ~odium dod~c~l sulfate 18DS), w~8 intrcduced ~nto ~ ac~dified sol. The amount of 5DS added to the ~o7 was ~uch tha~ aft~r ~t8 addition the 8~ conc~ntr~t~on in the -silica sol wa~ x 10 3 mole~ of SDS per liter of silica 20 sol. An immiscible ~rganic l~uid, trichloro~luorom~thane, better ~ncwn by ~t~ tr~demark, ~r~on-ll~ wa~ next introduced into the ilica ~ol. The ~eon-lI was addsd in ~ 50~
moth~nol ~olution, with the m~thanol ~erving not on~y a~ a Freon-ll ~olv~nt but al~o as a co-~uractant. It wa~
25 provia~a in a volum~ ~u~h t~i~t th~ cOhO~ntratiOn of th~
solu~ion con~tituted 3.3~ by volume, based on the tot~l volu~e of th~ sol. That is, a volume o~ the 50~ 301ution ~a~
~; ~dd:ed ~o th~t the Freon-ll solution con~titut~a 3.3~ by vol~m~ of the total volu~e. ~hu~, Froon-11 wa~ pre~ent in 3~ th~ ~ol in a volume aoncentration o~ 1.65~, b~d on th~
tot~l ~olume of th~ 601.

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~ ~2~9 ~ 11 of t~e above s~eps were condueted at a temperature o~ ~0C. Therefore, the hydxo~ol wa~ at a t~mperature of 20C. At ~hie point th~ tempbrature of ~he hydrosol ~as increa~ed to 30C and allowad to ag~ at th~
temperature for 30 mlnute~. To insure t~at this 30C
5 temperature was maintained con~ant, th~ be~ker containing the sol was ma~n~ained in a ~mperatur~ bath. A~ the ~nd of this pQriod gelation of the sol, a vi~co~lty of 80 c~ wa~
init~ated. At thiq point~ ~tirring of ~he qel wit4 a magnetic 8tirrer wa~ be~un. Stirr~ng pro~ot~d fo~ming whlah r~Ached its maximum height in a~out 1 minute.
The foa~d g~l, d~sposed in ~ bsak~r, which was ~o~red to prevent ~vaporation, wa~ ~tored at 30DC for 12 houxY. The foamed gol was stored for an addit~onal fiv~ days at room temperature w~th th~ beaker ~till covered to re~uce 15 gel drying. The cover wa~ ther~upon removed and the foamed 9~1 wa~ al~ow~d to ~main ~ 30C for an additional 24 hour~.
The partia~y dried foamed materi~l r~ulting ~rom the above proc-~ur~, wa~ dispo~ed in an oven and remained h~at~d at a tempcratur~ of 70C for on~ week. Thereupon, the 2~ foam~d material wa~ txansferred ~o a hi~her tempera~ure oven, an ov~n mn~ntained ~t 400~C, and there~n haat~d for two days.
Finally, ~he fo~m~d material wn~ sintered in air at a temperature of app~oxi~ately 1100C to produce a cellular inorganic mat~rlal.
~5 The thus fc?rmed cell~ar inorganic material was cut into di~k-~ha~ed ~a~ple~. The average pore di~m~t~lr of ~e disk-shap~d s~ple~ waJ m~asuxed on diamond ~wed ~urface~ :
and t~e av-rag~ pore ~iz~ ~alculated by multiplying the average measur~d d~ameter by 1.~2 in aaaordana~ with the :
3~ procedur~ enumerat~d in ~,L, ~ullman, "Neasurement of ;~
Particle Siz~8 in Opa~u~ Bodies,~ Journal of M~dal~, 565-575 :~
~1953). The quantity and Bi8e of th~ microporosity w~r~
det~mined by meraur~ poro~metry.

3~ -:

~2~9 The result~ o~ this me~surement e~t~bli~hed that l the ~ellular material had a r~lativ~ bulk ~n~i~y ~ 17~
Rel~ive bulk d~nsity, as those skilled in the ~r~ ar~ awa~e, is a ratio, expressed in perc~nt, o~ tbe total wel~h~ to the t~tal volu~e of the matexial divided by the theoretlcal den~ity of t~ material. The lnorganic cellular product w~8 det~rmined t~ ha~e an average c~ izo of 400 micxo~ hla example i~ summarized in the Table below.

.,,.'' .' ` ~ ` ' ' `

` 2~2~5~9 EXAMPLES 2 ~0 5 ~..

The p~:ocedure of Example 1 wa~ repeat~d in ~our 5 add ~ tior~a} examples . Thei3e example~, denoted a~ Ex~mple~ 2 to 5, differed ~rom Ex~mpl~ 1 in that ~he vi~osi'cy of ~he sol at ~h~ on~et oî 61ela~on wa~ varied by changing the p~
caus~d by th~ ~ddition o~ dif fer~nt con~ntration of sulfuric acid, and th~ p~riod of in~bation. The~e ~arla~ ere ~: :
'1 ad~usit~d s~ th~t th~ vi~oo~i~y of th~ hydro~ol o~ each ~xampl~ ~a~ in exc~ of the vi~cooi~y of lo~er numbered oxa~ple~ I~ iJ3 emphasized, however, tha~ ei~ch of th~o example~ wa~ wit~ t~e scope of the in~tant inventlon.
The r~bul~A of the~e examples are ~un~n~riz~d in the 15 ~ble.

:~ ~5 ~ ~ -. . .

:

I ' ` " ' ~ : ~ , , --21~
:`: 2~2~
COMPARA~ ~E EXAMP~E

PrQparation o~ a Cellular Material Example 1 w~s re~eated exaept th~t the amount of S ~ulfurlc acid add~d to the ~ilica ~ol d~crean~d the ~H o~ th~
~ol ~o 5.80. Moreover, ~he inoub~tion p~riod wa~ d t~
18 min~lt~ . Thi~ combination o~ factor~ r~ulted in ~n ~ncreas~ csf viscosi~y of th~3 ~ilica ss~l to ~nly 30 cp, ~low ~he minimum 90'1 vi~co-i~y reguir~d by the present lnvent~on.
At thiY vl~cosity, the sub~quent ~teps, conducted in accordance with the proc~dure c~f Exampl~ 1, did ~c~t re~ult ~n'~eoamlng and geldtion and ~o cellul~r produe~ coula b~
~ormed .
~ or completene~, this ex~mple is inc:l~ded in the X~ p~ovided ~y the T~le.

~,.:i . , ... -- , ,,., ,., ., , . , ~. ~- : ~ :

,i,;: . . , ,. . . .
; .

2026~5~
CONPARAT~V}~ EXAMPLE_ 2 ~ ~'.
Exa3nple 1 was repeated but for ~he steps of ~ -hydrosol acidification and incubation. Acidifi~a~ion, by :~
adaing suluric acid ~c~ th~ hydxo~ol, wa~ redua~d to produc~
a hydrc)~ol hav~ng a pH of 5.80, i~stead of S~25. Moreo~e~, ~he period o~ incubation wa~ reduced ~rom 30 minutes to 29 minute~. The combined eP~ec~ of th~se change~ r~ulte~ ~n 10 ~ncxease of the ~ViYcosity of the hydro307 to 15,00~ cp.
Sul~eg~nt proae~sirlg of the }~ydrou~l into a ce~lular ~a~erial in ~cco~dance with Ex~ple 1 resulted in ~he formation of A cellular material having a c~17 ~ize o~
180 m$0ron8 and el relative bulk den~ity of 4~ 'rhis d~nE~ity 15 is far too higher to be corlsidered a lightweight cellular mater~ al having th~ d~sir~ble propertle~ of inorganic -~
materials sought in the proces~ of ~he present inv~ntion. -~

:~0 ~:

.''' ~ 02~59 TA~LE

Relativ~
~eriod of ~yd~clsol Bulk Cell si ze, .x~mple No. ydro~olL~ ~D~ Vi~Y~ !n Den~ tY, ~ m~cron~

1 S. 25 30 80 17 400 2 5.65 ~S 150 18 340 :~ 3 5 . ~0 24 300 ~0 300 :~ 4 i~,40 30 500 31 90 ~ 5 S . 80 26 l, S00 28 235 ; ~ CEl 5 . 80 18 30 No Foam Not ~ormed CE2 5.80 ;~9 15,000 40 180 ~:~
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--~4--202~9 EXAMpr.E 6 ~rom Inorqe.nic_Particl~

Th~ proce3~ of Example ~ w~ rep6ated but for the addition o~ s~li¢on carb~e w}~i~ker~ to ~he ~iliaa ~ol ~udox ttradema~k] HS-4~, whi~h in this example wa~ ~ta~ilized with Na2SO4. Th~ SiC whl~kor~ (F-9, manuf~ctured by Compo~lt~
Materlal Corp., ~;r~r, S.C. ) w~re add~d to the BiliC21 ~ol in a concen~ration such that the S I C ~rh~ ~kers r~preser~t~d 209~ by volume, balse~ or~ the total ~rolume o~ ica p~r~ialeA and ~i~icon carbido t~hisker~ (20 vol 36 on ~ dry solid ba~i3).
Upon addit~o~2 of t~ SiC whi~kars, the mix~ure was mill~d in a plast~c ~ar ft~r ~ ht hour~ he~eupon th~
proa~dur~ of Exalnple 1 was ~s'e~nti~lly r~p~a~d ~ut for ~h~
preseno~ o* the ~ on ~arbldR ~bisker~
The c~ ular material formed in ~ordance with ~ ~
thi~ example wa6 chara~terizea by ~pproxima~ely th~ ~me ~ :-rel~tive den~i~y, 20%, ~a ~n Exampl~ 3.
2~ Th~ cellular product of this ex~3QplQ wa~ tested to determin~ ~t~ xural ~tr~ngth. Fl~xural ~r~ngth w~
obta~n~d by th~ three point bending m~thod, a~ defin~d by F~. Baratta, "R~lqtlirements fo~ Flexure T~sting p~ ~rittl~
e~ial~ MMRC TR 82-20, Wa~elrtown, ~A, April, 1982, which 25 technic:al p3per ~8 $nc~7~rated herein ~y referenc-, ~t A
loadtn~ rate o~ 0.5 m~ p~r minute. It w~s f~und that the flexur~l 8trength O~ the ~ple was about 7.0 Ml~. For c~mpari~on ~e ~ompl~3 of Ex~mple~ 3 wa~ teatea ~nd found to pos~ea~ a ~lexu~al ~trength o~ about ~ . 9 MP~ ~

~ ' .
3!i - .

..... ..

i~ q;~

2~2~9 The above embodiments and examples are given to illus~ra~e ~he scope and ~pirit of ~he pre~ent inventic: n .
~hese ~odlment~ and e~campl~ will mak~ apparent, to those ~kil}ed in the ~r~, other embodiments and exarnpl~. Th~se other embodiments ~nd examples are within the cont~mplation 5 of the pre~ent ~nvention. Therefore, the present invention sholl3,d be limited only by the app~nded ~l~ims.

lC~

~0 r 1...... ~ ~ ; ;
.; ~ .. .. . . .

Claims

1. A process for making a cellular inorganic material comprising:
(a) forming a sol by disposing inorganic particles having a size of less than about 1000 .ANG. in a dispersant liquid, said dispersant liquid having the structural formula ROH, where R is hydrogen or lower alkyl;
(b) adding an organic material, a liquid immiscible in said dispersant liquid, to said sol;
(c) introducing a stabilizing effective amount of a surfactant to said sol, said surfactant added to said sol prior to, concurrently with or subsequent to said introduction of said immiscible organic liquid;
(d) increasing the viscosity of said sol wherein a gel is formed;
(e) treating said gel such that said immiscible organic liquid is dispersed into a plurality of liquid droplets or vaporized into an interconnected gaseous network wherein the gel becomes cellular;
(f) removing said immiscible organic material and said dispersant liquid from said cellular gel with the proviso that the first removed of said immiscible organic and said dispersant liquid has the lower vapor pressure;
(g) removing said surfactant from said immiscible organic-free and dispersant-free cellular gel; and (h) sintering said dispersant surfactant-free cellular gel.

2. A process in accordance with Claim 1 including the step of acidifying said sol prior to the introduction of said surfactant, whereby the pH of the sol is reduced to a range of between about 5 and about 6.

3. A process in accordance with Claim 2 wherein said acidification occurs by adding a mineral acid to said sol.

4. A process in accordance with Claim 3 wherein said mineral acid is selected from the group consisting go hydrochloric acid, sulfuric acid and nitric acid.

5. A process in accordance with Claim 4 wherein said mineral acid is sulfuric acid.

6. A process in accordance with Claim 1 comprising the step of introducing a co-surfactant into said sol simultaneous with the introduction of said surfactant, simultaneously with the introduction of said immiscible organic liquid, prior to the introduction of said surfactant and said immiscible organic liquid or subsequent to the introduction of said surfactant and said immiscible liquid.

7. A process in accordance with Claim 6 wherein said co-surfactant is an alkanol.

8. A process in accordance with Claim 1 wherein said particles having a size of less than about 1000 .ANG. is an inert inorganic material.

9. A process in accordance with Claim 8 wherein said inert inorganic particles are selected from the group consisting of silica, alumina, zirconia, magnesia, beryllia, mullite, ferrite, barium titanate, Pb(Zr,Ti)O3, silicon nitride and mixtures thereof.

10. A process in accordance with Claim 9 wherein said inorganic particles are silica.

11. A process in accordance with Claim 1 wherein said surfactant is selected from the group consisting of anionic and cationic surfactants.

12. A process in accordance with Claim 11 wherein said surfactant is sodium dodecyl sulfate.

13. A process in accordance with Claim 11 wherein said surfactant is cetyltrimethylammonium bromide.

14. A process in accordance with Claim 1 wherein said immiscible organic liquid is selected from the group consisting of a saturated hydrocarbon, an unsaturated hydrocarbon, a saturated hydrocarbon substituted with halogen and an unsaturated hydrocarbon substituted with halogen.

15. A process in accordance with Claim 1 wherein the viscosity of the sol in step (d) is increased to a range of between about 80 cp and 1,500 cp.

16. A process in accordance with Claim 1 wherein said step of forming a cellular gel, step (e), comprises heating said gel to a temperature below the boiling point of said dispersant liquid.

17. A process in accordance with Claim 16 wherein said immiscible organic has a lower vapor pressure than said dispersant.

18. A process in accordance with Claim 17 wherein said immiscible organic liquid is a fluorochlorocarbon.

19. A process in accordance with Claim 16 wherein said immiscible organic has a higher vapor pressure than said dispersant.

20. A process in accordance with Claim 18 wherein said step of removing said immiscible organic from said cellular gel comprises heating said cellular gel to a temperature in the range of between ambient and about 200°C.

21. A process in accordance with Claim 1 wherein said step of removing said dispersant liquid from said cellular gel comprises heating said cellular gel to a temperature in the range of between about 20°C and about 100°C for a period of between about 1 day and 1 week.

22. A process in accordance with Claim 1 wherein said step of removing said surfactant from said cellular gel, step (g), comprises heating said cellular gel to a temperature in the range of between about 300°C and about 500°C over a period of time in the range of about 1 day and about 3 days.

23. A process in accordance with Claim 1 wherein said sintering step, step (h), comprises heating said surfactant-free cellular gel at a sintering effective temperature.

24. A process in accordance with Claim 23 wherein said sintering step occurs at a temperature in the range of between about 900°C and about 2400°C.

25. A process for making a cellular inorganic material comprising:
(a) forming a silica hydrosol by disposing silica particles, having a size less than about 1000 .ANG., in water;
(b) adding an organic liquid, immiscible in water, to said silica hydrosol;
(c) introducing a stabilizing effective amount of a surfactant to said hydrosol, said surfactant added prior to, simultaneously with or subsequent to said introduction into said hydrosol of said immiscible organic liquid;
(d) adding a co-surfactant to said hydrosol concurrent with or subsequent to said introduction of said immiscible organic liquid;
(e) increasing the viscosity of said hydrosol to a range of between about 80 cp and about 1500 cp wherein said hydrosol is converted into a gel;
(f) converting said gel into a cellular gel by heating said gel to a temperature below the boiling point of the dispersant liquid;
(g) heat treating said cellular gel to remove said immiscible organic liquid;
(h) removing said dispersant liquid from said immiscible organic-free cellular gel;
(i) removing said surfactant from said dispersant liquid-free cellular gel; and (j) forming a cellular inorganic material by sintering said surfactant-free cellular gel in air.

26. A process in accordance with Claim 25 wherein said step (e), said step of increasing the viscosity of said hydrosol, is effectuated by acidification and incubation of said hydrosol.

27. A process in accordance with Claim 26 wherein said acidification results in a decrease in the pH of said hydrosol to between about 5 to about 6.

28. A process in accordance with Claim 25 wherein said surfactant added in step (c) is sodium dodecyl sulfate.

29. A process in accordance with Claim 28 wherein said immiscible organic liquid added in step (b) is a fluorochlorocarbon.

30. A process in accordance with Claim 29 wherein said fluorochlorocarbon is trichlorofluoromethane.

31. A process in accordance with Claim 28 wherein said co-surfactant, added in step (d), is an alkanol.

32. A process in accordance with Claim 31 wherein said alkanol is methanol.

33. A process in accordance with Claim 32 wherein said methanol is introduced into said hydrosol concurrently with the addition of said immiscible organic liquid.

34. A process in accordance with Claim 25 wherein step (g), said step of heat removing said immiscible organic from said foamed gel, comprises heating said cellular gel to a temperature in the range of between ambient and about 200°C.

35. A process in accordance with Claim 25 wherein step (h), said step of removing said dispersant liquid from said foamed gel, comprises heating said cellular gel to a temperature in the range of between about 25°C and 75°C over a period of between about 2 days and about 3 days.

36. A process in accordance with Claim 25 wherein said step (i), said step of removing said surfactant, comprises heating said cellular gel to a temperature in the range of between about 350°C and about 450°C for a period in the range of between about 1 1/2 days and about 2 1/2 days.

37. A process in accordance with Claim 25 wherein step (j), said sintering step, occurs at a temperature in the range of between about 1000°C and about 1100°C.

38. A process for making a cellular inorganic material comprising:
(a) forming a sol by disposing inorganic particles, having a size of less than about 1000 .ANG. and an inorganic material selected from the group consisting of inorganic whiskers and inorganic fibers, said inorganic material present in a concentration such that said inorganic material comprises between about 1% and about 50% by volume on a dry volume basis, in a dispersant liquid, said dispersant liquid having the structural formula ROH, where R is hydrogen or lower alkyl;
(b) adding an organic liquid, immiscible in said dispersant liquid, to said sol;
(c) introducing a stabilizing effective amount of a surfactant to said sol, said surfactant added to said sol prior to, concurrently with or subsequent to said introduction of said immiscible organic liquid;
(d) increasing the viscosity of said sol wherein a gel is formed;
(e) treating said gel such that said immiscible organic liquid is dispersed into a plurality of liquid droplets or vaporized into an interconnected gaseous network wherein a cellular gel is formed;
(f) removing said immiscible organic and said dispersant liquid from said cellular gel;
(g) removing said surfactant from said immiscible organic-free and dispersant liquid-free cellular gel;
(h) sintering said surfactant-free cellular gel.

39. A process in accordance with Claim 28 wherein said inorganic material comprises between about 5% and about 50% by volume, based on total volume of said inorganic particles and said inorganic material.

40. A process in accordance with Claim 39 wherein said inorganic material is present in a concentration such that it represents between about 10% and about 40% by volume, based on the total volume of said inorganic particles and said inorganic material.

41. A process in accordance with Claim 40 wherein said inorganic material is present in a concentration such that it represents between about 15% and about 30% by volume, based on the total volume of said inorganic particles and said inorganic material.

42. A process in accordance with Claim 38 wherein said inorganic material has an aspect ratio of at least more than about 5:1.

43. A process in accordance with Claim 38 wherein said inorganic material is selected from the group consisting of silicon carbide, alumina, silicon nitride, mullite and mixtures thereof.

44. A process in accordance with Claim 43 wherein said inorganic material is monocrystalline inorganic whiskers.

45. A process in accordance with Claim 44 wherein said inorganic material is silicon carbide whiskers.

46. A process in accordance with Claim 43 wherein said inorganic material is polycrystalline inorganic fiber.

47. A product made in accordance with the process of Claim 1.

48. A product made in accordance with the process of Claim 25.

49. A product made in accordance with the process of Claim 38.

50. A process for making a cellular inorganic material comprises:
(a) forming a sol by disposing inorganic particles having a size of less than 1000 .ANG. in a non-polar organic liquid;
(b) adding a polar material, in the liquid state, immiscible in said non-polar organic dispersant liquid, to said sol;
(c) introducing a stabilizing effective amount of a surfactant to said sol, said surfactant added to said sol prior to, concurrently with or subsequent to said introduction of said immiscible polar liquid;
(d) increasing the viscosity of said sol wherein a gel is formed;
(e) treating said gel such that said immiscible polar liquid is dispersed into a plurality of liquid droplets or vaporized into an interconnected gaseous network wherein said gel becomes cellular;
(f) removing said immiscible polar material and said non-polar dispersant from said cellular gel;
(g) removing said surfactant from said cellular gel; and (h) sintering said cellular gel.

51. A product made in accordance with the process of Claim 50.