CA1090832A - Method of making a cellular body from a high silica borosilicate composition - Google Patents
Method of making a cellular body from a high silica borosilicate compositionInfo
- Publication number
- CA1090832A CA1090832A CA291,241A CA291241A CA1090832A CA 1090832 A CA1090832 A CA 1090832A CA 291241 A CA291241 A CA 291241A CA 1090832 A CA1090832 A CA 1090832A
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- Canada
- Prior art keywords
- mixture
- cellular body
- pulverulent
- percent
- making
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B19/00—Other methods of shaping glass
- C03B19/08—Other methods of shaping glass by foaming
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C11/00—Multi-cellular glass ; Porous or hollow glass or glass particles
Abstract
TITLE
A METHOD OF MAKING A CELLULAR BODY FROM
A HIGH SILICA BOROSILICATE COMPOSITION
ABSTRACT OF THE DISCLOSURE
An intimate mixture of an amorphous silica (pref-erably an amorphous, precipitated hydrated silica) potassium oxide, boric oxide, alumina and a cellulating agent is pre-pared. The intimate mixture is thereafter subjected to a temperature of between about 1390°C to 1450°C for a sufficient period of time to coalesce the mixture and gasify the cel-lulating agent and form a cellular body having a substantially uniform cell structure. In one embodiment the intimate mixture is prepared by first forming a slurry of the constituents and thereafter drying the slurry to form aggregates. The dried aggregates are thereafter comminuted if necessary to a suitable size to form a pulverulent batch. The pulverulent batch is subjected to a cellulating temperature in a cellulating furnace and forms a foam-like mass. The foam-like mass is comminuted to a suitable size to form a precellulated material. The pre-cellulated material is thereafter intimately mixed with additional cellulating agent and pulverulent batch in pre-selected proportions and subjected to cellulating temperatures in the cellulating furnace where the constituents coalesce and gasify the cellulating agent to form a cellular body having a substantially uniform cell structure. In another embodiment alumina, boric oxide, an alkali metal salt and a cellulating agent are comminuted and intimately mixed in a ball mill to form a first mixture. Thereafter, amorphous silica (preferably an amorphous, precipitated hydrated silica) is added to the first mixture to form a second mixture or batch that contains more than 80% by weight amorphous silica. The second mixture is milled in the ball mill and thereafter the second mixture is subjected to a temperature sufficient to coalesce the second mixture and gasify the cellulating agent to form a cellular body having a substantially uniform cell structure.
A preselected portion of the trimmings from the cellular body may be added to and comminuted with the first mixture before the amorphous silica is added to the first mixture to form the second mixture.
A METHOD OF MAKING A CELLULAR BODY FROM
A HIGH SILICA BOROSILICATE COMPOSITION
ABSTRACT OF THE DISCLOSURE
An intimate mixture of an amorphous silica (pref-erably an amorphous, precipitated hydrated silica) potassium oxide, boric oxide, alumina and a cellulating agent is pre-pared. The intimate mixture is thereafter subjected to a temperature of between about 1390°C to 1450°C for a sufficient period of time to coalesce the mixture and gasify the cel-lulating agent and form a cellular body having a substantially uniform cell structure. In one embodiment the intimate mixture is prepared by first forming a slurry of the constituents and thereafter drying the slurry to form aggregates. The dried aggregates are thereafter comminuted if necessary to a suitable size to form a pulverulent batch. The pulverulent batch is subjected to a cellulating temperature in a cellulating furnace and forms a foam-like mass. The foam-like mass is comminuted to a suitable size to form a precellulated material. The pre-cellulated material is thereafter intimately mixed with additional cellulating agent and pulverulent batch in pre-selected proportions and subjected to cellulating temperatures in the cellulating furnace where the constituents coalesce and gasify the cellulating agent to form a cellular body having a substantially uniform cell structure. In another embodiment alumina, boric oxide, an alkali metal salt and a cellulating agent are comminuted and intimately mixed in a ball mill to form a first mixture. Thereafter, amorphous silica (preferably an amorphous, precipitated hydrated silica) is added to the first mixture to form a second mixture or batch that contains more than 80% by weight amorphous silica. The second mixture is milled in the ball mill and thereafter the second mixture is subjected to a temperature sufficient to coalesce the second mixture and gasify the cellulating agent to form a cellular body having a substantially uniform cell structure.
A preselected portion of the trimmings from the cellular body may be added to and comminuted with the first mixture before the amorphous silica is added to the first mixture to form the second mixture.
Description
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, I' , BACRGROUND OF T~IE INVE~TION
1. ~ield of the Invention ii Thi~ inventlon relate~ to a method of making a cellula~ body ~rom a high borosilicate c~mposition, ~nd more particularly, to a method of cellulating high boro~ll$cate composition~ by form~ng an intimate mixture o~ the pulverulent , constltuent~ and a portion of previously cellulated high boro-Qilicate compo~ition~ and thereafter sub~ectin~ the mixture to cellulatlng temperature~ to ~orm a cellular body, '.
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, I' , BACRGROUND OF T~IE INVE~TION
1. ~ield of the Invention ii Thi~ inventlon relate~ to a method of making a cellula~ body ~rom a high borosilicate c~mposition, ~nd more particularly, to a method of cellulating high boro~ll$cate composition~ by form~ng an intimate mixture o~ the pulverulent , constltuent~ and a portion of previously cellulated high boro-Qilicate compo~ition~ and thereafter sub~ectin~ the mixture to cellulatlng temperature~ to ~orm a cellular body, '.
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2. Description of the Prior Art Conventional glas~es that are melted in conventional glass melting tanks contain about 70% by weight ~ilica. High silica glasses that are melted in special high temperature melting tanks contain about 80% by weight silica. It i~
extremely difficult to melt glasses containing above 80% by j weight ~ilica or above 90% by weight of a combination of silica and alumina in either conventional glas~ melting tanks or in 1I the ~pecial high temperature glass melting tanks.
10 j, The process of melting the constituent~ in a glass tanX consists of decomposing all or some of the constituents, forming a liquid mixture of the constituent~, removing the trapped gases and improving the homogeneity of the molten mass.
The proces3 of removing gase~ and improving the mixing and homogeneity depends on a number of parameters especially the I viscosity of the molten mass. The melting proce~s requires il liquidity and a reduction in the viscosity of the molten mass and u~ually takes place in the highest temperature zone of the glas~ melting ~ank~. When attempts are made to melt the glass ~ compositions containing above 80% by w0ight silica and a '.
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mixture of silica and alumin~a that comprises above 90% by weight of batch in special high temperature gla~s melting , tanks, it has been ob~erved that the temperatures obtained are high enough to ju~t melt the batch and are not hi~h enough to create the thermal current~ necessary to intimately mix and obtain homogeneity of the con~tituent~ in the vitrified product.
In the high temperature glass melting tanks, the cor-¦1 rosion rate of reractories i~ extremely high, and thc lo~ of ll fluxe~ for long period~ at this high meltlng temperature is bothlO l, undesirable and unacceptable. In high temperature melting tanXs, the top temperature i~ re~tricted to slightly above 1600C due ; ¦I to the re~triction~ on the capabilitie~ of the firing 3y~tem~ ~nd l; due to ~he limitations of the silica crown~ in the melting tank.
Attempts have been made to obtain high melting temperatureR and 1. reduce the above discu~sed problems. Electria melt~ng haR been 1l utilized to obtain higher temperatures in the body of the melt~
~ ing ma~ while maintaining lower temperature~ at the ~urface o~
: I the melting mass as well a~ at the refractory interfaces~ The ' method of electric melting can generate temperature~ in excess : 20 ' of 1700C in the body of the melting ma6~ while malntaining ~ i lower temperature~ at the refractory interface~
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, jl In electric melting, the heat ~ generated by the I ionic conduction taking place between two electrodes positioned I in the glas~ batch with the gla~e batch acting a~ the electrolyte.
The capacity of the gla~s batch to carry ionic current depend~
en the mobility of the varioue ~ons contained ln the gla~, batch.
In a high silica glas~, tha monovalent cation~ carry more than 90 percent of the current. Among the commonly occurring mono-!1 valent cations~ i.e. Na+, K+ and Li~, the Na~ lons have a much ,, higher mobility than K+ ion~. Therefore, in a glass compo~ition 1; where it i5 more desirable and preferred to have K+ ion~ rather than Na+ ion~ for rea~ons }ater di~cussed, it i~ difficult ~o attain the desired temperatures. For example; with a preferred composition that contains le~ than 3 percent by weight potas~ium ' oxide (K2O), it i~ extremely difficult with electric meltlng to , attain the high levels of currents and the prerequisite high Il, temperature~ required for att~ining a 6uitabl~ homogeneou~ melt.
¦ In a conventional glas~ tank, the pulverulent const~tu-1, entq~, commonly referred to a~ the glas~ batch, are ~ed to the , tank through a suitable opening and are vitrified by melting.
The melt, however, is not homogeneous ln compos1t1on. To atta1n 1~9C~3~
Il homogeneity, it i~ nece~sary to increase the temperature of ¦I the molten glas to provide thermal current~ in the molten body.
This re~ults in a mixing of ~he molten makerialg and the compo-I ~ition thu~ become~ more homogeneou~. Diffusion of the cations ¦¦ increaae3 at the higher temperatures to al~o increa~e the ¦ homogeneity of the molten ma~s.
¦ Removing the molten ma~s from the melting tank require, the molten ma~s to have certain characteri~tics, as I for example, a sufficiently low visco~ity to permit the gla~
il ~o flow out of the tank. Agaln, the~e flow characteri~tic~ can ¦¦ be obtained by attaining su~ficiently high temperature~ in the melt. The temperature6 required for obtaining homogeneity o~
the conventional glas~ compo~itions and ~or obta~ing the : ¦ required degree of fluidity are ~ub~tantially the ~ame, although the temperature for attaining homogeneity may be 61ightly higher.
The level of temperature re~uired to obtain homogenaity o~ the I conventional glas~ composition~ or for obtaining the nece~ary 1~ fluidity for conventional glass compo~ition~ i~ much lower than the temperature required to attain both the homogeneity and fluidity of gla~ses containing above ~0 percent ~illca or having i, ' - -
extremely difficult to melt glasses containing above 80% by j weight ~ilica or above 90% by weight of a combination of silica and alumina in either conventional glas~ melting tanks or in 1I the ~pecial high temperature glass melting tanks.
10 j, The process of melting the constituent~ in a glass tanX consists of decomposing all or some of the constituents, forming a liquid mixture of the constituent~, removing the trapped gases and improving the homogeneity of the molten mass.
The proces3 of removing gase~ and improving the mixing and homogeneity depends on a number of parameters especially the I viscosity of the molten mass. The melting proce~s requires il liquidity and a reduction in the viscosity of the molten mass and u~ually takes place in the highest temperature zone of the glas~ melting ~ank~. When attempts are made to melt the glass ~ compositions containing above 80% by w0ight silica and a '.
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mixture of silica and alumin~a that comprises above 90% by weight of batch in special high temperature gla~s melting , tanks, it has been ob~erved that the temperatures obtained are high enough to ju~t melt the batch and are not hi~h enough to create the thermal current~ necessary to intimately mix and obtain homogeneity of the con~tituent~ in the vitrified product.
In the high temperature glass melting tanks, the cor-¦1 rosion rate of reractories i~ extremely high, and thc lo~ of ll fluxe~ for long period~ at this high meltlng temperature is bothlO l, undesirable and unacceptable. In high temperature melting tanXs, the top temperature i~ re~tricted to slightly above 1600C due ; ¦I to the re~triction~ on the capabilitie~ of the firing 3y~tem~ ~nd l; due to ~he limitations of the silica crown~ in the melting tank.
Attempts have been made to obtain high melting temperatureR and 1. reduce the above discu~sed problems. Electria melt~ng haR been 1l utilized to obtain higher temperatures in the body of the melt~
~ ing ma~ while maintaining lower temperature~ at the ~urface o~
: I the melting mass as well a~ at the refractory interfaces~ The ' method of electric melting can generate temperature~ in excess : 20 ' of 1700C in the body of the melting ma6~ while malntaining ~ i lower temperature~ at the refractory interface~
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, jl In electric melting, the heat ~ generated by the I ionic conduction taking place between two electrodes positioned I in the glas~ batch with the gla~e batch acting a~ the electrolyte.
The capacity of the gla~s batch to carry ionic current depend~
en the mobility of the varioue ~ons contained ln the gla~, batch.
In a high silica glas~, tha monovalent cation~ carry more than 90 percent of the current. Among the commonly occurring mono-!1 valent cations~ i.e. Na+, K+ and Li~, the Na~ lons have a much ,, higher mobility than K+ ion~. Therefore, in a glass compo~ition 1; where it i5 more desirable and preferred to have K+ ion~ rather than Na+ ion~ for rea~ons }ater di~cussed, it i~ difficult ~o attain the desired temperatures. For example; with a preferred composition that contains le~ than 3 percent by weight potas~ium ' oxide (K2O), it i~ extremely difficult with electric meltlng to , attain the high levels of currents and the prerequisite high Il, temperature~ required for att~ining a 6uitabl~ homogeneou~ melt.
¦ In a conventional glas~ tank, the pulverulent const~tu-1, entq~, commonly referred to a~ the glas~ batch, are ~ed to the , tank through a suitable opening and are vitrified by melting.
The melt, however, is not homogeneous ln compos1t1on. To atta1n 1~9C~3~
Il homogeneity, it i~ nece~sary to increase the temperature of ¦I the molten glas to provide thermal current~ in the molten body.
This re~ults in a mixing of ~he molten makerialg and the compo-I ~ition thu~ become~ more homogeneou~. Diffusion of the cations ¦¦ increaae3 at the higher temperatures to al~o increa~e the ¦ homogeneity of the molten ma~s.
¦ Removing the molten ma~s from the melting tank require, the molten ma~s to have certain characteri~tics, as I for example, a sufficiently low visco~ity to permit the gla~
il ~o flow out of the tank. Agaln, the~e flow characteri~tic~ can ¦¦ be obtained by attaining su~ficiently high temperature~ in the melt. The temperature6 required for obtaining homogeneity o~
the conventional glas~ compo~itions and ~or obta~ing the : ¦ required degree of fluidity are ~ub~tantially the ~ame, although the temperature for attaining homogeneity may be 61ightly higher.
The level of temperature re~uired to obtain homogenaity o~ the I conventional glas~ composition~ or for obtaining the nece~ary 1~ fluidity for conventional glass compo~ition~ i~ much lower than the temperature required to attain both the homogeneity and fluidity of gla~ses containing above ~0 percent ~illca or having i, ' - -
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above 90 percent by weight of a combination of silica and alumina. In fact, the necessary high temperature to obtain both fluidity and homogeneity of the above high silica glass compositions cannot be commercially obtained in existing melting tanks now in common use.
In copending Canadian application, Serial No.
277,327 filed April 29, 1977, entitled "A Pulverulent Borosilicate Composition And A Method Of Making A Cellular Borosilicate Body Therefrom", there is disclos~d a process for preparing a cellular body from high silica borosili-cate glass which includes preparing an aqueous slurry from an intimate mixture of colloidal silica, caustic potash, boric acid and alumina. The slurry is dried, and the aggregates are comminuted and thereafter calcined and rapidly quenched to form a ceramic frit. The ceramic frit is thereafter comminuted and mixed with a cellulating agent and introduced into a cellulating furnace and subjected to cellulating temperatures to form cellular bodies.
The high silica borosilicate cellular body form-ed according to the process set forth in the above copend-ing application has the desirable properties of resisting . ,, - .
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ll l de~radation by an electrolytic salt bath and corrosive gase~
at elevated temperatures. The cellular body further retains physical integrity, especially in3ulating propertie~, under a 1 load of about 17 p.~.i. at abou~ 700C.
I The above proces~ now make3 it pos~lble to obtain cellular ceramic bodie~ which have the above desirable prop-~1 ertie~ without the use of a melting tank. The proces~ asdescribed, however, requires calcining the entire batch and j rapidly quench~ng the calcined material. As ~tated in the 1 specification, it is preferred to use a pla~ma arc flame to ~ calcine and rapidly quench the frit to prevent devitrification 1' of the calcined material. There is a need to obtain a high silica borosilicate cellular body that ha3 the abov~-discussed desirable properties without calcining the glass batch.
A~te~pts have also been made in the pa~t to make celluIar ceramic bodie~ from either naturally occurring gla~es ~uch as volcanic ash or from other materials that contain silica.
I / For example, United State~ Patents 2,466,001 and 3,174,870 dis-i l close processes for making cellular products from volcanic a~h, 20 1I feldspar and granite. United States Patent 3,441,396 d$~clo~e~
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¦ a proces~ for making cellular material~ from pulverulent ¦~ materials that include fly a~hO None of the~e processes how-ever are directed to a proce~ where a cellular body is forme~
¦ from a high borosilicate composition such a~ a compo~ition con-, taining more than 80% by weight silica.
1,' SUMM~RY OF THE INVENTIQN
This invention i~ directed to a method of making a . cellular body from a high silica boro~ilicate gla~s compo-~ ion by preparing a pulverulent homogeneou~ mixture from , constituents comprising amorphous ~ilica, alumina, boric oxide, alkali metal oxide and a cellulating agent with the mixture con-taining more than 80% by weight amorphous silica. The pulver-I ulent homogeneou~ mixture i~ thereafter sub~ected to a tem-¦' perature suf~icient to coalesce the homogeneous mixture and Il gasify the cellulating agent to form a cellular body having a ¦I substantially uniform cell structure. The con~tituents of the ¦I pulverulent homogeneou~ mixture expressed in weight percent and a~ oxide~ compri~es between about 80 and 88% amorphou~ slllca ¦ with about 88~ by weight amorphou~ silica being mo~t preferred, j about 4~ alumina, between about S and 13~ boric oxide with about 7~ boric oxide being mo~t preferred and bet~een about 1 and 3-, ,, f .
l l alkali metal oxide with about 1~ alkali metal oxide being most ! preferred. The cellulating agent in the admixture expresseda~ a percent by weight of the other constituents comprise~
between about 0.2% and 0.5~ carbon with about 0.4~ carbon being 1, prePerred and between about 0.3% and 0.8~ antimony trioxide with about 0.5~ antimony trioxide being preferred. A portion of the cellular body formed ~rom the above mixture may be co~-minuted and added to and mixed with the pulverulent homogeneou~
mixture. It is preferred to mix between about 15 to 40~ by ¦ weight of the comminuted cellular body with between about 60 to , 85% by weight of the pulverulent homogeneou~ mlxture.
" In one embodiment the constituent6 are intimately mixed as a slurry and the slurry is thereafter dried to form particles of the solid constituents in the ~lurry. The ~olid constituents or aggregates are thereafter comminuted to a relatively fine size and introduced into the cellulating furnace. The comminuted aggregates or particles, hereinafter referred to a~ the pulverulent batch, i~ subjected to elevated ~ cellulating temperature~ within the cellulatiny furnace to 1 coale~ce the pulverulent batch and gasify the cellulating agent and form a foam-llke mass having a nonuniform cell structure.
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The foam-like mass is thereafter comminuted to form a pre-cellulated material which i8 mixed with additional cellulating agent. The mixture of precellulated material and cellulating ¦1 agent i9 thereafter subjected to a temperature sufficient to ¦I coale6ce the precellulated material and ga~ify the cellulating agent and cellulate the precellulated material to form a cel-lular body having ~ubstantially uniform cell ~tructure.
¦ In another embodiment alumina, boric oxide, alkali metal oxide in the form of potassium carbonate and a cel-~ lulating agent are comminu~ed to form a fir~t mixture. There-after amorphou~ silica is added to the first mixture to form a eecond mixture that contains more than 80~ by weight amorphous silica. The secona mixture is further mixed to form an intimats homogeneou~ mixture. The second mixture i~ heated to an elevated i temperature ~ufficient to coalesce the second mixture and gasify the cellulating agent and form a cellular body having a ~ub-stantially uniform cell struct~tre. A portion of the cellulax body may be comminuted and added to the irst mixture before the I amorphou~ silica i~ added to the first mixture to form the second mixt~re.
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l, ~ lore specifically the mixture of alumina, boric oxide, alkali metal carbonate, a cellulating agent and a por-tion of the scrap trimming~ from previou~ly cellulated material are introduced into a ball mill and subjected to comminution for a ~ufficient period of time to intimately mix the con-stituents and form a first mixture containing a preselected amount of comminuted scrap trimmings. Thereafter amorphous silica is added to the fir~t mixture in the ball mill to form a second pulverulent mixture. The ~econd pulverulent mixture is thereafter positioned in ~uitable covered mold~ and intro-duced into a cellulating furnace. The mold~ are immediately subjected to a temperature of 1200C and maintainsd at that temperature until the carbon is fixed in the mixture. The tem-perature of the furnace is ~hen increased at a pre~elected rate to about 1390C, where it is maintained for a ~ufficient period of time to coalesce the mixture and gasify the cellulating ag~nt and form a cellular body that ha~ a ~ubstantially uniform cell structure. Thereafter, the temperature to which the cellular body is 3ubjected is rapidly reduceù to a temperature of about I' .
, , - 13 -I' 10~0832 I,i ,, 760C whexe it is maintained for a sufficient period of time to permit the cellular body to cool. The cellular body i~
thereafter ~lowly cooled from 760C to a~bient temperature and trimmed and shaped to form a cellular body having a desired configuration.
¦ ~RIEF DESCRIPTION OF THE DRAWINGS
I Figure 1 is a flow diagram of the proce~s for making the cellular body in which the constituent~ are admixed in li ~lurry form, dried and comminuted before they are introduced 1' into the cellulating furnace.
i Figure 2 is a flow diagram of the proces~ for making ! the cellular body from a composition in which the con~tituent~
are admixed and comminuted in a ball mill before being intro-duced into a cellulating furnace.
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DESCRIPTION OF T~E PREEERRED_EMBODIME~TS
¦ The process for making cellular bodie~ from high , silica borosilicate glass compositions includes first forming a boric acid solution by admixing boric acid and water at an I elevated temperature in a suitable container 10. A heater 12 ¦ may be employed to elevate the temperature of the water to dissolve the boric acid and form a solution thereof.
~ In a ~eparate mixing tank 14, an a~ueou~ slurry is ¦ formed of silica (preferably an amorphous, precipitated, I hydrated silica), an alkali metal hydroxide in the form of KOH, I alumina (preferably in the form of an alpha monohydrate) and ¦ cellulating agent~, i.e. carbon black a~d antimony trioxide.
il Sufficient alkali metal hydroxide is added to the slurry to provide a p~ of about 10. The slurry is subjected to high shear mixing by the mixer 16, and a preselected amount of boric acid solution is introduced into the mixer 14 through a conduit 18 and controlled by valve 20. After the bor~c acid solution is added and mixed again by high shear mixing with the ~lurry, l~ additional silica i8 added to the slurry until the ~lurry con-tains about 22 percent solids by weight.
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,, il ¦ A ~uitable compo3it:ion for making the precellulated material for the process conC;ists of the following range of con-stituents expressed in percent by weight. The cellulating agent~, i.e. the Carbon Black and Sb2O3 are expre~ed in weight pexcent of the other con~tituents.
80 - 88 SiO2 S - 1~ B2O3 j 4 A12O3 0.5 Carbon Black i 0.5 sb23 It should be understood that other type~ of cellulating , agents may also be employed to provide the nece~sary gases during the cellulation proce~s for providing the high ~urface area during cellulation. It has been found, ho~ever, that the preRence of a ¦ cellulating agent that is a mixture of carbon, preferably channel Il carbon, and antimony trioxide inhibit~ sub~tantially the <trans-¦, formation of the material to cristobalite after heating. The ¦1 antimony trioxide is also believed to serve as a flux or provide ~ a fluxing action and thu~ causing a foaming action as the tem-p~rature increases during cellulation. Throughout the 3pecifi-` cation, the term~ cellulating agent and cellulating agent~ are j u~ed interchangeably to de~ignate a material or mixture of mate-I rials that gasify during the cellulation proces~. Channel carbon ¦¦ also known as channel black i~ carbon manufactured by the incom-¦ plete com~ustion of natural ga~ collected on a cold channel.
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, jl The ~lurry, after the high shear mixing in mixer 14, ¦ is withdrawn therefrom through conduit 22 and introduced into a drier 24. The drier 24 may be any conventional drier, how-ever, a spray drier is preferred which remove~ the water from the slurry and forms discrete Rpherical agglomerate~. Where a i! conventional pan drier i8 employed, the dried agglomerates are I introduced into a crusher 26 through conduit 28 where the j agglomerates are reduced to a size suitable for cellulation in li the cellulating furnace 30. It has been found that ~pray drying 1~ form~ ~pherical particles having a size le~s than 20 mesh Tyler Standard Screen, and the drying i8 fast enough to retain the ¦I B203 on the particles. ~here pan drying i8 emplo~ed, a drying temperature schedule must be employed to retain the ~23 on the I aggrega~es. Therefore, although the crusher 26 is illustrated Il in the drawing where particles of a suitable size are obtained, ¦I the crusher 26 may be omitted.
'~ A portion of the pulverulent batch from the crusher is preferably positioned in a container and conveyed by conveyor 32 to the cellulating furnace 30. Within the cellulating furnace 30, the pulverulent batch in the container i~ ~ub~ected to a - 17 ~
heating schedule which include~ 6ubjecting the pulverulent batch to a temperature of about 1450~C for a pre~elected period of time, a~ for example, 90 minutes. While ~ubjected to the cellulating temperature, the pulverulent batch coalesce~ and cellulates to form a foamed ma g having a nonuniform cellular structure with a den~ity of about 25 lb~./ft~ The container with the foamed mass is withdrawn ~rom the cellulating furnace by conveyor 34 and the foamed mass is introduced into a crusher mixer 36. The cru~hed foamed mass is referred to as precellu-lated material. Additional cellulating agents, ~uch as carbon and antimony trioxide, are introduced into the cru~her mixer 36 and are mixed with the precellulated material. Where desired, the precellulated material with the added cellulating agents may be withdrawn from the cru~her mixer 36, positioned in a container and introduced by conveyor 38 to the cellulating furnace for a second cellulation step. The product obtained i~ a cellular body having a substantially uniform cell structure and tha previouily discuised derirable properties.
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The pulverulent batch material from crusher 26 i~
I also introduced by means of conveyor 40 into the crusher mixer 36. The pulverulent batch and precellulated material are admixed in mixer 36 in pre~elected proportions with the addi-tional cellulating agents and introduced through conveyor 38 to i the cellulating furnace 30. It ha~ been found that a mixture of between 70 and 80 percent by weight pulverulent batch and between 20 and 30 percent by weight precellulated material will I¦ cellulate in furnace 30 and form cellular bodie~ having sub~tan-¦I tially uniform cells and the previou~ly discussed de~irableproperties. The mixture introduced into the cellulating furnace 1, 30 through conveyor 38 may be subjected to substantially the ¦1 6ame heating schedule as the precellulated material.
The silica in the above-described borosilicate compo~i~
,I tion is preferably a colloidal silica o~ a micron ~ize. A fumed ¦I silica formed by the burning o~ SiFL4 or SiCL4 may be used. A
i preferred silica i8 an amorphous, precipitated, hydrated ~ilica ¦~ ~old by PPG Industries, Pittsburgh, Pennsylvania, under the txade-11 mar~, Hi-Sil-EP. This amorphous, precipitatedt hydrated silica ha~ a surface area (B. E. ~.) of between 50 - 70 sq. m./gm. A
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typical analysi~ of this amoxphous, precipitated, hydrated ~ilica is as follows: ¦
~I SiO2 (as ~hipped, dry ba~i~) 94.
¦' NaCl 1.7 CaO 0.80 ~
R2O3 (Fe ~ Al) 0.63 %
pH in 5% Water Suspen~ion 7.0 %
¦ Loss at 105C (a~ shipped) 5.3 Il Cu and Mn ~Combined Total) 0.003~
~I Surface Area (B. E. T.) 60 ~q. m./gm.
Ultimate Particle Size 0.04 micron~
Refractive Index 1.45 i DBP Absorption 182 ml/100 gm.
Retained on 325 ~e~h 0.3 (pellet~) 0.07 (powder) Il It is believed that the high sur4ace area o~ the ¦l amorphouR, precipitated silica contribute~ ~ubstantially to i forming an intimate admixture with the alumina and further pro-vides a eub~tar~tial area that may be coated with B203 flux.
l Another type o~ amorphous ~ilica which is auitable for u~e in the above de~crlbed boroeilicate composition ie an amorphou~
~, ~
, I' - 20 ~
9~33~
silica sold by Cabot Corporation, Boston, Massachusetts, under the trademark CAB-0-SIL.
Any suitable alumina of colloidal size may be used as a constituent for the borosilicate composition. A
preferred alumina is a pseudo-boehmite or alpha monohy-drate of colloidal size. The boehmite is prepared by the thermal dehydration of a gibbsite (bayerite, an amorphous aluminum hydroxide). The material has a range of surface areas from 15 m2/g to 400 m2/g. The preferred alumina sold by Kaiser Chemicals, Baton Rouge, Louisiana, under the trade name, Substrate Alumina - sa, has a B. E. T. of between 300 - 350 m/g. The typical chemical analysis of the alumina is as follows:
Na20 (as is) 0.01,o - 0.086 Bayerite (as is) 0.000~O - 3.00~O
Fe203 (1000 C) 0~020~o - 0.02~o Sio2 (as is) 0.100Yo - 0.10,o C1 (as is) 0.010o - 0.01~o S04 (as is) 0.050o - 0.05~O
A123 Remainder lO9D83~:
¦ ~he typical physical propertie~ of the alumina are a~ followQ:
Bulk den~ity, lbs/ft, calcined at 1100F -12.5 - 17.
Surface Area (1100~F, 1 hr), m /gm -Pore Volume ~15,000 psia, 1100F, 1 hr) cc/g -1.5- ~.,0 Los~ on ignition, ~ (from ambient to 1000C) -The alumina is principally used as a catalytic grade alumina substrate which is formed into spheres, extrudated, or l tabulated. The alumina i~ a high-chemical purity alumina powder I having a low density and high surface area which can be formed Il into a varie~y of shapes ready for impregnation with a variety Il of active catalytic agents. One of the principal function~ of ¦ the colloidal alumina in the borosilicate composition i8 to min-imize devitrification of the composition sub~e~uent to calcination.
1~90~32 I
The alkali metal oxide i5 preferably pota~sium hydroxide since the potas~ium ion ha~ several advantageous properties. Since the potassium hydroxide i~ strongly basic, it increases the pH of the slurry to facilitate forming a high ¦' ~olids slurry from the con~tituents. The pota~ium hydroxide ¦I further serve~ as a flux in the composition; and of greater !1 importance, however, it increases the corro~ion re~istance of the boroRilicate composition. With the potassium in the composi-1~ tion, the cellular borosilicate body has a greater resistance ¦, to corrosion by non-ferrous liquids, ~he potaRsium further serve~ as a poison to the reaction between the ~ilica and non-ferrous liquid metal~.
I The boric acid in the form of B203 is ab~orbed onto ¦~ the surface of the colloidal particles and serves a~ a flux in the composition. The B203 i~ preferably eupplied a~ a boric ucid solution to the ulurry.
'.
i 1~90~3Z
EXAMPLES
Example_l ~I The high silica boro~ilicate batch contained the , following con~tituents expres~ed a~ oxide~ and in part~ by weight:
88.0~ SiO2 ll 4.0~ A123 ¦ 6 ~ B203 ,. 1 % KOH
10~l O.S~ Carbon Black 1, 0.5~ Sb23 ll ¦I The boric acid wa~ dissolved in hot water to form a ¦ boric acid ~olution. The potas~ium hydroxide waY di~solved in water. The SiO2, KQH, A1203, C and Sb203 were mlxed in a high ~hear mixer; and the boric acid solution waB added thereto.
, After thorough mixing, the material wa~ dried in a drum drier until it contained about 2 pe~cent water by weight. The dri~d ', material wa3 ground in a ball mill until the pulverulent gla~s 1, batch had an average particle ~ize of about 2.5 micron~. The ground materiaI wa~ positloned iD a graphlte tray and then , , I .
. jl ,.
1, .
I - 2~ -83'~ 1 ll ¦ compacted by mechanical shak:ing. The tray was covered with a ~I graphite plate a~d introduced into an electrically fired cel-!i lulating furnace. The tray with the pulverulent glas~ batch ¦ was subjected to the following heating schedule in the cel-lulating furnace: An initlal temperature of 1200C at which .
temperature the material was maintained ~or about one-half hour.
Thereafter, the temperature within the furnace wa~ rai~ed to 1450C and held at that temperature for about 90 min~tes. The Il temperature of the furnace wa~ then reduced to 1200C, and the I tray was removed from the furnace at that elevated temperature.
Il The foamed ma~s within the graphite tray was then, after cooling, placed in a crusher mixer and .4 percent by weight carbon and .5 i percent by weight antimony trioxide based on the weight of the foamed ma~3 wa~ added thereto to fo~ a precellula~ed material.
~, The precellulated material wa~ crushed and muxed in the ball ¦¦ mill until an average particle size of about 2.5 micron~ wa~
- ¦¦ obtained. The precellulated material wa~ then placed in a i graphite tray and compacted by mechanical ~haking. The tray ¦ was introduced into a cellulating furnace and ~ubjected to aub-2D stantially the same heating ~chedule. After romcval ~rom the .~ I v !
' ~0901~3Z
!
furnace, the graphite tray wa~ insulated to permlt 810w cooling of the cellulated body.
The re~ultant cellular gla~ body was tested and compared with products made from the ~ame gla88 batch by melting and al~o the ~ame gla3s batch by calcinlng. The te~t~ indicated that the product obta$ned by the above-d~cus~ed proces~ had ~ub~tantially ~he ~ame properties as matexial obtained by eith~r melting or calcining.
! Example 2 I
Ij Twenty percent by weight of the precellulat~d material, 'i i.e. th~ material ~ubjected to the ~ingle firing, wa0 admixed with 80 percent by weight of the pulverulent batch obtained from , the ball mill and with about 0.2 percent by weight carbon and ¦¦ about 0.5 percent by weight antimony trioxide. The material was 11 ground in a ball mill to an average particle ~ize of about 2~5 microns and placed in a graphite tray. The tray wa~ po~itioned in a cellulating furnace and subjected to ~ub~tantially the aame ~¦ heating ~chedule and when removed ~rom the furnace was slowly I cooled. The cellular body obtained had ~ub~tantially the same properties as the cellular body obtained by the cellulation of only the pr-!~ellulated mater1al.
, !l In another embodimelnt of this invention, as illu~-trated in Figure 2, the proce~s for making the cellular gla~s bodies from high silica borosilicate compositions includen introducing boric oxide, po~a~sium carbonate, alumina, channel carbon, antimony trioxide and comminuted scrap trimminq~ from previously.cellulated material into a ball mill de~ignated by the numeral 100, The con~tituents are bo~h comminuted and mixed in the ball mill for a sufficient period of time, a~ for example BiX hours, until a homogeneou~ admixture of the~e con- ¦
6tituent5 iB formed. The constituent~ after milling have an average particle ~ize of bet.ween about 1 and 4 microns a~
measured by Fi~her Subsieve apparatus. Where desired the com-minuted scrap trimmings may be omitted from the fir6t mixture.
Thereafter, amorphou~ silica i~ $ntroduced into a ball mill 100 and mill~d with the ~bove de~cribed first mixture for a ufficient period of time to form a homoganeou~ ~econd mixture containing the c4nstituents of the Pir~t mixture and the silica. The ~econd mixture also ha~ an average particle size of be~ween about 1 and 4 microns. It i~ believed that the u~e of the amorphous silica and the extending mixing and milling of the constituents in the ball mill re~ults in a mixture which is i~otropic and has a degree of homogeneity compara~le to that which can be obtained by melting.
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., , ~ 27 -~ ` ~
~0~083Z
¦1 A ~uitable composition for the constituent~ excluding the cellulating agent and the comminuted ~crap trimmings may be the ~ame a~ the range of con~tituents previoucly de~cribed.
The following i~ a preferred range of the constituent~ expre~ed a~ oxides and in percent by weight:
85 - 88 SiO2 ¦1 4 A123 1 - 1.5 X2o 1 6 - 10 82o3 The most preferred composition o the con~tituent~
I excluding the cellulating agent and the scrap trimmings consi~t~
I ¦ of the ~ollowing expressea a~ oxide~ and in percent by weight:
SiO2 ~8 ¦ A123 4 ll K20 : B2O3 7 : I The Si02 in the above compo~ition i~ prefer~bly an amorphou~, precipitated, hydrated silica previously descrlbed and the al~ina i5 preferably the alpha monohydrate previou~ly de~crlbed.
1l .
, ~1 - 28 -ll l ~-lO90h3Z
I The amount of comminuted ~crap trimmings introduced ¦ into the first mixture i9 between about 15 and 40~ by weight I of the above compo~ition including the silica. The scrap I trimmings are introduced into the mill with the alumina, alkali metal oxide, boric oxide and the cellulating agent. A more pre-ferxed range of scrap trimming~ i between about 20 and 30%.
The mo t preferred i~ about 25~ by weight o~ the scrap trimmings.
The amount and composition of the cellulating agent ~ expressed in percent by weight of the above enumerated com-, position and qcrap trimmings con3i~ts of the following con-~tit-uent~ in the following amount~:
j Carbon 0.2 - 0.5%
23 0.3 - 0.8%
The preferred amount of the cellulating agent based I on the percent by weight of the abovc con~tituents and ~crap ¦ trimmings is:
I Carbon 0.4~
23 0-5%
I The second mixture including the oxide~ above enumer-j ated, the cellulating agent and the ~crap tri~mings is intro-¦ duced by means of a vibratory feeder into a graphite mold to pxovide an even packing denfiity of the second mixture in the graphite moLd. The mold is preferably covered w1th a graphite !l lid and introduced into a c:ellulating furnace 102. The graphite mold with the homogeneous ~econd mixture po~itioned therein, upon being introduced into the cellulating furnace 102 wa~
immediately subjected to a temperature of 1200C and held at !' that tempera~ure ~or a ~ufficient period of tlme to rapidly ¦ elevate the temperature of the second mixture above the carbon fixation thre~hold temperature and thus minimize the oxidation of the cellulating agent.
I It has been observed ~hat the carbon in a pulverulent I mixture oxidizes substantially faster than carbon fixed in a glas~ structure. It i~ believed that the carbon i8 rapidly fixed in a pulverulent mixture and the oxidation of the carbon is minimized when a mixture i~ introduced into a cellulating furnace which i8 at a temperature of at lea~t 1200C. The tem-1 perature at which the carbon is fixed in the mixture i~ de~ig-¦l nated as the "carbon fixation threshold temperature".
¦I The mold with the pulverulent ~econd mixture therein ¦1 is ~ubjected to a temperature of at least 1200C to attain the il carbon fixation threshold temperature and to fix the carbon ~ within the mixture. For a mo d having a height of ~bout i Il , ,1 .
83'~
,1 1 . I
3 inches, the time to attain the carbon fixation thre6hold temperature ranye~ between about 3 and 6 minutes. It should ~e under~tood, this time will vary depending upon the YiZe and height of the mold.
Afte~ attaining the carbon fixation threshold tem-perature, the temperature of the furnace i~ increased from 1200C to a temperature of about 1390C. It i~ de~irable to slowly rai~e the temperature from 1200C to 1390C over a period of about 35 minutes. Again the time to rai3e the tem-perature will depend on the size of the mold and the thermal inertia of the material. The temperature of the furnace i~
maintained at about 1390C for a sufficient period of time to soften and coalesce the mixture in the mold and form a body having a substantially uniform cell ~tructure. It has been found that the material will cellulate in a period of about 60 minutes at the above temperature. It ~hould be understood, however, that temperature~ and time~ for cellulatlon and carbon fixation are dependent on thermal lnertia, that i~, the temperatures and time~ depend on the size of the mold and th~
power of the furnace. It i~ highly desirable, however, to dis~olve the pulverulent material at a relatively rap$d rate to prevent dev1trif1cation.
,~ '.
Il - 31 -11)9083Z
After the cellular body i~ formed within the mold, it i preferred that the temperature i8 rapidly reduced to about 760~C and maintained at that temperature for a ~ufficient period of time to permit the cellular body to cool. The cel-lular body i~ thereafter slowly cooled from 760C to ambient temperature. Preferably, the mold with the cellular body therein i~ ~rapped in zuitable insulation to ~lowly cool the cellular bodie~ therein to ambient temperature. Where desired after the cellular body is formed within the mold the temperature may be rapidly reduced to about 1100C and when that temperature i8 reached the mold i8 removed from the furnace and permitted to 810wly cool to ambient ~emperature.
After the cellular bodies are cooled to ambient I temperature, the cellular bodies are removed from the mold and then introduced into a ~uitable ~haper 104 euch ~8 saw devicee or the like where the cellular bodies are trlmmed and fini~hed to a pre~elected configuration. The scrap trimmings are removed ¦ $rom the shaper and introduced into a cru~her 106 where the scrap tri~nings are co~ninuted before they are introducQd lnto the ball mill. A~ previou~ly di~cus~ed, preselected amounts of comminuted scrap trimmings from the cru~her 106 are introduced into the ball mill 100 to be admixed with the constituents thereln a~ previou~ly deecribed.
l ~
¦I The shaped cellular bodie~ made from the preferred ¦I compo4itions have the following physical properties:
Average Densi-ty 25 pcf Compre~ive Strength 600 p8i Flexural Strength 200 p8i Elastic Modulus 600,000 p~i Coefficient of 13 - 16 x 10-7/C
Thermal Expan~ion The cellular ~odie~ had the following thermal con-ductivlties expressed in watt~/meter/K at the following mean temperature~ in degrees centigrade:
Thermal Conductivity Mean Temperature C
Il 24 .155 : 1 246 .205 1~' 468 .285 1! 69~
The apparent vi~c08ity points for the cellular I ma~erial are as follows:
I ~ C _ Strain Point (n = 1014-5 poi~e) 1081~1124 583-607 Anneallng Point (n ~ 1013 poise)1234-1~65 668-685 Softening Point (n = 107~6 poise)2078-2177 1137-1192 r , I I
~9~0832 l I
Exam~le 3 The high borosilicate mixture contains the following con~tituents expres~ed a~ oxides and in parts by weight:
88% SiO2 j 4~ A12O3 ! 1~ K20 7% ~23 ¦ Scrap ri~uning~ of previou~ly formed cellular bodie~
I in an amour~t of 25~s by weight of the above mixture are added 10 I thereto. The cellulating agent expre~ed in part6 by weight of the above mixture and ~crap trimmings added to the mixture included 0.4~ by weight channel carbon and 0.5~ by weight ¦ sb2o3.
' The boric oxide, potassium carbonate, alumina, channel carbon, antimony trioxide and comminuted scrap trimming~ were ¦l introduced into a ball mill and were ~ub~ected to comminution ¦i and mixing in the ball mill for a period of about six hour~.
¦¦ Thereafter the amorphouY ~ilica was introduced into the ball Il mill and milled with the fir~t mixture and comminuted scrap 1 trimmings for a period of about two hours. A~ter milling for two hours, the second mixture was ~creened through a 40 me~h screen to remcve chlps from the balls Ln the bell mlll.
Il I
Il .
, .
~ - 3~ -I ~09C~83'~ 1 I . i The mix was stored in premeasured batches in plastic bags to minimize moisture absorbtion during ~torage. Fourteen pound~ of the mixture was introduced by means of a vibratory feeder into a rectangular graphite mold h~ving d~men~ioni of about 20" x Z4" x 3". The vibratory feeder introduced the pul-verulent material into the graphite mold and provided an even packing density. A graphite cover wa~ po~itioned on top of the mold and the mold was introduced into a cellulating furnace. The cellulating furnace was at a temperature of 1200C and the mold wa~ immediately subjected to that elevated temperature for a period of about three minutes when the material attained a car-bon fixation threshold temperature. Thereafter, the temperature of the mold was ilowly increased from 1210C to 1390C. The period of time required to attain the higher temperature was approximately 3S minute~. The mold wa~ maintained at 1390C for a period of 60 minutes during which the mixture coalesced and gasified the cellulating agent to form a cellular body. Sub~-quently, the temperature of the mold wai reduced to 1093C a~
rapidly as practical and wa8 removed from the furnace and per-mitted to co~ll at a controlled rate to amoient temperaturo du~ing Il ~
Il I :, . - 3S -. ~
091~3~
a period of about 12 hour~, After removal from the furnace the mold~ are covered with .in~ulatiny material to control the rate of cooling.
The shaped cellular body wa~ then removed from the mold and aubjected to ~haping in which a portion of the top surface of the cellular body wa~ trimmed and the ~ides and face~ were trimmed to expo~e the cellular structure. The scrap trimming~ were returned to a crusher for later use in making additional cellular bodies.
The resultant cellular bodies were te~ted in a similar manner as exampleg 1 and 2 and the te~t~ indicated the product had the physical properties previou~ly enumerated.
Example 4 ! The percent by weight of scrap trimmings from pre-viously formed cellular bodie~ was reduced to about 20 percant by weight of the other constituents and the channel carbon in the cellulating agent wa~ increa~ed to 0.5~ by weight. Sub-stantially the ~ame proce~ ~tep~ were ~ollowed as ~et ~orth in example 3 and the resultant cellular bodiea had sub~tantially I the same phy~ical properties as the cellular bodie~ formed in ' example 3 with the exception that the den~ity wa~ ~lightly lower.
' '~
, I - 3 6 109~83Z
Il :
,' Il Example 5 ¦~ The #crap trimmings of previously formed cellular , bodies wa~ increased to an amount of about 30~ by weight of the other constituents and the channel carbon ln the cellulating agent wa3 reduced to about O.35%. Again, ~ub~tantlally the same process steps were followed as ~et forth in example 3 and the l cellular bodie~ formed had substantially the ~ame phy~ical propertie~ as the cellular bodies of example 3 with the Il exception that the den~ity was ~lightly higher.
¦~ According to the provi6ions of the Patent Statute~, jl I have explained the principle, preferred construction and mode of operati~n of my invention and have illustrated and described what I now consider to repre~ent its best embodiments. However, ~¦ it should be w~derstood that, within the ~cope of the appended claims, the invention may be practiced otherwi~e than as specifically il1uLtrated and described.
Il ..
I
Il .
Il .
above 90 percent by weight of a combination of silica and alumina. In fact, the necessary high temperature to obtain both fluidity and homogeneity of the above high silica glass compositions cannot be commercially obtained in existing melting tanks now in common use.
In copending Canadian application, Serial No.
277,327 filed April 29, 1977, entitled "A Pulverulent Borosilicate Composition And A Method Of Making A Cellular Borosilicate Body Therefrom", there is disclos~d a process for preparing a cellular body from high silica borosili-cate glass which includes preparing an aqueous slurry from an intimate mixture of colloidal silica, caustic potash, boric acid and alumina. The slurry is dried, and the aggregates are comminuted and thereafter calcined and rapidly quenched to form a ceramic frit. The ceramic frit is thereafter comminuted and mixed with a cellulating agent and introduced into a cellulating furnace and subjected to cellulating temperatures to form cellular bodies.
The high silica borosilicate cellular body form-ed according to the process set forth in the above copend-ing application has the desirable properties of resisting . ,, - .
.~
li 0~83'~
ll l de~radation by an electrolytic salt bath and corrosive gase~
at elevated temperatures. The cellular body further retains physical integrity, especially in3ulating propertie~, under a 1 load of about 17 p.~.i. at abou~ 700C.
I The above proces~ now make3 it pos~lble to obtain cellular ceramic bodie~ which have the above desirable prop-~1 ertie~ without the use of a melting tank. The proces~ asdescribed, however, requires calcining the entire batch and j rapidly quench~ng the calcined material. As ~tated in the 1 specification, it is preferred to use a pla~ma arc flame to ~ calcine and rapidly quench the frit to prevent devitrification 1' of the calcined material. There is a need to obtain a high silica borosilicate cellular body that ha3 the abov~-discussed desirable properties without calcining the glass batch.
A~te~pts have also been made in the pa~t to make celluIar ceramic bodie~ from either naturally occurring gla~es ~uch as volcanic ash or from other materials that contain silica.
I / For example, United State~ Patents 2,466,001 and 3,174,870 dis-i l close processes for making cellular products from volcanic a~h, 20 1I feldspar and granite. United States Patent 3,441,396 d$~clo~e~
I , ', _ 9 _ j!
:
¦ a proces~ for making cellular material~ from pulverulent ¦~ materials that include fly a~hO None of the~e processes how-ever are directed to a proce~ where a cellular body is forme~
¦ from a high borosilicate composition such a~ a compo~ition con-, taining more than 80% by weight silica.
1,' SUMM~RY OF THE INVENTIQN
This invention i~ directed to a method of making a . cellular body from a high silica boro~ilicate gla~s compo-~ ion by preparing a pulverulent homogeneou~ mixture from , constituents comprising amorphous ~ilica, alumina, boric oxide, alkali metal oxide and a cellulating agent with the mixture con-taining more than 80% by weight amorphous silica. The pulver-I ulent homogeneou~ mixture i~ thereafter sub~ected to a tem-¦' perature suf~icient to coalesce the homogeneous mixture and Il gasify the cellulating agent to form a cellular body having a ¦I substantially uniform cell structure. The con~tituents of the ¦I pulverulent homogeneou~ mixture expressed in weight percent and a~ oxide~ compri~es between about 80 and 88% amorphou~ slllca ¦ with about 88~ by weight amorphou~ silica being mo~t preferred, j about 4~ alumina, between about S and 13~ boric oxide with about 7~ boric oxide being mo~t preferred and bet~een about 1 and 3-, ,, f .
l l alkali metal oxide with about 1~ alkali metal oxide being most ! preferred. The cellulating agent in the admixture expresseda~ a percent by weight of the other constituents comprise~
between about 0.2% and 0.5~ carbon with about 0.4~ carbon being 1, prePerred and between about 0.3% and 0.8~ antimony trioxide with about 0.5~ antimony trioxide being preferred. A portion of the cellular body formed ~rom the above mixture may be co~-minuted and added to and mixed with the pulverulent homogeneou~
mixture. It is preferred to mix between about 15 to 40~ by ¦ weight of the comminuted cellular body with between about 60 to , 85% by weight of the pulverulent homogeneou~ mlxture.
" In one embodiment the constituent6 are intimately mixed as a slurry and the slurry is thereafter dried to form particles of the solid constituents in the ~lurry. The ~olid constituents or aggregates are thereafter comminuted to a relatively fine size and introduced into the cellulating furnace. The comminuted aggregates or particles, hereinafter referred to a~ the pulverulent batch, i~ subjected to elevated ~ cellulating temperature~ within the cellulatiny furnace to 1 coale~ce the pulverulent batch and gasify the cellulating agent and form a foam-llke mass having a nonuniform cell structure.
!
I' ~9~83;Z
The foam-like mass is thereafter comminuted to form a pre-cellulated material which i8 mixed with additional cellulating agent. The mixture of precellulated material and cellulating ¦1 agent i9 thereafter subjected to a temperature sufficient to ¦I coale6ce the precellulated material and ga~ify the cellulating agent and cellulate the precellulated material to form a cel-lular body having ~ubstantially uniform cell ~tructure.
¦ In another embodiment alumina, boric oxide, alkali metal oxide in the form of potassium carbonate and a cel-~ lulating agent are comminu~ed to form a fir~t mixture. There-after amorphou~ silica is added to the first mixture to form a eecond mixture that contains more than 80~ by weight amorphous silica. The secona mixture is further mixed to form an intimats homogeneou~ mixture. The second mixture i~ heated to an elevated i temperature ~ufficient to coalesce the second mixture and gasify the cellulating agent and form a cellular body having a ~ub-stantially uniform cell struct~tre. A portion of the cellulax body may be comminuted and added to the irst mixture before the I amorphou~ silica i~ added to the first mixture to form the second mixt~re.
Il ,, I :
- l ~- ~ l ~
~091~83Z
l, ~ lore specifically the mixture of alumina, boric oxide, alkali metal carbonate, a cellulating agent and a por-tion of the scrap trimming~ from previou~ly cellulated material are introduced into a ball mill and subjected to comminution for a ~ufficient period of time to intimately mix the con-stituents and form a first mixture containing a preselected amount of comminuted scrap trimmings. Thereafter amorphous silica is added to the fir~t mixture in the ball mill to form a second pulverulent mixture. The ~econd pulverulent mixture is thereafter positioned in ~uitable covered mold~ and intro-duced into a cellulating furnace. The mold~ are immediately subjected to a temperature of 1200C and maintainsd at that temperature until the carbon is fixed in the mixture. The tem-perature of the furnace is ~hen increased at a pre~elected rate to about 1390C, where it is maintained for a ~ufficient period of time to coalesce the mixture and gasify the cellulating ag~nt and form a cellular body that ha~ a ~ubstantially uniform cell structure. Thereafter, the temperature to which the cellular body is 3ubjected is rapidly reduceù to a temperature of about I' .
, , - 13 -I' 10~0832 I,i ,, 760C whexe it is maintained for a sufficient period of time to permit the cellular body to cool. The cellular body i~
thereafter ~lowly cooled from 760C to a~bient temperature and trimmed and shaped to form a cellular body having a desired configuration.
¦ ~RIEF DESCRIPTION OF THE DRAWINGS
I Figure 1 is a flow diagram of the proce~s for making the cellular body in which the constituent~ are admixed in li ~lurry form, dried and comminuted before they are introduced 1' into the cellulating furnace.
i Figure 2 is a flow diagram of the proces~ for making ! the cellular body from a composition in which the con~tituent~
are admixed and comminuted in a ball mill before being intro-duced into a cellulating furnace.
', ll - 14 -1090~33Z
~`
DESCRIPTION OF T~E PREEERRED_EMBODIME~TS
¦ The process for making cellular bodie~ from high , silica borosilicate glass compositions includes first forming a boric acid solution by admixing boric acid and water at an I elevated temperature in a suitable container 10. A heater 12 ¦ may be employed to elevate the temperature of the water to dissolve the boric acid and form a solution thereof.
~ In a ~eparate mixing tank 14, an a~ueou~ slurry is ¦ formed of silica (preferably an amorphous, precipitated, I hydrated silica), an alkali metal hydroxide in the form of KOH, I alumina (preferably in the form of an alpha monohydrate) and ¦ cellulating agent~, i.e. carbon black a~d antimony trioxide.
il Sufficient alkali metal hydroxide is added to the slurry to provide a p~ of about 10. The slurry is subjected to high shear mixing by the mixer 16, and a preselected amount of boric acid solution is introduced into the mixer 14 through a conduit 18 and controlled by valve 20. After the bor~c acid solution is added and mixed again by high shear mixing with the ~lurry, l~ additional silica i8 added to the slurry until the ~lurry con-tains about 22 percent solids by weight.
-1(119a~83Z
,, il ¦ A ~uitable compo3it:ion for making the precellulated material for the process conC;ists of the following range of con-stituents expressed in percent by weight. The cellulating agent~, i.e. the Carbon Black and Sb2O3 are expre~ed in weight pexcent of the other con~tituents.
80 - 88 SiO2 S - 1~ B2O3 j 4 A12O3 0.5 Carbon Black i 0.5 sb23 It should be understood that other type~ of cellulating , agents may also be employed to provide the nece~sary gases during the cellulation proce~s for providing the high ~urface area during cellulation. It has been found, ho~ever, that the preRence of a ¦ cellulating agent that is a mixture of carbon, preferably channel Il carbon, and antimony trioxide inhibit~ sub~tantially the <trans-¦, formation of the material to cristobalite after heating. The ¦1 antimony trioxide is also believed to serve as a flux or provide ~ a fluxing action and thu~ causing a foaming action as the tem-p~rature increases during cellulation. Throughout the 3pecifi-` cation, the term~ cellulating agent and cellulating agent~ are j u~ed interchangeably to de~ignate a material or mixture of mate-I rials that gasify during the cellulation proces~. Channel carbon ¦¦ also known as channel black i~ carbon manufactured by the incom-¦ plete com~ustion of natural ga~ collected on a cold channel.
I I .
~09~&~3Z
, jl The ~lurry, after the high shear mixing in mixer 14, ¦ is withdrawn therefrom through conduit 22 and introduced into a drier 24. The drier 24 may be any conventional drier, how-ever, a spray drier is preferred which remove~ the water from the slurry and forms discrete Rpherical agglomerate~. Where a i! conventional pan drier i8 employed, the dried agglomerates are I introduced into a crusher 26 through conduit 28 where the j agglomerates are reduced to a size suitable for cellulation in li the cellulating furnace 30. It has been found that ~pray drying 1~ form~ ~pherical particles having a size le~s than 20 mesh Tyler Standard Screen, and the drying i8 fast enough to retain the ¦I B203 on the particles. ~here pan drying i8 emplo~ed, a drying temperature schedule must be employed to retain the ~23 on the I aggrega~es. Therefore, although the crusher 26 is illustrated Il in the drawing where particles of a suitable size are obtained, ¦I the crusher 26 may be omitted.
'~ A portion of the pulverulent batch from the crusher is preferably positioned in a container and conveyed by conveyor 32 to the cellulating furnace 30. Within the cellulating furnace 30, the pulverulent batch in the container i~ ~ub~ected to a - 17 ~
heating schedule which include~ 6ubjecting the pulverulent batch to a temperature of about 1450~C for a pre~elected period of time, a~ for example, 90 minutes. While ~ubjected to the cellulating temperature, the pulverulent batch coalesce~ and cellulates to form a foamed ma g having a nonuniform cellular structure with a den~ity of about 25 lb~./ft~ The container with the foamed mass is withdrawn ~rom the cellulating furnace by conveyor 34 and the foamed mass is introduced into a crusher mixer 36. The cru~hed foamed mass is referred to as precellu-lated material. Additional cellulating agents, ~uch as carbon and antimony trioxide, are introduced into the cru~her mixer 36 and are mixed with the precellulated material. Where desired, the precellulated material with the added cellulating agents may be withdrawn from the cru~her mixer 36, positioned in a container and introduced by conveyor 38 to the cellulating furnace for a second cellulation step. The product obtained i~ a cellular body having a substantially uniform cell structure and tha previouily discuised derirable properties.
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I
The pulverulent batch material from crusher 26 i~
I also introduced by means of conveyor 40 into the crusher mixer 36. The pulverulent batch and precellulated material are admixed in mixer 36 in pre~elected proportions with the addi-tional cellulating agents and introduced through conveyor 38 to i the cellulating furnace 30. It ha~ been found that a mixture of between 70 and 80 percent by weight pulverulent batch and between 20 and 30 percent by weight precellulated material will I¦ cellulate in furnace 30 and form cellular bodie~ having sub~tan-¦I tially uniform cells and the previou~ly discussed de~irableproperties. The mixture introduced into the cellulating furnace 1, 30 through conveyor 38 may be subjected to substantially the ¦1 6ame heating schedule as the precellulated material.
The silica in the above-described borosilicate compo~i~
,I tion is preferably a colloidal silica o~ a micron ~ize. A fumed ¦I silica formed by the burning o~ SiFL4 or SiCL4 may be used. A
i preferred silica i8 an amorphous, precipitated, hydrated ~ilica ¦~ ~old by PPG Industries, Pittsburgh, Pennsylvania, under the txade-11 mar~, Hi-Sil-EP. This amorphous, precipitatedt hydrated silica ha~ a surface area (B. E. ~.) of between 50 - 70 sq. m./gm. A
., ,, .
Il - 19 -`!
1~91~8~Z
!
typical analysi~ of this amoxphous, precipitated, hydrated ~ilica is as follows: ¦
~I SiO2 (as ~hipped, dry ba~i~) 94.
¦' NaCl 1.7 CaO 0.80 ~
R2O3 (Fe ~ Al) 0.63 %
pH in 5% Water Suspen~ion 7.0 %
¦ Loss at 105C (a~ shipped) 5.3 Il Cu and Mn ~Combined Total) 0.003~
~I Surface Area (B. E. T.) 60 ~q. m./gm.
Ultimate Particle Size 0.04 micron~
Refractive Index 1.45 i DBP Absorption 182 ml/100 gm.
Retained on 325 ~e~h 0.3 (pellet~) 0.07 (powder) Il It is believed that the high sur4ace area o~ the ¦l amorphouR, precipitated silica contribute~ ~ubstantially to i forming an intimate admixture with the alumina and further pro-vides a eub~tar~tial area that may be coated with B203 flux.
l Another type o~ amorphous ~ilica which is auitable for u~e in the above de~crlbed boroeilicate composition ie an amorphou~
~, ~
, I' - 20 ~
9~33~
silica sold by Cabot Corporation, Boston, Massachusetts, under the trademark CAB-0-SIL.
Any suitable alumina of colloidal size may be used as a constituent for the borosilicate composition. A
preferred alumina is a pseudo-boehmite or alpha monohy-drate of colloidal size. The boehmite is prepared by the thermal dehydration of a gibbsite (bayerite, an amorphous aluminum hydroxide). The material has a range of surface areas from 15 m2/g to 400 m2/g. The preferred alumina sold by Kaiser Chemicals, Baton Rouge, Louisiana, under the trade name, Substrate Alumina - sa, has a B. E. T. of between 300 - 350 m/g. The typical chemical analysis of the alumina is as follows:
Na20 (as is) 0.01,o - 0.086 Bayerite (as is) 0.000~O - 3.00~O
Fe203 (1000 C) 0~020~o - 0.02~o Sio2 (as is) 0.100Yo - 0.10,o C1 (as is) 0.010o - 0.01~o S04 (as is) 0.050o - 0.05~O
A123 Remainder lO9D83~:
¦ ~he typical physical propertie~ of the alumina are a~ followQ:
Bulk den~ity, lbs/ft, calcined at 1100F -12.5 - 17.
Surface Area (1100~F, 1 hr), m /gm -Pore Volume ~15,000 psia, 1100F, 1 hr) cc/g -1.5- ~.,0 Los~ on ignition, ~ (from ambient to 1000C) -The alumina is principally used as a catalytic grade alumina substrate which is formed into spheres, extrudated, or l tabulated. The alumina i~ a high-chemical purity alumina powder I having a low density and high surface area which can be formed Il into a varie~y of shapes ready for impregnation with a variety Il of active catalytic agents. One of the principal function~ of ¦ the colloidal alumina in the borosilicate composition i8 to min-imize devitrification of the composition sub~e~uent to calcination.
1~90~32 I
The alkali metal oxide i5 preferably pota~sium hydroxide since the potas~ium ion ha~ several advantageous properties. Since the potassium hydroxide i~ strongly basic, it increases the pH of the slurry to facilitate forming a high ¦' ~olids slurry from the con~tituents. The pota~ium hydroxide ¦I further serve~ as a flux in the composition; and of greater !1 importance, however, it increases the corro~ion re~istance of the boroRilicate composition. With the potassium in the composi-1~ tion, the cellular borosilicate body has a greater resistance ¦, to corrosion by non-ferrous liquids, ~he potaRsium further serve~ as a poison to the reaction between the ~ilica and non-ferrous liquid metal~.
I The boric acid in the form of B203 is ab~orbed onto ¦~ the surface of the colloidal particles and serves a~ a flux in the composition. The B203 i~ preferably eupplied a~ a boric ucid solution to the ulurry.
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i 1~90~3Z
EXAMPLES
Example_l ~I The high silica boro~ilicate batch contained the , following con~tituents expres~ed a~ oxide~ and in part~ by weight:
88.0~ SiO2 ll 4.0~ A123 ¦ 6 ~ B203 ,. 1 % KOH
10~l O.S~ Carbon Black 1, 0.5~ Sb23 ll ¦I The boric acid wa~ dissolved in hot water to form a ¦ boric acid ~olution. The potas~ium hydroxide waY di~solved in water. The SiO2, KQH, A1203, C and Sb203 were mlxed in a high ~hear mixer; and the boric acid solution waB added thereto.
, After thorough mixing, the material wa~ dried in a drum drier until it contained about 2 pe~cent water by weight. The dri~d ', material wa3 ground in a ball mill until the pulverulent gla~s 1, batch had an average particle ~ize of about 2.5 micron~. The ground materiaI wa~ positloned iD a graphlte tray and then , , I .
. jl ,.
1, .
I - 2~ -83'~ 1 ll ¦ compacted by mechanical shak:ing. The tray was covered with a ~I graphite plate a~d introduced into an electrically fired cel-!i lulating furnace. The tray with the pulverulent glas~ batch ¦ was subjected to the following heating schedule in the cel-lulating furnace: An initlal temperature of 1200C at which .
temperature the material was maintained ~or about one-half hour.
Thereafter, the temperature within the furnace wa~ rai~ed to 1450C and held at that temperature for about 90 min~tes. The Il temperature of the furnace wa~ then reduced to 1200C, and the I tray was removed from the furnace at that elevated temperature.
Il The foamed ma~s within the graphite tray was then, after cooling, placed in a crusher mixer and .4 percent by weight carbon and .5 i percent by weight antimony trioxide based on the weight of the foamed ma~3 wa~ added thereto to fo~ a precellula~ed material.
~, The precellulated material wa~ crushed and muxed in the ball ¦¦ mill until an average particle size of about 2.5 micron~ wa~
- ¦¦ obtained. The precellulated material wa~ then placed in a i graphite tray and compacted by mechanical ~haking. The tray ¦ was introduced into a cellulating furnace and ~ubjected to aub-2D stantially the same heating ~chedule. After romcval ~rom the .~ I v !
' ~0901~3Z
!
furnace, the graphite tray wa~ insulated to permlt 810w cooling of the cellulated body.
The re~ultant cellular gla~ body was tested and compared with products made from the ~ame gla88 batch by melting and al~o the ~ame gla3s batch by calcinlng. The te~t~ indicated that the product obta$ned by the above-d~cus~ed proces~ had ~ub~tantially ~he ~ame properties as matexial obtained by eith~r melting or calcining.
! Example 2 I
Ij Twenty percent by weight of the precellulat~d material, 'i i.e. th~ material ~ubjected to the ~ingle firing, wa0 admixed with 80 percent by weight of the pulverulent batch obtained from , the ball mill and with about 0.2 percent by weight carbon and ¦¦ about 0.5 percent by weight antimony trioxide. The material was 11 ground in a ball mill to an average particle ~ize of about 2~5 microns and placed in a graphite tray. The tray wa~ po~itioned in a cellulating furnace and subjected to ~ub~tantially the aame ~¦ heating ~chedule and when removed ~rom the furnace was slowly I cooled. The cellular body obtained had ~ub~tantially the same properties as the cellular body obtained by the cellulation of only the pr-!~ellulated mater1al.
, !l In another embodimelnt of this invention, as illu~-trated in Figure 2, the proce~s for making the cellular gla~s bodies from high silica borosilicate compositions includen introducing boric oxide, po~a~sium carbonate, alumina, channel carbon, antimony trioxide and comminuted scrap trimminq~ from previously.cellulated material into a ball mill de~ignated by the numeral 100, The con~tituents are bo~h comminuted and mixed in the ball mill for a sufficient period of time, a~ for example BiX hours, until a homogeneou~ admixture of the~e con- ¦
6tituent5 iB formed. The constituent~ after milling have an average particle ~ize of bet.ween about 1 and 4 microns a~
measured by Fi~her Subsieve apparatus. Where desired the com-minuted scrap trimmings may be omitted from the fir6t mixture.
Thereafter, amorphou~ silica i~ $ntroduced into a ball mill 100 and mill~d with the ~bove de~cribed first mixture for a ufficient period of time to form a homoganeou~ ~econd mixture containing the c4nstituents of the Pir~t mixture and the silica. The ~econd mixture also ha~ an average particle size of be~ween about 1 and 4 microns. It i~ believed that the u~e of the amorphous silica and the extending mixing and milling of the constituents in the ball mill re~ults in a mixture which is i~otropic and has a degree of homogeneity compara~le to that which can be obtained by melting.
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~0~083Z
¦1 A ~uitable composition for the constituent~ excluding the cellulating agent and the comminuted ~crap trimmings may be the ~ame a~ the range of con~tituents previoucly de~cribed.
The following i~ a preferred range of the constituent~ expre~ed a~ oxides and in percent by weight:
85 - 88 SiO2 ¦1 4 A123 1 - 1.5 X2o 1 6 - 10 82o3 The most preferred composition o the con~tituent~
I excluding the cellulating agent and the scrap trimmings consi~t~
I ¦ of the ~ollowing expressea a~ oxide~ and in percent by weight:
SiO2 ~8 ¦ A123 4 ll K20 : B2O3 7 : I The Si02 in the above compo~ition i~ prefer~bly an amorphou~, precipitated, hydrated silica previously descrlbed and the al~ina i5 preferably the alpha monohydrate previou~ly de~crlbed.
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, ~1 - 28 -ll l ~-lO90h3Z
I The amount of comminuted ~crap trimmings introduced ¦ into the first mixture i9 between about 15 and 40~ by weight I of the above compo~ition including the silica. The scrap I trimmings are introduced into the mill with the alumina, alkali metal oxide, boric oxide and the cellulating agent. A more pre-ferxed range of scrap trimming~ i between about 20 and 30%.
The mo t preferred i~ about 25~ by weight o~ the scrap trimmings.
The amount and composition of the cellulating agent ~ expressed in percent by weight of the above enumerated com-, position and qcrap trimmings con3i~ts of the following con-~tit-uent~ in the following amount~:
j Carbon 0.2 - 0.5%
23 0.3 - 0.8%
The preferred amount of the cellulating agent based I on the percent by weight of the abovc con~tituents and ~crap ¦ trimmings is:
I Carbon 0.4~
23 0-5%
I The second mixture including the oxide~ above enumer-j ated, the cellulating agent and the ~crap tri~mings is intro-¦ duced by means of a vibratory feeder into a graphite mold to pxovide an even packing denfiity of the second mixture in the graphite moLd. The mold is preferably covered w1th a graphite !l lid and introduced into a c:ellulating furnace 102. The graphite mold with the homogeneous ~econd mixture po~itioned therein, upon being introduced into the cellulating furnace 102 wa~
immediately subjected to a temperature of 1200C and held at !' that tempera~ure ~or a ~ufficient period of tlme to rapidly ¦ elevate the temperature of the second mixture above the carbon fixation thre~hold temperature and thus minimize the oxidation of the cellulating agent.
I It has been observed ~hat the carbon in a pulverulent I mixture oxidizes substantially faster than carbon fixed in a glas~ structure. It i~ believed that the carbon i8 rapidly fixed in a pulverulent mixture and the oxidation of the carbon is minimized when a mixture i~ introduced into a cellulating furnace which i8 at a temperature of at lea~t 1200C. The tem-1 perature at which the carbon is fixed in the mixture i~ de~ig-¦l nated as the "carbon fixation threshold temperature".
¦I The mold with the pulverulent ~econd mixture therein ¦1 is ~ubjected to a temperature of at least 1200C to attain the il carbon fixation threshold temperature and to fix the carbon ~ within the mixture. For a mo d having a height of ~bout i Il , ,1 .
83'~
,1 1 . I
3 inches, the time to attain the carbon fixation thre6hold temperature ranye~ between about 3 and 6 minutes. It should ~e under~tood, this time will vary depending upon the YiZe and height of the mold.
Afte~ attaining the carbon fixation threshold tem-perature, the temperature of the furnace i~ increased from 1200C to a temperature of about 1390C. It i~ de~irable to slowly rai~e the temperature from 1200C to 1390C over a period of about 35 minutes. Again the time to rai3e the tem-perature will depend on the size of the mold and the thermal inertia of the material. The temperature of the furnace i~
maintained at about 1390C for a sufficient period of time to soften and coalesce the mixture in the mold and form a body having a substantially uniform cell ~tructure. It has been found that the material will cellulate in a period of about 60 minutes at the above temperature. It ~hould be understood, however, that temperature~ and time~ for cellulatlon and carbon fixation are dependent on thermal lnertia, that i~, the temperatures and time~ depend on the size of the mold and th~
power of the furnace. It i~ highly desirable, however, to dis~olve the pulverulent material at a relatively rap$d rate to prevent dev1trif1cation.
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Il - 31 -11)9083Z
After the cellular body i~ formed within the mold, it i preferred that the temperature i8 rapidly reduced to about 760~C and maintained at that temperature for a ~ufficient period of time to permit the cellular body to cool. The cel-lular body i~ thereafter slowly cooled from 760C to ambient temperature. Preferably, the mold with the cellular body therein i~ ~rapped in zuitable insulation to ~lowly cool the cellular bodie~ therein to ambient temperature. Where desired after the cellular body is formed within the mold the temperature may be rapidly reduced to about 1100C and when that temperature i8 reached the mold i8 removed from the furnace and permitted to 810wly cool to ambient ~emperature.
After the cellular bodies are cooled to ambient I temperature, the cellular bodies are removed from the mold and then introduced into a ~uitable ~haper 104 euch ~8 saw devicee or the like where the cellular bodies are trlmmed and fini~hed to a pre~elected configuration. The scrap trimmings are removed ¦ $rom the shaper and introduced into a cru~her 106 where the scrap tri~nings are co~ninuted before they are introducQd lnto the ball mill. A~ previou~ly di~cus~ed, preselected amounts of comminuted scrap trimmings from the cru~her 106 are introduced into the ball mill 100 to be admixed with the constituents thereln a~ previou~ly deecribed.
l ~
¦I The shaped cellular bodie~ made from the preferred ¦I compo4itions have the following physical properties:
Average Densi-ty 25 pcf Compre~ive Strength 600 p8i Flexural Strength 200 p8i Elastic Modulus 600,000 p~i Coefficient of 13 - 16 x 10-7/C
Thermal Expan~ion The cellular ~odie~ had the following thermal con-ductivlties expressed in watt~/meter/K at the following mean temperature~ in degrees centigrade:
Thermal Conductivity Mean Temperature C
Il 24 .155 : 1 246 .205 1~' 468 .285 1! 69~
The apparent vi~c08ity points for the cellular I ma~erial are as follows:
I ~ C _ Strain Point (n = 1014-5 poi~e) 1081~1124 583-607 Anneallng Point (n ~ 1013 poise)1234-1~65 668-685 Softening Point (n = 107~6 poise)2078-2177 1137-1192 r , I I
~9~0832 l I
Exam~le 3 The high borosilicate mixture contains the following con~tituents expres~ed a~ oxides and in parts by weight:
88% SiO2 j 4~ A12O3 ! 1~ K20 7% ~23 ¦ Scrap ri~uning~ of previou~ly formed cellular bodie~
I in an amour~t of 25~s by weight of the above mixture are added 10 I thereto. The cellulating agent expre~ed in part6 by weight of the above mixture and ~crap trimmings added to the mixture included 0.4~ by weight channel carbon and 0.5~ by weight ¦ sb2o3.
' The boric oxide, potassium carbonate, alumina, channel carbon, antimony trioxide and comminuted scrap trimming~ were ¦l introduced into a ball mill and were ~ub~ected to comminution ¦i and mixing in the ball mill for a period of about six hour~.
¦¦ Thereafter the amorphouY ~ilica was introduced into the ball Il mill and milled with the fir~t mixture and comminuted scrap 1 trimmings for a period of about two hours. A~ter milling for two hours, the second mixture was ~creened through a 40 me~h screen to remcve chlps from the balls Ln the bell mlll.
Il I
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~ - 3~ -I ~09C~83'~ 1 I . i The mix was stored in premeasured batches in plastic bags to minimize moisture absorbtion during ~torage. Fourteen pound~ of the mixture was introduced by means of a vibratory feeder into a rectangular graphite mold h~ving d~men~ioni of about 20" x Z4" x 3". The vibratory feeder introduced the pul-verulent material into the graphite mold and provided an even packing density. A graphite cover wa~ po~itioned on top of the mold and the mold was introduced into a cellulating furnace. The cellulating furnace was at a temperature of 1200C and the mold wa~ immediately subjected to that elevated temperature for a period of about three minutes when the material attained a car-bon fixation threshold temperature. Thereafter, the temperature of the mold was ilowly increased from 1210C to 1390C. The period of time required to attain the higher temperature was approximately 3S minute~. The mold wa~ maintained at 1390C for a period of 60 minutes during which the mixture coalesced and gasified the cellulating agent to form a cellular body. Sub~-quently, the temperature of the mold wai reduced to 1093C a~
rapidly as practical and wa8 removed from the furnace and per-mitted to co~ll at a controlled rate to amoient temperaturo du~ing Il ~
Il I :, . - 3S -. ~
091~3~
a period of about 12 hour~, After removal from the furnace the mold~ are covered with .in~ulatiny material to control the rate of cooling.
The shaped cellular body wa~ then removed from the mold and aubjected to ~haping in which a portion of the top surface of the cellular body wa~ trimmed and the ~ides and face~ were trimmed to expo~e the cellular structure. The scrap trimming~ were returned to a crusher for later use in making additional cellular bodies.
The resultant cellular bodies were te~ted in a similar manner as exampleg 1 and 2 and the te~t~ indicated the product had the physical properties previou~ly enumerated.
Example 4 ! The percent by weight of scrap trimmings from pre-viously formed cellular bodie~ was reduced to about 20 percant by weight of the other constituents and the channel carbon in the cellulating agent wa~ increa~ed to 0.5~ by weight. Sub-stantially the ~ame proce~ ~tep~ were ~ollowed as ~et ~orth in example 3 and the resultant cellular bodiea had sub~tantially I the same phy~ical properties as the cellular bodie~ formed in ' example 3 with the exception that the den~ity wa~ ~lightly lower.
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, I - 3 6 109~83Z
Il :
,' Il Example 5 ¦~ The #crap trimmings of previously formed cellular , bodies wa~ increased to an amount of about 30~ by weight of the other constituents and the channel carbon ln the cellulating agent wa3 reduced to about O.35%. Again, ~ub~tantlally the same process steps were followed as ~et forth in example 3 and the l cellular bodie~ formed had substantially the ~ame phy~ical propertie~ as the cellular bodies of example 3 with the Il exception that the den~ity was ~lightly higher.
¦~ According to the provi6ions of the Patent Statute~, jl I have explained the principle, preferred construction and mode of operati~n of my invention and have illustrated and described what I now consider to repre~ent its best embodiments. However, ~¦ it should be w~derstood that, within the ~cope of the appended claims, the invention may be practiced otherwi~e than as specifically il1uLtrated and described.
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Claims (30)
1. A method of making a cellular body from a high borosilicate composition comprising, preparing a pulverulent homogeneous mixture from constituents comprising amorphous silica, alumina, boric acid, an alkali metal oxide and a cellulating agent, said mixture containing more than 80% by weight amorphous silica, and thereafter subjecting said pulverulent homogeneous mixture to a temperature sufficient to coalesce said homogeneous mixture and gasify said cellulating agent to form a cellular body having a substantially uniform cell structure.
2. A method of making a cellular body from R high borosilicate composition as set forth in claim 1 which includes, subjecting said pulverulent homogeneous mixture to a temperature of between about 1390°C and 1450°C for a sufficient period of time to coalesce said homogeneous mixture and gasify said cellulating agent to form a cellular body having a sub-stantially uniform cell structure.
3. A method of making a cellular body from a high borosilicate glass composition as set fortty in claim 1 which includes, subjecting said pulverulent homogeneous mixture to an initial temperature of at least 1200°C, maintaining said pulverulent homogeneous mixture at said initial temperature until said pulverulent homogeneous mix ure attains the carbon fixation temperature, thereafter subjecting said pulverulent homogeneous mixture to a higher temperature sufficient to coalesce said homogeneous mixture and gasify said cellulating agent to form a cellular body having a substantially uniform cell structure.
4. A method of making a cellular body from a high borosilicate composition as set forth in claim 1 in which, said constituents of said pulverulent homogeneous mixture excluding said cellulating agent and expressed in weight percent as oxides comprise between about 80 and 88 percent amor-phous silica, about 4 percent alumina, between about 5 and 13 percent boric oxide and between about 1 and 3 percent alkali metal oxide.
5. A method of making a cellular body from a high borosilicate composition as set forth in claim 4 in which, said cellulating agent expressed as percent by weight of the other constituents comprises between about 0.2 and 0.5 percent carbon and between about 0.3 and 0.8 percent antimony trioxide.
6. A method of making a cellular body from a high borosilicate composition as set forth in claim 1 which includes, comminuting a portion of said cellular body, mixing between about 15 to 40 percent by weight of said comminuted cellular body with between about 60 to 85 per-cent by weight of said pulverulent homogeneous mixture to form a pulverulent homogeneous mixture containing said comminuted cellular body, thereafter subjecting said pulverulent homogeneous mixture containing said comminuted cellular body to a temperature sufficient to coalesce said homogeneous mixture and gasify said cellulating agent to form a cellular body having a substantially uniform cell structure.
7. A method of making a cellular body from a high silica borosilicate composition comprising, preparing an aqueous slurry from a mixture comprising amorphous silica, alumina, boric acid, alkali metal hydroxide and a cellulating agent, said mixture containing more than 80 par-cent by weight precipitated amorphous silica, drying said slurry and forming particles of the solid constituents in said slurry, forming a pulverulent batch from said particles of the solid constituents in said slurry, thereafter subjecting said pulverulent batch to a temperature sufficient to coalesce said pulverulent batch and gasify said cellulating agent to form a form-like mass having a nonuniform cell structure, comminuting said foam-like mass to form a precellulated material, mixing said precellulated material with said cellulating agent to form a mixture of precellulated material and cellulating agent, and
7. A method of making a cellular body from a high silica borosilicate composition comprising, preparing an aqueous slurry from a mixture comprising amorphous silica, alumina, boric acid, alkali metal hydroxide and a cellulating agent, said mixture containing more than 80 par-cent by weight precipitated amorphous silica, drying said slurry and forming particles of the solid constituents in said slurry, forming a pulverulent batch from said particles of the solid constituents in said slurry, thereafter subjecting said pulverulent batch to a temperature sufficient to coalesce said pulverulent batch and gasify said cellulating agent to form a form-like mass having a nonuniform cell structure, comminuting said foam-like mass to form a precellulated material, mixing said precellulated material with said cellulating agent to form a mixture of precellulated material and cellulating agent, and
Claim 7 - continued thereafter subjecting said mixture of precellulated material and cellulating agent to a temperature sufficient to coalesce said precellulated material and gasify said cellulating agent and cellulate said precellulated material to form a cellular body having substantially uniform cell structure.
8. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 7 which includes, comminuting said particles of the soild consitutents in said slurry to form said pulverulent batch.
9. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 7 which includes, mixing said precellulated material, cellulating agent and pulverulent batch in preselected proportions, and thereafter subjecting said mixture of precellulated material, cellulating agent and pulverulent hatch at a temperature sufficient to coalesce said last named mixture and gasify said cellulating agent and cellulated said last named mixture to form a cellular body having a substantially uniform cell structure.
10. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 9 which includes, mixing between about 20 percent to 30 percent by weight of said precellulated material with between about 70 per-cent to 80 percent by weight of said pulverulent batch.
11. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 7 in which said cellulating agent includes, a mixture of pulverulent carbon and antimony trioxide.
12. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 7 which includes, subjecting said precellulated material and cellulating agent to a temperature of about 1450°C for about 90 minutes to cellulate said precellulated material to form said cellular body.
13. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 12 which includes, subjecting said pulverulent batch to a temperature of about 1450°C for about 90 minutes to form said foam-like mass.
14. A method of making a cellular body from a high silica borosilicate composition as set forth in claim 7 in which said pulverulent batch has an average particle size of about 2.5 microns.
15. A method of forming a precellulated material suitable for cellulation into a cellular body having a substantially uniform cell structure comprising, preparing an aqueous slurry from a mixture comprising amorphous silica, alumina, boric acid, alkali metal hydroxide and a cellulating agent, said mixture containing more than 80 percent by weight silica,
15. A method of forming a precellulated material suitable for cellulation into a cellular body having a substantially uniform cell structure comprising, preparing an aqueous slurry from a mixture comprising amorphous silica, alumina, boric acid, alkali metal hydroxide and a cellulating agent, said mixture containing more than 80 percent by weight silica,
Claim 15 - continued drying said slurry and forming particles of the solid constituents in said slurry, forming a pulverulent batch from said particles of the solid constituents in said slurry, thereafter subjecting said pulverulent batch to a temperature sufficient to coalesce said pulverulent batch and gasify said cellulating agent to form a foam-like mass having a nonuniform cell structure, and comminuting said foam-like mass to form a precellulated material suitable for cellulation into a cellular body having a substantially uniform cell structure.
16. A method of making a cellular body from a high silica borosilicate composition comprising, preparing an aqueous slurry from a mixture consisting essentially of amorphous silica alumina, boric acid, alkali metal hydroxide, and a cellulating agent, said mixture having between 80 and 88 percent by weight amorphous silica, Claim 16 - continued drying said slurry and forming aggregates of the solid constituents in said slurry, comminuting said aggregate to a size of about 2.5 microns and forming therefrom a pulverulent batch, thereafter subjecting said pulverulent batch to a temperature of about 1450°C for a sufficient time to coalesce said pulverulent batch and gasify said cellulating agent to form a foam-like mass having a nonuniform cell structure, comminuting said foam-like mass to a size of about 2.5 microns to form a precellulated material therefrom, mixing said precellulated material with about 1 per-cent by weight cellulating agent to form a mixture of precellu-lated material and cellulating agent,
16. A method of making a cellular body from a high silica borosilicate composition comprising, preparing an aqueous slurry from a mixture consisting essentially of amorphous silica alumina, boric acid, alkali metal hydroxide, and a cellulating agent, said mixture having between 80 and 88 percent by weight amorphous silica, Claim 16 - continued drying said slurry and forming aggregates of the solid constituents in said slurry, comminuting said aggregate to a size of about 2.5 microns and forming therefrom a pulverulent batch, thereafter subjecting said pulverulent batch to a temperature of about 1450°C for a sufficient time to coalesce said pulverulent batch and gasify said cellulating agent to form a foam-like mass having a nonuniform cell structure, comminuting said foam-like mass to a size of about 2.5 microns to form a precellulated material therefrom, mixing said precellulated material with about 1 per-cent by weight cellulating agent to form a mixture of precellu-lated material and cellulating agent,
Claim 16 - continued mixing between about 20 to 30 percent by weight of said mixture of precellulated material and cellulating agent with between about 70 and 80 percent by weight pulverulent batch, and thereafter subjecting said last named mixture to a temperature of about 1450°C for a sufficient period of time to coalesce said precellulated material and said pulverulent batch and gasify said cellulating agent and form a cellular body having a substantially uniform cell structure.
17. A method of making a cellular body from a high borosilicate composition comprising, comminuting and mixing constituents comprising alumina, boric acid, alkali metal salt and a cellulating agent to form a first mixture, adding amorphous silica to said first mixture to form a second mixture, said second mixture containing more than 80 percent by weight amorphous silica, and thereafter subjecting said second mixture to a temperature sufficient to coalesce said second mixture and gasify said cellulating agent to form a cellular body having a substantially uniform cell structure.
18. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 which includes, comminuting and mixing said first mixture in a ball mill for a sufficient period of time to form a homogeneous first mixture.
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- -
19. A method of making a cellular body from a high borosilicate composition as set forth in claim 18 which includes, comminuting and mixing said first mixture in a ball mill for about six hours to form a homogeneous first mixture.
20. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 in which, said first mixture has an average particle size between 1 and 4 microns.
21. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 which includes, milling Said second mixture in a ball mill for a sufficient period of time to form a homogeneous second mixture.
_ _
_ _
22. A method of making a cellular body from a high borosilicate composition as set forth in claim 21 which includes, milling said second mixture in a ball mill for about two hours to form a homogeneous second mixture.
23. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 in which, said second mixture has an average particle size between 1 and 4 microns.
24. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 which includes, comminuting a portion of said cellular body, mixing said comminuted cellular body with said first mixture in a ratio of between about 20 to 30 percent by weight of said comminuted cellular body and between about 70 to 80 percent by weight of said second mixture.
25. A method of making a cellular body from a high borosilicate composition as set forth in claim 17 in which, said constituents in said second mixture excluding said cellulating agent and expressed in weight percent as oxides comprise about 88 percent amorphous silica, about 4 per-cent alumina, about 7 percent boric oxide and about 1 percent potassium oxide.
26. A method of making a cellular body from a high borosilicate composition as set forth in claim 25 in which, said cellulating agent expressed as percent by weight of said second mixture comprises about 0.4 percent channel carbon and about 0.5 percent antimony trioxide.
27. A method of making a cellular body from a high borosilicate composition comprising, comminuting and mixing alumina, boric oxide, an alkali metal salt and a cellulating agent in a ball mill for a suf-ficient period of time to form a pulverulent homogeneous mixture having an average particle size of between 1 and 4 microns, thereafter adding amorphous silica to said pul-verulent homogenous first mixture to form a second mixture, said second mixture containing more than 80 percent by weight amorphous silica, milling said second mixture in a ball mill for a sufficient period of time to form a pulverulent homogeneous second mixture, positioning a preselected quantity of said pulverulent homogeneous second mixture in a mold, subjecting said mold to an initial temperature of about 1200°C for a sufficient period of time for said pulverulent homogeneous second mixture to attain a carbon fixation temperature, thereafter subjecting said mold to a cellulating temperature of about 1390°C for a sufficient period of time to coalesce said pulverulent homogeneous mixture and gasify said cellulating agent to form a cellular body having a substantially uniform cell structure.
28. A method of making a cellular body from a high borosilicate composition as set forth in claim 27 which includes, increasing the temperature to which the mold is subjected from 1200°C to 1390°C at a controlled rate of about 5°C per minute.
29. A method of making a cellular body from a high borosilicate composition as set forth in claim 27 which includes, comminuting a portion of said cellular body, mixing said comminuted cellular body with said first mixture in a ratio of about 25 percent by weight of said com-minuted cellular body and about 75 percent by weight of said second mixture, thereafter positioning said second mixture with said comminuted cellular body added thereto in said mold.
30. A method of making a cellular body from a high borosilicate composition comprising, mixing at ambient temperature constituents comprising amorphous silica having particles of submicron size, alumina, boric acid, an alkali metal oxide and a cellulating agent and forming a pulverulent homogeneous mixture, said mixture containing more than 80% by weight amorphous silica and less than 3% by weight alkali metal oxide, and thereafter subjecting said pulverulent homo-geneous mixture to a temperature sufficient to coalesce but insufficient to further homogenize said homogeneous mixture, said temperature being sufficient to gasify said cellulating agent and form a cellular body having a substantially uniform cell structure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US74321876A | 1976-11-19 | 1976-11-19 | |
| US743,218 | 1976-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090832A true CA1090832A (en) | 1980-12-02 |
Family
ID=24987956
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,241A Expired CA1090832A (en) | 1976-11-19 | 1977-11-18 | Method of making a cellular body from a high silica borosilicate composition |
Country Status (2)
| Country | Link |
|---|---|
| BE (1) | BE860993A (en) |
| CA (1) | CA1090832A (en) |
-
1977
- 1977-11-18 BE BE182763A patent/BE860993A/en unknown
- 1977-11-18 CA CA291,241A patent/CA1090832A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| BE860993A (en) | 1978-05-18 |
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