CA2140376A1 - Process for preparing ceramic products - Google Patents
Process for preparing ceramic productsInfo
- Publication number
- CA2140376A1 CA2140376A1 CA002140376A CA2140376A CA2140376A1 CA 2140376 A1 CA2140376 A1 CA 2140376A1 CA 002140376 A CA002140376 A CA 002140376A CA 2140376 A CA2140376 A CA 2140376A CA 2140376 A1 CA2140376 A1 CA 2140376A1
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- CA
- Canada
- Prior art keywords
- ceramic
- acid
- weight
- group
- percent
- 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
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
- C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
- C04B35/632—Organic additives
- C04B35/634—Polymers
- C04B35/63404—Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
- C04B35/63424—Polyacrylates; Polymethacrylates
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
- C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
- C04B35/632—Organic additives
- C04B35/634—Polymers
Abstract
A method for improving the properties of ceramic green bodies is provided. In particular, ceramic green bodies having improved green strength are provided.
Incorporating certain acid-containing polymers as binders at a level of at least about 1 to about 15, preferably at least about 3 to about 10 percent by weight based on the weight of ceramic particles improves the green strength of the resulting ceramic green bodies.
Incorporating certain acid-containing polymers as binders at a level of at least about 1 to about 15, preferably at least about 3 to about 10 percent by weight based on the weight of ceramic particles improves the green strength of the resulting ceramic green bodies.
Description
PROCESS FOR PREPAR~G CERAMIC PRODUC F5 The present invention relates to a process for ~ie~ g ceramic products. More particularly, the present invention relates to a dry-pressing process for ~iey~illg 5 ceramic products by using selected binders. Ceramic green bodies ~r~ared using these s~lerte.l binders have illl~roved green strength and illl~r~ved green density.
Ceramic materials are often used to l,r~are lightweight, strong, thermally and chemically resistant products useful as chromalo~ hic media, grinding aids, 10 abrasives, catalysts, adsorbents, electronic components, construction colll~nents and mad~ine components.
In the manufacture of ceramic products, ceramic materials in the form of a powder are subjected to elevated pressures to produce what is known as a ceramic15 green body. Methods for romp~cting, or subjecting the ceramic materials to elevated pressures, to produce ceramic bodies include pressing, extrusion, roll compaction and injertion mokling. Pressing methods indude dry ~r~:,sillg, isostatic pressing and semi-wet pressing. Using these methods, ceramic green bodies can be prepared in various shapes and sizes. The size and shape of the green bodies can also be altered by 20 machining, cutting or stamping the green body.
The properties of the green bodies generally affect the ~lo~el Lies of the finalceramic product. The final ceramic product is generally prepared by silllelillg the ceramic green body. If the green density of the ceramic green body is too low, the 25 medhanical properties of the final ceramic product, sudh as hardness, will diminish. If the green strength of the ceramic green body is too low, it becomes difficult orimpossible to process the ceramic green body. Thus, it is desirable to provide ceramic green bodies with increased green densities and green strengths.
One method for increasing green strengths of ceramic green bodies is to use a binder as a processing aid in the preparation of ceramic green bodies. Currently, the primary commercial binders used in the manufacture of ceramic green bodies are polyvinyl alcohol ("PVA") and poly(ethylene glycol) ("PEG"). These binders are somewhat effective at increasing the green strength of ceramic green bodies. However, PEG and PVA suffer from several drawbacks. PEG does not result in particularly good green strength. PVA results in acceptable green strength, but causes a lowering in green -density. Also, these polymers are sensitive to changes in hllmi~lity. Furth~nnore, PEG
and PVA tend to produce a substantial increase in the viscosity of the ceramic slurries contAining them.
Another commonly used binder, which also functions as a dispersant, is lignosulfonate. T ignoslllfonates, also known as lignin sulfonates and sulfite lignins, generally provide sllffi~i~nt green strength to enable hAn~lling of the green bodies.
However, lignoslllfonate suffers from other drawbacks. For example, when ceramicproducts are prepared using lignosulfonate, high levels of sulfurous by-products are liberated when the ceramic is fired. It is desirable to replace lignosulfonates with a binder which m~int~ins or improves the ~lroll~lance while reducing or eliminating the harmful sulfurous by-products. Furthermore, lignosulfonates do not impart sllffiri~nt green strength to ceramic green bodies for the green bodies to withstand milling, drilling, grinding, cutting and other conventional machining pro. P~s~c.
United States Patent 5,215,693 to Lee discloses a method for preparing machinable ceramic products. The method ~ lose~l by Lee uses organic binders such as paraffin wax, thermoplastic polymers such as polymethylmethacrylate/styrene polymers, and other water-insoluble polymers. However, the method lisrlQse~l by Lee has several drawbacks because it requires the impregnation of the binders after the green bodies are formed. Furthermore, the impregnation is generally conducted wi th an organic solvent which increases the time, costs and hazards assori~te-l with the process.
The present invention seeks to ovelcollle the problems assori~tell with the previously known methods. The present invention seeks to provide a process for preparing ceramic green bodies using polymeric additives which (1) provide good dispersant ~ lies; (2) provide good mold release during the ~res~ing stage; (3) impart goQd strength at room temperature as well as at the higher temperatures; (4) provide high green density to the green part; (5) burn-out cleanly in air, and (6) leave low burn out residuals in nitrogen.
In a first aspect of the present invention there is provided a metholl for ~ g ceramic green bodies comprising:
1) forming a ceramic mixture by mixing (a) ceramic partides;
(b) one or more binders sPlP~P~l from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylPni~Ally l-n~At--rated acids, and salts thereof; and optionally, (c) water; and optionally (d) one or more conventional additives;
Ceramic materials are often used to l,r~are lightweight, strong, thermally and chemically resistant products useful as chromalo~ hic media, grinding aids, 10 abrasives, catalysts, adsorbents, electronic components, construction colll~nents and mad~ine components.
In the manufacture of ceramic products, ceramic materials in the form of a powder are subjected to elevated pressures to produce what is known as a ceramic15 green body. Methods for romp~cting, or subjecting the ceramic materials to elevated pressures, to produce ceramic bodies include pressing, extrusion, roll compaction and injertion mokling. Pressing methods indude dry ~r~:,sillg, isostatic pressing and semi-wet pressing. Using these methods, ceramic green bodies can be prepared in various shapes and sizes. The size and shape of the green bodies can also be altered by 20 machining, cutting or stamping the green body.
The properties of the green bodies generally affect the ~lo~el Lies of the finalceramic product. The final ceramic product is generally prepared by silllelillg the ceramic green body. If the green density of the ceramic green body is too low, the 25 medhanical properties of the final ceramic product, sudh as hardness, will diminish. If the green strength of the ceramic green body is too low, it becomes difficult orimpossible to process the ceramic green body. Thus, it is desirable to provide ceramic green bodies with increased green densities and green strengths.
One method for increasing green strengths of ceramic green bodies is to use a binder as a processing aid in the preparation of ceramic green bodies. Currently, the primary commercial binders used in the manufacture of ceramic green bodies are polyvinyl alcohol ("PVA") and poly(ethylene glycol) ("PEG"). These binders are somewhat effective at increasing the green strength of ceramic green bodies. However, PEG and PVA suffer from several drawbacks. PEG does not result in particularly good green strength. PVA results in acceptable green strength, but causes a lowering in green -density. Also, these polymers are sensitive to changes in hllmi~lity. Furth~nnore, PEG
and PVA tend to produce a substantial increase in the viscosity of the ceramic slurries contAining them.
Another commonly used binder, which also functions as a dispersant, is lignosulfonate. T ignoslllfonates, also known as lignin sulfonates and sulfite lignins, generally provide sllffi~i~nt green strength to enable hAn~lling of the green bodies.
However, lignoslllfonate suffers from other drawbacks. For example, when ceramicproducts are prepared using lignosulfonate, high levels of sulfurous by-products are liberated when the ceramic is fired. It is desirable to replace lignosulfonates with a binder which m~int~ins or improves the ~lroll~lance while reducing or eliminating the harmful sulfurous by-products. Furthermore, lignosulfonates do not impart sllffiri~nt green strength to ceramic green bodies for the green bodies to withstand milling, drilling, grinding, cutting and other conventional machining pro. P~s~c.
United States Patent 5,215,693 to Lee discloses a method for preparing machinable ceramic products. The method ~ lose~l by Lee uses organic binders such as paraffin wax, thermoplastic polymers such as polymethylmethacrylate/styrene polymers, and other water-insoluble polymers. However, the method lisrlQse~l by Lee has several drawbacks because it requires the impregnation of the binders after the green bodies are formed. Furthermore, the impregnation is generally conducted wi th an organic solvent which increases the time, costs and hazards assori~te-l with the process.
The present invention seeks to ovelcollle the problems assori~tell with the previously known methods. The present invention seeks to provide a process for preparing ceramic green bodies using polymeric additives which (1) provide good dispersant ~ lies; (2) provide good mold release during the ~res~ing stage; (3) impart goQd strength at room temperature as well as at the higher temperatures; (4) provide high green density to the green part; (5) burn-out cleanly in air, and (6) leave low burn out residuals in nitrogen.
In a first aspect of the present invention there is provided a metholl for ~ g ceramic green bodies comprising:
1) forming a ceramic mixture by mixing (a) ceramic partides;
(b) one or more binders sPlP~P~l from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylPni~Ally l-n~At--rated acids, and salts thereof; and optionally, (c) water; and optionally (d) one or more conventional additives;
2) introducing the ceramic mixture into a mold; and 3) subjecting the mold corltAining the ceramic mixture to elevated pressure to form a ceramic green body.
In a second aspect of the present invention there is provided a method for improving the mArhin~hility of ceramic green bodies co~ ising:
incol ~Ol ating into a ceramic mixture precursor of the ceramic green bodies oneor more binders sel.octe l from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof.
In a third aspect of the present invention there is provided a machinable ceramic green body comprising, (a) ceramic particles; and (b) one or more binders s~lecte-l from the group consisting of polymers 25 comprising, as polymerized units, at least 20 percent by weight of one or more monoethyl~ni~Ally unsaturated acids, and salts thereof.
Ceramic particles suitable for the present invention include oxide, nitride and carbide ceramics. Examples of suitable ceramic partides include alumina, aluminum 30 nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titaniu~n boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof. The morphology of the ceramic partides is not critical but is 35 preferably approximately spherical. Preferably, the ceramic partides are in the form of a powder. The ceramic particles may also be in the form of a slurry. When used as a 2l~0376 slurry, the slurry generally contAinc the one or more ceramic particles are at a level of from about 10 to about 98, preferably from about 30 to about 80 percent by weight of the ceramic slurry.
The polymers suitable for the present invention are polymers co,l,~,ising, as polymerized units, at least 20 percent by weight of one or more monoethyl~nirAlly unsaturated acids, or salts thereof. Monoethyl~nirAlly llnsAtllrated acids can be mono-- acids, di-acids or polyacids and the acids may be cd~ ylic acids, sulphonic acids, phosphonic acids, salts or combinAtionc thereof. Suitable monoethyleni~Ally unsaturated acidc are, for example, acrylic acid, methArrylic acid, crotonic acid, vinylacetic acid and the alkali metal and ammonium salts thereof. Suitable monoethyl~ni~Ally lmsAhlrated dicarboxylic acids and the anhydrides of the cis-dicarboxylic acids are, for example, maleic acid, maleic anhydride,1,2,3,6-tetrahydrophthalic anhydride, 3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, bicydo[2.2.2]-5-octene-2,3 dic~bo~cylic anhydride, 3-methyl-1,2,6-tetrahydrophthalic anhydride, 2-methyl-1,3,6-tetrahydrophthalic anhydride, itaconic acid, mesAconic acid, fumaric acid, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, allylphosphonic acid, allyloxybPn7Pnesulfonic acid, 2-hydroxy-3-(2-propenyloxy) propAnr-clllfonic acid, isopropenylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid, vinylsulfonic acid and the alkali metal and ammonium salts thereof. Most ~rereiably, the one cr more monoethylenically unsaturated acids are acrylic acid, methacrylic acid or the alkali metal salts thereof. The one or more monoethylenically unsaturated acids represent at least about 20 percent by weight of the total monomer weight, ~rerel ably at least about 40 percent by weight of the total monomer weight.
In A~l~itiC~n~ the polymers of the present invention may contain, as polymerizedunits, one or more monoethylenically unsaturated acid-free monomers. Suitable monoethyl~nicAlly unsaturated acid-free monomers include C1~4 alkyl esters of acrylic or methA~rylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobutyl methacrylate;
hydroxyalkyl esters of acrylic or methacrylic acids sudh as hydroxyethyl acrylate, hydroxyplo~yl acrylate, hydroxyethyl methacrylate, and hydroxy~ro~yl methacrylate.
Other monoethylenically unsaturated acid-free monomers are acrylamides and alkyl-substituted acrylamides induding acrylamide, methacrylamide, N-tertiarybutylacrylamide, N-methylacrylamide, and N,N-dimethylacrylamide. Other examples of monoethylenirAlly unsaturated acid-free monom~rs indude acrylonitrile, methAf~rylonitrile, allyl Alcohol, phosphoethyl methacrylate, 2-vinylpyridene, ~vi~lyl~ylidene, N-vinyl~ olidone, N-vinylformAmi(le, N-vinylir~i~lA7~1e, vinyl AcePte, and styrene. If used, the one or more mc-noethyl~ni~Ally unsaturated acid-free 5 monomPrs r~resent less than about 80 percent by weight of the total monomer weight, e~elably less than about 60 ~lC~l~t by weight of the total morlom~r weight.
If desired, it is possible to incol~olate polyethylenically lln~Atllrated coll,~unds into the polymerization. Polyethylenically unsaturated com~ounds function as 10 crosslinking agents and will result in the formAtion of higher molerlllAr weight polymers.
The polymers useful in the present invention preferably have a weight average moleclllAr weight ("Mw") of at least about 1,000, more preferably from about 1,500 to 15 about 50,000, and most preferably from about 2,000 to about 30,000. At molecular weights below about 1,000, the polymers do not generally ~lfUllll well as a binder.
Polymers having Mw below about 50,000 are generally con~ red low molecular weight polymers. Several te~ hniques for preparing low moleclllAr weight polymers are 20 known to those skilled in the art. One such method is by using an increased amount of initiator. One method for ~ al;ng low molecular weight polymers uses sodium metabisulfite and sodium persulfate as a redox initiAtion system. This method produces polymers useful in the present invention. However, for ceramic process where eliminating the production of sulfurous by-products is an obje~tive, this approach for 25 preparing polymers should be avoided. Other techniques for preparing low molecular weight polymers is by inco~oldlil,g into the monomer mixture one or more chain terminating or chain transfer agents. Suitable chain terminating agents and chain transfer agents are also well known to those skilled in the art of polymerization induding, for example, hypophosphorous acid and hypophosphite salts. When 30 preparing low molecular weight polymers, crosslinking agents should be avoided because the presence of crosslinking agents, sudh as compounds having two or more sites of a-,13-unsaturation, results in a dramatic increase in the moleclll~r weight of the resulting polymer.
Other aspects of polymerization, such as the selection and levels of initiators,processing conditions (temperature, pressure, feed rates, stirring), pH and the like are ~1~0376 -within the ordinary skill of persons skilled in the art of polymerization and do not form a part of the ~.esent invention.
The polymers useful in the present invention are generally prepared at a 5 polymers solids level of from about 20 percent to about 70 ~e~ t, most preferably from about 25 ~rcent to about 65 p~ lt by weight based on the total weight of the emulsion. The polymers can be used as solutions, but are preferably used in a solid form. The solid form of the polymer may be prepared by drying the polymer, such as by spray-drying, tumbling, vacuum drying and the like.
The one or more ceramic partides and the one or more polymers are mixed by any collvf~ ior~l means, such as by ball milling or m~h~ni.~l mi~ing, to form a mixture. If the one or more ceramic partides are used as a slurry, then the mixture is referred to as a wet-mixture. If the one or more ceramic partides and the one or more 15 polymers are dried, then the mixture, together with one or more plasticizers, is referred to as a "semi-wet powder." The one or more polymers are preferably used in amount of from about 1 to about 15 percent, more preferably from about 3 to about 10 ~lcellt by weight of the one or more ceramic partides.
In A~lriition, the mixture may contain one or more conv~ntion~l ceramic processing aids or other conventional additives. Conventional processing aids and additives indude, for example, other binders, plasticizers, dispersants, lubricants, sintering aids and foam suppressants. For example, water, poly(ethylene glycol) and aLkyl alcohols are known plasticizers. If used, each of the one or more conventional processing aids or other conventional additives may be present at a level of up to about 15, preferably from about 0.1 to about 10 percent by weight based on the weight of the one or more ceramic partides.
If a wet-mixture is prepared, then the wet mixture should be dried by any conventional method such as by tumble drying, pan drying, oven drying, microwavedrying and spray drying to produce a dried ceramic mixture. Preferably the wet mixture is dried by spray drying.
To form a ceramic green body, the ceramic mixture is compacted. Methods for compacting, or subjecting the ceramic materials to elevated pressures, to produce ceramic bodies indude pressing, extrusion, roll compaction and injection molding.
21~0376 -Pressing ~netho~ indude dry pressing, i~ostAffr pressing and semi-wet ~r~si~lg.
Preferably the ceramic green body is formed from the ceramic mixture by dry pressing at room l~ alure at a pressure of at least about 1,000 pounds per square inch ("psi"), most ~re~:lably from about 2,000 to about 50,000 psi. The resulting green body preferably has a green strength of at least about 0.2, most ~le~lably at least about 0.4 megaPascals ("MPa").
Before the green bodies are milled, drilled, ground, cut or subjected to other conv~nffon~l machining ~r~:esses, it is desirable to con~liffon the green bodies.
10 Cor ~litioning the green bodies may result in the removal of trace amounts of water, plasti i7prs or other additives. The green bodies may be con~liffoned by allowing them to stand at room l~ eldture, but are preferably corl~lihoned by subjecting them to an elevated temperature of from about 30C to about 300C, more ~l~feldbly from about 40C to about 200C. Depending upon the temperature, the green bodies are generally 15 con-liffone~ for from about 5 minutes to about 5 days or more.
To form a final ceramic product, the green body is fired, or sintered. The ~re~ ed temperature and time needed to sinter a green body to form a ffnal ceramic product is partly dependent upon the type of ceramic used to make the ceramic green 20 body. In general, it is ~leÇelled to sinter the ceramic green body to make the final ceramic product by heating the ceramic green body to a temperature of at least about 800C, most preferably from about 1,000C to about 2,000C, preferably for from about 5 mintlt.o~ to about 5 hours, most preferably for from about 10 minutes to about 60 minutes.
Ceramic Mixture Preparation Ceramic mixtures were prepared in the following manner:
To a 00-ball mill jar was added 100 grams of alumina grinding media 30 (approximately 1/2 indh x 1/2 inch cylinders), ceramic particles (either Alcoa A-16SG
alumina having a mean partide size of 0.5 microns or 800 grit silicon carbide), and po~ymer. The ball mill jar was sealed and the contents were milled for 1~15 minutes at about 84 revolutions per minute. The ball mill jar was opened and the mixture was decanted to separate it from the grinding media. Deionized water and other additives, 35 if used, were added and the mixture was stirred with a spatula.
21~0376 Evaluation of Green Strength and Green Density A 0.5 inch diameter hardened steel die with polichell surfaces was lubricated with a solution of 2 percent by weight stearic acid and 98 percent by weight Acetone Excess lubricant was removed by buffing. A 1.0 gram sample of cerarnic mixture was 5 loaded into the die and conlp~cte~l for 15 seron~lc to a pressure of 5,000 psi to form a ceramic green body.
The green strength of the ceramic green bodies was evaluated by r~eAcllring the green tensile strength using a ~ metrical compression test. Green tensile strength is 10 r~lr llAte.i by the following formula:
~F = 2-~
7~-D-l where ~F iS the tensile strength, p is the applied load at failure, D is the diameter of the sample and l is the thickness of the sample. Diametrical compression tests were conducted to determine the applied load at failure using a Soiltest ~) G-900 Versa-loader 20 equipped with a 50 pound electronic force gauge (available from Ametek) o~aled at a loading rate of 0.005 inches per minute until the sample fractured. The green strength reported in the tables below are the average of at least three measurements r~ol ~ed in MPa.
The densities of the ceramic green bodies r~ol led in the tables below are densities based on an average of four measurements. The green densities were calc~ te~1 in the following manner:
mass/volume = pmeasured and are r~l,~ led in the tables below in units of grams per cubic centimeter ("g/ cm3").
Measu~ements of green strength and green density at elevated temperatures reported in the tables below were conducted on samples which had been heated to the temperature indicated, in an oven, for 1-4 hours.
The following polymers appearing in the tables below were evaluated as bin-lPr.sfor alumina and silicon carbide according to the above procedure. The polymers had the following compositions and ~ ~l Lies:
Polymer A: spray-dried sodium salt of polyacrylic acid having moleclllAr weight of 4,500, prepared using sodium persulfate and sodium metAhisulfite.
Polymer B: spray-dried sodium salt of polyacrylic acid having mc~lectllAr weight of 3,500, prepared using sodiurn hypoplloshitP
Polymer C: spray-dried sodium salt of copolymer of 70 ~cent by weight acrylic acid 10and 30 ~lCt~llt by weight methacrylic acid having molPclllAr weight of 3,500.
Polymer D: spray-dried sodium salt of polyacrylic acid having molectllAr weight of 2,000, prepared using sodium persulfate and sodium metabisulfite Polyrner E: spray-dried sodium salt of poly(acrylic acid) having m( lPctllAr weight of 50,000 prepared using ammonium persulfate.
15Polymer F: spray-dried sodium salt of copolymer of 70 percent by weight acrylic acid and 30 ~rc~llt by weight maleic acid having rr olectllAr weight of 30,000.
Polymer G: spray-dried sodium salt of copolymer of 80 ~l cent by weight acrylic acid and 20 percent by weight maleic acid having ~oleclllAr weight of 15,000.
Polymer H: spray-dried polyacrylic acid having nlolectllAr weight of 3,500, prepared 20using sodium hypophoshite.
Polymer I: spray-dried ammonium salt of polyacrylic acid having molecular weight of 3,500, prepared using sodium hypophoshite.
ComparativePolymer: CalciumLignosulfonate Table I, below, shows the preparations of ceramic mixtures of 50 grams of Alcoa A-16SG
alumina and the amount (in grams) and type of polymer and amount of ~1P;OI i7e~1water as shown.
- TABLE I
ExamplePolymer Type Polymer Water Note Amount (g) Amount (g) Polymer A 2.5 2.5 ball mill only 2 Polymer F 2.5 2.5 "
3 Polymer G 2.5 2.5 "
4 Polymer C & A 1.25 each 2.5 "
Polymer D 2.5 2.5 "
6 Polymer E 2 2.5 7 Polymer B* 5.75 3.25 "
8 Ugnosulfonate 2.5 2.5 "
9 Polymer B 2.5 2 ball mix and hand mix 10 Polymer C & A 1.25 each 2 "
11Lignosulfonate 2.5 2 "
12 Polymer C & A 1.25 each 1 blender mixed 13 Polymer C & A 1.25 each 1 "
14 Polymer C & A 1.25 each 1 "
15 Polymer C & A 1.25 each 2.5 16 Polymer C & A 1.25 each 3.5 17 Polymer C & A 1.25 each 5 18 Polymer H 2.5 3.5 19 Polymer 1 2.5 3.5 Polymer H 2.5 3.5 21 Polymer H 2.5 3.5 22 Polymer H 2.5 3.5 23 Polymer 1 2.5 3.5 24 Polymer H 2.5 3.5 Polymer A** 2.5 3.5 26 Polymer A 2.5 3.5 ~ Polymer B was used as a 43% by weight aqueous polymer solution.
*~ Polymer A was used in the acid form rather than the sodium salt form.
The data in Table II show the green density and green strength for the ceramic 10 mixtures shown in Table I above.
214~376 TABLE ~
Example Green Density Green Strength Green Density Green Strength (g/cm3, 25C) (MPa, 25C) (g/cm3, (MPa,420C) 420C) 2.34 0.62 2.23 2.46 2 2.18 0.22 2.06 0.16 3 2.25 0.34 2.15 0.37 4 2.30 0.66 2.20 2.56 2.30 0.48 2.21 1.53 6 2.27 0.41 2.13 0.67 7 2.22 0.30 2.16 0.53 8 2.27 2.02 2.18 1.64 9 2.34 0.42 2.17 0.90 2.30 0.52 2.20 0.46 11 2.23 1.54 2.14 0.97 12 2.06 0.37 13 2.11 0.41 14 2.19 0.99 2.34 0.53 2.31 2.03 16 2.40 0.74 2.30 2.99 17 2.40 0.88 2.34 2.27 18 2.25 3.50 2.18 0.94 19 2.37 0.67 2.27 2.37 2.37 0.50 21 A 2.25 1.30 22AA 2.25 3.56 2.16 1.18 23AA 2.39 0.58 2.28 1.54 24AA 2.29 1.20 2.16 1.02 2.34 0.59 2.17 2.29 26 2.44 0.47 2.31 3.47 5 A the green body was con-litione~l at 60C for 5 hours before measurements were taken.
^^ the green body was ronrlitirned at room temperature for 4 days before measurements were taken The data in Table Il show that the green bodies prepared according to the present 10 invention have green strengths and green densities comparable to or better than green bodies prepared with lignosulfonate.
Table m below, shows the ~r~ald~l,s of ceramic mixtures silicon carbide ("SiC") ~re~ared from silicon carbide in the amount shown, and the amount (in grams) and type of polymer and amount of leioni7~l water as shown. Where noted, the pH of the ~l~ioni7~ water was adjusted with either hydrochloric acid or ammonium 5 h~oxide. Also, poly(ethylene glycol) ("PEG") having a mol~llAr weight of 200 was used in the amounts in~ Ate~1 in Examples 28 and 37.
TABLE m Example Amount SiC Polymer Type Polymer Water Amount Note Amount (g) (g) 27 50Polymer H 2 3.5 28 50lignosulfonate 2 2 0.5 9 PEG
29 20Polymer 1 0.8 0.7 pH 3 20Polymer 1 0.8 0.7 pH 6 31 20Polymer 1 0.8 0.7 pH 9 32 20Polymerl 0.8 0.7 pH 11 33 50Polymer H 2 1.75 34 50Polymer 1 2 2.5 50Polymer 1 2 3.5 36 50Polymer 1 2 4.5 37 50lignosulfonate 2 2 0.5 9 PEG
38 50Polymer H & 1 1 each 3.5 39 50Polymer H 2 3.5 pH 3 50Polymer H 2 3.5 pH 11 41 40Polymer H 1.6 1.2 42 40Polymer H 1.6 2 43 40Polymer H 2.6 2.8 21~0376 -The data in Table IV show the green density and green strength for the ceramic mixtures shown in Table m above.
TABLE I V
Example Green Green Green Green Green Green Density Strength DensityStrength DensityStrength (g/cm3, (MPa, (g/cm3,(MPa,120 (g/cm3,(MPa,420 25C) 25C) 120C) C) 420C) C) 27 1.76 0.07 1.65 1.96 1.57 0.14 28 1.83 `0.03 1.64 0.22 1.57 0.12 29 1.70 0.16 1.63 1.02 1.61 0.25 1.68 0.27 1.64 1.28 1.60 0.23 31 1.67 0.37 1.64 1.26 1.60 0.27 32 1;68 0.54 1.64 1.38 1.58 0.25 33 1.66 0.72 1.68 1.83 1.59 0.1 34 1.71 0.03 1.66 0.67 1.60 0.17 1.74 0.03 1.66 0.75 1.61 0.19 36 1.78 0.03 1.66 0.84 1.61 0.19 37 1.69 0.11 1.65 0.25 1.58 0.07 38 1.68 0.28 1.65 2.65 1.6 0.18 39 1.67 0.56 1.72 0.27 41 1.67 0.09 42 1.68 0.26 43 1.72 0.24 The data in Table IV show that the green bodies prepared according to the present invention have green strengths and green densities comparable to or better than green bodies prepared with lignosulfonate.
Preparation of ~A~hinAble Parts l~A/~hinAble parts were prepared in the following manner:
Ceramic mixtures were prepared in a similar manner as described above using 15 the amounts of alumina, polymer and water as shown in Table V below. When used, the internal lubricants and plasticizers were dissolved in the water.
~140376 TABLE V
Example Alumina Polymer Polymer Water Additive Additive (g) Type Amount Amount Type Amount (g) (g) (g) 44 300 H 15 21 none none 200 H 10 14 aluminum o 3 stearate poly(ethylene 2.0 glycol)~
46 250 H 12.5 17.5 aluminum 0.75 stearate poly(ethylene 5 0 glycol)~
* The poly(ethylene glycol) used had a molec ll~r weight of 200.
Machinable green parts were prepared from the ceramic mixtures in the following manner: A 1.2 inch ~ metpr cylindrical hardened steel die or a 1 inch by 2.5 inch rectangular die with polished surfaces was lubricated with a solution of 2 ~rcellt by weight stearic acid and 98 percent by weight acetone. Excess lubricant was removed 10 by buffing. A 15-35 gram sample of ceramic mixture was loaded into the die and compacted for 30 seconds to a pressure of 4,000 psi to form a ceramic green body. The green bodies were then conllitione-l by heating the green bodies in a convection oven to 60C for 2 hours. After the green bodies were conditioned, they were subjected to various machining processes as set forth in Table VI below. After being machined, the 15 green bodies were sintered by heating them to about 400C for 1~ hours, then to 1650C-1700C at a rate of from 1 to 5 C/minute ("Sintering Co~lihon") and held at 1650C-1700C for from about 0.5 to about 1.5 hours. Other observations after m~(~hining and after sintering (Final Ceramic Product) are shown in Table VI below.
`
TABLE VI
Example l~rhining OL~se, valions Sintering Obsel valions of upon Con~ition Final Ceramic ~rhining (C/minute) Product 44 lathed, drilled, smooth surfaces 2 smooth surfaces s~n-l~, no cracking 1-2 mapr fractures no chipping no star-cracking no chipping lathed, milled, smooth surfaces 2 smooth surfaces drilled, sanded, some hairline 1 major fractures cut, cracking nostar-cracking no chipping no chipping 46 lathed, milled, smooth surfaces 5 smooth surfaces ~1rille~1, sAn~le~l, some hairline no fractures cut, cracking no star-cracking no chipping no chipping The data in Table VI show that the green bodies prepared according to the present invention have 5llfflriently high green strengths so that the green bodies can be m~- hinel1 to a desired shape .
In a second aspect of the present invention there is provided a method for improving the mArhin~hility of ceramic green bodies co~ ising:
incol ~Ol ating into a ceramic mixture precursor of the ceramic green bodies oneor more binders sel.octe l from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof.
In a third aspect of the present invention there is provided a machinable ceramic green body comprising, (a) ceramic particles; and (b) one or more binders s~lecte-l from the group consisting of polymers 25 comprising, as polymerized units, at least 20 percent by weight of one or more monoethyl~ni~Ally unsaturated acids, and salts thereof.
Ceramic particles suitable for the present invention include oxide, nitride and carbide ceramics. Examples of suitable ceramic partides include alumina, aluminum 30 nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titaniu~n boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof. The morphology of the ceramic partides is not critical but is 35 preferably approximately spherical. Preferably, the ceramic partides are in the form of a powder. The ceramic particles may also be in the form of a slurry. When used as a 2l~0376 slurry, the slurry generally contAinc the one or more ceramic particles are at a level of from about 10 to about 98, preferably from about 30 to about 80 percent by weight of the ceramic slurry.
The polymers suitable for the present invention are polymers co,l,~,ising, as polymerized units, at least 20 percent by weight of one or more monoethyl~nirAlly unsaturated acids, or salts thereof. Monoethyl~nirAlly llnsAtllrated acids can be mono-- acids, di-acids or polyacids and the acids may be cd~ ylic acids, sulphonic acids, phosphonic acids, salts or combinAtionc thereof. Suitable monoethyleni~Ally unsaturated acidc are, for example, acrylic acid, methArrylic acid, crotonic acid, vinylacetic acid and the alkali metal and ammonium salts thereof. Suitable monoethyl~ni~Ally lmsAhlrated dicarboxylic acids and the anhydrides of the cis-dicarboxylic acids are, for example, maleic acid, maleic anhydride,1,2,3,6-tetrahydrophthalic anhydride, 3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, bicydo[2.2.2]-5-octene-2,3 dic~bo~cylic anhydride, 3-methyl-1,2,6-tetrahydrophthalic anhydride, 2-methyl-1,3,6-tetrahydrophthalic anhydride, itaconic acid, mesAconic acid, fumaric acid, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, allylphosphonic acid, allyloxybPn7Pnesulfonic acid, 2-hydroxy-3-(2-propenyloxy) propAnr-clllfonic acid, isopropenylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid, vinylsulfonic acid and the alkali metal and ammonium salts thereof. Most ~rereiably, the one cr more monoethylenically unsaturated acids are acrylic acid, methacrylic acid or the alkali metal salts thereof. The one or more monoethylenically unsaturated acids represent at least about 20 percent by weight of the total monomer weight, ~rerel ably at least about 40 percent by weight of the total monomer weight.
In A~l~itiC~n~ the polymers of the present invention may contain, as polymerizedunits, one or more monoethylenically unsaturated acid-free monomers. Suitable monoethyl~nicAlly unsaturated acid-free monomers include C1~4 alkyl esters of acrylic or methA~rylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobutyl methacrylate;
hydroxyalkyl esters of acrylic or methacrylic acids sudh as hydroxyethyl acrylate, hydroxyplo~yl acrylate, hydroxyethyl methacrylate, and hydroxy~ro~yl methacrylate.
Other monoethylenically unsaturated acid-free monomers are acrylamides and alkyl-substituted acrylamides induding acrylamide, methacrylamide, N-tertiarybutylacrylamide, N-methylacrylamide, and N,N-dimethylacrylamide. Other examples of monoethylenirAlly unsaturated acid-free monom~rs indude acrylonitrile, methAf~rylonitrile, allyl Alcohol, phosphoethyl methacrylate, 2-vinylpyridene, ~vi~lyl~ylidene, N-vinyl~ olidone, N-vinylformAmi(le, N-vinylir~i~lA7~1e, vinyl AcePte, and styrene. If used, the one or more mc-noethyl~ni~Ally unsaturated acid-free 5 monomPrs r~resent less than about 80 percent by weight of the total monomer weight, e~elably less than about 60 ~lC~l~t by weight of the total morlom~r weight.
If desired, it is possible to incol~olate polyethylenically lln~Atllrated coll,~unds into the polymerization. Polyethylenically unsaturated com~ounds function as 10 crosslinking agents and will result in the formAtion of higher molerlllAr weight polymers.
The polymers useful in the present invention preferably have a weight average moleclllAr weight ("Mw") of at least about 1,000, more preferably from about 1,500 to 15 about 50,000, and most preferably from about 2,000 to about 30,000. At molecular weights below about 1,000, the polymers do not generally ~lfUllll well as a binder.
Polymers having Mw below about 50,000 are generally con~ red low molecular weight polymers. Several te~ hniques for preparing low moleclllAr weight polymers are 20 known to those skilled in the art. One such method is by using an increased amount of initiator. One method for ~ al;ng low molecular weight polymers uses sodium metabisulfite and sodium persulfate as a redox initiAtion system. This method produces polymers useful in the present invention. However, for ceramic process where eliminating the production of sulfurous by-products is an obje~tive, this approach for 25 preparing polymers should be avoided. Other techniques for preparing low molecular weight polymers is by inco~oldlil,g into the monomer mixture one or more chain terminating or chain transfer agents. Suitable chain terminating agents and chain transfer agents are also well known to those skilled in the art of polymerization induding, for example, hypophosphorous acid and hypophosphite salts. When 30 preparing low molecular weight polymers, crosslinking agents should be avoided because the presence of crosslinking agents, sudh as compounds having two or more sites of a-,13-unsaturation, results in a dramatic increase in the moleclll~r weight of the resulting polymer.
Other aspects of polymerization, such as the selection and levels of initiators,processing conditions (temperature, pressure, feed rates, stirring), pH and the like are ~1~0376 -within the ordinary skill of persons skilled in the art of polymerization and do not form a part of the ~.esent invention.
The polymers useful in the present invention are generally prepared at a 5 polymers solids level of from about 20 percent to about 70 ~e~ t, most preferably from about 25 ~rcent to about 65 p~ lt by weight based on the total weight of the emulsion. The polymers can be used as solutions, but are preferably used in a solid form. The solid form of the polymer may be prepared by drying the polymer, such as by spray-drying, tumbling, vacuum drying and the like.
The one or more ceramic partides and the one or more polymers are mixed by any collvf~ ior~l means, such as by ball milling or m~h~ni.~l mi~ing, to form a mixture. If the one or more ceramic partides are used as a slurry, then the mixture is referred to as a wet-mixture. If the one or more ceramic partides and the one or more 15 polymers are dried, then the mixture, together with one or more plasticizers, is referred to as a "semi-wet powder." The one or more polymers are preferably used in amount of from about 1 to about 15 percent, more preferably from about 3 to about 10 ~lcellt by weight of the one or more ceramic partides.
In A~lriition, the mixture may contain one or more conv~ntion~l ceramic processing aids or other conventional additives. Conventional processing aids and additives indude, for example, other binders, plasticizers, dispersants, lubricants, sintering aids and foam suppressants. For example, water, poly(ethylene glycol) and aLkyl alcohols are known plasticizers. If used, each of the one or more conventional processing aids or other conventional additives may be present at a level of up to about 15, preferably from about 0.1 to about 10 percent by weight based on the weight of the one or more ceramic partides.
If a wet-mixture is prepared, then the wet mixture should be dried by any conventional method such as by tumble drying, pan drying, oven drying, microwavedrying and spray drying to produce a dried ceramic mixture. Preferably the wet mixture is dried by spray drying.
To form a ceramic green body, the ceramic mixture is compacted. Methods for compacting, or subjecting the ceramic materials to elevated pressures, to produce ceramic bodies indude pressing, extrusion, roll compaction and injection molding.
21~0376 -Pressing ~netho~ indude dry pressing, i~ostAffr pressing and semi-wet ~r~si~lg.
Preferably the ceramic green body is formed from the ceramic mixture by dry pressing at room l~ alure at a pressure of at least about 1,000 pounds per square inch ("psi"), most ~re~:lably from about 2,000 to about 50,000 psi. The resulting green body preferably has a green strength of at least about 0.2, most ~le~lably at least about 0.4 megaPascals ("MPa").
Before the green bodies are milled, drilled, ground, cut or subjected to other conv~nffon~l machining ~r~:esses, it is desirable to con~liffon the green bodies.
10 Cor ~litioning the green bodies may result in the removal of trace amounts of water, plasti i7prs or other additives. The green bodies may be con~liffoned by allowing them to stand at room l~ eldture, but are preferably corl~lihoned by subjecting them to an elevated temperature of from about 30C to about 300C, more ~l~feldbly from about 40C to about 200C. Depending upon the temperature, the green bodies are generally 15 con-liffone~ for from about 5 minutes to about 5 days or more.
To form a final ceramic product, the green body is fired, or sintered. The ~re~ ed temperature and time needed to sinter a green body to form a ffnal ceramic product is partly dependent upon the type of ceramic used to make the ceramic green 20 body. In general, it is ~leÇelled to sinter the ceramic green body to make the final ceramic product by heating the ceramic green body to a temperature of at least about 800C, most preferably from about 1,000C to about 2,000C, preferably for from about 5 mintlt.o~ to about 5 hours, most preferably for from about 10 minutes to about 60 minutes.
Ceramic Mixture Preparation Ceramic mixtures were prepared in the following manner:
To a 00-ball mill jar was added 100 grams of alumina grinding media 30 (approximately 1/2 indh x 1/2 inch cylinders), ceramic particles (either Alcoa A-16SG
alumina having a mean partide size of 0.5 microns or 800 grit silicon carbide), and po~ymer. The ball mill jar was sealed and the contents were milled for 1~15 minutes at about 84 revolutions per minute. The ball mill jar was opened and the mixture was decanted to separate it from the grinding media. Deionized water and other additives, 35 if used, were added and the mixture was stirred with a spatula.
21~0376 Evaluation of Green Strength and Green Density A 0.5 inch diameter hardened steel die with polichell surfaces was lubricated with a solution of 2 percent by weight stearic acid and 98 percent by weight Acetone Excess lubricant was removed by buffing. A 1.0 gram sample of cerarnic mixture was 5 loaded into the die and conlp~cte~l for 15 seron~lc to a pressure of 5,000 psi to form a ceramic green body.
The green strength of the ceramic green bodies was evaluated by r~eAcllring the green tensile strength using a ~ metrical compression test. Green tensile strength is 10 r~lr llAte.i by the following formula:
~F = 2-~
7~-D-l where ~F iS the tensile strength, p is the applied load at failure, D is the diameter of the sample and l is the thickness of the sample. Diametrical compression tests were conducted to determine the applied load at failure using a Soiltest ~) G-900 Versa-loader 20 equipped with a 50 pound electronic force gauge (available from Ametek) o~aled at a loading rate of 0.005 inches per minute until the sample fractured. The green strength reported in the tables below are the average of at least three measurements r~ol ~ed in MPa.
The densities of the ceramic green bodies r~ol led in the tables below are densities based on an average of four measurements. The green densities were calc~ te~1 in the following manner:
mass/volume = pmeasured and are r~l,~ led in the tables below in units of grams per cubic centimeter ("g/ cm3").
Measu~ements of green strength and green density at elevated temperatures reported in the tables below were conducted on samples which had been heated to the temperature indicated, in an oven, for 1-4 hours.
The following polymers appearing in the tables below were evaluated as bin-lPr.sfor alumina and silicon carbide according to the above procedure. The polymers had the following compositions and ~ ~l Lies:
Polymer A: spray-dried sodium salt of polyacrylic acid having moleclllAr weight of 4,500, prepared using sodium persulfate and sodium metAhisulfite.
Polymer B: spray-dried sodium salt of polyacrylic acid having mc~lectllAr weight of 3,500, prepared using sodiurn hypoplloshitP
Polymer C: spray-dried sodium salt of copolymer of 70 ~cent by weight acrylic acid 10and 30 ~lCt~llt by weight methacrylic acid having molPclllAr weight of 3,500.
Polymer D: spray-dried sodium salt of polyacrylic acid having molectllAr weight of 2,000, prepared using sodium persulfate and sodium metabisulfite Polyrner E: spray-dried sodium salt of poly(acrylic acid) having m( lPctllAr weight of 50,000 prepared using ammonium persulfate.
15Polymer F: spray-dried sodium salt of copolymer of 70 percent by weight acrylic acid and 30 ~rc~llt by weight maleic acid having rr olectllAr weight of 30,000.
Polymer G: spray-dried sodium salt of copolymer of 80 ~l cent by weight acrylic acid and 20 percent by weight maleic acid having ~oleclllAr weight of 15,000.
Polymer H: spray-dried polyacrylic acid having nlolectllAr weight of 3,500, prepared 20using sodium hypophoshite.
Polymer I: spray-dried ammonium salt of polyacrylic acid having molecular weight of 3,500, prepared using sodium hypophoshite.
ComparativePolymer: CalciumLignosulfonate Table I, below, shows the preparations of ceramic mixtures of 50 grams of Alcoa A-16SG
alumina and the amount (in grams) and type of polymer and amount of ~1P;OI i7e~1water as shown.
- TABLE I
ExamplePolymer Type Polymer Water Note Amount (g) Amount (g) Polymer A 2.5 2.5 ball mill only 2 Polymer F 2.5 2.5 "
3 Polymer G 2.5 2.5 "
4 Polymer C & A 1.25 each 2.5 "
Polymer D 2.5 2.5 "
6 Polymer E 2 2.5 7 Polymer B* 5.75 3.25 "
8 Ugnosulfonate 2.5 2.5 "
9 Polymer B 2.5 2 ball mix and hand mix 10 Polymer C & A 1.25 each 2 "
11Lignosulfonate 2.5 2 "
12 Polymer C & A 1.25 each 1 blender mixed 13 Polymer C & A 1.25 each 1 "
14 Polymer C & A 1.25 each 1 "
15 Polymer C & A 1.25 each 2.5 16 Polymer C & A 1.25 each 3.5 17 Polymer C & A 1.25 each 5 18 Polymer H 2.5 3.5 19 Polymer 1 2.5 3.5 Polymer H 2.5 3.5 21 Polymer H 2.5 3.5 22 Polymer H 2.5 3.5 23 Polymer 1 2.5 3.5 24 Polymer H 2.5 3.5 Polymer A** 2.5 3.5 26 Polymer A 2.5 3.5 ~ Polymer B was used as a 43% by weight aqueous polymer solution.
*~ Polymer A was used in the acid form rather than the sodium salt form.
The data in Table II show the green density and green strength for the ceramic 10 mixtures shown in Table I above.
214~376 TABLE ~
Example Green Density Green Strength Green Density Green Strength (g/cm3, 25C) (MPa, 25C) (g/cm3, (MPa,420C) 420C) 2.34 0.62 2.23 2.46 2 2.18 0.22 2.06 0.16 3 2.25 0.34 2.15 0.37 4 2.30 0.66 2.20 2.56 2.30 0.48 2.21 1.53 6 2.27 0.41 2.13 0.67 7 2.22 0.30 2.16 0.53 8 2.27 2.02 2.18 1.64 9 2.34 0.42 2.17 0.90 2.30 0.52 2.20 0.46 11 2.23 1.54 2.14 0.97 12 2.06 0.37 13 2.11 0.41 14 2.19 0.99 2.34 0.53 2.31 2.03 16 2.40 0.74 2.30 2.99 17 2.40 0.88 2.34 2.27 18 2.25 3.50 2.18 0.94 19 2.37 0.67 2.27 2.37 2.37 0.50 21 A 2.25 1.30 22AA 2.25 3.56 2.16 1.18 23AA 2.39 0.58 2.28 1.54 24AA 2.29 1.20 2.16 1.02 2.34 0.59 2.17 2.29 26 2.44 0.47 2.31 3.47 5 A the green body was con-litione~l at 60C for 5 hours before measurements were taken.
^^ the green body was ronrlitirned at room temperature for 4 days before measurements were taken The data in Table Il show that the green bodies prepared according to the present 10 invention have green strengths and green densities comparable to or better than green bodies prepared with lignosulfonate.
Table m below, shows the ~r~ald~l,s of ceramic mixtures silicon carbide ("SiC") ~re~ared from silicon carbide in the amount shown, and the amount (in grams) and type of polymer and amount of leioni7~l water as shown. Where noted, the pH of the ~l~ioni7~ water was adjusted with either hydrochloric acid or ammonium 5 h~oxide. Also, poly(ethylene glycol) ("PEG") having a mol~llAr weight of 200 was used in the amounts in~ Ate~1 in Examples 28 and 37.
TABLE m Example Amount SiC Polymer Type Polymer Water Amount Note Amount (g) (g) 27 50Polymer H 2 3.5 28 50lignosulfonate 2 2 0.5 9 PEG
29 20Polymer 1 0.8 0.7 pH 3 20Polymer 1 0.8 0.7 pH 6 31 20Polymer 1 0.8 0.7 pH 9 32 20Polymerl 0.8 0.7 pH 11 33 50Polymer H 2 1.75 34 50Polymer 1 2 2.5 50Polymer 1 2 3.5 36 50Polymer 1 2 4.5 37 50lignosulfonate 2 2 0.5 9 PEG
38 50Polymer H & 1 1 each 3.5 39 50Polymer H 2 3.5 pH 3 50Polymer H 2 3.5 pH 11 41 40Polymer H 1.6 1.2 42 40Polymer H 1.6 2 43 40Polymer H 2.6 2.8 21~0376 -The data in Table IV show the green density and green strength for the ceramic mixtures shown in Table m above.
TABLE I V
Example Green Green Green Green Green Green Density Strength DensityStrength DensityStrength (g/cm3, (MPa, (g/cm3,(MPa,120 (g/cm3,(MPa,420 25C) 25C) 120C) C) 420C) C) 27 1.76 0.07 1.65 1.96 1.57 0.14 28 1.83 `0.03 1.64 0.22 1.57 0.12 29 1.70 0.16 1.63 1.02 1.61 0.25 1.68 0.27 1.64 1.28 1.60 0.23 31 1.67 0.37 1.64 1.26 1.60 0.27 32 1;68 0.54 1.64 1.38 1.58 0.25 33 1.66 0.72 1.68 1.83 1.59 0.1 34 1.71 0.03 1.66 0.67 1.60 0.17 1.74 0.03 1.66 0.75 1.61 0.19 36 1.78 0.03 1.66 0.84 1.61 0.19 37 1.69 0.11 1.65 0.25 1.58 0.07 38 1.68 0.28 1.65 2.65 1.6 0.18 39 1.67 0.56 1.72 0.27 41 1.67 0.09 42 1.68 0.26 43 1.72 0.24 The data in Table IV show that the green bodies prepared according to the present invention have green strengths and green densities comparable to or better than green bodies prepared with lignosulfonate.
Preparation of ~A~hinAble Parts l~A/~hinAble parts were prepared in the following manner:
Ceramic mixtures were prepared in a similar manner as described above using 15 the amounts of alumina, polymer and water as shown in Table V below. When used, the internal lubricants and plasticizers were dissolved in the water.
~140376 TABLE V
Example Alumina Polymer Polymer Water Additive Additive (g) Type Amount Amount Type Amount (g) (g) (g) 44 300 H 15 21 none none 200 H 10 14 aluminum o 3 stearate poly(ethylene 2.0 glycol)~
46 250 H 12.5 17.5 aluminum 0.75 stearate poly(ethylene 5 0 glycol)~
* The poly(ethylene glycol) used had a molec ll~r weight of 200.
Machinable green parts were prepared from the ceramic mixtures in the following manner: A 1.2 inch ~ metpr cylindrical hardened steel die or a 1 inch by 2.5 inch rectangular die with polished surfaces was lubricated with a solution of 2 ~rcellt by weight stearic acid and 98 percent by weight acetone. Excess lubricant was removed 10 by buffing. A 15-35 gram sample of ceramic mixture was loaded into the die and compacted for 30 seconds to a pressure of 4,000 psi to form a ceramic green body. The green bodies were then conllitione-l by heating the green bodies in a convection oven to 60C for 2 hours. After the green bodies were conditioned, they were subjected to various machining processes as set forth in Table VI below. After being machined, the 15 green bodies were sintered by heating them to about 400C for 1~ hours, then to 1650C-1700C at a rate of from 1 to 5 C/minute ("Sintering Co~lihon") and held at 1650C-1700C for from about 0.5 to about 1.5 hours. Other observations after m~(~hining and after sintering (Final Ceramic Product) are shown in Table VI below.
`
TABLE VI
Example l~rhining OL~se, valions Sintering Obsel valions of upon Con~ition Final Ceramic ~rhining (C/minute) Product 44 lathed, drilled, smooth surfaces 2 smooth surfaces s~n-l~, no cracking 1-2 mapr fractures no chipping no star-cracking no chipping lathed, milled, smooth surfaces 2 smooth surfaces drilled, sanded, some hairline 1 major fractures cut, cracking nostar-cracking no chipping no chipping 46 lathed, milled, smooth surfaces 5 smooth surfaces ~1rille~1, sAn~le~l, some hairline no fractures cut, cracking no star-cracking no chipping no chipping The data in Table VI show that the green bodies prepared according to the present invention have 5llfflriently high green strengths so that the green bodies can be m~- hinel1 to a desired shape .
Claims (21)
1. A method for preparing ceramic green bodies comprising:
1) forming a ceramic mixture by mixing (a) ceramic particles;
(b) one or more binders selected from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof; and optionally, (c) water; and optionally (d) one or more conventional ceramic processing aids or other conventional additives;
1) forming a ceramic mixture by mixing (a) ceramic particles;
(b) one or more binders selected from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof; and optionally, (c) water; and optionally (d) one or more conventional ceramic processing aids or other conventional additives;
2) introducing the ceramic mixture into a mold; and
3) subjecting the mold containing the ceramic mixture to elevated pressure to form a ceramic green body.
2. The method of claim 1, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof.
3. The method of claim 1, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, zirconia, silicon nitride and silicon carbide.
2. The method of claim 1, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof.
3. The method of claim 1, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, zirconia, silicon nitride and silicon carbide.
4. The method of claim 1, wherein: the one or more monoethylenically unsaturatedacids, and salts thereof are selected from the group consisting of monoethylenically unsaturated carboxylic acids, sulphonic acids, phosphonic acids, salts thereof and combinations thereof.
5. The method of claim 1, wherein: the one or more monoethylenically unsaturatedacids, and salts thereof are selected from the group consisting of acrylic acid,methacrylic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid alkali metal and ammonium salts thereof.
6. The method of claim 1, wherein: the polymer is selected from the group consisting of homopolymers of acrylic acid and alkali metal and ammonium salts thereof.
7. The method of claim 1, wherein:
(a) the ceramic particles are present at a level of from about 10 to about 98 percent by weight of the ceramic mixture precursor;
(b) the one or more binders are present at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) the water is present at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) the conventional ceramic processing aids or other conventional additives arepresent at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
(a) the ceramic particles are present at a level of from about 10 to about 98 percent by weight of the ceramic mixture precursor;
(b) the one or more binders are present at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) the water is present at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) the conventional ceramic processing aids or other conventional additives arepresent at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
8. A method for improving the machinability of ceramic green bodies comprising:
incorporating into a ceramic mixture precursor of the ceramic green bodies one or more binders selected from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof.
incorporating into a ceramic mixture precursor of the ceramic green bodies one or more binders selected from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof.
9. The method of claim 8, wherein: the ceramic mixture precursor comprises ceramic particles are selected from the group consisting of alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof.
10. The method of claim 8, wherein: the ceramic mixture precursor comprises ceramic particles are selected from the group consisting of alumina, aluminum nitride, zirconia, silicon nitride and silicon carbide.
11. The method of claim 8, wherein: the one or more monoethylenically unsaturated acids, and salts thereof are selected from the group consisting of monoethylenically unsaturated carboxylic acids, sulphonic acids, phosphonic acids, salts thereof and combinations thereof.
12. The method of claim 8, wherein: the one or more monoethylenically unsaturated acids, and salts thereof are selected from the group consisting of acrylic acid,methacrylic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid alkali metal and ammonium salts thereof.
13. The method of claim 8, wherein: the polymer is selected from the group consisting of homopolymers of acrylic acid and alkali metal and ammonium salts thereof.
14. The method of claim 9, wherein: the ceramic mixture precursor comprises (a) the ceramic particles at a level of from about 10 to about 98 percent by weight of the ceramic mixture precursor;
(b) the one or more binders at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) water at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) conventional ceramic processing aids or other conventional additives at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
(b) the one or more binders at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) water at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) conventional ceramic processing aids or other conventional additives at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
15. A machinable ceramic green body comprising, (a) ceramic particles; and (b) one or more binders selected from the group consisting of polymers comprising, as polymerized units, at least 20 percent by weight of one or more monoethylenically unsaturated acids, and salts thereof.
16. The machinable ceramic green body of claim 15, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, silica, silicon, silicon carbide, silicon nitride, sialon, zirconia, zirconium nitride, zirconium carbide, zirconium boride, titania, titanium nitride, titanium carbide, barium titanate, titanium boride, boron nitride, boron carbide, tungsten carbide, tungsten boride, tin oxide, ruthenium oxide, yttrium oxide, magnesium oxide, calcium oxide, and mixtures thereof.
17. The machinable ceramic green body of claim 15, wherein: the ceramic particles are selected from the group consisting of alumina, aluminum nitride, zirconia, silicon nitride and silicon carbide.
18 18. The machinable ceramic green body of claim 15, wherein: the one or more monoethylenically unsaturated acids, and salts thereof are selected from the group consisting of monoethylenically unsaturated carboxylic acids, sulphonic acids, phosphonic acids, salts thereof and combinations thereof.
19. The machinable ceramic green body of claim 15, wherein: the one or more monoethylenically unsaturated acids, and salts thereof are selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, allylphosphonic acid, vinylphosphonic acid, styrenesulfonic acid alkali metal and ammonium salts thereof.
20. The machinable ceramic green body of claim 15, wherein: the polymer is selected from the group consisting of homopolymers of acrylic acid and alkali metal and ammonium salts thereof.
21. The machinable ceramic green body of claim 15, wherein:
(a) the ceramic particles are present at a level of from about 10 to about 98 percent by weight of the ceramic mixture precursor;
(b) the one or more binders are present at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) the water is present at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) the conventional ceramic processing aids or other conventional additives arepresent at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
(a) the ceramic particles are present at a level of from about 10 to about 98 percent by weight of the ceramic mixture precursor;
(b) the one or more binders are present at a level of from about 1 to about 15 percent by weight of the ceramic particles (c) the water is present at a level of from about 0.1 to about 10 percent by weight based on the ceramic particles; and (d) the conventional ceramic processing aids or other conventional additives arepresent at a level of from about 0.1 to about 10 percent by weight of the ceramic particles.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/185,746 US5401695A (en) | 1994-01-24 | 1994-01-24 | Process for preparing ceramic products |
| US08/185,746 | 1994-01-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2140376A1 true CA2140376A1 (en) | 1995-07-25 |
Family
ID=22682299
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002140376A Abandoned CA2140376A1 (en) | 1994-01-24 | 1995-01-17 | Process for preparing ceramic products |
Country Status (8)
| Country | Link |
|---|---|
| US (2) | US5401695A (en) |
| EP (1) | EP0665197B1 (en) |
| JP (1) | JP3970944B2 (en) |
| KR (1) | KR100365106B1 (en) |
| BR (1) | BR9500280A (en) |
| CA (1) | CA2140376A1 (en) |
| DE (1) | DE69423333T2 (en) |
| ES (1) | ES2143532T3 (en) |
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| US5567353A (en) * | 1995-04-13 | 1996-10-22 | Rohm And Haas Company | Method for dispersing ceramic material in an aqueous medium |
| WO1996035651A1 (en) * | 1995-05-10 | 1996-11-14 | Saint-Gobain Industrial Ceramics, Inc. | High solids silicon nitride slurries |
| JPH08311290A (en) * | 1995-05-23 | 1996-11-26 | Showa Denko Kk | Composition for liquid-absorbing material, molding of liquid-absorbing material, and production thereof |
| US6426383B1 (en) * | 1997-05-28 | 2002-07-30 | Nalco Chemical Company | Preparation of water soluble polymer dispersions from vinylamide monomers |
| AU6595498A (en) * | 1997-06-26 | 1999-01-07 | Rohm And Haas Company | Process for preparing green bodies |
| US5945470A (en) * | 1997-10-15 | 1999-08-31 | Ali; Mir Akbar | Ceramic-polymer composite material and its use in microelectronics packaging |
| GB9821663D0 (en) * | 1998-10-05 | 1998-11-25 | Abonetics Ltd | Foamed ceramics |
| US6541539B1 (en) * | 1998-11-04 | 2003-04-01 | President And Fellows Of Harvard College | Hierarchically ordered porous oxides |
| JP3248505B2 (en) * | 1999-02-12 | 2002-01-21 | 相田化学工業株式会社 | Noble metal sintered product and method for producing the same |
| FR2813603B1 (en) | 2000-09-01 | 2003-04-25 | Atofina | CERAMIC PREFORMS, AND PARTICULARLY IN RAW MACHINABLE AIN AND THEIR PROCESS FOR OBTAINING |
| GB0520778D0 (en) * | 2005-10-12 | 2005-11-23 | Environmental Monitoring And C | Ceramic component and fabrication method |
| WO2007070673A1 (en) * | 2005-12-15 | 2007-06-21 | Cabot Corporation | Transparent polymer composites |
| US20080004645A1 (en) | 2006-06-30 | 2008-01-03 | Atheromed, Inc. | Atherectomy devices and methods |
| CA2656594A1 (en) | 2006-06-30 | 2008-01-10 | Atheromed, Inc. | Atherectomy devices and methods |
| US20090018566A1 (en) | 2006-06-30 | 2009-01-15 | Artheromed, Inc. | Atherectomy devices, systems, and methods |
| US8361094B2 (en) | 2006-06-30 | 2013-01-29 | Atheromed, Inc. | Atherectomy devices and methods |
| US7470974B2 (en) * | 2006-07-14 | 2008-12-30 | Cabot Corporation | Substantially transparent material for use with light-emitting device |
| JP2010535696A (en) * | 2007-08-03 | 2010-11-25 | エアシブ・インコーポレーテッド | Porous body and method |
| US8070762B2 (en) | 2007-10-22 | 2011-12-06 | Atheromed Inc. | Atherectomy devices and methods |
| AT506893B1 (en) * | 2008-05-21 | 2010-04-15 | Swarovski & Co | TWO-TONE CERAMIC MOLDING PART |
| US8277743B1 (en) | 2009-04-08 | 2012-10-02 | Errcive, Inc. | Substrate fabrication |
| US8359829B1 (en) | 2009-06-25 | 2013-01-29 | Ramberg Charles E | Powertrain controls |
| US9833932B1 (en) | 2010-06-30 | 2017-12-05 | Charles E. Ramberg | Layered structures |
| EP2945994B1 (en) | 2013-01-18 | 2018-07-11 | Basf Se | Acrylic dispersion-based coating compositions |
| CN107140961A (en) * | 2017-05-09 | 2017-09-08 | 沈阳明禾石英制品有限责任公司 | Enhanced ceramic core of a kind of alumina-silicate ceramic fibre and preparation method thereof |
| CN107010983A (en) * | 2017-05-09 | 2017-08-04 | 沈阳明禾石英制品有限责任公司 | Enhanced ceramic core of a kind of mullite fiber and preparation method thereof |
| DE102018132904B4 (en) * | 2018-12-19 | 2020-10-29 | RF360 Europe GmbH | Piezoelectric material and piezoelectric device |
| CN111377720A (en) * | 2020-02-28 | 2020-07-07 | 徐州华焰特种陶瓷有限公司 | High-temperature-resistant low-expansion ceramic material and preparation method thereof |
| US11304723B1 (en) | 2020-12-17 | 2022-04-19 | Avantec Vascular Corporation | Atherectomy devices that are self-driving with controlled deflection |
| CN112979286B (en) * | 2021-01-18 | 2022-08-12 | 成都宏科电子科技有限公司 | Alumina ceramic for high-density packaging shell, preparation method thereof and raw porcelain tape |
| CN115572152B (en) * | 2022-10-20 | 2023-03-21 | 湖南省醴陵市浦口电瓷有限公司 | High-voltage hollow porcelain bushing and preparation process thereof |
| CN115849880B (en) * | 2022-11-29 | 2023-11-07 | 湖南圣瓷新材料有限公司 | Preparation method of ceramic arm based on hot die casting molding |
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| JPS5516044B2 (en) * | 1973-07-04 | 1980-04-28 | ||
| DE3123732A1 (en) * | 1981-06-15 | 1982-12-30 | Basf Ag, 6700 Ludwigshafen | MEASURING AGENTS AND DISPERSING AGENTS FOR PIGMENTS |
| US4587068A (en) * | 1983-06-24 | 1986-05-06 | Materials Research Corporation | Method of making ceramic tapes |
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| JPS60122770A (en) * | 1983-12-06 | 1985-07-01 | 株式会社日本触媒 | Binder for ceramic forming |
| JPS60195053A (en) * | 1984-03-15 | 1985-10-03 | 日本石油化学株式会社 | Water-soluble ceramic binder |
| KR920000160B1 (en) * | 1984-03-15 | 1992-01-09 | 니혼 세끼유 가가꾸 가부시끼가이샤 | A preparing method of water-soluble copolymer bind for the ceramic |
| US4968460A (en) * | 1986-03-07 | 1990-11-06 | Basf Aktiengesellschaft | Ceramics |
| US5266622A (en) * | 1988-05-05 | 1993-11-30 | Bayer Aktiengesellschaft | Aqueous dispersions containing a synergistic dispersant combination |
| DE3815239A1 (en) * | 1988-05-05 | 1989-11-16 | Bayer Ag | AQUEOUS DISPERSIONS WITH A SYNERGISTIC DISPERSING AGENT COMBINATION |
| US5086093A (en) * | 1990-04-02 | 1992-02-04 | Allied-Signal Inc. | Aqueous organic compositions as ceramic binders for casting and molding |
| DE4129952C2 (en) * | 1991-09-10 | 1995-02-09 | Bayer Ag | Molding compositions for the production of inorganic sintered moldings and processes for the production of inorganic sintered moldings |
| US5215693A (en) * | 1991-10-23 | 1993-06-01 | General Motors Corporation | Method for forming machinable unfired ceramic compacts |
| US5342563A (en) * | 1991-11-22 | 1994-08-30 | The Lubrizol Corporation | Methods of preparing sintered shapes and green bodies used therein |
| US5281650A (en) * | 1991-11-22 | 1994-01-25 | The Lubrizol Corporation | Process for preparing sintered shaped and articles so prepared thereby |
-
1994
- 1994-01-24 US US08/185,746 patent/US5401695A/en not_active Expired - Lifetime
- 1994-12-07 DE DE69423333T patent/DE69423333T2/en not_active Expired - Fee Related
- 1994-12-07 EP EP94309137A patent/EP0665197B1/en not_active Expired - Lifetime
- 1994-12-07 ES ES94309137T patent/ES2143532T3/en not_active Expired - Lifetime
-
1995
- 1995-01-17 CA CA002140376A patent/CA2140376A1/en not_active Abandoned
- 1995-01-23 KR KR1019950001108A patent/KR100365106B1/en not_active IP Right Cessation
- 1995-01-23 BR BR9500280A patent/BR9500280A/en active Search and Examination
- 1995-01-24 JP JP02722895A patent/JP3970944B2/en not_active Expired - Fee Related
-
1996
- 1996-06-05 US US08/660,693 patent/US5656562A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US5401695A (en) | 1995-03-28 |
| JPH07223870A (en) | 1995-08-22 |
| DE69423333T2 (en) | 2000-11-30 |
| DE69423333D1 (en) | 2000-04-13 |
| KR950032741A (en) | 1995-12-22 |
| BR9500280A (en) | 1995-10-03 |
| EP0665197A1 (en) | 1995-08-02 |
| EP0665197B1 (en) | 2000-03-08 |
| US5656562A (en) | 1997-08-12 |
| KR100365106B1 (en) | 2003-02-25 |
| JP3970944B2 (en) | 2007-09-05 |
| ES2143532T3 (en) | 2000-05-16 |
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