USH522H - Method of forming ceramic bricks - Google Patents

Method of forming ceramic bricks Download PDF

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Publication number
USH522H
USH522H US07/041,266 US4126687A USH522H US H522 H USH522 H US H522H US 4126687 A US4126687 A US 4126687A US H522 H USH522 H US H522H
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US
United States
Prior art keywords
powder
brick
slip
mixture
temperature
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.)
Abandoned
Application number
US07/041,266
Inventor
Roger B. Poeppel
Terry D. Claar
Peter Silkowski
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
US Department of Energy
Emhart Enterprises Corp
Original Assignee
US Department of Energy
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by US Department of Energy filed Critical US Department of Energy
Priority to US07/041,266 priority Critical patent/USH522H/en
Assigned to UNITED STATES OF AMERICA, THE, AS REPRESENTED BY THE UNITED STATES DEPARTMENT OF ENERGY reassignment UNITED STATES OF AMERICA, THE, AS REPRESENTED BY THE UNITED STATES DEPARTMENT OF ENERGY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: CLAAR, TERRY D., SILKOWSKI, PETER, POEPPEL, ROGER B.
Assigned to EMHART ENTERPRISES CORP. reassignment EMHART ENTERPRISES CORP. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE DATE: MAY 8, 1987 Assignors: USM CORPORATION
Application granted granted Critical
Publication of USH522H publication Critical patent/USH522H/en
Abandoned legal-status Critical Current

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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
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics

Definitions

  • This invention relates to a process for the formation of ceramic bricks and more particularly for the formation of freestanding sintered bricks of lithium carbonate.
  • Lithium containing ceramics such as LiAlO 2
  • LiAlO 2 are generally used as a tritium breeder material in a breeder blanket in nuclear fusion technology. Lithium nuclei are split by high energy neutrons yielding tritium, an isotope of hydrogen. A spatially uniform distribution of lithium isotopes reduces the complexity of many mathematical calculations concerning the dispersion of neutrons and the production of tritium.
  • ceramics can be used as neutron absorbing material where appropriate. Lithium carbonate is the most readily available lithium-containing ceramic. In the past, such lithium containing ceramics have been used in particle form or packed in various containers.
  • the cost involved in the utilization of the ceramics in particle form is significant and in particle form the ceramic can have a fairly inefficient packing or density. It is essential that breeder materials be distributed as uniformly as possible, thereby requiring minimal variations in packing, if discrete particles are used, a factor which can vary significantly in individual applications. If bricks are used, the bricks may not exhibit any striations or other disruptive imperfections and variations in content. In addition, when forming the bricks, the green strength must be sufficient to permit handling of the green brick without a loss of integrity.
  • an object of the present invention is an improved method for forming a lithium carbonate freestanding ceramic brick for use as a tritium breeder material.
  • Another object of the subject invention is a method of cold pressing and sintering said ceramic brick, employing an organic binder material to maintain the unsintered brick in the desired shape until the brick is sintered.
  • a further object of the subject invention is the use of the sintering aids sodium carbonate and potassium carbonate in combination with the organic binder and lithium carbonate for the provision of a freestanding ceramic brick of high density.
  • the subject invention provides for a method of forming such a freestanding ceramic brick through the steps of preparing an aqueous solution of sodium carbonate and potassium carbonate, preparing an aqueous dispersion of a water dispersible organic hydrocolloid, and mixing both until a full solution is provided in the first and a uniform dispersion is provided in the second.
  • the solution is mixed with the dispersion until a uniform consistency is achieved, at which point a fine lithium carbonate powder is added to form a smooth, consistent white slip.
  • the water is removed from the combined mixture such as by spray drying and bricks formed from the resulting powder by pressing and sintering.
  • the resulting green brick may be handled without a loss in integrity.
  • the sintered bricks are shaped by sanding or filing to a desired geometric shape and are ready for use. No striation or other non-uniform distribution of its composition in the sintered brick is observed.
  • the water dispersible organic hydrocolloid for use as an organic binder of the green brick is preferably a blend of 85% microcrystalline cellulose and 15% sodium carboxymethylcellulose.
  • the hydrocolloid is used to bind the ceramic particles in the green, unsintered state, thereby holding the brick's shape until sintered, when the organic portion is essentially burned out.
  • a preferred water dispersible hydrocolloid may be procured as FMC Avicel Type CL-611.
  • the Avicel hydrocolloid binder is added to water to form a uniform dispersion.
  • Sufficient hydrocolloid was added to form a 2-4% by weight of the total solution.
  • An aqueous solution containing a mixture of alkali carbonates other than lithium carbonate, and preferably approximately 10% each of Na 2 CO 3 and K 2 CO 3 is prepared. The dispersion and solution are mixed, lithium carbonate is added with continuous stirring and the slip is then dried.
  • the slip is run through a spray dryer such as a Buchi spray dryer, which is a small, laboratory-size spray dryer, which sucks up the solution and blows it out through a two fluid nozzle.
  • the resulting spray is mixed with heated air adjusted to an outlet temperature of 100° C. ⁇ 5° C., as known in the art.
  • Other spray dryers are contemplated for use in the subject invention and may have a two fluid nozzle or a centrifugal nozzle; the solution may be sucked into the spray dryer or forced through by the application of pressure: further, the drying air may be heated by gas or electricity.
  • the resulting powder should have a moisture content of approximately 0.5-2%.
  • the dried powder is then pressed into a desired shape at approximately 1,000-10,000 psi, and placed in an oven where it is fired, at temperatures increasing 50° C./hr. to a temperature between 385° C. and 450° C. where it is held for 4 hours.
  • a fine particle size of Li 2 CO 3 may be used such as may be achieved by sieving the Li 2 CO 3 through a 100 mesh screen.
  • a fine powder such as this will provide a higher density in the sintered brick. It has been found that utilization of a coarse powder, i.e. that passing through a screen of approximately 60 mesh, will result in a higher density in the green or unsintered brick.
  • the fine powder (100 mesh) Li 2 CO 3 is preferred both for its facility in spray drying and the higher density in the fired brick.
  • the following examples relate to the subject method of forming freestanding ceramic bricks.
  • the green brick was sintered by heating the brick to 450° C. at the rate of 50° C. per hour, holding at 450° C. for four hours and then allowing the sintered brick to cool to room temperature.
  • the resulting density of the sintered brick was 88%.
  • the sintered brick was slightly warped, and no striations or other non-uniform distribution of its composition was observed.
  • the sintered brick was ready for use as a tritium breeder material.
  • the binder is vaporized or oxydized; a eutectic mixture of the sintering aids, i.e. the sodium carbonate and potassium carbonate, with a small portion of lithium carbonate, are liquified, causing the lithium carbonate particles to consolidate.
  • the resultant brick is lithium carbonate grains with a grain boundary phase of lithium carbonate with sodium carbonate and/or potassium carbonate.
  • a sintered lithium carbonate brick which may be formed in a specific reproducible size and shape.
  • the brick may be handled in the green unsintered state, as a result of the green strength provided by the organic hydrocolloid binder material.
  • the green brick may be more easily molded and sintered, while retaining a substantially uniform distribution of its composition for use as a tritium breeder material.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

A method for forming free standing ceramic bricks for use as tritium breeder material is disclosed. Aqueous solutions of sodium carbonate and potassium carbonate are mixed with an organic hydrocolloid dispersion and powdered lithium carbonate, spray dried, and ceramic bricks formed by molding in a die and firing.

Description

CONTRACTUAL ORIGIN OF THE INVENTION
The U.S. Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and the University of Chicago, the operator of Argonne National Laboratory.
BACKGROUND OF THE INVENTION
This invention relates to a process for the formation of ceramic bricks and more particularly for the formation of freestanding sintered bricks of lithium carbonate.
Lithium containing ceramics, such as LiAlO2, are generally used as a tritium breeder material in a breeder blanket in nuclear fusion technology. Lithium nuclei are split by high energy neutrons yielding tritium, an isotope of hydrogen. A spatially uniform distribution of lithium isotopes reduces the complexity of many mathematical calculations concerning the dispersion of neutrons and the production of tritium. In addition, such ceramics can be used as neutron absorbing material where appropriate. Lithium carbonate is the most readily available lithium-containing ceramic. In the past, such lithium containing ceramics have been used in particle form or packed in various containers. The cost involved in the utilization of the ceramics in particle form is significant and in particle form the ceramic can have a fairly inefficient packing or density. It is essential that breeder materials be distributed as uniformly as possible, thereby requiring minimal variations in packing, if discrete particles are used, a factor which can vary significantly in individual applications. If bricks are used, the bricks may not exhibit any striations or other disruptive imperfections and variations in content. In addition, when forming the bricks, the green strength must be sufficient to permit handling of the green brick without a loss of integrity.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is an improved method for forming a lithium carbonate freestanding ceramic brick for use as a tritium breeder material.
Another object of the subject invention is a method of cold pressing and sintering said ceramic brick, employing an organic binder material to maintain the unsintered brick in the desired shape until the brick is sintered.
A further object of the subject invention is the use of the sintering aids sodium carbonate and potassium carbonate in combination with the organic binder and lithium carbonate for the provision of a freestanding ceramic brick of high density.
In accordance with the above objects, the subject invention provides for a method of forming such a freestanding ceramic brick through the steps of preparing an aqueous solution of sodium carbonate and potassium carbonate, preparing an aqueous dispersion of a water dispersible organic hydrocolloid, and mixing both until a full solution is provided in the first and a uniform dispersion is provided in the second. The solution is mixed with the dispersion until a uniform consistency is achieved, at which point a fine lithium carbonate powder is added to form a smooth, consistent white slip. The water is removed from the combined mixture such as by spray drying and bricks formed from the resulting powder by pressing and sintering. The resulting green brick may be handled without a loss in integrity. The sintered bricks are shaped by sanding or filing to a desired geometric shape and are ready for use. No striation or other non-uniform distribution of its composition in the sintered brick is observed.
DETAILED DESCRIPTION OF THE INVENTION
In the production of the freestanding brick according to the subject invention, the water dispersible organic hydrocolloid for use as an organic binder of the green brick is preferably a blend of 85% microcrystalline cellulose and 15% sodium carboxymethylcellulose.
The hydrocolloid is used to bind the ceramic particles in the green, unsintered state, thereby holding the brick's shape until sintered, when the organic portion is essentially burned out. A preferred water dispersible hydrocolloid may be procured as FMC Avicel Type CL-611. The Avicel hydrocolloid binder is added to water to form a uniform dispersion. Sufficient hydrocolloid was added to form a 2-4% by weight of the total solution. An aqueous solution containing a mixture of alkali carbonates other than lithium carbonate, and preferably approximately 10% each of Na2 CO3 and K2 CO3, is prepared. The dispersion and solution are mixed, lithium carbonate is added with continuous stirring and the slip is then dried. In a preferred method of drying, the slip is run through a spray dryer such as a Buchi spray dryer, which is a small, laboratory-size spray dryer, which sucks up the solution and blows it out through a two fluid nozzle. The resulting spray is mixed with heated air adjusted to an outlet temperature of 100° C.±5° C., as known in the art. Other spray dryers are contemplated for use in the subject invention and may have a two fluid nozzle or a centrifugal nozzle; the solution may be sucked into the spray dryer or forced through by the application of pressure: further, the drying air may be heated by gas or electricity. The resulting powder should have a moisture content of approximately 0.5-2%.
The dried powder is then pressed into a desired shape at approximately 1,000-10,000 psi, and placed in an oven where it is fired, at temperatures increasing 50° C./hr. to a temperature between 385° C. and 450° C. where it is held for 4 hours.
A fine particle size of Li2 CO3 may be used such as may be achieved by sieving the Li2 CO3 through a 100 mesh screen. A fine powder such as this will provide a higher density in the sintered brick. It has been found that utilization of a coarse powder, i.e. that passing through a screen of approximately 60 mesh, will result in a higher density in the green or unsintered brick. However, the fine powder (100 mesh) Li2 CO3 is preferred both for its facility in spray drying and the higher density in the fired brick.
The following examples relate to the subject method of forming freestanding ceramic bricks.
EXAMPLE Solution 1
30 grams distilled water
3.5 grams Na2 CO3
3.5 grams K2 CO3
The above ingredients are mixed until full solution is obtained; mixing is continued.
Dispersion 2
70 grams distilled water
4.0 grams Avicel
The above materials are mixed. White globs are formed at first but after a few minutes, the globs go away and a smooth dispersion of eggwhite consistency is attained. Mixing is continued. The solution is added to the dispersion and mixing continued. 93.0 grams of Li2 CO3 fine powder (100 mesh) is added to the combination and mixed until a smooth consistent white slip is obtained. The slip is then spray dried at 100° C. outlet temperature utilizing a Buchi spray dryer. The resulting spray dried powder has a moisture content of 1.5%. A green brick is pressed at 6,000 pounds (1,100 psi) using this spray dried powder in a die press. The resulting green brick satisfactorily holds its shape during handling and has a density equal to approximately 60% of theoretical. The green brick was sintered by heating the brick to 450° C. at the rate of 50° C. per hour, holding at 450° C. for four hours and then allowing the sintered brick to cool to room temperature. The resulting density of the sintered brick was 88%. The sintered brick was slightly warped, and no striations or other non-uniform distribution of its composition was observed. After being sanded to the necessary specified size and coated with a tritium barrier comprising an epoxy paint to make the resulting brick impermeable to water vapor and other gases, the sintered brick was ready for use as a tritium breeder material.
During the sintering phase, the binder is vaporized or oxydized; a eutectic mixture of the sintering aids, i.e. the sodium carbonate and potassium carbonate, with a small portion of lithium carbonate, are liquified, causing the lithium carbonate particles to consolidate. The resultant brick is lithium carbonate grains with a grain boundary phase of lithium carbonate with sodium carbonate and/or potassium carbonate.
As shown in the above example, a sintered lithium carbonate brick which may be formed in a specific reproducible size and shape. The brick may be handled in the green unsintered state, as a result of the green strength provided by the organic hydrocolloid binder material. As a result of the improved handling properties thereby imparted in the green state, the green brick may be more easily molded and sintered, while retaining a substantially uniform distribution of its composition for use as a tritium breeder material.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (8)

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:
1. A method of forming free-standing ceramic bricks comprising the steps of:
mixing an aqueous solution of a mixture of alkali carbonates selected from the group consisting of K2 CO3 and Na2 CO3 with an aqueous dispersion of an organic hydrocolloid to form a second aqueous mixture,
blending in powdered lithium carbonate to form a slip,
drying said slip to form a powder,
molding said powder to form a green brick, and firing said green brick to form a sintered brick.
2. The method of claim 1 wherein said slip is dried to result in a powder having 0.5% to 2.0% moisture content.
3. The method of claim 1 wherein said powder is molded at 1000-10,000 psi.
4. The method of claim 1 wherein said green brick is fired by firing in an oven having the temperature raised at 50° C./hr. to a temperature between 385° C. and 450° C., where it is kept for 4 hours.
5. A method of forming free-standing ceramic bricks comprising the steps of:
mixing an aqueous solution of a mixture of
alkali carbonates selected from the group consisting of K2 CO3 and Na2 CO3 with an aqueous dispersion of an organic hydrocolloid to form a aqueous mixture,
blending powdered lithium carbonate into said mixture to form a slip,
spray-drying said slip to form a powder of 0.5% to 2.0% moisture content,
molding said powder to form a green brick, and
firing said green brick in an oven by raising the temperature of the oven 50° C./hr. until a temperature between 385° C. to 450° C. is reached and holding for 4 hours to form a sintered brick.
6. The method of claim 5 wherein said organic hydrocolloid comprises a blend of microcrystalline cellulose and sodium carboxymethylcellulose.
7. The method of claim 7 wherein said blend comprises 85% microcrystalline cellulose and 15% sodium carboxymethylcellulose.
8. A method of forming free-standing ceramic bricks for use as neutron absorbing material comprising the steps of:
mixing an aqueous solution of a mixture of alkali carbonates selected from the group consisting of K2 CO3 and Na2 CO3 with an aqueous dispersion of a blend of 85% microcrystalline cellulose and 15% sodium carboxymethylcellulose to form an aqueous mixture,
blending powdered lithium carbonate into said mixture to form a slip,
spray-drying said slip to form a powder of 0.5% to 2.0% moisture content,
molding said powder at 1,000 to 10,00 psi to form a free-standing green brick, and
firing said green brick in an oven by raising the temperature of the oven 50° C./hr. until a temperature between 385° C. to 450° C. is reached and holding for 4 hours to form a sintered brick.
US07/041,266 1987-04-22 1987-04-22 Method of forming ceramic bricks Abandoned USH522H (en)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3234308A (en) 1961-11-21 1966-02-08 Corning Glass Works Method of molding ceramic articles
US3352656A (en) 1966-05-16 1967-11-14 English Electric Co Ltd Method of making glass-ceramics by devitrification in a single stage
US3361684A (en) 1966-01-18 1968-01-02 Werner H Kreidl Thermosetting resin matrix containing boron compounds of specific size distribution and method of making
US3879514A (en) 1971-10-08 1975-04-22 Elkem Spigerverket As Method of producing burned crystalline carbonate minerals
US4207297A (en) 1978-03-27 1980-06-10 Foote Mineral Company Process for producing high purity lithium carbonate
US4265845A (en) 1978-11-25 1981-05-05 Didier-Werke Ag Process for the production of a ceramic heat-retaining brick
US4369154A (en) 1980-11-03 1983-01-18 International Business Machines Corp. Process for producing smoother ceramic surfaces

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3234308A (en) 1961-11-21 1966-02-08 Corning Glass Works Method of molding ceramic articles
US3361684A (en) 1966-01-18 1968-01-02 Werner H Kreidl Thermosetting resin matrix containing boron compounds of specific size distribution and method of making
US3352656A (en) 1966-05-16 1967-11-14 English Electric Co Ltd Method of making glass-ceramics by devitrification in a single stage
US3879514A (en) 1971-10-08 1975-04-22 Elkem Spigerverket As Method of producing burned crystalline carbonate minerals
US4207297A (en) 1978-03-27 1980-06-10 Foote Mineral Company Process for producing high purity lithium carbonate
US4265845A (en) 1978-11-25 1981-05-05 Didier-Werke Ag Process for the production of a ceramic heat-retaining brick
US4369154A (en) 1980-11-03 1983-01-18 International Business Machines Corp. Process for producing smoother ceramic surfaces

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Dow Chemical Company, "Methocel", Product Information Sheet, May 1982.

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Owner name: UNITED STATES OF AMERICA, THE, AS REPRESENTED BY T

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:POEPPEL, ROGER B.;CLAAR, TERRY D.;SILKOWSKI, PETER;SIGNING DATES FROM 19870325 TO 19870413;REEL/FRAME:004746/0287

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Owner name: EMHART ENTERPRISES CORP.

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Effective date: 19871104

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