US2968551A - Method of sintering compacts - Google Patents

Method of sintering compacts Download PDF

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Publication number
US2968551A
US2968551A US761798A US76179858A US2968551A US 2968551 A US2968551 A US 2968551A US 761798 A US761798 A US 761798A US 76179858 A US76179858 A US 76179858A US 2968551 A US2968551 A US 2968551A
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US
United States
Prior art keywords
compacts
furnace
granules
mixture
sintering
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.)
Expired - Lifetime
Application number
US761798A
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English (en)
Inventor
Edward D North
James A Rode
Gervaise W Tompkin
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.)
Mallinckrodt Chemical Works
Original Assignee
Mallinckrodt Chemical Works
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
Priority to NL243509D priority Critical patent/NL243509A/xx
Application filed by Mallinckrodt Chemical Works filed Critical Mallinckrodt Chemical Works
Priority to US761798A priority patent/US2968551A/en
Priority to FR805187A priority patent/FR1235187A/fr
Priority to GB31967/59A priority patent/GB897689A/en
Priority to DEM42788A priority patent/DE1189832B/de
Priority to BE582803A priority patent/BE582803A/fr
Application granted granted Critical
Publication of US2968551A publication Critical patent/US2968551A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/42—Selection of substances for use as reactor fuel
    • G21C3/58—Solid reactor fuel Pellets made of fissile material
    • G21C3/62—Ceramic fuel
    • G21C3/623—Oxide fuels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • 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
    • C04B35/51—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on compounds of actinides
    • 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
    • C04B35/64—Burning or sintering processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Definitions

  • the present invention relates to powder metallurgy and more particularly to the production of sintered fuels for use in nuclear reactors.
  • the method of the present invention relates to the formation of sintered compacts of metallic oxides and metals by continuous means.
  • the method employs unsintered compacts of at least one powdered metal substance and sinters these without sacrifice of density of product and without substantial fracture of the compacts or agglomeration thereof.
  • the method is particularly useful for sintering uranium dioxide compacts which are to be used in fuel elements for nuclear reactors.
  • Fig. 1 is an elevation partly in section
  • Fig. 2 is a perspective of a compact.
  • the uranium dioxide may be enriched or depleted with respect to U or it may contain the naturally occurring proportions of isotopes. While the invention will be more fully described in terms of preparing such products, its usefulness is not so limited.
  • the purpose of the binder is twofold. First, it increases the density of the compacts by reducing interparticle friction and friction between the particles and the walls of the die in which the compacts are formed.
  • the binder is then driven off during the subsequent sintering operation.
  • the binder In the case of uranium 2,968,551 Patented Jan. 17, 1961 dioxide, it is important for the binder to be one which is completely removed from the compacts without leaving any carbonaceous residue which might form uranium carbide during the sintering operation.
  • the compacts are next heated to a temperature suflicient to drive off the binder, which in the case of paraffin is in the neighborhood of 400-500" C. Thereafter, the temperature is increased to 1500 C. or above to complete the sintering of the compacts.
  • the green, uranium dioxide compacts are dispersed in a body of roughly spherical, chemically pure, free-flowing granules of a more refractory material such as fused alumina or zirconia, the granules being of such a size that they effectively surround each compact and prevent it from coming in contact with other compacts or with the walls of the furnace.
  • This mixture is then allowed to gravitate slowly through a vertical, substantially tubular furnace filled with the mixture, preferably in a protective atmosphere such as that provided, in the case of uranium dioxide, by a countercurrent stream of hydrogen or steam.
  • the furnace is provided with heating means so that the compacts are gradually heated to their sintering temperature as they move through the furnace. This temperature is insufficient to sinter the refractory granules.
  • the binder if one is present, is driven off and carried away with the stream of gas passing through the furnace.
  • the lower end of the furnace which is unheated, provides a zone wherein the compacts are gradually cooled by the stream of gas to a temperature at which they can be conveniently removed and handled.
  • the granular refractory material It is important for the granular refractory material to be pure with respect to certain impurities, especially iron oxide and silicon dioxide, which may act as fluxes and cause the granules to become fused together or to the compacts themselves at the temperatures employed.
  • the refractory granules should also be free-fiowing and of sufficiently uniform particle size to minimize packing.
  • the particle size is not critical, provided that it is small enough so that the granules effectively separate the individual uranium dioxide compacts from each other and from the wall of the furnace, but not so small as to cause excessive interference with the passage of gas through the furnace.
  • a particle size corresponding to about 8-12 mesh has been found generally satisfactory.
  • the furnace consists essentially of a tube of a refractory material such as, for example, fused zirconium oxide. It should of course be free from any volatile impurities which might contaminate the uranium dioxide.
  • the dimensions of the furnace will depend upon its intended capacity and the output of the heating element used. These in turn will depend upon the maximum sintering temperature to be attained and the length of time .the compacts are to be kept at or near this temperature.
  • the upper portion of the furnace is conveniently heated by means of an electrical resistance element, either placed externally around the furnace or actually embedded in the walls of the furnace itself, an arrangement which is feasible with non-conductive furnace materials.
  • the lower unheated end of the furnace serves both as a cooling zone for the sintered compacts and as a preheater for the stream of protective gas passing through the furnace.
  • the rate at which the mixture of compacts and alumina pass through the furnace is determined by the rate at which the fired mixture is removed from the lower end of the furnace. This may be accomplished in a simple manner by attaching a length of flexible tubing to the lower end of the furnace. The end of the tube is then closed with a suitable clamp, or even with the fingers, and opened periodically to permit removing a portion of the fire mixture. Alternatively, the lower end may be a constriction of such a size that the mixture is allowed to escape from the furnace at a rate corresponding to the desired rate of passage of the mixture through the furnace. Using the previously described length of flexible tubing, the mixture can be withdrawn from the furnace in the following manner without substantial escape of hydrogen or without interrupting its flow through the furnace.
  • the flexible tubing With the lower end closed, the flexible tubing is closed off at a second point a suitable distance from the end, thus isolating the portion of the mixture to be removed.
  • the lower end of the tubing is now opened and the isolated portion is emptied into a suitable receptacle.
  • the contents of the furnace move a corresponding distance downwards.
  • sintered material is removed from the lower end of the furnace fresh quantities of green mixture are added at the top.
  • the process of the present invention is useful for sintering compacts at temperatures up to the sintering temperature of the refractory granules.
  • This upper temperature varies depending upon the chemical nature and physical form of the granules which are used.
  • Aluminum oxide (Alundum) bubbles for example, begin to sinter at temperatures near 1650 C. While zirconia bubbles and sand begin sintering at somewhat lower temperatures, up to about 1600 C.
  • the temperatures given above are illustrative only, and are subject to some variation depending upon the source of the granules and the criteria used to determine the sintering temperature.
  • the method is equally applicable to the sintering or heat treatment of other solid compositions and substances, such as the sintered metal and metal oxide objects commonly fabricated by powder metallurgy.
  • the method is applicable to the sintering of oxide mixtures which are even more refractory than uranium dioxide, the upper limit being determined by the sintering temperature of the refractory granules themselves and/ or the limitations of the furnace.
  • the furnace may be operated with an atmosphere of some other gas, such as, for example, nitrogen, oxygen, argon, carbon dioxide, or air, depending upon the nature of the material being sintered.
  • the green compacts may be prepared by compressing them in a suitable die, or they maybe prepared by slip casting or by extrusion.
  • binders may be used either in addition to or in place of paraffin.
  • other waxes, stearic acid, cellulose derivatives such as carboxymethylcellulose, and heat-fugitive polymeric materials such as polyvinyl alcohol and polyethylene glycol are other materials used for this purpose, while esters of organic acids are frequently used as lubricants for extruded shapes.
  • the process of the present invention can be operated either continuously or semi-continuously using simple equipment. Even without the aid of any mechanical or automatic equipment little handling of the compacts is required since the green mixture is easily prepared and the sintered compacts are readily separated from the fired mixture by a screening operation, whereby the alumina is recovered for use in sintering additional compacts.
  • a suitable furnace is easily constructed from standard materials and apparatus, no specially manufactured forms or devices being necessary.
  • Example 1 A furnace 1 suitable for use with the method of the present invention was constructed from a 36 in. length of fused zirconium oxide combustion tube 3 having an internal diameter of 1% in. Tube 3 was supported in a vertical position and the upper one-half of its length was heated by surrounding it with a heavy duty resistance heater 5 having a silicon carbide element 7. To control the rate at which the contents of the furnace gravitate through tube 3, a length of rubber tubing 9 was attached to the lower end of combustion tube 3 and closed with a series of pinch clamps 11. An inlet 13 for the introduction of hydrogen was also provided at the lower end of combustion tube 3 above clamps 11 closing the rubber tubing.
  • the furnace 1 was next filled with fused alumina bubbles 15, i.e., hollow spheres 8-12 mesh in size, and heated to an operating temperature of 1520 C. Hydrogen was introduced into gas inlet 13 at a rate sufficient to exclude all air from the furnace, particularly from the zone at the upper end of the combustion tube where the pellets are heated to the sintering temperature. Bubbles 15 were withdrawn from the bottom of the furnace by manipulating pinch clamps 11 in the manner previously described and recycled to the top of the furnace to establish that they would flow satisfactorily.
  • Example 2 Green uranium dioxide compacts 17 similar to those described in Example 1 but containing 0.5% parafiin and 1% polyvinyl alcohol were also fired in the same furnace. In this case the maximum temperature of the firing zone was 1500 C. and the compacts were passed through the furnace at the rate of about 8 inches per hour. Sintered compacts having a density of 9.0-9.5 g./cc. were produced in this manner.
  • Example 3 Example 1 was repeated except that the refractory granular material 15, which serves as a support for the uranium dioxide compacts during the sintering operation, was composed of fused zirconium dioxide rather than fused aluminum oxide.
  • the granules were solid and of a size comparable to those employed in Example 1. The results were essentially comparable to those obtained when the granular refractory material was fused aluminum oxide.
  • the method which comprises adding freeflowing granules of refractory material having dispersed therein unsintered compacts of at least one powdered metal substance selected from the group consisting of metallic oxides and metals, which compacts sinter substantially below the sintering temperature of the refractory granules, to the top of a vertical, substantially tubular furnace filled with the mixture, only the upper portion of the furnace being heated; removing the mixture of compacts and granules from the lower end of the furnace at a controlled rate so that the mixture slowly gravitates through the furnace and is thereby gradually heated to a temperature sufiicient to sinter the compacts but insufficient to sinter the refractory granules and then gradually cooled; and thereafter separating the sintered compacts from the refractory granules.
  • the method which comprises adding free-flowing granules of refractory material having dispersed therein unsintered compacts of powdered uranium dioxide, which compacts sinter substantially below the sintering temperature of the refractory granules, to the top of a vertical, substantially tubular furnace filled with the mixture, only the upper portion of the furnace being heated; removing the mixture of compacts and granules from the lower end of the furnace at a controlled rate so that the mixture slowly gravitates through the furnace and is thereby gradually heated to a temperature of at least 1500 C. but insufiicient to sinter the refractory granules and then gradually cooled; and thereafter separating the sintered uranium dioxide compacts from the refractory granules.
  • the method which comprises adding free-flowing granules of refractory material dispersed therein unsintered compacts of powdered uranium dioxide and a heat-fugitive binder, to the top of a vertical, substantially tubular furnace filled with the mixture, only the top of the furnace being heated and the furnace further being provided with means for passing a flow of gas through the furnace countercurrent to the direction of movement of the mixture; removing the mixture of compacts and granules from the lower end of the furnace at a controlled rate so that the mixture slowly gravitates through the furnace and is gradually heated to a maximum temperature of approximately 1500 'C., during which time the heat-fugitive binder is driven off and removed with the outgoing gas, and then gradually cooled; and thereafter separating the sintered uranium dioxide compacts from the refractory granules.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Structural Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Metallurgy (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
US761798A 1958-09-18 1958-09-18 Method of sintering compacts Expired - Lifetime US2968551A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL243509D NL243509A (en, 2012) 1958-09-18
US761798A US2968551A (en) 1958-09-18 1958-09-18 Method of sintering compacts
FR805187A FR1235187A (fr) 1958-09-18 1959-09-15 Perfectionnements apportés aux agglomérés frittés d'oxydes métalliques et de métaux et à leurs procédés de préparation
GB31967/59A GB897689A (en) 1958-09-18 1959-09-18 Improvements in methods of sintering compacts of metal substances
DEM42788A DE1189832B (de) 1958-09-18 1959-09-18 Verfahren zum Sintern von Presslingen aus Metall- oder Metalloxydpulver
BE582803A BE582803A (fr) 1958-09-18 1959-09-18 Procédé de frittage d'agglomérés d'une substance métallique, et agglomérés frittés obtenus

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Application Number Priority Date Filing Date Title
US761798A US2968551A (en) 1958-09-18 1958-09-18 Method of sintering compacts

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US2968551A true US2968551A (en) 1961-01-17

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US761798A Expired - Lifetime US2968551A (en) 1958-09-18 1958-09-18 Method of sintering compacts

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US (1) US2968551A (en, 2012)
BE (1) BE582803A (en, 2012)
DE (1) DE1189832B (en, 2012)
FR (1) FR1235187A (en, 2012)
GB (1) GB897689A (en, 2012)
NL (1) NL243509A (en, 2012)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3026177A (en) * 1961-04-25 1962-03-20 Gen Electric Process for producing transparent polycrystalline alumina
US3091027A (en) * 1958-11-20 1963-05-28 Pechiney Prod Chimiques Sa Method and composition for assembling together refractory bodies
US3238049A (en) * 1963-01-23 1966-03-01 Gen Motors Corp Dry grinding of ceramics
US3238048A (en) * 1963-01-23 1966-03-01 Gen Motors Corp Ceramics
US3249662A (en) * 1962-01-10 1966-05-03 Philips Corp Method of manufacturing ceramic articles by sintering preformed bodies and ceramic articles thus manufactured
US3252809A (en) * 1963-01-23 1966-05-24 Gen Motors Corp Dry grinding of ceramics
US3252810A (en) * 1963-01-23 1966-05-24 Gen Motors Corp Dry grinding of ceramics
US3442994A (en) * 1966-02-07 1969-05-06 Coors Porcelain Co Method for making curved ceramic plates
US3950463A (en) * 1969-10-22 1976-04-13 The Electricity Council Production of β-alumina ceramic tubes
US4056584A (en) * 1974-09-30 1977-11-01 General Atomic Company Method of making a graphite fuel element having carbonaceous fuel bodies
US4064204A (en) * 1974-09-30 1977-12-20 General Atomic Company Manufacture of nuclear fuel compacts
US4217174A (en) * 1974-09-30 1980-08-12 General Atomic Company Manufacture of nuclear fuel compacts
US4445851A (en) * 1981-05-08 1984-05-01 Avx Corporation Apparatus and method for firing ceramic articles or the like
US5346883A (en) * 1987-08-21 1994-09-13 The Furukawa Electric Co., Ltd. Method of manufacturing superconductive products
US5762838A (en) * 1995-11-06 1998-06-09 Mitsubishi Nuclear Fuel Co. Method of producing nuclear fuel pellet
EP1674177A1 (de) * 2004-12-21 2006-06-28 Dr. Fritsch Sondermaschinen GmbH Drucksintervorrichtung

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1260709B (de) * 1961-11-29 1968-02-08 Siemens Ag Verfahren zum Sintern von Pressteilen aus Zwei- oder Mehrstoffsystemen in Gegenwart einer fluessigen Phase
EP0216436B1 (en) * 1985-09-26 1989-04-26 "Studiecentrum voor Kernenergie", "S.C.K." Method for manufacturing a sintered product

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2515790A (en) * 1949-04-22 1950-07-18 Gen Electric Ceramic dielectric material and method of making
US2568157A (en) * 1951-09-18 Process of making refractory bodies

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE289864C (en, 2012) *
FR801730A (fr) * 1936-02-07 1936-08-14 Ig Farbenindustrie Ag Procédé pour fabriquer des objets moulés
CH310889A (de) * 1953-04-21 1955-11-15 Intercito Holding Verfahren und Einrichtung zur Herstellung von Strängen aus Metallpulvern.

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2568157A (en) * 1951-09-18 Process of making refractory bodies
US2515790A (en) * 1949-04-22 1950-07-18 Gen Electric Ceramic dielectric material and method of making

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3091027A (en) * 1958-11-20 1963-05-28 Pechiney Prod Chimiques Sa Method and composition for assembling together refractory bodies
US3026177A (en) * 1961-04-25 1962-03-20 Gen Electric Process for producing transparent polycrystalline alumina
US3249662A (en) * 1962-01-10 1966-05-03 Philips Corp Method of manufacturing ceramic articles by sintering preformed bodies and ceramic articles thus manufactured
US3238049A (en) * 1963-01-23 1966-03-01 Gen Motors Corp Dry grinding of ceramics
US3238048A (en) * 1963-01-23 1966-03-01 Gen Motors Corp Ceramics
US3252809A (en) * 1963-01-23 1966-05-24 Gen Motors Corp Dry grinding of ceramics
US3252810A (en) * 1963-01-23 1966-05-24 Gen Motors Corp Dry grinding of ceramics
US3442994A (en) * 1966-02-07 1969-05-06 Coors Porcelain Co Method for making curved ceramic plates
US3950463A (en) * 1969-10-22 1976-04-13 The Electricity Council Production of β-alumina ceramic tubes
US4056584A (en) * 1974-09-30 1977-11-01 General Atomic Company Method of making a graphite fuel element having carbonaceous fuel bodies
US4064204A (en) * 1974-09-30 1977-12-20 General Atomic Company Manufacture of nuclear fuel compacts
US4217174A (en) * 1974-09-30 1980-08-12 General Atomic Company Manufacture of nuclear fuel compacts
US4445851A (en) * 1981-05-08 1984-05-01 Avx Corporation Apparatus and method for firing ceramic articles or the like
US5346883A (en) * 1987-08-21 1994-09-13 The Furukawa Electric Co., Ltd. Method of manufacturing superconductive products
US5762838A (en) * 1995-11-06 1998-06-09 Mitsubishi Nuclear Fuel Co. Method of producing nuclear fuel pellet
EP1674177A1 (de) * 2004-12-21 2006-06-28 Dr. Fritsch Sondermaschinen GmbH Drucksintervorrichtung

Also Published As

Publication number Publication date
GB897689A (en) 1962-05-30
DE1189832B (de) 1965-03-25
NL243509A (en, 2012)
BE582803A (fr) 1960-03-18
FR1235187A (fr) 1960-07-01

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