CA1076846A - Thermally stable sintered porous metal articles - Google Patents
Thermally stable sintered porous metal articlesInfo
- Publication number
- CA1076846A CA1076846A CA266,220A CA266220A CA1076846A CA 1076846 A CA1076846 A CA 1076846A CA 266220 A CA266220 A CA 266220A CA 1076846 A CA1076846 A CA 1076846A
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- CA
- Canada
- Prior art keywords
- particles
- article
- base metal
- dispersoid
- sintered
- 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
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8875—Methods for shaping the electrode into free-standing bodies, like sheets, films or grids, e.g. moulding, hot-pressing, casting without support, extrusion without support
-
- 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
- B22F3/11—Making porous workpieces or articles
- B22F3/1103—Making porous workpieces or articles with particular physical characteristics
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/80—Porous plates, e.g. sintered carriers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
- H01M4/8882—Heat treatment, e.g. drying, baking
- H01M4/8885—Sintering or firing
-
- 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
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
-
- 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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- 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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Powder Metallurgy (AREA)
- Inert Electrodes (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A sintered porous metal article is provided which is essentially thermally stable at elevated temperatures. In addition, a method for producing such an article is also pro-vided which method comprises preparing a blend of base metal particles and active dispersoid particles, forming the mixture into an article of the desired shape, and heating the so-formed article at sintering temperatures; the article has many uses and may be employed in the manufacture of high temperature heating elements, conductive metallic grids for high temperature use and electrodes for high temperature fuel cells.
A sintered porous metal article is provided which is essentially thermally stable at elevated temperatures. In addition, a method for producing such an article is also pro-vided which method comprises preparing a blend of base metal particles and active dispersoid particles, forming the mixture into an article of the desired shape, and heating the so-formed article at sintering temperatures; the article has many uses and may be employed in the manufacture of high temperature heating elements, conductive metallic grids for high temperature use and electrodes for high temperature fuel cells.
Description
D-56~3 6~346 Background of the Invention The sub~ect invention concerns porous sintered metal articles, preferably nickel articles, which are characterized by their thermal stability when subsequently heated to elevated temperatures, that is, temperatures approach-ing that at which they were originally sintered.
In addition, the sub~ect invention also concerns a unique method of producing the before-described type of article.
Description of the Prior Art The formation of porous metal articles typically involves the steps of shaping metal powders into a green com-pact, for example, by loose packing, compaction, extrusion, rolling, or molding, and further consolidation of the green compact into the desired article by the mechanism of sintering.
In this general process, a quantity of loose starting material, usually irregularly shaped metal cr metal alloy particles ranging in size from Ool microns to 200 microns~ is used. The particles of the desired size are typically obtained by means of a sieve of predetermined mesh opening. The classi-fied powders are then shaped by loose packing or under pressure into a green compact wherein the metal particles contact each other at many points and areas of their surfaces. In most cases, the interparticle voids left between the particles re-main open to form inter-connected pore channels penetrating the body of the compact. These openings are generally of irregular cross-section with ~agged, sharp-edged walls. However, the green preform is mechanically weak due to insufficient bonding between the particles.
In order to enhance ~ody strength, the ~reen compact is sintered, that is, heated for a specific length of time at D-S~3 8~6 a temperature at which diffusion of metal is activated at the _ points of contact between the particles so that they become bonded to each other. As sintering progresses~ the particle contacts grow to form neck-like joints and the pore channels assume a rounded, cylindrical shape due to surface tension forces acting on their surfaces. These forces also enhance diffusion flow of metal into the empty channels, decreasing their cross-sectional area to the point where the channels become unstable and reduce into spherical voids separ~ted from each other by the body of densified metal.
To obtain a framework or structure with intercon-necting pore channels, it is accordingly necessary to ter-minate sintering prior to pore channel breakdown. However, it is recognized that for irregularly shaped powder particles having a size distribution around an average value, the several stages of sintering occur at different times within the body of the compact. Closure of pore channels takes place sooner at some locations in the body than in others, causing gross in-homogeneities in the structure. It i9 therefore practically impossible by this technique to control pore size, strength ` and thermal stability of the finished structure. The minimum pore size within the wide range of pore sizes found in such a framework is generally limited by the size of metal particles.
This restriction on minimum pore size is due to the surface 25 ~ension forces causing pore closure which are inversely pro-- portional to the diameter of the pore. The stability o~ the open channels decreases sharply with diameter. This results in inherent shrinkage in the framework throughout further heat treatment.
Several modifications of the conventional sinter-ing technique have been utilized by the art in an attempt to ' . ~ . .. ~ .: ,:. :. - , ~ . :: : . : ,- -~ D-56~3 more closely control the structure of the formed framehork.
Some of these modified processes suffer disadvanta~es and, in - common with the basic technique, do not inhibit shrinkage in further heat treatment applications of the sintered structure.
By one such conventional technique, carefully sized, spherical powders are utilized to form the porous body with the choice of particle size determining the pore diameter o the interconnected channels. For pore diameters larger than a~out 5 microns, sintering can be terminated prior to breakdown o~
the pore channels since particles uniform in size and shape sinter uniformly. Growth of interparticle ~joints, formation~
and shrinkage of cylindrical channels, and their eventual breakdown into separated voids, accordingly occur in the same sequence throughout the whole compact. A ma~ior disadvantage 15 of this technique, in addition to the limitation on pore size, is the cost and availability of spherical particles. Illustra-tive processes are disclosed in German Patent No. 918,357 (1954) and Japanese Patent No. 2033580 (1953) dealing with self-lubrication bearings, and U.S. Patent No. 2,863,5~2 (I958) : 20 dealing with porous filters. By another conventional technique, p~re-forming materials which volatilize during sintering are ~ ;
blended with the initial powder mlxture of the more conven-tional non-uniform particles. Upon completion of the sintering operation, the resultant body will contain pore channels 25 everywhere the pore formerly initially resided. By virtue of ; the non-uniformity of the initial metal particles, the result-ant framework contains a large size distribution of inter-connected channels. Illustrative processes are disclosed in U.S. Patent Nos. 2,721,378 (1955); 2,792,302 (1957); and
In addition, the sub~ect invention also concerns a unique method of producing the before-described type of article.
Description of the Prior Art The formation of porous metal articles typically involves the steps of shaping metal powders into a green com-pact, for example, by loose packing, compaction, extrusion, rolling, or molding, and further consolidation of the green compact into the desired article by the mechanism of sintering.
In this general process, a quantity of loose starting material, usually irregularly shaped metal cr metal alloy particles ranging in size from Ool microns to 200 microns~ is used. The particles of the desired size are typically obtained by means of a sieve of predetermined mesh opening. The classi-fied powders are then shaped by loose packing or under pressure into a green compact wherein the metal particles contact each other at many points and areas of their surfaces. In most cases, the interparticle voids left between the particles re-main open to form inter-connected pore channels penetrating the body of the compact. These openings are generally of irregular cross-section with ~agged, sharp-edged walls. However, the green preform is mechanically weak due to insufficient bonding between the particles.
In order to enhance ~ody strength, the ~reen compact is sintered, that is, heated for a specific length of time at D-S~3 8~6 a temperature at which diffusion of metal is activated at the _ points of contact between the particles so that they become bonded to each other. As sintering progresses~ the particle contacts grow to form neck-like joints and the pore channels assume a rounded, cylindrical shape due to surface tension forces acting on their surfaces. These forces also enhance diffusion flow of metal into the empty channels, decreasing their cross-sectional area to the point where the channels become unstable and reduce into spherical voids separ~ted from each other by the body of densified metal.
To obtain a framework or structure with intercon-necting pore channels, it is accordingly necessary to ter-minate sintering prior to pore channel breakdown. However, it is recognized that for irregularly shaped powder particles having a size distribution around an average value, the several stages of sintering occur at different times within the body of the compact. Closure of pore channels takes place sooner at some locations in the body than in others, causing gross in-homogeneities in the structure. It i9 therefore practically impossible by this technique to control pore size, strength ` and thermal stability of the finished structure. The minimum pore size within the wide range of pore sizes found in such a framework is generally limited by the size of metal particles.
This restriction on minimum pore size is due to the surface 25 ~ension forces causing pore closure which are inversely pro-- portional to the diameter of the pore. The stability o~ the open channels decreases sharply with diameter. This results in inherent shrinkage in the framework throughout further heat treatment.
Several modifications of the conventional sinter-ing technique have been utilized by the art in an attempt to ' . ~ . .. ~ .: ,:. :. - , ~ . :: : . : ,- -~ D-56~3 more closely control the structure of the formed framehork.
Some of these modified processes suffer disadvanta~es and, in - common with the basic technique, do not inhibit shrinkage in further heat treatment applications of the sintered structure.
By one such conventional technique, carefully sized, spherical powders are utilized to form the porous body with the choice of particle size determining the pore diameter o the interconnected channels. For pore diameters larger than a~out 5 microns, sintering can be terminated prior to breakdown o~
the pore channels since particles uniform in size and shape sinter uniformly. Growth of interparticle ~joints, formation~
and shrinkage of cylindrical channels, and their eventual breakdown into separated voids, accordingly occur in the same sequence throughout the whole compact. A ma~ior disadvantage 15 of this technique, in addition to the limitation on pore size, is the cost and availability of spherical particles. Illustra-tive processes are disclosed in German Patent No. 918,357 (1954) and Japanese Patent No. 2033580 (1953) dealing with self-lubrication bearings, and U.S. Patent No. 2,863,5~2 (I958) : 20 dealing with porous filters. By another conventional technique, p~re-forming materials which volatilize during sintering are ~ ;
blended with the initial powder mlxture of the more conven-tional non-uniform particles. Upon completion of the sintering operation, the resultant body will contain pore channels 25 everywhere the pore formerly initially resided. By virtue of ; the non-uniformity of the initial metal particles, the result-ant framework contains a large size distribution of inter-connected channels. Illustrative processes are disclosed in U.S. Patent Nos. 2,721,378 (1955); 2,792,302 (1957); and
2,877,11L~ (1957).
_~_ .... - ~. : .. . .
D-56~3 ~07684G
Both of the above techniques require precise control of sintering conditions to ensure termination thereof prior to pore channel breakdown.
One recently developed technique, where a dispersed phase of critical amounts of inert dispersoid particles of specified size are incorporated in sintered metal or metal alloy, apProximates controlling the pore size, its distribution, and shrinkage inhibition. To be effective, the inert particles must form with the sintered particles a wetting angle of at least 90 as measured from the sintered metal-dispersoid parti-cle interface to the sintered metal-atmosphere interface. The resulting materials exhibit a network of stabiliæed inter-connected pore channels of narrow size distribution.
Particles of any shape can be used in the matrix so long as the voids remaining bet~een them after they have been loosely packed or pressed together form inter-connected pore channe-ls penetrating the body of the compact. This process, as it is described in U. S. Patent No. 3,397,96~, has certain critical disadvantages, specifically, sintered metal articles produced by the concerned technique e~hibit limited electrical conductivity. Accordingly, when it is desired to provide a thermally stable sintered porous metal article which is con-ductive, the technique of U. S. Patent No. 3,397,96~ cannot be used.
~he instant invention provides a means of overcoming various limitations found in prior art methods of producing ` sintered porous metal articles. Specifically, the instant invention provides sintered porous metal articles which are both thermall~ stable and characterized by their degree of electrical conductivity. Such articles h.~ve a myriad of uses, ~`` 1C~76846 such as, for example, high temperature heating elements, conductive metallic grids which are to be utilized at high temperature, electrodes for fuel cells (especially high temperature fuel cells), and as conductive elements for high temperature electrostatic precipitators. These uses are not exclusive, but are merely set forth herein as typical examples.
The instant invention concerns a unique thermally stable, electrically conductive porous sintered metal article which comprises a structure or framework of sintered base metal particles defining a network of inter-connected pore channels formed therein with dispersoid particles distributed through the basic structure which interconnect or are inter-locked with adjacent base metal particles.
~he physical dimensions of the interconnecting pore channels which may be randomly formed do not essentially change on heating to temperatures approaching the original !
sintering temperature.
The dispersoid particles are both conductive and refractory.
In the preferred embodiment of the invention the conductive metal particles are present in an amount ranging from a trace amount up to about 30 weight percent of the sintered porou~ metal article.
In addition, the present invention is concerned with a method of producing a sintered metal article which is electrically conductive and essentially thermally stable when used at elevated temperatures which includes the steps of preparing a mixture or blend of base metal particles and dispersoid particles which are both conductive and refractory, forming the mixture into an article of the desired shape, and heating the formed article at sintering temperatures ~ 6 -. .
-: 4~; `
to form a sintered article characterized by its thermal stability and by interconnected pores, the physical dimensions of which do not essentially change on subsequent heating to temperatures approaching the original sintering temperature.
In the preferred practice of the invention, after the porous metal article has been sintered it is sometimes subjected to a compacting and then an annealing treatment, depending on contemplated applications.
- 6a-D-56~3 1C~76846 Description of the Preferred Embodiments of the Invention Base metal particles used in the practice of the invention can be made of any metal. Preferably such metal is one selected from the group consisting of nickel, iron, cobalt, and mixtures thereof. In this regard, it is to be noted that more than one base metal or alloy of base metals may be utilized in the practice of the invention.
In the practice of the invention it has been found to be preferable to utilize base metal particles having a particle size ranging from about 0.-1 to about 200 microns.
The active or conductive dispersoid particles used in the practice of the instant invention must be both refractory and conductive. Preferably, such particles are fashioned from a metal selected from the group consisting of chromium, molyb-denum~ tungsten, and mixtures thereof. Lîke the base metalparticles, dispersoid particles of different metals or alloys can be utilized in the practice of the invention. Essentially, all that is required is that the dLspersoid particles are (1) conductive, refractory, and capable of interlocking with ad-~acent base metal particles to form a unitary porous mass and (2) do not form a liquid phase during sintering.
In the practice of the invention it is preferred to utilize dispersoid particles having a particle size distri- `~
bution ranging from about 0.01 to about 50 micron$.
The dispersoid particles in the starting mixture should be as small as possible to prevent their interference with the pore channel network with the only limitation on minimum size being the practical limit of the availability of sizes below 0.01 microns. It has been noted that dispersoid particles are desirably less than one-third the size of the pore channels.
D-56~3 768~6 For larger sizes, the particles tend to block and close many of the pores to the detriment of usable pore volume. To ensure that the dispersoid particlès in the materials of the invention are within these limits~ there must be taken into account the tendency of many particles to grow during sinter-ing. When such growth occurs, the dispersoid particles in the initial mixture prior to processin~ must naturally be smaller than the aforementioned sizes. Such growth can readily be compensated for by workers skilled in the art.
Base metal particles and dispersoid particles can be mixed together by any convenient means. In practice, it is preferred to use a V-twin shell-type of blender. The exact `
duration of blending is not critical. All that is required is that the materials are uniformly mixed.
The preferred mixture of base metal and dispersoid particles should range from about 95 to about 70 weight percent base metal and from about 5 to about 30 weight percent dis-persoid particles.
The mixture of base metal particles and dispersold ;
particles can be formed into any desired shape b~ conventional techniques which are known to the art and will not be dis-cussed herein in detaiI. The initial powder mi~ture should be -~
such as to ensure uniform distribution of the dispersoid particles at the surfaces of the metal particles during forma-tion of a uniform mixture wherein the dispersoid particles are located at or on the surfaces of the metal particles. No si~nificant separation of the phases should occur causing some metal particles to be devoid of or have less dispersoid on their surfaces than others. AEglomeration of the dispersoid should also be avoided in the mixture. The relative concentration : -- .: : : , , : -1~76~46 and sizes of the metal and dispersoid po~ders must naturally be such as to produce, upon further processing, the desired microstructure in the finished body.
In the preferred practice of the invention, articles are formed by filling a mold with the desired amount of material.
Obviously, there are many ways in which the desired article can be fabricated.
The pore size of channels in the finished product !:
is influenced not only by the concentrations and slzes of metal and dispersoid particles and sintering conditions but also by - the degree of compaction experienced in forming the green com- i pact. The compact may be formed by any of the various ~ell-known techniques, including uni- or multidirectional die pres-sing, isostatic pressing, powder rolling, extruding, and roll-bar molding. ~arious degrees of compaction are achieved in these processes, resulting in a ~ariety of pore size ranges in the green compact.
The sintering of the formed powder metal articles is preferably accomplished in a sintering furnàce having an inert or reducing atmosphere, usually hydrogen. The sintering tem-perature depends on the type of metal particles utilized for both the base metal and the dispersoid particles. Sintering is usually carried out at a temperature ~ich is approxima~ely 75% of the melting point of the base metal. It being preferred that when nic~el is employed as the base metal and chromium as the dispersoid the sintering temperature should range from about 1900 F to about 2050. The sintered article is uSually cooled to about room temperature before it is removed from the furnace.
In the preferred practice of the invention the sintered article is then compacted, if required, by any con-_9_ 1~768~6 ventional means to form an article having the desired degree of porosity. In the preferred practice of the invention, it is desirable to have a porosity in the final article of about 55 to about 85%. This article is then subjected to an annealing treatment, if required. The exact temperature and duration of annealing depends on the materials used to rOrm the porous metal article.
In addition to the foregoing, another method for obtaining the desired mixture of base metal particles and dispersoid particles is realized by depositing the dispersoid on the surface of the base metal particles by chemical means.
The process described by N. J. Grant in "Powder Metallurgy", volume 10, pp. 1 through 12, and also in U. S. Patent 3,175,904, issued March 30, 1965, are particularly effective in forming 15 initial mixtures by chemical means. ~-Specific examples of procedures used in making materials and articles of manufacture of the invention are given belo~. These examples are to be considered as iIlustra-tive only and not as limiting in any manner the scope and spirit of the invention as defined by the ap~ended claims.
Example 1 About 90 grams of nickel having a particle size distribution ranging from about 3 microns to about 7 microns was mixed with about 10 grams of chromium having a particle size distribution ranging from about 3 microns to about 5 microns in a ~-twin shell-type of blender for about 10 minutes.
The resultant mixture was essentially homogeneous and contained, in weight percent, about 90 nickel and about 10 chromium. This mixture was then screened through a 100-mesh screen and about . .
100 grams of the through-100-mesh material was placed into a D-56~3 - 1~76846 6" by 6" by .070" rectangular mold to form a porous compacted _ green metal body having an apparent density of about 1.3 g/cc.
The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature of about 1400F for a period of about 15 minutes and then to a temperature of about 1950F for a period of about 15 minutes. The sintered metal article was then cooled to room temperature and subsequently compacted by mechanical means to a porosity of about 70~ It was then subjected to an annealing treatment by heating it in a hydrogen atmosphere to a temperature of about 1950F for a period of about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tests and found to be electrically conductive and to exhibit a porosity of about 70%, with a mean pore siz`e of 5 microns.
The so-produced sintered porous metal article was then placed in an oven having a reducing atmosphere and heated at a temperature of about 1400F for a period of about
_~_ .... - ~. : .. . .
D-56~3 ~07684G
Both of the above techniques require precise control of sintering conditions to ensure termination thereof prior to pore channel breakdown.
One recently developed technique, where a dispersed phase of critical amounts of inert dispersoid particles of specified size are incorporated in sintered metal or metal alloy, apProximates controlling the pore size, its distribution, and shrinkage inhibition. To be effective, the inert particles must form with the sintered particles a wetting angle of at least 90 as measured from the sintered metal-dispersoid parti-cle interface to the sintered metal-atmosphere interface. The resulting materials exhibit a network of stabiliæed inter-connected pore channels of narrow size distribution.
Particles of any shape can be used in the matrix so long as the voids remaining bet~een them after they have been loosely packed or pressed together form inter-connected pore channe-ls penetrating the body of the compact. This process, as it is described in U. S. Patent No. 3,397,96~, has certain critical disadvantages, specifically, sintered metal articles produced by the concerned technique e~hibit limited electrical conductivity. Accordingly, when it is desired to provide a thermally stable sintered porous metal article which is con-ductive, the technique of U. S. Patent No. 3,397,96~ cannot be used.
~he instant invention provides a means of overcoming various limitations found in prior art methods of producing ` sintered porous metal articles. Specifically, the instant invention provides sintered porous metal articles which are both thermall~ stable and characterized by their degree of electrical conductivity. Such articles h.~ve a myriad of uses, ~`` 1C~76846 such as, for example, high temperature heating elements, conductive metallic grids which are to be utilized at high temperature, electrodes for fuel cells (especially high temperature fuel cells), and as conductive elements for high temperature electrostatic precipitators. These uses are not exclusive, but are merely set forth herein as typical examples.
The instant invention concerns a unique thermally stable, electrically conductive porous sintered metal article which comprises a structure or framework of sintered base metal particles defining a network of inter-connected pore channels formed therein with dispersoid particles distributed through the basic structure which interconnect or are inter-locked with adjacent base metal particles.
~he physical dimensions of the interconnecting pore channels which may be randomly formed do not essentially change on heating to temperatures approaching the original !
sintering temperature.
The dispersoid particles are both conductive and refractory.
In the preferred embodiment of the invention the conductive metal particles are present in an amount ranging from a trace amount up to about 30 weight percent of the sintered porou~ metal article.
In addition, the present invention is concerned with a method of producing a sintered metal article which is electrically conductive and essentially thermally stable when used at elevated temperatures which includes the steps of preparing a mixture or blend of base metal particles and dispersoid particles which are both conductive and refractory, forming the mixture into an article of the desired shape, and heating the formed article at sintering temperatures ~ 6 -. .
-: 4~; `
to form a sintered article characterized by its thermal stability and by interconnected pores, the physical dimensions of which do not essentially change on subsequent heating to temperatures approaching the original sintering temperature.
In the preferred practice of the invention, after the porous metal article has been sintered it is sometimes subjected to a compacting and then an annealing treatment, depending on contemplated applications.
- 6a-D-56~3 1C~76846 Description of the Preferred Embodiments of the Invention Base metal particles used in the practice of the invention can be made of any metal. Preferably such metal is one selected from the group consisting of nickel, iron, cobalt, and mixtures thereof. In this regard, it is to be noted that more than one base metal or alloy of base metals may be utilized in the practice of the invention.
In the practice of the invention it has been found to be preferable to utilize base metal particles having a particle size ranging from about 0.-1 to about 200 microns.
The active or conductive dispersoid particles used in the practice of the instant invention must be both refractory and conductive. Preferably, such particles are fashioned from a metal selected from the group consisting of chromium, molyb-denum~ tungsten, and mixtures thereof. Lîke the base metalparticles, dispersoid particles of different metals or alloys can be utilized in the practice of the invention. Essentially, all that is required is that the dLspersoid particles are (1) conductive, refractory, and capable of interlocking with ad-~acent base metal particles to form a unitary porous mass and (2) do not form a liquid phase during sintering.
In the practice of the invention it is preferred to utilize dispersoid particles having a particle size distri- `~
bution ranging from about 0.01 to about 50 micron$.
The dispersoid particles in the starting mixture should be as small as possible to prevent their interference with the pore channel network with the only limitation on minimum size being the practical limit of the availability of sizes below 0.01 microns. It has been noted that dispersoid particles are desirably less than one-third the size of the pore channels.
D-56~3 768~6 For larger sizes, the particles tend to block and close many of the pores to the detriment of usable pore volume. To ensure that the dispersoid particlès in the materials of the invention are within these limits~ there must be taken into account the tendency of many particles to grow during sinter-ing. When such growth occurs, the dispersoid particles in the initial mixture prior to processin~ must naturally be smaller than the aforementioned sizes. Such growth can readily be compensated for by workers skilled in the art.
Base metal particles and dispersoid particles can be mixed together by any convenient means. In practice, it is preferred to use a V-twin shell-type of blender. The exact `
duration of blending is not critical. All that is required is that the materials are uniformly mixed.
The preferred mixture of base metal and dispersoid particles should range from about 95 to about 70 weight percent base metal and from about 5 to about 30 weight percent dis-persoid particles.
The mixture of base metal particles and dispersold ;
particles can be formed into any desired shape b~ conventional techniques which are known to the art and will not be dis-cussed herein in detaiI. The initial powder mi~ture should be -~
such as to ensure uniform distribution of the dispersoid particles at the surfaces of the metal particles during forma-tion of a uniform mixture wherein the dispersoid particles are located at or on the surfaces of the metal particles. No si~nificant separation of the phases should occur causing some metal particles to be devoid of or have less dispersoid on their surfaces than others. AEglomeration of the dispersoid should also be avoided in the mixture. The relative concentration : -- .: : : , , : -1~76~46 and sizes of the metal and dispersoid po~ders must naturally be such as to produce, upon further processing, the desired microstructure in the finished body.
In the preferred practice of the invention, articles are formed by filling a mold with the desired amount of material.
Obviously, there are many ways in which the desired article can be fabricated.
The pore size of channels in the finished product !:
is influenced not only by the concentrations and slzes of metal and dispersoid particles and sintering conditions but also by - the degree of compaction experienced in forming the green com- i pact. The compact may be formed by any of the various ~ell-known techniques, including uni- or multidirectional die pres-sing, isostatic pressing, powder rolling, extruding, and roll-bar molding. ~arious degrees of compaction are achieved in these processes, resulting in a ~ariety of pore size ranges in the green compact.
The sintering of the formed powder metal articles is preferably accomplished in a sintering furnàce having an inert or reducing atmosphere, usually hydrogen. The sintering tem-perature depends on the type of metal particles utilized for both the base metal and the dispersoid particles. Sintering is usually carried out at a temperature ~ich is approxima~ely 75% of the melting point of the base metal. It being preferred that when nic~el is employed as the base metal and chromium as the dispersoid the sintering temperature should range from about 1900 F to about 2050. The sintered article is uSually cooled to about room temperature before it is removed from the furnace.
In the preferred practice of the invention the sintered article is then compacted, if required, by any con-_9_ 1~768~6 ventional means to form an article having the desired degree of porosity. In the preferred practice of the invention, it is desirable to have a porosity in the final article of about 55 to about 85%. This article is then subjected to an annealing treatment, if required. The exact temperature and duration of annealing depends on the materials used to rOrm the porous metal article.
In addition to the foregoing, another method for obtaining the desired mixture of base metal particles and dispersoid particles is realized by depositing the dispersoid on the surface of the base metal particles by chemical means.
The process described by N. J. Grant in "Powder Metallurgy", volume 10, pp. 1 through 12, and also in U. S. Patent 3,175,904, issued March 30, 1965, are particularly effective in forming 15 initial mixtures by chemical means. ~-Specific examples of procedures used in making materials and articles of manufacture of the invention are given belo~. These examples are to be considered as iIlustra-tive only and not as limiting in any manner the scope and spirit of the invention as defined by the ap~ended claims.
Example 1 About 90 grams of nickel having a particle size distribution ranging from about 3 microns to about 7 microns was mixed with about 10 grams of chromium having a particle size distribution ranging from about 3 microns to about 5 microns in a ~-twin shell-type of blender for about 10 minutes.
The resultant mixture was essentially homogeneous and contained, in weight percent, about 90 nickel and about 10 chromium. This mixture was then screened through a 100-mesh screen and about . .
100 grams of the through-100-mesh material was placed into a D-56~3 - 1~76846 6" by 6" by .070" rectangular mold to form a porous compacted _ green metal body having an apparent density of about 1.3 g/cc.
The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature of about 1400F for a period of about 15 minutes and then to a temperature of about 1950F for a period of about 15 minutes. The sintered metal article was then cooled to room temperature and subsequently compacted by mechanical means to a porosity of about 70~ It was then subjected to an annealing treatment by heating it in a hydrogen atmosphere to a temperature of about 1950F for a period of about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tests and found to be electrically conductive and to exhibit a porosity of about 70%, with a mean pore siz`e of 5 microns.
The so-produced sintered porous metal article was then placed in an oven having a reducing atmosphere and heated at a temperature of about 1400F for a period of about
3,000 hours. Thereafter, the physical properties of the metal article were again measured with the result being that essenti-ally no deterioration in such properties was observed. That is, the article was still highly electrically conductive and -evidenced the same general physical properties set forth above.
There was no further sintering due to this high temperature testing.
Due to its extreme thermal stability, together with its electrical conductivity, the foregoing article finds utility as an electrode which is especially adapted for use in a high temperature fuel cell.
.
D-~6~3 - ~0~6846 Example 2 About 90 grams of nickel having a particle size distribution ranging from about 3 to 7 microns was mixed with about 10 grams o~ alloyed chromium and tungsten having a particle size distribution ranging from about 9 to about 11 microns in a V-twin shell-type of blender for about 10 minutes.
The resultant mixture was essentially homogeneous and contained, in weight percent, about 90% nic~el and about 10% chromium and tungsten. This mixture was then screened through a 100-mesh screen and about 100 grams of the through-100-mesh material was placed into a 6" by 6" by .070" rectangular mold to form a porous compacted green metal body having an apparent density of about 1.3 g/cc. The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature oE about 1400F for a period of about 15 minutes and then to a temperature of about 1950 F for a period of about 15 minutes. The sintered metal article was ~hen cooled to room temperature and subsequently compacted by mechanical means to a porosity of about 70~. It was then sub-jected to an annealing treatment by heating it in a hydrogenatmosphere to a temperature of about 1950F for a period o~
about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tests and found to be electrically 25 conductive and to exhibit a porosity of about 70%, with a mean pore size ranging from about 7 microns.
The test procedure used to measure stability was similar to that used in Example 1.
Example_3 30About 90 grams of cobalt having a particle size - distribution ranging from about 9 to about 15 microns was .; .
1C~768~6 mixed with about 10 grams of chromium having a particle size ' distribution ranging from about 3 to about 5 microns in a V-twin shell-type of blender for about 10 minutes. The result-ant mixture was essentially homogeneous and contained, in weight percent~ about 9 ~0 cobalt and about lO~o chromium. This mixture was then screened through a 100-mesh screen and about 100 granls of the through-100-mesh material was placed into a 6" by 6"
by .070" rectangular mold to form a porous compacted green ` metal body having an apparent-density of abouk 1.3 g/cc. The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature of about 1400F for a period of about 15 minutes and then to a temperature of about 1950 F for a period of about 15 minutes. The sintered metal article was then cooled to room temperature and subsequent]y compacted by mechanical means to a porosity of about 70%. It was then subjected to an annealing treatment by heatirlg it in a hydrogen atmosphere to a temperature of about 1950 1l~ for a period of about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tesks and found to be electrically conductive and to exhibit a porosity of about 70,~0, with a mean pore size ranging from about 6 microns.
The stability tests were similar to those of previous 25 examples.
While there have been described herein what are, at present, considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made kherein without 30 departing from the spirit and scope of the invention as herein-after claimed. r "
.
There was no further sintering due to this high temperature testing.
Due to its extreme thermal stability, together with its electrical conductivity, the foregoing article finds utility as an electrode which is especially adapted for use in a high temperature fuel cell.
.
D-~6~3 - ~0~6846 Example 2 About 90 grams of nickel having a particle size distribution ranging from about 3 to 7 microns was mixed with about 10 grams o~ alloyed chromium and tungsten having a particle size distribution ranging from about 9 to about 11 microns in a V-twin shell-type of blender for about 10 minutes.
The resultant mixture was essentially homogeneous and contained, in weight percent, about 90% nic~el and about 10% chromium and tungsten. This mixture was then screened through a 100-mesh screen and about 100 grams of the through-100-mesh material was placed into a 6" by 6" by .070" rectangular mold to form a porous compacted green metal body having an apparent density of about 1.3 g/cc. The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature oE about 1400F for a period of about 15 minutes and then to a temperature of about 1950 F for a period of about 15 minutes. The sintered metal article was ~hen cooled to room temperature and subsequently compacted by mechanical means to a porosity of about 70~. It was then sub-jected to an annealing treatment by heating it in a hydrogenatmosphere to a temperature of about 1950F for a period o~
about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tests and found to be electrically 25 conductive and to exhibit a porosity of about 70%, with a mean pore size ranging from about 7 microns.
The test procedure used to measure stability was similar to that used in Example 1.
Example_3 30About 90 grams of cobalt having a particle size - distribution ranging from about 9 to about 15 microns was .; .
1C~768~6 mixed with about 10 grams of chromium having a particle size ' distribution ranging from about 3 to about 5 microns in a V-twin shell-type of blender for about 10 minutes. The result-ant mixture was essentially homogeneous and contained, in weight percent~ about 9 ~0 cobalt and about lO~o chromium. This mixture was then screened through a 100-mesh screen and about 100 granls of the through-100-mesh material was placed into a 6" by 6"
by .070" rectangular mold to form a porous compacted green ` metal body having an apparent-density of abouk 1.3 g/cc. The molded green metal body was then placed in a sintering oven and sintered in a hydrogen atmosphere by heating first to a temperature of about 1400F for a period of about 15 minutes and then to a temperature of about 1950 F for a period of about 15 minutes. The sintered metal article was then cooled to room temperature and subsequent]y compacted by mechanical means to a porosity of about 70%. It was then subjected to an annealing treatment by heatirlg it in a hydrogen atmosphere to a temperature of about 1950 1l~ for a period of about 15 minutes.
The article, produced as above described, was sub-jected to certain physical tesks and found to be electrically conductive and to exhibit a porosity of about 70,~0, with a mean pore size ranging from about 6 microns.
The stability tests were similar to those of previous 25 examples.
While there have been described herein what are, at present, considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made kherein without 30 departing from the spirit and scope of the invention as herein-after claimed. r "
.
Claims (17)
1. A method of producing a porous sintered metal article which is electrically conductive and essentially thermally stable when used at elevated temperatures which method comprises the steps of:
preparing a mixture of base metal particles and dispersoid particles, said dispersoid particles being both refractory and conductive;
forming said mixture into an article of the desired shape, and heating said formed article at sintering temperatures to form a sintered article which is characterized by having interconnecting pores, the physical dimensions of which do not essentially change on subsequent heating to temperatures approaching the original sintering temperature.
preparing a mixture of base metal particles and dispersoid particles, said dispersoid particles being both refractory and conductive;
forming said mixture into an article of the desired shape, and heating said formed article at sintering temperatures to form a sintered article which is characterized by having interconnecting pores, the physical dimensions of which do not essentially change on subsequent heating to temperatures approaching the original sintering temperature.
2. The method of claim 1, wherein after sintering the formed article is further compacted.
3. The method of claim 2, wherein said article is com-pacted in such a manner so as to exhibit a porosity ranging from about 55 to about 85 volume percent.
4. The method of claim 2, wherein said compacted article is subsequently subjected to an annealing treatment.
5. The method of claim 1, wherein said base metal is a metal selected from the group consisting of nickel, cobalt, iron and mixtures thereof.
6. A method of claim 5, wherein said base metal is nickel.
7. The method of claim 1, wherein said dispersoid particles are composed of a metal selected from the group consisting of chromium, tungsten, molybdenum and mixtures thereof.
8. The method of claim 7, wherein said dispersoid particles are composed of chromium.
9. The method of claim 1, wherein said base metal particles have a particle size ranging from about 0.1 microns to about 200 microns.
10. The method of claim 1, wherein said dispersoid parti-cles have a particle size ranging from about 0.01 microns to about 50 microns.
11. The method of claim 1, wherein said mixture of base metal particles and dispersoid particles is obtained by depositing the dispersoid particles on the surface of the base metal particles.
12. The method of claim 10, wherein said dispersoid particles are deposited on said base metal particles by chemical means.
13. A sintered porous metal article which is electrically conductive and characterized by its thermal stability when heated to elevated temperatures comprising a continuous structure of sintered base metal particles defining a network of interconnecting pore channels, the physical dimensions of which do not essentially change on heating to temperatures approaching the original sintering temperature, said channels penetrating said structure, dispersoid particles distributed throughout the structure, said dispersoid particles interconnecting adjacent base metal particles, said dispersoid particles being both conductive and refractory.
14. The article of claim 13, wherein said base metal particles are selected from the group consisting of nickel, iron, cobalt and mixtures thereof.
15. The article of claim 14, wherein said base metal particles are nickel.
16. The article of claim 14, wherein said dispersoid particles are selected from the group consisting of chromium, tungsten, molybdenum and mixtures thereof.
17. The article of claim 16, wherein said dispersoid particles are composed of chromium.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64412475A | 1975-12-24 | 1975-12-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1076846A true CA1076846A (en) | 1980-05-06 |
Family
ID=24583544
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA266,220A Expired CA1076846A (en) | 1975-12-24 | 1976-11-22 | Thermally stable sintered porous metal articles |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5281008A (en) |
| BE (1) | BE849639A (en) |
| CA (1) | CA1076846A (en) |
| CH (1) | CH612108A5 (en) |
| DE (1) | DE2657434A1 (en) |
| FR (1) | FR2336204A1 (en) |
| GB (1) | GB1572180A (en) |
| NO (1) | NO764308L (en) |
| SE (1) | SE7613459L (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4129099A (en) * | 1977-04-15 | 1978-12-12 | General Motors Corporation | Galvanic exhaust gas sensor with solid electrolyte |
| US4752500A (en) * | 1986-04-02 | 1988-06-21 | Institute Of Gas Technology | Process for producing stabilized molten carbonate fuel cell porous anodes |
| DE19611306A1 (en) * | 1996-03-22 | 1997-09-25 | Agni Waerme Und Werkstofftechn | Porous electrically conducting composite material production |
| CN115229189B (en) * | 2022-06-27 | 2024-04-05 | 北京科技大学 | Preparation method of uniform porous tungsten product |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3175903A (en) * | 1963-06-10 | 1965-03-30 | Bendix Corp | Process for forming porous tungsten |
| FR1520916A (en) * | 1966-04-08 | 1968-04-12 | Lockheed Aircraft Corp | Porous sintered material obtained from a metal or a metal alloy |
| FR2031787A5 (en) * | 1969-02-07 | 1970-11-20 | Onera (Off Nat Aerospatiale) |
-
1976
- 1976-11-22 CA CA266,220A patent/CA1076846A/en not_active Expired
- 1976-11-24 GB GB49060/76A patent/GB1572180A/en not_active Expired
- 1976-12-01 SE SE7613459A patent/SE7613459L/en not_active Application Discontinuation
- 1976-12-17 DE DE19762657434 patent/DE2657434A1/en not_active Withdrawn
- 1976-12-20 NO NO764308A patent/NO764308L/no unknown
- 1976-12-20 BE BE173460A patent/BE849639A/en unknown
- 1976-12-21 CH CH1612376A patent/CH612108A5/en not_active IP Right Cessation
- 1976-12-23 FR FR7638951A patent/FR2336204A1/en active Granted
- 1976-12-24 JP JP51155173A patent/JPS5281008A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| CH612108A5 (en) | 1979-07-13 |
| FR2336204B1 (en) | 1982-07-02 |
| DE2657434A1 (en) | 1977-06-30 |
| BE849639A (en) | 1977-04-15 |
| FR2336204A1 (en) | 1977-07-22 |
| NO764308L (en) | 1977-06-27 |
| JPS5281008A (en) | 1977-07-07 |
| SE7613459L (en) | 1977-06-25 |
| GB1572180A (en) | 1980-07-23 |
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