CA1236711A - Method for making ultrafine metal powder - Google Patents
Method for making ultrafine metal powderInfo
- Publication number
- CA1236711A CA1236711A CA000445826A CA445826A CA1236711A CA 1236711 A CA1236711 A CA 1236711A CA 000445826 A CA000445826 A CA 000445826A CA 445826 A CA445826 A CA 445826A CA 1236711 A CA1236711 A CA 1236711A
- Authority
- CA
- Canada
- Prior art keywords
- powder
- molten
- particles
- droplets
- plasma
- 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
Links
Classifications
-
- 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
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
-
- 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
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/10—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying using centrifugal force
Abstract
ABSTRACT
A fine powder is prepared by directing a high velocity stream of molten droplets at a repellent surface. Droplets which impact the surface are fragmented and solidified to form a very fine powder having smoothly curvilinear surfaces and diameters less than about 10 micrometers.
A fine powder is prepared by directing a high velocity stream of molten droplets at a repellent surface. Droplets which impact the surface are fragmented and solidified to form a very fine powder having smoothly curvilinear surfaces and diameters less than about 10 micrometers.
Description
D-24,689 METHOD FOR MAKING ULTRAFINE METAL POWDER
FIELD OF INVENTION
The present invention relates to a process for making rapidly cooled fine metal powders.
BACKGROUND OF T~IE INVENTION
U.S. patent 3,646,177 to Tnompson discloses a method for producing powdered metals and alloys that are Eree from oxidation by a process which involves atomi~ing molten metal with a fluid j~t to form discrete particles of the molten metal. The jet is directed into a reservoir of an inert cryogenic liquid to solidify the particles and prevent oxidation during cooling.
U.S. patent 4,069,045 to Lundgren describes a process wherein a jet of molten metal is impinged against a rotating flat disc. Relatively thin, brittle, easily shattered, and essentially dentrite free metal flakes are obtained. These flakes are also described in .S. patent 4,063,9 42 to Lundgren~
U.S. patent 4,221,587 to Ray relates to a method of making powder by impinging a jet oE molten alloy at an acute angle against -the inner surface of a rotating cylindrical chill body. As set forth in column 5, the impinging molten metal breaks into a stream of discrete droplets which bounce off the surface and move in the direction of the chill surface. Upon impact wi-th the chill surface, -the droplets are solidified at a rapid ~3~
D-24,689 rate. As set forth in column 6, "the glassy metal powder particles ... have relatively sharp notched edges which enable the particles to interlock during compaction." As se-t forth in the first example, the particle size of the powder is such that 90~ oE the particles have a particle slze range between about 25 and 300 microns. In the second e~ample, the par-ticle size of the powder ranges between 100 and 1000 microns. Herbert Herman and Hareesh Bha-t, in an article entitled "Metastable Phases Produced by Plasma Spraying"
appearing in the proceedings of a symposium sponsored by the T~S-AIME alloy Phases Committee at the Fall meeting of the Metallurgical Society of AIME, Pittsburgh, Pennsylvania, October 5-9, 1980 describes -the high velocity deposition of plasma-melting particles on a substrate. On page 118, the article indica-tes that good physical and thermal contact should exist between the solidifying liquid and substrate. Li~uid spreading occurs away from the impact point. As illustrated in the drawings, the particles have a flat surface adjacent the substrate with a central raised core region and a circular rim area.
DRAWINGS
Figure 1 is a schematic drawing of a device including a plasma spray apparatus and drum.
Figure 2 is a schematic drawing of a device including a plasma spray apparatuC~ substra-te and gas discharge device.
Figure 3 is a schematic drawing oE plasma spray apparatus, endless belt, and discharge device for substrate material.
SUMMARY OF INVENTION
Atomi2ed metal or metal alloy powders in the one to ten micrometer size range are desirable for many applications such as electrostatic copying and ~or rapid D-24,689 -3-solidification processes. Elowever, particles in this size range are very difficult to obtain. Standard atomization techniques, whefe a gas or liquid impinges a molten metal exiting an orifice, are not eEfective in producing particles in the above range. Agglomeration and plasma melting methods are also not effective since it is necessary to start with particles or agglomerates of about the same si~e as the ending particles.
Agglomerates oE very small si~e are difficult to form and uniformity in particle composition is even more difficult to obtain. In general, very fine powders are often high in atrnosphere impurities such as oxygen, nitrogen or impurities Erom the grinding medium used to obtain the small size.
In accordance with the presen-t invention, there is provided a fine powder wherein a substantial portion of the particles have smoothly curvilinear surfaces and an average particle size less than about ten micrometers.
Also, in accordance with the present inven-tion, there is provided a process for making very fine metal powder. A high velocity stream of molten metal droplets is directed toward a repellent surface. The molten droplets are impac-ted against the surface to fragment the droplets and form still molten fragmented portions which are rapidly cooled to form a fine metal powder.
The resulting powder comprises particles less than about ten micrometers with curvilinear surface.
DETAILED DESCRIPTION
High velocity streams of molten metal droplets may be ~ormed by thermal spraying. A wide range of materials, both organic and inorganic may be thermally sprayed. Typical organic materials include high melting polymers such as high temperature aromatic polyester plastics. One such polymer is sold under the trade name ~3~
D-24,689 EKO~OL*by the Carborundum Company. Inorganic materials for thernal spraying include ceramlcs and cermets.
The preferred powders are metals and metal alloys.
Low melting metals or alloys may include zinc, lead, silver or gold. Higher melting point metals and àlloys typically contain copper, cobalt, iron and nickel may be used. The re~ractory metals and alloys which typically have melting points in excess of 1800 degrees centirade are of particular interest. The refractory type metals include molybdenum, niobium, tungsten, tantalum, chromium alloys and mixtures thereof. The term metals include elemental metals, alloys, pure or mixed oxides, borides, carbides and nitrides of metal with or without additives.
Since the powders of the present invention are produced by rapid cooling, at least some of the powders contain particles having amorphous phases or metastable crystal structures. Metal alloys which are most easily obtained in the amorphous state by rapid quenching or by deposition techniques are mix-tures of transition metals.
The cooling rate necessary to achieve the amorphous state depends on the composition of the alloys.
Generally, there is a small range of compositions surrounding each of the known compositions where the amorphous state can be obtained. However, apart rom quenching the alloys, no practical guideline is kno-~n for predicting with certainty which of the multitude of different alloys will yield an amorphous me-tal with given processing conditions. Examples of arnorphous alloys formed by rapid quenching are described in U.S.
patent 3,856,513 to Ohen et al, U.S. patents 3,427,154 and 3,981,722, as well as others.
The amorphous and crystalline state are distinguished most readily by differences in X-ray diffraction measurement. Diffraction patterns of an * Trade Mark ~ !; ` . ~
D-24,689 amorphous substance reveal a broad halo similar to a liquid. Crystalline materials produce a line or broadened line diffrac-tion pattern. The amorphous alloys provided by the present invention appear to be liquid when studied from x-ray diffraction patternsl but the alloy is soli~ when studied in terms of hardness anc1 viscosity. An amorphous alloy structure is inherently metastable, i.e., the sta-te is non-equilibrium. Since the atoms of the amorphous structure are no-t arranged in a periodic array, there is at any temperature a tendency of the amorphous structure to transform toward the crystalline structure oE the equilibrium state through diffusion or segregation of components of the alloy.
The rapidly cooled powder particles of the present invention preferably have a particle size distribution wherein at least about 80 percent of the particles have an average particle size less than about 10 microns.
Depending on the composition and exact conditions of powder formation, even smaller particle size distributions wherein at least 90 percen-t oE the particles have an average particle size less -than about 10 microns may be formed. Another particle distribution includes greater than about 80 percent of the particles having average particle size grea-ter than about 0.5 and less than about 8 microns.
The particles of the presen-t inven-tion are preferably cooled from ultrafine portions of molten materials to give a charac-teristic curvilinear surface to the particles. Due to surface tension, airborn 3() molten material tends to contract un-til the smallest surEace area consistent with its volume is occupied.
Due to the repellent nature of the repellent surface droplet forma-tion is favored. The -tendency of the molten material is to form spheres. If the rapidly cooled part;cles solidify prior to assuming the shape of D-24,689 a sphere or molten particles collide during cooling, the molten portions may form elliptically shaped or elonga-ted particles with rounded ends.
The powders of the present invention differ from milled or fractured powders which are characterized by an irregularly shaped outline which may have sharp or rough edges.
According to -the srunauer, Emmett and Teller tBET) method and equation for determining the surEace area and diameter, the particles of the present invention exhibit BET diameters from about 1/2 micrometers to about 10 micrometers.
A scanning Election Micrograpn (SE~) photo of molybdenum powder oE the presen-t invention has particles which have substantially smoothly curvilinear surfaces.
The particles appear as small blobs or globs which are spheroidally and ovoidally shaped with arcua-te and curved surfaces. The particles comprise cells of from about 0.01 to about 0.1 micrometers which are indicative oE rapid cooling.
In preparing the powders of the present invention, a high velocity stream of molten metal droplets is Eormed. Such a stream may be Eormed by any thermal spraying technique such as electric-arc spraying, combustion spraying and plasma spraying. Typically, the velocity oE the molten drople-ts is greater than about 100 meters per second, preferably greater than about 200 meters per second, and more preferably greater than 250 meters per second. Velocities on -the order oE 900 meters per second or grea-ter may be achieved under certain conditions which Eavor these speeds which may include spraying in a vacuum.
In the preferred process of the present invention, a powder is fed through a thermal spray appara-tus. Feed 3'~
D-24,689 powder is entrained in a carrier gas and then fed through a high temperature reactor. The temperature in the reactor is preferably above the melting point of the highest melting componen-t of -the metal powder and even more preferably above the vaporization point of the lowest vaporizing componen-t of the material to enable a relatively short residence time in the reaction zone.
The stream of dispersed entrained mol-ten me-tal droplets may be produced by plasma-jet torch or gun apparatus of conventional nature. Typical plasma jet apparatus is of the resistance arc or induction typeO
In general, a source of metal powder is connected to a source of propellant gas. A means is provided to mix the gas with the powder and propel the gas with entrained powder through a conduit communicating with a nozzle passage of the plasma spray apparatus. In the arc type apparatus, the entrained powder may be fed into a vortex cham~er which communica-tes with and is coaxial with the nozzle passage which is bored centrally through the nozzle. In an arc type plasma apparatus, an electric arc is maintained between an interior wall of the nozzle passage and an electrode present in the passage. The electrode has a diameter smaller than the nozzle passage with which it is coax.ial to so tha-t the gas is discharged from the nozzle in the form of a plasma jet. The current source is normal.ly a DC source adapted to deliver very large currents at relatively low vol-tages. By adjusting the magnitude of the arc power and the rate of gas flow, torch temperatures can range from 150 degrees centigrade up to about 15,000 degrees centigrade. The apparatus generally mus-t be adjus-ted in acco.rdance with the melting point of the powclers being sprayed and the gas e:mployed. In general, the electrode may be re-tracted within the nozzle when lower melting powders are utilized with an inert gas such as nitrogen ~3~
D-24,689 while the electrode may be more fully extended within the nozzle when higher melting powders are utilized with an inert gas such as argon.
In the induction type plasma spray apparatus, me-tal powder entrained in an inert gas is passed at a high velocity through a strong magne-tic ~ield so as to cause a voltage to be generated in the gas. The current source is adapted to deliver very high currents, on the order o~ 10,000 amperes, although the voltage may be relatively low such as 10 volts. Such currents are required -to generate a very strong direct magnetic field and create a plasma. Such plasma devices may include additional means for aiding in the initiation of a plasma generation, a cooling means for the torch in the ~orm o~ annular chamber around the nozzle.
In the plasma process, a gas which i5 ionized in the torch regains its heat o~ ionization on exiting the nozzle to create a highly intense flameO In general, the ~low of gas through the plasma spray apparatus is e~ected at speeds a-t least approaching the speed of sound. The typical torch comprises a conduit means having a convergent portion which converges in a downstream direction to a throat. The convergent portion communicates with an adjacent outlet opening so that the discharge o~ plasma is ef~ected ollt the outlet opening.
Other types of torches may be used such as an oxy-acetylene type having high pressure ~uel gas flowing through the nozzle. The powder may be introduced into the gas by an aspirating eEfect. The fuel is iynited at the nozzle outlet -to provide a high temperature flame.
Pre~erably the powders utilized for -the torch should be uniform in size, and composi-tion and relatively free flowing. Flowability is desirable to aid in the transpor-tation and injection of the powder into the plasma ~lame. In general, ~ine powders (less 3~
D-24,689 _g _ than 40-micrometers average diameter) do not e~hibit good ~low characteristics. A narrow size distribution is disirable because, under set flame conditions, the largest particles may not melt completely, and the smallest particles may be heated to the vaporization point. Incomplete melting is a detriment to -the product uniformity, whereas vaporization and decomposition decreases process efficiency. Typically, the size ranges Eor plasma feed powders are such that 80 percent of the particles fall within a 30 micrometer diameter range with the range of substantially all -the particles within a 60 micrometer ranqe.
U.S. Patent 3,909,241 to Cheney et al describes a process for preparing smooth, substantially spherical particles having an apparent density of at least 40 percent of the theoretical density of the material. sy plasma densifying an agglomerate obtained by spray drying, me-tals which typically will not alloy in a melt may be intimately mixed in non-equilibrium phases to form a uniform powder composition.
The stream of entrained molten metal droplets which issues from the nozzle tends to expand outwardly so that the density of the droplets in the stream decreases as the dis-tance from the nozzle increases. Prior to impacting the repellent surface, the stream typically passes through a gaseous atmosphere which tends -to cool and decrease the velocity of the droplets. As the atmosphere approaches a vacuum, the cooling and velocity 108s iS diminished. It is desirable that -the nozzle be positioned sufficiently close to the repellent surface so that the droplets are in a molten condition during impact. IE the nozzle is too far away, the droplets may solidify prior -to impact. IE the nozzle is too close the droplets may impinge on previously sprayed mol-ten droplets so as to form a pool of molten ma-terial or D-24,689 -10-increase the droplet size. It is generally desriable that the stream flow in a radial direction toward the repellent surface if the surEace is curved, and in a normal direction, if the surface is flat.
The repellent surface is preferably a sur~ace that is not weted by the molten material so as to increase the propensity of the material to form droplets on the sur~ace. The wettability and relative surEace energy of molten metal and a surface can be determined by measuring the contac-t angle between the liquid phase of the molten metal and the surface through the liquid phase. To Ea~or droplet formation it is preferably to have con-tact angles greater than about ninety degrees.
Typical surfaces may include ceramics such as alumina, silicon nitride, quartz; metal surfaces such as aluminum, copper, and inert solids which may be liquid or solid at room temperatures such as dry ice (CO2) or normal ice (H2O). The surfaces are preferably smooth.
Molten droplets which impact the repellent surface are Eragmented to form molten fragmented portions which are typically a-t leas-t about one third the volume of the original droplet. After impact, the molten fragmented portions solidify to Eorm the powder of the present invention which has substantially smoothly curvilinear surfaces. The molten fragmented portions may be cooled by contact with the repellent surface or by an atmosphere near the repellent surface. The cooling medium, either repellent surface or atmosphere is preferably below the solidification temperature of the molten materialO When a cooling a-tmosphere is uti]i~ed, the fragmented particles may solidiEy after bouncing or rebounding off the surface. When the repellent surface is -the primary cooling medium, the major quenching may occur on or closely adjacent -the surface.
D 24,6~9 It is theorized that the particles tend toward sphericity due ~.o the fact that molten fragmen-ts on the surface tend toward sphericity due to the repellent nature of the surface and rebounding molten fragments tend toward sphericity due to the tendency to contrac-t to the smallest sur~ace area consistent with volume. It is believed that the high velocity tends to promote fragmentation of the particles. As droplets impact the surface, the component of velocity in the direction of :Eliyht is immediately changed -to a velocity componen-t in a direction which is parallel to or at a slight angle to the surface. This force tends to promo-te fragmen-tation of the droplets.
It is preferable -that the rebounding fragmented molten portions and solidified particles have a component of velocity in a given direction normal to the stream direction so as to remove fragmented portions from the path of oncoming droplets. If the nozzle is stationary with respect to the repellent surface, this may be accomplished by passing an inert gas over -the surface at a velocity sufficient to remove fragmented portions. The nozzle or the surface may also be moved relative to each other so as to remove fragmented portions from the oncoming stream of en-trained particles. To prevent impingement of droplets on fragmented portions, it is desirable that the previously fragmented droplets be passed out o:E the range of the oncoming droplets.
Figure 1 describes an apparatus for carrying out the method fo the present inven-tion. There is shown a plasma gun schematically represented at 15. The gun 15 includes a nozzle radially directed at repellent surface 17 which is in the form of a drum. A source of high pressure gas 19 communicates with a powder source 21 for entraining metal powder. The entrained powder is fed to nozzle 15. A source of D.C. powder 23 is electrically connected between the nozzle 15 and the elements 23 for D-24,689 -12-forming plasma 25. After impacting the surface 17, fragmented portions are collected in a container 27.
The drum is rotated so as to impart a tangential component oE velocity -to rebounding particles and remove the fragmen-ted portions 31 from -the path of -the oncoming entrained droplets.
Figure 2 illustrates another embodiment of the presen-t invention where a nozzle 51 directs a plasma stream 53 against a rota-ting disc repellen-t surEace 55.
Another nozzle 57 is directed at the loca-tion cf impact so as to direct a stream of inert yas 61 at rebounding Eragmented portions 65 which are propelled toward container 59 where collected.
Figure 3 illustrates another embodiment where plasma 70 from nozzle 71 is directed against a moving bed of repellent material 75 such as dry ice. The ma-terial 75 is deposited from hopper 77 at one end of the moving endless belt 79. The plasma 70 is directed at the moving bed so as to Eorm fragmented portions 85 which are collected in container 81 at the other end of the endless belt 79.
In Figure 1 through 3 the velocity of the molten droplets in the respective plasma streams 25, 53, 70 is sufficient so that upon impacting respective repellent 25 surfaces 17, 55 and 75 the droplets form fragmented portions. The surEaces 17, 55 and 75 are sufficiently repellent so as to favor drople-t Eorma-tion. Droplets of higher viscosities may require higher velocities for fraymenting droplets.
It is contemplated that a -turbulent yaseous medium adjacent repellen-t surEace may aid the solidification o:E
rebounding particles. A turbulent gaseous rnedium or permitting the rebounding fragmented portions to fall away from the surface under the influence of yravity may enhance the solidification oE the fragmented portions ~L~3~7~
D-24,6~9 -13-awa~ from the surface and thus permit the utilization of less repellent surfaces. The use of a vacuum and permit-ting fragmented molten portions to fall back onto the repellent surface may en'nance the solidification of the fragmented portions on the surface. In this later case, a highly repellent sur~ace may be desirable.
~ _.
A Baystate, PGl20-4* plasma gun is mounted in a chamber about 4 to about 6 inches from a block of dry ice. Agglomerated molybdenum powder (99.9 percent molybdenum) having a size distribution of about 56 percen-t -270 + 325 and about 44 percent -325 mesh is fed to the gun at the rate of 8.85 pounds per hour entrained in argon at about lO cubic feet per hour. The argon plasma gas is fed to the torch at the rate of about 63 cubic feet per hour. The torch power is about 30 volts at 600 amperes. The chamber has a nitrogen atmosphere.
The powder is sprayed in a normal- direction onto a block of dry ice as the nozzle is moved back and for-th over the block. About 85 grams of molybdenum powder is collected. A Scanning Electron Micrograph indicates that about 90 percent of the particles appear to be less than about lO micrometers. At least a portion of the particles appear to have a cellular structure with the 25 cells being from about 0.01 to 0.1 micrometers in size.
The particles have smooth curvilinear surEaces tending toward sphericity. The particles which are most rapidly cooled appear to have amorphous properties.
In a manner similar to example 1, copper powder having a starting size oE about 30 to 40 micrometers is reduced to copper particles having a particle size of about 1 to about 10 micrometers. The star-ting powder *Trade Mark ~3~
D-24,639 -14-has a size distribution of 100 percent less than 270 mesh. The apparatus used is as described in Example 1 except the powder feed rate is 5.7 pounds per hour, plasma gas feed ra-te is 60 cubic feet per hour, and about 405 grams oE -the powder is collected. The final powder exhibits the curvilinear structure similar to the powder structure as of Example 1.
EX~MPLE 3 In a manner similar to Example 2, a powder consisting of nickel, chromium, and boron is plasma sprayed. The resulting powder which tends toward sphericity has an amorphous metastable structure.
In a manner similar to Example 1, the dry ice bed is replaced with a ceramic substrate comprising quartz which has a high thermal shock resistance. The substrate surface is smooth and the cooling gas of nitrogen is directed at the surface in the impact area in a direction tangential to the plasma stream.
Rebounding fragmented particles which are collected exhibit the spherical powder shape and have an average particle size less than about 10 micrometers~
FIELD OF INVENTION
The present invention relates to a process for making rapidly cooled fine metal powders.
BACKGROUND OF T~IE INVENTION
U.S. patent 3,646,177 to Tnompson discloses a method for producing powdered metals and alloys that are Eree from oxidation by a process which involves atomi~ing molten metal with a fluid j~t to form discrete particles of the molten metal. The jet is directed into a reservoir of an inert cryogenic liquid to solidify the particles and prevent oxidation during cooling.
U.S. patent 4,069,045 to Lundgren describes a process wherein a jet of molten metal is impinged against a rotating flat disc. Relatively thin, brittle, easily shattered, and essentially dentrite free metal flakes are obtained. These flakes are also described in .S. patent 4,063,9 42 to Lundgren~
U.S. patent 4,221,587 to Ray relates to a method of making powder by impinging a jet oE molten alloy at an acute angle against -the inner surface of a rotating cylindrical chill body. As set forth in column 5, the impinging molten metal breaks into a stream of discrete droplets which bounce off the surface and move in the direction of the chill surface. Upon impact wi-th the chill surface, -the droplets are solidified at a rapid ~3~
D-24,689 rate. As set forth in column 6, "the glassy metal powder particles ... have relatively sharp notched edges which enable the particles to interlock during compaction." As se-t forth in the first example, the particle size of the powder is such that 90~ oE the particles have a particle slze range between about 25 and 300 microns. In the second e~ample, the par-ticle size of the powder ranges between 100 and 1000 microns. Herbert Herman and Hareesh Bha-t, in an article entitled "Metastable Phases Produced by Plasma Spraying"
appearing in the proceedings of a symposium sponsored by the T~S-AIME alloy Phases Committee at the Fall meeting of the Metallurgical Society of AIME, Pittsburgh, Pennsylvania, October 5-9, 1980 describes -the high velocity deposition of plasma-melting particles on a substrate. On page 118, the article indica-tes that good physical and thermal contact should exist between the solidifying liquid and substrate. Li~uid spreading occurs away from the impact point. As illustrated in the drawings, the particles have a flat surface adjacent the substrate with a central raised core region and a circular rim area.
DRAWINGS
Figure 1 is a schematic drawing of a device including a plasma spray apparatus and drum.
Figure 2 is a schematic drawing of a device including a plasma spray apparatuC~ substra-te and gas discharge device.
Figure 3 is a schematic drawing oE plasma spray apparatus, endless belt, and discharge device for substrate material.
SUMMARY OF INVENTION
Atomi2ed metal or metal alloy powders in the one to ten micrometer size range are desirable for many applications such as electrostatic copying and ~or rapid D-24,689 -3-solidification processes. Elowever, particles in this size range are very difficult to obtain. Standard atomization techniques, whefe a gas or liquid impinges a molten metal exiting an orifice, are not eEfective in producing particles in the above range. Agglomeration and plasma melting methods are also not effective since it is necessary to start with particles or agglomerates of about the same si~e as the ending particles.
Agglomerates oE very small si~e are difficult to form and uniformity in particle composition is even more difficult to obtain. In general, very fine powders are often high in atrnosphere impurities such as oxygen, nitrogen or impurities Erom the grinding medium used to obtain the small size.
In accordance with the presen-t invention, there is provided a fine powder wherein a substantial portion of the particles have smoothly curvilinear surfaces and an average particle size less than about ten micrometers.
Also, in accordance with the present inven-tion, there is provided a process for making very fine metal powder. A high velocity stream of molten metal droplets is directed toward a repellent surface. The molten droplets are impac-ted against the surface to fragment the droplets and form still molten fragmented portions which are rapidly cooled to form a fine metal powder.
The resulting powder comprises particles less than about ten micrometers with curvilinear surface.
DETAILED DESCRIPTION
High velocity streams of molten metal droplets may be ~ormed by thermal spraying. A wide range of materials, both organic and inorganic may be thermally sprayed. Typical organic materials include high melting polymers such as high temperature aromatic polyester plastics. One such polymer is sold under the trade name ~3~
D-24,689 EKO~OL*by the Carborundum Company. Inorganic materials for thernal spraying include ceramlcs and cermets.
The preferred powders are metals and metal alloys.
Low melting metals or alloys may include zinc, lead, silver or gold. Higher melting point metals and àlloys typically contain copper, cobalt, iron and nickel may be used. The re~ractory metals and alloys which typically have melting points in excess of 1800 degrees centirade are of particular interest. The refractory type metals include molybdenum, niobium, tungsten, tantalum, chromium alloys and mixtures thereof. The term metals include elemental metals, alloys, pure or mixed oxides, borides, carbides and nitrides of metal with or without additives.
Since the powders of the present invention are produced by rapid cooling, at least some of the powders contain particles having amorphous phases or metastable crystal structures. Metal alloys which are most easily obtained in the amorphous state by rapid quenching or by deposition techniques are mix-tures of transition metals.
The cooling rate necessary to achieve the amorphous state depends on the composition of the alloys.
Generally, there is a small range of compositions surrounding each of the known compositions where the amorphous state can be obtained. However, apart rom quenching the alloys, no practical guideline is kno-~n for predicting with certainty which of the multitude of different alloys will yield an amorphous me-tal with given processing conditions. Examples of arnorphous alloys formed by rapid quenching are described in U.S.
patent 3,856,513 to Ohen et al, U.S. patents 3,427,154 and 3,981,722, as well as others.
The amorphous and crystalline state are distinguished most readily by differences in X-ray diffraction measurement. Diffraction patterns of an * Trade Mark ~ !; ` . ~
D-24,689 amorphous substance reveal a broad halo similar to a liquid. Crystalline materials produce a line or broadened line diffrac-tion pattern. The amorphous alloys provided by the present invention appear to be liquid when studied from x-ray diffraction patternsl but the alloy is soli~ when studied in terms of hardness anc1 viscosity. An amorphous alloy structure is inherently metastable, i.e., the sta-te is non-equilibrium. Since the atoms of the amorphous structure are no-t arranged in a periodic array, there is at any temperature a tendency of the amorphous structure to transform toward the crystalline structure oE the equilibrium state through diffusion or segregation of components of the alloy.
The rapidly cooled powder particles of the present invention preferably have a particle size distribution wherein at least about 80 percent of the particles have an average particle size less than about 10 microns.
Depending on the composition and exact conditions of powder formation, even smaller particle size distributions wherein at least 90 percen-t oE the particles have an average particle size less -than about 10 microns may be formed. Another particle distribution includes greater than about 80 percent of the particles having average particle size grea-ter than about 0.5 and less than about 8 microns.
The particles of the presen-t inven-tion are preferably cooled from ultrafine portions of molten materials to give a charac-teristic curvilinear surface to the particles. Due to surface tension, airborn 3() molten material tends to contract un-til the smallest surEace area consistent with its volume is occupied.
Due to the repellent nature of the repellent surface droplet forma-tion is favored. The -tendency of the molten material is to form spheres. If the rapidly cooled part;cles solidify prior to assuming the shape of D-24,689 a sphere or molten particles collide during cooling, the molten portions may form elliptically shaped or elonga-ted particles with rounded ends.
The powders of the present invention differ from milled or fractured powders which are characterized by an irregularly shaped outline which may have sharp or rough edges.
According to -the srunauer, Emmett and Teller tBET) method and equation for determining the surEace area and diameter, the particles of the present invention exhibit BET diameters from about 1/2 micrometers to about 10 micrometers.
A scanning Election Micrograpn (SE~) photo of molybdenum powder oE the presen-t invention has particles which have substantially smoothly curvilinear surfaces.
The particles appear as small blobs or globs which are spheroidally and ovoidally shaped with arcua-te and curved surfaces. The particles comprise cells of from about 0.01 to about 0.1 micrometers which are indicative oE rapid cooling.
In preparing the powders of the present invention, a high velocity stream of molten metal droplets is Eormed. Such a stream may be Eormed by any thermal spraying technique such as electric-arc spraying, combustion spraying and plasma spraying. Typically, the velocity oE the molten drople-ts is greater than about 100 meters per second, preferably greater than about 200 meters per second, and more preferably greater than 250 meters per second. Velocities on -the order oE 900 meters per second or grea-ter may be achieved under certain conditions which Eavor these speeds which may include spraying in a vacuum.
In the preferred process of the present invention, a powder is fed through a thermal spray appara-tus. Feed 3'~
D-24,689 powder is entrained in a carrier gas and then fed through a high temperature reactor. The temperature in the reactor is preferably above the melting point of the highest melting componen-t of -the metal powder and even more preferably above the vaporization point of the lowest vaporizing componen-t of the material to enable a relatively short residence time in the reaction zone.
The stream of dispersed entrained mol-ten me-tal droplets may be produced by plasma-jet torch or gun apparatus of conventional nature. Typical plasma jet apparatus is of the resistance arc or induction typeO
In general, a source of metal powder is connected to a source of propellant gas. A means is provided to mix the gas with the powder and propel the gas with entrained powder through a conduit communicating with a nozzle passage of the plasma spray apparatus. In the arc type apparatus, the entrained powder may be fed into a vortex cham~er which communica-tes with and is coaxial with the nozzle passage which is bored centrally through the nozzle. In an arc type plasma apparatus, an electric arc is maintained between an interior wall of the nozzle passage and an electrode present in the passage. The electrode has a diameter smaller than the nozzle passage with which it is coax.ial to so tha-t the gas is discharged from the nozzle in the form of a plasma jet. The current source is normal.ly a DC source adapted to deliver very large currents at relatively low vol-tages. By adjusting the magnitude of the arc power and the rate of gas flow, torch temperatures can range from 150 degrees centigrade up to about 15,000 degrees centigrade. The apparatus generally mus-t be adjus-ted in acco.rdance with the melting point of the powclers being sprayed and the gas e:mployed. In general, the electrode may be re-tracted within the nozzle when lower melting powders are utilized with an inert gas such as nitrogen ~3~
D-24,689 while the electrode may be more fully extended within the nozzle when higher melting powders are utilized with an inert gas such as argon.
In the induction type plasma spray apparatus, me-tal powder entrained in an inert gas is passed at a high velocity through a strong magne-tic ~ield so as to cause a voltage to be generated in the gas. The current source is adapted to deliver very high currents, on the order o~ 10,000 amperes, although the voltage may be relatively low such as 10 volts. Such currents are required -to generate a very strong direct magnetic field and create a plasma. Such plasma devices may include additional means for aiding in the initiation of a plasma generation, a cooling means for the torch in the ~orm o~ annular chamber around the nozzle.
In the plasma process, a gas which i5 ionized in the torch regains its heat o~ ionization on exiting the nozzle to create a highly intense flameO In general, the ~low of gas through the plasma spray apparatus is e~ected at speeds a-t least approaching the speed of sound. The typical torch comprises a conduit means having a convergent portion which converges in a downstream direction to a throat. The convergent portion communicates with an adjacent outlet opening so that the discharge o~ plasma is ef~ected ollt the outlet opening.
Other types of torches may be used such as an oxy-acetylene type having high pressure ~uel gas flowing through the nozzle. The powder may be introduced into the gas by an aspirating eEfect. The fuel is iynited at the nozzle outlet -to provide a high temperature flame.
Pre~erably the powders utilized for -the torch should be uniform in size, and composi-tion and relatively free flowing. Flowability is desirable to aid in the transpor-tation and injection of the powder into the plasma ~lame. In general, ~ine powders (less 3~
D-24,689 _g _ than 40-micrometers average diameter) do not e~hibit good ~low characteristics. A narrow size distribution is disirable because, under set flame conditions, the largest particles may not melt completely, and the smallest particles may be heated to the vaporization point. Incomplete melting is a detriment to -the product uniformity, whereas vaporization and decomposition decreases process efficiency. Typically, the size ranges Eor plasma feed powders are such that 80 percent of the particles fall within a 30 micrometer diameter range with the range of substantially all -the particles within a 60 micrometer ranqe.
U.S. Patent 3,909,241 to Cheney et al describes a process for preparing smooth, substantially spherical particles having an apparent density of at least 40 percent of the theoretical density of the material. sy plasma densifying an agglomerate obtained by spray drying, me-tals which typically will not alloy in a melt may be intimately mixed in non-equilibrium phases to form a uniform powder composition.
The stream of entrained molten metal droplets which issues from the nozzle tends to expand outwardly so that the density of the droplets in the stream decreases as the dis-tance from the nozzle increases. Prior to impacting the repellent surface, the stream typically passes through a gaseous atmosphere which tends -to cool and decrease the velocity of the droplets. As the atmosphere approaches a vacuum, the cooling and velocity 108s iS diminished. It is desirable that -the nozzle be positioned sufficiently close to the repellent surface so that the droplets are in a molten condition during impact. IE the nozzle is too far away, the droplets may solidify prior -to impact. IE the nozzle is too close the droplets may impinge on previously sprayed mol-ten droplets so as to form a pool of molten ma-terial or D-24,689 -10-increase the droplet size. It is generally desriable that the stream flow in a radial direction toward the repellent surface if the surEace is curved, and in a normal direction, if the surface is flat.
The repellent surface is preferably a sur~ace that is not weted by the molten material so as to increase the propensity of the material to form droplets on the sur~ace. The wettability and relative surEace energy of molten metal and a surface can be determined by measuring the contac-t angle between the liquid phase of the molten metal and the surface through the liquid phase. To Ea~or droplet formation it is preferably to have con-tact angles greater than about ninety degrees.
Typical surfaces may include ceramics such as alumina, silicon nitride, quartz; metal surfaces such as aluminum, copper, and inert solids which may be liquid or solid at room temperatures such as dry ice (CO2) or normal ice (H2O). The surfaces are preferably smooth.
Molten droplets which impact the repellent surface are Eragmented to form molten fragmented portions which are typically a-t leas-t about one third the volume of the original droplet. After impact, the molten fragmented portions solidify to Eorm the powder of the present invention which has substantially smoothly curvilinear surfaces. The molten fragmented portions may be cooled by contact with the repellent surface or by an atmosphere near the repellent surface. The cooling medium, either repellent surface or atmosphere is preferably below the solidification temperature of the molten materialO When a cooling a-tmosphere is uti]i~ed, the fragmented particles may solidiEy after bouncing or rebounding off the surface. When the repellent surface is -the primary cooling medium, the major quenching may occur on or closely adjacent -the surface.
D 24,6~9 It is theorized that the particles tend toward sphericity due ~.o the fact that molten fragmen-ts on the surface tend toward sphericity due to the repellent nature of the surface and rebounding molten fragments tend toward sphericity due to the tendency to contrac-t to the smallest sur~ace area consistent with volume. It is believed that the high velocity tends to promote fragmentation of the particles. As droplets impact the surface, the component of velocity in the direction of :Eliyht is immediately changed -to a velocity componen-t in a direction which is parallel to or at a slight angle to the surface. This force tends to promo-te fragmen-tation of the droplets.
It is preferable -that the rebounding fragmented molten portions and solidified particles have a component of velocity in a given direction normal to the stream direction so as to remove fragmented portions from the path of oncoming droplets. If the nozzle is stationary with respect to the repellent surface, this may be accomplished by passing an inert gas over -the surface at a velocity sufficient to remove fragmented portions. The nozzle or the surface may also be moved relative to each other so as to remove fragmented portions from the oncoming stream of en-trained particles. To prevent impingement of droplets on fragmented portions, it is desirable that the previously fragmented droplets be passed out o:E the range of the oncoming droplets.
Figure 1 describes an apparatus for carrying out the method fo the present inven-tion. There is shown a plasma gun schematically represented at 15. The gun 15 includes a nozzle radially directed at repellent surface 17 which is in the form of a drum. A source of high pressure gas 19 communicates with a powder source 21 for entraining metal powder. The entrained powder is fed to nozzle 15. A source of D.C. powder 23 is electrically connected between the nozzle 15 and the elements 23 for D-24,689 -12-forming plasma 25. After impacting the surface 17, fragmented portions are collected in a container 27.
The drum is rotated so as to impart a tangential component oE velocity -to rebounding particles and remove the fragmen-ted portions 31 from -the path of -the oncoming entrained droplets.
Figure 2 illustrates another embodiment of the presen-t invention where a nozzle 51 directs a plasma stream 53 against a rota-ting disc repellen-t surEace 55.
Another nozzle 57 is directed at the loca-tion cf impact so as to direct a stream of inert yas 61 at rebounding Eragmented portions 65 which are propelled toward container 59 where collected.
Figure 3 illustrates another embodiment where plasma 70 from nozzle 71 is directed against a moving bed of repellent material 75 such as dry ice. The ma-terial 75 is deposited from hopper 77 at one end of the moving endless belt 79. The plasma 70 is directed at the moving bed so as to Eorm fragmented portions 85 which are collected in container 81 at the other end of the endless belt 79.
In Figure 1 through 3 the velocity of the molten droplets in the respective plasma streams 25, 53, 70 is sufficient so that upon impacting respective repellent 25 surfaces 17, 55 and 75 the droplets form fragmented portions. The surEaces 17, 55 and 75 are sufficiently repellent so as to favor drople-t Eorma-tion. Droplets of higher viscosities may require higher velocities for fraymenting droplets.
It is contemplated that a -turbulent yaseous medium adjacent repellen-t surEace may aid the solidification o:E
rebounding particles. A turbulent gaseous rnedium or permitting the rebounding fragmented portions to fall away from the surface under the influence of yravity may enhance the solidification oE the fragmented portions ~L~3~7~
D-24,6~9 -13-awa~ from the surface and thus permit the utilization of less repellent surfaces. The use of a vacuum and permit-ting fragmented molten portions to fall back onto the repellent surface may en'nance the solidification of the fragmented portions on the surface. In this later case, a highly repellent sur~ace may be desirable.
~ _.
A Baystate, PGl20-4* plasma gun is mounted in a chamber about 4 to about 6 inches from a block of dry ice. Agglomerated molybdenum powder (99.9 percent molybdenum) having a size distribution of about 56 percen-t -270 + 325 and about 44 percent -325 mesh is fed to the gun at the rate of 8.85 pounds per hour entrained in argon at about lO cubic feet per hour. The argon plasma gas is fed to the torch at the rate of about 63 cubic feet per hour. The torch power is about 30 volts at 600 amperes. The chamber has a nitrogen atmosphere.
The powder is sprayed in a normal- direction onto a block of dry ice as the nozzle is moved back and for-th over the block. About 85 grams of molybdenum powder is collected. A Scanning Electron Micrograph indicates that about 90 percent of the particles appear to be less than about lO micrometers. At least a portion of the particles appear to have a cellular structure with the 25 cells being from about 0.01 to 0.1 micrometers in size.
The particles have smooth curvilinear surEaces tending toward sphericity. The particles which are most rapidly cooled appear to have amorphous properties.
In a manner similar to example 1, copper powder having a starting size oE about 30 to 40 micrometers is reduced to copper particles having a particle size of about 1 to about 10 micrometers. The star-ting powder *Trade Mark ~3~
D-24,639 -14-has a size distribution of 100 percent less than 270 mesh. The apparatus used is as described in Example 1 except the powder feed rate is 5.7 pounds per hour, plasma gas feed ra-te is 60 cubic feet per hour, and about 405 grams oE -the powder is collected. The final powder exhibits the curvilinear structure similar to the powder structure as of Example 1.
EX~MPLE 3 In a manner similar to Example 2, a powder consisting of nickel, chromium, and boron is plasma sprayed. The resulting powder which tends toward sphericity has an amorphous metastable structure.
In a manner similar to Example 1, the dry ice bed is replaced with a ceramic substrate comprising quartz which has a high thermal shock resistance. The substrate surface is smooth and the cooling gas of nitrogen is directed at the surface in the impact area in a direction tangential to the plasma stream.
Rebounding fragmented particles which are collected exhibit the spherical powder shape and have an average particle size less than about 10 micrometers~
Claims
1. A process for producing a fine densified metal powder comprising forming a flowable agglomerated powder en-training said agglomerated powder in a high pressure gas for transporting said powder to a plasma torch, creating a plasma in said gas and heating said entrain-ed powder to a molten condition to form a high velocity stream of molten metal droplets, said stream being discharged from said torch at a speed greater than 200 meters per second, directing said stream toward a repellent surface, impacting said molten droplets against said repellent surface, fragmenting said molten droplets upon impact with said surface to form molten fragmented portions, rebounding said molten fragmented molten portions from said surface and cooling said fragmented portions to form a metal powder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US46070983A | 1983-01-24 | 1983-01-24 | |
| US460,709 | 1983-01-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1236711A true CA1236711A (en) | 1988-05-17 |
Family
ID=23829772
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000445826A Expired CA1236711A (en) | 1983-01-24 | 1984-01-23 | Method for making ultrafine metal powder |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0134808B1 (en) |
| JP (1) | JPS60500872A (en) |
| CA (1) | CA1236711A (en) |
| DE (1) | DE3483189D1 (en) |
| WO (1) | WO1984002864A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4783214A (en) * | 1988-02-29 | 1988-11-08 | Gte Products Corporation | Low oxygen content fine shperical particles and process for producing same by fluid energy milling and high temperature processing |
| US5294242A (en) * | 1991-09-30 | 1994-03-15 | Air Products And Chemicals | Method for making metal powders |
| WO2002047856A2 (en) * | 2000-12-15 | 2002-06-20 | Omg Americas, Inc. | Irregular shaped copper particles and methods of use |
| ES2328395T3 (en) | 2005-10-21 | 2009-11-12 | Sulzer Metco (Us) Inc. | A METHOD OF MANUFACTURE OF HIGH PURITY AND FLUID METAL OXIDE POWDER FOR A PLASMA SYSTEM. |
| KR101134501B1 (en) | 2009-12-07 | 2012-04-13 | 주식회사 풍산 | method for manufacture of high purity copper powder use of plasma |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3829538A (en) * | 1972-10-03 | 1974-08-13 | Special Metals Corp | Control method and apparatus for the production of powder metal |
| US3974245A (en) * | 1973-12-17 | 1976-08-10 | Gte Sylvania Incorporated | Process for producing free flowing powder and product |
| DE2528999C2 (en) * | 1975-06-28 | 1984-08-23 | Leybold-Heraeus GmbH, 5000 Köln | Process and device for the production of high-purity metal powder by means of electron beam heating |
| US4264641A (en) * | 1977-03-17 | 1981-04-28 | Phrasor Technology Inc. | Electrohydrodynamic spraying to produce ultrafine particles |
| DE2743090C3 (en) * | 1977-09-24 | 1980-04-30 | Battelle-Institut E.V., 6000 Frankfurt | Device for the production of film-shaped granulates from metallic melts |
| US4408971A (en) * | 1978-03-27 | 1983-10-11 | Karinsky Viktor Nikolaevich | Granulation apparatus |
| US4326841A (en) * | 1979-03-23 | 1982-04-27 | Allied Chemical Corporation | Apparatus for making metallic glass powder |
| US4221587A (en) * | 1979-03-23 | 1980-09-09 | Allied Chemical Corporation | Method for making metallic glass powder |
| US4376740A (en) * | 1981-01-05 | 1983-03-15 | National Research Institute For Metals | Process for production fine metal particles |
| US4390368A (en) * | 1981-04-01 | 1983-06-28 | Gte Products Corporation | Flame spray powder |
| US4374075A (en) * | 1981-06-17 | 1983-02-15 | Crucible Inc. | Method for the plasma-arc production of metal powder |
| US4435342A (en) * | 1981-11-04 | 1984-03-06 | Wentzell Jospeh M | Methods for producing very fine particle size metal powders |
| US4395279A (en) * | 1981-11-27 | 1983-07-26 | Gte Products Corporation | Plasma spray powder |
| US4419060A (en) * | 1983-03-14 | 1983-12-06 | Dow Corning Corporation | Apparatus for rapidly freezing molten metals and metalloids in particulate form |
-
1984
- 1984-01-06 EP EP84900776A patent/EP0134808B1/en not_active Expired - Lifetime
- 1984-01-06 WO PCT/US1984/000019 patent/WO1984002864A1/en active IP Right Grant
- 1984-01-06 DE DE8484900776T patent/DE3483189D1/en not_active Expired - Fee Related
- 1984-01-06 JP JP50082184A patent/JPS60500872A/en active Pending
- 1984-01-23 CA CA000445826A patent/CA1236711A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0134808A1 (en) | 1985-03-27 |
| DE3483189D1 (en) | 1990-10-18 |
| EP0134808B1 (en) | 1990-09-12 |
| EP0134808A4 (en) | 1985-07-01 |
| WO1984002864A1 (en) | 1984-08-02 |
| JPS60500872A (en) | 1985-06-06 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4592781A (en) | Method for making ultrafine metal powder | |
| US4613371A (en) | Method for making ultrafine metal powder | |
| US4687510A (en) | Method for making ultrafine metal powder | |
| US5707419A (en) | Method of production of metal and ceramic powders by plasma atomization | |
| US5294242A (en) | Method for making metal powders | |
| US4221587A (en) | Method for making metallic glass powder | |
| US4386896A (en) | Apparatus for making metallic glass powder | |
| US4772315A (en) | Hydrometallurgical process for producing finely divided spherical maraging steel powders containing readily oxidizable alloying elements | |
| US4802915A (en) | Process for producing finely divided spherical metal powders containing an iron group metal and a readily oxidizable metal | |
| JPS63243212A (en) | Wet metallurgical method for producing finely divided globular high melting point metal base powder | |
| US4787934A (en) | Hydrometallurgical process for producing spherical maraging steel powders utilizing spherical powder and elemental oxidizable species | |
| US5114471A (en) | Hydrometallurgical process for producing finely divided spherical maraging steel powders | |
| US4778517A (en) | Hydrometallurgical process for producing finely divided copper and copper alloy powders | |
| CN111470481B (en) | Method for preparing high-purity aluminum nitride spherical powder by plasma reaction atomization | |
| US4502885A (en) | Method for making metal powder | |
| US4523621A (en) | Method for making metallic glass powder | |
| US4859237A (en) | Hydrometallurgical process for producing spherical maraging steel powders with readily oxidizable alloying elements | |
| CA1236711A (en) | Method for making ultrafine metal powder | |
| CA1133671A (en) | Method for making metallic glass powder and product | |
| JP2004183049A (en) | Method and apparatus for producing fine metal powder by gas atomization method | |
| CA1330622C (en) | Hydrometallurgical process for producing finely divided iron based powders | |
| US4781741A (en) | Process for producing spherical glass particles | |
| JPH10317019A (en) | Production and device for metal powder | |
| US4326841A (en) | Apparatus for making metallic glass powder | |
| JPH01111805A (en) | Rapid solidification of plasma spray magnetic alloy |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |