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
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
• • 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
  • B22F9/023—Hydrogen absorption
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy

Definitions

• Titanium, manganese, iron, cobalt, nickel, copper, germanium, yttrium, zirconium, rhodium, palladium, silver, antimony, hafnium, platinum, gold, praseodymium, thorium and uranium are essential to industry, either as pure metals or as alloys. These metals are used in the aerospace, nuclear, electronic, machine tool, chemical and heavy industries for a myriad of applications. Many of these metals are difficult to process into pure metals having less than 10,000 parts per million by weight (“PPM" herein) contaminates, such as alkali metals, halides, hydrogen, nitrogen, oxygen and carbon. In addition, it is difficult to combine these metals to form mixtures or alloys, such as a nickel-titanium alloy, of these metals having less than 10,000 PPM contaminates.
• PPM parts per million by weight
• Impurities outside specification values in these metals can cause such metals and alloys based thereon to be brittle and of little use.
• Impurities such as halides, carbon, oxygen, nitrogen and silicon can cause the Group IVb metals and alloys based thereon to be greatly reduced in strength and chemical resistance.
• Small amounts of silicon and oxygen can be used in Group IVb transition metal alloys, such as hafnium and zironium alloys.
• Zinc Soluble Metal-Based Metal is a metal or a mixture or alloy of two or more of such metals that has a solubility of at least about 3% by weight in molten zinc at 900"C.
• the Zinc Soluble Metal-Based Metal can contain alloying agents that do not meet the solubility, vapor pressure and melting point criteria of the Zinc Soluble Metal-Based Metal.
• Zinc Soluble Metal-Based Metals are Ti, Mn, Fe, Co, Ni, Cu, G, Y, Zr, Rh, Pd, Ag, Sb, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Pt, Au, Ac, Th, Pa, U and mixtures thereof, including alloys thereof.
• the mixtures and alloys consist essentially of one or more Zinc Soluble Metal-Based Metals and lesser amounts of other elements; provided, however, that such mixtures and alloys can contain up to 50% or more by weight of the other elements if the resulting mixtures and alloys meet the above solubility, vapor pressure, and melting point specifications.
• a very important advantage of this invention is the capability of producing metal shapes, i.e. , near net shapes, directly from metal sponge particles without the necessity of any expensive arc melting step which is required in conventional technology for consolidation or alloying of the Group IVb transition metals.
• such passified Zinc Soluble Metal-Based Metal particles are produced by heating a Zinc Soluble Metal-Based Metal-zinc alloy which is substantially free of halides at a temperature between 5 about 500 " C and about 1150"C under conditions which are operative to vaporize and separate the zinc from such alloy and to produce a Zinc Soluble Metal-Based Metal sponge thereon which is substantially free of both zinc and halides.
• Conventional metal sponges have an internal
• the metal sponges of the present invention have internal porosities of between about 5% to about 40% by volume.
• substantially free of zinc herein is meant less than 0.1% by weight zinc.
• Zinc Soluble Metal-Based Metal Preferably the Zinc Soluble Metal-Based Metal
• the Zinc Soluble Metal-Based Metal-zinc alloy can be comminuted to or formed into powder, and the zinc distilled off as
• Zinc Soluble Metal-Based Metal powder Some Zinc Soluble Metal-Based Metal-zinc alloys are brittle and comminute easily, and other metal-zinc alloys are tough, which renders the alloy more difficult to comminute.
• 30 alloy can be formed into small particles by conventional means known to the art, such as shot-tower processing.
• Zinc Soluble Metal-Based Metals prepared by conven ⁇ tional processes such as the Hunter process or Kroll process for titanium may contain halide salts, such as
• Zinc Soluble Metal-Based Metal-zinc alloy herein (also referred to as “Metal-zinc alloy” and “Metal values zinc alloy” herein) is meant an alloy of zinc and Zinc Soluble Metal-Based Metal.
• the zinc may be sublimed from the metal-zinc alloy by heating the alloy to a temperature of from about 500 ⁇ C to about 1150 ⁇ C to produce Zinc Soluble
• the sponge may be sintered by heating it to a temperature below the melting point of the Zinc Soluble Metal-Based Metal ("sintering temperature range" herein) under conditions which are operative to sinter the metal sponge.
• the sintering is conducted at a temperature equal to about 0.6 to 0.7 of the Zinc Soluble Metal-Based Metal melting point temperature in degrees Kelvin. Sintering is necessary in order to reduce the surface area of the Zinc Soluble Metal-Based Metal sponge and thus reduce the amount of oxygen or nitrogen required for subsequent passification of the metal sponge so that it may be readily and safely stored and used for powder metallurgy at a later time. If the Zinc Soluble Metal-Based Metal particles do not require passification, the sintering step is optional since the particle's surface
• the sponge particles of Zinc Soluble Metal-Based Metal shrink in size by about 50 to about 85% in volume but, in general, retain their original shape.
• Such sintered particles are not fused together, although usually there is some sticking or adhering of the particles to each other.
• adhered particles an be readily separated by mechanical means.
• the particles of sintered Zinc Soluble Metal-Based Metal are cooled or allowed to cool to a temperature of between about 300 ⁇ C and 700 ⁇ C, during which time they are simultaneously contacted with hydrogen or a gaseous stream containing hydrogen under conditions which are operative to hydride and embrittle the sintered metal. Not all Zinc Soluble Metal-Based Metals can be hydrided.
• Zinc Soluble Metal-Based Metal-zinc alloys are brittle and can be ground to powder to a- predetermined particle size distribution .before removal of zinc by sublimination. Many of the Metals values can be ground or comminuted to a predetermined particle size distribution after removal of zinc by sublimination.
• the Zinc Soluble Metal-Based Metal-zinc alloys can be formed or cast into particles by casting techniques, such as the following techniques: melt extrusion, centrifugal atomization, gas and water atomization, gun, drum splat quenching, melt spinning, gas atomization, pendant drop-melt extraction, shoting and casting.
• Some Zinc Soluble Metal- Based Metal-zinc alloys are not brittle and are more economically formed or cast into particles, or comminuted, after removal of the zinc and embrittling the resulting metal sponge by hydriding with hydrogen.
• the hydrided and embrittled Zinc Soluble Metal-Based Metal can be readily comminuted to a predetermined particle size distribution.
• Such hydrided and embrittled Zinc Soluble Metal-Based metal particles are comminuted under a nondeleteriously- reactive atmosphere, to a predetermined particle size distribution.
• the comminuted Metal values are treated at a temperature between about 400" and about 700"C, preferably between about 600° and about 700 ⁇ C under conditions operative to remove essentially all hydrogen values from the comminuted particles.
• Metal values Zinc Soluble Metal-Based Metals.
• removing essentially all hydrogen values from the comminuted transition metal values is meant that the Metal values retain.no more than about 200 PPM of hydrogen.
• the dehydrided zinc soluble metal-based metal particles are then contacted with a small or effective amount of a gas selected from the group consisting of oxygen, nitrogen and mixtures thereof, under conditions operative to pass * ify the metal particles, thereby producing passified Zinc Soluble Metal-Based Metal particles.
• the passification step is preferably controlled to prevent excess contamina ⁇ tion of the Metal values with nitrogen and/or oxygen or to control the amount of oxygen or nitrogen introduced into the Metal values. For example, it is advantageous to fully oxidize the europium in a 99% Ti-1% Eu alloy to Eu 2 0 3/ passifying the Metal values sponge with a sufficient oxygen to passify the Metal values surface and oxidize the europium.
• Some Metal values such as gold, do not require passification to prevent further oxidation.
• Thecontrolled comminuting of the hydrided and embrittled metal values is such that the passified Zinc Soluble Metal-Based Metal particles ultimately produced have at least a significant amount by weight of Zinc Soluble Metal-Based Metal particles which are suitable for powder metallurgy usage without further particle size reduction.
• SUBSTITUTE SHE significant amount is meant to be at least about 50% by weight of the particles produced.
• the improved controlla ⁇ bility afforded by the hydriding of the Zinc Soluble Metal-Based Metals can be a particularly important aspect of this invention because it ultimately enables the production of a passified Zinc Soluble Metal-Based Metal particles of a size distribution readily adaptable and operable for powder metallurgy usage.
• particles with no greater than about 300 mesh, preferably no greater than 100 mesh (U.S. Sieve Series), are suitable for powder metallurgy usage without further particle size reduction.
• this embodiment of this invention is particularly useful where fine powder metallurgical particles are required, or where a high yield of suitable powder is required, or where a highly tailored particle size distribution is required which is not easily or economically obtainable by other means.
• Very fine particles, 400 mesh or finer, are not preferred because of their high surface area to volume ratio; such particles can absorb deleterious amounts of oxygen and/or nitrogen during passification.
• the heating of the Zinc Soluble Metal-Based Metal-zinc alloy to vaporize zinc therefrom, and the subsequent sintering of the transition Metal values produced thereby is conducted in the same zone or vessel.
• the hydriding and embrittle ent of the sintered Metal values are also conducted in the same zone or vessel as the zinc vaporization and sintering steps.
• the nondeleteriously-reactive atmosphere used during the comminuting of the embrittled hydrided Metal values and/or sintering of the Metal values is an inert gas, such as argon or helium.
• the heating or distillation of the Zinc Soluble Metal-Based Metal-zinc alloy to vaporize and separate zinc therefrom is conducted under a partial vacuum.
• such heating is conducted under a continuous flow of a nondeleteriously-reactive sweep gas.
• the sweep gas is selected from the group consisting of hydrogen, inert gas (such as argon or helium) and mixtures thereof.
• the dehydriding and/or sintering of the particles of Metal values is conducted under a partial vacuum.
• a Metal values-zinc alloy by forming a Zinc Soluble Metal-Based Metal-zinc alloy which is substantially free of halides, into particles having a particle size of less than 30 mesh, and then heating such particles in a zone maintained at a temperature between about 500 ⁇ C and 1150 ⁇ C, optionally under a partial vacuum or ' under a continuous flow of a nondeleteriously-reactive sweep gas.
• the zinc is sublimed off at a temperature not exceeding the Metal values sintering temperature, which is preferably about 0.6 to about 0.7 of the Metal values melting point temperature in degrees Kelvin. Frequently, this will require that the sublimation be conducted under a vacuum.
• the zone is maintained under conditions operative to vaporize and separate zinc from the metal-zinc alloy particles, and thereby produce particles of Zinc Soluble Metal-Based Metal which are substantially free of zinc and halides.
• Such metal values will comprise essentially the pure Zinc Soluble Metal-Based Metal or mixtures or alloys thereof optionally containing other alloying agents desirable in the ultimate final product, that is, alloys thereof.
• such other alloying agents which may be desirable in the final product and known to those skilled in the art include, but are not limited to, berylium, boron, carbon, oxygen, aluminum, silicon, phosphorus, calcium, vanadium, chromium, arsenic, selenium, gallium, polybdenum, cadium, iridium, tin, cesium, niobium, barium, thallium, lead, bismuth, zinc and the like. These other elements may be used in the processes described herein.
• Such alloying agents may be incorporated in small amounts as, for example, less than 5 weight percent individually and less than 10 weight percent collectively, because of limited solubility in molten zinc or because they possess a low boiling point as, for example, a boiling point below 900°C.
• the Zinc Soluble Metal-Based Metal containing the alloying agents must have a boiling point above 1000 " C to prevent loss of the alloying agents during the zinc sublimation stage of the Metal values-zinc alloy.
• Zinc Soluble Metal-Based Metals containing such other alloying agents will consist of a major portion of Ti, Mn, Fe, Co, Ni, Cu, Ge, Y, Zr, Rh, Pd, Ag, Sb, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Pt, Au, Ac, Th, Pa, U and mixtures thereof, and a minor portion of alloying agents, such as B, C, O, N, Al, Si, P, Ca, V, Cr, As, Se, Ga, Mo, Cd, Ir, Sn, Cs, Nb, Ba, Pb, Bi, Zn and mixtures thereof.
• the alloying agents made up the minor portion of the Metal values.
• each alloying agent, if present, is alloyed in the Metal values in the following amounts, in weight percent:
• alloying agents can be incorporated into the Metal values.
• the total collective amount of alloying agents in the Metal values will not usually exceed 15 weight percent, although some Metal values can contain up to 50% of alloying agents.
• the thusly formed particles which are substantially free of zinc, unless zinc is intentionally left in the Metal values, and halides are then heated to, or main ⁇ tained at, a sintering temperature range under conditions operative to sinter such particles.
• sintering results in a reduction of the surface are of such particles and because of the reduction in surface area, subsequent passification with a passifying gas will require a substan ⁇ tially less amount of such gas and thus reduce the oxygen and/or nitrogen content of the Zinc Soluble Metal-Based Metal.
• the sintered particles are then cooled, or allowed to cool, to a temperature between about ambient and about 200 ⁇ C, and then contracted with a small or effective amount of a gas selected from the group consisting of oxygen, nitrogen and mixtures thereof, under conditions operative
• the sintering step is optional. In all embodiments of this invention, it is preferably that the passified Zinc Soluble Metal-Based Metal particles be substantially free of halides because halide contamination of the final product can cause voids, loss of strength and fracture toughness, and welding problem.
• An important feature of this embodiment of the invention is the forming of the Zinc Soluble Metal-Based Metal-zinc alloy of a specified and particular particle size distribution such that the particles will have a particle size of less than 30 mesh, preferably between about 100 and 200 mesh.
• the subsequent sintering of such particles at a sintering temperature range is operative to cause the passified Zinc Soluble Metal-Based Metal particles ultimately produced to have a particle size distribution such that a significant amount by weight of such particles are suitable for powder metallurgy usage with additional particle size reduction.
• significant amount of weight suitable for powder metallurgy usage without additional particle size reduction is meant at least 50% by weight.
• This embodiment of this invention is, however, capable of producing particles wherein at least about 80% by weight or more are suitable for powder metallurgy usage without additional particle size reduction.
• An advantage of the invention is that the shape or configuration of the feed Zinc Soluble Metal-Based Metal- zinc alloy particles prior to vaporization • of the zinc therefrom, and the subsequent sintering of the particles produced from said vaporization of the zinc from the metal-zinc alloy is retained through these sequence of steps.
• particles formed by comminuition will retain their angular shape and particles produced by rapid quench methods will retain their non-angular shape during the zinc distillation or subli iation step.
• the vaporization of zinc produces particles having about 15 to about 50% of the volume of the feed alloy particles.
• the heating or distillation of the particles of Zinc Soluble Metal-Based Metal-zinc alloy at a temperature between about 500° and 1150"C, .and the subsequent sintering of the zinc-free particles there ⁇ from, are conducted in the same zone or vessel.
• the cooling and passification of the sintered particles are also conducted in the same zone or vessel as the zinc vaporization and sintering steps.
• the heating or distillation of the Zinc Soluble Metal-Based Metal-zinc alloy to vaporize and separate zinc therefrom is conducted under a partial vacuum.
• the nondeleteri ⁇ ously-reactive sweep gas used in the heating or distil ⁇ lation of the metal-zinc alloy is an inert gas.
• such nondeleteriously-reactive sweep gas is hydrogen.
• hydrogen is used as the sweep gas, it is necessary to remove all hydrogen values from the final Zinc Soluble Metal-Based Metal particles that form hydrides, since hydrogen may cause e brittlement of such particles. Hydrogen can be removed in a dehydrid- ing step described herein.
• the Zinc Soluble Metal-Based Metal particles have a particle size distribution of about 90% by weight between about 60 mesh and about 20 mesh before such particles are heated or dis- tilled at a temperature between about 500 and about 1150 ⁇ C.
• the forming of a metal-zinc alloy into such particles is by comminuting of the alloy.
• such particles are formed by casting the metal-zinc alloy into particles; preferably, particles of -1/4 mesh or smaller.
• the Zinc Soluble Metal-Based Metal-zinc alloy may be prepared by adding zinc soluble metal-based metal scrap or sponge into a molten batch of zinc agitated to form the Zinc Soluble Metal-Based Metal-zinc alloy substantially free of halide. If the metal sponge of scrap contains halide, such as sodium halide, the halide salt separates from the metal-zinc alloy when the metal-zinc alloy is formed. The halide salt is immiscible with the metal zinc alloy and floats to the surface of the molten alloy as a separate phase which can be separated from the alloy by conventional means to produce a Zinc Soluble Metal-Based Metal-zinc alloy substantially free of halide.
• halide such as sodium halide
• zinc metal and Zinc Soluble Metal-Based Metal such as scrap Zinc Soluble Metal-Based Metal containing halide salts, may be melted together to form the Zinc Soluble Metal-Based Metal-zinc alloy substantially free of halide.
• the halide salts float to the top of the zinc alloy melt and can be removed from the zinc alloy melt by concentrated means.
• the alloying agent may be incorporated into the molten zinc batch prior to intro ⁇ duction of the Zinc Soluble Metal-Based Metal, or added with the Zinc Soluble Metal-Based Metal to the molten-zinc batch, or co-melted with the zinc metal and the Zinc Soluble Metal-Based Metal.
• the Metal values-zinc alloy can be prepared from Zinc Soluble Metal-Based Metal chloride salts as set forth in the process described herein by adding the Metal values chloride salt with zinc and a reductant metal such as, aluminum, and melting and agitating the resulting mixture to reduce the salt.
• Metal fluoride salts can be reduced with aluminum metal.
• some metal chloride, bromide or iodide salts, such as refractory metal chloride salts require a stronger reducing metal, such as sodium, magnesium, calcium or the like, to be reduced.
• an alkali metal halide salt may be added to the mixture to form a floating phase immiscible with the Metal values to inhibit the vaporization of the molten zinc.
• alloying agents may be added to produce a Zinc Soluble Metal-Based Metal-zinc alloy containing the desired alloying agents to yield a Zinc Soluble Metal-Based Metal- zinc alloy product as described herein.
• the various compo ⁇ nents may be mixed together and melted as a mix or, alternatively, the various ingredients may be added to molten zinc or the molten batch of zinc and the reductant metal.
• a Zinc Soluble Metal-Based Metal fluoride salt may be contacted with the zinc and reductant metal to form the metal-zinc alloy substantially free of halide. Alloying agents may then be added to the molten Metal values-zinc alloy to incorporate the desired alloying agents. Such Metal values-alloy, with or without addi ⁇ tional alloying agents, may be treated as described herein to produce passified Zinc Soluble Metal-Based Metal powders, suitable for metallurgy usage, substantially free of halide and zinc.
• the entire process is conducted at temperatures which are no higher than about 1300"C and, in a preferred
• the entire process is conducted at temperatures which are no higher than about 1200"C and, in an especially preferred embodiment, at a temperature no higher than 1150 ⁇ C to prevent sintering of the Zinc Soluble Metal-Based Metal particles.
• temperatures reached during the con ⁇ ventional high temperature arc melting processes required for consolidation of, and/or alloying of, for example, titanium products produced by conventional processes, such as the "Kroll Process", are not required. In other words, the high temperatures required for arc melting are simply not required for this process.
• Arc melting processes generally require temperatures which exceed the melting point of the particular Zinc Soluble Metal-Based Metal by about 50 to 100 ⁇ C.
• Such high temperature processes, including those requiring arc melting, require costly equipment which is simply not required by this invention.
• a distinct advantage of this invention is the avoidance of very high temperatures required in processes which comprise arc melting.
• Some of the advantages of using hydrogen as the sweep gas in the sublimination or distillation step to vaporize zinc from the Metal values-zinc alloy are: (1) hydrogen, because of its low molecular weight, facilitates the dif ⁇ fusion of zinc out of the metal values sponge pores and, by virtue of such improved diffusion, improved heat transfer during the distillation is also realized, (2) hydrogen is cheaper than helium and argon and other inert gases, and (3) although the hydrogen tie bond between hydrogen and many Zinc Soluble Metal-Based Metals are weak, hydrogen will more readily displace zinc than inert gases because there is no tie bond between the inert gas and the Zinc Soluble Metal-Based Metal.
• substantially all hydrogen values must be removed from the Metal values particle product wherein the Metal values are capable of being hydrided.
• Hydrogen can be removed from such Metal values particles by heating the particles to a temperature at from 600 ⁇ C to about 700"C, preferably under a partial vacuum.
• substantially all hydrogen values being removed from the final Metal values particle product it is meant that no more than about 200 PPM of hydrogen is permitted in the final Metal values particles produced, and preferably no more than about 50 PPM of hydrogen is in the final product. This is to be compared with some conventional processes which produce particles having 200 PPM or more of hydrogen.
• the process is capable of producing product particles having less than 50 PPM hydrogen.
• Zinc Soluble Metal-Based Metal particles which are substantially free of oxygen, nitrogen and carbon.
• substantially free of oxygen, nitrogen and carbon as used herein is meant to be no more than about 2500 PPM oxygen, 400 PPM of nitrogen and 800 PPM of carbon. In some embodiments of this invention, no more than about 800 PPM of oxygen, 90 PPM of nitrogen, and/or 150 PPM of carbon are contained in the product particles of the Metal values.
• the metal sponge, comprising Zinc Soluble Metal-Based Metal, of the present invention is characterized in having less than 50 PPM of halides and an internal porosity of between 5% and 40% by volume. Preferably, the metal has less than about 10 PPM halide and an internal porosity of at least 20% by volume.
• the powdered metal, comprising Zinc Soluble Metal-Based Metal and alloys thereof, of the present invention have the same low halide content and high internal porosity as the metal sponge.
• the powdered metal will have angular-shaped or non-angular shaped powder particles, depending upon the powder forming technique employed. Angular-shaped powder particles formed by comminution are irregular-shaped particles with irregular surface faces on 1 walls and irregular edges.
• Non-angular-shaped particles formed by rapid quenching can have a variety of shapes with regular or irregular edges, depending upon the rapid quenching technique employed.
• the major surfaces of the 5 non-angular shaped-particles are non-angular; that is, they are relatively smooth and continuous.
• the metal sponge of the present invention is unequaled, and no Zinc Soluble Metal-Based Metal sponge having the low halide, hydrogen, oxygen, nitrogen and carbon contamination
• the powder metal of the present invention is unique and no Zinc Soluble Metal-Based Metal powder having the low halide, hydrogen, oxygen, nitrogen and carbon con ⁇ tamination and high internal porosity set forth herein and
• the Zinc Soluble Metal-Based Metal powder and sponge of the present invention are superior metals for metallur-
• the low halide content enhances maximum metal strength, toughness and durability.
• the high internal porosity and particle shape of the powder permits the fabrication by conventional powder metallurgical processes of strong, durable and defect-free shaped Zinc Soluble
• Metal-Based Metal pieces such as shaped articles, plates, sheets, pipes, rods, beams and billets.
• the compressibility of the powder and the size and shape of the particles of the powder permit the particles to be closely pressed together and securely interlocked when pressed into the desired
• the metal-zinc alloy can contain additional alloying agents, such as aluminum, vanadium or other beneficial elements, which may be desirable in the final product particles. Such alloying agents are not required to be added in a high temperature arc melting step. In fact, arc melting is not required in this invention.
• the alloying agents can be added to the Metal values when it is in the form of a Zinc Soluble Metal-Based Metal-zinc alloy or when such alloy is made.
• the .alloying agent can be added to molten zinc to form a molten zinc alloy.
• the Zinc Soluble Metal-Based Metal such as titanium metal sponge, can be added to the molten zinc alloy to form a Zinc Soluble Metal-Based Meta ⁇ -zin ⁇ alloy.
• a Zinc Soluble Metal-Based Metal fluoride salt such as sodium fluotitanate
• a Zinc Soluble Metal-Based Metal fluoride salt can be added to a molten bath of zinc, alloying agent and reductant metal, such as aluminum, to reduce the fluoride salt and produce the Zinc Soluble Metal-Based Metal-zinc alloy which is recovered by separating it from the floating slag containing the fluoride salt of the reductant metal, formed during the reduction of the Metal values fluoride salt.
• the alloying agents remain with the Metal values as the zinc is vaporized and separated therefrom.
• the heating or distillation of zinc from the metal-zinc alloy is conducted at a temperature between about 900" and 950 ⁇ C, sintering is conducted between about 1020 and 1060 ⁇ C, embrittlement and hydriding is conducted between about 600* and about 700 ⁇ C, and passification is conducted at about ambient to about 60 ⁇ C.
• ⁇ — ⁇ ⁇ _# i5*2> lation to vaporize and separate zinc and the sintering may be conducted in the same zone, reactor or vessel.
• Figure 1 is a flow sheet of one embodiment of this invention which comprises hydriding and dehydriding steps.
• Figure 2 is an alternate embodiment of this invention which does not require hydriding and dehydriding steps.
• Figure 3 is an alternate embodimment of this invention where in the particles are passified before comminution.
• Figure 4 is an alternate embodiment of this invention which does not require a sintering step.
• Figure 5 is a further alternate embodiment of this invention which does not require the hydriding and dehydriding and, optionally, does not require the sintering step.
• Figure 6 is a flow sheet of one embodiment of this invention which comprises preparing a passified Zinc Soluble Metal-Based Metal powder from a passified Zinc Soluble Metal-Based Metal sponge.
• the halide salt of a Zinc Soluble Metal-Based Metal sponge that can be hydrided that is, the Metal value can be hydrided, such as sodium fluo- titanate, is introduced via stream 82 and reduced in a molten state in zone 90 and a molten zinc-aluminum alloy introduced in stream 84. If a metal value chloride, bromide or iodide salt is used, a more electro-positive reducing metal, such as sodium or magnesium, is used in place of aluminum to reduce the halide salt.
• the molten metal fluoride salts and the zinc-aluminum alloy are essentially immiscible.
• Reduction is conducted at a temperature of at least about 650"C up to about 1000 ⁇ C with agitation. After reduction is completed, agitation is ceased and the mixture is separated into separation zone 100, into an upper phase comprising an aluminum fluoride salt which is removed in stream 102, and a lower denser phase comprising a Zinc Soluble Metal-Based Metal-zinc alloy, which is removed in stream 110.
• the Metal values-zinc alloy is substantially free of halides.
• the amount of Metal values in the zinc can be substantially increased by operating zone 90 under a positive pressure.
• the Metal values-zinc alloy removed in stream 110 which is substantially free of halides, is heated or distilled in zone 200 at an elevated temperature, while simultaneously introducing into zone 200 a continuous flow of hydrogen sweep gas in stream 202 under conditions effective for vaporizing and separating zinc from the alloy and to produce Metal values which are substantially free of zinc and halides.
• the zinc is removed via stream 204.
• Such metal values are then heated in the same vessel, depicted as zone 210, to a sintering temperature range under conditions operative to sinter such Metal values.
• the sintered Metal values are cooled to a temperature between about 600° and about 700"C in the same vessel, depicted as zone 220, and simultaneously treated, as depicted in zone 230, with hydrogen introduced in stream 224 under conditions operative to hydride and embrittle the sintered Metal values.
• the hydrided and embrittled Metal values are then crushed in zone 240 under an inert atmosphere, preferably helium, introduced through stream 242, to form particles of Metal values.
• the particles of Metal values are dehydrided in zone 250 at a temperature between about 600" and 700 ⁇ C under conditions operative to remove essentially all hydrogen values from the particles of metal values.
• the dehydrided particles are cooled in depicted zone 260 to a temperature between ambient and about 60°C, and then passified in zone 270 with a relatively small amount of air introduced in stream 264.
• An effective amount of air is introduced under the passification con- ditions to passify the particles. Excess air is not required or desirable.
• At least a substantial part of the passified Zinc Soluble Metal-Based Metal particles thusly produced and removed in stream 272 are suitable for powder metallurgy usage without further particle size reduction.
• a molten stream of Zinc Soluble Metal-Based Metal-zinc alloy 110 which can be pre-alloyed with other desirable alloying agents, such as aluminum or vanadium, is introduced into casting zone 300, wherein it is formed into particles having a particle size distribution between about 60 mesh and about 200 mesh.
• the Metal values are cast into particles by (a) gas and water atomization, centrifugal atomization, melt spinning, gas atomization or shotting to produce spheroidal-shaped particles, (b) drum or disk splat quenching to produce splat particulates, ( ⁇ ) free-jet melt spinning to produce flake particulates, or (d) chill-block melt spin and anvil and piston to produce flat particulates.
• Particles produced from Zinc Soluble Metal-Based Metal-zinc alloy by a rapid quench techniques are preferred over the other particle casting techniques when the Metal values contain more than one element, such as titanium alloyed with aluminum and vanadium.
• Particles produced by rapid quenching techniques are rapidly cooled; between about 10 2 ⁇ C/second to about 10 7 ⁇ C/second, to a temperature below the melting temperature of the metal value.
• Rapid cooling techniques yield uniform and homogenous Metal value alloys. With the rapid quenching techniques, the alloy in this particle does not have time to undergo substantial alloy phase segregation. In addition, rapid quenching techniques can form Metal value alloy particles having:
• Small grain size e.g., less than 1 micrometer
• Relatively homogenous microstructure e.g., Relatively homogenous microstructure
• Extended solid solubility limits New metastable crystalline structures
• Amorphous or non-crystalline phase e.g., Amorphous or non-crystalline phase.
• Homogenous metal value alloys can have superior mechanical properties, superior hot and cold working properties, superior corrosion resistance and superior chemical reactivity properties.
• the 60 to 200 mesh particles are removed in stream 302 and introduced into heating or distillation zone 310, along with a continuous flow of helium sweep gas introduced through stream 304.
• heating zone 310 which is operated at atmosphere pressure, the zinc is vaporized from the Metal values-zinc alloy at a zinc sublimation temperature and removed through stream 306.
• Particles of metal values which are substantially free of zinc and halides, are removed by stream 308 and introduced into sintering zone 320, which is maintained at a sintering temperature range to sinter the particles of Metal values.
• the particles of Metal values shrink but do not fuse, though some weak adhering of particle-to-particle usually occurs.
• the zinc sublimation temperature and sintering temper ⁇ ature are below the melting point temperature of the Metal values, preferably at least 100 ⁇ C below the melting point temperature and, most preferably, about 0.6 to about 0.7 of the melting point temperature of the Metal values in degrees Kelvin.
• the sintered particle mases are removed through stream 322 and introduced into cooling zone 330, wherein they are cooled to a temperature between about ambient and about 60"C.
• the cooled particles are removed through stream 332 and introduced into breaking zone 340, wherein the weakly adhered particle masses are broken apart by suitable mechanical means under nondeleteriously-reactive environ ⁇ ment.
• This breaking step is optional and can be deleted, depending upon the degree of particle-to-particle adherence. In some embodiments, such breaking is not required.
• the thusly separated particles removed in stream 342 are introduced into passification zone 350, where they are passified with a relatively small amount of air introduced through stream 352.
• Passified Zinc Soluble Metal-Based Metal particles are removed through stream 354 and intro ⁇ quizzed into screening zone 360, wherein oversized particles and oversized adhered particle masses are separated and removed through stream 362, and particles having desirable particle size are removed through stream 364.
• a substantial amount of weight of passified particles of Metal values having a desired particle size suitable for powder metal- lurgy usage without additional particle size reduction are removed through stream 364.
• the oversized particles in stream 362 can be remelted and introduced into the casting zone 300.
• FIG. 3 An alternative embodiment of the process of Figure 2 is shown in Figure 3.
• the sintered particle masses are passed from cooling zone 330 (shown in Figure 2) through stream 332 to passification zone 350, where they are passified with air introduced through stream 352 as described above.
• the passified sintered particle masses are passed from zone 350 into breaking zone 340 through stream 354, wherein the weakly adhered particle masses are broken apart by conventional mechanical means under a nondeleteri ⁇ ously-reactive environment as described above.
• the separated particles are passed from zone 340 into screening zone 360 through stream 342, wherein oversized particles and over ⁇ sized adhered particle masses are separated and removed through stream 362.
• the particles having the desired particle size are removed through stream 364.
• a Zinc Soluble Metal-Based Metal capable of being hydrided, such as titanium, zirconium, hafnium, thorium and molybednum is shown.
• a Zinc Soluble Metal-Based Metal, optionally alloyed with other alloying agents, which is substantially free of halides, is passed to heating zone 400 through stream 110, wherein the alloy is heated to distill off the zinc at a ainc sublimation or distillation temperature, while simul ⁇ taneously introducing into zone 400 a flow of hydrogen sweep gas from stream 402 under conditions effective for the distillation of the zinc from the metal alloy to produce Metal values which are substantially free of zinc and halide.
• the zinc is removed in stream 404.
• the Metal values are passed to hydriding zone 410, wherein the Metal values are treated with hydrogen introduced through stream 412 under conditions operative to hydride and embrittle the Metal values.
• the hydrided Metal values are comminuted in comminuting zone 420 under an inert atmosphere, such as argon or helium, introduced in stream 422 to form particles of Metal values.
• the hydrided Metal values may be comminuted with conventional equipment known to the art for comminuting metals. Such equipment may be modified for comminuting under an inert atmosphere.
• the particles of Metal values from zone 420 are passed to dehydriding zone 430 wherein the particles are heated to a temperature between about 600° and 700°C under conditions operative to remove essentially all the hydrogen values from the particles.
• the dehydrided particles are cooled in cooling zone 440 to a temperature between about ambient to about 60°C and then passed to a passifica ⁇ tion zone 450 and passified with a small or effective amount of air introduced in stream 452.
• the passified particles of Zinc Soluble Metal-Based Metal re passed to screening zone 460, wherein oversized particles are separated and removed through stream 462 and particles having the desired particle size distribution are removed through stream 464.
• the oversized particles in stream 462 can be introduced into the hydriding zone 410 for further processing as described above.
• a Zinc Soluble Metal-Based Metal-zinc alloy which may be optionally alloyed with other alloying agents, is introduced into comminuting zone 500 through stream 110, wherein the alloy is crushed or ground to predetermined particle size, preferably from about 80 mesh to about 100 mesh, to form particles of the metal-zinc alloy.
• the metal-zinc alloy can be formed or cast into particles, as described with reference to the process shown in Figure 2, of a predetermined particle size in a casting zone (not shown) rather than comminuted as described herein.
• the metal-zinc alloy can also be formed into particles by conventional shot-forming techniques (not shown) , such as the shot-tower techniques.
• the particles are preferably deformed into splat or flat particles by dropping, throwing, ejecting or spinning the molten metal values-zinc alloy particles or droplets on a hard, cooled surface.
• the particles are passed to a distillation zone 510, optionally a nondeleteriously reactive sweep gas may be introduced through stream 512, wherein the zinc is vaporized at a zinc sublimation temperature from the metal values-zinc alloy particles and the zinc is removed in stream 514.
• the resulting particles of Metal values which are substantially free of zinc and halides, are introduced in a stream 516 into sintering zone 520, wherein the Metal values are then heated to a sintering temperature under conditions operative to sinter such Metal values.
• the sintered Metal values are introduced in stream 522 into cooling zone 530, wherein the sintered Metal values are cooled to a temperature between about ambient and about 60°C.
• the cooled sintered Metal values are introduced into passification zone 540 wherein Metal values are passified with an effective amount of air introduced in stream 542 to produce passified Zinc Soluble Metal-Based Metal particles suitable for powder metallurgy usage which are removed in stream 544.
• the sintering step in zone 520 is eliminated and Metal values from distillation zone 510 are introduced into cooling zone 530 through stream 518, wherein the Metal values, substantially free of halides and zinc, are cooled to a temperature between ambient and about 60"C.
• the cooled Metal values are introduced into passification zone 540 wherein the Metal values are passified with an effective amount of air introduced in stream 542 to produce passified Zinc Soluble Metal-Based Metal particles; a significant amount by weight of the particles are suitable for powder metallurgy usage without additional particle size reduction.
• Such passified Metal particles may be screened in a screening zone (not shown) to separate oversized particles from the particles of the desired particle size range.
• This alterna ⁇ tive embodiment may be practical on a Metal values sponge or powder which has a sufficiently reduced surface area that does not require the sintering step to further reduce the surface area.
• an alternate process employs sintered-passified Zinc Soluble Metal-Based Metal sponge substantially free of halides and zinc, which is produced from a Zinc Soluble Metal-Based Metal-zinc alloy substantially free of halide by distilling off the zinc to produce Metal values sponge substantially free of halides and zinc, sintering the Metal sponge at a sintering temperature range under conditions operative to sinter such Metal values, and passifying the sintered Metal values sponge with an effective amount of oxygen, nitrogen or air at a temperature between about ambient an about 60°C.
• the sintered, passified Zinc Soluble Metal-Based Metal sponge is introduced through stream 112 into heating zone 600 to heat the sintered Metal values sponge to a tempera- ture between about 600° to 700*C.
• the heated Metal values sponge which is a Zinc Soluble Metal-Based Metal sponge capable of being hydrided, is contacted with hydrogen gas introduced in stream 612 under conditions operative to hydride the heated Metal values sponge at a temperature between about 600° and about 700°C.
• the heating step and dehydriding steps in zones 600 and 610, respectively, can be carried out in the same vessel.
• the dehydrided Metal sponge is passed to comminuting zone 620, wherein the Metal sponge is crushed to a desired particle size distribution using conventional metal comminuting or crushing equipment known to the art.
• the com ⁇ minuting is performed under an inert atmosphere or gas introduced in stream 622 into zone 620.
• the Metal values particles are introduced into dehydriding zone 630 wherein the Metal values particles are dehydrided at a temperature between about 600° and 700°C under conditions operative to remove essentially all of the hydrogen values from the particles.
• the dehydrided Metal value particles are cooled in cooling zone 640 and passified in passification zone 650 with an effective amount of air introduced in stream 652 as described above with respect to Figure 1.
• the resulting passified Zinc Soluble Metal-Based Metal particles are recovered from stream 654.
• a significant amount by weight of the Metal values particles in stream 654 are suitable for powder metallurgy usage without additional particle size reduction. These particles may be screened in a screening zone (not shown) to remove the oversized particles from the particles of the desired particle size range.
• a Zinc Soluble Metal-Based Metal powder must have a particle size of less than 30 mesh and preferably about 100 mesh. The powder must not, however, be too fine, as many of the Zinc Soluble Metal-Based Metals rely on an oxide or nitrogen
• the component made by powder metallurgy technology from the powder may be hard, brittle, and lack ductility. Therefore, the Metal values powder cannot be made by sintering fine particles, such as -400 mesh particles, which have previously been passified because the oxygen or nitrogen level in the powder may be too high and result in a Metal values powder, because of oxygen contamination or nitrogen contamination, unsuitable for metallurgical applications.
• the internal porosity of the Zinc Soluble Metal-Based Metal sponge and powder must result from relatively large pores in the sponge or powder, rather than small pores which would increase the surface area to volume ratio of the sponge and powder and which, in turn, may cause unacceptable contamination of the Zinc Soluble Metal-Based Metal during processing.
• the internal porosity of the Metal values powder is advantageous because it permits the powder to be deformed during pressing, thus yielding greater green strength and minimizing the formation of large voids in the green body.
• the Metal value powders prepared by present processes have relatively large pores with rounded boundaries.
• the surface area of the particles and sponge should not exceed one square meter per gram (M 2 /g) of Metal values, preferably it should not exceed about 0.1 M 2 /g.
• the Zinc Soluble Metal-Based Metal powders (+100 to -80 mesh) have a total surface area (external surface area and surface area of pores) of about 0.1 M 2/g of Metal.
• the surface area of the pores of the Metal value powders can be varied by sintering temperatures and constitutes about 90% of the total surface area of the powder. Because of the large pore size, some of the Metal value powders, such as platinum powder, may be used as catalysts. Similarly, some of the Metal value powders, such as titanium powders, can be used as catalyst support.
• EXAMPLE 1 A charge of 340.4 grams of small zinc slabs, 16.45 grams nickel rod pieces and 13.3 grams titanium sponge was placed in a graphite crucible. The crucible was heated in an electric furnace to 800°C for two hours. The furnace was contained in a dry box filled with high purity argon. The contents of the crucible, which were fully molten, were cast in water cooled copper molds inside the dry box. After cooling, the castings were ground in a rod mill to powder, which was screened to -24/+80 mesh. The alloy was brittle and had a grinding yield of 80% to the desired particle size range. The titanium zinc alloy powder was placed in a 400 series stainless steel crucible and the zinc sublimed at 10" 5 torr in a furnace. The temperature profile on the furnace during sublimation was as follows:
• the product was loosely sintered and could be easily broken into individual particles by mechanical means.
• the product was examined by X-ray and microprobe and found to be almost entirely a 45-55% by weight titanium-nickel alloy sponge powder with 20% internal porosity. The pores were large, with rounded boundaries and the BET surface area was 0.09 M 2 /g.
• Zinc Soluble Metal-Based Metal sponges such as Metal sponges of the following compositions, in weight percent, may be prepared in accordance with the process described in Example 1, using zinc.
• EXAMPLE 3 Zinc (500g) and sodium (7.52g) are added to a tungsten crucible and co-melted in an electric furnace at a tempera ⁇ ture of between 750 and 850°C. Ferric chloride (53g) and sodium chloride (58g) are added to the zinc-sodium melt and the resulting mixture agitated for 1 hour. The insoluble phase of sodium chloride is decanted from the molten zinc alloy. The molten zinc alloy is heated in a furnace to
• the iron sponge can be reduced to powder for powder metallur- gical applications as described herein.
• EXAMPLE 4 The chloride salts of Ti, Mn, Co, Ni, Cu, Ge, Y, Zr, Rh, Pd, Ag, Sb, La, Pr, Nd, Sm, Gd, Tb, Dy, Hu, Er, Tm, Lu, Hf, Pt, Au, Ac, Th, Pa, U and mixtures thereof can be pro- Detd into the corresponding Metal sponges in accordance with the process of Example 3.
• the zinc sublimation and sintering temperature is adjusted for each Metal value so that the processing temperature is below the melting point temperature of the metal value.
• Such Metal sponges can be processed into powders for powder metallurgical applications in accordance with processes described herein.
• Mixtures of chloride salts, such as gold chloride and silver chloride may produce a Metal values alloy or mixture depending upon the solubility of each Metal values in the other Metal values present.
• Metal mixtures in contrast to Metal alloys, will consist of a substantially uniform matrix of microcrystals of each of such Metals in the mixture.
• Zinc (885 parts by weight), aluminum (15.3 parts by weight) and nickel (50 parts by weight) are melted in a carbon crucible at about 925°C.
• Cobalt fluoride - C0F2 (82.4 parts by weight) is added to the Metal melt and the resulting mixture is agitated for 2 hours.
• the floating molten salt phase of aluminum floride salts is separated from the Metal phase.
• the molten Metal phase is heated to about 750°C under a reduced pressure (about 10 Torr) to sublime off the zinc to leave a nickel-cobalt sponge.
• the sponge is cooled to ambient temperature and comminuted to
• the j reduce the sponge to an average particle size of about 100 mesh.
• the sponge is not sintered or passified.
• the nickel-cobalt-zin ⁇ melt after removal of the salt melt, can be cast into particles by rapid quenching techniques.
• Zinc (90 parts by weight) and aluminum (10 parts by weight) are melted in a carbon crucible at a temperature of about 900°C.
• Cupri ⁇ fluoride (27.2 parts by weight) and nickel fluoride (25.9 parts by weight) are added to the aluminum-zinc melt.
• the resulting mixture is stirred for 45 minutes.
• the molten salt of aluminum fluoride salt floating on top of the zinc alloy melt is decanted off to leave a copper-nickel-zinc melt.
• the metal melt is heated to about 700°C with an argon sweep gas to sublime off the zinc to produce a copper-nickel sponge.
• the sponge is sintered at a temperature of about between about 700°C and 1000°C.
• the sintered sponge does not have to be passified. After screening, the sintered sponge having a particle size of -30 mesh can be used for powder metallurgical purposes to produce solid metal particles.
• the copper-nickel alloy can be alloyed with alloying agents by including the alloying agent directly to the original metal melt or product metal melt after the reduction of copper and nickel fluoride salts.
• the alloying agent exists as a fluoride salt
• the alloying agent fluoride salt can be incorporated into the metal melt by reducing the salt with a stoichiometric amount of aluminum in the metal melt.

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• 1987
  • 1987-06-16 EP EP19870904440 patent/EP0309479A4/de not_active Withdrawn
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