US 2853401 A
Description (OCR text may contain errors)
p 3, 1958 v. N. MACKIW ETAL 2,853,
. METHOD OF INCORPORATING A METAL BINDER OR MATRIX PHASE IN MIXES 0F METALS AND/OR METALS AND METAL COMPOUNDS Filed April 11, 1956 METAL COMPOUND METAL COMPOUND METAL PREC/P/TA r50 ME TAL COMPOUND PREC/P/ TA TED ME FAL lnven tors MN- MACK/W v. KUNDA J. gJlAwon Amrn ry Uni: 5
METHOD OF KNKIQRPORATING A METAL BINDER 0R MATRIX PHASE IN M'IXES 0F METALS AND/0R METALS AND METAL COMPGUNDS Application April 11, 1956, Serial No. 577,447
6 Claims. (Cl. 117-65) This invention relates to a method of incorporating a metal as a binder or matrix phase in mixes of the metal and a hard, refractory metal compound. The invention is particularly directed to the preparation of an intimate mixture of a hard, refractory metal compound by the precipitation of a metal useful as a binder or matrix phase by gas reduction from a solution in which values of the binder metal are present as a soluble salt and which contains a physical dispersion of particles of a hard metal compound with which precipitated binder metal particles are to be intimately associated in the resulting product.
Metals in the form of powders are well known and are widely used in industry as such or in the form of compacts. Also, mixtures of powders of different metals or metal compounds having different physical and/or chemical properties are well known and are in widespread use, particularly in the powder metal industry. Heretofore, such metal powders have been produced by spraying or by sputtering the metals or metal compounds of interest at a temperature above their melting temperatures or by mechanical attrition. Production of metal powder by spraying or sputtering is restricted to metals having low melting temperatures and the size of the resulting particles varies over a wide range. Mechanical attrition is slow, costly and involves the use of fine grinding apparatus such as rod mills, rotary plates and ball mills, all of which require special, costly grinding media and/ or linings.
Powders of hard, refractory metal compounds intimately associated with powders of binder metals, such as tungsten carbide intimately associated with a powder of a metal such as nickel, copper or cobalt have a wide variety of uses, such as in tool tips, wire drawing dies, high temperature and wear and corrosion resistant materials. Although a limited number of these hard metals or hard, refractory metal compounds can be formed into solid components, or compacts, without the addition of a binder by the process of hot pressing, the addition of a softer metal usually is necessary as a binder to bind together the particles of the hard, refractory metal compound in the subsequent pressing and/or heating treatments to which the powders are subjected to form the desired compacts.
The production of intimate mixtures of powders of binder metals with hard, refractory metal compounds presents important production problems. Particles of the desired materials can be prepared by grinding, such as in a ball mill in air, or in a reducing atmosphere, or in an inert atmosphere, either dry or dispersed in a liquid such as water, benzene, acetone, paraffin, or other organic or inorganic solution. Usually costly, special Wear resistant linings and balls are required. The operation usually is costly, is very slow and, despite precautions, there is the danger of contamination of the desired product from the atmosphere of the mill and from the mill lining and grinding medium employed. Also, it is desired to smear the binder phase over the surfaces Stats Pate of the particles of the hard, refractory metal compound and this cannot be accomplished by conventional comminuting methods.
We have found that an intimate association of powders of binder metals with hard, refractory metal compounds can be produced very easily and inexpensively by dispersing particles of a hard, refractory metal compound having properties which are different from those of. the binder'metal with which it is to be intimately associated in the resulting mixture in an ammoniated solution containing dissolved salts of a binder metal adapted to be precipitated as a metal from the solution under reducing conditions to form a slurry, and subjecting the slurry to reaction with a reducing gas at elevated temperature and pressure.
By adjustment of the conditions of reduction, the dissolved metal salt can be reduced to and precipitated from the solution as a metal powder substantially free from impurities to form an intimate association with the particles of the hard, refractory metal compound dispersed in the solution.
The term hard refractory metal compound used throughout the description of this invention and in the claims in intended to mean metal compounds which have physical and/or chemical properties which are different from those of the binder metal with which they are associated in the resulting mixture. Such hard, refractory metal compounds include, but are not necessarily limited to, carbides of titanium, zirconium, hafnium, tantalum, vanadium, niobium, chromium, molybdenum, tungsten and of the metals of the actinide series of the periodic table; binary or tertiary and higher combinations of the above carbides.
Also, these compounds include the nitrides, borides and silicides of the metals in the fourth, fifth and sixth groups of the periodic table and also of the metals of the actinide series and combinations of these or combinations of these and the above mentioned carbides. While the invention can be employed with any of the numerous hard, refractory metal compounds in these groups, usually, the hard, refractory metal compound will be a member of the group consisting of tungsten, vanadium, zirconium, chromium, titanium and molybdenum with a member of the group consisting of carbon in the form of carbide, silicon in the form of silicide, boron in the form of boride, and nitrogen in the form of nitride. Also, of course, combinations of two or more of these metal compounds can be employed, either as a physical mixture or as an intercrystalline mixture.
Hard, refractory metal compounds employed in the present invention are, of course, insoluble or only slightly soluble in the solution undergoing treatment to the extent that the particles can be dispersed and remain as solid particles of matter in the solution during the reducing reaction.
Metal values which can be precipitated from solution by gas reduction and intimately associated with the particles of hard, refractory metal compound primarily are those of the group consisting of osmium, rhodium, ruthenium, iridium, gold, platinum, palladium, silver, copper, arsenic, tin, nickel, cobalt and cadmium. Usually, however, these precipitatable metals will be of the group silver, copper, nickel and cobalt. Values of these metals can be precipitated relatively easily in metallic state as metal powders.
The method is conducted very simply. Particles of hard, refractory metal compound, of .a size such that they can be dispersed and mechanically suspended in the solution undergoing treatment, are dispersed in the solution to form a slurry. Values of the binder metal which is to be precipitated are present in the solution as a soluble salt. Factors which afiect the reduction and precipitation of metal values from the solution are the nature and the characteristics of the metal values to be precipitated, the temperature and pressure at which the reducing reaction is conducted, the nature and the characteristics of the solution and the reducing gas employed. All these factors must be taken into consideration and the conditions of operation adjusted to produce optimum precipitation of the desired metal values.
The desired ratio of hard, refractory metal compound to binder metal can be obtained very easily. Under normal conditions, dissolved metal values in the ammoniated solution can be reduced to about one gram per litre very easily and very rapidly. Thus, it is only necessary to add to the solution a slight excess of the metal values to be precipitated, for example about 1 gram per litre excess, and the desired amount of the hard, refractory metal compound to produce the desired ratio. For example, if it is desired to produce a mixture containing about 1000 grams of tungsten carbide and 50 grams of cobalt as a binder, the prescribed amount of tungsten carbide is dispersed in a litre of an ammoniated solution containing about 51 grams of cobalt and suspended therein by active agitation. Reduction is continued until only about one gram of cobalt remains in the solution.
The solution is selected with regard to the solubility therein of the hard, refractory metal compound and the metal values to be precipitated and the reactivity of the reducing gas employed. Thus, the solution can be organic or inorganic, acid, basic or neutral, having regard to all the factors entering into the reduction.
. Usually, the solution to be treated will be an aqueous ammoniated sulphate or chloride solution.
Ammonia usually is preferred as the complex forming amine. However, organic amines such as methyl amine or ethylene diamine can be substituted for all or part of the ammonia.
The reducing gas also is selected with regard to all factors entering into the reducing reaction. It is preferred to employ hydrogen as the reducing gas in the precipitation of pure or substantially pure metal from the solution. However, other reducing gases such as carbon monoxide, methane, producer gas, natural gas or mixtures of reducing gases can be employed, if desired.
The anion of the metal to be precipitated is selected with regard to the solubility of the metal salt in the selected solvent and the reactivity of the anion with the reducing gas. Usually, in basic solutions, sulphate, chloride, carbonate and hydroxyl anions and in acid solutions sulphate, fluosilicate or acetate anions can be employed.
In the precipitation of metals from solution by gas reduction, certain metals, such as silver and copper do not require a hydrogenation catalyst to initiate and promote the reducing reaction. Other metals such as nickel and cobalt require a hydrogenation catalyst. Usually, the dispersed particles of hard, refractory metal compound serve as a catalyst and it is not necessary to add a catalyst or nucleating agent to the solution. However, in the event that the hard, refractory metal compound particles do not have the effect of catalyzing or nucleating the solution, an addition agent can be added to the solution to produce this effect. There are a number of suitable catalysts or nucleating agents which can be employed, of which ferrous sulphate, from about 0.1 to 1 gram per litre, is preferred in the reduction of nickel and a mixture of sodium sulphide and potassium cyanide, up to about 4 grams per litre, is employed inthe reduction of cobalt.
The time required for the reducing reaction is a function of the temperature and pressure at which the reaction is conducted and varies inversely therewith. Preferably, the reaction is conducted at a temperature within the range of from about 250 F. to about 500 F. The
reaction can be conducted at a temperature below about 250 F. but it tends to proceed too slowly for large scale commercial operation. Also, the reaction can be conducted at a temperature above about 500 F. but the increased rate of reduction does not warrant the increased cost of the high temperature-high pressure equipment required.
The reducing reaction is conducted under a partial pressure of reducing gas above about 50 pounds per square inch and preferably from about to about 500 pounds per square inch to produce a total pressure of from about to about 1000 pounds per square inch, preferably, from about 250 to about 700 pounds per square inch. At partial pressures of reducing gas below about 50 pounds per square inch, the reaction proceeds too slowly and the increased rate of the reaction above about 500 pounds per square inch usually does not warrant the cost of the high pressure equipment involved. The term total pressure is intended to mean the pressure autogenously produced by the temperature at which the reducing reaction is conducted plus the partial pressure or the over-pressure of the reducing gas employed.
The concentration of the metal salt in the solution is adjusted to that from which there is rapid precipitation of metal values from the solution but safely below that at which there would be any danger of crystallization in the reaction vessel or in pipe lines, valves and pumps. For example, in the precipitation of copper as powder metal from solution by gas reduction, copper sulphate is quite soluble in aqueous acid or basic solution, up to about 100 grams per litre of copper at ambient temperature and to a greater extent at higher temperatures. Therefore, concentrations of up to 75 to 100 grams of copper as sulphate per litre can be employed safely. Similarly, nickel and cobalt sulphates are relatively highly soluble in ammoniacal solution and while it is preferred to employ solutions containing about 50 gramsper litre, concentrations up to about 75 grams per litre of metal can be employed safely.
When precipitating metal powder from solution by gas reduction, the density of the resulting powder can be controlled by regulating the ammonia and/ or the ammonium sulphate concentration of the solution. For example, copper metal can be precipitated from solutions of widely varying hydrogen ion contents. Accordingly, the solutions may range from strongly basic amine solutions containing much free ammonia or other amine to those containing relatively large amounts of free acid. It is found that there should be the equivalent of from about 0.1 to 2.5 gram mols of ammonia present in the solution per gram atom of copper or from about 1.5 to 4 gram mols ammonia per gram atom of nickel or cobalt or nickel plus cobalt in the precipitation of copper, nickel and cobalt from solutions by gas reduction.
Metal values can be precipitated from the solution to form an intimate association with the hard, refractory metal compound. The association is produced by forming a slurry comprised of particles of the desired amount of hard, refractory metal compound and an ammoniated solution containing, in solution, the desired amount of metal values and, if necessary an added catalyst or nucleating agent. This slurry is charged into a reaction vessel, such as an autoclave, and reacted with a reducing gas at elevated temperature and superatmospheric pressure. The reducing reaction is continued until the desired amount of metal has been precipitated from the solution and deposited on the hard, refractory metal compound particles. At the end of the reduction period, the solid particles are separated from the solution, such as by filtration, and are in ideal condition for use as such or for treatment by conventional means for forming a desired compacted product, such as by sintering and/or compressing.
Resultant composite metal coated, metal compound particles are illustrated in the accompanying drawing in which:
Figure 1 illustrates enlarged cross-sections through typical composite metal coated, metal compound particles with metal compound cores of irregular shape; and
Figure 2 is a top plan of a compact formed of composite metal coated, metal compound particles illustrated in Figure 1;
g The particles illustrated in the drawing comprised of 25% by weight silicon nitride core and 75% by weight nickel coating. They were of a particle size of about 5.2 microns.
The following examples illustrate the operation of the method of the present invention to produce particles of a hard, refractory metal compound coated'with a binder metal.
1. The preparation of chromium carbide powder coated with nickel A charge of 1550 ml. nickel-ammonium sulphate solution containing, in solution, about 21 grams per litre 6 was closed and the air was replaced by hydrogen. The mixture was heated to about 350 F. and hydrogen was fed into the autoclave to produce and maintain a partial pressure ofhydrogen of about 350 pounds per square inch. The reduction of cobalt was completed in 6 minutes. The resulting product was in the form of very fine intimately associated powder particles comprised of about cobalt, and about 90% tungsten carbide which analyzed about 84% tungsten and about 5.5% carbon.
' The following Table 1 illustrates additional results obtained in the preparation of particles of a hard, refractory metal compound intimately associated with a binder metal. In each instance, the reduction was conducted at a temperature above about 300 F. preferably about 350 F., and at a partial pressure of hydrogen of about 350 pounds per square inch. Ammonia was present in the solution in the ratio of about 2 gram mols of ammonia per gram atom of cobalt and ammonium sulphate was present in the ratio of about 1 gram mol per gram atom of nickel or cobalt.
TABLE 1 Time of Calculated Experiment Metal Preoipi- Hard Metal or Hard Reduc- Composition Physical Characteristic of the Product N o. tated Metal Compound tion of Product (Microscopic Examination) I (Mins.) (Weight Percent) Grains of TiC coated with Ni of spherical shape N1 (55 T10 50-100p built from single crystals 4.6a.
Grains of CIaCz coated with Ni in the form of a Ni (33.4 g./1.) Cr Ct (65 g./l.) fine powder.
Grains of WC coated with Co in the form of a C0 g./l.) WC (180 g./l.) fine powder.
N130 g. ZIBZ 20 g. p 1 Ggtgsp 8% 2 2132 coated with N1 in the form of a N124 H32 18 p. 1 Gianuzgfyggi coated with N1 in the form of a N154 1 Mosh 54 g. p. Inn Ggalienspfivlligrsiiz coated with N1 in the form etc. 1 Ni 54 g. p. Sl3N4 18 g. p. 1 i gigg g i m the form 3 9 Ni g. p. l T10 10 g. p. 1 igggg coated with N1 m the form of a 10 Cu 8.5 g. p. 1.-.. TiC 60 g. p. l gig gg gg coated wlth Cu m the form of a Mixed grains of TiC and Cr coated with Ni in TiC 14.5 g. p. l 11 N1 51 g. p. 1 17.2 the form of a fine powder.
nickel, about 2.35 gram mols free ammonia per gram atom of nickel, and having dispersed therein about 130 grams per litre chromium carbide of particle size smaller than 325 mesh standard Tyler screen, 0.0017 inch, was charged into a high pressure autoclave of 1 gallon capacity. The autoclave was closed and the air was replaced by hydrogen. The charge was heated to about 350 F. When the desired temperature was reached, the autoclave was purged with hydrogen and a partial pressure of hydrogen of about 350 pounds per square inch was produced, total pressure about 500 pounds per square inch, and maintained for the period of the reduction. In about 25 minutes the nickel concentration in the solution dropped from about 21.3 g./ 1. to less than about 1 g./ 1. The product was obtained in the form of very fine powder comprised of about 19.3% nickel intimately associated with the chromium carbide which analyzed 69.2% chromium and 10.9% carbon.
2. Precipitation of tungsten carbide powders coated with cobalt About 191 grams of cobalt sulphate salt and about 89.5 grams ammonium sulphate salt were dissolved in 115 ml. concentrated ammonium-hydroxide and 1500 ml. of Water and diluted with water to about 2000 ml. The resulting solution contained about 14.4 grams per litre cobalt, about grams per litre ammonium sulphate and about 2.5 gram mols free ammonia per gram atom of cobalt. This solution was charged into a high pressure autoclave with about 360 grams tungsten carbide powder dispersed therein as the hard, refractory metal compound. The autoclave Hard, refractory metal compounds and precipitated binder metals intimately associated therewith and in the form of powders can be used as such, if desired, but usually they Will be compacted into desired shapes according to conventional practice such as by rolling or pressing with or without preliminary sintering and intermediate annealing steps. If there is any agglomeration of the particles during the precipitation step, such agglomerates can be disintegrated very easily by crushing and/or grinding and sizing operations prior to the compacting steps.
The method of the present invention possesses a number of important advantages. Intimate mixtures of desired binder metal and hard, refractory metal compound in the form of powders can be produced easily and inexpensively under moderate temperature and pressure conditions. The materials can be produced as composite mixtures of finely divided powders suitable for use as such and are ideally adapted for compacting into desired shapes such as by rolling or by compacting by conventional treatment.
It will be understood, of course, that modifications can be made in the preferred embodiment of the invention described hereinabove Without departing from the scope of the invention as defined by the appended claims.
What We claim as new and desire to protect by Letters Patent of the United States of America is:
l. The method of producing composite metal coated, metal compound particles which comprises the steps of dispersing solid particles of a metal compound selected from the group consisting of metal carbides, metal borides, metal silicides and metal nitrides in an ammoniated solution in which saidp'articles are insoluble' and whichcontains, in solution, a soluble compound of a metal selected from the group consisting of osmium, rhodium, ruthen-' 'ium, iridium, gold, platinum, palladium, silver, arsenic,: copper, tin, pickel and cobalt, reactingthe solution wlth a reducing gas at a temperature above about 200 F. and
' under a positive partial pressure 'ofreducing gasv to precipitate from said solution particles of metal inelemental formon said metal compound, particles, and continuing the reaction to coat saidmetal compound particles with said precipitated metal, said metal compound particles being present in said solution in amount sufficient to form with said precipitated metalpowder,v composite metal coated, metal compound'particles adapted to be compacted.
2; The method of producing compositemetal coated,
the soluble metal'compound is a member of the group consisting of silver, copperl, nickel and cobalt. I l v 3. The method of producing composite metal coated, metal'compound particles according to claim 1, in which the 'reducing'reaction, is continued tov obtain a predetermined ratio of dispersed metal compound particle the pre 7 cipitated metal powder.: i
4 The method of producing. composite metal coated, metalcompound particles according to claim 1, in which a i I catalysthaving ahigher reducing potential under reducing metal compound particles according to claim 1, in which i 7 conditions than the reducing gas employed is present in thersolutionsubjected,to reaction with the reducing gas.
5; The method of producing composite metal coated, metal compoundparticles according to claim 1, in which I I the dissolved metal values are present in the ammoniated solution as a salt selected from the group consisting of sul-r phate and chloride,
6. The method of producing composite metal coated,
metal compound particles'accordin'g toclaim 1, in which the dissolved metal values are present in the ammoniated solution as a salt selected from the group consisting of r I sulphate and chloride and thereducing reaction is coni 1 r ducted'at a temperatureabove about 200 F. and under a partialpressureof hydrogen above about 50 pounds per square inch.
i Referencescitediinxthe file of this'patent UNITED STATES PATENTS Sachs et 3.1. June 26,1894,