US3382062A - Process for dispersing refractory metal oxides in other metals - Google Patents

Description

United States Patent 3,382,062 PROCESS FOR DISPERSING REFRACTORY METAL OXIDES IN OTHER METALS Dale M. Hiller, Wilmington, Del., assignor, by mesne assignments, to Fansteel Metallurgical Corporation, a corporation of New York No Drawing. Filed Oct. 15, 1964, Ser. No. 404,154 4 Claims. (Cl. 75-.5)

ABSTRACT OF THE DISCLOSURE Power alloys of modybdenum with iron, cobalt, or chromium with or without copper, containing dispersed refractory oxides such as thoria, are made by precipitating a particulate solid containing the alloy constituents other than molybdenum, dispersing said solid in aqueous ammonium molybdate solution at pH 5.5 to 8.5 to deposit molybdenum-containing compound on it, calcining said product at 100 to 550 C., and reducing the calcined material at 450 to 1200 C.

This invention relates to processes for producing an alloy in powder form, said alloy having dispersed therein very fine particles of a refractory metal oxide and comprising a metal matrix consisting of (A) molybdenum and (B) at least one other metallic component selected from the group consisting of iron, cobalt, nickel, chromium, at least one metal of these four with tungsten, and at least one metal of said fourwith copper; and in such processes the invention is more particularly directed to the steps comprising (1) preparing a particulate solid comprising a compound of each metal other than molybdenum to be present in the final alloy, in which particulate solid there is so dispersed as to be inseparable by mechanical means, from 0.05 to by volume of refractory oxide particles having an average particle size of 2 to 500 millimicrons and a free energy of formation at 1000 C. of at least 95 kcaL/gram atom of oxygen; (2) dispersing said dispersion-modified particulate solid in an aqueous ammonium molybdate solution having a pH in the range of 5.5 to 8.5,- in an amount substantially exceeding the solubility of said solid in said solution, and maintaining the pH in that range until a molybdenum-containing coating is deposited on the surface of the particulate solid: (3) separating the coated solid from the solution and calcining it in the temperature range of 100 to 550 C.; and (4) heating the calcined product in the temperature range of 450 to 1200 C. in

contact with a reducing agent selected from the group consisting of hydrogen, carbon, carbon monoxide and hydrocarbon gases, whereby the dispersion-modified particulate solid and its molybdenum-containing coating are reduced to ther component metals and these metals are alloyed with each other. The dispersed refractory oxides having a free energy of formation at 1000 C. of at least 95 kcal./gram atom of oxygen are not reduced under these conditions, and remain as a dispersoid in the alloy product.

Molybdenum is a valuable alloying element for iron, cobalt, nickel, and chromium, forming with these metals alloys which have high strength at very high temperatures. When dispersion-modified alloys of these metals are prepared by prior art methods, for example by milling of dry powder mixtures, ditficulty is encountered in obtaining powders of completely homogeneous, uniform composition. This difficulty persists even when the powders are prepared by precipitation methods, as by precipitating oxidic compounds of the alloying metals and reducing the oxides with hydrogen or other reducing agents.

3,382,062 Patented May 7, 1968 Moreover, in precipitation methods heretofore known, undesirable impurities are often introduced, the removal of which poses special problems.

Other preparation methods, as, for example, Alexande r et al. US. Patent 2,972,529, have been described which have attempted to overcome the difficulty of impurity of the alloy product by restricting the choice of reagents to those whose by-products may be completely removed by subsequent calcination. However, the chemical composition, specifically the molybdenum content of the resultant alloy, remains a problem, i.e. the molybdenum content is subject to wide and unpredictable fluctuations.

Now according to the present invention, it has been found that the solution to the problem of molybdenum homogenization in its dispersion-modified alloys with iron, cobalt, nickel and chromium lies in processes wherein the oxidic compounds of iron, cobalt, nickel, and chromium or their mixtures, and of these with tungsten or copper, are first precipitated as a dispersion-modified particulate solid, and thereafter the oxidic molybdenum compound is deposited on this precipitate from an aqueous ammonium molybdate solution at a carefully controlled pH, followed by calcination and reduction of the product. The present invention provides processes whereby molybdenum-bearing, dispersion-modified alloys having closely controlled composition are produced, making it possible to duplicate alloy compositions from batch to batch within very specific limits, the molybdenum content of the product being controllable to, say, :0.2%. The invention also provides processes by which the impurity content of the alloys is kept to a minimum, thereby producing alloys of improved metallurgical characteristics. Therefore the present invention simultaneously solves the problems of inhomogeneity, impurity, and unpredictable fluctuations in chemical composition of dis persion-modified alloys.

The particulate solid which is to act as a substrate for the subsequent deposition of molybdenum values is selected from the group consisting of compounds of one or more of the metals iron, cobalt, nickel and chromium, and'compounds of at least one of these with tungsten or with copper-that is, it must contain a compound of each metal other than molybdenum which is to be present in the final alloy. There must be dispersed in the particulate solid matrix-metal substrate and mechanically inseparable therefrom, the refractory-oxide filler particles which serve to enhance the mechanical properties of the alloy products of this invention. The particulate, dispersionmodified solid is further characterized in that the particulate solid should not dissolve to an extent of more than 30 grams of metal per liter in aqueous ammonium molybdate solution at a pH of 5.5 to 8.5, and must be reducible to its component metals at a temperature in the range of 450 to 1200 C. after having been calcined at to 550 C. The presence of each of these characteristics can be determined quite independently of the use of the material in the process of the present invention.

The dispersion-modified particulate solid can be precipitated as an oxidic, i. e. oxygen-containing, compound with refractory-oxide filler being present. Thus the solid can be an oxide, hydroxide, hydrous oxide, oxycarbonate, or hydroxycarbonate of the metal or metals other than molybdenum to be present in the final alloy. One may precipitate the oxidic metal compound from any soluble salt thereof. The nitrate is preferred, but chlorides, sulfates, or acetates are also useful. Among the preferred starting materials are ferric nitrate, cobalt nitrate, and nickel nitrate.

A single refractory filler may be present, or there may be more than one filler present. The refractory oxide filler particles which serve to modify the properties, and particularly the strength, of the alloy products of this invention comprise relatively non-reducible oxides; that is, oxides which are not reduced to the corresponding metal under conditions whereby the oxidic precursors of the matrix alloy are converted to the metallic state. Such oxides can be used in the oxide form as starting materials, or they can be formed during the operation of the process by heating an oxide-forming material. Thus, the metal-oxygen-containing material from which the filler particles may be derived can be a metal oxide, hydrous oxide, carbonate, oxalate, or in general any compound which upon heating to constant weight at 1500C forms a refractory metal oxide. Typical oxides which are useful as filler particles include alumina, zirconia, titania, magnesia, hafnia and various other oxides, including especially thoria. A listing of refractory oxides which meet the requirements of this invention will be found in U.S. Patent 2,972,529, column 3, lines 21 to 45, issued to G.B. Alexander et al., Feb. 21, 1961.

Precipitation of the dispersion-modified particulate solid can be accomplished conveniently by adding suitable solutions of the matrix metal salt or salts to an aqueous alkaline solution while maintaining the pH above7. Alternatively, the matrix metal salt solution and suitable solution or aquasol of the refractory oxide-forming material can be added simultaneously but separately to a heel of water. It is preferred, however, not to coagulate or gel the colloidal dispersion of the filler particles. Coagulation and gelation are avoided by operating with dilute solutions, or by simultaneously adding solutions or dispersions of the filler and the alloying metal salt or salts to a heel of water as described above.

After the dispersion-modified oxidic compounds of the metal or metals other than molybdenum having been precipitated, it is desirable to remove by-product salts formed during the precipitation reaction by washing the precipitate. Since one generally uses an alkaline material such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium or tetramethylammonium hydroxide, ammonium carbonate or sodium carbonate to effect precipitation of the dispersion-modified particulate solid, salts such as sodium nitrate, ammonium nitrate, or potassium nitrate will be formed. These must be removed completely from a precipitated substrate material so that they will not interfere in the final molybdenum-modified alloy product.

One of the advantages of using the salts of nitric acid in combination with aqueous ammonia in the precipitation of the dispersion-modified particulate solid which is to be the substrate material for the molybdenum precipitation is that ammonium nitrate is volatile at relatively low temperatures, and therefore easily removed during the subsequent heating of the substrate material. However, the tendency of many metals such as, for example, cobalt and nickel to form amine complexes, is a complicating reaction in the precipitation step. Although these undesirable side reactions can be avoided to a large extent by carefully controlling the pH during the precipitation of the substrate, the precipitated product should be thoroughly washed in order to remove all possible impurities therefrom.

In a preferred embodiment of the invention, the particulate solid comprises hydrous oxides of filler particles and is prepared by coprecipitation of the alloying metal compounds and hydrous oxides of the filler particles, especially hydrous thoria, by mixing solutions of the alloying metal compounds, thorium nitrate, and aqueous ammonium carbonate. The carbonate-hydrous oxide substrate so obtained is thoroughly washed before being treated further to deposit the molybdenum-bearing coating thereon.

Colloidal metal oxide aquasols contain particles in the most desirable state of subdivision and size range and thus are an advantageous form for the introduction of refractory oxide-producing materials in the alloy processes of this invention. In alloys comprising thoria as a refractory oxide filler, for example, a preferred method of addition is to add a thoria sol prepared by calcining thorium oxalate at 550C. and dispersing the resulting thoria in aqueous thorium nitrate solution.

In operation of a preferred embodiment of the invention, therefore, molybdenum values can be deposited on a substrate material which may contain either embedded filler particles, or may have associated with it a metaloxygen-containing composition which upon subsequent heating form refractory-oxide particles.

The relative amounts of the component metal compounds, and filler particles, are varied depending on the composition desired in the finished alloyed product. A preferred level is from 0.5 to 10% by volume of refractory oxide particles in the alloy product. An even more preferred level is from 1 to 5% by volume. The percentage will be dependent to some extent upon the size of the particles, which in a preferred product may vary from, say, 5 to 150 millimicrons in average diameter. The preferred level of 0.5 to 10% by volume, and the more preferred range 1 to 5%, is based on the filler particles of about 25 m average diameter in the final molybdenumbearing dispersion-modified alloyed product.

In a specifically preferred embodiment of this invention, a substrate upon which molybdenum values are deposited comprises nickel carbonate in which there is dispersed submicron size thoria. Although the composition of the final nickel-molybdenum-thoria alloy may vary within quite wide ranges of, say, 1 to 20% molybdenum and 0.05 to 10% thoria, a preferred composition in the final product is nickel10% by weight molybdenum-- 2% by volume thoria. Particular advantage is gained in an alloy of this, or of similar composition prepared by the process of this invention, in that no high temperature heat treatment is required to effect alloying of the metal components, and undesirable growth of refractory oxide particles is thus avoided.

The use of ammonium molybdate as a source of the molybdenum-containing coating for the substrate is particularly advantageous in that no solid impurity ions are added to the slurry or to the circulated liquor to be picked up on the substrate along with the molybdenum values. The ammonium ion is readily volatilized during subsequent heating prior to reduction. To deposit the molybdenum values uniformly upon the substrate material, the pH of the slurry, i.e. of the ammonium molybdate solution, should be adjusted to a value in the range of 5.5 to 8.5 and maintained at the chosen value until the molybdenumcontaining coating is deposited. A preferred pH value is 6.5. To adjust the pH to these values and maintain the pH value at the desired point, acidification of the slurry is necessary and nitric acid is preferred as the acidifying agent. As in the case of ammonium molybdate solution, nitric acid introduces no foreign ions which cannot be removed by subsequent calcination without washing of the molybdenum-treated substrate material. The pH during deposition of the molybdenum values is held close to 6.5 to minimize in the supernatent solution the total concentration of molybdate and of redissolved metal ions from the substrate.

The deposition of molybdenum values upon the substrate material is not instantaneous; normally the deposition requires 2 to 4 hours to reach a steady state. Longer times of treatment may be required if higher levels of molybdenum deposition are desired; also longer times may be necessary if a pH of higher than 6.5 is maintained in the liquor. The equilibrium distribution of molybdate between the solid phase and the solution will diiier for substrates of varying compositions and methods of preparation and can be determined experimentally in each case. In each instance, however, conditions of time and pH will be found experimentally which will permit transfer of more than of the molybdate to the solid phase. Once a type of substrate has been characterized and the preferable procedure determined, the behavior is quite reproducible and material can be very satisfactorily duplicated from batch to batch.

After deposition of the molybdenum values has been accomplished, the solids are dewatered, usually by filtration but it is preferred not to wash the cake at this point because the amount of molybdate removed by washing is difficult to predict or control. Since the foreign ions intro duced into the slurry are removed by calcination, the product obtained is of satisfactory quality without a washing step.

The dewatered particulate solid with its molybdenumcontaining coating is dried and calcined at a temperature of from 100 to 550 C. to yield an intimate mixture of pure oxides. Ordinarily, heating at 100 C. is not thought of as calcination, but here dehydration of some hydroxides to oxides is effected. To effect complete calcination, however, the temperature is ordinarily carried well above 100 C. Higher temperatures than 550 C., on the other hand, are generally undesirable because they are more expensive and tend to sinter the oxide and retard the subsequent reduction of the oxide or oxides to metal. Also, higher temperatures tend to volatilize some of the oxides, as for example M00 or W0 The molybdenum-treated substrate material, which has been calcined at not over 550 C., is then pulverized, suitably in an impact mill such as a hammer mill, to provide a powder having maximum available surface for the subsequent step of reduction of the metal oxides to metal.

The pulverized oxides are next reduced at a temperature in the range of 450 to 1200 C. in contact with a reducing agent selected from the group consisting of hydrogen, carbon, carbon monoxide, and hydrocarbon gases, whereby the particulate solid and its molybdenum-containing coating are reduced to their component metals and these metals are alloyed with each other. Preferably such reduction is carried out in a flowing stream or" reducing gas until the dew point of the effluent gas drops to 50 C. Although hydrogen is the preferred agent for most of the metals, other reducing agents may be used instead of, or in combination with, hydrogen. The hydrocarbon gas may be methane or a higher hydrocarbon.

Whatever reducing agent or combination of reducing agents is used, it is important that the temperature during reduction be carefully controlled to avoid premature sintering of the product, which would result in entrapped, unreduced areas of metal oxide. Also, high temperatures are to be avoided before complete reduction of the matrix material is effected, so that no reaction may take place between the reducible compounds of the metal matrix and the refractory oxide particles. One way to avoid premature sintering is to place the molybdenum-treated substrate material in a furnace at a controlled temperature and add the reducing gas slowly so that sintering is avoided as reduction takes place. In such a method of operation, the reduction reaction will not proceed so rapidly that large amounts of heat are liberated and the temperature of the furnace thus uncontrollably increased. When a reducing gas, or mixture of reducing gases, is used, it may be diluted if desired with an inert gas such as argon to reduce the rate of reaction and avoid hot spots and local sintering.

After reduction is complete, the reactor is cooled to room temperature, purged with an inert gas, and the product discharged. In the product thus obtained, the molybdenum values, and the tiller particles if present, are distributed uniformly throughout the product.

Although no high-temperature treatments are necessary to alloy the molybdenum with other metal or metals which are present in the substrate, it may be found desirable for other reasons to heat the reduced product to an elevated temperature before subjecting it to further metallurgical treatments. By such heat treatment, any tendency of the powdered alloy product to reoxidize in air is diminished because such high-temperature treatment reduces the specific surface of the powdered alloy product. Also, it will be realized that the temperature at which a particular reduction reaction is carried out and the temperature of any subsequent heat treatment will vary with the composition of the substrate. Thus substrate materials comprising chromium and tungsten, for example, can be reduced and heat treated at temperatures higher than those used to reduce and heat treat substrate materials comprising, say, iron and copper. The time and temperature of reduction and subsequent heat treating will be in part determined by the volume loading of the filler in the alloy product and thegsize of the filler particles. In any case, it is preferred to maintain the temperature for both reduction and subsequent heat treatment at a point not higher than 50 C. below the melting point of the substrate metal or alloy.

In the foregoing description of this invention, reference has been made-repeatedly to refractory oxide filler particles. These are particles which are not reducible under the conditions of reduction effective on the matrix metals the particles serving to increase the strength of the final alloy product. Designating such particles as fillers is not meant to indicate that they are inert extenders or diluents; rather, they are effective constituents of the products of the invention and products including them are a preferred embodiment thereof.

The invention will be better understood by reference to the following examples, which illustrate preferred embodiments thereof but are not to be construed as limiting except as denoted in the appended claims. All parts are by weight unless otherwise indicated.

Example 1 In this example the particulate solid starting material upon which molybdenum was deposited comprised nickel carbonate in which was dispersed thoria of fine particle size. The particulate solid was prepared by mixing 3-molar solutions of (1) nickel nitrate, Ni(NO and (2) ammonium carbonate, (NH CO in the presence of (3) a colloidal dispersion of 1% thoria stabilized by the addition of thorium nitrate, Th(NO The mean particle diameter of the thoria was 11 millimicrons (rm) and the molar proportion of Th(NO to ThO was 15:100. Mixing of the solutions was effected by simultaneously introducing at separate inlets into a pipeline mixer the solutions of nickel nitrate, ammonium carbonate, and thorium nitrate-thoria dispersion, with vigorous agitation in the reactor. Upon mixing of these materials, solids precipitated, with the thoria uniformly dispersed throughout the precipitate. The nickel-to-thoria weight ratio in the precipitate was 97.8:2.2. The final pH of the slurry after precipitation of the nickel-thoria solids was 7.0.

The slurry thus obtained was filtered in a filter press, and the filter cake was thoroughly washed with demineralized water. The washed solids were repulped with vigorous agiLation in demineralized water to a slurry of 219 g. per liter, calculated on the nickel content. The total volume of this slurry was 282.1 liters. While the repulped slurry was being agitated, 41.1 liters of an ammonium molybdate solution containing 250 grams of (NH Mo O .4H O per liter was added. This calculated to a Mo/(Mo-l-Ni) content of 8.9%. After the addition of the ammonium molybdatc solution, the slurry had a pH of 7.65. To adjust the pH to the desired 6.5 value, addition of concentrated nitric acid was begun from a separatory funnel, and 6.75 liters of acid were added over a period of 0.8 hours. The pH of the slurry was now 7.00. Agitation and addition of acid were continued for an additional 3 hour period, during which time an additional 9.80 liters of nitric acid were added. The pH of the slurry was now 6.50, and over a period of an hour with constant agitation, the pH remained unchanged.

The acidified slurry was then pumped to a filter press, and the press cake discharged into trays. The cake was dried and calcined at a temperature held to not over 550 C. for a period of 16 hours to yield a mixture of pure oxides. The calcined cake was cooled and pulverized in a hammer mill.

The brown pulverized oxide thus obtained was charged in trays to a reduction reactor. Commercially pure electrolytic hydrogen was circulated over the oxide and the temperature was raised to 450 C. Reduction at this temperature was continued until the dew point of the effiuent hydrogen dropped to 30 C. The oxides were then heated to 600 C. while the flow of hydrogen was continued, and the reduction was continued until the dew point dropped to 50 C. at which point the reduction was considered to be completed. The metal powder was heated at 1000 to 1050 C. in hydrogen for an additional 3 hours time, was cooled to ambient temperature, the reactor purged with argon and opened to the air. The resulting metallic powder weighed 56.3 kg. and its properties were found to be as follows: thoria content 1.95%, Mo/(Mo-l-Ni) 8.26%; surface area 0.600 square meters per gram; and surface oxygen 0.131%.

To test the metallurgical properties of the material thus prepared, a portion of the powder was pressed into a 2" diameter by 2" long billet using a hydrostatic pressure of 40,000 p.s.i. The compressed billet was encased in a can, sintered in hydrogen for 1 /2 hours at 900 F. (480 C.) and then heated at 1650 F. (90 C.) for 2 /2 hours. The billet was evacuated while being cooled to room temperature and then sealed in the can, while under vacuum. The canned billet was extruded at an extrusion ratio of 10:1 at a temperature of 910 C., cooled and decanted.

Examination of the as-extruded billet at 500x under the light microscope and at 50,000 under the electron microscope showed no islands or stringers of thoria to be present. The extruded bar was cold worked to a 50% reduction in cross-sectional area and tested for mechanical properties. The properties are listed in Table 1 below.

TABLE 1 [Mechanical Properties of Ni-8.26% M1.95% 'IhOr Alloy] 1,200 F. (650 C.) 2,000 F. (1,090 C.)

Properties Ultimate tensile strength (13.5.1.) 65, 000 17,000 Reduction in area (percent) 25 5. 3 Elongation (percent) 8 5. 2 Stress-torupture life at 7,000 p.S.i. (hr.) .0

Example 2 Using the procedure of Example 1 for the precipitation of nickel carbonate-thoria press cake, a 22.75 kg. lot of this particulate solid starting material was prepared. This material contained 4.54 kg. of nickel values, and 102 grams thoria. The press cake was repulped in a 60-liter container by vigorous agitation in 13.65 liters of demineralized water.

The slurry thus formed was treated with 11.05 liters of ammonium molybdate solution at 250 grams molybdate per liter. The molybdate-treated slurry was acidified by the addition of concentrated nitric acid. A pH value of 6.5 was reached when the slurry had been acid treated over a period of 1.5 hours. The pH was held at 6.5 by continuing addition of nitric acid for 2 hours additional and the slurry was then filtered. The filtrate volume was 25.1 liters and contained 431 grams of molybdenum and 457 grams of nickel. This represents a 71.3% yield on the molybdenum values and a 90% yield on the nickel values in the slurry.

The press cake was dried, calcined, pulverized and reduced according to the procedure of Example 1. By this process there was produced 5.05 kg. of nickel-molybdenum-thoria alloy powder containing 1.82% by weight thoria and having Mo/(Ni-i-Mo)=20.8%. A portion of the alloy powder thus prepared was consolidated by the powder metallurgical techniques described in Example 1. Examined under the microscope, the product was found to be homogeneous with the thoria particles uniformly distributed in the nickel-molybdenum alloy matrix.

Example 3 A batch of 40.7 kg. of nickel carbonate-thoria press cake, made by the procedure of Example 1 but containing about 4% by weight thoria on a metal basis, was repulped with vigorous agitation in 22 liters of demineralized water. The slurry thus formed was treated with 6.0 liters of ammonium molybdate solution containing 772 grams of molybdenum. Over a period of 4 hours, 2.265 liters of concentrated nitric acid were added. The pH of the slurry was 6.5 during the last 3 hours of this 4 hour period. The slurry was filtered at the conclusion of this time and 32 liters of filtrate contained 46.7 grams molybdenum. This represented a yield of 93.95% of molybdenum values. The pressed cake was dried, calcined, pulverized, and reduced according to the schedule described in Example 1. The alloy powder product, weighing 9.2 kg, contained 3.95% ThO and 7.29% Mo/Ni-l-Mo. Powder metallurgical techniques applied to this powder produced massive metal which was homogeneous, with thoria particles evenly distributed in the nickel-molybdenum matrix.

Example 4 A 37.3 kg. quantity of washed nickel carbonate-thoria press cake, was prepared by precipitating a solution of nickel nitrate and thorium nitrate with ammonium carbonate solution at pH 7.0 to form a slurry, the solids content of which was about 2% thoria on a metal basis. This nickel carbonate-thoria press cake was repulped in 30 liters of demineralized water with vigorous agitation. The slurry was treated with 3.76 liters of solution containing 510 grams of molybdenum as ammonium molybdate, and was afterwards acidified to 6.5 pH by the addition of concentrated nitric acid. The acid was added over a period of 4 hours; the pH value of 6.5 was maintained during the final two hours of acid addition. The 37.3 liters of filtrate contained 0.966 grams of molybdenum per liter or a total of 36.0 grams of molybdenum; therefore the yield of molybdenum values deposited with the press cake was 92.94%.

The press cake was dried, calcined, pulverized, and reduced according to the schedule of Example 1. The alloy powder weighing 8.5 kilograms, contained 1.95% thoria; Mo/ (Ni-l-Mo) 5.30%. Powder metallurgical techniques applied to this powder produced massive metal which was homogeneous, with thoria particles uniformly distributed in the alloy matrix.

Example 5 In this example of the operation of this invention, a portion of the filtrate which was obtained after the washing of nickel carbonate-thoria precipitate was used to dissolve ammonium molybdate and this solution was pumped through the nickel carbonate-thoria filter cake to effect deposition of the molybdenum values on the precipitate. Thus the eifect of dispersion of the precipitated particulate solid in the ammonium molybdate solution was achieved by circulating the solution with respect to the solid particles, rather than circulating the particles in the solution as in Examples 1 to 4. These two practices are equivalent.

A nickel carbonate-thoria slurry containing 3.18 kg. of nickel values, prepared according to the procedure given in Example 1, was pumped to a small, recirculating filter press and washed clean. After the last wash water was discarded, 15.0 liters of fresh demineralized water was added to the system and recirculated through the filter press. A portion of the recycle water was used to dissolve ammonium molybdate equivalent to 265 grams molybdenum. The ammonium molybdate solution was re-added to the recycle stream. The recycle stream turned light green as the free ammonium ion redissolved some of the Ni values from the press cake. Over a period of 4.33 hours a total of 0.725 1. of concentrated nitric acid was added to the recycle stream. A pH value of 6.5 was maintained in the recycle stream over the final 3.5 hours of this acid addition period. At the conclusion of the 4.33 hours of recirculation of the filtrate through the press cake, the cake was filtered to dryness. The filtrate was analyzed and found to contain 1.72 g./l. Mo and 5.65 g./l Ni. This represents a yield of 90% on the molybdenum values and of 97.21% on the nickel values. The product was found to be 809410.173 Mo/(Mo+Ni), by analyses of nine samples.

The press cake was dried, calcined, pulverized, and reduced according to the procedure given in Example 1. Powder metallurgy techniques applied to this powder produced massive metal which was homogeneous, the thoria particles being uniformly distributed in the nickel-molybdenum-matrix.

Example 6 To show the effect of the pH value on the yield of molybdenum and of nickel values which may be obtained by the process of this invention, the following example was carried out.

Typical nickel carbonate-thoria press cake, prepared as given in Example 1 above, containing 2.2% thoria by weight on a metal basis, was dried at 150 C. to produce a light green solid which analyzed 47.5% nickel. This dried material was pulverized in a hammer mill and a batch of 190 grams of the pulverized green cake was slurried with 435 cc. solution containing 10.0 grams molybdenum as ammonium molybdate. The pH of the slurry initially was 7.75. Using 50 cc. of 2 N nitric acid, the pH was adjusted to 7.0 with vigorous agitation. The agitation was continued for 1 hour with the addition of 13 cc. more of 2 N nitric acid to maintain the pH value at 7.0. The slurry was filtered and the filtrate (285 cc.) was found to contain 5.28 grams of molybdenum per liter, and 1.79 grams of nickel per liter. This represents a yield of 85% on the molybdenum values, and of 99.5% on nickel values,

present and available in the slurries.

A similar run was made with the exception that pH was adjusted to 6.0 and held at this value for 1 hour. This experiment yielded a filtrate which contained 1.83 grams molybdenum per liter, and 11.68 grams nickel per liter. This represented a yield of 94.8% on molybdenum values, and 96.8% on the nickel values available in the slurries. Thus it is shown by this example that the molybdenum values deposited with the press cake increased and the nickel values decreased as the pH is decreased from 7.0 to 6.0, but in either case the yields are economically practicable.

Example 7 This example shows that molybdenum values may be deposited upon calcined Ni-ThO press cake. The deposition of such values, however, occurs quite slowly, even when the pH value is kept near the lower end of the permissible range of 5.5 to 8.5.

A nickel carbonate-thoria press cake was prepared as described in Example 1. This cake was dried, calcined, and pulverized to produce a fine black powder which upon analysis was found to be 73.5% nickel. A 24.5

. gram portion of this oxide (representing 18 grams of nickel) was mixed with 100 cc. of water containing 2.0 grams of molybdenum as ammonium molybdate. The slurry was shaken on a mechanical shaker for a period of hours. The pH of the slurry after this agitation was found to be 5.95. The slurry was filtered and the filtrate analyzed to show 4.05 grams of molybdenum per liter. This represents a 79.7% transfer of the molybdenum values to the solid phase.

A similar treatment, but shaken on the mechanical shaker for only 1 hour instead of 15 hours, had a final pH value of 5.5, and resulted in a supernatent solution containing 10.83 grams of molybdenum per liter. This corresponds to a transfer of only 45.8% of the molybdenum values to the solid phase. Thus it is shown that molybdenum values can be transformed from ammonium calcined cake, place quite slowly even at Example 8 This example illustrates the preparation of a nickeliron-molybdenum-zirconia alloy according to a process of this invention.

A slurry of intimately mixed nickel carbonate-ferric hydroxide-zirconia was prepared by mixing 30 liters each of the following:

(1) Three molar ammonium carbonate, (2) a solution 2 molar in nickel nitrate, and 0.67 molar in ferric nitrate, and (3) a zirconia aquasol containing g. ZrO so that the product contained 2.0% zirconia on a metal basis, calculated on yield of metal values and 100% yield of zirconia.

The slurry thus obtained was filtered, and washed until the filtrate was colorless. The filtered cake was reslurried in two thirds of its own weight of demineralized water. To this slurry was added 3.5 liters of a solution containing 250 grams of (NH Mo O '4H O. The pH was adjusted to 7.0 using concentrated nitric acid, and was held at that value, while agitating, for four hours, after which the slurry was filtered. The product was dried, calcined at 450 C. and pulverized. It was reduced in a flow of hydrogen at a maximum temperature of 850 C. for a period of 11 hours to produce a metallic powder. The product contained nickel:iron:molybdenum in the weight ratio of 27:9:4 with 1.8% zirconia dispersed uniformly throughout the alloy matrix.

I claim:

1. In a process for producing an alloy in powder form, said alloy comprising (A) molybdenum, (B) at least one other metallic component selected from the group consisting of (I) iron, (II) cobalt, (III) nickel, (IV) chromium, (V) at least one metal of these four with tungsten, and (VI) at least one metal of said four with copper, and (C) a refractory metal-oxygen component consisting of a refractory oxide having an average particle size of 2 to 500 millimicrons and a free energy of formation at 1000 C. of at least kcal. per gram atom of oxygen, which process includes the steps of (1) preparing a particulate solid comprising a compound of each metal other than molybdenum to be present in the final alloy, said particulate solid being further characterized in that, after calcination at to 550 C., the said metal compounds therein are reducible to their component metals at 450 to 1200 C., and said particulate solid having so dispersed therein as to be inseparable by mechanical means, from 0.05 to 10% by volume of a said refractory metal-oxygen component, (2) depositing a molybdenum-containing coating on the surface of the particulate solid from a solution containing a molybdenum compound, (3) separating the coated solid from the solution and calcining it at from 100 to 550C. and (4) heating the calcined product at 450 to 1200 C. in contact with a reducing agent selected from the group consisting of hydrogen, carbon, carbon monoxide, and hydrocarbon gases, whereby the particulate solid and its molybdenum-containing coating are reduced to their component metals and these metals are homogeneously alloyed with each other, while the refractory metal-oxygen component remains unreduced and uniformly distributed therein the improvement which comprises effecting the deposition of step 2 by dispersing the particulate solid of step 1 in an aqueous ammonium molybdate solution having a pH in the range of 5.5 to 8.5, in an amount substantially exceeding the solubility of said solid in said solution, and maintaining the pH in that range until the molybdenum-containing coating has deposited on the surface of the particulate solid.

2. A process according to claim 1 wherein the particulate solid of step 1 comprises a compound of nickel.

3. A process according to claim 1 in which the pH of the ammonium molybdate solution in step 2 is maintained at 6.5 to 7.5.

4. A process according to claim 1 in which the particulate solid of step 1 comprises a nickel compound and the refractory metal-oxygen component (C) cornprises thoria.

1 2 References Cited UNITED STATES PATENTS 3,085,876 4/1963 Alexander et al 75-O.55 3,150,443 9/1964 Alexander et al 29-4825 DAVID L. RECK, Primary Examiner. W. W. STALLARD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,382,062 May 7, 1968 Dale M. Hiller It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 13, "modybdenum" should read molybdenum line 55, "ther" should read their Column 4 line 54 "agent" should read reagent ..C0lumn 5, line 38, after "preferred" insert reducin Column 7, line 24, "(90C.)" should read (900 C.) line 29, "decanted" should read decanned same column 7, TABLE 1, third column, line 4 thereof, ".0" should read 1.0

Signed and sealed this 7th day of October 1969.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents