US3176386A - Dispersion strengthening of metals - Google Patents

Description

United States Patent 3,176,386 DISPERSION STRENGTHENING 0F METALS Nicholas J. Grant, 10 Leslie Road, Winchester, Mass., and Richard J. Murphy, Belmont, Mass; said Murphy assignor to said Grant No Drawing. Filed Oct. 26, 1961, Ser. No. 147,731 16 Claims. (Cl. 29420.5)

This invention relates to dispersion strengthened metals and, in particular, to a wet method of producing dispersion strengthened metals characterized by improved strength properties at elevated temperatures.

Ever since the discovery of SAP (sintered aluminum powder), much work has been done in studying the principles of dispersion strengthening and applying them to new systems. Such metals as Mg, Ag, Cu, Ni, Mo, Be, as well as Fe, W, Pt, Sn and Cr have been strengthened in this way by a variety of disperse phases. This type of strengthening has been studied primarily by means of powder metallurgy techniques, one method comprising using metal powder as the matrix-forming material which is blended with finely divided refractory oxide particles, such as A1 0 and the mix thereafter consolidated and hot worked to the desired shape. Another method of preparation is internal oxidation in which a dilute solid solution alloy, such as CuAl, in the form of powders or small chips, is selectively oxidized to produce a dispersion of A1 0 in a copper matrix powder which is thereafter processed in to a wrought shape. Other methods have included intimately mixing a reducible metal oxide with a refractory oxide, ball milling the mixture, selectively reducing the metal oxide and then processing the selectively reduced mix into a wrought metal shape by consolidation and extrusion.

Attempts were made to use wet mixing techniques in which a soluble decomposable salt dissolved in a solvent is mixed with fine metal powder and the solvent thereafter evaporated and the salt later decomposed to a refractory oxide, but these techniques were difiicult to control and, generally, the final product was inferior to those obtained by the dry methods.

For example, in an attempt to produce nickel dispersion strengthened with thoria by the wet method of mixing finely divided carbonyl nickel powder, for example up to 5 microns in size, with an alcohol solution of thorium nitrate, an exothermic reaction would usually occur when the nickel was mixed in bulk with the solution, thereby resulting in a hard dry residue. After decomposing the salt at 600 C. followed by reduction in dry hydrogen, the material would take on a high degree of pyrophoricity, and was difficult to handle. Wrought metal products produced from powder mixtures prepared in this manner were generally inferior to dry blending techniques.

We have now discovered a wet method of processing dispersion strengthened metals whereby superior high temperature strength properties are obtained heretofore not obtainable by the dry mixing methods.

It is the object of this invention to provide a wet method for producing dispersion strengthened metals by powder metallurgy characterized by improved high temperature strength.

It is also the object of this invention to provide a wet method for producing a uniform powder mixture of a metal powder and a refractory oxide from which wrought metal products exhibiting high resistance to creep at elevated temperature can be produced.

Another object is to provide a dispersion strengthened wrought metal article of manufacture.

These and other objects will more clearly appear when taken in conjunction with the disclosure which follows.

Our method comprises providing a finely divided ductile matrix metal powder, for example ranging up to about ice 44 microns in size and preferably not exceeding about 10 microns, providing a solution of a soluble decomposable refractory oxide-forming salt, slowly adding the matrix metal powder to the solution while rapidly stirring said solution to form a homogeneous slurry, to keep the metal particles from agglomerating together and to insure wetting of each of the particles with the solution, evaporating said mix under substantially protective conditions to form a highly viscous mix such that it is difiicult to stir it any further, confining the highly viscous mix in a container or mold, evaporating the remaining solvent therein to form a dry coherent mass or slug comprising said metal with the salt associated with the particles thereof, and then subjecting the coherent mass to heating in a dry protective atmosphere, e.g., a reducing atmosphere of hydrogen, at an elevated temperature sufficient to decompose the contained salt to form a refractory oxide finely and uniformly dispersed therethrough. The coherent mass in this form is generally free from blow holes, piping or severe local porosity and can be consolidated to a compact and then extruded under protective conditions to a wrought shape characterized by improved high temperature strength.

In producing the wet mix, we slowly add the metal powder to the salt solution while rapidly stirring to form the slurry. The rate of stirring should be at least sufficient to avoid isolated heavy concentration of the solution in the wet mix so as to inhibit a high rise of temperature which otherwise occurs exothermically when the mass is not homogeneously mixed. The rapid rate of stirring may go as high as 20,000 r.p.m. and range from about 5,000 to 20,000 rpm.

In one embodiment of our invention, we are able to achieve markedly high resistance to rupture at high stresses at up to about 815 C. and higher for wrought nickel by utilizing thoria as the disperse phase decomposed from thorium nitrate.

While, as stated herein, the particle size may range up to about 44 microns and more desirably up to 10 microns, we prefer it not exceed about 5 microns, and more preferably, range from about 0.1 to 1 or 2 microns.

The metal powder may be ductile metal having a melting point above 250 but usually may exceed 650 C. Such metals may include the copper group metals Cu, Ag, Au and alloys based on these metals; the metals Pb, Zn and alloys based on these metals; the iron group metals Fe, Ni, Co and alloys, particularly heat resisting alloys based on these metals; the precious metals Pt, Pd, Ru, Rh, Ir, Re and alloys of these metals with each other and other metals; certain of the refractory metals W, Cr. Mo, Ti, Zr, V, Cb, Ta and alloys thereof.

Examples of such copper-group alloys are: 90% copper and 10% nickel, copper and 20% nickel; 70% copper and 30% nickel; 70% copper and 30% gold; 65% copper, 30% gold and 5% nickel; silver and 10% copper; up to 15% nickel and the balance silver; 70% gold and the balance palladium, 69% gold, 25% silver and 6% platinum, and similar alloys.

Examples of iron group alloys include: steels, 64% iron and 36% nickel; 31% nickel, 4 to 6% cobalt, and the balance iron; 54% iron and 46% nickel; 90% iron and 10% molybdenum or tungsten; 90% nickel and 10% molybdenum or tungsten.

Heat resisting alloys based on one or more of the iron group metals nickel, iron and cobalt may also be dispersion strengthened.

With respect to precious metal alloys, the following are examples: platinum-rhodium alloys containing up to 50% rhodium; platinum-iridium alloys containing up to 30% iridium; platinum-nickel containing up to 6 or 10% nickel; platinum-palladium-ruthenium containing 77% 3 to platinum, 13 to 88% palladium, and 10 to 2% ruthenium; alloys of palladium-ruthenium containing up to 8% ruthenium; 60% palladium and 40% silver; 90% platinum and 10% rhenium, and others.

With regard to the decomposable refractory oxide- :forming salts, we prefer those salts which are soluble in non-residue leaving solvents, such as Water, or alcohol and other organic solvents, and which salts decompose to a refractory oxide whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about C. and, more preferably, at least about 120,000 calories.

The solvent should be one which evaporates below the decomposition temperature of the salt and does not leave aresidue.

We prefer that the soluble salt be one whose decomposition temperature does not exceed the melting point of the metal and preferably does not exceed 550 C. More preferably, it is desired the decomposition does not exceed about 375 C. Examples of soluble refractory oxideforming salts which decompose to form dispersions of refractory oxide are Th(NO -4H O; Al(NO -9H O;

etc. Certain of the chloride salts may be employed provided the prevailing conditions are such as to favor formation of oxides. Thus, the salts may comprise nitrates, oxalates, acetates, chlorides and the like. The foregoing salts are at least to some extent soluble in water, alcohol or both. The refractory oxides formed by the decomposition of these salts have negative free energy of formation of at least about 100,000 calories per gram atom of oxygen at about 25 C.

We prefer to use thorium nitrate as the source of the refractory oxide ThO as We have been able to realize exceptionally high strength properties with it. In addition, we find thorium nitrate easy to work with because of its high solubility in alcohol.

In order to insure optimum strength properties in the final product, we prefer that the metal powder be as fine as possible. We find the powder to be satisfactory for our purposes when it has been reduced to yield a high specific surface which is generally indicated when the powder exhibits pyrophoricity on exposure to an oxygencontaining atmosphere. However, in order to utilize the advantages of such a powder, particular care must be taken to handle the powder under substantially inert environment or conditions. When powder is being reduced for our purposes to sizes below 3 microns say, for example, in an attrition mill, we prefer the grinding be carried out in alcohol or other suitable liquid in a controlled atmosphere, such as argon or other inert gas. After the powder has been suitably ground, it is washed and dried in an inert or protective environment, e.g., argon, and retained protected for wet mixing with the dissolved refractory oxide-forming salt.

Of course, other means may be used to insure an inert or protective environment, such as a vacuum, or a liquid medium. A still further method would be to stabilize the finely ground metal powder during grinding. For example, during wet grinding, suflicient oxygen might be bled into the mill atmosphere so that any oxidation which takes place in the mill environment is controlled in accordance with the prevailing oxygen partial pressure. Thus, the finely ground metal powder would be stabilized to the extent that its pyrophoricity would be sufiiciently inhibited to render the powder easier to handle in subsequent operational steps. Thus, the terms inert environment, protective environment, inert conditions and similar terms are meant to cover those means of protecting the powder to avoid as far as possible from it markedly undergoing spontaneous ignition.

In order to obtain a better understanding of the invention, the following examples are given:

EXAMPLE 1 In producing Alloy No. 1, carbonyl nickel powder having a size ranging from about 2 to 5 microns was employed. The nickel powder amounted to 1000 parts by weight and was divided into 5 equal portions of 200 parts each. Five portions of thorium nitrate were provided, each comprising 45.2 parts by weight. The total amount of thorium salt corresponded to an oxide loading in the neighborhood of about 9 volume percent. Each portion of the salt was dissolved in about 118 parts by weight of methyl alcohol and to each solution was slowly added 200 parts by weight of the carbonyl nickel powder and the solution stirred in a Waring Blendor at about 15,000 rpm. for about 5 minutes to form a slurry. The five mixed batches were then combined and agitated while being heated at a temperature of about 60 C. until the slurry thickened by evaporation and became so viscous that it could no longer be stirred. The highly viscous slurry was then confined in a glass mold and the remaining solvent evaporated at C. and the thorium nitrate decomposed in dry hydrogen for 4 hours at 600 C.

A hard, solid residue remained which was ball-milled in a stainless steel ball mill for about one-half hour followed by a reduction treatment at 600 C. in dry hydrogen. The powder was then vacuum compacted in a rubber stoppered rubber sleeve within a perforated open end metal tube and then hydrostatically pressed at 25,000 psi. After evacuating air from the assembly, the compact inside the rubber sleeve was hydrostatically pressed at the aforementioned pressure. The pressed billet was then sintered in dry hydrogen at 950 C. for 8 hours. It was sealed in a mild steel can and heated for one hour at about 1093" C. and extruded in a 300 ton press at a ratio of 25 to 1. The extruded product was then prepared for testing to be described later.

EXAMPLE 2 Alloy No. 2 was prepared similarly to Example 1 except that after the slurry was evaporated to a point of high viscosity wherein it would no longer be mixed by stirring, it was poured into a mold having a dimension corresponding substantially to that of an extrusion can. The mold was lined with a removable flexible rubber or plastic sleeve closed at one end. The mold was adapted to be evacuated while being heated in a hot water bath at a temperature of about 60 C. During evacuation, the mold was vibrated until substantially all of the solvent had been removed and until the slurry had hardened in the mold in the form of a slug. Thereafter, the hardened slug was removed from the rubber sleeve and cut trans versely in half and the halves heated to 100 C. in argon for 1 hour and thereafter decomposed in dry hydrogen at 600 C. and then reduced in hydrogen at the same temperature for about 5 hours. The unsintered slugs were then cold compacted to a density of about 60% theoretical in a mild steel extrusion can 2 inches inside diameter by 3 inches long and then extruded at 1093 C. at an extrusion ratio of about 25/1 as aforementioned. The oxide loading was in the neighborhood of about 9 volume percent.

In a comparison example, an alloy designated as 3X was produced by dissolving 142 grams of thorium nitrate in sufiicient methyl alcohol to wet completely 500 grams of carbonyl nickel powder of about 2 to 5 microns in size, the mixture being stirred by hand. When all the nickel was added, an exothermic reaction occurred in which all of the alcohol was in some way reacted so that the residue was dry. After decomposing the residue in argon at 600 C. for 2 hours to form thoria, it was reduced in dry hydrogen at 600 C. and exhibited pyrophoricity and tended towards oxidation. After a second reduction treatment, the powder was vacuum compacted, hydrostatically pressed into a billet at 75,000 psi, followed by reduction in hydrogen at 600 C. and then sintered in dry hydrogen at 900 C. for 24 hours. Following this, the resulting compact was vacuumed sealed in a mild steel extrusion can and extruded under the same conditions as Alloy Nos. 1 and 2 except at an extrusion ratio of 34/ 1. The oxide loading was in the neighborhood of about 11 volume percent.

Room temperature properties were obtained on Alloy Nos. 1 and 2 and stress-rupture properties at elevated temperatures obtained for Alloy Nos. 1, 2 and 3X. The specimens had a gauge length of one inch and a diameter of 0.16 inch.

For comparison purposes, nickel dispersion strengthened with 9 volume percent A1 0 No. A, was also tested. This alloy was produced by dry mixing five micron nickel powder and 0.018 micron A1 0 powder, compressing the mixture into a slug and extruded the slug as in Examples 1 and 2 into a Wrought metal shape.

Also, for comparison purposes, a nickel-thon'a result, No. B, is included produced by wet mixing NiO (0.2 to 2 microns) and thorium nitrate, decomposing the nitrate, selectively reducing the nickel oxide and then compressing and extruding the mixture encased in a mild steel can. The room temperature properties (excluding No. 3X) are compared as follows:

It is apparent from Table 1 that Alloys 1 and 2 are markedly superior in physical properties to Alloys A and B.

A comparison of the stress-rupture characteristics at 815 C. is given as follows in Table 2:

Table 2 Stress-Rupture at 815 C. (p.s.i.)

A110 No.

y 1 Hr. 10 Hr. 100 Hr.

Stress Stress Stress It is likewise apparent that Alloy Nos. 1 and 2 are considerably superior to 3X, A and B at 815 C. Alloy No. 3X illustrates the importance of processing variables on the properties of the final product. Thus, in the case of 3X where an exothermic reaction occurred during powder mixing, it adversely affected the final properties of the alloy. On the other hand, where particular care was taken during the initial stages of wet mixing to produce a viscous slurry which could thereafter be handled easily in producing a hard slug prior to subsequent heating, optimum room and high temperature properties were obtained. The properties were even markedly superior to Alloy B prepared from NiO and thorium nitrate.

6 Additional comparison tests at about 982 C. (1800 F.) are given in Table 3.

Table 3 Stress-Rupture at 982 0.

Alloy N0.

1 Hr. 10 Hr. Hr.

Stress, p.s.i. Stress, p.s.1. Stress, p.s.1.

It will be noted that as the temperature increases, the comparative strength factor for Alloys 1 and 2 appears to increase over No. 3X and No. A.

It is apparent from the foregoing that the wet method of using thorium nitrate in conjunction with very fine metal powders enables obtaining high strength in the resulting wrought product. As is also apparent from the inferior results obtained on Alloy 3X and Alloy B, the wet method is very sensitive to process variables. Since the aim of this method is to coat each nickel particle with a thin layer of refractory oxide, it is important that, during the formulation of the mix, the mixing be effected through rapid stirring, such as is achieved by a Waring Blendor, in order to insure breaking down of agglomerates of metal powder. The adverse afiect of the mixing employed in producing 3X was apparent from a microstructure obtained of Alloy 3X which showed a coarser disperse phase than that obtained for Alloys 1 and 2. The rapid stirring is also important in that it inhibits as far as possible the exothermic reaction which otherwise occurs in bulk mixing.

In applying the inventive concept to the dispersion strengthening of copper or copper group metals or alloys with alumina, the procedure is similar. As in the case of nickel powder, copper powder in the neighborhood of about five microns is slowly added to an alcohol solution of aluminum nitrate while rapidly stirring the same. After all the copper has been added to form a slurry, the stirring is continued and the slurry gently heated at about 60 C. until the slurry thickens by evaporation and increases in viscosity so that it no longer can be mixed by stirring. The highly viscous slurry is then confined in a mold and dried at about 100 C. to form a coherent solid residue which is thereafter heated in dry hydrogen at 600 C. to decompose the aluminum nitrate. The copper powder slug which remains from this treatment is then prepared for extrusion as described above in Example 2, followed by encasing the copper in a copper can and extruding it at a temperature of about 760 C. Copper dispersion strengthened in this manner likewise exhibits improved high temperature strength.

In the production of platinum or platinum alloys dispersion strengthened with a refractory oxide, such as BeO, finely divided platinum in the size range of about 1 to 5 microns is slowly added to a solution of beryllium nitrate dissolved in alcohol and rapidly stirred as aforesaid to form a slurry which is thereafter thickened by evaporation and poured into a mold and thereafter dried to form a slug. The slug is decomposed by heating it to a temperature of about 205 C. in dry hydrogen. The decomposed platinum slug is then reduced in dry hydrogen at about 250 C., canned in a stainless steel can and extruded at about 1000 C. at an extrusion ratio of about 25 to 1. Platinum dispersion strengthened in this manner exhibits improved high temperature strength, e.g., at 1100 C., superior to similar compositions produced by dry mixing. Platinum dispersion strengthened with 8 volume percent of thoria in accordance with the invention is capable of exhibiting a 100 hour stress of 3200 psi. at 1100 C.

We have found that by this Wet method of mixing, we

are able to disperse refractory oxide in the sub-micron range of up to about 0.5, and more preferably from about .01 to 0.3 micron, whether the oxide is ThO A1 BeO, ZrO the rare earth metal oxides CeO La O Y O and the like, MgO, CaO, etc.

The amount of decomposable salt employed should be sufiicient to yield an oxide loading in the product ranging from about 2% to 25 volume percent and, more preferably, from about 4 to 12 volume percent.

While it has been indicated that the refractory oxide referred to should have a negative free energy of formation of at least about 100,000 calories per gram atom of oxygen at about 25 C. and, preferably 120,000 calories,-

it is also preferred that the melting point of such refractory oxide be at least about 1600 C.

Generally speaking, the extrusion ratio employed in producing the wrought metal product may range from about to 1 to 50 to 1, and more preferably from about to 1 to to 1.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

l. A wet method for producing a homogeneous metalcontaining mixture for use in the production of dispersion strengthened wrought ductile metals of melting point above 250 C. having a uniform dispersion therethrough of a refractory oxide phase whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C. which comprises, providing a solution of a soluble decomposable refractory oxide-forming salt with a non-residue leaving solvent, said salt being one which decomposes on heating to a refractory oxide whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C., slowly adding said finely divided ductile matrix metal powder of melting point above 250 C. to said solution while rapidly stirring and evaporating said solution to produce a highly viscous slurry which tends to resist further stirring, confining the highly viscous slurry in a mold, evaporating substantially all of the solvent therefrom to form a dry solid residue comprising said ductile metal with said salt associated with the particles thereof, and subjecting said residue to heating in a dry reducing atmosphere at an elevated temperature sufficient to decompose said salt to form a refractory oxide finely dispersed therethrough.

2. The method of claim 1 wherein the amount of refractory oxide-forming salt wet mixed with the metal powder corresponds to about 2% to 25% by volume of its corresponding refractory oxide taken on the dry basis of the metal powder mixture.

3. The method of claim 2 wherein the salt is a thorium salt which decomposes to thoria.

4. The method of claim 3 wherein the thorium salt is thorium nitrate, and wherein the amount of thorium nitrate present corresponds to about 4% to 12% by volume of thoria taken on the dry basis of the metal powder mixture.

5. The method of claim 4 wherein the particle size of the finely divided metal powder range up to about 10 microns.

6. A wet method for producing dispersion strengthened wrought ductile metals of melting point above 250 C. having a uniform dispersion therethrough of a refractory oxide whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C. which comprises, providing a solution of a soluble decomposable refractory oxide-forming salt with a non-residue leaving solvent, said salt being one which decomposes on heating to a refractory oxide whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C., slowly adding said finely divided ductile matrix metal powder of melting point above 250 C. to said solution while rapidly stirring and evaporating said solution to produce a highly viscous slurry which tends to resist further stirring, confining the highly viscous mix in a mold, evaporating substantially all of the solvent therefrom to form a dry solid residue comprising said ductile metal with said salt associated with the particles thereof, subjecting said residue to heating in a dry reducing atmosphere at an elevated temperature sufiicient to decompose said salt to form a refractory oxide finely dispersed therethrough, consolidating said residue into a hot workable compact, and hot working said compact into a wrought metal shape.

7. The method of claim 6 wherein the amount of refractory oxide-forming salt wet mixed with the metal powder corresponds to about 2% to 25% by volume of its corresponding refractory oxide taken on the dry basis of the metal powder mixture.

8. The method of claim 7 wherein the oxygen-containing salt is a thorium salt which decomposes to thoria.

9. The method of claim 8 wherein the thorium salt is thorium nitrate, and wherein the amount of thorium nitrate present corresponds to about 4% to 12% by volume of thoria taken on the dry basis of the metal powder mixture.

10. The method of claim 9 wherein the particle size of the finely divided metal powder ranges up to about 10 microns.

11. A Wet method for producing a homogeneous metalcontaining mixture for use in the production of dispersion strengthened wrought ductile metals selected from the group consisting of nickel and nickel-base alloys having a uniform dispersion therethrough of a refractory oxide phase whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C. which comprises, providing a solution of a soluble decomposable oxygen-containing refractory oxide-forming salt with a non-residue leaving solvent, said salt being one which decomposes on heating to a refractory oxide whose negative free energy of formation is at least about 100,000 calories per gram atom of oxygen at about 25 C., slowly adding said finely divided ductile matrix metal powder selected from said group consisting of said nickel and nickel-base alloys to said solution while rapidly stirring and evaporating said solution to produce a highly viscous slurry which tends to resist further stirring, confining the highly viscous slurry in a mold, evaporating substantially all of the solvent therefrom to form a dry solid residue comprising said ductile metal with said salt associated with the particles thereof, and subjecting said residue to heating in a dry reducing atmosphere at an elevated temperature sufficient to decompose said salt to form a refractory oxide finely dispersed therethrough.

12. The method of claim 11 wherein the amount of refractory oxide-forming salt wet mixed with the metal powder corresponds to about 2% to 25% by volume of its corresponding refractory oxide taken on the dry basis of the metal powder mixture.

13. The method of claim 12 wherein the oxygen-containing salt is a thorium salt which decomposes to thoria.

14. The method of claim 13 wherein the thorium salt is thorium nitrate, and wherein the amount of thorium nitrate present corresponds to about 4% to 12% by volume of thoria taken on the dry basis of the metal powder mixture.

15. The method of claim 14 wherein the particle size of the ductile metal powder ranges up to about 10 microns.

16. The method of claim 11 wherein the solid residue 9 10 is consolidated into a hot workable compact and wherein 2,766,032 10/56 Meister 75-206 said compact is hot extruded into a wrought metal shape. 3,019,103 1/62 Alexander 75-206 3,069,759 12/62 Grant et a1 75-206 X References Cited by the Examiner UNITED STATES PATENTS 5 WHITMORE A. WILTZ, Primary Examiner.

2,757,446 8/56 Boegehold 29-4205 HYLAND BIZOT, Examiner.

Claims (1)

1. A WET METHOD FOR PRODUCING A HOMOGENEOUS METALCONTAINING MIXTURE FOR USE IN THE PRODUCTION OF DISPERSION STRENGTHENED WROUGHT DUCTILE METALS OF MELTING POINT ABOVE 250*C. HAVING A UNIFORM DISPERSION THERETHROUGH OF A REFRACTORY OXIDE PHASE WHOSE NEGATIVE FREE ENERGY OF FORMATION IS AT LEAST ABOUT 100,000 CALORIES PER GRAM ATOM OF OXYGEN AT ABOUT 25*C. WHICH COMPRISES, PROVIDING A SOLUTION OF A SOLUBLE DECOMPOSABLE REFRACTORY OXIDE-FORMING SALT WITH A NON-RESIDUE LEAVING SOLVENT, SAID SALT BEING ONE WHICH DECOMPOSES ON HEATING TO A REFRACTORY OXIDE WHOSE NEGATIVE FREE ENERGY OF FORMATION IS AT LEAST ABOUT 100,000 CALORIES PER GRAM ATOM OF OXYGEN AT ABOUT 25*C., SLOWLY ADDING SAID FINELY DIVIDED DUCTILE MATRIX METAL POWDER OF MELTING POINT ABOVE 250*C. TO SAID SOLUTION WHILE RAPIDLY STIRRING AND EVAPORATING SAID SOLUTION TO PRODUCE A HIGHLY VISCOUS SLURRY WHICH TENDS TO RESIST FURTHER STIRRING, CONFINING THE HIGHLY VISCOUS SLURRY IN A MOLD, EVAPORATING SUBSTANTIALLY ALL OF THE SOLVENT THEREFROM TO FORM A DRY SOLID RESIDUE COMPRISING SAID DUCTILE METAL WITH SAID SALT ASSOCIATED WITH THE PARTICLES THEREOF, AND SUBJECTING SAID RESIDUE TO HEATING IN A DRY REDUCING ATMOSPHERE AT AN ELEVATED TEMPERATURE SUFFICIENT TO DECOMPOSE SAID SALT TO FORM A REFRACTORY OXIDE FINELY DISPERSED THERETHROUGH.