PROCESS FOR FORMING ALLOYS IN SITU IN ABSENCE OF LIQUID-PHASE SINTERING

Abstract: Oxide-free metallic, alloy or intermetallic compound formed by coating a powder of at least one member selected from the group consisting of elemental metallic, alloy and intermetallic compound with an oxide-replacing metal. The oxide-free compound may be compacted without the addition of a liquid sintering agent and at temperatures below the melting point of the compound, under sufficient pressure to form a uniform, consolidated intermetallic body.

Description: PROCESS FOR FORMING ALLOYS IN SITU IN ABSENCE OF LIQUID-PHASE SINTERING FIELD OF THE INVENTION The invention relates to a process of forming intermetallic alloys. In a preferred embodiment, the invention relates to processes for forming the interme¬ tallic alloys as in situ dental restorations. BACKGROUND Amalgams and related alloys have been incorporated into a variety of commercial applications and thus a number of processes for producing such amalgams are known. For example, U.S. Patent No. 4,664,855 discloses a univer¬ sally employed process which triturates elemental metal- lies or an intermetallic alloy, in the form of comminuted filings or atomized spherical powders, with the sintering agent mercury and compacts the resulting amalgam into a uniform, consolidated intermetallic alloy. The process may be considered a combination of liquid phase and reactive metal sintering. The finely comminuted metallic or intermetallic powders react with the Hg and when pres¬ sure is applied to the reaction product, form a compact, high density mass. U.S. Patent No. 3,933,961 discloses a process for preparing a pre-weighed alloy tablet of uniform weight which is then triturated with a weighed quantity of Hg to form a traditional amalgam alloy. Metallic powders have two basic forms: 1) minute lathe-cut filings and 2) atomized, spherical particles. Lathe-cut filings are subsequently milled and sifted to produce the desired particle size. The length of parti- cles in a commercial lathe-cut alloy might range from 60- 120μm long, 10-70μm wide and from 10-35μm thick. On the other hand, spherical particles, produced by means of an atomizing process whereby a spray of tiny drops is allowed to solidify in an inert gaseous (e.g., argon) or liquid (e.g., water) environment, have a maximum size between 40 and 50μm (Dental Amalgams, William J. O'Brien, Ph.D., Quintessence Publishing Co., 1989, at p. 264, 266). For more than 150 years, dental practitioners have applied a Ag-Sn system and related intermetallic alloys as dental amalgam preparations for use in dental restorations such as fillings and prostheses. The amalgamation reac- tion which forms Ag-Sn dental preparations is best repre¬ sented below (Dental Materials, supra, at p. 269); Ag 3 Sn + Hg ► Ag 2 Hg 3 + Sn 7 Hg + Ag 3 Sn; or gamma + Hg ► gamma 1 + gamma 2 • +- gamma (residual) . After completion of the amalgamation reaction, the high-melting Ag 3 Sn (gamma) products are embedded in a matrix of mercury reaction products. Both the Ag 2 Hg 3 (gamma 1) and Sn 7 Hg (gamma 2) phases form a continuous network. In the amalgam structure above, however, the Sn 7 Hg is susceptible to corrosion by the following reac¬ tion: Sn 7 Hg * +- 10^2O 2 + 21H 2 0 -I- 14C1 " ► 7Sn 4 (OH) 6 Cl 2 + 4Hg. Dental amalgam corrosion results in a weakened structure and further formation of unsupported, "margin" amalgam which easily fractures under tension. The introduction of contemporary amalgams in the 1960s (amalgams known as "high-copper" amalgams) elimi¬ nated the corrosive phenomenon of Sn 7 Hg by preventing the formation of Sn 7 Hg (gamma 2) . However, even though the addition of Cu into amalgam alloys markedly improved the integrity of the dental amalgam, the Cu 6 Sn 5 (the eta prime phase of the copper amalgam system) is prone to corrosion according to the following reaction (Dental Materials, supra, at 293) . 2Cu 6 Sn 5 + 4i;0 2 + 9H 2 0 + 6C1 " ► CuCl 2 ' 3Cu(OH) 2 + 10 SnO. Furthermore, the copper which is known to leach out during corrosion of the high-copper amalgam systems has raised concern regarding the bioco patibility of these contempo¬ rary copper amalgams. A more recent attempt to eliminate the well-known corrosive tendencies of the Ag-Sn and Ag-Sn-Cu amalgam systems is addressed in U.S. Patent No. 4,181,757 which discloses a process for surface coating parent metals with a slurry (composed of a low-melting-temperature gold alloy powder, an inorganic oxide-dissolving flux, and organic liquid) and firing the slurry to produce a bonded, corro- sion-resistant layer on the parent metal surface. The disclosed process is intended for use with dental pros- theses and is not readily adaptable for in situ dental restorations such as fillings. Additionally, recent evidence has raised new issues concerning the biocompatibility of currently used dental amalgams. Evidence has now been put forward that air expired by dental patients having dental restorations made from these amalgams, particularly after gum chewing, has a significantly higher mercury vapor content than that of amalgam free patients. In an attempt to replace traditional dental amalgams with a more biocompatible intermetallic, experi¬ ments have been conducted on gallium alloys formed by triturating liquid gallium with a metal powder (Journal of Fukuoka Dental College, "Gallium Alloys for Dental Resto¬ rations," Takashi Horibe et al. , 12(4) : 198-204, 1986). However, the Journal of Dental Health has reported that gallium alloys supplied orally to rats and mice induce toxic responses in the test subjects (J. of Dental Health, "Study on Toxicity of a New Gallium Alloy for Dental Restorations," 37. 361-371, 1987). This raises questions about their safety as an alternative to traditional amalgams used in dental restorations. SUMMARY OF THE INVENTION The invention pertains to an oxide-free metallic, alloy or intermetallic compound formed by coating a powder of at least one of either an elemental metallic, alloy or intermetallic compound with an oxide-replacing metal. The invention further pertains to a process for preparing an intermetallic alloy body by compacting the coated powder or a mixture of an elemental metallic powder and the coated powder without adding a liquid sintering agent to form an alloy body in situ. The compaction can be per¬ formed at temperatures below the melting points of the coated powder and a second elemental metallic powder and under sufficient pressure, to form a uniform alloy. Intermetallic compounds and alloys produced in accordance with the present invention are substantially more biocompatible than existing commercial or experi¬ mental alloys. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an x-ray diffraction spectrum for a compacted Ag-Sn intermetallic AGSN7. Fig. 2a is a second x-ray diffraction spectrum for the sample in Fig. 1. Figs. 2b-2d are reference x-ray silver-tin diffraction spectra. Fig. 3a is an x-ray diffraction spectrum for a compacted Ag-Sn intermetallic sample, AGSN19. Figs. 3b-3d are reference x-ray silver-tin diffraction spectra. Fig. 4a is an x-ray diffraction spectrum for an In-Sn compacted sample, INSN1. Figs. 4b-4d are reference x-ray indium-tin diffraction spectra. Figs. 5a and 5b are electron micrographs of a compacted Ga-Sn sample, DLL Figs. 6a and 6b are electron micrographs of a compacted Ga-Sn sample, DL2. Figs. 7a and 7b are electron micrographs of a compacted Ga-Sn sample, EE1. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A process for forming inteπnetallics according to the present invention which circumvents the need for - 4a - liquid sintering agents such as mercury, relies on an alternative to the amalgamation process. SUBSTITUTE SHEET - 5 - Such a "non-amalgamation" process involves the principle of fast-diffusion of metallic alloy or inter¬ metallic powders. Fast-diffusion is attributed to the ability of the diffusing species to penetrate intersti- tially into the host matrix. Diffusion takes place via an interstitial mechanism instead of the usual vacancy mechanisms characteristic of diffusion in most metal systems. Interstitial diffusion is usually much faster than diffusion governed by the metal-vacancy mechanism. In order to allow diffusion processes for metallic powders to reach completion in a reasonable time and at room temperature, naturally forming surface oxides are removed from the metallic, alloy or intermetallic powders. These surface oxides exist on most fast-diffusing metals and act as diffusion inhibitors. When the naturally forming surface oxides of metal, alloy or intermetallic powders are removed com¬ pletely, the metals, alloys or intermetallic compounds will form the desired intermetallic or related compounds without the use of a liquid sintering agent and under desirable conditions (for example, at or near body tem¬ perature and at pressures produced using normal or mod¬ ified dental instruments in dental applications) . Therefore, the present invention involves produc- ing at least one of an oxide-free metallic alloy or intermetallic compound by replacing the surface oxides with a non-oxidizing metal or a metal that forms a non- tenacious oxide. In an electrochemical process, an elemental metallic, alloy or intermetallic powder is coated with an oxide-replacing metal, such as Ag, Au, Pd or Pt, by immersing the powder in a solution containing an electro¬ lyte, and subsequently separating, by vacuum filtration, evaporation or other suitable means, the coated powder from the electrolyte solution. Examples of electrolytes useful in the present application include, but are not limited to, Ag, Au, Pd and Pt salts of the cyanide, nitrate, pyrophosphate and - 6 - sulfide ions. The silver salt of the nitrate ion is pre¬ ferred and is preferably used in concentrations ranging from about 1 x 10 ~5 to about 1 X 10 "2 M and more preferably in a concentration of about 1 X 10 "2 M. Other methods for removing oxides and preventing further oxide formation, than the electrochemical method described above, may also be used. For example, gas plasmas with inert or reducing atmospheres, such as a forming gas (5% H 2 and 95% N 2 ) , also remove surface oxides from metals. Similarly, vapor deposition or sputtering will coat the powder with protective layers of Ag, Au or a related alloy. Metal dendrites which form during electrolytic oxide removal inhibit the diffusion of the powders upon compaction. A metal complexing agent added to the elec¬ trolyte solution reduces the formation of undesirable metal dendrites on the powder surfaces. Examples of metal complexing agents suitable for use in the present inven¬ tion include, but are not limited to, ammonia, citrate, ethylenediaminetetraacetic acid, pyrophosphate, sodium chloride, tetrasodium pyrophospate, sodium potassium tar- trate, sulfamate, sulfite and thiourea. Thiourea is a preferred metal complexing agent. It is preferably used in concentrations of from about l X 10 "5 to l X 10 ~3 M, and more preferably in concentrations of about l X 10 ~3 M. Addition of other metal dendrite suppressing agents to the electrolyte solution will also suppress undesirable dendrite growth. Examples of metal dendrite suppressing agents suitable for use in the present inven- tion include, but are not limited to, salts of Au, Pt, Pd or Ir, as for example, AuCl 2 , PtCl 2 and PdCl 2 . AuCl 2 is a preferred metal dendrite suppressing agent. It is prefer¬ ably used in concentrations of about 1 X 10 ~5 M to about 1 X 10 "3 M. Examples of metallic powders coated in accordance with the present invention include, but are not limited to, powders of Au, Ag, Co, Cu, Fe, Ga, In, Ir, La, Ni, Pd, Pt, Re, Rh, Ru, Sn, Ti, Y or Zn. Sn is preferred. - 7 - Typically, when compacted at clinical temperatures and under pressures achieved using dental instruments, many metals have such low fast-diffusion reaction rates at body temperatures that their use in dental applications is impractical. The biocompatible Ag-Sn system in accordance with the present invention belongs to a group of binary metal¬ lic systems that have been found to exhibit so-called "ultra-fast diffusion" behavior. These members include Ag, Au, Co, Cu, Ga, In and Sn. Ultra-fast diffusion is characterized by diffusion rates higher, by many orders of magnitude, of a small size, low-valence constituent (e.g., Ag) within the matrix of the large size, usually high valence component (e.g., Sn) . Similar behavior has been observed for mono-valent metals (e.g., Ag, Au and Cu) and some transition metals (e.g., Co, Fe, Ni and Pd) as diffusing species and Zn, Group IV-B metals (e.g, Sn) and transition metals (e.g.. La, Ti, Y and Zn) as active metal matrices. Examples of alloys or intermetallic powders useful in the present invention include but are not limited to powders having at least one first elemental metal selected from the group consisting of La, Sn, Ti, Y and Zn and at least one second elemental metal selected from the group consisting of Ag, Au, Co, Cu, Fe, In, Ir, Ga, Ni, Pd, Pt, Re, Rh and Ru. A preferred alloy or intermetallic powder contains a first elemental metal, Sn, and a second elemental metal, Ag. A preferred Ag:Sn atomic ratio of the Ag-Sn alloy or intermetallic powder is from about 1:1 to about 10:1. More preferably, the Ag:Sn atomic ratio is about 3:1. Properties of the Ag-Sn intermetallic compound can be altered by blending small additions of elemental powders with other powders or by small additions of elements to the alloy or intermetallic powders. After the elemental metallic, alloy or inter¬ metallic powder is coated with an oxide-replacing metal, a consolidated alloy body such as dental restoration may be - 8 - formed, in situ (e.g., in a dental cavity or mold for a commercial mounting press) , by compacting at least one of the oxide-free, coated powders or a mixture of an elemen¬ tal metallic powder and a coated powder, preferably without adding a liquid sintering agent. Examples of compacting include, but are not limited to, "hipping" (hot isostatic pressing) and "hot pressing." An in situ dental restoration, as for example dental fillings, is a preferred application of the com- pacted alloy thus formed. In one embodiment of the invention, Ag and Sn powders, separately coated with an oxide-replacing metal, are compacted at body temperature. A preferred coated powder used in dental applica¬ tions is Sn and a preferred elemental powder is Ag with a preferred Ag:Sn atomic ratio of the Ag-Sn alloy or inter¬ metallic powder ranging from about 1:1 to about 10:1. Preferably, the intermetallic powder is Ag 3 Sn with Sn being present in a near stoichiometric excess. The in situ formation of the alloy preferably occurs at a temperature below the melting point of the coated powders and under an applied pressure. Exemplary ranges of temperature and pressure under which the alloys may be formed include, but are not limited to, from about 20°C to about 100°C, and from about 20 KSI (1 KSI = 1000 PSI) to about 75 KSI, respectively. A preferred tempera¬ ture for alloy formation is about body temperature. A preferred pressure is about 45 KSI. It is preferred to keep the diffusion lengths of the metallic or intermetallic components down to the order of 2 to 5μm. Therefore, in the process for preparing intermetallic alloys according to the present invention, powders have an exemplary equiaxial particle size of from about 0.5μm to about lOOμm. Preferably, the particle size of the powders will range from about 0.5μmto about 50μm. Ag-Sn intermetallic powders having atomized, spherical particles with particle sizes ranging from 2μm to 50μm are preferred in the electrochemical process for producing an oxide-free metallic or intermetallic com- - 9 - pound. The preferred Ag 3 Sn intermetallic powder compacted to form the in situ alloy is preferably comprised of atomized, spherical particles having a particle size of from 0.5μm to 50μm. Exemplary preparation and properties of powders and alloys formed according to the present invention will be described in the following examples. EXAMPLES Example l A 1.0 x 10 ~2 M AgN0 3 electrolyte solution and 1 x 10" M thiourea solution are prepared according to the following procedure: 1.90365 grams of thiourea are weighed and added to 250 m£ of distilled water to make a 1.0 x 10 -1 M thiourea solution. 25 m£ of the 1.0 x 10 -1 M thiourea solution are pipetted and added to 250 m£ of distilled water to make a 1.0 x 10~ 2 M thiourea solution. A final 25 m£ volume of the 1 x 10~ 2 M thiourea solution is pipetted and added to 250 m£. of distilled water to make 1.0 x 10~ 3 M thiourea solution. 16.992 grams of silver nitrate are measured and added to 1 liter of distilled Water in a 1 liter lask to make a 1.0 x 10 -1 M AgN0 3 solution. 25 m£ of the 1.0 x 10 _1 M AgN0 3 are pipetted and mixed with a 25 m£ pipetted volume of the 1.0 x 10" 3 M thiourea solution. The 50 ml AgN0 3 and thiourea solution is then diluted to 250 m with distilled water to make a 1.0 x 10" 2 M AgN0 3 , 1.0 x 10~ 4 M thiourea electrolyte solution. A commercially available 2.5 g/£ AuC12 (1«3 X 10~ 3 M) solution is used as a metal dendrite sup¬ pressing agent. 2.4363 grams of Fisher Sn powder, Cat. No. T129, Lot No. 743145, are weighed and added to a Buchner filter. 25 cc of a 1:1 solution of the 1.0 x 10~ 2 M AgN0 3 , 1.0 x 10~ 3 M thiourea and 1.3 x 10 ~3 M AuCl 2 solution is added to the Buchner filter and stirred for four minutes. The mixture containing the Sn powder is allowed to sit for one minute and the liquid is then removed by vacuum filtration. The - 10 - resulting coated powder is rinsed twice with distilled water and dried for 48 hours. Example 2 A 1.0 x 10 _2 M AgN0 3 and 1.0 x lθ "3 M thiourea solu- tion is prepared as directed in Example 1. 1.4259 grams of Fisher Sn metal powder are weighed and placed in a Buchner filter. 20 cc of the 1.0 x lθ "2 M AgN0 3 , 1.0 x lθ "3 M thiourea solution is added to the Buchner filter containing the Sn metal and stirred with a glass rod for four minutes. The electrolyte solution containing the Sn powder is allowed to sit for one minute and then filtered for 30 minutes to remove the electrolyte solution using vacuum filtration. A sufficient quantity of dis¬ tilled water is added to rinse the resulting coated powder and the distilled water is filtered off by vacuum filtra¬ tion. A final rinse is performed using commercially available spectral grade methanol. The Buchner filter containing the coated Sn powder is then placed in a vacuum desiccator for one hour. The damp powder and Buchner filter are then removed from the vacuum desiccator and the powder is removed from the Buchner filter, placed on an evaporating dish and evacuated for approximately one hour. The coated and dried Sn powder prepared above is mixed with 4.2778 grams of Fisher Ag powder. A commer- cially available dental mixer (Vortex-Genie mixer model S8223, Scientific Products) is used to blend the Sn and Ag powders in a 0.25 inch diameter mold for the PR-22 mounting press. The powder is then heated to 100°C for approximately 1 hour and compacted at 22 KSI. The result- ing consolidated Ag-Sn intermetallic is labeled as AGSN7 and an x-ray diffraction analysis is conducted. Figures 1 and 2a are the resulting x-ray diffraction spectra. Figs. 2b-2d illustrate selected reference silver-tin diffraction spectra identifying peaks of the spectrum in Fig. 2a. Using a TUKON microhardness tester, the Knoop hardness of sample AGSN7 is determined and reported in Table I. SUBSTITUTESHEET - 11 - Example 3 A 1:1 solution of 1.0 x 10 AgN0 3 , 1.0 x 10 ~3 M thiourea and 1.3 x lθ "3 M AuCl 2 is made by mixing 15 cc of the 1.0 x 10 AgN0 3 , 1.0 x lθ "3 M thiourea solution (pre- pared according to the procedure in Example 1) to 15 cc of 1.3 x lθ "3 M AuCl 2 solution. The resulting 1:1 solution is then filtered through a fine Buchner filter. A non-excess of AgN0 3 is verified by combining a drop of the 1:1 solu¬ tion and a drop of AgN0 3 which causes AgCl to precipitate. A 0.6945 gram sample of Sn powder is weighed and mixed with 5 cc of the above prepared 1:1 electrolyte solution and stirred for four minutes. The electrolyte solution and powder are allowed to rest for one minute. 2.0853 grams of Ag powder are then added to the existing electro- lyte solution in the medium Buchner filter and mixed for 30 seconds. A partial evacuation removes some liquid through the filter until the mixture remains "moist." The resulting powders are rinsed with 10 cc of distilled water and the water is removed by vacuum filtration. The mixture is then mixed with a spatula and some material is placed in a 0.25 inch diameter compression mold and com¬ pacted to 43.6 KSI at 36°C for 10 hours. A portion of the remaining powder mixture is placed in a "Baker-test your adaptation" lucite mold and compacted and consolidated using dental tools for compact¬ ing and burnishing. The mold and consolidated inter¬ metallic powder, which develops a shiny, metallic appear¬ ance, is annealed overnight at 40°C. The sample, AGSN19, is x-rayed and the resulting x-ray diffraction spectrum are shown in Fig. 3a. Figs. 3b-3d illustrate selected reference diffraction spectra identifying peaks of the spectrum in Fig. 3a. The Knoop hardness of AGSN19 is shown in Table I. Example 4 A 1:1 solution of 1.0 x 10% AgN0 3> 1.0 x lθ "3 M thiourea and 1.3 x lθ "3 M AuCl- > is prepared by combining 25 cc of the 1 x 10 *2 M AgN0 3 , 1 x lθ "3 M thiourea solution as prepared in Example 1 with 25 cc of 1.3 x 10 " M AuCl 2 - 12 - solution as used in Example 2. The resulting 50 cc of solution are filtered through a fine Buchner filter. 0.4772 grams of pure Sn powder prepared above are weighed and combined with a weighed 1.9090 gram sample of Indium powder. The two powders are weighed in plastic test tubes, and manually mixed. Indium powder is broken up manually. The manually mixed powders are then mixed using a dental "shaker" (such as a "Wig-L-Bug Amalgam- ator," Model LP-60, from Crescent Dental Mfg. Co.) for 30 seconds. A 1.0 gram weighed sample of the Sn-In inter¬ metallic powder is placed in a 0.25 inch diameter mold and compressed to 21 KSI at room temperature for 10 minutes. After 4 minutes, the pressure drops, but continuous and subsequent pumping returns the pressure to 21 KSI. Upon removal from the compression mold, the material is reacted, is liquified and forms a thin foil specimen within the mold. A small round sample is cut from the foil specimen, INSN1, and an x-ray diffraction pattern obtained. The resulting diffraction spectrum is shown in Fig. 4a. Figs. 4b-4d illustrate selected indium-tin reference diffraction spectra identifying peaks of the spectrum in Fig. 4a. The Knoop hardness results are shown in Table I. . Example 5 Small granular Ga material is prepared for use by smashing between the polished ends of two stainless steel cylinders (approximately 1.5 and 2 cm in diameter) . 0.3207 grams Sn powder are weighed in a plastic test tube and 0.9616 grams Ag powder are weighed and added to the plastic test tube. The resulting combined powder is mixed well with a Vortex-Genie dental mixer for approximately 30 seconds. A 0.06044 gram sample of the above crushed Ga is weighed out and a small particle of the crushed Ga (approximately 1 mm diameter) is placed in a "Baker" plastic mold. A small amount of the 3:1 Ag-Sn powder prepared above is added, mixed and then compressed with dental tools. One additional specimen is prepared in a like manner. A third compact intermetallic is layered - 12a - until a small "pill" is formed. The specimens are labeled DLl, DL2 and EEl, respectively. Micrographs for the above specimens (DLl, DL2 and EEl) are shown in Figures 5a and 5b, 6a and 6b and 7a and 7b. - 13 - TABLE I Calculated Hardness Values Using 50g Load (Except Where Indicated) +++++++ Comminuted Alloys +++++++ Calculated Specimen Dial Units Knoop Hardness Average (Kg/mm 2 ) AGSN7 503 61.6 53.6 584 45.7 AGSN19 572 47.6 46.9 581 46.2 INSN1 (5g load) 926 1.8 1.9 878 2.0

Claims: - 14 - WHAT IS CLAIMED IS: 1. A process comprising coating a powder of at least one member selected from the group consisting of elemental metallic, alloy and intermetallic compounds with an oxide-replacing metal. 2. The process according to claim 1 wherein the coating is done by: immersing said powder in a solution containing an electrolyte; and separating the coated powder from the elec¬ trolyte solution. 3. The process according to claim 2 wherein the electrolyte solution further contains a complexing agent for said oxide-replacing metal. 4. The process according to claim 3 wherein the electrolyte solution further contains a dendrite suppress¬ ing agent for said oxide-replacing metal. 5. The process according to claim 3 wherein the complexing agent is selected from the group consisting of ammonia, citrate, ethylenediaminetetraacetic acid, pyro- phosphate, sodium chloride, tetrasodium pyrophospate, sodium potassium tartrate, sulfamate, sulfite and thio¬ urea. 6. The process according to claim 3 wherein the complexing agent is thiourea. 7. The process according to claim 6 wherein the thiourea is used in a concentration of from about 1 x 10~ 5 to about 1 x 10 "3 M. 8. The process according to claim 6 wherein the thiourea is used in a concentration of about l x 10 ~3 M. 9. The process according to claim 4 wherein the dendrite suppressing agent is a salt of a metal selected from the group consisting of Au, Pt, Pd and Ir. 10. The process according to claim 4 wherein the dendrite suppressing agent is AuCl 2 . 11. The process according to claim 10 wherein the AuCl 2 is used in a concentration of from about 1 x 10~ 5 to about 1 x 10 "3 M. - 15 - 12. The process according to claim 10 wherein the AuCl 2 is used in a concentration of about 1 x 10 "3 M. 13. The process according to claim 2 wherein the electrolyte is at least one cyanide, nitrate, pyrophos- phate or sulfide salt of a metal selected from the group consisting of Ag, Au, Pd or Pt. 14. The process according to claim 2 wherein the electrolyte is AgN0 3 . 15. The process according to claim 14 wherein the AgN0 3 is used in a concentration of from about 1 x 10 -5 to about 1 x 10 "2 M. 16. The process according to claim l wherein the elemental metallic compound is selected from the group consisting of Au, Ag, Co, Cu, Fe, Ga, In, Ir, La, Ni, Pd, Pt, Re, Rh, Ru, Sn, Ti, Y and Zn. 17. The process according to claim 1 wherein the elemental metallic compound is Sn. 18. The process according to claim l wherein the intermetallic compound contains at least one first ele- mental metal selected from the group consisting of La, Sn, Ti, Y and Zn and at least one second elemental metal selected from the group consisting of Ag, Au, Co, Cu, Fe, In, Ir, Ga, Ni, Pd, Pt, Re, Rh and Ru. 19. The process according to claim 18 wherein the first elemental metal is Sn and the second elemental metal is Ag. 20. The process according to claim 19 wherein the Sn and the Ag have a Ag:Sn atomic ratio ranging from about 1:1 to about 10:1. 21. The process according to claim 20 wherein the Ag:Sn atomic ratio is about 3:1. 22. The process according to claim 21 wherein the powder is comprised of atomized, spherical particles having an equiaxial particle size of from about 0.5μm to about 50μm. 23. A process for preparing an intermetallic alloy body comprising the steps of: - 16 - a) coating a first powder of at least one member selected from the group consisting of elemental metallic, alloy and intermetallic compound ' s with an oxide- replacing metal; and b) compacting the coated first powder or a mixture of an elemental metallic second powder and the coated first powder without adding a liquid sintering agent to form an alloy body in situ. 24. The process according to claim 23 wherein the compacting of the coated first powder and elemental second powder is done by hipping. 25. The process according to claim 23 wherein the compacting of the coated first powder and elemental second powder is done by hot pressing. 26. The process according to claim 23 wherein the alloy body is a dental restoration compacted orally, in situ. 27. The process according to claim 23 wherein the coated first powder is coated Sn and the elemental second powder is Ga. 28. The process according to claim 27 wherein the Ga and Sn are used in an atomic ratio of about 1:20. 29. The process according to claim 23 wherein the coated first powder is a coated Ag-Sn intermetallic and the elemental second powder is Ga. 30. The process according to claim 23 wherein the compacting takes place at a temperature below the melting points of the coated first powder and the second powder and under an applied pressure. 31. The process according to claim 30 wherein the temperature is in a range of from about 20°C to about 100°C and the applied pressure is in a range of from about 20 KSI to about 75 KSI. 32. The process according to claim 30 wherein the applied pressure ranges from about 20 KSI to about 75 KSI. 33. The process according to claim 30 wherein the temperature is approximately body temperature. - 17 - 34. The process according to claim 30 wherein the coated first powder is coated Sn powder and the elemental metallic second powder is Ag powder. 35. The process according to claim 34 wherein an atomic ratio of Ag in said second powder to Sn in said coated first powder ranges from about 1:1 to 10:1. 36. The process according to claim 23 wherein the powder is Ag 3 Sn atomized, spherical particles having an equiaxial particle size of from about 0.5μ to about 50μ. 37. The process according to claim 23 wherein the first powder before coating has an equiaxial particle size of from about 0.5μm to about lOOμm. 38. The process according to claim 23 wherein the first powder before coating has an equiaxial particle size of from about 0.5μm to about 50μm. 39. A composition comprising an oxide-free elemental metallic, alloy or intermetallic powder coated with an oxide-replacing metal. 40. The composition according to claim 39 wherein the elemental metallic powder is selected from the group consisting of Au, Ag, Co, Cu, Fe, Ga, In, Ir, La, Ni, Pd, Pt, Re, Rh, Ru, Sn, Ti, Y and Zn. 41. The composition according to claim 39 wherein the elemental metallic powder is Sn. 42. The composition according to claim 39 wherein the intermetallic powder contains at least one first elemental metal selected from the group consisting of La, Sn, Ti, Y and Zn and at least one second elemental metal selected from the group consisting of Ag, Au, Co, Cu, Fe, In, Ir, Ga, Ni, Pd, Pt, Re, Rh and Ru. 43. The process according to claim 42 wherein the first elemental metal is Sn and the second elemental metal is Ag. 44. The process according to claim 43 wherein the Sn and the Ag have a Ag:Sn atomic ratio ranging from about 1:1 to about 10:1. 45. The process according to claim 44 wherein the Ag:Sn atomic ratio is about 3:1. - 18 - 46. The process according to claim 44 wherein the powder is comprised of atomized, spherical particles having an equiaxial particle size of from about 0.5μm to about 50μm. 47. The compound according to claim 39 wherein the powder before coating has an equiaxial particle size of from about 0.5μm to about lOOμ . 48. The process according to claim 39 wherein the first powder before coating has an equiaxial particle size of from about 0.5μm to about 50μm. 49. A process for compacting Ag and Sn powders at body temperature, whereby the Ag and Sn powders are separately coated with an oxide-replacing metal.

Inventors: DARIEL MOSHE P, ESCALANTE EDWARD, LASHMORE DAVID S, TESK JOHN A, DARIEL, MOSHE, P., ESCALANTE, EDWARD, LASHMORE, DAVID, S., TESK, JOHN, A.
Applicants: US COMMERCE, THE UNITED STATES OF AMERICA, AS REPRESENTED BY TH
Application year: 1992
Main classification: B22F1
IPC codes: A61K6, B22F1, C22C1, C22C5, C23C30