Method for manufacturing alloys of precious metals and alloys of precious metals thus obtained

Abstract

A method for manufacturing an alloy formed from a boride of a precious metal, the method involving reacting a source of the precious metal with a source of boron in a salt or a mixture of salts in the molten state. The present invention also relates to an alloy formed from a boride of a precious metal, the alloy including crystalline nanoparticles of M x B y with M which is a precious metal, distributed in an amorphous matrix of B or in an amorphous matrix of B and of M z B a .

1 . A method for manufacturing a powder of alloy of a precious metal and of boron to obtain a boride of precious metal, the precious metal being chosen from the group formed by gold, silver, platinum, palladium, ruthenium and iridium, the method involving reacting a source of said precious metal with a source of boron in one or more salts in the molten state and comprising for this purpose the following steps:
 mixing the source of boron, the source of precious metal and the salt(s) in the solid state;   heating the mixture to a temperature between 355 and 900° C. to react the source of boron and the source of precious metal in order to obtain the metal boride of the precious metal;   cooling the mixture;   separating the solidified salt(s) from the boride of precious metal, said boride of precious metal being in the form of a powder including aggregates formed by crystalline nanoparticles of boride of precious metal MxBy distributed in a matrix of amorphous boron B, the ratio y/x of the crystalline nanoparticles of boride of precious metal MxBy being greater than or equal to 2.   
     
     
         2 . The method for manufacturing a powder of alloy according to  claim 1 , wherein the source of said precious metal is chosen from the group formed by the sulphates, the carbonates, the acetates, the nitrates, the acetylacetonates and the halides of the precious metal. 
     
     
         3 . The method for manufacturing a powder of alloy according to  claim 2 , wherein the source of said precious metal is an chloride of the precious metal MClx where M is the precious metal. 
     
     
         4 . The method for manufacturing a powder of alloy according to  claim 1 , wherein the source of boron is chosen from the group formed by the boranes and the borohydrides. 
     
     
         5 . The method for manufacturing a powder of alloy according to  claim 4 , wherein the source of boron is sodium borohydride NaBH4. 
     
     
         6 . The method for manufacturing a powder of alloy according to  claim 1 , wherein the following additional steps for modifying the composition of the boride of precious metal:
 providing at least one quantity of powder of said precious metal and/or of a powder of another precious metal;   providing a quantity of powder of said boride of precious metal;   mixing the powder of said precious metal and/or of said other precious metal with the powder of said boride of precious metal to obtain a mixture of said boride of precious metal with said precious metal and/or with said other precious metal.   
     
     
         7 . The method for manufacturing a powder of alloy according to  claim 6 , wherein the powder of said precious metal and/or of said other precious metal has a d50 of less than 70 μm, and wherein the powder of the boride of precious metal has a d50 of less than 70 μm. 
     
     
         8 . The method for manufacturing a part using a boride of precious metal obtained via the method for manufacturing a powder of alloy according to  claim 1 , comprising:
 providing the powder of boride of precious metal;   compacting the mixture of the powder of boride of precious metal and of the powder of precious metal by applying a uniaxial pressure;   subjecting the compacted powder to a treatment of spark plasma sintering also called flash sintering under a pressure between 0.5 GPa and 10 GPa, or to a treatment of hot isostatic pressing also called HIP under a pressure between 80 bar and 2200 bar, the treatment being carried out at a temperature between 400° C. and 2100° C. in order to obtain at least one ingot of an alloy of the boride of the precious metal; and   machining said ingot in order to obtain the desired part, or   reducing said ingot to the state of a powder by a treatment of micronisation, and obtaining the desired part by treatment of the powder resulting from the micronisation treatment.   
     
     
         9 . The method for manufacturing a part according to  claim 8 , wherein, in order to obtain the desired part, the powder resulting from the micronisation treatment is introduced into a mould and subjected to a uniaxial or isostatic pressure. 
     
     
         10 . The method for manufacturing a part according to  claim 8 , wherein, in order to create the desired part, the powder resulting from the micronisation treatment is subjected to a treatment of three-dimensional additive manufacturing. 
     
     
         11 . The method for manufacturing a part according to  claim 10 , wherein the three-dimensional additive manufacturing is of the direct printing type chosen from the group formed by the laser sintering called Selective Laser Melting or SLM in abbreviated form and the sintering by electron bombardment called e-beam melting. 
     
     
         12 . The method for manufacturing a part according to  claim 10 , wherein the treatment of three-dimensional additive manufacturing is of the indirect printing type chosen from the group formed by inkjetting, NanoParticle Jetting and Digital Light Projecting. 
     
     
         13 . The method for manufacturing a part according to  claim 8 , wherein, in order to create the desired part, the powder resulting from the micronisation treatment is subjected to a treatment of three-dimensional additive manufacturing, of injection or of micro-injection in the presence of a polymer binder. 
     
     
         14 . The method for manufacturing a part according to  claim 13 , comprising:
 mixing the powder resulting from the treatment of micronisation of the ingot with the polymer binder in order to obtain a feedstock;   creating a green body, the shape of which corresponds to the profile of the desired part, by subjecting the feedstock to an injection or micro-injection;   obtaining a brown body by subjecting the green body to a step of elimination of the polymer binder called step of debinding during which the green body is treated chemically, then thermally in a furnace to burn the residual polymer binder, this step of debinding being carried out in gaseous phase in an atmosphere of nitric acid or of oxalic acid and at a temperature between 100° C. and 140° C.;   subjecting the brown body to a treatment of sintering under a protected atmosphere and at a temperature between 700° C. and 1800° C. in order to obtain the desired part.   
     
     
         15 . The method for manufacturing a part according to  claim 13 , comprising:
 creating a green body, the shape of which corresponds to the profile of the desired part, by subjecting the powder resulting from the treatment of micronisation of the ingot to the treatment of three-dimensional additive manufacturing;   obtaining a brown body by subjecting the green body to a step of elimination of the polymer binder called step of debinding during which the green body is treated chemically then thermally in a furnace to burn the residual polymer binder, this step of debinding being carried out in gaseous phase in an atmosphere of nitric acid or of oxalic acid and at a temperature between 100° C. and 140° C.;   subjecting the brown body to a treatment of sintering under a protected atmosphere and at a temperature between 700° C. and 1800° C. in order to obtain the desired part.   
     
     
         16 . The method for manufacturing a part according to  claim 15 , wherein the technique of additive manufacturing is chosen from the group formed by solvent on granulate jetting, fused filament deposition and micro-extrusion. 
     
     
         17 . The method for manufacturing a part according to  claim 15 , wherein the technique of additive manufacturing is binder jetting. 
     
     
         18 . The method for manufacturing a part according to  claim 14 , wherein, after the sintering treatment, the part coming from the sintering step is subjected to a step of post-treatment by hot isostatic pressing called HIP in abbreviated form, under a pressure between 500 bar and 2200 bar, and at a temperature between 600° C. and 2100° C. 
     
     
         19 . The method for manufacturing a part according to  claim 15 , wherein, after the sintering treatment, the part coming from the sintering step is subjected to a step of post-treatment by hot isostatic pressing called HIP in abbreviated form, under a pressure between 500 bar and 2200 bar, and at a temperature between 600° C. and 2100° C. 
     
     
         20 . The method for manufacturing a part according to  claim 13 , wherein the binder is chosen from the group formed by polyethylene glycol, cellulose acetate butyrate, nano-cellulose, corn starch, sugar, polylactic acid, polyethylene, polypropylene, synthetic or natural wax and stearic acid. 
     
     
         21 . The method for manufacturing a part according to  claim 14 , wherein the binder is chosen from the group formed by polyethylene glycol, cellulose acetate butyrate, nano-cellulose, corn starch, sugar, polylactic acid, polyethylene, polypropylene, synthetic or natural wax and stearic acid. 
     
     
         22 . The method for manufacturing a part according to  claim 15 , wherein the binder is chosen from the group formed by polyethylene glycol, cellulose acetate butyrate, nano-cellulose, corn starch, sugar, polylactic acid, polyethylene, polypropylene, synthetic or natural wax and stearic acid. 
     
     
         23 . An alloy formed by a boride of a precious metal chosen from the group comprising gold Au, silver Ag, platinum Pt, palladium Pd, ruthenium Rh and iridium Ir, said alloy comprising crystalline nanoparticles of MxBy with M which is the precious metal, the ratio y/x of the crystalline nanoparticles of boride of precious metal MxBy being greater than or equal to 2, the crystalline nanoparticles of MxBy being distributed in an amorphous matrix of boron B or in an amorphous matrix of B and of boride of precious metal MzBa with  z  and  a  which can be equal to or less than  x  and  y , respectively. 
     
     
         24 . The alloy according to  claim 23 , wherein the ratio y/x of the crystalline nanoparticles of MxBy is greater than or equal to 2. 
     
     
         25 . The alloy according to  claim 23 , wherein the precious metal is gold and is 18-karat gold with a composition MxBy in which  x  is equal to 1 and  y  is close to 6. 
     
     
         26 . The alloy according to  claim 24 , wherein the precious metal is gold and is 18-karat gold with a composition MxBy in which  x  is equal to 1 and  y  is close to 6. 
     
     
         27 . The alloy according to  claim 23 , wherein said alloy contains other alloyed elements. 
     
     
         28 . A part for horology or part for jewellery made from the alloy according to  claim 23 .