CH711352B1 - Process for manufacturing a material of a colored solid noble metal - Google Patents

Abstract

The invention relates to a method for producing a material comprising between 12 and 23 carats of a colored solid noble metal, formed of a noble metal-containing nanoparticle assembly in a matrix of an inorganic material, the material comprising at least one minus 50% by weight of the noble metal; the process comprising the steps of: providing in a reactor a mixture comprising a noble metal precursor (S3), for example a gold salt, a precursor of the inorganic material, and a solvent including water (S1), a alcoholic solvent, and a polar aprotic solvent (S2); heating said mixture to a first temperature, to reflux, so as to reduce the noble metal precursor (S3); cooling the mixture to a second temperature below the first temperature so as to obtain a suspension; and filter the suspension. The mixture comprises between 5 and 20% -vol of water; between 40 and 60% -vol of the aprotic polar solvent, between 25 and 50% -vol of the alcoholic solvent. And between 50 and 100 g of the noble metal precursor. The invention also relates to a watchmaking product, a jewel or a writing instrument made of the material obtained by the method according to the invention.

Description

The invention also relates to a watch product, a jewel or a writing instrument, made from the material obtained by the process according to the invention.

CH 711 352 B1

Description Technical Field The present invention relates to a process for manufacturing a material comprising between 12 and 23 carats of a solid noble metal of adjustable color as well as the material obtained by the process.

STATE OF THE ART [0002] Precious metals such as gold, silver or one of their alloys are widely used in the manufacture of luxury goods such as watchmaking products, jewelry or writing instruments. Precious metals can be used in the form of a thin or thick decorative layer but also in solid form.

The use of such precious metals makes it possible to obtain products in a certain range of colors. For example, in the case of gold, 18-carat "yellow" gold can be used, as well as gold commonly known in goldsmithery "white gold" (gold and nickel alloys), "red gold" ( gold and copper alloys), "green gold" (gold and silver alloys), "gray gold" (gold and iron alloys), "purple gold" (gold and silver alloys) aluminum) "yellow gold", or "rose" (alloys of gold, silver and copper), etc. The palette of colors obtained by these different alloys remains however limited essentially to nuances on the original color of gold.

It is impossible to obtain a wide range of colors and colors by the use of precious metals or alloys of precious metals. In particular, it is difficult, if not impossible, to obtain until now certain ranges or varieties of colors such as red which are frank, lively and stable over time.

The covering of the piece of metal or precious alloy with a coating in order to add a surface coloration is not satisfactory since the colored layer is liable to wear out and the part will discolour partially or completely with time.

The use of metallic nanoparticles for coloring is known in the case of coloring glasses and ceramics. For example, in EP 1 887 052, ceramics have been pigmented with coated nanoparticles, in particular nanoparticles coated with silica, have been used to manufacture a pigmented ceramic material in the mass, for example of saturated red color.

[0007] However, none of the known methods makes it possible to color in the mass in order to obtain metals or alloys of precious metals in these color tones.

The document EP 2 369 022 describes a solid material of noble metal of adjustable color formed from an assembly of nanoparticles, the nanoparticles containing a noble metal and being coated with an inorganic (or dielectric) matrix. In particular, the noble metal nanoparticles are coated with an inorganic matrix which makes it possible to obtain a specific coloring in the solid state. Indeed, the inorganic matrix is capable of influencing the wavelength of the plasmon resonance band and therefore of the perceived color. The inorganic matrix can comprise an oxide such as silica, zirconia or alumina or their derivatives. The nanoparticles are shaped so as to obtain an unconsolidated compact, the compact is sintered to obtain a colored noble metal material. The colored noble metal material comprises at least 50% by weight of the noble metal, its color being determined by the composition and the chemical environment, the shape and size of the nanoparticles.

The noble metal nanoparticles of controlled size and geometry (spheres, cubes, rods, etc.) can be synthesized by reduction of a metal precursor (for example a metal salt) in solution to produce fine colloidal particles of the noble metal. A layer of an inorganic material, such as an oxide, is produced, for example, by adding a precursor of Si or Al to a suspension of colloids in a preferably aqueous or alcoholic solvent (in particular methanol, ethanol, propanol, or Isopropanol) and in the presence of a mineralization, hydrolysis and or catalysis agent such as for example ammonia.

However, the concentrations of the metal precursor which can be used in the synthesis solution remain low, that is to say typically less than one tenth of a gram of the metal precursor per liter of synthesis solution. The production yields of the solid material of noble metal synthesized therefore remain relatively low. In addition, the synthesis reaction must be carried out in several stages. For example, it is necessary to carry out the reduction of the metal precursor before the formation of the inorganic matrix. To this end, the precursor of the inorganic material must be added to the synthesis solution after the reduction of the metallic precursor.

BRIEF SUMMARY OF THE INVENTION The present invention relates to a process for manufacturing a solid noble metal material of adjustable color formed from an assembly of nanoparticles containing a noble metal in a matrix of an inorganic material, free of limitations of known methods.

More particularly, the present invention relates to a method of manufacturing a material comprising between 12 and 23 carats of a solid noble metal of adjustable color formed from an assembly of nanoparticles containing a metal

CH 711 352 B1 noble in a matrix of an inorganic material, the material comprising at least 50% by weight of the noble metal; the process comprising the steps of:

providing in a reactor a synthesis mixture comprising a noble metal precursor, a precursor of the inorganic material, and a solvent including water, an alcoholic solvent, and a polar aprotic solvent; and heating said mixture to a first temperature so as to reduce the noble metal precursor;

said mixture comprising between 5 and 20% -vol of water; between 40 and 60% -vol of the polar aprotic solvent, between 25 and 50% -vol of the alcoholic solvent; and between 50 and 100 g of the noble metal precursor.

An advantage of the manufacturing process described here is that the synthesis mixture can comprise up to 1 to 2 g / L of the noble metal precursor, that is to say approximately 40 to 80 times the admissible concentration in known methods. The production yields of the massive synthesized noble metal material are therefore relatively higher. In addition, the reduction of the metal precursor can be carried out with the formation of the inorganic matrix, making it possible to synthesize the noble material in a single step.

Brief description of the figures Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

fig. 1 illustrates a sequence of adding to a reactor the various components of a synthesis mixture, according to a first embodiment; and fig. 2 illustrates a sequence for adding the various components of a synthesis mixture to a reactor, according to a second embodiment.

Example (s) of embodiment of the invention According to one embodiment, a method of manufacturing a composite material of adjustable color comprising a noble metal and an inorganic matrix, the method comprising steps of:

providing in a reactor a mixture comprising a noble metal precursor, a precursor of the inorganic material, and a solvent including water, an alcoholic solvent, and a polar aprotic solvent; and heating said mixture to a first temperature T-ι so as to reduce the noble metal precursor and to form the inorganic matrix.

Preferably, the mixture comprises between 8 and 14% -vol of water; between 47 and 53% -vol of the polar aprotic solvent, and between 33 and 38% -vol of the alcoholic solvent.

The reduction of the noble metal precursor in the mixture allows a higher concentration of the noble metal precursor in the mixture than in the known manufacturing processes. Preferably, the mixture can comprise between 1 and 2 g / L of the noble metal precursor. The mixture therefore makes it possible to have higher production yields.

Such a concentration of the noble metal precursor makes it possible to manufacture the solid noble metal material with a concentration of the noble metal of between 12 and 23 carats, that is to say between approximately 50% and 95% by weight.

In the present process, the noble metal precursor and the precursor of the inorganic material are supplied together in the reactor, before heating the mixture to the first temperature Τ _Ί . Heating the mixture to Ti makes it possible to reduce the noble metal precursor and to react the precursor of the inorganic material in order to form the inorganic matrix. The addition of a chemical reducing agent to the mixture may be necessary to reduce the noble metal and react the precursor of the inorganic material during the heating step. This is the case for the reduction of a gold precursor in the presence of a silica precursor, as described below. The reduction of the noble metal precursor and the reaction of the precursor of the inorganic material are therefore carried out in a single step, in contrast to known methods where the reduction of the noble metal precursor is carried out before the reaction of the precursor of the inorganic material. The heating step makes it possible to obtain a suspension (colloidal dispersion) formed by the noble metal in its inorganic matrix.

Alternatively, a chelating agent is added to the mixture to reduce the reaction rate of the inorganic precursor.

According to one embodiment, the alcoholic solvent is isopropanol. Preferably, the polar aprotic solvent is Ν, Ν-dimethylformamide (or DMF).

CH 711 352 B1 [0022] Still according to one embodiment, the noble metal comprises a gold salt. The precursor of the inorganic material comprises a zirconia precursor, for example zirconium propoxide or also a silica precursor, for example a tetraethyl orthosilicate (TEOS).

According to the invention, the method comprises a step of cooling the mixture to a second temperature T ₂ lower than the first temperature. The second temperature T ₂ can be around 30 ° C. The method comprises a step of filtering the suspension, for example on a membrane. After passing the solution over the filter, a powder is recovered.

The method can also include a step of passing the powder through an oven, for example at a temperature of about 80 ° C for about 12 hours. The method can also include a step of grinding and sieving the powder in order to obtain a fine and homogeneous powder. In particular, the grinding and sieving step makes it possible to control the granulometry of the powder. The process can also include a heat treatment of the powder between 450 and 900 ° C in air or in a neutral atmosphere. The heat treatment allows a pre-consolidation of the inorganic material. The method can also include a post-treatment of sieving the heat-treated powder.

The method comprises a step of compacting the powder by a sintering process. The sintering process is preferably a flash sintering process (or SPS sintering (English acronym for Spark Plasma Sintering)).

According to one embodiment, an inorganic adjuvant such as mica is added to the mixture supplied to the reactor, before the step of heating the mixture to the first temperature Τ _Ί . The purpose of the inorganic adjuvant is to modify the optical and colorimetric properties of the solid noble metal material, for example the gloss. The amount of inorganic adjuvant added is controlled according to the synthesis reaction so as to keep the preciousness of the material. Alternatively, the inorganic adjuvant is added and mixed with the powder obtained after the filtration step, but before the compacting step.

According to one embodiment, the solvent introduced into the reactor comprises between 4 to 6 L, but preferably 5.5 L, of water, between 20 to 25 L, but preferably 23.5 L, of DMF and between 12 and 17 L , but preferably 15.75 L, of isopropanol and the noble metal precursor comprises between 50 and 100 g of gold salt in between 300 and 320 ml, but preferably 310 ml, of water. The addition of DMF creates an exothermic reaction resulting in a low temperature rise of the mixture of water and DMF.

According to a first embodiment, the precursor of the inorganic material comprises between 200 and 300 ml, but preferably 250 ml, of isopropanol, about thirty ml of zirconium propoxide (precursor, polymer) as well as between 1 and 2 mL, but preferably 1.43 mL, of acetylacetone as a chelating agent.

According to the first embodiment illustrated in FIG. 1, the various components of the mixture are added to the reactor in the following order:

water (S1);

the polar aprotic solvent (S2);

the noble metal precursor, with stirring (S3); and the precursor of the inorganic material (S4).

According to a second embodiment, the precursor of the inorganic material comprises a first solution containing between 200 and 400 ml of isopropanol but preferably 250 ml of isopropanol, between 20 and 60 ml of silica precursor but preferably 45 ml silica precursor, such as TEOS. A second solution contains between 300 and 400 g of sodium citrate in 1 L of H ₂ O.

According to the second embodiment illustrated in FIG. 2, the different components of the mixture can be added to the reactor in the following order:

water (S1);

the polar aprotic solvent (S2);

the noble metal precursor, with stirring (S3);

the first solution (S4);

the second solution (S5); and the step of heating the mixture to the first temperature T-, is carried out between the addition of the first solution and the addition of the second solution.

CH 711 352 B1 The first temperature Τ _Ί to which the mixture is heated makes it possible to reduce the noble metal precursor between 90 and 130 ° C. The mixture is heated to the first temperature T-ι for approximately three hours from the time when the mixture is at reflux. A first temperature of 130 ° C allows the mixture to reach approximately 95 ° C.

Example 1 This example relates to the manufacture of a material comprising a gold content of between 50 and 95% minimum by mass of gold, which corresponds respectively to objects between 12K and 23K minimum, in a matrix of silica.

A mixture comprises 77.28 g of HAuCI ₄ , 5.81 L of ultra-pure water, between 20 to 25 L, but preferably 23.5 L, of N, N dimethylformamide, between 12 and 17 L, but preferably 15.4 L, of isopropanol. The amount of silica precursor (tetraethyl orthosilicate or TEOS) can be between 25.5 and 400 mL. In this example, the mixture comprises 80 ml of TEOS. The mixture is initially yellow, characteristic of gold salt.

The mixture is supplied to a 60 L reactor and is then brought to reflux at a first temperature of around 130 ° C. Once the reflux is reached, between 300 and 500 g, but preferably 391 g, of sodium citrate previously dissolved in between 300 and 900 ml of ultra-pure water, but preferably 500 ml, of ultra-pure water are added to the mixture (reaction medium). The mixture discolours and becomes transparent. About ten minutes after the addition of the sodium citrate, between 150 and 250 ml, but preferably 200 ml, of ammonia are added to the mixture. The particles of Au-silica form and the medium becomes dark blue. Once the particles have been formed, the medium is left at temperature T-ι for approximately two hours in order to obtain a suspension before falling again to a second temperature T ₂ corresponding to ambient temperature.

The suspension is then filtered through a 0.22 μm nylon membrane. The powder precipitate is then rinsed by re-soaking in ultrapure water. About 45 g of powder are collected at the end of the reaction. The Au-silica powder thus obtained has a title of 91% by mass of gold.

The powder is precooked between 400 and 900 ° C, for 1 to 5 hours, in an oven allowing to work in air, under nitrogen and under argon. The powder is preferably precooked under an inert atmosphere, preferably under argon and preferably at 700 ° C for two hours. The powder is then ground and then sieved in order to obtain a fine particle size, preferably below 50 μm.

The shaping is carried out by flash sintering. To this end, the powder is introduced into a graphite or tungsten carbide mold, preferably tungsten carbide, the internal chamber of which is protected by a graphite sheet. The pressure is applied cold or hot, preferably cold. The pressure range varies between 2 and 400 MPa. The temperature rise takes place before or after the nominal pressure is applied, preferably after. The shaping temperature is between 500 and 900 ° C, preferably at 700 ° C. The working atmosphere for sintering can be nitrogen, argon or vacuum but is preferably argon. The sintering lasts between 7 and 19 minutes, preferably 12 minutes. The compactness of the pellets obtained is between 87 and 100%.

For example, an Au-silica powder dosed at 94% by mass of gold, precooked at 450 ° C, with shaping under argon, pressure of 32 MPa applied cold and then mounted to 700 ° C all for 7 minutes leads to the formation of a pellet having a density of 14.4 g.cm ^-3 and a compactness of 95%.

Example 2 This example relates to the manufacture of a material comprising a gold content of between 50 and 95% minimum by mass of gold, which corresponds respectively to objects between 12K and 23K minimum, in a matrix of zirconium.

A mixture comprises between 50 and 100 g of HAuC4 but preferably 77.28 g of HAuCI ₄ , between 3.5 and 8 L of ultra-pure water but preferably 5.81 L of ultra-pure water, between 20 and 25 L of N, N dimethylformamide but preferably 23.5 L of N, N dimethylformamide, between 14 and 20 L of isopropanol but preferably 15.75 L of isopropanol. The amount of zirconia precursor can be between 6 and 55 mL of zirconium isopropoxide and the amount of chelating agent (acetylacetone) can be between 1.4 and 12 mL. In this example, the mixture comprises 6.58 ml of zirconium isopropoxide (Zr (OiPr) ₄ ) and 1.43 ml of acetylacetone (a chelating agent). The mixture is initially yellow, characteristic of gold salt.

The mixture is supplied in a 60L reactor and is then brought to reflux at a first temperature Τ _Ί of 130 ° C. One hour after reflux is reached, the mixture (reaction medium) discolours and becomes transparent, then recolours in brown. The reaction in the mixture is left under reflux for two hours, then the mixture is allowed to descend to a second temperature T ₂ corresponding to room temperature, so as to obtain a suspension.

The suspension obtained is then filtered through a 0.22 μm nylon membrane. About 45 g of powder product are collected at the end of the reaction. The Au-zirconia powder thus obtained contains 94% by mass of gold.

The powder is precooked between 400 and 900 ° C, for 1 to 5 hours, in an oven allowing to work in air, under nitrogen and under argon. The powder is preferably precooked under an inert atmosphere, preferably under

CH 711 352 B1 argon and preferably at 450 ° C for two hours. The powder is then ground and then sieved in order to obtain a fine particle size, preferably below 50 μm.

Shaping is carried out by flash sintering. To this end, the powder is introduced into a graphite or tungsten carbide mold, preferably tungsten carbide, the internal chamber of which is protected by a graphite sheet. The pressure is applied cold or hot, preferably cold. The pressure range varies between 2 and 400 MPa. The temperature rise takes place before or after the nominal pressure is applied, preferably after. The shaping temperature is between 500 and 900 ° C, preferably at 700 ° C. The working atmosphere for sintering can be nitrogen, argon or vacuum but is preferably argon. Sintering lasts between 9 and 20 minutes, preferably 11 minutes. The compactness of the pellets obtained is between 95 and 100%.

Claims (18)

For example, an Au-zirconia powder dosed at 73.4% by mass of gold, precooked at 450 ° C, with shaping under argon, pressure of 300 MPa applied cold and then raised to 700 ° C all for 19 minutes leads to the formation of a tablet having a density of 12.99 g.cm ^-3 and a compactness of 98%. Example 3 We start with an Au-zirconia powder produced by the method described above, its gold content is measured by coupellation to 84% gold. A total of the inorganic adjuvant such as mica with a mass representing 8% of the total mass of the powder is added to the powder. The whole is then finely mixed and ground in order to control the particle size. The mixture obtained is then shaped under argon, with a pressure of 300 MPa applied cold and then mounted at 700 ° C, all for 19 minutes, so as to form a pellet having a density of 12.3 g.cm ^-3 and a compactness of 98%. claims 1. A method of manufacturing a material comprising between 12 and 23 carats of a colored solid noble metal formed from an assembly of nanoparticles containing a noble metal in a matrix of an inorganic material, the material comprising at least 50% by weight of the noble metal; the process comprising the steps of: providing in a reactor a mixture comprising a noble metal precursor, a precursor of the inorganic material, and a solvent including water, an alcoholic solvent, and a polar aprotic solvent; heating said mixture at a first temperature, until reflux, so as to reduce the noble metal precursor; cooling the mixture to a second temperature lower than the first temperature so as to obtain a suspension; and filter the suspension; characterized in that said mixture comprises between 5 and 20% -vol of water; between 40 and 60% -vol of the polar aprotic solvent, and between 25 and 50% -vol of the alcoholic solvent; and in that said mixture comprises between 50 and 100 g of the noble metal precursor. 2. The method of claim 1, wherein the noble metal precursor and the inorganic material precursor are supplied together in the reactor, before heating the mixture to the first temperature. 3. Method according to one of claims 1 and 2, wherein the noble metal precursor comprises a gold salt. 4. Method according to one of claims 1 to 3, wherein the material comprises between 50% and 95% by weight of the noble metal. 5. Method according to one of claims 1 to 4, wherein the alcoholic solvent is isopropanol. 6. Method according to one of claims 1 to 5, wherein the polar aprotic solvent is N, N-dimethylformamide. 7. Method according to one of claims 1 to 5, wherein the inorganic material comprises a zirconia precursor. 8. The method of claim 7, wherein the zirconia precursor is a zirconium propoxide. 9. Method according to one of claims 7 and 8, wherein the mixture comprises a chelating agent. 10. Method according to one of claims 1 to 6, wherein the inorganic material comprises a silica precursor. 11. The method of claim 10, wherein the silica precursor is a tetraethyl orthosilicate. 12. The method of claim 10 or 11, wherein the mixture further comprises an aqueous solution of sodium citrate. 13. Method according to one of claims 1 to 12, wherein the first temperature is about 130 ° C. 14. The method of claim 1 to 13, further comprising a step of grinding and sieving the filtered suspension in order to obtain a powder. 15. The method of claim 14, further comprising a step of compacting the powder by a sintering process. CH 711 352 B1 16. Method according to one of claims 1 to 14 and claim 16, wherein an inorganic adjuvant is added to the mixture supplied to the reactor, before the step of heating the mixture to the first temperature, or added and mixed with the powder obtained after the filtration step, but before the compacting step. 17. Material obtained by the process according to one of claims 1 to 17. 18. Watchmaking product made of the material according to claim 17.