EP4731715A2

EP4731715A2 - Methods and apparatus for preparing high-karat gold in various colors

Info

Publication number: EP4731715A2
Application number: EP24826613.2A
Authority: EP
Inventors: David BEKE; Laszlo Forro; Bence Gabor MARKUS
Original assignee: University of Notre Dame
Current assignee: University of Notre Dame
Priority date: 2023-06-21
Filing date: 2024-06-20
Publication date: 2026-04-29
Also published as: WO2024263732A2; WO2024263732A3

Abstract

A metallurgically-produced compound possessing an amount of gold and having a non-gold dominant color is formed by providing a composite of titanium dioxide nanowires (TiO2NW) and gold nanoparticles (AuNP); processing the composite into a powder; compacting the powder to form a green body; and sintering the green body to form compound.

Description

METHODS AND APPARATUS FOR PREPARING HIGH-KARAT GOLD IN VARIOUS COLORS

Technical Field

[0001] The present description relates generally to gold samples having non-gold dominant coloring.

Cross-Reference to Related Application

[0002] This application claims the benefit of U.S. Patent Application No. 63/509,383 filed June 21, 2023, the contents of which are incorporated herein in their entirety and for all purposes.

Brief Description of the Drawings

[0003] FIG. 1 is a flow chart of an example method for forming a gold sample having nongold dominant coloring.

[0004] FIG. 2 is a flow chart of an example method for forming a gold sample having nongold dominant coloring.

[0005] FIG. 3 is an image of a compound formed as part of the method of FIG. 1.

[0006] FIG. 4 is a set of images of powders formed as part of the method of FIG. 1.

[0007] FIG. 5 is a progression of images of compounds formed as part of the method of FIG. 2.

[0008] FIG. 6 is a set of images of gold samples formed according to the methods described herein.

[0009] FIG. 7 is a set of images of gold samples formed according to the methods described herein.

[0010] FIG. 8A is an image of a gold sample formed according to the methods described herein.

[0011] FIG. 8B is a set of images of gold samples formed according to the methods described herein. Detailed Description

[0012] The following description of example methods and apparatus is not intended to limit the scope of the description to the precise form or forms detailed herein. Instead, the following description is intended to be illustrative so that others may follow its teachings.

[0013] Gold is a popular material for both cosmetic and scientific purposes. While advances have been made in forming gold alloys having different dominant coloring than the traditional gold - particularly “white” gold and “rose gold” - most alterations to the color of gold are surface-level. For example, gold may be plated or coated with materials of other colors to lend their color to the gold. However, these combinations are deficient both cosmetically (as they are prone to chipping and damage) and technologically (as the plating can interfere with the properties of gold, and is not strong enough to last the lifetime of any device in which the material is used).

[0014] One popular surface modification technique for forming black gold involves the submersion of gold in an electroplating bath of black rhodium or black ruthenium formed by a solution of the respective elements with a black ink dye. Another technique involves the deposition of amorphous carbon onto the surface of gold using femtosecond laser treatment. However, as noted above, these techniques only result in a very thin (e.g., less than one micron) layer of the black material.

[0015] Attempts to combine various alloys with gold have led to inconsistent results. For example, a gold/aluminum (AuAh) alloy possesses an intense purple color and qualifies as 18-karat gold by weight, and a gold/indium (Aulm) alloy exhibits a blue color and nearly qualifies as 12-karat gold by weight. However, both of these alloys (along with most other alloys of gold intermetallic phases) are intrinsically brittle, which limits their utilities.

[0016] The methods described herein address these concerns by forming gold that possesses sufficient strength and durability (e.g., a hardness value of at least 300) and a consistent coloration throughout the sample.

[0017] FIG. 1 is a flow chart of a first method 100 for producing gold having a non-gold dominant color. As shown, the method 100 begins at block 110 with synthesizing titanium dioxide (TiO ) into nanowires (NW). These T1O2NW may be a substantially-linear arrangement of T1O2 molecules having a diameter on the nanometer range (e.g., 10^-9 meters). The TiChNW may be synthesized according to any suitable method and, in some examples, may be conducted in an aqueous solution of distilled water. At block 120, the TiO2NW are blended into this aqueous solution using ultrasound waves.

[0018] At block 130, gold (Au) nanoparticles (NP) are added to the blended solution. These AuNP may be prepared according to any suitable method and, in some examples, may be prepared according to the Turkevich method and may be prepared at the presence of the TiO2 NWs. The ratio of TiChNW to AuNP affects the purity (e.g., karat value) of the final gold product, and may be found according to the table below:

Carat Au T1O2 th wt% wt% (g/cm³)

18 75 25 9.7

16 66.7 32.3 8.4

14 58.3 41.7 7.2

12 50 50 6.5

1 4.2 95.8 4.0

[0019] As shown, a ratio by weight of TiO2NW to AuNP of 1 :3 is expected to result in a final gold of 18-karat with a density of 9.7 g/cm³, a ratio of 1:2 is expected to result in a final gold of 16-karat with a density of 8.4 g/cm³, a ratio of 4:5 is expected to result in a final gold of 14-karat with a density of 7.2 g/cm³, a ratio of 1 : 1 is expected to result in a final gold of 12- karat with a density of 9.7 g/cm³, and a ratio of approximately 23 : 1 is expected to result in a final gold of 18-karat with a density of 9.7 g/cm³.

[0020] At block 140, a sediment forms in the solution and, at block 150, the sediment is filtered, cleaned, and ground into a powder. FIG. 3 is an image of the sediment from block 140 taken using transmission electron microscopy (“TEM”). As shown, the TiChNW are decorated along their lengths by the AuNP. FIG. 4 is an image of exemplary powders from block 150. As shown, bottle A includes a powder having a ratio of T1O2NW to AuNP expected to result in 18-karat gold, bottle B includes a powder having a ratio of TiChNW to AuNP expected to result in 12-karat gold, and bottle C includes a powder having a ratio of TiChNW to AuNP expected to result in 1 -karat gold.

[0021] At block 160, the powder from block 150 is compacted into shape, for instance, the final shape of a product, a disc, or other suitable shape - referred to in metallurgical terms as a ‘"green body.” In one example, the green body has a thickness ranging from 0.7-2mm and a diameter of 12-60mm. In some examples, the powder is compacted by pressing an amount of

- 3 -

SUBSTITUTE SHEET (RULE 26) powder into a closed die. By compacting the powder at this stage, voids between various TiC NW and AuNP composites are eliminated in order to bring the particles close together for the next stage.

[0022] At block 170, this green body is sintered to raise the heat of the composite, which causes the TiCFNW to collapse into NP and to bind with the AuNP. In some examples, the sintering may utilize spark plasma sintering (SPS) in which the green body is placed between opposite conducting metallic pistons and 100-800 A of current at 1-50 V is applied. The voltage and current is dependent upon at least the sample dimensions and the equipment and the provided examples are typical values and may vary dependent upon the exact process utilized. The amount of sintering is limited in order to constrain the migration and coalescence of the AuNP within the composite so that they bind to the TiOzNW rather than to each other. In some examples, the sintering period is limited to 20 minutes.

[0023] The sintering atmosphere may be adjusted in order to affect the resultant sample. For example, introducing a mixture of gas of 0-100% hydrogen and inert gas which includes but not limited to nitrogen or argon can increase the concentration of the dominant color, such that a sample sintered in an environment containing 5% or more hydrogen would exhibit a deeper black. Alternatively, sintering the sample in a high-oxygen environment can lighten the color, leading to a whiter gold.

[0024] FIG. 2 is a flow chart of a second method 200 for producing gold having a non-gold dominant color. In contrast to the method 100 in which TiC NW is synthesized in an aqueous solution prior to introduction of the AuNP, the method 200 synthesizes TiChNW in a solution already containing AuNP. As such, the method 100 produces TiChNW with a coating of AuNP, while the method 200 produces AuNP with formations of TiC on the surface of the AuNP. In some examples, such as those in which a higher concentration of AuNP is desired (e.g., for higher karat gold), the second method 200 may be preferred.

[0025] As shown, method 200 begins at block 210 with the creation of a solution of AuNP by dispersing AuNP in isopropanol. To ensure proper pH balance, an amount of aqueous ammonia may be added. At block 220, a titanium precursor, which includes but are not limited to titanium isopropoxide - which is also referred to as titanium tetraisopropoxide (TTIP) - is added to the solution and, at block 230, the resultant hydrolysis reaction is allowed to run for a period of time (e.g., 12 hours). During hydrolysis, the TTIP yields TiCF that forms on the surface of the AuNP in the solution. [0026] At block 240, the solvent (e.g., the isopropanol) is evaporated to retrieve the TiOz- coated AuNP nanostructures and, at block 250, the nanostructures are re-dispersed in aqueous ammonia or other alkali solution as part of undergoing an alkali treatment. As shown in the progression image of FIG. 5, the alkali treatment causes the TiCF-coated AuNP nanostructures to cluster more closely together. Image A of FIG. 5 illustrates the nanostructures prior to alkali treatment (e.g., post-evaporation at block 240), and image B of FIG. 5 illustrates the nanostructures following alkali treatment.

[0027] From there, the method 200 proceeds to grind the treated compound into powder at block 260, compact the powder at block 270, and sinter the compacted powder at 280. These blocks are identical to blocks 150, 160, and 170 respectively from method 100.

[0028] FIG. 6 shows two TEM images of gold samples formed according to the methods described herein. Image A is of a sample of 1-karat gold (e.g., 4.2% gold by weight), and image B is of a sample of 18-karat gold (e.g., 75% gold by weight). As can be seen in image B, the higher concentrations of gold can cause coalescence of the AuNPs in the sample.

[0029] FIG. 7 shows five images of different gold samples formed according to the methods described herein. Image A shows 12-karat gold formed according to method 100, image B shows 18-karat gold formed according to method 100, image C shows 18-karat gold formed according to method 200 using AuNP of 5nm diameter, image D shows 18-karat gold formed according to method 200 using AuNP of 20nm diameter sintered in ambient air, and image E shows 18-karat gold formed according to method 200 using AuNP of 20nm diameter sintered in an atmosphere comprised of 5% hydrogen and argon (HzAr).

[0030] Forming gold samples according to the methods herein provides two additional benefits. First, as shown in FIGS. 8A-B, by mixing powders of different compositions at the compacting stage (e.g., blocks 160 and 270), samples having a mixture of colors. FIG. 8A illustrates a sample in which the face of the sample presents different colors, and FIG. 8B illustrates a sample in which the sample has layers of different colors.

[0031] Second, the gold formed by these methods possesses high hardness values (e.g., greater than 300 on the Vickers scale) which enables their use in wide-ranging fields. In some examples, the hardness of gold formed herein may exceed that of gold formed according to standard methods, with 18-karat gold formed according to method 100 having a hardness value of 320 while 18-karat gold formed according to standard methods has a hardness value around 150. [0032] Although certain example apparatuses have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.

Claims

Claims What is claimed is:

1. A method comprising: providing a composite of titanium dioxide nanowires (TiChNW) and gold nanoparticles (AuNP); processing the composite into a powder; compacting the powder to form a green body; and sintering the green body to form an amount of gold having a dominant color of black.

2. The method of claim 1, wherein providing the composite comprises: blending water with an amount of TiOzNW using ultrasound waves to form a solution; adding an amount of AuNP to the solution; allowing a sediment to form from the solution; and filtering and cleaning the sediment to retrieve the composite.

3. The method of claim 2, wherein the composite comprises AuNP coating TiCPNW.

4. The method of claim 1, wherein providing the composite comprises: blending water with an amount of AuNP to form a solution; synthesizing TiO NW within the solution; allowing a sediment to form from the solution; and filtering and cleaning the sediment to retrieve the composite.

5. The method of claim 4, wherein the composite comprises TitTNW coating AuNP.

6. The method of claim 1 , wherein the dominant color is pervasive throughout the amount of gold.

7. The method of claim 1, wherein: a ratio by weight of TiCbNW to AuNP is 1:3, and a purity of the amount of gold is 18 karat.

8. The method of claim 1 , wherein: a ratio by weight of TiC NW to AuNP is 1:2, and a purity of the amount of gold is 16 karat.

9. The method of claim 1 , wherein: a ratio by weight of TiChNW to AuNP is 1:1, and a purity of the amount of gold is 12 karat.

10. The method of claim 1, wherein the green body is sintered for no more than 20 minutes.

11. The method of claim 1 , wherein the sintering comprises spark plasma sintering.

12. The method of claim 1, wherein the amount of gold has a hardness value of at least 300.

13. A metallurgically-produced compound possessing an amount of gold and having a nongold dominant color, the compound formed by: providing a composite of titanium dioxide nanowires (TiOzNW) and gold nanoparticles (AuNP); processing the composite into a powder; compacting the powder to form a green body; and sintering the green body to form the compound.

14. The metallurgically-produced compound of claim 13, wherein the non-gold dominant color comprises black.

15. The metallurgically-produced compound of claim 13, wherein the dominant color is pervasive throughout the amount of gold.

16. The metallurgically-produced compound of claim 13, wherein: a ratio by weight of TiChNW to AuNP is 1:3, and a purity of the compound is 18 karat.

17. The metallurgically-produced compound of claim 13, wherein: a ratio by weight of TiCPNW to AuNP is 1 :2, and a purity of the compound is 16 karat.

18. The metallurgically-produced compound of claim 13, wherein: a ratio by weight of TiChNW to AuNP is 1: 1, and a purity of the compound is 12 karat.

19. The metallurgically-produced compound of claim 13, wherein the amount of gold has a hardness value of at least 300.

20. The metallurgically-produced compound of claim 13, wherein the sintering comprises spark plasma sintering.