Gold alloy and method for manufacturing gold alloy

Abstract

A gold alloy and a manufacturing method thereof, the gold alloy including: gold; and an Au-X-RE metamaterial dispersed in a gold matrix, the Au-X-RE metamaterial being represented by a composition formula Au 100‑(a+b) X a RE b represents, in the composition formula, X represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, RE represents a rare earth element, a and b are contents of X and RE, respectively, represented by at%, satisfy the following (1) and (2), 10 ≤ a ≤ 40 (1) 13 ≤ b ≤ 17 (2).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a gold alloy and a manufacturing method of a gold alloy. BACKGROUND

[0002] Gold has been valued as a noble metal since ancient times because of its beautiful luster and high rarity, and is the oldest metal used as an ornament by humans. Gold is easy to process because of its ductility, but on the other hand, is soft and easily scratched, so the hardness of gold needs to be improved when used as a jewelry ornament.

[0003] For example, as a method of improving the hardness of an aluminum alloy other than gold, in Japanese Patent Application Publication No. 2009-191327, for example, a strengthening method of an aluminum alloy substrate in which a strengthening film is formed on the surface of an aluminum alloy substrate is disclosed, characterized in that the strengthening film uses a strengthening material having a higher strength than the aluminum alloy substrate, and is formed by a non-melting process.

[0004] Further, as a high-strength aluminum alloy, in Japanese Patent Application Publication No. 2008-069438, a high-strength magnesium alloy is disclosed, characterized in that it is composed of a composition formula Mg 100-(a+b) Zn a X b is represented, X is one or more selected from Zr, Ti, Hf, a, b are the contents of Zn, X respectively represented by at%, and satisfy the following relationships of formulas (1), (2), (3):

[0005] a / 28≤b≤a / 9···(1)

[0006] 2<a<10····(2)

[0007] 0.05<b<1.0···(3)

[0008] and in the Mg matrix phase, Mg-Zn-X quasi-crystals and their approximate crystals are dispersed in the form of fine particles.

[0009] Further, in Japanese Patent Application Publication No. 2005-113235, a high-strength magnesium alloy is disclosed, characterized in that it is composed of a composition formula Mg 100-(a+b) Zn a Y b is represented, a, b are the contents of Zn, Y respectively represented by at%, and satisfy the following relationships of formulas (1), (2):

[0010] a / 12≤b≤a / 3···(1)

[0011] 1.5≤a≤10····(2)

[0012] And as the age precipitation phase, Mg3Zn6Y1 quasi-crystal and its near-crystal are dispersed in the form of fine particles. SUMMARY

[0013] As a method of improving the hardness of gold, hitherto, generally, as a material improvement method, solid solution strengthening using elements such as silver, copper, and the like mixed with gold has been used. However, since the mixing of other elements with gold, that is, the lowering of the purity of gold (gold content) in gold jewelry results in a price reduction, the workability is in a trade-off relationship with the price of gold jewelry. Therefore, it is sought to impart a certain degree of hardness in gold alloys without lowering the purity of gold.

[0014] Japanese Patent Application Publication No. 2009-191327, Japanese Patent Application Publication No. 2008-069438, and Japanese Patent Application Publication No. 2005-113235 are all technologies related to aluminum alloys, and none of them describe or teach increasing the hardness of the alloy to a degree in which the workability is excellent without lowering the content of the parent phase (aluminum).

[0015] The problem that embodiments of the present disclosure seek to solve is to provide a gold alloy that has a high purity of gold and a high hardness.

[0016] Further, the problem that other embodiments of the present disclosure seek to solve is to provide a manufacturing method of a gold alloy that has a high purity of gold and a high hardness.

[0017] Among the means for solving the above problem, the following methods are included.

[0018] <1> A gold alloy comprising:

[0019] gold; and

[0020] Au-X-RE type metamaterials represented by the composition formula Au 100-(a+b) X a RE b represents,

[0021] X in the composition formula represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn,

[0022] RE represents a rare earth element,

[0023] a and b are the contents of X and RE, respectively, represented by at%, and satisfy the following (1) and (2)

[0024] 10 ≤ a ≤ 40 (1)

[0025] 13 ≤ b ≤ 17 (2)

[0026] The Au-X-RE type metamaterials are dispersed in a gold parent phase.

[0027] The gold alloy according to <1>, wherein

[0028] The content of Au is 80 mass% or more with respect to the total mass of the gold alloy.

[0029] The gold alloy according to <1> or <2>, wherein

[0030] The rare earth element is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb.

[0031] The gold alloy according to any one of <1> to <3>, wherein

[0032] The X is Si, and the at% ratio of a to b (a:b) is 8:7.

[0033] The gold alloy according to any one of <1> to <3>, wherein

[0034] The X is Ge, and the at% ratio of a to b (a:b) is 9.5:7.

[0035] The gold alloy according to any one of <1> to <3>, wherein

[0036] In the composition formula, a and b further satisfy the following (3).

[0037] The at% ratio of a to b (a:b) is 8 to 9.5:7 (3)

[0038] A method of producing the gold alloy according to any one of <1> to <6>, comprising:

[0039] A step of dissolving Au, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and one rare earth element in an inert atmosphere.

[0040] Effects of the Invention

[0041] According to an embodiment relating to the present disclosure, it is possible to provide a gold alloy having high purity of gold and high hardness. Furthermore, according to other embodiments relating to the present disclosure, it is possible to provide a method of producing a gold alloy having high purity of gold and high hardness. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a graph showing the results of X-ray diffraction of an example of a gold alloy obtained by the method of producing a gold alloy relating to the present disclosure.

[0043] Figure 2is a graph showing the results of X-ray diffraction of an example of a gold alloy obtained by the production method of the gold alloy according to the present disclosure.

[0044] Figure 3 is an example of an SEM (scanning electron microscope) photograph of an example of a gold alloy obtained by the production method of the gold alloy according to the present disclosure.

[0045] Figure 4 is a graph showing the relationship between the rare earth element contained in an example of a gold alloy obtained by the production method of the gold alloy according to the present disclosure and the Vickers hardness of the gold alloy.

[0046] Figure 5 is a graph showing the relationship between the Au purity of an example of a gold alloy obtained by the production method of the gold alloy according to the present disclosure and the Vickers hardness of the gold alloy. DETAILED DESCRIPTION

[0047] Hereinafter, the content according to the present disclosure will be explained in detail. The explanation of the constituent elements described below is made based on a representative embodiment according to the present disclosure, but the present disclosure is not limited to such an embodiment.

[0048] In the present disclosure, the numerical range represented by “~” is the range of the values recited before and after “~” as the minimum value and the maximum value, respectively. In the numerical range recited in the present disclosure in an interval, the upper limit value or the lower limit value recited in a certain numerical range can be replaced with the upper limit value or the lower limit value of the other interval recited. In addition, in the numerical range recited in the present disclosure, the upper limit value or the lower limit value recited in a certain numerical range can be replaced with the value shown in the examples.

[0049] In the present disclosure, a combination of two or more preferred modes is a more preferred mode.

[0050] In the present disclosure, in the term such as “process”, not only an independent process, but also a process in which the desired purpose of the process can be achieved even if it cannot be clearly distinguished from other processes is included in the term.

[0051] In the present specification, “purity of gold (Au)” and “content of gold (Au)” are synonymous. For example, “the purity of gold is 95 mass%” means that the content of gold is 95 mass% with respect to the total mass of a compound containing gold (gold alloy).

[0052] In addition, in the present specification, “high hardness” means that the Vickers hardness of the obtained alloy is 100 or more.

[0053] (Gold alloy)

[0054] The gold alloy according to the present disclosure contains:

[0055] Au; and

[0056] Au-X-RE type metamaterials composed of a composition formula Au 100-(a+b) X a RE b denotes,

[0057] X in the composition formula denotes at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn,

[0058] RE denotes a rare earth element,

[0059] a and b are contents of X and RE, respectively, expressed in at%, and satisfy the following (1) and (2),

[0060] 10 ≤ a ≤ 40 (1)

[0061] 13 ≤ b ≤ 17 (2)

[0062] Au-X-RE type metamaterials are dispersed in a gold matrix. The gold alloy according to the present disclosure has a high purity of gold and a high hardness by having the above composition.

[0063] As described above, since gold has a beautiful color, a low yield, and a high price, it is used as a jewelry ornament. Pure gold (so-called 24K, a content of gold is 99.99 mass%) is too soft because its hardness (Vickers hardness) is about 20 HV to 30 HV, and thus it is easily scratched. In addition, in a case where pure gold is processed as a jewelry ornament, processing of a thin shape such as a gold wire is difficult. On the other hand, for example, since a carbon steel SS400 as a structural steel material has a hardness (Vickers hardness) of about 130 HV to 140 HV, the processability is excellent, and thus it is widely used in architectural structures, machines, and the like.

[0064] Generally, as a method of strengthening gold, a solid solution strengthening method in which a solute atom (for example, Ag, Cu, or the like) is solid-solved in a gold matrix is known. However, in the solid solution strengthening method, the hardness of gold can be increased, but on the other hand, there is a concern that the purity of gold will decrease due to the mixing of other elements.

[0065] Thus, in a case where it is provided as a gold alloy with a high added value, a hardness (preferably, a hardness of low carbon steel, and more preferably, a hardness of a steel material) of a degree in which the purity of gold is high and the processability is excellent is sought.

[0066] As a result of intensive studies by the present inventors and the like, it has been found that a gold alloy in which the purity of gold is not decreased and the hardness is increased is obtained by dispersing a metamaterial composed of a specific composition in a gold matrix.

[0067] The detailed mechanism by which the above effects are obtained is not clear, but it is presumed as follows.

[0068] The super material is one of intermetallic compounds, and in general, it is known that dislocations of intermetallic compounds are difficult to move and have high hardness. In particular, the super material is a crystal having more than several hundred atoms in a unit cell, and in addition to being an intermetallic compound, it is considered that this complex long-period structure is a main reason for showing high hardness.

[0069] Further, since the Au-based super material contains a large amount of Au in the crystal structure, it is possible to suppress a decrease in Au concentration when dispersing the Au-based super material in a gold matrix.

[0070] Further, the gold alloy according to the present disclosure is high in hardness and excellent in workability because the super material having higher hardness than the gold matrix is dispersed.

[0071] Hereinafter, each component of the gold alloy according to the present disclosure will be described.

[0072] The Au-X-RE-based super material is a super material represented by the composition formula Au

[0073] The Au-X-RE-based super material is a super material represented by the composition formula Au 100-(a+b) X a RE b The Au-X-RE-based super material is a super material represented by the composition formula Au

[0074] Here, the super material refers to a substance group (material) that is uniformly described in a high-dimensional space including a complementary space, that is, a substance (material) of a high-dimensional space (hyperspace).

[0075] The super material has a cluster structure in which atomic polyhedra are nested. As an example of the cluster of the super material, the following illustrates a regular icosahedral symmetric cluster in the Au-X-RE-based super material of Tsai type. However, the present disclosure is not limited thereto.

[0076] In the Au-X-RE-based super material of Tsai type, the innermost shell (illustrated at the left end in the following) is a tetrahedron formed of Au atoms or X atoms, and a second shell of a regular dodecahedron (illustrated at the second from the left in the following) formed of Au or X atoms surrounds the outside thereof. Further, a third shell of a regular icosahedron (illustrated at the second from the right in the following) formed of a rare earth element (corresponding to RE in the composition formula) surrounds the outside thereof, and an icosidodecahedron (dodecahedron / icosahedron) (illustrated at the right end in the following) formed of 30 Au and X atoms is surrounded on the outermost shell. Further, the cluster formed of the concentric arrangement of such four layers of shells is referred to as a cluster of Tsai type.

[0077] [Chemical Formula 1]

[0078]

[0079] As specific examples of the metamaterial, there are mentioned quasi-crystals, approximants, and the like.

[0080] Here, the quasi-crystal means a compound having a long-range ordered structure (typically having five-fold symmetry) but not having a translational symmetry which is a characteristic of a general crystal. As compositions which produce quasi-crystals, there are known so far Al-Pd-Mn, Al-Cu-Fe, Cd-Yb, Mg-Zn-Y, and the like. Since the quasi-crystal is a specific structure, it has various specific properties such as high hardness, high melting point, low coefficient of friction, and the like, compared with a crystalline intermetallic compound similar in composition.

[0081] The approximant means a crystalline compound having a complex structure derived from a quasi-crystal, and partially having the same structure as the quasi-crystal, and has properties similar to those of the quasi-crystal from which it is derived.

[0082] Further, the Au-X-RE-based metamaterial dispersed in the gold alloy can be confirmed by XRD (X-ray diffraction) measurement.

[0083] Specifically, using a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation, radiation source: CuKa), the sample is measured, and the resulting XRD peak waveform is compared with the peak inherent to the metamaterial (the peak of a known quasi-crystal or approximant) to confirm it.

[0084] Composition formula Au 100-(a+b) X a RE b >

[0085] [X]

[0086] In the composition formula, X represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn.

[0087] The above composition formula can contain only one X or two or more Xs. As an example of the composition formula in which two atoms are contained as X, there is mentioned a composition formula represented by Au-Al-Ga-Gd, and the like.

[0088] As X, from the viewpoint of improving the purity of gold in the gold alloy, it is preferred to contain at least one atom selected from the group consisting of Al, Ga, Si, Ge, and Sn, more preferably Al, Ga, Si, Ge, or Sn, further preferably Al, Ga, Si, or Ge, and particularly preferably Si or Ge.

[0089] [RE]

[0090] In the composition formula, RE represents a rare earth element. There is no particular limitation on the rare earth element, and Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu is exemplified.

[0091] Among these, from the viewpoint of improving the purity of gold in the gold alloy, as RE, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb is preferable, and La, Ce, Pr, Nd, or Sm is more preferable.

[0092] From the viewpoint of obtaining a gold alloy having high purity of gold and high hardness, X preferably contains at least one atom selected from the group consisting of Al, Ga, Si, Ge, and Sn (more preferably Al, Ga, Si, Ge, or Sn, further preferably Ga, Si, or Ge, and particularly preferably Si or Ge), and RE is preferably La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb (more preferably La, Ce, Pr, Nd, or Sm).

[0093] From the viewpoint of obtaining a gold alloy having high purity of gold and high hardness, in the case where X is Si, RE is preferably La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb, and among these, RE is more preferably a rare earth element having a small atomic number, and is preferably La, Ce, Pr, Nd, or Sm.

[0094] From the viewpoint of obtaining a gold alloy having high purity of gold and high hardness, in the case where X is Ge, RE is preferably La, Pr, Nd, Sm, Eu, or Gd, and among these, RE is more preferably a rare earth element having a small atomic number, and is preferably La, Ce, Pr, Nd, or Sm.

[0095] In the composition formula, a and b are the contents of X and RE, respectively, expressed in at%, and satisfy the following (1) or (2). By making the super material distribution satisfying the following (1) and (2) a gold mother phase, a gold alloy having high purity of gold and high hardness is obtained.

[0096] From the above viewpoint, in the composition formula, a and b preferably further satisfy (3) (i.e., satisfy the following (1) to (3)), and more preferably satisfy the following (1), (2), and (3').

[0097] 10 ≤ a ≤ 40 (1)

[0098] 13 ≤ b ≤ 17 (2)

[0099] The at% ratio (a:b) of a and b is 8 to 9.5:7 (3)

[0100] the at% ratio (a:b) of a to b is 8:7 or 9.5:7 (3')

[0101] at% means atomic percentage.

[0102] Regarding the super material represented by the composition formula Au 100-(a+b) X a RE b The kind of X and RE and whether the above (1) and (2) are satisfied can be confirmed using a scanning electron microscope: SEM-EDS.

[0103] Specifically, after mirror polishing of the obtained gold alloy sample, observation with SEM-EDS is performed, regarding the gray portion of the SEM image (a portion equivalent to the Au-X-RE-based super material), the contained elements and their contents can be confirmed using EDS (energy dispersive X-ray spectrometer).

[0104] From the viewpoint of obtaining a gold alloy having high purity and high hardness of gold, as the formula (1), it is preferable that 10≤a≤21, and more preferable that 10≤a≤14.

[0105] From the viewpoint of obtaining a gold alloy having high purity and high hardness of gold, as the formula (2), it is preferable that 13≤b≤15, and more preferable that 13≤b≤14.

[0106] From the viewpoint of obtaining a gold alloy having high purity and high hardness of gold, in the case where X is Si in the composition formula, the at% ratio (a:b) of a to b in the composition formula is preferably 8:7, and more preferably the gold alloy is represented by the composition formula Au 85 Si8RE7.

[0107] From the viewpoint of obtaining a gold alloy having high purity and high hardness of gold, in the case where X is Ge in the composition formula, the at% ratio (a:b) of a to b in the composition formula is preferably 9.5:7, and more preferably the gold alloy is represented by the composition formula Au 83.5 Ge 9.5 RE7.

[0108] <Content of Gold>

[0109] From the viewpoint of high added value, the content of gold is preferably 80 mass% or more, more preferably 85 mass% or more, further preferably 90 mass% or more, and particularly preferably 95 mass% or more, with respect to the total mass of the gold alloy.

[0110] (Method for manufacturing gold alloy)

[0111] The method for manufacturing the gold alloy disclosed herein includes a step of dissolving Au, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge and Sn, and a rare earth element in an inert atmosphere.

[0112] The method for manufacturing gold alloys disclosed herein, by including the above-described steps, yields gold alloys with high purity and high hardness.

[0113] The gold alloy manufacturing method disclosed herein uses at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and has the composition Au as described above. 100-(a+b) X a RE b The X represented in the text is synonymous, and the preferred method is also the same.

[0114] The rare earth element used in the manufacturing method of the gold alloy disclosed herein is in the above-mentioned composition formula Au. 100-(a+b) X a RE b The RE in the text is synonymous, and the preferred method is also the same.

[0115] From the viewpoint that pure metamaterials can be easily obtained, the purity of Au, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge and Sn, and one rare earth element (hereinafter referred to simply as "raw material") used in the manufacturing method of the gold alloy disclosed herein is preferably 99% by mass or more, more preferably 99.9% by mass or more, and even more preferably 99.99% by mass.

[0116] The shape of Au is not particularly limited; it can also be foil, plate, etc.

[0117] At least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and the shape of rare earth elements are not particularly limited and can be appropriately selected. Examples of shapes include granular, foil-like, plate-like, and block-like forms.

[0118] When the above-mentioned raw material is in granular form, it is preferably 1 mm to 8 mm, and more preferably 2 mm to 5 mm.

[0119] As for the method of dissolving the above-mentioned raw materials, there is no particular limitation on dissolving each raw material in an inert atmosphere, but from the viewpoint of making it easier to dissolve, electric arc dissolution is preferred.

[0120] Arc dissolution is preferably carried out in an inert atmosphere such as helium, argon, or nitrogen, and more preferably in an inert atmosphere replaced by argon.

[0121] In the manufacturing method of the gold alloy according to the present disclosure, from the viewpoint of further preventing oxidation, arc melting is preferably performed in an inert gas atmosphere of argon after a vacuum atmosphere is formed.

[0122] The arc melting can be performed using a vacuum arc melting device. Specifically, the arc melting places a test material prepared as a raw material for supplying each element on the same water-cooled copper furnace, performs vacuuming to form a pressure set in advance, and is performed by applying a desired current value in an inert gas atmosphere.

[0123] The pressure vacuuming at the time of the arc melting can be adjusted to a range of 1 x 10 -2 Pa or less, and preferably 1 x 10 -3 Pa or less. For example, after the vacuuming, the arc melting can be performed in an inert gas of 0.01 MPa to 0.1 MPa, for example.

[0124] The current value applied at the time of the arc melting is preferably adjusted to a range of 20 A (ampere) to 100 A, for example. The application time of the voltage is, for example, four times of 5 seconds to 30 seconds of voltage application, and the like, and is appropriately selected depending on the situation.

[0125] The manufacturing method of the gold alloy according to the present disclosure can also include a process (other process) other than the above processes as needed.

[0126] As the other process, a raw material preparation process, a refining process of the obtained gold alloy, and the like are exemplified.

[0127] Examples

[0128] Hereinafter, the present disclosure will be specifically described by examples. Furthermore, the present disclosure is not limited by any of these examples.

[0129] (Example 1)

[0130] (1) As a gold (Au) raw material, an Au plate manufactured by Kikuchi Precious Metal Industry Co., Ltd. (shape: irregular shape, purity: 99.99%) was prepared.

[0131] As one of the raw materials of the Au-X-RE metamaterial (X in the composition formula), a Ge particle manufactured by High Purity Chemical Laboratory Co., Ltd. (shape: Grain 2 mm to 5 mm, purity: 99.99%) was prepared as a germanium (Ge) raw material, and a Si particle manufactured by High Purity Chemical Laboratory Co., Ltd. (shape: Grain, purity 99.999%) was prepared as a silicon (Si) raw material.

[0132] As the rare earth element (RE in the composition formula), grain (shape: irregular block 5 mm to 10 mm, purity: 99.9%, packing form: oil immersion) manufactured by Japan Yttrium Co., Ltd. was prepared as a raw material of lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd, samarium Sm, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, and ytterbium Yb.

[0133] (2) As for the above La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb raw materials, in order to remove the oil, acetone manufactured by GODO Co., Ltd. was put into a beaker (B-100 SCI, manufactured by HARIO Co., Ltd.), and the mixture was washed for ten minutes using an ultrasonic cleaner (Au-16C, manufactured by Eiko Riko Co., Ltd.).

[0134] (3) As for the above Au, Ge, Si, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb raw materials, the raw materials were cut into a size of 1 mm to 3 mm x 1 mm to 3 mm using a forceps (TESKYU-260 TYPE, manufactured by ENUSHIKI Co., Ltd., N-31, manufactured by HOZAN Co., Ltd.), and were set as samples.

[0135] (4) The obtained gold alloy satisfied the composition formula Au 83.5 Ge 9.5 RE7 (in the composition formula, RE represents La, Ce, Pr, Nd, Sm, Eu, or Gd, and the numbers represent at% respectively. The same applies hereinafter) or the composition formula Au 85 Si8RE7 (in the composition formula, RE represents La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb, and the numbers represent at% respectively. The same applies hereinafter), and the total mass was 1 g, the samples obtained in the above (3) were weighed respectively, and seventeen kinds of mixed samples were obtained.

[0136] (5) Next, using a super-small vacuum arc melting device (NEV-AD03 type, manufactured by Nissei Engineering Inc.), the mixed samples weighed as above were placed on a water-cooled copper furnace respectively, and vacuum was drawn for about two hours to reach a pressure of 3 x 10 -3 Pa, and then the current value was adjusted to about 40 A to 80 A under an argon atmosphere to arc-melt each of the mixed samples.

[0137] Further, in order to uniformly melt the mixed samples, after the arc irradiation of the samples, the mixed samples were inverted using an inversion rod, and the process of arc irradiation was performed twice again. Thus, seventeen kinds of alloy samples in a spherical shape with a diameter of 4 mm to 7 mm were obtained: Au 83.5 Ge 9.5 RE7 (RE = La, Ce, Pr, Nd, Sm, Eu, or Gd) and Au85 Si8RE7(RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb).

[0138] (6) The obtained alloy sample was cut off using isomet (manufactured by Buehler).

[0139] (7) The sample cut off in order of particle sizes P800, 1000, and 2000 was polished in stages using a doctor-lap (manufactured by MARUTO), carbomax paper (manufactured by Refinetech), and the mixed sample was adjusted to be parallel on the upper and lower surfaces. Further, a few drops of diamond suspension (MetaDi™ Supreme Polycrydtalline Diamond Suspension, manufactured by Buehler) were dropped on a polishing cloth (TriDent Polishing Cloth, manufactured by Buehler), and mirror polishing was performed on the alloy sample in order of diamond sizes 3 μm and 1 μm.

[0140] < Evaluation based on X-ray diffraction >

[0141] (8) The alloy sample mirror-polished above was evaluated using a powder X-ray diffraction device (MiniFleX600, manufactured by Rigaku, radiation source: CuKα).

[0142] XRD (X-ray diffraction) patterns are shown in Figure 1 and Figure 2 As shown in Figure 1 and Figure 2 , it was confirmed that the peaks inherent to the Au-X-RE metamaterial and Au could be confirmed in the composition of any of the alloy samples.

[0143] Further, the 1 / 1 metamaterial is described as Tsai-type clusters having a body-centered cubic structure disposed at each vertex and the center of a cube, and a crystal structure having Im-3 symmetry.

[0144] As shown in Figure 1 and Figure 2 , it was confirmed that the peaks inherent to the Au-X-RE metamaterial and Au could be confirmed in the composition of any of the alloy samples. 83.5 Ge 9.5 RE7(RE = Gd, Eu, Sm, Nd, Pr, Ce, or La) and Au 85 Si8RE7(RE = Yb, Dy, Tb, Gd, Eu, Sm, Nd, Pr, Ce, or La) were successful in the production of a two-phase alloy of the Au-X-RE metamaterial and gold.

[0145] < Evaluation based on SEM >

[0146] (9) Again, the alloy sample was polished in stages in order of particle sizes P1000, 2000, and 4000 using the polishing table and polishing paper shown in (7). A few drops of diamond suspension were dropped on the polishing paper TriDent, and the alloy sample was mirror-polished in order of diamond sizes 3 μm and 1 μm. A few drops of alumina suspension (MasterPrep™ Polishing Suspension 0.05 μm) were dropped on the polishing paper (MasterTex Polishing Cloth, manufactured by Buehler), and the alloy sample was mirror-polished.

[0147] (10) The alloy sample obtained in (9) was evaluated using a scanning electron microscope: SEM-EDS (JSM-IT100, manufactured by JEOL).

[0148] The results are shown in Figure 3 . Figure 3 In the figure, the white portion is Au, and the gray portion is the Au-X-RE metamaterial. According to Figure 3 , it was found that the Au-X-RE metamaterial was dispersed in the gold matrix.

[0149] Further, regarding the obtained gold alloy containing the metamaterial (Au-Ge-La), after EDS analysis, Au was 74 at%, Ge was 13 at% (a in the composition formula), and La was 13 at% (b in the composition formula), and the metamaterial (Au-Ge-La) satisfied formula (1) and formula (2).

[0150] <Hardness>

[0151] (11) The micro Vickers hardness of the alloy sample was measured and evaluated using a Shimadzu micro hardness tester (HMV-G21, manufactured by Shimadzu Corporation). The results are shown in Figure 4 and Table 1.

[0152] The alloy sample was a value of Vickers hardness exceeding 156 HV.

[0153] [Table 1]

[0154]

[0155] (Example 2)

[0156] (12) The obtained gold alloy was made to have the composition formula Au x Ge y La z (x = 81.2, 86.0, 91.3, or 97 at%, y:z = 9.5:7 (at% ratio)), Au x Siy Ce z (x = 87 or 89 at%, y:z = 8:7 (at% ratio)) and the total mass becomes 1 g, the raw materials prepared in Example 1 were weighed in such a manner, and six kinds of mixed samples were prepared.

[0157] (13) Except for using the six kinds of mixed samples prepared above, an alloy sample was obtained by arc melting under the same conditions as (5) of Example 1.

[0158] (14) After the alloy sample obtained in (13) was cut, polished, and mirror-polished under the same conditions as (6), (7), and (8) of Example 1, X-ray diffraction measurement was performed.

[0159] (15) Mirror-polishing was performed again under the same conditions as (7) of Example 1, and the material structure was evaluated using SEM-EDS.

[0160] (16) Micro Vickers hardness was measured under the same conditions as (11) of Example 1. The results thereof are shown in Table 2. Figure 5

[0161] The region of Vickers hardness of 130 HV to 140 HV is a hardness (i.e., a hardness excellent in workability) suitable for calendering, wire drawing, and the like, and shows a desirable hardness as a jewelry material.

[0162] Further, in pure gold (purity of gold: 99.99%), the Vickers hardness is 20 HV to 30 HV.

[0163] It can be seen that in the Au-Ge-La-based and Au-Si-Ce-based super material-dispersed gold alloys produced in Example 2, there is a linear relationship between the purity of gold and the hardness, and the hardness linearly changes depending on the amount of dispersion of the super material. Further, in the Au-Si-Ce-based super material-dispersed gold alloys, in the range of 93 mass% to 96 mass% of the purity of gold, the Vickers hardness of 145 HV to 200 HV is shown.

[0164] As shown in Examples 1 and 2, it is clear that the manufacturing method of the gold alloy according to the present disclosure and the gold alloy obtained by the manufacturing method have high purity of gold and high hardness.

[0165] Further, it is clear that in the Au-Ge-La-based and Au-Si-Ce-based gold alloys, a desired hardness can be achieved with an extremely high purity of gold (content of gold) of 93.1 mass% and 95.9 mass% respectively. This is a high purity compared to 18K (content of Au: 75 mass%) generally used as a jewelry material so far.

[0166] ​The gold alloy and the manufacturing method thereof involved in the present disclosure are Japanese Society for the Promotion of Science Research Grant Aid Business: New Academic Field Research (Research Field Proposal Type) "Metamaterials: New Material Science Created by Metaspace" (Project Number: 19H05817, 19H05818, 2019-2023).

[0167] The disclosure of Japanese Patent Application No. 2021-056093 filed on March 29, 2021 is incorporated herein by reference in its entirety.

[0168] All of the documents, patent applications and technical standards cited in the present specification are incorporated herein by reference to the same extent as if each individual document, patent, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A gold alloy consisting of gold and an Au-X-RE metamaterial, The Au-X-RE metamaterial is represented by the composition formula Au 100-(a+b) X a RE b represents, X in the composition formula represents at least one kind of atom selected from the group consisting of Ga, In, Si, Ge, and Sn, RE represents a rare earth element, a and b are contents of X and RE, respectively, expressed in at%, and satisfy the following (1) and (2), 10≤a≤40 (1) 13≤b≤17 (2) the Au-X-RE metamaterial is dispersed in a gold matrix.

2. The gold alloy according to claim 1, wherein the content of Au is 80 mass% or more with respect to the total mass of the gold alloy.

3. The gold alloy according to claim 1 or 2, wherein the rare earth element is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb.

4. The gold alloy according to claim 1 or 2, wherein X is Si, and the at% ratio of a to b (a:b) is 8:

7.

5. The gold alloy according to claim 1 or 2, wherein X is Ge, and the at% ratio of a to b (a:b) is 9.5:

7.

6. The gold alloy according to claim 1 or 2, wherein in the composition formula, a and b further satisfy the following (3), the at% ratio of a to b (a:b) is 8 to 9.5:7 (3).

7. A method of producing the gold alloy according to any one of claims 1 to 6, comprising: a step of dissolving Au, at least one kind of atom selected from the group consisting of Ga, In, Si, Ge, and Sn, and one kind of rare earth element in an inert atmosphere.

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