Anti-tarnish silver ornament material and preparation method thereof

Abstract

The invention relates to the technical field of precious metal materials, and provides an anti-tarnish silver ornament material and a preparation method thereof.The anti-tarnish silver ornament material comprises Ag, Cu, Zn, Pt and In. The Pt element is added into S925 silver, the silver content is kept to be 92.5 wt%, the element type and content in 7.5 wt% are changed, and by means of the unique raw material stacking sequence and the copper mold pouring technology, Pt segregation is effectively restrained, the alloy structure and performance are regulated and controlled, the alloy hardness and discoloration resistance are improved, and the service life of the alloy is prolonged. The problems that an existing alloy anti-tarnishing technology is high in cost, poor in anti-tarnishing capacity and low in hardness, and high-melting-point elements are prone to segregation are solved.

Description

Technical Field

[0001] This invention relates to the field of precious metal materials technology, and in particular to an anti-tarnishing silver jewelry material and its preparation method. Background Technology

[0002] Silver readily reacts with sulfides (H₂S, SO₂, etc.) to form Ag₂S, causing surface discoloration. Current international standards for silver jewelry alloys require 92.5 wt% silver and 7.5 wt% Cu, Zn, and other elements, known as S925 silver. This alloy is brighter, harder, and more wear-resistant than pure silver. However, 925Ag-Cu-Zn has a darker color, is prone to discoloration, and its hardness and wear resistance need further improvement.

[0003] While adding the precious metal Pt may improve the alloy's resistance to discoloration, the density difference (Pt density 21.45 g / cm³) can hinder this improvement. 3 Ag density 10.50 g / cm³ 3 The difference in melting points (Pt melting point 1772℃, Ag melting point 961.8℃) easily leads to segregation during smelting, resulting in significant fluctuations in alloy composition. Existing technologies, such as CN100999792A, employ rare earth elements and multiple alloying elements for multi-element alloying, which improves tarnish resistance, but do not address the addition of Pt and its impact on the tarnish resistance and segregation control of silver alloys. CN109112386A discloses a silver-based precision hardware material, but its composition is complex, containing multiple high-melting-point elements, and does not reveal the specific role and optimal content of Pt in the silver alloy. CN116770122A targets gold alloys, improving tarnish resistance by adding Pd / Pt, but its matrix is ​​gold, fundamentally different from the silver alloy system, and it does not solve the segregation problem of high-melting-point Pt in the silver matrix. Therefore, designing and developing a silver alloy with strong tarnish resistance and uniform composition after Pt addition has significant commercial value. Summary of the Invention

[0004] In view of this, the present invention proposes a silver alloy with strong anti-tarnishing ability and uniform composition, and its preparation method. Pt and In are added to S925 silver, keeping the silver content constant at 92.5 wt%, while changing the types and contents of elements in 7.5 wt%. Through a unique raw material stacking order and copper mold casting process, Pt segregation is effectively suppressed, the alloy microstructure and properties are controlled, and the alloy hardness and anti-tarnishing ability are improved. This aims to solve the problems of high cost, poor anti-tarnishing ability, low hardness, and easy segregation of high-melting-point elements in existing alloy anti-tarnishing technologies.

[0005] The technical solution of the present invention is implemented as follows: On the one hand, the present invention provides an anti-tarnishing silver jewelry material, wherein the components of the silver jewelry material include Ag, Cu, Zn, Pt and In.

[0006] Specifically, the addition of Pt can refine the alloy grains, increase hardness, and enhance alloy brightness; In also has the effect of refining grains, while filling vacancies and reducing defects and pores. The strong oxidation-resistant tarnishing silver alloy in this invention has the following characteristics: (a) Hardness is maintained at 80 HV. 0.05 (a) Under accelerated corrosion testing, the alloy’s resistance to discoloration was significantly improved.

[0007] Based on the above technical solutions, the preferred solution, calculated according to a mass fraction of 100%, includes Ag 92.5%, Cu 2.4%-3.33%, Zn 1.57%-3.2%, 0 < Pt ≤ 3%, and 0 < In ≤ 0.1%.

[0008] Based on the above technical solutions, preferably, the mass fraction of Pt is 1%-2%, and most preferably 2wt%.

[0009] Specifically, this invention discovered that changes in Pt content alter the anti-tarnishing ability of silver alloys. The silver alloy exhibits the strongest anti-tarnishing ability at a Pt content of 2 wt%. This is due to the synergistic optimization of Pt distribution, interfacial effects, and corrosion mechanisms. At the structural level, it forms fully covered grain boundary pinning, blocking sulfur diffusion; at the chemical level, it maximizes the efficiency of Pt's catalytic decomposition of H2S; and at the electrochemical level, it avoids localized galvanic corrosion and maintains a minimum corrosion current. Beyond this content, Pt coarsening and electrochemical side effects dominate performance degradation; therefore, 2 wt% is the optimal addition.

[0010] On the other hand, the present invention also provides a method for preparing an anti-tarnishing silver jewelry material, comprising the following steps: S1, Ag particles, Cu particles, Zn particles, Pt particles and In particles are placed in a vacuum induction melting furnace, a vacuum is drawn and a protective gas is introduced for induction melting; S2, after heating the raw material until it is completely melted, keep it at that temperature, and then pour the alloy melt into a copper mold to cool, thus obtaining a silver alloy.

[0011] Based on the above technical solutions, preferably, before smelting, raw materials are placed in a graphite crucible in a stacked manner, with Zn particles, In particles, 3wt%-5wt% Ag particles, Cu particles, Pt particles, and the remaining Ag particles placed from bottom to top.

[0012] This stacking order is one of the key aspects of this invention. It aims to effectively reduce the evaporation and burn-off of low-boiling-point Zn and In by using Ag as a cover and Cu and Pt as a top layer, while promoting the melting and diffusion of high-melting-point Pt and preventing segregation. If the raw materials are not stacked in the specified order during smelting, problems such as severe evaporation of alloying elements, inaccurate composition, and difficulty in achieving uniform melting will occur. This is because Zn and In have low boiling points, resulting in significant evaporation and burn-off during smelting. Cu and Pt, with higher melting points than Ag, are placed on top to effectively prevent evaporation and ensure accurate alloy composition.

[0013] The 3wt%-5wt% Ag is placed in the middle to cover the Zn and In elements below. If it is not placed, Zn will be burned off, and the target component cannot be obtained, as shown in Comparative Example 3.

[0014] Based on the above technical solutions, the preferred vacuum degree during melting is 5×10⁻⁶. -3 Pa-8×10 -3 Pa.

[0015] Based on the above technical solutions, the preferred method is to use argon gas with a purity of 99.999% as the protective gas during smelting, with an atmosphere pressure of -0.015 to -0.02 MPa.

[0016] Based on the above technical solutions, preferably, in step S1, the maximum current during melting is 450A; in step S2, the holding time does not exceed 9 minutes, the holding temperature is 950-1050℃, and the cooling rate of the copper mold is 100-150℃ / s.

[0017] Based on the above technical solutions, preferably, before smelting, the raw materials are first ground to remove their surface oxide scale, and then ultrasonically cleaned and dried in anhydrous ethanol.

[0018] Based on the above technical solutions, preferably, the purity of the Ag particles, Cu particles, Zn particles, Pt particles, and In particles is ≥99.95wt%.

[0019] The anti-tarnishing silver jewelry material and its preparation method of the present invention have the following advantages over the prior art: (1) Innovative composition design: This invention focuses on the individual role of Pt in Ag-based alloys and the discovery of its optimal content range (1-2 wt%). It also finds that excessive Pt leads to a decrease in the alloy's resistance to discoloration, breaking through the misconception that "the more Pt, the better" and precisely controlling costs. In addition, the composition system of this invention is simple and efficient, avoiding the problems of complex interactions, high costs, and uncontrollable performance that may be caused by multiple alloying elements.

[0020] (2) Breakthrough preparation process: In response to the industry technical problem that high-melting-point Pt is prone to segregation in Ag-based materials, this invention creates a proprietary technology of "specific order stacking of raw materials + rapid cooling of copper mold", which effectively ensures the uniformity of composition and solves the problem of uniformity of Pt / Ag system melting.

[0021] (3) Excellent comprehensive performance and cost advantages: While achieving or even surpassing the anti-discoloration performance of existing technologies (see L value data in the examples), the alloy of the present invention has high hardness (>80 HV). 0.05 Furthermore, because the Pt content is controlled within the optimal range and no other precious metals or rare earth elements need to be added, the raw material cost is lower, making it easier to commercialize and promote.

[0022] (4) The method for preparing the anti-oxidation and discoloration silver alloy provided by the present invention improves the cooling rate through the copper mold casting process after vacuum induction melting, effectively solving the problem of Pt segregation and being compatible with existing vacuum melting equipment. It only adds a copper mold casting step and does not require additional expensive equipment. The present invention fills the gap in the technology of regulating the anti-discoloration performance of silver alloys with specific Pt content and its industrial preparation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows the EDS elemental distribution of the silver alloy in Example 1 of this invention. Image A is the upper image, and image B is the lower image.

[0025] Figure 2 This is a bar chart showing the L-values ​​of the alloy after the discoloration corrosion resistance test.

[0026] Figure 3 The image shows the EDS elemental distribution of the furnace-cooled silver alloy in Comparative Example 2. Image A is the upper image, and image B is the lower image.

[0027] Figure 4 For comparative example 3, EDS elemental analysis was performed on the alloy after the raw materials were melted without stacking.

[0028] Figure 5 This is a microstructure diagram of Comparative Example 4. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] The present invention provides an anti-tarnishing silver jewelry material, the composition of which is: Ag 92.5wt%, Cu 2.4wt%-3.6wt%, Zn 1.8wt%-3.2wt%, Pt≤3wt%, In≤0.1wt%.

[0031] This invention also provides a method for preparing an anti-tarnishing silver jewelry material, comprising the following steps: S1, Raw material pretreatment The platinum-containing 925 silver alloy is composed of Ag, Cu, Zn, Pt, and In elements in a fixed mass percentage ratio, where Ag remains constant at 92.5 wt%, In remains constant, and Cu and Zn decrease proportionally as Pt increases.

[0032] Preferably, the raw materials include Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt%. Weighing is performed using an electronic balance with an error of <0.001 g. Further, the raw materials are polished to remove surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and dried before smelting.

[0033] S2, Vacuum Induction Melting Process The raw materials prepared in step S1 are placed in a vacuum induction melting furnace for vacuum induction melting to obtain a silver alloy. Specifically, before the induction melting operation, after checking and confirming that the water and electrical circuits are working properly, the inner cavity of the vacuum furnace and the crucible are cleaned. The raw materials are stacked in the crucible in sequence. After closing all valves in the furnace, a vacuum is drawn to a vacuum degree of 5 × 10⁻⁶. -3 Pa ~ 8×10 -3 Then, 99.999% pure argon gas is introduced into the vacuum chamber until the chamber pressure reaches -0.015 to -0.02 MPa. The heating button is then turned on, and the current is adjusted for heating.

[0034] It is important to note that Zn and In have low boiling points, and their melting will result in significant evaporation and burning losses. Cu and Pt, on the other hand, have higher melting points than Ag. Placing these two elements on top can effectively prevent element evaporation and ensure accurate alloy composition. Therefore, they should be stacked in the following order: place Zn at the bottom of the crucible, then add In, followed by a small amount (3wt%-5wt%) of Ag to cover the Zn and In elements, then add Cu and Pt, and finally place the remaining Ag on top.

[0035] The raw materials are melted to complete melting (950-1050℃), and then held at that temperature for a time that ensures complete melting and diffusion of Pt (less than or equal to 9 minutes). The crucible is then poured out and the molten metal is poured into a copper mold for a time of ≤5 seconds. The cooling rate is 100-150℃ / s. After the alloy melt has cooled, the vent valve is opened and the pressure is increased to atmospheric pressure. The alloy ingot is then removed, and the silver alloy is obtained.

[0036] The above technical solution will be described in detail below with reference to specific embodiments.

[0037] Example 1 This embodiment provides a method for preparing an anti-tarnishing silver jewelry material, including the following steps: S1 was made from Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt%. The alloy was weighed according to the following proportions: Ag 92.5 wt%, Cu 2.94 wt%, Zn 2.5 wt%, Pt 2 wt%, and In 0.06 wt%. This alloy sample was designated Pt2.

[0038] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0039] S2. Place the prepared raw materials into the graphite crucible in the induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Place Zn at the bottom of the crucible, then stack In, then place 5wt% Ag to cover the previous Zn and In, then stack Cu and Pt, and finally place the remaining 87.5wt% Ag on top for melting.

[0040] Vacuum up to 5×10 -3The pressure was increased to -0.02 MPa by introducing 99.999% pure argon gas into the vacuum chamber. The raw material was then melted by gradually increasing the melting current from 300 A to 450 A, with an increase of 50 A per minute. After the raw material in the crucible was completely melted, it was held at 950 °C for no more than 9 minutes. The crucible was then tilted and copper molds were poured in. After cooling to room temperature, silver alloy ingots were obtained at a cooling rate of 150 °C / s.

[0041] The silver alloy prepared in Example 1 was subjected to the following tests, using the following methods: (1) Composition test: After cutting the alloy into samples and polishing them to prepare metallographic samples, the microstructure of the samples was observed using a GeminiSEM300 scanning electron microscope, and the elemental composition was analyzed using the EDS function.

[0042] (2) Discoloration Resistance Test: The test includes the preparation of the etching solution, the formal etching test, and the surface brightness test. First, the thioacetamide etching solution is prepared according to the international standard ISO 4538:1995. The formal etching test is carried out in a test chamber, where the specified temperature and humidity conditions are maintained. During the first hour of the test, observations are made every 5 minutes. If there is no change, observations are made every hour, and the results are recorded up to 7 hours. Optical parameters such as the L value of the sample surface after etching are collected using professional optical equipment, and the corrosion morphology evolution diagram is used to determine the sample's discoloration resistance.

[0043] Figure 1 The images show the EDS elemental analysis spectra of the silver alloy in Example 1. The left and right images were taken from the top and bottom of the cast alloy ingot, respectively. It can be seen that the Pt content is consistent in different regions of the alloy, and no segregation phenomenon is observed. Figure 2 The bar chart shows the L-values ​​of the alloys after corrosion testing. L represents the black and white channels, i.e., the brightness, and ranges from 0 to 100. It can be seen that Pt2 has the largest L-value, at 48.23, indicating that it has the best resistance to discoloration.

[0044] (3) Hardness test: The test was conducted in accordance with the national standard GB / T 4340.1-2009, and the hardness was 86 HV. 0.05 .

[0045] Example 2 This embodiment provides a method for preparing an anti-tarnishing silver jewelry material, including the following steps: S1 was made from Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt%. The alloy was weighed according to the following proportions: Ag 92.5 wt%, Cu 2.40 wt%, Zn 2.04 wt%, Pt 3 wt%, and In 0.06 wt%. This alloy sample was designated Pt3.

[0046] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0047] S2. Place the prepared raw materials into a graphite crucible in an induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Place Zn at the bottom of the crucible, then stack In, then place 3wt% Ag to cover the previous Zn and In, then stack Cu and Pt, and finally place the remaining 89.5wt% Ag on top for melting to obtain the sample of this embodiment.

[0048] Vacuum up to 6×10 -3 Pa, then 99.999% pure argon gas is introduced into the vacuum chamber until the chamber pressure is -0.015 MPa, and the raw material is melted. The melting current is gradually increased from 300 A to 50 A every 1 minute, and finally maintained at 450 A. After the raw material in the crucible is completely melted, it is held at 1000℃ for no more than 9 minutes. Then the crucible is poured out and copper mold is cast. After cooling to room temperature, a silver alloy ingot is obtained. The cooling rate is 120℃ / s.

[0049] The alloy prepared in this example was tested using the same method as in Example 1, and the hardness was 93 HV. 0.05 .

[0050] Figure 2 The bar chart shows the L-values ​​of the alloy after corrosion testing. L represents the black and white channels, i.e., the brightness, and ranges from 0 to 100. It can be seen that the L-value of Pt3 is 45.02, indicating that it has good resistance to discoloration.

[0051] Example 3 This embodiment provides a method for preparing an anti-tarnishing silver jewelry material, including the following steps: S1 was made from Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt%. The alloy was weighed according to the following proportions: Ag 92.5 wt%, Cu 3.48 wt%, Zn 2.96 wt%, Pt 1 wt%, and In 0.06 wt%. This alloy sample was designated Pt1.

[0052] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0053] S2. Place the prepared raw materials into a graphite crucible in an induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Place Zn at the bottom of the crucible, then stack In, then place 4wt% Ag to cover the previous Zn and In, then stack Cu and Pt, and finally place the remaining 88.5wt% Ag on top for melting to obtain the sample of this embodiment.

[0054] Vacuum up to 8×10 -3 The pressure was increased by 99.999% argon gas until the chamber pressure reached -0.018 MPa. The raw material was then melted by gradually increasing the melting current from 300 A to 450 A, increasing by 50 A every minute. After the raw material in the crucible was completely melted, it was held at 1050 °C for no more than 9 minutes. The crucible was then tilted and a copper mold was poured in. After cooling to room temperature, a silver alloy ingot was obtained at a cooling rate of 100 °C / s.

[0055] The alloy prepared in this example was tested using the same method as in Example 1, and the hardness was 84 HV. 0.05 .

[0056] Figure 2 The bar chart shows the L-values ​​of the alloy after corrosion testing. L represents the black and white channels, i.e., the brightness, and ranges from 0 to 100. It can be seen that the L-value of Pt1 is 44.21, indicating that it has good resistance to discoloration.

[0057] Example 4 The difference between Example 4 and Example 1 is that the content of Ag is 92.5 wt%, the content of Cu is 3.33 wt%, the content of Zn is 1.57 wt%, the content of Pt is 2.5 wt%, and the content of In is 0.1 wt%, while the rest are the same.

[0058] The alloy prepared in this example was tested using the same method as in Example 1, and the result was: hardness 85 HV. 0.05 The L value is 44.85.

[0059] Example 5 The difference between Example 5 and Example 1 is that the Ag content is 92.5 wt%, the Cu content is 3.0 wt%, the Zn content is 3.2 wt%, the Pt content is 1.2 wt%, and the In content is 0.1 wt%, while the rest are the same.

[0060] The alloy prepared in this example was tested using the same method as in Example 1, and the result was: hardness 88 HV. 0.05 The L value is 45.35.

[0061] Comparative Example 1 Comparative Example 1 provides a platinum-free silver-based material, the preparation method of which is as follows: S1 was made from Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt%. The alloy was weighed according to the following proportions: Ag 92.5 wt%, Cu 4.02 wt%, Zn 3.42 wt%, and In 0.06 wt%. This alloy sample was designated Pt0.

[0062] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0063] S2. Place the prepared raw materials into a graphite crucible in an induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Place Zn at the bottom of the crucible, then stack In, then place 5wt% Ag to cover the previous Zn and In, then stack Cu, and finally place the remaining 87.5wt% Ag on top for melting to obtain the sample of this embodiment.

[0064] Vacuum up to 5×10 -3 The pressure was increased to -0.02 MPa by introducing 99.999% pure argon gas into the vacuum chamber. The raw material was then melted using a melting current that was gradually increased from 300 A to 450 A, with an increase of 50 A per minute. After the raw material in the crucible was completely melted, it was held at that temperature for no more than 9 minutes. The crucible was then tilted and copper molds were poured in. After cooling, a silver alloy ingot was obtained.

[0065] The alloy prepared in this example was tested using the same method as in Example 1, and the hardness was 75 HV. 0.05 .

[0066] Figure 2 The bar chart shows the L-values ​​of the alloy after corrosion testing. L represents the black and white channels, i.e., the brightness, and ranges from 0 to 100. It can be seen that the L-value of Pt0 is 41.22, indicating that its resistance to discoloration is weaker than that of the silver alloy with added platinum.

[0067] Comparative Example 2 Comparative Example 2 provides a platinum-containing silver alloy, the difference being that the alloy was not cast and cooled with the crucible, and its preparation method is as follows: S1 uses Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt% as raw materials. The materials are weighed according to the following proportions: Ag 92.5 wt%, Cu 2.94 wt%, Zn 2.5 wt%, Pt 2 wt%, and In 0.06 wt%.

[0068] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0069] S2, the prepared raw materials are placed in a graphite crucible in an induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Zn element is placed at the bottom of the crucible, then In element is stacked, then 5wt% Ag element is placed to cover the previous Zn and In elements, then Cu and Pt elements are stacked, and finally the remaining 87.5wt% Ag element is placed on top for melting to obtain the sample of this embodiment.

[0070] Vacuum up to 5×10 -3 The pressure was increased to -0.02 MPa by introducing 99.999% pure argon gas into the vacuum chamber. The raw material was then melted by gradually increasing the melting current from 300 A to 450 A, with an increase of 50 A per minute. After the raw material in the crucible was completely melted, it was held at that temperature for no more than 9 minutes. Then the heating current was turned off, and the molten metal was cooled with the crucible to obtain a silver alloy ingot.

[0071] EDS analysis of samples taken from the top and bottom of the furnace-cooled alloy ingot revealed a Pt content difference of over 1 wt%, indicating a severe segregation problem. Figure 3 As shown. Its hardness is 78 HV. 0.05 The L value is 43, and the tissue properties are very uneven.

[0072] Comparative Example 3 Comparative Example 3 provides a platinum-containing silver-based material, the difference being that the alloy raw materials are not stacked in the crucible, but rather mixed and placed into the crucible. The preparation method is as follows: S1 uses Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt% as raw materials. The materials are weighed according to the following proportions: Ag 92.5 wt%, Cu 2.94 wt%, Zn 2.5 wt%, Pt 2 wt%, and In 0.06 wt%.

[0073] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0074] S2, after the prepared raw materials are mixed evenly, they are placed in a graphite crucible in an induction melting furnace for melting to obtain the sample of this embodiment.

[0075] Vacuum up to 5×10 -3 The pressure was increased to -0.02 MPa by introducing 99.999% pure argon gas into the vacuum chamber. The raw material was then melted by gradually increasing the melting current from 300 A to 450 A, with an increase of 50 A per minute. After the raw material in the crucible was completely melted, it was held at that temperature for no more than 9 minutes. The crucible was then tilted and copper molds were poured in. The heating current was then turned off, and the material was cooled to obtain a silver alloy ingot.

[0076] The silver alloy prepared in Comparative Example 3 was subjected to EDS composition analysis, and the results are as follows: Figure 4 As shown, In cannot be detected at this point, and the Zn content is lower than the designed composition, while the evaporation rate is higher. Hardness: 73 HV 0.05 This is lower than that of Example 1.

[0077] Comparative Example 4 Comparative Example 4 provides a silver-based material with a platinum content exceeding the specified range, and its preparation method is as follows: S1 uses Ag particles with a purity of 99.95 wt%, Cu particles with a purity of 99.95 wt%, Zn particles with a purity of 99.95 wt%, Pt particles with a purity of 99.95 wt%, and In particles with a purity of 99.95 wt% as raw materials. The materials are weighed according to the following proportions: Ag 92.5 wt%, Cu 1.86 wt%, Zn 1.58 wt%, Pt 4 wt%, and In 0.06 wt%.

[0078] The raw materials are polished to remove the surface oxide scale, then ultrasonically cleaned in anhydrous ethanol, and finally dried.

[0079] S2. Place the prepared raw materials into a graphite crucible in an induction melting furnace. Due to the difference in melting points, placing Zn, Ag, and In on the upper layer of the crucible will cause a large amount of elements to evaporate and burn off. Therefore, the raw materials need to be stacked in order. Place Zn at the bottom of the crucible, then stack In, then place a small amount of 5wt% Ag to cover the previous Zn and In, then stack Cu and Pt, and finally place the remaining 87.5wt% Ag on top for melting to obtain the sample of this embodiment.

[0080] Vacuum up to 5×10 -3 The pressure was increased to -0.02 MPa by introducing 99.999% pure argon gas into the vacuum chamber. The raw material was then melted using a melting current that was gradually increased from 300 A to 450 A, with an increase of 50 A per minute. After the raw material in the crucible was completely melted, it was held at that temperature for no more than 9 minutes. The crucible was then tilted and copper molds were poured in. After cooling, the silver alloy ingot was obtained.

[0081] Figure 5 The microstructure diagram of Comparative Example 4 shows that due to the Pt content exceeding the optimal range, a Pt-rich phase (the white phase in the diagram) precipitates in the alloy, resulting in a discontinuous microstructure.

[0082] The alloy prepared in this example was tested using the same method as in Example 1. The results showed that the L value of Comparative Example 4 was 39, indicating that its resistance to discoloration was lower than that of Pt0 without the addition of Pt. Due to the presence of the precipitated phase, the hardness continued to increase, reaching 106 HV. 0.05 .

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A material for anti-tarnishing silver jewelry, characterized in that, The silver jewelry material comprises Ag, Cu, Zn, Pt, and In.

2. The anti-tarnishing silver jewelry material as described in claim 1, characterized in that, Calculated based on a mass fraction of 100%, including Ag 92.5%, Cu 2.4%-3.33%, Zn 1.57%-3.2%, 0 < Pt ≤ 3%, and 0 < In ≤ 0.1%.

3. The anti-tarnishing silver jewelry material as described in claim 2, characterized in that, The mass fraction of Pt is 1%-2%.

4. A method for preparing an anti-tarnishing silver jewelry material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1, Ag particles, Cu particles, Zn particles, Pt particles and In particles are placed in a vacuum induction melting furnace, a vacuum is drawn and a protective gas is introduced for induction melting; S2, after heating the raw material until it is completely melted, keep it at that temperature, and then pour the alloy melt into a copper mold to cool, thus obtaining a silver alloy.

5. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, Before smelting, raw materials are placed in a graphite crucible in a stacked manner, with Zn particles, In particles, 3wt%-5wt% Ag particles, Cu particles, Pt particles, and the remaining Ag particles placed from bottom to top.

6. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, The vacuum degree during melting is 5×10 -3 Pa-8×10 -3 Pa.

7. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, The protective gas used during smelting is argon with a purity of 99.999%, and the atmosphere pressure is -0.015 to -0.02 MPa.

8. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, In step S1, the maximum current during melting is 450A; in step S2, the holding time does not exceed 9 minutes, the holding temperature is 950-1050℃, and the cooling rate of the copper mold is 100-150℃ / s.

9. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, Before smelting, the raw materials are first polished to remove the oxide scale on their surface, and then ultrasonically cleaned and dried in anhydrous ethanol.

10. The method for preparing an anti-tarnishing silver jewelry material as described in claim 4, characterized in that, The purity of the Ag, Cu, Zn, Pt, and In particles is ≥99.95wt%.

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