A sulfite electroforming gold solution and its preparation method

Abstract

This invention discloses a sulfite electroplating gold solution and its preparation method. The preferred composition of the electroplating gold solution is: sodium gold sulfite 10-16 g / L, sodium sulfite 80-100 g / L, sodium citrate 40-55 g / L, disodium EDTA 10-15 g / L, disodium hydrogen phosphate 50-70 g / L, sodium m-nitrobenzoate 1.5 g / L, potassium antimony tartrate 20-50 mg / L, and ammonium chloroplatinate 10-50 mg / L. Hard gold jewelry made using this plating solution has high purity, good toughness, and easily adjustable hardness. The electroplated gold layer contains trace amounts of the precious metal platinum, making it more acceptable to customers. Furthermore, jewelry manufacturers do not need to operate multiple electroplating tanks to meet the requirements of various types of hard gold jewelry.

Description

Technical Field

[0001] This invention belongs to the field of gold plating technology, specifically a sulfite electroplating gold solution and its preparation method. Background Technology

[0002] Gold has a long history of use in jewelry making. Historically, gold jewelry has primarily been handcrafted. However, with the continuous innovation and development of various metal processing techniques in recent years, the craftsmanship of gold jewelry making has also made significant progress. Hard gold electroforming is a novel gold jewelry making process that has emerged in recent years. This process involves molten gold and preparing an electroplating solution, then electrochemically depositing a pure gold plating layer of over 100 micrometers onto the surface of a low-temperature metal model or a conductive paraffin wax model. The low-temperature metal or paraffin wax inside the model is then removed, resulting in a pure gold piece with a hollow internal structure. Hard gold electroformed jewelry of the same size weighs less than one-third of traditionally made pieces, but its hardness is more than three times greater. It is also less prone to deformation and scratches during wear. Hard gold electroforming is particularly advantageous for complex and delicate pure gold jewelry.

[0003] Currently, cyanide-based solutions are commonly used in the market for hard gold electroforming. These systems are widely adopted due to their ease of operation, good stability, and relatively low cost. However, cyanide is a highly toxic substance, posing significant potential risks in storage, production, and wastewater treatment. Its application must be strictly controlled, causing considerable inconvenience for hard gold electroforming manufacturers. In recent years, cyanide-free sulfite hard gold electroforming techniques have become popular in the jewelry industry. Electroforming with this solution produces a bright, smooth, and fine gold layer with higher hardness than cyanide-based electroforming. The entire production process avoids the use of highly toxic cyanide, making it popular with manufacturers and the market. Currently, this cyanide-free system shows a strong trend towards completely replacing cyanide electroforming systems.

[0004] In recent years, due to record-high gold prices, the production cost and sales price of gold jewelry have increased dramatically. This has forced jewelry manufacturers to focus more on intricate designs, smaller weights, and thinner gold layers in their hard gold jewelry, thereby reducing costs by minimizing the amount of gold used. Currently, some hard gold filigree jewelry with a gold layer thickness of less than 100 micrometers has appeared on the market. These pieces have complex designs, small weights, and thin gold layers, requiring extremely high hardness and toughness from the electroplated gold. Hard gold jewelry made using cyanide hard gold electroplating systems generally has a Vickers hardness of around 80 HV. While these pieces have good toughness, their low gold layer hardness results in insufficient support, making them prone to deformation during wear. On the other hand, hard gold jewelry made using cyanide-free sulfite plating systems generally has a hardness of around 120 HV. While these pieces offer high support, their thin gold layer reduces toughness, making them prone to breakage under pressure during wear. Some manufacturers have increased the Vickers hardness of the gold layer to 130 HV or even higher by adding base metal ions such as copper, cobalt, nickel, indium, and antimony to the sulfite gold plating system. However, the addition of base metal elements not only leads to insufficient gold purity, but also makes the gold layer more brittle and prone to breakage. Summary of the Invention

[0005] To address the problems mentioned in the background art, the present invention provides the following technical solution: a sulfite electroforming gold solution, comprising: 5-20 g / L gold sulfite (calculated as gold), 60-120 g / L complexing agent, 40-80 g / L stabilizer, 40-80 g / L buffer, 1-2 g / L wetting agent, 5-200 mg / L brightener, and 0-80 mg / L hardener.

[0006] A further option is that the gold sulfite is one of ammonium gold sulfite, sodium gold sulfite, or potassium gold sulfite, preferably sodium gold sulfite, and the amount used is preferably 10-16 g / L.

[0007] A further option is that the complexing agent is one of ammonium sulfite, sodium sulfate, or potassium sulfite, preferably sodium sulfite, and its dosage is preferably 80-100 g / L;

[0008] A further embodiment is as follows: the stabilizer is one of ammonium citrate, sodium citrate or potassium citrate and ethylenediaminetetraacetic acid salt, preferably sodium citrate and disodium ethylenediaminetetraacetic acid, wherein sodium citrate is 40-55 g / L and disodium ethylenediaminetetraacetic acid is 10-15 g / L;

[0009] A further option is that the buffer is one of diammonium hydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate, preferably disodium hydrogen phosphate, and the dosage is 50-70 g / L.

[0010] A further option is that the wetting agent is sodium m-nitrobenzoate, preferably used at a dosage of 1.5 g / L;

[0011] A further option is that the brightener is one of sodium tellurate, selenic acid, and potassium antimony tartrate, preferably potassium antimony tartrate, and its dosage is 20-50 mg / L.

[0012] Further option: The hardening agent is one of ammonium chloroplatinate, sodium chloroplatinate or potassium chloroplatinate, preferably ammonium chloroplatinate, and the dosage is 10-50 mg / L.

[0013] In a further embodiment, the preferred composition of the sulfite electroforming gold solution is: sodium gold sulfite 10-16 g / L, sodium sulfite 80-100 g / L, sodium citrate 40-55 g / L, disodium EDTA 10-15 g / L, disodium hydrogen phosphate 50-70 g / L, sodium m-nitrobenzoate 1.5 g / L, potassium antimony tartrate 20-50 mg / L, and ammonium chloroplatinate 10-50 mg / L.

[0014] A further embodiment specifies the operating conditions of the sulfite electroforming gold solution as follows:

[0015] pH: 7.2-7.8;

[0016] Temperature: 35-65℃;

[0017] Current density: 0.5-2 amperes / dm².

[0018] A further embodiment of the preferred operating conditions for the sulfite electroforming gold solution is as follows:

[0019] pH: 7.3-7.6

[0020] Temperature: 40-60℃

[0021] Current density: 0.75-1.5 amperes per square decimeter

[0022] On the other hand, a sulfite electroforming gold solution is prepared by the following steps:

[0023] Preparation of S10 platinum salt: Take 2.28 grams of commercially available ammonium chloroplatinate, 2 grams of sodium citrate and 2 grams of disodium hydrogen phosphate and put them into a beaker. Add pure water and heat to boiling until the solid powder is completely dissolved.

[0024] Preparation of S20 antimony salt: Place 1 gram of potassium antimony tartrate in a beaker, add pure water, and stir until completely dissolved.

[0025] Preparation of S30 sulfite electroforming gold solution:

[0026] Add pure water to the S301 glass beaker and heat it to 60℃-80℃.

[0027] S302 Weigh out measured amounts of sodium sulfite, disodium hydrogen phosphate, sodium citrate, disodium ethylenediaminetetraacetate, and sodium m-nitrobenzoate, and add them sequentially to the glass container S301, stirring until completely dissolved;

[0028] S303 Weigh out a measured amount of commercially available sodium gold sulfite solution, add it to the S302 solution, and stir until homogeneous;

[0029] Weigh out the measured amounts of S10 platinum salt and S20 antimony salt, add them to the S303 solution, and stir until homogeneous.

[0030] For S305, adjust the pH of the S304 plating solution to the required range using a 30% phosphoric acid or sodium hydroxide solution before attempting plating.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention provides a cyanide-free sulfite electroplating gold solution and its preparation method. Hard gold jewelry made with this solution exhibits high purity and good toughness, and is not easily deformed or broken under pressure. The hardness of the electroplated gold layer can be adjusted from low to high by controlling the amount of platinum salt added as a hardening agent. Jewelry manufacturers can meet the requirements of various types of hard gold jewelry without needing to operate more electroplating tanks. Secondly, while platinum salt is added to the electroplating gold solution provided by this invention, antimony salt as a brightening agent is also essential. Trace amounts of platinum and antimony elements will coexist in the hard gold layer. Surprisingly, the addition of platinum ions increases the hardness and toughness of the electroplated gold layer while reducing the antimony content, resulting in higher gold purity in the hard gold jewelry. Furthermore, the presence of trace amounts of the precious metal platinum in the electroplated gold layer is more acceptable to customers compared to the base metals such as copper, cobalt, nickel, and indium currently found in hard gold layers on the market. Detailed Implementation

[0033] 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 some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, all raw materials used in the following embodiments of this invention are commercially available. All embodiments require the use of antimony salt as a brightener and platinum salt as a hardener; both additives are obtained according to the following steps:

[0035] Preparation of platinum salt: Take 2.28 g of commercially available ammonium chloroplatinate, 2 g of sodium citrate and 2 g of disodium hydrogen phosphate and put them into a 1 L beaker. Add 100 mL of pure water and heat in an electric resistance furnace until the solid powder is completely dissolved. Dilute to 1000 g for later use. The platinum ion content is 1 mg / g solution.

[0036] Preparation of antimony salt: Place 1 gram of potassium antimony tartrate into a 1-liter beaker, add 100 ml of pure water, stir until completely dissolved, and dilute to 1000 grams for later use. The potassium antimony tartrate content is 1 mg / g.

[0037] In this embodiment, a uniform jewelry model is selected, and the following steps are followed for preliminary preparation and subsequent demolding:

[0038] A cylindrical cryogenic alloy model is fixed on an electroplating fixture. It is first electroplated in an alkaline copper electroplating bath for 5 minutes, then cleaned and electroplated in an acidic copper electroplating bath for 5 minutes, followed by an acidic nickel electroplating bath for 5 minutes. The model is then removed and ready for use in various embodiments. After electroforming gold, the jewelry model is agitated in a 200°C oven to remove the molten cryogenic alloy for two hours until completely removed. It is then boiled in a 30% nitric acid solution for 1 hour to remove the copper and nickel layers. Finally, it is dried in a 200°C oven for 1 hour before testing its various properties.

[0039] Example 1:

[0040] Add approximately 600 ml of pure water to a 1-liter beaker and heat to 70°C. Add 85 g of sodium sulfite, 60 g of disodium hydrogen phosphate, 50 g of sodium citrate, 10 g of disodium ethylenediaminetetraacetate, and 1.5 g of sodium m-nitrobenzoate. Stir until completely dissolved. Add a sodium gold sulfite solution containing 16 g of gold and 20 mg of potassium antimony tartrate solution. Adjust the pH of the plating solution to 7.5. Add plating solution to a final volume of 1 liter. A trial plating test is then performed under the following conditions:

[0041] pH: 7.5

[0042] Plating bath temperature: 55℃

[0043] Current density: 0.5 A / dm²

[0044] Plating solution circulation: electromagnetic stirring

[0045] Electroforming time: 10 hours

[0046] Electroforming under the above conditions yields hard gold jewelry with a uniform, smooth, and bright gold layer after 10 hours.

[0047] Example 2:

[0048] Using the same formula as in Example 1, except that the amount of platinum salt added was 15 mg / L of plating solution, and electroforming was performed under the working conditions of Example 1. After 10 hours, a hard gold jewelry with a uniform, smooth, and bright gold layer was obtained.

[0049] Example 3:

[0050] Add approximately 600 ml of pure water to a 1-liter beaker and heat to 80°C. Add 90 g of sodium sulfite, 60 g of disodium hydrogen phosphate, 50 g of sodium citrate, 12 g of disodium ethylenediaminetetraacetate, and 1.5 g of sodium m-nitrobenzoate. Stir until completely dissolved. Add a sodium gold sulfite solution containing 16 g of gold, 40 mg of potassium antimony tartrate solution, and 30 mg of platinum salt solution. Adjust the pH of the plating solution to 7.5. Add plating solution to a final volume of 1 liter. The plating process is then ready for trial plating. The working conditions are as follows:

[0051] pH: 7.5

[0052] Plating bath temperature: 55℃

[0053] Current density: 0.5 A / dm²

[0054] Plating solution circulation: electromagnetic stirring

[0055] Electroforming time: 10 hours

[0056] Electroforming under the above conditions yields hard gold jewelry with a uniform, smooth, and bright gold layer after 10 hours.

[0057] Example 4:

[0058] Using the same formula as in Example 3, except that the amount of platinum salt added was 50 mg / L of plating solution, and electroforming was performed under the conditions of Example 3. After 10 hours, a hard gold jewelry with a uniform, smooth, and bright gold layer was obtained.

[0059] The sample test data for each embodiment are shown in Table 1. It should be noted that "electroplated gold hardness" in the table refers to the hardness measured directly after the jewelry is electroplated, while "finished product hardness" refers to the hardness measurement of the finished product after the jewelry has undergone processes such as demolding, acid boiling, and drying.

[0060] Table 1 Comparison of Gold Layer Hardness and Component Content

[0061]

[0062]

[0063] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A sulfite electroforming bath, characterized by: The composition of the electroforming gold solution is: 10-16 g / L of sodium sulfite gold, 80-100 g / L of sodium sulfite, 40-55 g / L of sodium citrate, 10-15 g / L of ethylenediaminetetraacetic acid disodium, 50-70 g / L of sodium hydrogen phosphate, 1.5 g / L of sodium m-nitrobenzoate, 20-50 mg / L of potassium antimony tartrate and 10-50 mg / L of chloroplatinic acid ammonium.

2. A sulfite electroforming bath according to claim 1, characterized in that: The working condition of the electroforming gold solution is: pH 7.3-7.6; temperature 40-60℃; current density 0.75-1.5 ampere / square decimeter.

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