現代の産業におけるプラチナめっきの主な方法と用途は何ですか?

ジュエリーへのプラチナメッキについて学びましょう！このガイドでは、塩化物や硫酸塩などの様々なメッキ液に加え、Pt-AuやPt-Coなどの合金についても解説しています。ジュエリーショップ、デザイナー、ブランドにとって最適な内容です。詳細なテクニックと応用例を参考に、ジュエリーをより耐久性と魅力のあるものにする方法を学びましょう。カスタムメイドジュエリーにも最適です。

現代の産業におけるプラチナめっきの主な方法と用途は何ですか?

Platinum Plating Techniques: Solutions, Alloys, and Applications for Jewelry

はじめに

Wondering about platinum plating? This guide covers everything from the basics to advanced techniques. Learn about different plating solutions, including chloride and sulfate-based options, and discover how to improve them. Explore thin and thick plating solutions for various applications. Intrigued by platinum alloys? We cover popular ones like Pt-Au, Pt-Co, and Pt-Ir. Plus, dive into chemical plating for unique applications. Whether you’re a jewelry designer, retailer, or custom maker, this comprehensive overview will help you enhance your products with platinum plating.

Section I Overview

Platinum has an atomic number of 78 in the periodic table, with the element symbol Pt, a relative atomic mass of 195.7, a density of 21.09g/cm³ (20℃), and a melting point of 1768℃.

Some main parameters of platinum are shown in Table 3-1.

Table 3-1 Some Main Parameters of Platinum

Characteristic parameters	Characteristic value
Element name, element symbol, atomic number 分類 Group, Period Density, hardness カラー相対原子質量原子半径 Covalent bond radius Chemical valency Crystalline structure melting point boiling point 気化熱 Heat of dissolution 比熱容量 Conductivity Thermal conductivity	Platinum、Pt、78 遷移金属 10(Ⅷ),6 21090kg/m³, 3.5 Grayish white 195.084 135pm 128pm 2、4 面心立方 2041. 4K( 1768.3℃) 4098K (3825℃) 510kJ/mol 19:6kJ/mol 130J/(kg • K) 9. 66X 10⁶m ・Ω 71. 6W/(m ・ K)

Section II Electroplating of Platinum

When Pt is used as decorative plating, its coating appears somewhat dark compared to Rh plating, and the color is not very attractive. It is mainly used for earrings, necklaces, watch cases, eyeglass frames, etc. Industrially, platinum is widely used in aerospace, electronic products, medical devices, etc. Table 3-2 shows some industrial applications of platinum plating.

Table 3-2 Industrial Applications of Pt Plating Coatings

Product	材料	Plating thickness/μm	Product	材料	Plating thickness/μm
Aerospace Components Aviation Components Safety Bulkhead Trays Electrodes	Niobium-containing superalloys SUS347 チタン SUS316	10 10 5 10	Electrodes Electrodes Electrodes -	チタン Titanium mesh Tungsten Wire -	2〜7 2〜7 10 -

The experiment of Pt plating began more than 100 years ago, conducted by Ellington, who obtained a patent in 1873. In 1878, Borttger also obtained a patent related to platinum plating. However, these solutions were all unstable metal salts, and their plating layers were impractical. Pt plating solutions can be divided into two main categories, namely divalent and tetravalent platinum salts. Typical platinum salts are shown in Table 3-3.

Table 3-3 Typical Platinum Salts

2, 4-valent salts	Typical platinum salts
Pt(II) salts	Chloroplatinic acid：H₂PtCl₆ • 6H₂O Diammine platinum nitrite：Pt(NH₃)₂(NO₂)₂ Platinum nitrite sulfate：H₂Pt(NO₂)₂SO₄
Pt(Ⅳ) salts	Sodium hydroxyplatinate：Na₂Pt(OH)₆ · 2H₂O

1. Various Platinum Plating Solutions

Table 3-4 shows some Pt plating solution compositions and process conditions developed.

Table 3-4 Various Pt Plating Solution Compositions and Process Conditions

Composition and process conditions	Chloride		Diammonium sulphite						DNS	Hydroxybasic salts				リン酸
Composition and process conditions	No. 1	No. 2	No. 3	No. 4	No. 5	No. 6	No. 7	No. 8	No. 9	No. 10	No. 11	No. 12	No. 13	No. 14
Chloroplatinic acid H₂PtCl₆/(g/L)	10 〜50
Ammonium chloroplatinate (NH₄)₂PtCl₆/ (g/L)		15
Diammine platinum nitrite Pt(NH₃)₂(NO₂)₂/(g/L)			8~16. 5	20	6~20	8	6~20	16.5
Platinum nitrite sulfate H₂Pt(NO₂)₂SO₄/ (g/L)									10
Sodium hydroxyplatinate Na₂Pt(OH)₆ ・ 2H₂O/(g/L)										20	18.5
Hydroxyplatinic acid H₂Pt (OH)₆/ (g/L)												20
Potassium hydroxyplatinate K₂Pt(OH)₆/ (g/L)												20
Platinum chloride PtCl₄· 5H₂O/(g/L)														7.5
Ammonia(28%)/(g/L)
Hydrochloric acid/(g/L)	180~300
Sodium citrate/(g/L)		100												20~25
Ammonium chloride/(g/L)		4~5
Ammonium nitrate/(g/L)			100
Sodium nitrite/(g/L)			10
Fluoroboric acid/(g/L)				50~100
Sodium fluoborate/(g/L)				80~120
Sulfonic acid/(g/L)					20~100
Phosphoric acid/(g/L)						80	10~100
Sulfuric acid/(g/L)							10~100		pH2
Sodium acetate/(g/L)								70
Sodium carbonate/(g/L)								100
Sodium hydroxide/(g/L)										10	5.1
Sodium oxalate/(g/L)											5.1
Sodium sulfate/(g/L)											30.8
Potassium hydroxide/(g/L)												15
Ammonium Hydrogen Phosphate)(g/L)														20
Sodium hydrogen phosphate/(g/L)														100
Potassium sulfate/(g/L)													40
Plating solution temperature/°C	45~90	80~90	90~95	70~90	65~100	75~100	75~100	80~90	30~70	75	65~80	75	70~90	70~90
Current density/(A/dm²)	3.0	0.5~1.0	0.3~2.0	2~5	0.2~2	0.5~0.3	0.5~0.3	0.5	2.5	0.8	0.8	0.75	0.3~1	0.3~1
Current efficiency/%	15~20	70~10	10	14~18	15	15	15	35~40	10~15	100	80	100	10~50	15~50

(1) Chloride plating solution

The first technically successful Pt plating solution used chloroplatinic acid (H₂PtCl₆・6H₂O) as the base salt. A soluble Pt electrode was used, and its conditions were 10~15g/L chloroplatinic acid, 180~300g/L hydrochloric acid, plating solution temperature of 45~90℃, current density of 2.5~3.5A/dm², and cathode current efficiency of 15%~20%. The plating film obtained from this solution can reach 20μm with no cracks and good ductility. However, the pH must be controlled within a narrow range to prevent hydrolysis of the plating solution. When the pH of the plating solution begins hydrolysis it reaches 2.2.

(2) Diamminonitrite Plating Solution

To ensure the concentration of divalent Pt and prevent it from oxidizing to Pt(Ⅳ), an appropriate amount of amine compounds needs to be added to form a complex with Pt (II). The basic component of this plating solution is diamminonitritoplatinum Pt(NH₃)₂(NO₂)₂, often referred to as Pt-P salt (II). The plating solution using this salt was discovered by W. Keitel in 1931 (plating solution No. 3 in Table 3-4). When the nitrite concentration in the solution increases, it affects the dissociation of the Pt complex, thereby influencing the behavior of the plating solution. After boiling, NH₄OH is added to react with NaNO₃ to generate NH₄ノー₂ to restore the initial current efficiency, producing, which then decomposes into nitrogen and hydrogen gases. In this way, almost all the non-metallic components of the Pt-P salt in the plating solution become gases and disappear, making the plating solution’s lifespan longer than that of chloride plating solutions. The advantage of this plating solution is that its component adjustment is relatively easy.

A. B. Triper and others used PR as the power source, achieving an electroplating speed of 5μm/h. The conditions were: 5~6A/dm², cathode electrolysis time of 5 s and anode electrolysis time of 2 s. The plating solution No. 4 in Table 4-3 was proposed in Lacroix’s 1967 patent in France. This plating solution can produce a coating thickness of up to 7.5μm. Plating solution No. 5 is from a US patent (US PAT. 2984603, 2984604), proposed in 1961, which involves adding sulfonic acid to the Pt-P salt plating solution. No. 6 contains phosphoric acid, while No. 7 uses phosphoric-sulfuric acid as the basic solution, proposed in a 1960 French patent (Fr PAT. 1299226). They used insoluble anodes and flexibly applied crucial methods such as stirring and shaking.

No. 8 uses sodium acetate and sodium carbonate to replace ammonium salts, thereby achieving maximum current efficiency and improving the stability of the plating solution. The coating obtained from this solution is smooth and flat, with a plating thickness of up to 10μm without pinholes or cracks.
In Japan, this plating solution is widely used industrially. Below is one example:

Platinum(Diammineplatinum Nitrite)

Ammonium nitrate

Sodium nitrite

Ammonium hydroxide

10g/L

100g/L

10g/L

35g/L

Solution Temperature

Current density

Current efficiency

90~92℃

1A/dm²

10%~20%

However, the current efficiency of this plating solution is not very good, and the plating speed is about 1μm/10min. A coating without pinholes and cracks can be obtained. The plating solution temperature is high; ammonia evaporates quickly, and the solution evaporates rapidly, so the liquid surface is maintained by adding 10% ammonia water. This plating solution is suitable for plating thick platinum; this solution can be used when a thickness of 5~10μm is required. Since the plating solution is close to boiling during use, it is unsuitable for preparing large volumes of plating solution. At most 10~20L, indirect heating is the best method. Most metals will be corroded because ammonia water is used as the base solution. Therefore, the anode uses Ti/Pt plates or Pt plates, and other metals should be avoided around the tank.

(3) Platinum Nitrosulfuric Acid Plating Solution

This plating solution does not contain ammonia or amine components but uses platinum nitrosulfuric acid［H₂Pt (OH)₆ · 2H₂O］as the basic ingredient. The preparation of the plating solution involves using nitro salts, potassium salts of platinum chloride, or platinum sulfuric acid (［K₂Pt(NO₂)₃Cl, K₂Pt (NO₂)₂Cl₂ or K₂Pt (NO₂)₂SO₄］). A low current density is used for bright plating, and sulfuric acid is added to adjust the pH below 2.0. Representative compositions are shown in Table 3-4, No. 9. This plating solution can produce relatively thick plating layers.

(4) Alkaline Hydroxyplatinic Acid Metal Salt Plating Solution

In a typical alkaline plating solution, a sodium or potassium salt of hydroxyplatinic acid such as Na₂Pt(OH)₆ or K₂Pt(OH)₆ is used. Representative plating solution compositions are shown in Table 3-4, No. 11. The plating solution temperature of 75℃, current density of 0.8A/dm², and current efficiency can reach 100%, and the anode uses Ni or stainless steel materials.

No. 10 was proposed by A.R. Powell in 1913, and a British patent was obtained (Brit PAT. 363569). A bright coating comparable to the Rh plating solution can
be obtained from this plating solution. When the Pt concentration is below 3g/L, the current efficiency drops sharply. A current density can be up to 2.5A/dm² when the concentration is high (12g/L ). At a solution temperature of 65 ~ 70°C, the current efficiency can reach about 80%. However, further increasing the temperature does not significantly improve the effect.

(5) Phosphate Plating Solution

As early as 1855, Roseleuer proposed the phosphate scheme. This plating solution uses a tetravalent Pt chloride coordination salt, alkali metal phosphate salts, and ammonium salts as conductive salts. In 1949, W. Pfanhauser proposed the No. 14 plating solution, which, under these conditions, can produce a coating of 0.5μm.

Druve reported experimental results using the same plating solution. The biggest drawback of this plating solution is the difficulty in adjustment. Precipitates formed when newly prepared plating solution must dissolve over a long time. Ammonium phosphate must be used to avoid porous and spongy coatings. Ammonium phosphate helps dissolve the platinum complex. Under certain conditions, an insoluble yellow salt forms on the anode surface in the plating solution, becoming an insulating layer estimated to be ammonium hydroxyplatinate salt.

(6) Sulfate-Based Platinum Plating

Plating platinum on titanium or tantalum is not problematic even if it is not bright, but when plating platinum on decorative items, brightness becomes an important issue, and cracks are also a problem that cannot be ignored. Masashi and others proposed using a sulfate plating solution to address this issue. The characteristics of this plating solution are dissolving platinum salt into sulfate, adding sulfite to the solution, and adjusting the pH to less than 2 with sulfuric acid. Because the addition of sulfite can make the platinum potential more negative than hydrogen ions, it ensures a low hydrogen content in the platinum plating layer, resulting in low internal stress and brightness in the plating layer. However, if the sulfite concentration is too high, platinum may be reduced. If pH>2, the sulfite is easily hydrolyzed. Also pH<2 will help stabilize the platinum complex.

The pretreatment for plating is alkaline→electrolytic degreasing→acid dipping, and 2min cathodic electrolysis.

The plating process is shown in Table 3-5.

Table 3-5 Platinum Plating Process Conditions in Sulfuric Acid Series

Composition and process conditions	No. 1	No. 2
HAuCl₄ (counted as Au） K₂SO₄ K₂SO₃ pH (adjusted with sulfuric acid) temperature Current density Plating time Plating thickness Plating layer	10g/L 50g/L 1.0g/L 1.0 75℃ 2A/dm² 60min 7 μm Brightness	10g/L 100g/L 2. 0g/L 2.0 65℃ 1 A/dm² 100min 5/μm Beautiful appearance, good bonding

In Table 3-5 No.1, a dichroic coating of Pt-Au can be obtained by pre-plating flash gold on the substrate, thickly plating 7μm of platinum, and plating 2μm of gold on the platinum.

2. Thin Plating Solution

Another application of platinum plating has been in decorative items in recent years. In the clothing field, amid the calls for personalization and differentiation, although its tone is not particularly outstanding, its demand has continuously increased. Eyeglass frames have adopted Pt, and the Pt thickness on watch cases has already exceeded the range of thin plating. In this regard, Japan’s demand is higher than that of Europe, America, and other Asian countries.

3. Thick Plating Solution

(1) Decorative Plating

As mentioned earlier, platinum-plated products such as eyeglass frames and watch cases have emerged due to the emphasis on the platinum brand itself. The plating thickness of platinum-plated products is generally below 5μm.

Recently, another new technology has emerged in the field of decorative items, which is electroforming.

The thickness of electroformed products is generally 100~150μm, and making them hollow can reduce weight and lower costs. When plating with ordinary plating solutions using conventional electroplating methods, cracks will appear once the plating thickness exceeds 10μm, making it technically challenging.

(2) Industrial Applications

The Pt plating of stainless steel parts for aviation has been put into practical use. The process is as follows:

PR electrolysis → acid activation → thin Au plating → Pt plating

A representative industrial use of platinum is as an insoluble anode; Pt-plated anodes are indispensable for electroplating precious metals such as Au, Rh, Pd, etc. Additionally, they can serve as auxiliary anodes for Cr, Ni, and acidic Cu electroplating. Besides Ti, materials such as Nb and Ta are also used for Pt plating. Table 3-6 lists some properties of Pt-plated anode materials.

Table 3-6 Performance of Pt Anode Materials

Properties	白金	ティ	Nb	タ
Density(20℃)/(g/cm³) 融点 Hardness (after heat treatment) Thermal conductivity/[W/(m·K)] Resistivity/μΩ·cm Coefficient of linear expansion (x10⁵)/[mm/(mm·K)]	21. 45 1769 37〜42 (Vickers) 71. 6 10. 6 9. 1	4. 54 1668 120 (Brennel) 16.8 48 8. 5	8. 57 2468 84 (Vickers) 67. 4 13. 1 7. 1	16. 6 2996 E-60 (Rockwell) 54. 8 12.4 6. 5

Generally, the thickness of the Pt plating layer is about 2μm, so the current density is high. Under conditions such as short circuits when the cathode is contacted, and operations involving ammonium bifluoride, fluoroboric acid, strong alkalis, and high-cyanide solutions, the consumption of Pt accelerates. Therefore, extending its lifespan as much as possible is necessary, which can be achieved by increasing the anode-to-cathode area ratio. When plating Pt on Ti electrodes, the Ti can first be roughened by sandblasting, then acid-activated to remove the surface oxide film, followed by Pt electroplating.

The typical aging process of Pt-plated Ti anodes is: ① Ti oxide film at the pinhole of Pt plating is destroyed; ② Ti begins to dissolve; ③ the Pt-Ti interface experiences pitting corrosion as dissolution progresses, and the Pt film peels off. At this time, if it occurs during gold plating, it will cause a sudden increase in the deviation of the gold plating thickness. When encountering such problems in practice, inspecting the anode is best.

4. Other Improvements to the Plating Solution

(1) Improvements to the Pretreatment

There are also methods to improve the adhesion between sodium and its alloys and the platinum plating layer by enhancing the pretreatment process. Kamata proposed in a patent that an acid strike plating is performed in an pH=1 acid strike plating solution, followed by plating the required thickness of the platinum layer in an alkaline plating solution. The main components of the acid strike plating solution are 0.3~3g/L chloroplatinic acid (calculated as platinum) and 5%~15% halide ions (mass fraction). The pH must be controlled below 1; otherwise, the activity of titanium decreases, leading to poor adhesion. Suppose the halide ion concentration is too low. In that case, the removal of the passive film on the titanium surface may be incomplete, which in turn affects the adhesion of the plating layer. The conditions for strike plating are plating solution temperature of 40~80℃ and current density of 5~25A/dm². The plating conditions and results for platinum plating are shown in Table 3-7.

Table 3-7 Platinum Plating Conditions and Their Results (concentration values are in parentheses)

シリアル番号	Impact plating solution		Platinum plating solution		Plating thickness/μm	Stripping test
シリアル番号	Platinum ion/(g/L)	Halogen ion (mass fraction)/%	Platinum ion/(g/L)	pH	Plating thickness/μm	Stripping test
1 2 3 4 5 6 7 8 9	H₂PtCl₆ (0. 1) H₂PtCl₆ (0. 1) H₂PtCl₆ (0. 1) H₂PtCl₆ (1. 0) H₂PtCl₆ (1. 0) H₂PtCl₆ (1.0) H₂PtCl₆ (5.0) H₂PtCl₆ (5.0) H₂PtCl₆( 5. 0)	HCl (5) HCl (5) HCl (5) HCl (10) HCl (10) HCl (10) HCl (20) HCl (20) HCl (20)	K₂Pt(OH)₆ (5) K₂Pt(OH)₆ (10) K₂Pt(OH)₆ ⑸ Platinum dinitrate (5) Platinum dinitrate (10) Platinum dinitramide (20) K₂Pt(OH)₆ ⑸ K₂Pt(OH)₆ (10) K₂Pt(OH)₆ (20)	12. 0 13. 0 13. 5 12. 0 13. 0 13. 5 12.0 13. 0 13. 5	10 15 20 10 15 20 10 15 20	グッドグッドグッドグッドグッドグッドグッドグッドグッド

From Table 3-7, it can be seen that the thickness of the Pt plated on titanium is all above 10μm. Moreover, a mirror-bright platinum plating layer with strong adhesion can be obtained even without roughening treatment.

(2) Plating Platinum Using a Neutral Plating Solution

Using a nearly neutral plating solution is beneficial for pattern plating, as it avoids using alkali metals such as Na, preventing the adverse effects caused by the accumulation of alkali metals. The platinum plating solution proposed by Otani meets this condition. Table 3-8 shows the composition of the plating solution and its process condition tests.

Table 3-8 Composition and Process Conditions of Neutral Platinum Plating Solution Test

Ingredients and their process conditions	No. 1	No. 2	No. 3
Dinitrodiammine platinum(Pt concentration)/(g/L) Glycine/(mol/L) Iminodiacetic acid/(mol/L) Diaminotriacetic acid/(mol/L) рH Temperature/°C Current density/(A/dm²) Precipitation speed/(μm/min) Current efficiency/%	12 0. 57 - - 5.0 70 1. 0 0. 3 80	12 - 0. 3 - 5. 0 70 1. 0 0. 2 65	12 - 0. 1 0. 1 5. 0 70 1. 0 0. 1 65

Since this plating solution is close to neutral, it is favorable for pattern plating and will not adversely affect the counter-plating film.

Kamata from Japan also studied the effect of alkaline earth metals as brighteners. It was found that alkaline earth metals, such as Ca, Ba, Mg, etc., have a brightening effect on alkaline plating solutions. The suitable concentration of alkaline earth ions is (2×100)×10^-6. The degree of brightness is also controlled by varying the concentration of alkaline earth metal ions added.

The main components and operating conditions of the plating solution are as follows:

Main components of plating solution	KOH 40g/L Pt [added in the form of K₂Pt(OH)₆] 20g/L Ca [added in the form of CaCl₂ aqueous solution] Adequate amount
Operating conditions	рH 13.5 Temperature 80℃ Current density 3A/dm² Base metal Calendered copper plate Plating thickness 20μm

The brightness level according to different amounts of Ca added is shown in Table 3-9.

Table 3-9 Effect of Ca Ion Concentration on the Brightness of the Pt Plating Layer

Ca ion concentration/x10^-6	外観	Ca ion concentration/x10^-6	外観
0 0. 1 0. 3 0. 5 0. 7 1. 0	Non-glossy Non-glossy Non-glossy Non-glossy Non-glossy Semi-glossy	1. 5 2. 0 2. 5 3. 0 5. 0 -	Semi-glossy Semi-glossy Semi-glossy Semi-glossy Mirror Bright -

Although the principle of brighteners for alkaline earth metals is unclear, based on experiments with Ca, Mg, Sr, and Ba, these metal ions have a brightening effect.

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Section III Platinum Alloy Plating

The reported platinum alloy platings so far include Pt-Ag alloy, Pt-Co alloy, Pt-Fe alloy, Pt-Mo alloy, Pt-Ni alloy, Pt-Sn alloy, Pt-Zn alloy, Pt-Au alloy, Pt-Cu alloy, Pt-Au alloy, Pt-Ir alloy, Pt-W alloy, etc. A portion of these alloys will be introduced below.

(1) Platinum-Iridium Alloy

Electroplated Pt-Ir alloy can be used on electrodes for soda ash production and electroplating.

The plating process conditions for the alloy proposed by Kamada et al. are shown in Table 3-10.

Table 3-10 Electroplating Pt-Ir Alloy Process Conditions

Composition and process conditions	No. 1	No. 2
Sodium iridium hexachloride Boric acid Disodium malonate Sodium tetrachloroplatinate Potassium oxalate Sodium tetrabromoplatinate рH 温度 Current density	10g/L 40g/L 0. 02mol/L 0. 5~3g/L - - 5 85℃ 0. 5 A/dm²	10g/L 40g/L - - 0. 02mol/L 0. 5〜3g/L 2 85℃ 0. 5 A/dm²

The electroplating steps are to first flash plate 1μm gold on the brass sheet, then plate gold off, and finally plate a Pt-Ir alloy on top. The coating obtained by this method has good hardness, adhesion, heat resistance, and metal wire bonding connectivity, with a current efficiency reaching 100%.

Regarding this plating solution, if the pH is too low, the current density is too small to be practical; if the pH is too high, hydroxide precipitates are easily formed. If the temperature is too low, the alloy is difficult to deposit; if the temperature is too high, the plating solution evaporates quickly, which is unfavorable for maintaining the plating solution. If the current density is too low, the deposition rate is too slow; if the current density is too high, the cathodic reaction is mainly hydrogen evolution.

At the same time, the alloy composition in the plating film can also be controlled by adjusting the metal concentration ratio in the plating solution. Figure 3-1 shows the variation of alloy coating composition with the metal concentration ratio in the plating solution.

As can be seen from the figure, within the experimental concentration range, the Pt-Ir composition ratio in the plating layer has a linear relationship with the metal ion concentration ratio in the plating solution.

(2) Electroplating of Platinum-Iron Alloy

Alloys containing Fe are generally used as magnetic materials. The higher the recording density, the better. Platinum-iron alloys have high magnetic anisotropy, good corrosion resistance, and wear resistance and are expected to improve the performance of magnetic films.

Katsutsugu Koda proposed a plating solution formula with good stability that allows continuous electroplating. Since trivalent iron ions in the plating solution tend to form gels, this is detrimental to the appearance of the plating layer and reduces the concentration of divalent iron, negatively affecting the plating solution’s stability. Trivalent iron is generated based on the following reaction:

白金⁴⁺ + 2e^–→ Pt²⁺

2Fe²⁺→ 2Fe³⁺+ 2e^–

From the above formula, from the perspective of considering the stability of iron ions, tetravalent platinum ions play a negative role, which led to the invention of divalent platinum to replace tetravalent platinum. The practice has proven that divalent platinum can be used for electroplating.

Table 3-11 shows the process conditions and results of binary Pt-Fe alloy electroplating. From the table, it can be seen that the metal atomic ratio of the Pt-Fe alloy coating obtained in No. 1~No. 3. It is close to. When the atomic ratio of the alloy is 50%, it is optimal as a magnetic film for recording.

Table 3-11 Process Conditions for Pt-Fe Binary Alloy Plating and Their Results

Composition and process conditions		No. 1	No. 2	No. 3	No. 4	No. 5
Platinum salt	タイプ	Pt(NH₃)₂(NO₂)₂	[Pt(NH₃)₄]Cl₂	Pt(NH₃)₂(NO₂)₂	Pt(NH₃)₂(NO₂)₂	Na[Pt(C₂O₄)₂
Platinum salt	内容	5g/L	5g/L	5g/L	5g/L	10g/L
Iron Salt	タイプ	FeSO₄ • 7H₂O	FeSO₄ • 7H₂O	FeSO₄ • 7H₂O	FeSO₄ • 7H₂O	FeSO₄ • 7H₂O
Iron Salt	内容	2g/L	30g/L	30g/L	10g/L	20g/L
Antioxidants	タイプ	Sodium sulfite	Hydroxyammonia chloride	L-Ascorbic acid	Citric acid hydrate	Hydroxyammonia sulfate
Antioxidants	内容	5g/L	3g/L	3g/L	40g/L	50g/L
Complexing agent	タイプ	Triammonium citrate	EDTA-2Na	Triammonium citrate	EDTA-2Na	Sodium oxalate
Complexing agent	内容	50g/L	10g/L	15g/L	2g/L	30g/L
Additives	タイプ	-	Potassium dihydrogen phosphate	Potassium dihydrogen phosphate	Potassium ascorbyl phosphate	-
Additives	内容	-	15g/L	15g/L	5g/L	-
Temperature of plating solution		40℃	30℃	60℃	50℃	70℃
рH		8	2	3	4	8
Current density		1A/dm²	2A/dm²	1A/dm²	1A/dm²	1.5A/dm²
Plating composition (atomization)	白金	51%	49%	55%	72%	37%
Plating composition (atomization)	フェ	49%	51%	45%	28%	63%
Appearance of plated layer		O	O	O	O	O

(3) Electroplating of Platinum-Cobalt Alloy

The Pt-Co alloy film has a very high magnetic recording density, which is very attractive for the large capacity of magnetic recording media. Especially when its atomic ratio is 1:1, the performance is optimal.

Koda also researched Pt-Co alloys (see Table 3-12).

Table 3-12 Process Conditions and Results of Pt-Co Binary Alloy Plating

Composition and process conditions		No. 1	No. 2	No. 3	No. 4	No. 5
Platinum salt	タイプ	Pt(NH₃)₂(NO₂)₂	[Pt(NH₃)₄]Cl₂	Pt(NH₃)₂(NO₂)₂	Pt(NH₃)₂(NO₂)₂	Na[Pt(C₂O₄)₂
Platinum salt	内容	2g/L	5g/L	5g/L	2g/L	10g/L
Iron Salt	タイプ	CoSO₄ • 7H₂O	CoSO₄ • 7H₂O	CoSO₄ • 7H₂O	CoSO₄ • 7H₂O	CoSO₄ • 7H₂O
Iron Salt	内容	30g/L	30g/L	2g/L	45g/L	20g/L
Buffer(1)	タイプ	EDTA-2Na	Triammonium citrate	Triammonium citrate	Boric acid	Ammonium oxalate
Buffer(1)	内容	30g/L	5g/L	50g/L	30g/L	30g/L
Buffer(2)	タイプ	Triammonium citrate	-	-	EDTA-2Na	-
Buffer(2)	内容	5g/L	-	-	2g/L	-
Conductive salt	タイプ	Sulfamic acid	Ammonium sulfate	Ammonium sulfate	Sulfamic acid	Ammonium sulfate
Conductive salt	内容	15g/L	15g/L	15g/L	20ml/L	15g/L
Antiprecipitant	タイプ	-	Ammonia	-	-	-
Antiprecipitant	内容	-	3g/L	-	-	-
Temperature of plating solution		60℃	50℃	40℃	50℃	70℃
рH		3	2	4	3	4
Current density		1A/dm²	2A/dm²	4A/dm²	3A/dm²	4A/dm²
Plating composition (atomization)	白金	65%	49%	30%	40%	37%
Plating composition (atomization)	フェ	35%	51%	70%	60%	63%
Appearance of plated layer		O	O	O	O	O

The alloy atomic ratio of the coating obtained from No. 2 in Table 3-11 is about 50%.

Hu Zhongmin et al. also proposed a plating Pt-Co alloy formula. Its main components are as follows:

Pt(NH₃)₂(NO₂)₂ (as Co) 0.2~15g/L

CoSO₄ (as cobalt) 5~70g/L (Maintain Co:Pt=30:1)

pH 1.2 (adjusted with NH₂SO₃H)

Temperature 70℃

Current density 2A/dm²

When Co/Pt (mass ratio) = 30/1 in the plating solution, the content ratio of the resulting alloy coating was confirmed by EDS as Co/Pt (mass ratio) = 5/95.

(4) Platinum-Rhodium Alloy

Because Pt-W alloy coating has higher oxidation catalytic ability than Pt coating, people’s interest in Pt-W alloy plating has been aroused. Matsunori Sawada et al. proposed a platinum-tungsten alloy formula that can achieve a uniform appearance, good catalytic ability, and good plating solution stability.

A stable plating solution is obtained by adding organic acids or organic acid salts to the main components and then aging the mixture.

The organic acids used can be acetic acid, citric acid, oxalic acid, tartaric acid, etc. Representative components and concentrations are as follows:

H₂PtCl₄ 2g/L（as Pt）

Na₂WO₄ • 2H₂O 25g/L（as W）

Sodium citrate 5g/L

Citric acid 5g/L

Sodium sulfate 15g/L

Aging conditions 60℃×8h

Plating conditions 65℃ ,6mA/cm² , 10min

Plating material Stainless steel wire mesh with a diameter of 0.3mm

Pre-plating treatments are:

Electrolytic degreasing→Water rinse→Hydrochloric acid soaking→Water rinse→Flash gold plating→Sulfuric acid soaking→Water rinse→Electroplating Pt-W Alloy

Suppose no aging treatment is applied and plating is done immediately using the prepared plating solution. In that case, the co-deposition of tungsten will be unstable, especially since the initial tungsten deposition will be low. The plating solution will gradually stabilize with continued use, and tungsten co-deposition will increase. A stable tungsten-containing plating layer can be obtained if the above aging treatment is used.

(5) Electroplating Platinum-Nickel Alloy

Hu Zhongmin proposed the main components of the electroplating Pt-Co alloy formula as follows:

(5) Electroplating Platinum-Nickel Alloy

Hu Zhongmin proposed the main components of the electroplating Pt-Co alloy formula as follows:

Pt(NH₃)₂(NO₂)₂ (as Pt) 0.2~15g/L

Nickel sulfamate (as Ni) 5~70g/L

(maintain Ni:Pt=30:1)

Sulfamic acid Adequate amount

pH 1~1.4 (adjusted with sulfamic acid)

Temperature 70°C

Current density 2A/dm²

If the mass ratio of metal ions Ni/P in the plating solution is 6/1, then an alloy plating layer Ni/Pt=9/1 can be obtained.

Section IV Chemical Plating of Platinum

In addition to being used in jewelry, catalysis, and heat-resistant materials, platinum can also be used as a thin film electrode for semiconductor components. Obtaining platinum thin films through chemical plating is a new approach. The reducing agents are generally hydrazine or hydrazine hydrate; hypophosphite is sometimes used.

Raitian refines platinum salts by passing carbon dioxide into a solution of hexaammineplatinum complex [Pt(NH₃)₆(オハイオ州)₄], causing the platinum salt to precipitate and achieving stable and high-speed platinum electroplating.

The specific refining method is to pass carbon dioxide into a solution of hexaammineplatinum complex [Pt(NH₃)₆(オハイオ州)₄] for about 3 hours to obtain a platinum salt precipitate. Then, filter, wash, dry the precipitate and dissolve the carbonate with an organic acid to obtain refined platinum salt for electroplating. The purpose of using organic salts is to avoid contamination by inorganic ions. Halide ions tend to adsorb onto the plated parts, reducing the deposition rate and causing the platinum film to darken. The presence of sulfate and nitrate ions can also cause appearance issues with the plating. The organic acids used are sulfonic acids, such as methanesulfonic or ethanesulfonic acid, or low molecular weight organic carboxylic acids, such as acetic or propionic acid.

To facilitate the volatilization and removal of carbon dioxide, the solution can be kept under reduced pressure when dissolving the platinum carbonate precipitate with organic acid.

Plating solution and process conditions:

Pt(NH₃)₆(CH₃COO)₄ (as Pt dissolved in acetic acid) 3g/L

Hydrazine hydrate 3mL/L

Glycerol ester (leveling agent) 20×10^-6

pH (Adjusted with ammonia) 11

Temperature 60℃

Plated parts Aluminum oxide plate (activated)

Deposition speed 1.8μm/h

The leveling agent can be polyoxyethylene dodecyl ether, and the reducing agent can be replaced with hypophosphite.

Also using hydrazine hydrate as the reducing agent, Koslov Alexander’s formula is:

Pt(NH₃)₂(NO₂)₂ (as Pt) 2g/L

Hydrazine hydrate (reducing agent) 3g/L

NH₂OH – HC1（as stabilizer) Adequate amount

pH (adjusted with acetic acid) 3

Temperature 50℃

Deposition speed 0. 1μm/h

To plate chemical platinum on an ion exchange membrane, in 2007, Japan’s Arimoto Sazo proposed a process of first soaking the workpiece to be plated in a platinum-containing solution and then taking the workpiece out and soaking it in a solution containing a reducing agent. This method can produce a plated piece with a platinum thickness of 0.1 mm. Electrodes used in fuel cells need to form platinum on the ion exchange membrane. In such cases, chemical plating of platinum is required. There are also cases where platinum is formed on non-conductors to serve as a catalyst. These generally require a dense platinum film. The method invented by Arimoto Sazo features alkaline earth metals, and the experimental results are shown in Table 3-13.

Table 3-13 Chemical Plating Pt Test

項目	Test 1	Test 2	Test 3
Test Characteristics	The ion-exchange membrane soaked in 5% (NH₄)₄PtCl₂ solution was placed in a solution of 1g/L sodium hydroboride+1mg/L magnesium carbonate at 50℃ for 1h.	Ion exchange membrane soaked in 5% (NH₄)₄PtCl₂ solution was placed in a solution of 1g/L sodium hydroboride + 10mg/L magnesium sulfate at 30℃ for 1h.	HPtCl₄ 1g/L Sodium hydroboride 1g/L Calcium carbonate 10ml/L 80℃,1h Reaction of plate Al in the above solution by immersion
Base material	Cation exchange membrane	Cation exchange membrane	Aluminum plate
Platinum thickness	0. 1mm	0. 1mm	0. 1mm
Platinum particle diameter	Below 10μm	Below 10μm	Below 10μm
Surface resistance	10Ω/cm	10Ω/cm	10Ω/cm

In this reaction, alkaline earth metals are required; they can dissolve with the reducing agent (as in Experiment 1, Experiment 2) or be added to the plating solution (as in Experiment 3). However, the mechanism of action of alkaline earth metals is unclear. The better the compactness of the plating layer, the fewer defects, such as cracks in the plating layer, which can ensure a relatively low resistance and thus guarantee the quality of the electrode.

Kenji Takahashi proposed a chemical plating scheme using tetravalent platinum ammonium salt as the main salt. The general form of the platinum salt is ［Pt(NH₃)₆X］. In the formula X can be a halide ion, OH^– group, SO₄^2-等々。

Its composition is:

Platinum salt (tetravalent platinum ammonium salt) (in platinum) 0. 5〜5.0g/L

Ammonia (28%) 10〜100g/L

Water and hydrazine (reducing agent) 0. 5〜5g/L

рH 10〜12. 5

Plating solution temperature 50〜70℃

With modern industry’s needs, platinum plating requirements have become diverse. Experts will also continuously propose more new suggestions to meet these new demands.

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