JPH0351773B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The disclosed technology is a glossy rhodium plating film used for electrical contacts, decorative items, etc., which is hard, corrosion-resistant, abrasion-resistant, and has a beautiful luster. It belongs to the technical field of plating liquid. <Summary of the gist> This invention provides high hardness such as abrasion resistance to the surface of industrial products such as electrical contacts and decorative crafts,
This invention relates to a bright rhodium plating solution in which a brightening agent is added to a rhodium sulfate plating solution in order to increase its glossiness, and in particular, nitrate radical (NO ₃ ) is added as a brightening agent from 0.1 to 300 g, and
This invention relates to a bright rhodium plating solution containing amines in an amount of 0.001 mole or more and 10 moles or less. <Prior Art> As is well known to those skilled in the art, rhodium plating is used for industrial purposes such as improving the hardness of electrical contacts, and for improving the aesthetics of the surfaces of decorative crafts. It is widely known that the plated coating surface of the product is smooth, resulting in a corrosion-resistant and abrasion-resistant plated coating with good gloss. Therefore, the rhodium plating solution is strongly required to have a smoothing function and a brightening function. The rhodium plating solutions that have been used so far can be roughly divided into sulfuric acid baths, phosphoric acid baths, and
Although there are mixed baths of sulfuric acid and phosphoric acid, sulfuric acid baths are widely used because of their ease of use and cost. When using a sulfuric acid bath to function as a bright rhodium plating solution, a smoothing agent or brightening agent (hereinafter collectively referred to as a brightening agent) is added to the rhodium sulfate plating solution to help promote smoothing. There are many cases where it is used. Conventionally, as brighteners added to rhodium sulfate plating solutions in sulfuric acid baths, for example, Mg compounds, Se compounds, and other organic and inorganic compounds have been used. <Problems to be Solved by the Invention> Therefore, Mg compounds, Se compounds, etc. used in brighteners added to the rhodium sulfate plating solution of the seed bright rhodium plating solution smooth the plating film. However, as shown in the content written on page 273 of ``Practical Knowledge of Precious Metals'', a publication by Yuzo Yamamoto published by Toyo Keizai Inc. in 1971, However, the disadvantage is that the rhodium plating film formed thereby is dark in color and lacks sufficient gloss. In addition, rhodium in the rhodium sulfate plating solution is initially in a trivalent state, but it tends to be oxidized during storage and the like, resulting in an increase in highly oxidized tetravalent or hexavalent rhodium. As the amount of rhodium increases, the white glossy rhodium plated surface will become dotted with black spots, and the amount will increase over time, leading to the risk that the beautiful whitening effect of rhodium plating will be completely lost. Therefore, there has been a strong demand for a rhodium plating solution that prevents such phenomena and does not change over time. <Object of the invention> The object of the present invention is to solve the problems of the rhodium sulfate plating solution based on the above-mentioned prior art, and to improve the inherent smoothing function and gloss imparting function of the rhodium sulfate plating solution. To obtain a beautiful white, high-gloss rhodium plating film with good reproducibility, without causing black spots due to rhodium oxidation, even under normal use or storage conditions without any damage. It is an object of the present invention to provide an excellent bright rhodium plating solution that is useful for processing technology applications in the metal manufacturing industry. <Means/effects for solving the problem> In order to solve the above problem, the structure of the present invention, which is based on the scope of the above-mentioned claims, is as follows:
The true chemical reason for the above problem is still not fully clear, but it is probably due to the high oxidation state of 4
Based on the assumption that it is due to valent or hexavalent rhodium, amines for complexing these and nitrate radicals that are electrolytically reduced to produce hydroxylamine at the cathode interface are added, A technical means that partially reduces and complexes rhodium in a highly oxidized state, prevents the occurrence of black spots, and makes it possible to permanently obtain a white glossy rhodium plating film with the same solution. This is what I learned. <Background of the Invention> In view of the above-mentioned problems, the inventor has developed an inorganic and organic plating method in order to prevent the formation of black spots, which are thought to be caused by the oxidation of trivalent rhodium in the solution, during rhodium sulfate plating. Although investigations were carried out including experiments with reducing agents, no lasting antioxidant effect could be obtained because none of the chemicals itself oxidizes. However, it was found that compounds with an amino group (-NH ₂ ), such as hydrazine hydrate and hydrazine sulfate, have the effect of eliminating black spots in addition to being effective as reducing agents. It has been found that even in such a form, amines have the effect of eliminating or at least reducing the species black spots to a greater or lesser extent. However, even if these black spots disappear,
The color of the rhodium plating film is slightly darker overall,
The problem of not being able to obtain the same white gloss immediately after preparing the plating solution remained, but as a result of intensive investigation based on experiments, we found that adding NO ₃ ^- ions returned the dark color to its original color and made it possible to achieve a white color. I found it to be shiny. The NO ₃ ^- ions may be added with the same effect regardless of whether nitric acid (HNO ₃ ), potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), or ammonium nitrate (NH ₄ NO ₃ ) is added. Divided. The reason for this white color is speculation as mentioned above, but NO ₃ ^- ions are electrolytically reduced to produce hydroxylamine (NH ₂ OH), and hydroxylamine acts both as an amine and as a reducing agent. Because it has a high oxidation state of 4 or 6
It was thought that the effect of rhodium on the valence would disappear. Incidentally, when hydroxylamine was added to the aged dyeing solution, a white rhodium plating film was obtained. Since the hydroxylamine is easily oxidized,
In reality, the color of the plating film is darkened according to the aged matting solution, but the most effective method is to add NO ₃ ^- ions in combination with a type of amine that has the function of eliminating black spots. I also understood that. In this case, the amount of NO ₃ ^- ions added should be 0.1 g/or more, and there is no particular upper limit, but the effect level off at a concentration of several g/or more, and it is limited by the solubility of the nitrate to be added. It has been confirmed through experiments that it is better to set the amount to 300g/or less. Although there are many types of amines, compounds having the following general formula have the effect of eliminating black spots. (a)RN=R

【formula】

【formula】

[Formula] (e) N≡R (f) X・N≡R (However, R, R′, and R″ in the formula are various atoms,
Or, it represents an atomic group, and up to two of R, R', and R'' can represent the same atom or atomic group, and X represents an acid group.) The concentration should be 0.001 mol/or more, and the effect will level out at 0.01 mol/or more, and adding a large amount will only cause decomposition or increase polymerization products, which is also uneconomical. Since this has been confirmed through experiments, the amount is set at 10 mol/or less. <Example> Next, an example of the present invention will be explained as follows. (First Example) Rhodium sulfate ( (as Rh) 2.0g/ Total sulfuric acid (as SO ₄ ) 60g/ Triethanolamine {N(CH ₂ CH ₂ OH) ₃ } 1g/(0.007 mol/
) Using bright rhodium plating solution 1 consisting of 0.5 g/ nitric acid (as NO ₃ ), the solution temperature was
At 50℃, a 0.2 dm ² Ti plate plated with platinum was used as the anode, and a 0.5 dm ² Ti plate plated with mirror polish was used as the cathode.
Using a Ni plate, rhodium plating was performed on the Ni plate for 5 minutes at a cathode current density of 1 A/dm ² . As a result, a rhodium-plated surface with white metallic luster was obtained on the cathode. When this solution was stored and used after two months, no black spots were formed, and a rhodium-plated coating surface with the same white metallic luster as the initial one was obtained. The amount of triethanolamine was 10g/, NO ₃ ^-
Exactly the same results were obtained when the amount of ions was 100g/. (Second Example) Using the same bright rhodium plating solution as in the first example above, hydrazine sulfate {(NH ₂ ) ₂ H ₂ SO ₄ }1 g/(0.008 mol/
) was added and plated, the same results as in the first example were obtained. Even after using this solution for about half a year, no black spots appeared, and a rhodium-plated coating surface with the same white metallic luster as the initial one was obtained. Furthermore, the amount of hydrazine sulfate was 50g/NO ₃ ^-
Exactly the same results were obtained when 200 g/ion of ions were used. (Third Example) When plating was carried out using the same bright rhodium plating solution as in the first example, 1 g/(0.01 mol/) of sulfamic acid (NH ₂ SO ₃ H) was added instead of triethanolamine. Results similar to those of the first example were obtained. Even after using this solution for about one year, no black spots were generated, and a rhodium-plated coating with white metallic luster similar to the initial coating was obtained. Furthermore, the amount of sulfamic acid is 500g/,
Exactly the same results were obtained when 250 g/NO ₃ ^- ions were used. (Comparative example) Using rhodium plating solution 1 containing 2.0 g of rhodium sulfate (as Rh) and 60 g of total sulfuric acid (as SO ₄ ), plating was carried out under the same conditions as in the first example, and a white metal was formed on the cathode. A glossy rhodium-plated coating was obtained, but when this liquid was stored and used after one month, many black spots of about 1 mm diameter were scattered on the rhodium-plated surface with a white metallic luster, and the decorative effect was completely lost. Ta. <Effects of the Invention> As described above, according to the present invention, in the bright rhodium plating liquid in which a brightening agent is added to the rhodium sulfate liquid,
By adopting the structure as claimed in the claims above, not only the effect of smoothing the plating film is produced, but also the excellent effect of maintaining the beautiful white effect of the plating over time is produced. Therefore, we tried to make it easier to use by using a sulfuric acid bath.
It is possible to reduce costs, and in addition, nitrate radicals can be added to the brightening agent added to the rhodium sulfate plating solution in the sulfuric acid bath.
0.1g/or more and 300g/or less, and amines
By containing 0.001 mole or more and 10 moles or less, rhodium in a highly oxidized state is reduced, and furthermore, it is complexed to prevent the occurrence of black spots, and in a permanent state, rhodium with a strong white luster can be coated with the same rhodium plating solution. It has the excellent effect of being able to obtain a coated film.

Claims (1)

[Claims] 1. In a bright rhodium plating solution in which a brightener is added to a rhodium sulfate plating solution, nitrate radical (NO ₃ ) is added as a brightener to the rhodium sulfate plating solution.
0.1g/or more, 300g/or less, and amines
A bright rhodium plating solution characterized by containing 0.001 mole or more and 10 moles or less.