EP3067444B1 - Deposition of decorative palladium iron alloy coatings on metallic substances - Google Patents

Description

The present invention is directed to an electrolytic bath composition for depositing white, high-gloss, crack-free, abrasion and corrosion-resistant palladium-iron alloys from alkaline aqueous baths, objects and articles coated with these alloys, and a process for producing the coated objects Items.

Methods for the deposition of palladium-iron alloys from aqueous alkaline electrolytes are known from the AiF research project No. 10302 N of the Research Institute for Precious Metals and Metal Chemistry Schwäbisch Gmünd, "Galvanic deposition of palladium-iron alloy coatings for functional applications and their characterization". However, with the electrolyte described there, no high-gloss alloys could be deposited under the conditions described there. In addition, the electrolyte described is based on ammonium salts, the pH is adjusted with ammonia. At electrolyte temperatures of 55 ° C, therefore, ammonia must be constantly replenished in order to keep the pH constant, and in addition there are enormous odor and health nuisances for the operators of such baths.

The electrolytes are out JP, 2001-192885, A are also based on ammonium salts and contain additional brighteners and possibly different alloying metals such as iron or tellurium.

JP, 2001-181887, A describes palladium-iron alloy baths which are also based on ammonium salts, and additionally contain EDTA. However, strong chelating agents are generally undesirable in electrolytes since they introduce difficulties in wastewater treatment.

JP, 10-046384, A describes palladium alloy baths for the electronics industry. Iron as alloying metal is mentioned, the electrolytes are based on ammonium salts. The examples, however, relate only to palladium-cobalt alloys. Alloys of palladium-iron, palladium-nickel, palladium-rhodium and palladium-ruthenium should be produced in the same way.

DE2657925 describes ammonia-free, semi-glossy to bright palladium and palladium alloy baths for electrical engineering, but iron is not mentioned as alloying metal.

From the EP 1396559A1 is an electrolytic bath for the cathodic deposition of binary alloys to form white, corrosion-resistant, crack-free and (high) glossy coatings on at least on their surface metallic or electrically conductive or conductive coated objects known which bath as alloying metals at least one palladium compound as the primary metal and contains at least one iron compound as secondary metal, and for the deposition of a Pd / Fe alloy having a content in the range of 5 to 15 wt% Fe - as an aqueous alkaline solution having a pH of 7.5 to 9 and as essential other components at least one wetting agent from the group of amphoteric surfactants and additionally contains at least one of the usual in palladium baths contained gloss additives and conductive salts, pH stabilizers and voltage reducer, wherein the electrolyte bath has a content of palladium of 0.5 to 15 g / l and of iron from 0.2 to 2 g / l au fweist.

Also the DE 2741347A1 shows such a bath.

It is the object of the present invention to develop baths from which high gloss, binary palladium-iron alloys can be deposited without any addition of other metals and. In particular, the alloy baths during operation should not present an odor nuisance or health hazard through the release of irritating gases or vapors, and moreover contain no strong complexing agents such as EDTA or NTA, which would cause problems in wastewater treatment.
In addition, the production is to be cheapened by the use of such alloy baths, and resources of the expensive palladium are spared.
A cost saving of about 15% when using such alloy baths in comparison to pure palladium baths results on the one hand from the lower density of the deposited palladium-iron alloy, on the other hand from lower Ausleppungsverlusten of precious metal, since pure palladium baths usually about with a palladium concentration of 10 g / l Palladium work, but the palladium-iron alloy bath of the present invention can get by with about half the concentration.

Such alloys are therefore particularly well suited for any metallic white decorative coating, e.g. of costume jewelery, but also for industrial applications, especially in the electronics industry.

In the present invention, the baths contain 0.5-15 g / l of palladium, 0.2-2 g / l of iron, conductive salts, brighteners and wetting agents. It is possible to deposit layer thicknesses> 5 μ high gloss, crack-free. The corrosion resistance is comparable to pure palladium, the abrasion resistance is better than pure palladium.

The invention relates to a novel electrolyte bath for the cathodic deposition of binary alloys with the formation of white, corrosion-resistant, crack-free and (high) glossy coatings on at least metallic or electrically conductive or conductively coated objects on its surface, which bath contains at least one palladium compound as alloying metals. in particular a palladium salt, as a primary metal and at least one iron compound, in particular an iron salt, as a secondary metal, which for the deposition of a Pd / Fe alloy with a content in the range of 5 to 15 wt% Fe - as an aqueous, alkaline solution with a pH value of 7.5 to 9, and in addition to the metal compounds mentioned as essential further components at least one wetting agent from the group of amphoteric surfactants, and at least one brightener and conductive salts, pH stabilizers and voltage reducer, wherein the electrolyte bath a Content of P alladium of 0.5 to 15 g / l and iron of 0.2 to 2 g / l and is free of ammonia and ammonium compounds. The new electrolyte bath is characterized in that it contains betaines and sulfobetaines in quantities of 0.5-2 g / l as wetting agents from the group of the amphoteric surfactants, and aromatic N-heterocycles substituted as brightening agents, and as stress relievers saccharin or organic sulfonates, and as conductive salts and / or pH stabilizers, sodium or potassium sulfate, chloride, nitrate, citrate, tartrate, or malonate.

The pH of the new alloy bath should be maintained in the range of 7.5 - 9, since at lower pH values (approximately between 7 and 7.5) the incorporation rates of iron decrease. At higher pH values (approximately between 9 and 10), burns occur in the high current density range. The pH is advantageously adjusted by means of sodium or potassium hydroxide.

According to the present invention, the iron content of the deposited alloy at 5-15 wt .-% Fe, since at incorporation rates> 15 wt .- Fe Fe the layers are cracked, and at incorporation rates <5% by weight, the deposition receives a milky appearance.
In the context of the present invention, it has proved to be advantageous if palladium in divalent form, for example as palladium chloride, sulfate or nitrate, and iron as iron sulfate, chloride, nitrate or citrate are present in the electrolyte bath.
Accordingly, for the deposition of a coating, an electrolyte bath is advantageously provided, which is characterized in that it has a content of palladium of 2 to 8 g / l, and more preferably of 4 to 6 g / l and of iron preferably 0.5 to 1 Contains 5 g / l.
Further included are conductive salts and pH stabilizers such as sodium or potassium sulfate, - nitrate, chloride, citrate, tartrate, or malonate, and further as wetting agents alkyl ether sulfonates, alkyl ether phosphates or fatty alcohol alkoxylates.
All conductive salts or pH stabilizers used in the invention are sodium or potassium salts. When using ammonia or ammonium salts at elevated temperatures of about 50 ° C, ammonia is constantly expelled. As a result, the pH of the bath constantly adjusted and continuous work is much more difficult.
In addition, there is a constant odor nuisance and health hazard for the operator of the electrolyte.
Furthermore, in the electrolyte of the present invention, organic acids or salts are not used which release vapors during operation of the bath at elevated temperature, which can lead to an odor nuisance and / or health hazard for the operators of the electrolyte, for example propionic acid / propionates, acetic acid / acetates.
The various advantageous electrolyte baths according to the invention or used according to the invention are described in detail in claims 2 to 4.
On the basis of the present invention, objects or articles, in particular jewelery or decorative articles, as well as electrotechnical or electronic components and components of a preferably physiologically acceptable metal, in particular brass, zinc, tin, iron or steel, or alloys thereof or a conductive plastic with one of the above said coating deposited from a binary alloy of palladium and iron, in which the iron is present at a level of from 5 to 12% by weight.
The total thickness of the binary palladium-iron coating to be achieved in the context of the invention is in each case 0.1 to 5 μm, in particular approximately 0.5 to 3 μm, depending on the field of use.
On the outside of the palladium-iron coating, a further, electrodeposited final layer of gold and / or another noble metal, such as, in particular, rhodium, platinum, ruthenium or an alloy of the same, can be arranged, by means of which the already high usability and the gloss of the coating is still increased.
For further improvements of the novel coatings of said articles, an adherent gold adherent intermediate layer adhered thereto may be disposed on the palladium-iron overlay and an electrolytically deposited, adherent final layer of gold and / or another thereon Noble metal, in particular rhodium, platinum, ruthenium or an alloy of the same.
The intermediate layer of adhesive gold may have a thickness of 0.05 to 0.3 microns.
Furthermore, the coated new objects or articles can be coated with a final layer of an alloy formed with rhodium and ruthenium, preferably in the weight% ratio of (70 to 90) to (30 to 10), in particular of about 80 to 20 his.
It is the object of the present invention to adjust the concentration of the metal salts, wetting agents, brighteners and the additional ingredients in the mold and to vary within the weight ratios according to the invention so that the electrolyte solution is clear and remains, so that no metal salts precipitate, and that just according to the invention desired, shiny, adherent, crack-free, abrasion and corrosion resistant layers or coatings are deposited.
The process for the production of objects with a white coating or with such a corrosion-resistant, crack-free, highly abrasion-resistant and adherent, glossy coating from the group jewelry or decorative items, from the group of electrical or electronic components and components Brass, zinc, tin, iron or steel or of their alloys or else of a conductively equipped plastic, wherein, preferably on a metallic background layer, in particular of copper, located on the surface of the object or article blank, a Pd / Fe Alloy is deposited, is characterized in that the objects to be coated or articles, optionally after a base coat with copper, by electrolysis in an electrolyte bath according to one of claims 1 to 4 at temperatures of 35 to 75 ° C and current densities of 0.1 to 10 A / dm ² , in particular from 0.2 to 5 A / dm ² , are subjected to the use of at least one insoluble anode of the electrolysis.
In the course of the process for electrolytic application of the new binary palladium-iron alloys to the respective base materials to be coated objects, objects or articles are immersed in the respective inventive electrolyte bath and switched there as a cathode.
The working temperature of the electrolyte baths according to the invention is between 35 and 75 ° C. The current density can be set to between 0.01 and 10 amps / dm ² , depending on the type of coating system.
Thus, in drum coating processes, current densities between 0.05 and 0.50 A / dm ^{2 are} particularly preferred. In rack coating processes, preference is given to choosing current densities between 0.2 and 10 A / dm ² , particularly preferably 0.2 to 5 A / dm ² .
When using the electrolyte baths according to the invention, various insoluble anodes can be used.
As insoluble anodes, those of a material selected from the group consisting of platinum-plated titanium and iridium-transition metal mixed oxide or combinations of these materials may be used, with platinized titanium anodes being preferred.
The production of the objects or articles coated according to the invention is usually carried out as follows:
On a respective base material, for example consisting of brass, zinc, iron, steel or their alloys or other materials made conductive at least on its surface is either directly or on a previously applied copper undercoat, deposited from cyanide or non-cyanidic alkaline and / or from acidic copper baths, the new binary palladium-iron alloy is deposited either directly or on Cu / Sn / Zn alloy of cyanide bronze baths applied there.

This palladium-iron alloy is in itself a final layer. However, it can be further coated by methods known per se. Other coatings may, as mentioned above, be gold-containing or other noble metal-containing layers, such as those of rhodium, platinum, ruthenium or their alloys.

From the prior art is - in addition to the documents already mentioned - known per se that palladium is used as a nickel substitute, as a diffusion barrier and as corrosion protection. In these products, the base material is first copper-plated, then coated with palladium and finally receives the desired finish by coating with gold, rhodium or other precious metals or their alloys.
In order to provide sufficient corrosion protection, a thickness of the palladium layer of about 0.5-5 microns is recommended. Usually a layer thickness of about 1 μm is considered sufficient.

According to the present invention, it has been found that the application of an equally thick palladium alloy layer leads to equally good corrosion results as are achieved in pure palladium-coated base materials, but the abrasion resistance is better. The cost savings alone is about 15% due to the lower density.

If you want to produce the products particularly efficient, you can deposit a rhodium-ruthenium alloy instead of a rhodium final layer. If, for example, an alloy in the ratio by weight of rhodium to ruthenium of 80:20 is deposited as the final layer, in addition to the savings in the intermediate layers mentioned above, 20% of the very expensive rhodium would be saved.

The invention further relates to a per se conventional method for cathodic deposition of the binary alloys according to the invention with an Fe content of 5-15% by weight on at least on their surface metallic or electrically conductive or conductive coated objects or articles using the electrolyte according to the invention ,

Reference to the following, non-limiting examples, the invention is explained in more detail:

Example 1: electrolyte:

• 4 g / l Pd of Pd-II chloride
• 0.6 g / l Fe of Fe-III sulfate
• 80 g / l potassium sulfate
• 40 g / l citric acid
• 1 g / l wetting agent PF (betaine, product of the company Ing. W. Garhöfer GesmbH)

The corrosion resistance of the palladium-iron alloy in comparison with a coating of a pure palladium electrolyte (Gapal TS, product of Garhöfer GesmbH), produced on the same base material in the SO ₂ test is equally good.

Abrasion resistance with Taser Abraser

In each case, a brass disc in the palladium-iron electrolyte of example 1 and a brass disc in a pure palladium electrolyte (Gapal TS, product of Garhöfer GesmbH) were coated with 2 .mu.m. Anschießend both discs were abraded. The pure palladium was rubbed much earlier than the palladium-iron alloy.

Examples 2: Electrolyte:

• 4 g / l Pd of Pd-II chloride
• 0.6 g / l Fe of Fe-III sulfate
• 80 g / l potassium sulfate
• 40 g / l citric acid
• 1 g / l wetting agent PF (betaine, product of the company Ing. W. Garhöfer GesmbH)
• 0.1 g / l fatty alcohol ethoxylate
• 2 g / l saccharin
• 2 ml / l brightener: Brightener PF (mixture of substituted aromatic N-heterocycles, product of the company Ing. W. Garhöfer GesmbH)
• pH value: 8.0 adjusted by means of KOH

A jewelery blank made of die-cast zinc is electrolytically degreased in a weakly alkaline cyanide-free cleaner (degreasing 1018, product of the company Ing. W. Garhöfer GesmbH) at 25 ° C. for 30 seconds at 10 A / dm ² .

Subsequently, the jewelry blank is rinsed in deionized water and in an alkaline cyanide Vorkupferbad with 22 g / l Cu and 34 g / l KCN ("Cuproga", product of the company Ing. W. Garhöfer GesmbH) were 5 microns of copper at 1 A / dm ² and 50 ° C deposited.

The pre-coppered jewelry blank is then dekapiert in 5% sulfuric acid solution for 30 s and in an acidic copper bath with 50 g / l Cu and 60 g / l sulfuric acid ("IWG Cu 550", product of the company Ing. W. Garhöfer GesmbH) 15μm copper leveling and high gloss deposited at 4 A / dm ² and 25 ° C. The thus coppered part is rinsed and pre-immersed in a 10% KCN solution.

² μm of bronze alloy are then removed from the electrolyte within a period of 10 minutes from a bronze electrolytic bath (Weissbronze CT 15 LF, product of the company Ing. W. Garhöfer GesmbH) and then rinsed in deionized water and decanted in 5% sulfuric acid solution.

Then from a palladium-iron-Elektroytbad according to the present invention 2μm palladium-iron of the composition palladium: 90.3%, iron: 9.7%, at 50 ° C, and 1 A / dm ² within 10 minutes from the electrolyte bath deposited.

After renewed rinsing and acid immersion with 0.1 μm adhesive gold from a weakly acidic electrolyte with 2.5 g / l Au ("MC 218", product of the company Ing. W. Garhöfer GesmbH), the jewelery thus obtained is 1.5 A / dm ² and 35 ° C provided. Then rinsed thoroughly in demineralized water, dekapiert in 5% sulfuric acid solution and 0.2 .mu.m rhodium from an electrolyte with 2 g / l Rh and 50 g / l sulfuric acid ("rhodium C2", product of the company Ing. W. Garhöfer GesmbH) rhodinated at 3V and 35 ° C.

Finally, the galvanized part was rinsed in deionized water and dried.

Optical assessment:

The obtained in this way, galvanized jewelry or its surface was pure white and high gloss.

Corrosion resistance according to DIN 50018:

The galvanized part of the jewelry performed just as well in the corrosion tests as a jewelery part coated with pure palladium using the same process.

Claims (5)

1. Electrolyte bath for the cathodic deposition of binary alloys with the formation of white, corrosion-resistant, crack-free and (highly) glossy coatings on objects that are at least on their surface metallic or electrically conductive or conductively coated, which bath contains as alloying metals at least one palladium compound, in particular a palladium salt, as primary metal and at least one iron compound, in particular an iron salt, as secondary metal, which for the deposition of a Pd/Fe alloy with a content in the range 5 to 15 % by weight Fe is present as an aqueous, alkaline solution with a pH value from 7.5 to 9, and in addition to said metal compounds contains as essential further components at least one wetting agent from the group of amphoteric surfactants, and at least one brightening agent as well as conductive salts, pH stabilisers and voltage reducers, wherein the electrolyte bath has a content of palladium from 0.5 to 15 g/l and of iron from 0.2 to 2 g/l and is free of ammonia and ammonium compounds, characterised in that
   it contains as wetting agent from the group of amphoteric surfactants betaine and sulfobetaine in quantities from 0.5-2 g/l, and contains as brightening agent substituted aromatic N-heterocycles, as voltage reducers saccharin or organic sulfonates, and as conductive salts and/or pH stabilisers sodium or potassium sulfate, chloride, nitrate, citrate, tartrate, or malonate.
2. Electrolyte bath according to claim 1, characterized in that the electrolyte bath has a content of palladium from 2 to 8 g/l, and preferably from 4 to 6 g/l, and of iron from 0.5 to 1.5 g/l.
3. Electrolyte bath according to Claim 1 or 2, characterized in that the alloying metals contained therein are present as palladium in divalent form, as palladium chloride, sulfate or nitrate, and iron as iron (III) sulphate, chloride, nitrate or citrate.
4. Electrolyte bath according to any one of claims 1 to 3, characterized in that it contains as further wetting agents alkyl ether sulfonates, alkyl ether phosphates or fatty alcohol alkoxylates.
5. A process for the production of objects or articles selected from the group of jewellery or decorative articles, from the group of electrotechnical or electronic components and components of brass, zinc, tin, iron or steel or their alloys, or of conductive plastics material, which objects or articles have a white coating or a corrosion-resistant, crack-free, highly abrasion-resistant and adherent, glossy coating of that kind, wherein a Pd/Fe alloy is deposited, preferably on a metallic base layer, in particular of copper, located on the surface of the object or article blank, characterised in that the article or object to be coated, optionally after base coating with copper, is subjected to electrolysis utilising at least one insoluble anode, by electrolysis in an electrolyte bath according to any one of claims 1 to 4 at temperatures from 35 to 75°C and current densities from 0.1 to 10 A/dm², in particular from 0.2 to 5 A/dm².