Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/567—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of platinum group metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating

Definitions

• the present invention relates to an electrolytic process for the deposition of coatings comprising an alloy of platinum and rhodium on, in particular, decorative articles.
• the process of the invention is characterized in that the electrolytically deposited layer has, contrary to expectations, a high whiteness which comes extraordinarily close to the appearance of silver.
• Coatings can be applied to such articles in various ways. Coating by electrolytic methods is an option for electrically conductive articles. Different coating processes are usually used in the electroplating industry as a function of the type and nature of the parts to be coated. The processes differ, inter alia, in respect of the current densities which can be employed. Mention may be made of essentially 3 different coating processes.
• Drum coating for loose material and mass-produced parts in this coating process, relatively low working current densities are employed (order of magnitude: 0.05 - 0.5 A/dm 2 )
• DE-B 1229816 describes a coating comprising a metal alloy of the platinum group metals and containing at least 50% by weight of platinum, at least 50% by weight of rhodium or at least 50% by weight of platinum together with rhodium for an anode. This document merely mentions that the platinum alloy can be obtained, inter alia, by electroplating. The coating formed in this way is intended to protect the anode against corrosion.
• US 3748712 describes the coating of silver articles with an alloy which has a thickness of from 1 to 50 microinches and contains from 91 to 99% by weight of rhodium and from 1 to 9% by weight of platinum.
• the electrolytic bath is said to contain from 0.5 to 20 g/l of the sulphate compound of the noble metals and be operated at a pH of from 1 to 3.5.
• the current density to be applied is reported as being from about 0.5 to 4.3 A/dm 2 .
• the stated object is particularly surprisingly achieved in a simple but nonetheless advantageous manner by the electrolysis in a process for the electrolytic deposition of an alloy of platinum and rhodium on, in particular, decorative articles, where the rhodium content of the alloy ranges from at least 40% by weight to not more than 85% by weight, preferably from 45% by weight to 80% by weight, particularly preferably from 48% by weight to 70% by weight, very particularly preferably from 49% by weight to 60% by weight, and extremely preferably about 50% by weight, being carried out at a pH of ⁇ 1 and a current density of >2 A/dm 2 in an aqueous solution comprising: a) 0.4 - 5.0 g/l of platinum ions, b) 1.0 - 5.0 g/l of rhodium ions and optionally c) one or more additives selected from the group consisting of supporting electrolytes, brighteners, surfactants, wetting agents and ligands which complex noble metals and stabilisers, as electrolytic bath.
• the process of the invention makes it possible to make do with less rhodium in a platinum-rhodium coating and nevertheless obtain firmly adhering, stable coatings which are nevertheless attractive and look like silver on appropriate goods and articles.
• the coatings are generally 2 lightness units (according to the Cielab system - http://www.cielab.de/) lighter than would have been expected theoretically from the proportion of pure rhodium.
• the throwing power of the platinum-rhodium electrolyte used in the process of the invention is particularly good. In electroplating, the throwing power is the ability of an electrolyte to achieve an improved coating distribution on the workpiece to be coated despite a non-uniform current distribution. In detail, a distinction is made between macro and micro throwing power. Macro throwing power is the ability of an electrolytic bath to achieve an approximately uniform layer thickness over the entire surface of the workpiece including the lower regions. Micro throwing power is the ability of an electrolytic bath to deposit metal in pores and scratches.
• the metals rhodium and platinum to be deposited are present in dissolved form as their ions. They are preferably introduced in the form of water-soluble salts which are preferably selected from the group consisting of pyrophosphates, carbonates, hydroxidecarbonates, hydrogencarbonates, sulphites, sulphates, phosphates, nitrites, nitrates, halides, hydroxides, oxidehydroxides, oxides and combinations thereof. Very particular preference is given to the embodiment in which the metals are used in the form of salts with ions selected from the group consisting of pyrophosphate, carbonate, sulphate, hydroxidecarbonate, oxidehydroxide, hydroxide and hydrogencarbonate.
• the type and amount of salts introduced into the electrolyte can likewise be decisive for the colour of the resulting decorative coating and can be set according to customer requirements.
• the metals to be deposited are, as indicated, present in ionically dissolved form in the electrolyte for the application of decorative layers on jewellery, consumer goods and industrial articles.
• the ion concentration of platinum can be set in the range 0.4 - 5.0 g/l of electrolyte, preferably from 0.5 to 4.0 g/l of electrolyte, and the ion concentration of rhodium can be set in the range 1.0 - 5.0 g/l of electrolyte, preferably 1.5 - 2.5 g/l of electrolyte.
• the metals to be deposited as sulphate or phosphate, carbonate or hydroxidecarbonate so that the resulting ion concentration is in the range from 0.5 to 1.0 gram of platinum and from 1.0 to 2.0 gram of rhodium, in each case per litre of electrolyte.
• the electrolyte can contain one or more of the additives indicated.
• further additives including organic additives, which perform functions as supporting electrolytes (e.g. H/Na/K/NH 4 sulphates, phosphates, sulphonates or mixtures thereof (Handbuch der Galvanotechnik, Carl Hanser Verlag, 1966)), brighteners (including aromatic or heterocyclic sulphonic acids, selenous acid, aluminium, magnesium (Galvanische Abscheidung der Platinmetalle, reprint by the DGO from Issue No. 2 + 4, Volume 91 , 2000)), wetting agents (such as polyfluorinated sulphonic acids, aliphatic sulphates (A. v.
• brighteners and wetting agents is particularly preferred only in the case of the appearance of the decorative layers to be deposited having to meet special requirements. These make it possible to adjust, in addition to the colour of the coating which depends mainly on the ratio of the metals to be deposited (Fig. 3), the brightness of the layer in all gradations between matt silk and high gloss. Preference is also given to adding one or more compounds selected from the group consisting of monocarboxylic and dicarboxylic acids, alkanesulphonic acids, betaines, sulphamic acids, sulphites, selenous acid and aromatic nitro compounds. These compounds act as electrolyte bath stabilisers or as brighteners.
• alkanesulphonic acids in particular methanesulphonic acid, or nitrobenzotriazoles or mixtures thereof.
• Suitable alkanesulphonic acids may be found in EP1001054.
• a possible carboxylic acid is, for example, citric acid and its Na/K salts (Galvanische Abscheidung der Platinmetalle, reprint by the DGO from Issue No. 2 + 4, Volume 91 , 2000).
• Betaines to be used are preferably those which may be found in WO2004/005528.
• Particular preference is given to using those described in EP636713. In this context, very particular preference is given to using 1-3(3- sulphopropyl)pyridinium betaine or 1-(3-sulphopropyl)-2-vinylpyridinium betaine.
• a supporting electrolyte can be added to the electrolyte in the process of the invention.
• Possible supporting electrolytes are alkali metal or alkaline earth metal salts with anions such as pyrophosphates, carbonates, hydroxidecarbonates, hydrogencarbonates, sulphites, sulphates, phosphates, nitrites, nitrates, halides, hydroxides or carboxylate anions, phosphonate anions, sulphonate anions.
• sulphuric acid and phosphoric acid which are added in excess to the reaction in the production of rhodium sulphate or phosphate from, for example, rhodium oxide hydrate (Galvanische Abscheidung der Platinmetalle, reprint by the DGO from Issue No. 2 + 4, Volume 91 , 2000).
• Surfactants e.g. anionic, cationic and/or nonionic surfactants, with and without polyfluorinated substituents, which withstand the very low pH in the long term (electroplating chemicals, TIB Chemicals AG, Mannheim) can also be added.
• the application of the coating to decorative articles, consumer goods and industrial articles using the electrolyte according to the invention is carried out, as indicated, in an electrochemical process. It is important here that the metals to be deposited are permanently kept in solution during the process, regardless of whether electroplating is carried out in a continuous or batch process. To ensure this, the electrolyte according to the invention can contain complexing agents. As ligands which complex the noble metals, mention may also be made of those having sulphur atoms or phosphorus atoms e.g.
• rhodium sulphate or phosphate from, for example, rhodium oxide hydrate (Galvanische Abscheidung der Platinmetalle, reprint by the DGO from Issue No. 2 + 4, Volume 91 , 2000).
• the amount of compounds which complex noble metals in the electrolyte can be set in a targeted manner by a person skilled in the art. It is limited by the fact that the concentration in the electrolyte should be above a minimum amount in order to bring about the effect concerned to a sufficient extent.
• the pH of the electrolyte is in the range of ⁇ 1 required for this electroplating application.
• a lower limit is set by the fact that the electrolyte tends to be unstable at pH values which are too low. Preference is therefore given to a range of 0 - 0.8 and very particularly preferably about 0.2.
• Acidification of the electrolyte can generally be carried out using inorganic acids. Preference is given to using, inter alia, sulphuric acid for this purpose. In a very particularly preferred embodiment, the aqueous electrolytic bath is acidified using up to 100 ml/l of cone, sulphuric acid.
• the process of the invention can be operated at a temperature which a person skilled in the art will choose on the basis of his general technical knowledge. Preference is given to a range from 20 to 70 0 C in which the electrolytic bath is maintained during the electrolysis. Greater preference is given to selecting a range of 30-50°C.
• the process is especially preferably carried out at a temperature of about 45°. When the process of the invention is employed, it is possible to use various anodes. Preference is given to insoluble anodes.
• insoluble anodes use is advantageously made of anodes composed of a material selected from the group consisting of platinised titanium, graphite, iridium-transition metal mixed oxide and a specific carbon material ("diamond-like carbon", DLC) or combinations of these anodes.
• DLC diamond-like carbon
• MMO mixed oxide anodes
• Further materials may be found in Cobley, A.J. et al. (The use of insoluble Anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001 ,79(3), pages 113 and 114).
• Very particular preference is given to using an MMO of the type Platinode ® 177 (which can be procured from Umicore Galvanotechnik GmbH).
• An important advantage of the present invention is that the deposition of the alloy composition does not alter significantly over a wide current density range at or above 2 A/dm 2 (Fig. 2). This also results in a surface quality which appears to be sufficiently homogeneous even at current densities which are relatively high for rack applications.
• a person skilled in the art will choose the current density range on the basis of economic and technical boundary conditions so as to obtain the result which is considered to be optimal. It is advantageous to choose a current density of not more than 7.0 A/dm 2 , preferably 6.0 A/dm 2 , and the current density is particularly preferably in the range 3.0 A/dm 2 - 4.0 A/dm 2 .
• Platinum ions can also be used in previously complexed form in the process of the invention.
• Commercially available compounds of this type are, for example, ammonia complexes of platinum [Pt(NH 3 ) 4 SO 4 ] or [Pt(NH 3 ) 2 SO 4 ]. Since nitrogen-containing ligands can be present in the electrolyte, these are preferably introduced in the form of the corresponding platinum complexes into the electrolyte.
• the platinum ions are therefore preferably used in the form of complex salts with nitrogen ligands such as ammonia, monoamines or oligoamines.
• polydentate ligands in particular ligands based on diamines, triamines or tetramines, is advantageous here.
• ligands having from 2 to 11 carbon atoms Particular preference is given to ligands having from 2 to 11 carbon atoms. Very particular preference is given to using ligands selected from the group consisting of ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1 ,2-propylenediamine, trimethylenetetramine, hexamethylenetetramine.
• EDA ethylenediamine
• the process of the invention allows the deposition of white platinum-rhodium layers, in particular on decorative metal articles made of silver, in an economically advantageous way.
• the whiteness (lightness) of an about 50:50 alloy is significantly increased over that which would have been expected theoretically and approximates that of alloys containing > 90% of rhodium metal (Overview 1 ).
• Rhodium-platinum alloy
• Electrolytically deposited platinum layers having improved whiteness and electrolyte for this purpose
• Electrolyte composition :
• Anodes MMO (type Platinode ® 177; titanium anodes coated with mixed metal oxide for strongly acidic rhodium or platinum electrolytes, commercially available from Umicore
• Deposition rate about 0.084 ⁇ m/min (at 2.0 A/dm 2 )
• Fig. 1 The lightness (whiteness) of the coating is shown here as a function of the proportion of rhodium in the alloy. It can be seen that above a proportion of 40% of rhodium, the lightness of the alloy increases above the value to be expected theoretically.
• Fig. 2 The lightness (whiteness) of the coating is approximately constant when the applied current density is varied, as long as a current density of >2 A/dm 2 is selected.
• Fig. 4 The alloy composition remains approximately constant over a wide current density range from >2 A/dm 2 upwards.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
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• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electroplating Methods And Accessories (AREA)

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• 2008
  • 2008-10-04 DE DE102008050135A patent/DE102008050135B4/de not_active Expired - Fee Related
• 2009
  • 2009-09-23 US US13/122,371 patent/US20110308959A1/en not_active Abandoned
  • 2009-09-23 KR KR1020117010196A patent/KR20110071106A/ko not_active Application Discontinuation
  • 2009-09-23 WO PCT/EP2009/006874 patent/WO2010037495A1/en active Application Filing
  • 2009-09-23 EP EP09778674A patent/EP2344684A1/en not_active Withdrawn
  • 2009-09-23 JP JP2011529465A patent/JP2012504701A/ja not_active Withdrawn
  • 2009-09-23 CN CN2009801386317A patent/CN102171387B/zh not_active Expired - Fee Related
  • 2009-09-24 TW TW098132331A patent/TW201026909A/zh unknown

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