WO2004001101A2 - Electrolytic bath for the electrodeposition of noble metals and their alloys - Google Patents

Electrolytic bath for the electrodeposition of noble metals and their alloys Download PDF

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WO2004001101A2
WO2004001101A2 PCT/EP2003/006637 EP0306637W WO2004001101A2 WO 2004001101 A2 WO2004001101 A2 WO 2004001101A2 EP 0306637 W EP0306637 W EP 0306637W WO 2004001101 A2 WO2004001101 A2 WO 2004001101A2
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electrolytic bath
accordance
silver
alloys
sources
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PCT/EP2003/006637
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French (fr)
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WO2004001101A3 (en
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Pietro Luigi Cavallotti
Massimiliano Bestetti
Antonello Vicenzo
Luca Magagnin
Massimo Seregni
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Politecnico Di Milano
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    • 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

Definitions

  • the present invention refers to an electrolytic bath for the electrodeposition of noble metals, of their alloys, with or without tin and the electrodeposition of noble metals, of their alloys, with or without tin using said bath.
  • the baths used for the electrodeposition of noble metals normally contain cyanides and therefore are highly toxic, need special attention during the electrodeposition process and also require special treatments of the waste waters from the spent baths.
  • object of the present invention is to provide an electrolytic bath for the electrodeposition of noble metals and their alloys with tin that is free of cyanides.
  • said object is achieved by means of un electrolytic bath for the electrodeposition of noble metals and their alloys comprising: noble metal sources; halides; stabilizing additives; thiourea; acids.
  • said object is also achieved by means of the electrodeposition of noble metals and their alloys by means of an electrolytic bath in accordance with claim 1.
  • the present invention acid solutions and solutions free of cyanides can be produced.
  • the copper is present as cuprous and not cupric ion.
  • the composition of the solution is simple and permits easy control of the composition of the electrodeposited alloys.
  • acid is intended as sulphuric acid, sulphamic acid, succinic acid, hydrochloric acid, phosphoric acid (Au), fluoroboric acid (Ag, Cu).
  • halides we intend iodide, bromide and chloride of alkali metals or alkaline-earth metals.
  • silver sources we intend metallic silver (Ag), silver carbonate (Ag 2 CO 3 ), silver oxide (Ag 2 0), silver sulphate (Ag 2 S0 4 ), silver chloride (AgCl).
  • gold sources metallic gold (Au); solutions of sodium, potassium or ammonium sulphite of Au(I) (Na, K, NH 4 - AuSO 3 ); solutions of sodium or potassium gold chloride (Na, K - AuCl 4 ); gold chloride acid (HAuCl ).
  • copper sources we intend metallic copper (Cu), cuprous oxide (Cu O), cuprous chloride (CuCl).
  • tin sources we intend stannous oxide (SnO), stannous sulphate (SnS0 4 ), tin methanesulfonate (Sn(CH 3 S0 3 ) 2 ).
  • stabilizing additives we intend pyrocatechol (C 6 O 2 H 6 ), hydroquinone, ascorbic acid (C 6 H 8 O 6 ), glucose (C 6 H ⁇ 2 0 6 ) (Au), lactose (Au).
  • the composition of the Ag-Sn alloys can be controlled in particular by acting on the concentrations of the ions Ag(I) and Sn(II) in solution and on the current density.
  • the preparation of the deposition solution is carried out by diluting or dissolving the chemical reagents listed in the recipe in water according to the following schedule: • dilution of the sulphuric acid in distilled water;
  • the electrodeposition is conducted according to the usual procedure, making electric current circulate in a cell composed of an anode and a cathode immerged in the electrolytic solution described above.
  • the electrode functioning as anode must be pure silver, while that functioning as cathode can be metal or a different alloy, as long as it is pre-silver-plated.
  • Deposits of pure silver are obtained at direct current up to 40mA/cm 2 , from ambient temperature to 40°C and stirred electrolyte from solution:
  • the substrate can be brass or copper, previously coated with a fine film of silver by immersion, steel, nickel or silver and its alloys with copper.
  • the pre-silver-plating solution is the following:
  • the deposits with thickness up to 50 ⁇ m, of colour ranging from silver grey to milk white, are semi-shiny or opaque in relation to the current and to the temperature.
  • the deposits are obtained, even with higher thickness, with semi-shiny appearance and greyish- white colouring, at current from 10 to 40 mA/cm at 40°C with stirred bath, with growing speed of about 0.6 at about 2 ⁇ m/min.
  • the substrate can be brass or copper, previously coated with a fine film of Ag by immersion, or silver and its alloys with copper.
  • the pre-silver-plating solution is the following
  • the deposits With thickness up to 10 ⁇ m, become from semi-shiny opaque on the diminishing of the content of tin in alloy, with colouring from silver grey to white.
  • Example 3 Deposits of alloy with composition Ag-Sn from 16 to 20%at are obta liinneedd iinn ddiirreecctt ccuurrrreenntt from 4 to 8 mA/cm , ambient temperature and tin electrolyte from solution
  • the substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or silver and its alloys with copper.
  • the deposits, with thickness up to 10 ⁇ m, are semi-shiny or shiny, of a silver grey colour if Sn ⁇ 16%at circa.
  • the substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or silver and its alloys with copper.
  • the deposits with thickness up to 10 ⁇ m, are opaque and even.
  • the solutions at examples 2 to 4 permit first pure silver to be deposited, in the same conditions mentioned above except that the stirring of the bath, that should be vigorous; and successively, excluding the devices by means of which the stirring is carried out, a coating of Ag-Sn alloy, according to what is indicated in the examples, without modifying any other operative parameter.
  • Tin anode is used and vigorous stirring of the solution.
  • the substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or steel.
  • Tin anode is used and vigorous stirring of the solution.
  • the substrate can be brass, copper or steel.
  • the deposits of pure silver possess a bland preferential orientation (111) and grain of dimensions from 1 to 5 ⁇ m, in relation to the thickness and to the deposition temperature.
  • phase structure of the deposits of Ag-Sn alloy changes in relation to the content of Sn in alloy according to the phase succession: solid solution of Sn in Ag with face-centered cubic lattice (cfc) for content of Sn up to about 10%at (1 l%wt); intermediate phase ⁇ with hexagonal lattice with diminishing axial ratio with the content of Sn, in the interval of composition from about 13 to 24%at (from 14 to 26%wt); biphasic structures ⁇ + ⁇ Sn for content of Sn in alloy exceeding about 24%at (26%wt).
  • the mechanical properties of the coatings of Ag-Sn with content of Sn from 13 to 24%at have been characterised by means of measurements of micro-indentation at variable load.
  • the micro hardness resulted as 260HV and practically independent from the load up to 500mN.
  • the modulus of elasticity is about 85GPa.
  • Micro hardness and modulus of elasticity show only a slight growth at the increase of the content of Sn of the alloy of phase ⁇ and can substantially be considered constant in the interval from 12 to 24% of content of Sn.
  • the micro hardness of the silver electrodeposited is around 100HV; lower values (about 60 HV) are typical are typical of the massive silver at the annealed state.
  • the samples are exposed to vapours of thioacetamide, in atmosphere with relative humidity at 75%, regulated by means of a saturate solution of sodium acetate.
  • the coatings of silver coated with Ag-Sn alloy and with Ag ⁇ are exposed to vapours of thioacetamide, in atmosphere with relative humidity at 75%, regulated by means of a saturate solution of sodium acetate.
  • Sn alloy have shown a resistance exceeding that of silver, both massive with titer 99.9% and electrodeposited.
  • the solution is used at temperatures from 25 to 40°C, direct current from 1 to 15 mA/cm 2 and is kept stirred.
  • direct current from 1 to 15 mA/cm 2
  • electrodeposition of Au-Sn alloys you work either in direct current or by means of pulse deposition, at temperatures from 25 to 40°C, under stirring.
  • the preparation of the deposition solution is carried out by diluting or dissolving in water the chemical reagents listed in the recipe according to the following schedule :
  • Example 7 Gold coatings, even at high thickness with interest for electroforming, are obtained at direct current up to 14 (20) mA/cm 2 and at 40°C from the following solution
  • the deposits are shiny (thickness up to 5 ⁇ m) or semi-shiny, with preferential orientation (111).
  • the surface micro hardness from measurements of microindentation, is always above about 100 HV and shows maximum values of about 150 HV (at load 10 mN on deposits of 5 ⁇ m).
  • the micro hardness results lower at the limit indicated int he case in which the direct current of deposition is lower than about 5 mA/cm 2 .
  • the anode is of Au 999 and the bath is kept stirred.
  • Au-Sn alloys with content of Sn from 4 to 1 l%at (from 2.5 to 7%wt) are obtained by deposition in direct current from the following solution :
  • the temperature is 40°C, the stirred bath and the direct current variable from 5 to 12 mA/cm 2 , the content of Sn in alloy growing with the direct current.
  • the deposits are shiny, uniform and of a pale yellow colour up to about Sn 6%at, with silver grey reflections for higher contents of Sn.
  • the anode is of Au 999 and the bath is kept stirred.
  • the deposits can be obtained with thickness up to about 5 ⁇ m.
  • Au-Sn alloys with content of Sn in the interval from 7.5 to 9.5 %at (from 4.5 to 6%wt) are obtained by deposition at pulsed current from the following solution
  • the temperature is 40°C
  • the anode is of Au 999 and the bath is kept stirred.
  • t on is the duration of the current pulse at direct current indicated in correspondence and t 0ff is the duration of the pulse at nil current.
  • Au-Sn alloys with content of Sn in the interval from about 10 to 16%at (from 6 to 10%wt) are obtained by deposition at pulsed current from the following solution
  • the temperature is 40°C
  • the anode is of Au 999 and the bath is kept stirred.
  • t on is the duration of the current pulse at direct current indicated in correspondence and t 0ff is the duration of the pulse at nil current.
  • Au-Sn alloys with content of Sn about 36%at (25%wt) are obtained by deposition at pulsed current from the composition solution as shown in example 9.
  • the temperature is 40°C
  • the anode is of Au 999 and the bath is kept stirred.
  • t on is the duration of the current pulse at direct current indicated in correspondence and t 0ff is the duration of the pulse at nil current.
  • Au-Sn alloys with content of Sn about 48%at (35%wt) are obtained by deposition at pulsed current from the composition solution as shown in example 9.
  • the temperature is 40°C
  • the anode is of Au 999 and the bath is kept stirred.
  • t on is the duration of the current pulse at direct current indicated in correspondence and t off is the duration of the pulse at nil current.
  • phase structure of the deposits of alloy Au-Sn is characterised by the presence of three phases: for content of Sn up to about 5%at, the deposits have face-centered cubic lattice; for content of Sn of between 10%at and about 16%at the deposits have hexagonal lattice with axial ratio variable with the content of Sn, corresponding to the phase ⁇ of the equilibrium diagram; in the interval between 5%at and 10%at the deposits are biphasic (fee + hep); for content of Sn exceeding about 16%at the deposits are biphasic ⁇ + ⁇ -AuSn.
  • the microhardness (load 10 mN, film of 3 ⁇ m) of the deposits of Au-Sn increases from about 100 HV for pure Au up to about 150 HV within the phase region ⁇ . With the further increase of the content of Sn up to about 13%at (about 8%wt) there is a marked increase, with maximum values around 250 HV.
  • the deposits with content of Sn in the interval from about 13 to about 25%at (about 16.5%wt) have microhardness values around 150 HV; for content of Sn exceeding and up to about 50%at ( ⁇ 37.5%wt) the microhardness again increases and remains around 200 HV.
  • the modulus of elasticity has a maximum of about 120 GPa around 10%at ( ⁇ 6%wt) of the content of Sn and remains in the interval 80-100 GPa for content of Sn of between 10 and 50%at.
  • the composition of the Cu-Sn alloys can be controlled by acting on the concentrations in solution of the ions Cu(I), Sn(II) and thiourea and on the current density.
  • Zinc salts (such as sulphate, halides, carbonate, oxide) are suitably added in small quantities (from 0.001 to 0.5 mol/1) to improve the appearance of the deposits and the resistance to blackening in regard to the case in which there is no zinc in solutions.
  • the preparation of the deposition solution is carried out by diluting or dissolving in water the chemical reagents listed in the recipe according to the following schedule:
  • the electrodeposition of the copper-tin alloys comes about by circulating electric current in a cell containing the above described electrolyte between an anode and a cathode.
  • the electrode functioning as anode must be copper or tin or copper-tin alloy according to the composition of alloy of the final product, while that functioning as cathode can be metal or different alloy.
  • Deposits of pure Cu are obtained at direct current of lOmA/cm , at temperatures of about 55°C and electrolyte stirring.
  • Copper anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of ⁇ m, of a pink colour, are semi-shiny or opaque in relation to the direct current and to the temperature.
  • Deposits containing Cu 91at% Sn 8.7at% S 0.3at% are obtained at direct current of 10mA/cm2, at temperatures of 60°C and electrolyte stirring.
  • Copper anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of ⁇ m, of a pink colour, are semi-shiny.
  • Deposits containing Cu 75 at% Sn 17 at% S 8 at% are obtained at direct current of 10 mA/cm 2 , at temperatures of 60°C and electrolyte stirring.
  • Copper anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of ⁇ m, of a pink-yellow colour, are semi-shiny.
  • Deposits containing Cu 73 at% Sn 27 at% are obtained at direct current of lOmA/cm , at temperatures of 60°C and electrolyte stirring.
  • Copper anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of ⁇ m, of a pink-yellow colour, are semi-shiny.
  • Deposits containing Cu 55at% Sn 45at% are obtained at direct current of 20mA/cm 2 , at temperatures of 60°C and electrolyte stirring.
  • Copper anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of ⁇ m, of a pale grey colour have a glazed appearance.
  • Deposits containing Cu 2 at% Sn 98 at% are obtained at direct current of 80mA/cm 2 , at temperatures of 45°C and electrolyte stirring.
  • Tin anode is used.
  • the substrate can be brass, copper, steel, nickel or silver and its alloys with copper.
  • the deposits, of a few tenths of Dm, of a pale grey colour, are opaque.
  • Au-Cu alloy anode is used.
  • the substrate can be gold and alloys, or any metal substrate on condition that are gilt.
  • the deposits, with thickness until to 10 ⁇ m, are semi-shine or shine, with pink colour.
  • the electrolytic bath for the electrodeposition of noble metals and their alloys with tin comprises the following elements with the relative concentrations.
  • concentrations are as follows.
  • the electrodeposition of Cu and Cu-Sn alloys can be used for different purposes. Electrodeposition of copper for covering not very noble substrates. Cu-Sn alloys at a low content of tin ( ⁇ 1%) for applications in microelectronics (metallization in copper with improved properties of resistance to electromigration). Cu-Sn20% alloys as decorative finishing (yellow). Cu-Sn45% alloys as functional or decorative finishing (white) in replacement of nickel (allergenic). Sn-Cu alloys (about 0.7%) as weldable covering in replacement of alloys containing lead.
  • the electrodeposition of Ag and of Ag-Sn alloys, with weight content of tin in the interval 15-22% can be used as protective finishing of silver against blackening due to sulphuration, carrying out the function of conserving the aesthetical and functional characteristics ofthe surface.
  • the electrodeposition of Au and Au-Sn alloys can be used for different purposes: in the decorative field as finishing for costume jewellery and for functional applications as weldable alloy (eutectic Au-Sn).
  • the electrodeposition of noble metals and gold alloys with tin can be used as covering for manufactured products (vases, jewellery and various objects); for electric and electronic contacts; for metallization in electronic devices for telecommunications and in microelectronics, and for weldable coatings for electronics.
  • copper from acid thiourea solutions can be used for covering the steel cords used for reinforcing pneumatic tyres.
  • the reinforcements are generally made up of carbon steel wires having a diameter around tenths of a millimetre.
  • the copper covering is conventionally followed by a coating of zinc and a successive treatment of thermal diffusion ofthe zinc in the copper to form brass.

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Abstract

The present invention herein refers to an electrolytic bath for the electrodeposition of noble metals, of their alloys, with or without tin and to the electrodeposition of noble metals and their alloys with tin using said bath. In an embodiment the electrolytic bath for the electrodeposition of noble metals and their alloys comprises: noble metal sources; halides; stabilizing additives; thiourea; acids.

Description

"Electrolytic bath for the electrodeposition of noble metals and their alloys"
* * * *
DESCRPTION
The present invention refers to an electrolytic bath for the electrodeposition of noble metals, of their alloys, with or without tin and the electrodeposition of noble metals, of their alloys, with or without tin using said bath.
The baths used for the electrodeposition of noble metals normally contain cyanides and therefore are highly toxic, need special attention during the electrodeposition process and also require special treatments of the waste waters from the spent baths.
In view of the state of the technique described, object of the present invention is to provide an electrolytic bath for the electrodeposition of noble metals and their alloys with tin that is free of cyanides. In accordance with the present invention, said object is achieved by means of un electrolytic bath for the electrodeposition of noble metals and their alloys comprising: noble metal sources; halides; stabilizing additives; thiourea; acids.
In accordance with the present invention, said object is also achieved by means of the electrodeposition of noble metals and their alloys by means of an electrolytic bath in accordance with claim 1.
Thanks to the present invention, acid solutions and solutions free of cyanides can be produced. In the case of the solutions of copper and copper tin, the copper is present as cuprous and not cupric ion. The composition of the solution is simple and permits easy control of the composition of the electrodeposited alloys.
In the case of the process of Ag and Ag-Sn alloys, an important peculiarity is found in the fact that the solution permits the depositing of Ag and AgSn in succession. In other words, with only one bath the silver film can be silver-plated and then coated with a protective layer of AgSn, regulating the thicknesses deposited of the two metals according to convenience.
The characteristics and advantages of the present invention will appear evident from the following detailed description of an embodiment thereof, illustrated as non-limiting example.
Following the description and the successive claims, the term acid is intended as sulphuric acid, sulphamic acid, succinic acid, hydrochloric acid, phosphoric acid (Au), fluoroboric acid (Ag, Cu).
By the term halides we intend iodide, bromide and chloride of alkali metals or alkaline-earth metals.
By the term silver sources we intend metallic silver (Ag), silver carbonate (Ag2CO3), silver oxide (Ag20), silver sulphate (Ag2S04), silver chloride (AgCl).
By the term gold sources we intend: metallic gold (Au); solutions of sodium, potassium or ammonium sulphite of Au(I) (Na, K, NH4 - AuSO3); solutions of sodium or potassium gold chloride (Na, K - AuCl4); gold chloride acid (HAuCl ).
By the term copper sources we intend metallic copper (Cu), cuprous oxide (Cu O), cuprous chloride (CuCl). By the term tin sources we intend stannous oxide (SnO), stannous sulphate (SnS04), tin methanesulfonate (Sn(CH3S03)2).
By the term stabilizing additives (reducers) we intend pyrocatechol (C6O2H6), hydroquinone, ascorbic acid (C6H8O6), glucose (C6Hι206) (Au), lactose (Au). The composition of the Ag-Sn alloys can be controlled in particular by acting on the concentrations of the ions Ag(I) and Sn(II) in solution and on the current density.
The preparation of the deposition solution is carried out by diluting or dissolving the chemical reagents listed in the recipe in water according to the following schedule: • dilution of the sulphuric acid in distilled water;
• addition of silver carbonate, keeping the solution stirred and at about 50°C, and its complete dissolution;
• addition of thiourea (CS(NH2)2), potassium iodide, stannous sulphate and pyrocatechol.
Then you proceed to regulating the final volume of the solution. The electrodeposition is conducted according to the usual procedure, making electric current circulate in a cell composed of an anode and a cathode immerged in the electrolytic solution described above. The electrode functioning as anode must be pure silver, while that functioning as cathode can be metal or a different alloy, as long as it is pre-silver-plated.
Example 1.
Deposits of pure silver are obtained at direct current up to 40mA/cm2, from ambient temperature to 40°C and stirred electrolyte from solution:
Figure imgf000004_0001
Silver anode is used. The substrate can be brass or copper, previously coated with a fine film of silver by immersion, steel, nickel or silver and its alloys with copper. The pre-silver-plating solution is the following:
Figure imgf000005_0001
The deposits, with thickness up to 50 μm, of colour ranging from silver grey to milk white, are semi-shiny or opaque in relation to the current and to the temperature.
Example La
Figure imgf000005_0002
Deposits of silver with thickness up to 20μm, opaque and white, are obtained at 10 mA/cm2 and at stirred bath ambient temperature, with growing speed of about 0.6 μm/min.
Example 1.b
Figure imgf000005_0003
The deposits are obtained, even with higher thickness, with semi-shiny appearance and greyish- white colouring, at current from 10 to 40 mA/cm at 40°C with stirred bath, with growing speed of about 0.6 at about 2μm/min.
Example 2.
Deposits of alloy with composition Ag-Sn up to 10%at are obtained at direct current from 10 to 20 mA/cm , ambient temperature and stirred electrolyte from solution
Figure imgf000006_0001
Silver anode is used. The substrate can be brass or copper, previously coated with a fine film of Ag by immersion, or silver and its alloys with copper. The pre-silver-plating solution is the following
Figure imgf000006_0002
The deposits, with thickness up to 10 μm, become from semi-shiny opaque on the diminishing of the content of tin in alloy, with colouring from silver grey to white.
Example 3. Deposits of alloy with composition Ag-Sn from 16 to 20%at are obta liinneedd iinn ddiirreecctt ccuurrrreenntt from 4 to 8 mA/cm , ambient temperature and tin electrolyte from solution
Figure imgf000007_0001
Silver anode is used. The substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or silver and its alloys with copper. The deposits, with thickness up to 10 μm, are semi-shiny or shiny, of a silver grey colour if Sn < 16%at circa.
Example 4.
Deposits of alloy with composition Ag-Sn from 20 to 24%at are obtained at direct current from 5 to 10 mA/cm2, ambient temperature and tin electrolyte from solution
Figure imgf000007_0002
Silver anode is used. The substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or silver and its alloys with copper. The deposits, with thickness up to 10 μm, are opaque and even.
The solutions at examples 2 to 4 permit first pure silver to be deposited, in the same conditions mentioned above except that the stirring of the bath, that should be vigorous; and successively, excluding the devices by means of which the stirring is carried out, a coating of Ag-Sn alloy, according to what is indicated in the examples, without modifying any other operative parameter.
Example 5.
Deposits of alloy with composition type Ag-Sn85%at are obtained at direct current of 12 mA/cm2 and ambient temperature from solution
Figure imgf000008_0001
Tin anode is used and vigorous stirring of the solution. The substrate can be brass or copper, previously coated with a fine film of Ag by immersion (see example 2), or steel.
Example 6.
Deposits of alloy with composition type Ag-Sn96%at are obtained at direct current of 5 mA/cm and ambient temperature from solution
Figure imgf000009_0001
Tin anode is used and vigorous stirring of the solution. The substrate can be brass, copper or steel.
The deposits of pure silver possess a bland preferential orientation (111) and grain of dimensions from 1 to 5 μm, in relation to the thickness and to the deposition temperature.
The phase structure of the deposits of Ag-Sn alloy changes in relation to the content of Sn in alloy according to the phase succession: solid solution of Sn in Ag with face-centered cubic lattice (cfc) for content of Sn up to about 10%at (1 l%wt); intermediate phase ζ with hexagonal lattice with diminishing axial ratio with the content of Sn, in the interval of composition from about 13 to 24%at (from 14 to 26%wt); biphasic structures ζ + βSn for content of Sn in alloy exceeding about 24%at (26%wt).
The mechanical properties of the coatings of Ag-Sn with content of Sn from 13 to 24%at (about from 14 to 24%wt) have been characterised by means of measurements of micro-indentation at variable load. The micro hardness resulted as 260HV and practically independent from the load up to 500mN. The modulus of elasticity is about 85GPa. Micro hardness and modulus of elasticity show only a slight growth at the increase of the content of Sn of the alloy of phase ζ and can substantially be considered constant in the interval from 12 to 24% of content of Sn. The micro hardness of the silver electrodeposited is around 100HV; lower values (about 60 HV) are typical are typical of the massive silver at the annealed state.
The resistance to sulphuration has been assessed according to the procedure prescribed by the standard UNI EN ISO 4538:1998 (test of exposure to the thioacetamide).
The samples are exposed to vapours of thioacetamide, in atmosphere with relative humidity at 75%, regulated by means of a saturate solution of sodium acetate. The coatings of silver coated with Ag-Sn alloy and with Ag¬
Sn alloy have shown a resistance exceeding that of silver, both massive with titer 99.9% and electrodeposited.
For the electrodeposition of gold, the solution is used at temperatures from 25 to 40°C, direct current from 1 to 15 mA/cm2 and is kept stirred. For the electrodeposition of Au-Sn alloys, you work either in direct current or by means of pulse deposition, at temperatures from 25 to 40°C, under stirring.
In both cases a soluble gold anode is used.
The preparation of the deposition solution is carried out by diluting or dissolving in water the chemical reagents listed in the recipe according to the following schedule :
• dilution of the sulphuric acid in distilled water;
• addition of the thiourea to the solution, keeping it at a relatively high temperature (50-60°C); • addition of the gold salt (I);
• addition of the pyrocatechol.
Then you proceed with then usual operations correcting the acidity and regulating the volume.
Example 7. Gold coatings, even at high thickness with interest for electroforming, are obtained at direct current up to 14 (20) mA/cm2 and at 40°C from the following solution
Figure imgf000011_0001
The deposits are shiny (thickness up to 5 μm) or semi-shiny, with preferential orientation (111). The surface micro hardness, from measurements of microindentation, is always above about 100 HV and shows maximum values of about 150 HV (at load 10 mN on deposits of 5 μm). The micro hardness results lower at the limit indicated int he case in which the direct current of deposition is lower than about 5 mA/cm2. The anode is of Au 999 and the bath is kept stirred.
Example 8.
Au-Sn alloys with content of Sn from 4 to 1 l%at (from 2.5 to 7%wt) are obtained by deposition in direct current from the following solution :
Figure imgf000011_0002
The temperature is 40°C, the stirred bath and the direct current variable from 5 to 12 mA/cm2, the content of Sn in alloy growing with the direct current. The deposits are shiny, uniform and of a pale yellow colour up to about Sn 6%at, with silver grey reflections for higher contents of Sn. The anode is of Au 999 and the bath is kept stirred. The deposits can be obtained with thickness up to about 5μm.
Example 9.
Au-Sn alloys with content of Sn in the interval from 7.5 to 9.5 %at (from 4.5 to 6%wt) are obtained by deposition at pulsed current from the following solution
Figure imgf000012_0001
The temperature is 40°C, the anode is of Au 999 and the bath is kept stirred.
The following table shows two examples with the data relating to the pulsed current feed; ton is the duration of the current pulse at direct current indicated in correspondence and t0ff is the duration of the pulse at nil current.
Figure imgf000012_0002
Example 10.
Au-Sn alloys with content of Sn in the interval from about 10 to 16%at (from 6 to 10%wt) are obtained by deposition at pulsed current from the following solution
Figure imgf000013_0001
The temperature is 40°C, the anode is of Au 999 and the bath is kept stirred.
The following table shows two examples with the data relating to the pulsed current feed; ton is the duration of the current pulse at direct current indicated in correspondence and t0ff is the duration of the pulse at nil current.
Figure imgf000013_0002
Example 11.
Au-Sn alloys with content of Sn about 36%at (25%wt) are obtained by deposition at pulsed current from the composition solution as shown in example 9.
The temperature is 40°C, the anode is of Au 999 and the bath is kept stirred.
The following table shows two examples with the data relating to the pulsed current feed; ton is the duration of the current pulse at direct current indicated in correspondence and t0ff is the duration of the pulse at nil current.
Figure imgf000014_0001
Example 12.
Au-Sn alloys with content of Sn about 48%at (35%wt) are obtained by deposition at pulsed current from the composition solution as shown in example 9.
The temperature is 40°C, the anode is of Au 999 and the bath is kept stirred.
The following table shows two examples with the data relating to the pulsed current feed; ton is the duration of the current pulse at direct current indicated in correspondence and toff is the duration of the pulse at nil current.
Figure imgf000014_0002
The phase structure of the deposits of alloy Au-Sn is characterised by the presence of three phases: for content of Sn up to about 5%at, the deposits have face-centered cubic lattice; for content of Sn of between 10%at and about 16%at the deposits have hexagonal lattice with axial ratio variable with the content of Sn, corresponding to the phase ζ of the equilibrium diagram; in the interval between 5%at and 10%at the deposits are biphasic (fee + hep); for content of Sn exceeding about 16%at the deposits are biphasic ζ + δ-AuSn.
The microhardness (load 10 mN, film of 3 μm) of the deposits of Au-Sn increases from about 100 HV for pure Au up to about 150 HV within the phase region ζ. With the further increase of the content of Sn up to about 13%at (about 8%wt) there is a marked increase, with maximum values around 250 HV. The deposits with content of Sn in the interval from about 13 to about 25%at (about 16.5%wt) have microhardness values around 150 HV; for content of Sn exceeding and up to about 50%at (~37.5%wt) the microhardness again increases and remains around 200 HV. The modulus of elasticity has a maximum of about 120 GPa around 10%at (~6%wt) of the content of Sn and remains in the interval 80-100 GPa for content of Sn of between 10 and 50%at. The composition of the Cu-Sn alloys can be controlled by acting on the concentrations in solution of the ions Cu(I), Sn(II) and thiourea and on the current density. Zinc salts (such as sulphate, halides, carbonate, oxide) are suitably added in small quantities (from 0.001 to 0.5 mol/1) to improve the appearance of the deposits and the resistance to blackening in regard to the case in which there is no zinc in solutions.
The preparation of the deposition solution is carried out by diluting or dissolving in water the chemical reagents listed in the recipe according to the following schedule:
• dilution of the sulphuric acid in distilled water; • addition ofthe thiourea to the solution, keeping it at a relatively high temperature (50-60°C);
• addition ofthe copper salt (I) or the copper oxide (I);
• addition of the pyrocatechol.
Then you proceed to the usual operations of correcting the acidity and regulating the volume.
The electrodeposition of the copper-tin alloys comes about by circulating electric current in a cell containing the above described electrolyte between an anode and a cathode. The electrode functioning as anode must be copper or tin or copper-tin alloy according to the composition of alloy of the final product, while that functioning as cathode can be metal or different alloy.
Example 13.
Deposits of pure Cu are obtained at direct current of lOmA/cm , at temperatures of about 55°C and electrolyte stirring.
Figure imgf000016_0001
Copper anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of μm, of a pink colour, are semi-shiny or opaque in relation to the direct current and to the temperature.
Example 14.
Deposits containing Cu 91at% Sn 8.7at% S 0.3at% are obtained at direct current of 10mA/cm2, at temperatures of 60°C and electrolyte stirring.
Figure imgf000016_0002
Copper anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of μm, of a pink colour, are semi-shiny.
Example 15.
Deposits containing Cu 75 at% Sn 17 at% S 8 at% are obtained at direct current of 10 mA/cm2, at temperatures of 60°C and electrolyte stirring.
Figure imgf000017_0001
Copper anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of μm, of a pink-yellow colour, are semi-shiny.
Example 16.
Deposits containing Cu 73 at% Sn 27 at% are obtained at direct current of lOmA/cm , at temperatures of 60°C and electrolyte stirring.
Figure imgf000017_0002
Copper anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of μm, of a pink-yellow colour, are semi-shiny.
Example 17.
Deposits containing Cu 55at% Sn 45at% are obtained at direct current of 20mA/cm2, at temperatures of 60°C and electrolyte stirring.
Figure imgf000018_0001
Copper anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of μm, of a pale grey colour have a glazed appearance.
Example 18.
Deposits containing Cu 2 at% Sn 98 at% are obtained at direct current of 80mA/cm2, at temperatures of 45°C and electrolyte stirring.
Figure imgf000018_0002
Tin anode is used. The substrate can be brass, copper, steel, nickel or silver and its alloys with copper. The deposits, of a few tenths of Dm, of a pale grey colour, are opaque.
According to the present invention, it is also possible to deposit binary and ternary alloys of noble metals with or without tin.
Example 19.
Deposits of Au-Cu alloys with Cu composition of about 60%at are obtained with pulsed current (20 mA/cm2 for 0.2 seconds and nil current for 0.5 seconds), at 40°C and from the following solution
Figure imgf000019_0001
Au-Cu alloy anode is used. The substrate can be gold and alloys, or any metal substrate on condition that are gilt. The deposits, with thickness until to 10 μm, are semi-shine or shine, with pink colour.
In accordance with the present invention, the electrolytic bath for the electrodeposition of noble metals and their alloys with tin comprises the following elements with the relative concentrations.
Figure imgf000019_0002
More preferably the concentrations are as follows.
Figure imgf000020_0001
The electrodeposition of Cu and Cu-Sn alloys can be used for different purposes. Electrodeposition of copper for covering not very noble substrates. Cu-Sn alloys at a low content of tin (<1%) for applications in microelectronics (metallization in copper with improved properties of resistance to electromigration). Cu-Sn20% alloys as decorative finishing (yellow). Cu-Sn45% alloys as functional or decorative finishing (white) in replacement of nickel (allergenic). Sn-Cu alloys (about 0.7%) as weldable covering in replacement of alloys containing lead. The electrodeposition of Ag and of Ag-Sn alloys, with weight content of tin in the interval 15-22% can be used as protective finishing of silver against blackening due to sulphuration, carrying out the function of conserving the aesthetical and functional characteristics ofthe surface.
The electrodeposition of Au and Au-Sn alloys can be used for different purposes: in the decorative field as finishing for costume jewellery and for functional applications as weldable alloy (eutectic Au-Sn).
Therefore the electrodeposition of noble metals and gold alloys with tin can be used as covering for manufactured products (vases, jewellery and various objects); for electric and electronic contacts; for metallization in electronic devices for telecommunications and in microelectronics, and for weldable coatings for electronics.
In addition copper from acid thiourea solutions can be used for covering the steel cords used for reinforcing pneumatic tyres. The reinforcements are generally made up of carbon steel wires having a diameter around tenths of a millimetre. The copper covering is conventionally followed by a coating of zinc and a successive treatment of thermal diffusion ofthe zinc in the copper to form brass.

Claims

I. Electrolytic bath for the electrodeposition of noble metals and their alloys comprising: noble metal sources; zinc salts; halides; stabilizing additives; thiourea; acids.
2. Electrolytic bath in accordance with claim 1 characterised in that it comprises tin sources.
3. Electrolytic bath in accordance with claim 2 characterised in that said tin sources include stannous oxide, stannous sulphate, tin methanesulfonate.
4. Electrolytic bath in accordance with claim 1 characterised in that said halides include iodide, bromide e chloride of alkaline metals or alkaline- earth metals.
5. Electrolytic bath in accordance with claim 1 characterised in that said acids include sulphuric acid, sulphamic acid, succinic acid, hydrochloric acid, phosphoric acid, fluoroboric acid.
6. Electrolytic bath in accordance with claim 1 characterised in that said stabilizing additives include pyrocatechol, hydroquinone, ascorbic acid, glucose, lactose.
7. Electrolytic bath in accordance with claim 1 characterised in that said noble metal sources include gold sources.
8. Electrolytic bath in accordance with claim 1 characterised in that said noble metal sources include silver sources.
9. Electrolytic bath in accordance with claim 1 characterised in that said noble metal sources include copper sources.
10. Electrolytic bath in accordance with claim 7 characterised in that said gold sources include: metallic gold; solution of sodium, potassium or ammonium sulphite of gold; sodium or potassium tetrachloride of gold, gold chloride acid.
I I . Electrolytic bath in accordance with claim 8 characterised in that said silver sources include metallic silver, silver carbonate, silver oxide, silver sulphate, silver chloride.
12. Electrolytic bath in accordance with claim 9 characterised in that said copper sources include metallic copper, cuprous oxide, cuprous chloride.
13. Electrolytic bath in accordance with claim 1 characterised in that it comprises: noble metal sources in quantities of between 0.0001 and 1 mol/1; zinc salts in quantities of between 0.0001 and 1 mol/1; stabilizing additives in quantities of between 0.0001 and 0.5 mol/1; thiourea in quantities of between 0.1 and 3 mol/1; acids in quantities of between 0.05 and 2 mol/1.
14. Electrolytic bath in accordance with claim 1 characterised in that it comprises tin sources in quantities of between 0.001 and 0.5 mol/1.
15. Electrolytic bath in accordance with claim 1 characterised in that it comprises zinc salts.
16. Electrolytic bath in accordance with claim 15 characterised in that it comprises zinc salts in quantities of between 0.0001 and 1 mol/1.
17. Electrodeposition of noble metals and their alloys by means of an electrolytic bath in accordance with claim 1.
18. Electrodeposition of noble metals and their alloys in accordance with claim 15 characterised in that said electrodeposition is carried out on metallic wires and metallic hardware.
PCT/EP2003/006637 2002-06-24 2003-06-23 Electrolytic bath for the electrodeposition of noble metals and their alloys WO2004001101A2 (en)

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EP1876267A2 (en) 2006-07-06 2008-01-09 Matsushita Electric Works, Ltd. Silver layer formed by electrosilvering substrate material
EP1876267A3 (en) * 2006-07-06 2008-07-09 Matsushita Electric Works, Ltd. Silver layer formed by electrosilvering substrate material
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US10260159B2 (en) * 2013-07-05 2019-04-16 The Boeing Company Methods and apparatuses for mitigating tin whisker growth on tin and tin-plated surfaces by doping tin with gold
CN104120463A (en) * 2014-06-25 2014-10-29 济南大学 Cyanide-free cuprous copper-plating surface modification method for steel matrix
CN104120468A (en) * 2014-06-25 2014-10-29 济南大学 Cyanide-free cuprous copper-zinc alloy electroplating solution
CN110396705A (en) * 2019-08-07 2019-11-01 中国科学院合肥物质科学研究院 The method of the porous silver of electrodeposited nanocrystalline
CN110396705B (en) * 2019-08-07 2021-08-31 中国科学院合肥物质科学研究院 Method for preparing nano porous silver by electrodeposition

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