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
  • C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals

Definitions

• This invention concerns platinum plating bath electrolytes.
• Precious metals are used as films on surfaces for a variety of reasons.
• precious metals including platinum
• Platinum are used to improve the appearance of an article and to create special effects.
• Platinum may be used as a film to protect metals and other materials from corrosion, such as the coating of bursting discs.
• Platinum films are also used to provide conducting paths in electrical circuits.
• Platinum films can have more than one use in a particular application, such as with platinised titanium electrodes, where the platinum film acts as an electrical conductor and also protects the titanium, allowing the electrodes to be used in corrosive environments.
• Platinised surfaces may also have a catalytic function, for example in the reduction of the hydrogen overpotential of anodes.
• platinum films are reacted with components of the substrate or with additional materials to create reaction products, such as in the coating of turbine blades and subsequent treatment to form the erosion- and corrosion-resistant platinum aluminide. Platinum alloy films may also be formed and treated in this way.
• Electroplated films find many other applications, for example the metallurgical and biological fields.
• platinum and platinum alloy films may be electro-deposited from a number of aqueous systems which are optimised for the particular application.
• Such processes are based on materials such as diamminedinitroplatinute(II) (platinum 'P' salt), alkali metal hexa- hydroxyplatinates(IV), hydrogen hexachloroplatinate(IV) and hydrogen dinitrosulphatoplatinate(II) (DNS), and present a variety of problems in use.
• a system or systems for the electro-deposition of platinum or platinum alloy films which overcome or improve upon a number of the difficulties described above is therefore highly desirable and there is considerable interest in the development of electrolytes which allow the rapid deposition of high quality, thick layers of platinum.
• EP 0358375 discloses a platinum or platinum-alloy electroplating bath comprising an alkaline aqueous solution of a complexed platinum(II) salt in which the anion component is a group or radical derived from an organic or inorganic acid other than a hydrohalic acid, in alkaline aqueous solution.
• An object of the present invention is to provide a further improved plating electrolyte.
• the platinum species in solution must be highly soluble and stable, but reduced readily so that platinum deposition then occurs at potentials positive to hydrogen evolution. These requirements can only be met by careful choice of ligands interacting with the platinum centre.
• the selection of plating electrolyte components is made more difficult by the fact that Pt(II) complexes are substitution inert and kinetic factors as well as thermodynamics determine their behaviour. For example, in the baths of EP 0358375 it may be demonstrated that it is the inertness of the Pt(NH,)j + which necessitates operating temperatures of above 9()°C. The reduction of Pt(NH 3 ) 4 2+ to Pt is strongly kinetically controlled.
• the present invention provides an improved platinum plating bath electrolyte comprising a platinum(H) salt in which the Pt(II) is present in solution as Pt(H O) ⁇
• Said plating electrolyte permits deposition of Pt with a current efficiency similar to that of the bath of EP 0358375, and. surprisingly, maintains its high performance over a wide range of temperatures, including room temperature. It may be shown that even at room temperature (15°C) or below. Pt(H O) 4 :+ undergoes facile reduction, and at a suitable temperature the reduction of Pt(II) to Pt is mass transport controlled. Hence, with a suitable choice of Pt(II) concentration and stirring conditions, it is possible to achieve a high rate of deposition even at room temperature.
• the anion component of the salt may suitably be one or more group or radical derived from an organic acid or an inorganic acid. Such anion component(s) may for example, but not exclusively, be selected from such inorganic acid groups as perchlorate, sulphate and phosphate.
• Temperatures of 0-100°C may be employed during use of the electrolyte. Preferably use is at a temperature between room temperature and 70°C.
• the concentration of the platinum salt may vary, and may be measured as platinum from 0.005 molar (lg/litre) to 0J50 molar (30g/litre) or more. Preferred platinum concentrations depend upon the plating rate, cell geometry and mode (vat or barrel), degree of agitation etc. but are typically around 0.005 molar (lg/litre) to 0J00 molar (20g/litre) such as 0.005 molar (lg/litre) to 0.025 molar (5g/litre).
• the electrolyte may be agitated or not depending on the application.
• Suitable substrates for plating are generally metal and alloy surfaces and other conducting surfaces.
• Typical metal surfaces are copper, gold, nickel, titanium and tungsten.
• Typical alloy surfaces are stainless steels, brass, nickel alloys and superalloys containing niobium, zirconium and vanadium.
• Other surfaces include conductive resins and composites.
• the surfaces may be prepared for plating by the use of conventional cleaning procedures and as necessary, the incorporation of an undercoat of nickel, gold or other metal before the deposition of platinum.
• the electroplating cell may utilise conventional or specialised anodes, as with existing electroplating systems, including carbon, graphite, platinum, platinised titanium, and iridised titanium.
• Current densities for plating according to the invention are suitably in the range 0.03-10 A dm '* , preferably OJ 0-2.5 A dm "2 .
• the Pt content of the Pt(H O) (ClO ) ; solution was determined by atomic absorption spectroscopy using a Perkin Elmer 2380 atomic absorption spectrometer with an air/acetylene flame after addition of LaCl 3 to prevent interference from the high concentration of perchlorate. 1 mol dm "3 perchloric acid was then added to make the Pt(II) concentration exactly 8mmol dm 3 .
• the deposits were reflective and smooth. Moreover, the adhesion of the deposits was excellent at all current densities and no cracking occurred when the electroplated Cu panels were repeatedly bent through 120°.
• the bath electrolyte of Examples 2, 3 and 4 were prepared in the same way as the bath electrolyte of Example 1.
• a bath electrolyte containing 3.5g/litre platinum as Pt(H 2 O) 4 2+ was prepared and a nickel panel was electroplated using a still bath at room temperature.
• current densities of 0J A dm '2 and 0.2 A dm '2 metallic deposits were obtained and the current efficiencies were >80%.
• a bath electrolyte containing 3.5g/litre platinum as Pt(H 2 O) 4 2+ in 1 mole dm' 3 HClO was prepared and a nickel panel was electroplated using a still bath at 60°C.
• current densities of OJ, 0.2 and 0.4 A dm '2 metallic deposits were obtained and the current efficiencies were >80%.
• a bath electrolyte containing 3.5g/litre platinum as Pt(H 2 O). 2+ 4 in 1 mole dm "3 HClO 4 was prepared and a nickel panel was electroplated using a highly agitated bath at 60°C. At current densities of 0.2, 0.4 and 0.8 A dm '2 , metallic deposits were obtained and the current efficiencies were >80%.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Fuel Cell (AREA)
• Measuring Oxygen Concentration In Cells (AREA)

Applications Claiming Priority (3)

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• 1992
  • 1992-06-17 GB GB929212831A patent/GB9212831D0/en active Pending
• 1993
  • 1993-06-14 WO PCT/GB1993/001255 patent/WO1993025733A1/en not_active Application Discontinuation
  • 1993-06-14 CA CA 2138396 patent/CA2138396A1/en not_active Abandoned
  • 1993-06-14 AU AU43461/93A patent/AU4346193A/en not_active Abandoned
  • 1993-06-14 EP EP93913357A patent/EP0644956A1/en not_active Withdrawn
  • 1993-06-14 JP JP6501289A patent/JPH07507841A/ja active Pending

Non-Patent Citations (1)

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