Title of Invention | AN IMPROVED PROCESS FOR THE ELECTRO DEPOSITION OF IRIDIUM |
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Abstract | The present invention relates to an improved process for the electrodeposition of iridium on titanium and other non-ferrous metals. The process consists of electrode position of iridium using iridium (IV) bromide bath containing 2 to 5 gm. per litre of iridium on various substrates like copper, brass, nickel and titanium with or without any gold under layer at 0.1 to 0.5 Amp.dm-2, 60 to 80°C, pH 0.5 to 2.5 using platinum or platinised titanium anode. |
Full Text | The present invention relates to an improved process for the e lectrodeposition of iridium on titanium and other non-ferrous metals. The e lectrodeposited iridium apart from its decorative application, finds use for the tips of pen nibs and occasionally for gramophone record stylli and the bearings of clocks and watches. Iridium alloy with platinum is used for porcelain dental restorations. Pure iridium has so far found few industrial applications because of its high cost. Interest in the development of coatings both for corrosion protection and for electrical contacts has focussed attention on the e lectrodeposition of this platinium group metal. Hitherto, it has been proposed to electrodeposit iridium from: (i) Fused salt baths. (J.C.Withers and P.E.Ritt, Tech. Pro. Am. Electroplaters Soc.,44th Ann.Conv., 1957, p 124). Iridium plating was done from a cyanide based fused salt bath containing iridium at 600° C in the o current density ranges of 1 to 2A.-dm . (ii) Sulphamate baths (Gordon A.Conn, Plating, (12) (1965) 1258 Iridium was deposited at a concentration of 8.3gpl as iridium (III) chloride (Varlacoid- Chemi-cal Company, 116 Broad Street. New York, 10006) and 42 gpl of sulphamic acid with a current density of O.lA.dm-2. The current efficiency was 63% at 90°C. (iii) Bromide bath (C.J.Tyrell. Trans. Inst.of Metal Finish.,43 (1965) 161 Iridium deposition from iridium bromide bath gives an efficiency of 45% on titanium and 65% on gold undercoated copper,brass,nickel etc,. with O.l5A.dm-2 as current density. (iv) Chloro iridic acid bath. (E.L.McNamara, J.Electro-chem.Soc., Jan. 1962, Page No.61. Iridium coating was made from chloro-iridic acid bath containing about lOgpl of iridium in the current density range of 2-9.0A.dm-2 These have the following disadvantages: (i) The fused salt bath involves molten cyanides, causing environmental pollution. Also heating the substrate material to high temperature leads to changes in its physical properties. (ii) Deposition from a sulphamate bath has the following drawbacks: (a) Works only in one specific make of the bath. (b) Sulphamic acid as its metal salt is likely to decompose at the bath temperature similar to the nickel salt. (c) Requires auxiliary a .c electrode. (iii) The starting material for the preparation of the bromide was ammonium chlororidate which is a very costly material compared to iridium chloride. Further the electrolyte so prepared requires an undercoat of gold for deposition on copper, brass, nickel etc. (iv) The chlororidic acid electrolyte needs very high metal concentration (10 gpl of iridium) the current density was high (about 2.2 A/dm-2) and the cathode current efficiency is very poor. (Around 14%) The main object of the present invention is to provide a process for the electrodeposition of iridium on various substrates with or without gold undercoat which obviates the drawbacks detailed above. Accordingly, the present invention provides an improved process for the electrodeposition of Iridium on various substrates like copper, nickel, brass and titanium optionally with gold undercoat which comprises; cleaning the substrate by known method, washing, rinsing, characterized in that cathodic deposition of iridium by electrolysing an iridium salt solution containing 1-5 gpl iridium at 0.1-0.5 A/dm2, pH 0.5-2.5 at 60-80°C using platinum or platinised titanium anode. In an embodiment of the present invention the iridium(IV) bromide bath containing 2 to 5 gm. per liter of iridium can be used to deposit iridium directly on substrates like copper, brass, nickel and titanium with or without any gold under layer. The process consists of electrodeposition of iridium using iridium(IV) bromide bath containing 2 to .5 gm.per litre of iridium on various substrates like copper, brass, nickel and titanium with or without any gold under layer at 0.1 to 0.5 Amp-dm-2, 60 to 80°C, pH 0.5 to 2.5 using plati num or platinised titanium anode. The novelty of the invention is: (i) the appreciable stability and shelf life of the plating bath (ii) the bath can be operated at concentrations as low as 2 gpl of iridium - 75°C. (iii) satisfactory performance of the bath at temperatures in the range of 65 (iv) ability of the bath to operate -2 at low current densities, viz., 0.2A.dm The inventive step of the process is that iridium deposition can be obtained on substrates like copper, nickel, brass and titanium etc., without gold undercoat at a moderately low current density and temperature with current efficiency upto 55%. The following typical examples are given to illustrate the invention and should not be construed to limit the scope of this invention: Example I Sandblasted and etched titanium plate (ASTM Grade II) of 1x5 cm was used as the cathode and platinum foil of twice the area was used as the anode. The electrodeposition was conducted at 65-75°C for Ihr in a solution containing 3 gpl of iridium. Adherent deposition of iridium was obtained with a plating of 0.85 u/hr(l um = 10-cm) with a current efficiency of 55%. Example II Polished copper panel of 5x1 cm was degreased in trich-loroethylene, eiectrolytically cleaned in a solution of sodium, hydroxide, sodium carbonate and trisodium phosphate, washed, rinsed and then plated directly with iridium from a solution containing. Ir as iridium (IV) bromide - 1.0 gpl at pH 2.0 and at 70°C for 3hrs to get 0.25 - O.Sum thick deposit with 5-10% cathode efficiency. Example III Ir was deposited on gold plated copper electrodes from a solution containing Ir as IrBr4 - lg/1 at 60 - 65°C, pH 1.80 for Ihr to get 0.75 - 1.0 um thick deposits with 40% current efficiency at current density and 0.2 A.dm Example IV From the stock solution of iridium bromide prepared as in Example II, iridium was deposited on etched perforated titanium plates of 4x4cm to a thickness of 3 um in 5hrs in a solutif bromide: 5g/l at pH: 2.0 and at 75° C, with 0.2A.dm-2 as current density. Example V Iridium was directly deposited on degreased, anodically etched nickel foils of 1x5cm to a thickness of 0.5u, in an iridium bromide solution containing l.Og/1 Ir at pH 2.0 and at 70° C with current density of 0.2A.dm-2. The main advantages of the present invention are: I. Adherent white deposits upto 3um can be obtained directly on titanium for funtionai applications. II. The bath does not attack the substrate being plated with iridium and thus adherent bright deposits can be directly plated on copper, nickel, gold and brass substrates. III. The stability of the bath is very good and can be used for extended periods of service. V. The process has been studied for the preparation of electrodes on a semi-pilot scale. In our co-pending patent application No. NF 252. 798 we have described & claimed a process for the preparation of iridium (IV) bromide useful for plating iridium. We Claim: 1. An improved process for the electrodeposition of Iridium on various substrates like copper, nickel, brass and titanium optionally with gold undercoat which comprises; cleaning the substrate by known method, washing, rinsing, characterized in that cathodic deposition of iridium by electrolysing an iridium salt solution containing 1-5 gpl iridium at 0.1-0.5 A/dm2, pH 0.5-2.5 at 60-80°C using platinum or platinised titanium anode. 2. An improved process as claimed in Claim 1 wherein iridium was deposited from iridium (IV) bromide electrolyte on sand blasted and etched titanium substrate to a thick-ness of 3.0 µm directly from a bath containing 3 gpl of iridium as iridium bromide at 75°C and pH 1.5 with 55% current efficiency. 3. An improved process as claimed in Claims 1 and 2, wherein iridium was deposited from iridium (IV) bromide electrolyte on sand blasted, etched and gold plated titanium substrate to a thickness of 3.0µm directly from a bath containing 3 gpl of iridium as iridium bromide at 75°C and pH 1,5 with 45% current efficiency. 4. An improved process as claimed in Claim 1 to 3, wherein the electrodeposition of iridium on polished, electrocleaned copper substrate using a iridium bromide electrolyte containing 1.0 g/1 of iridium at 65°C, 0.15 A/dm2, and Ph 1.5 with 40% current efficiency. 5. An improved process for the electrodeposition of iridium as claimed in Claims 1 to 4 wherein iridium was deposited on etched nickel substrate to a thickness of 3µm directly from a bath containing 1 g/1 of iridium as iridium bromide at 75°C and pH 1.5. 6. An improved process for the electrodeposition of iridium as claimed in Claims 1 to 5 wherein deposition of iridium on gold plated copper or brass substrates from a bath containing 1 gpl of Ir as iridium bromide, operated at pH 2.0 and at 70°C. 7. An improved process for the electrodeposition of iridium on various substrates with or without gold undercoat substantially as herein described with reference to the examples. |
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397-del-2001-correspondence-others.pdf
397-del-2001-correspondence-po.pdf
397-del-2001-description (complete).pdf
Patent Number | 193317 | ||||||||||||
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Indian Patent Application Number | 397/DEL/2001 | ||||||||||||
PG Journal Number | N/A | ||||||||||||
Publication Date | 17-Jul-2004 | ||||||||||||
Grant Date | 06-Jan-2006 | ||||||||||||
Date of Filing | 29-Mar-2001 | ||||||||||||
Name of Patentee | COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH | ||||||||||||
Applicant Address | RAFI MARG, NEW DELHI-110001, INDIA. | ||||||||||||
Inventors:
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PCT International Classification Number | C25D 3/50 | ||||||||||||
PCT International Application Number | N/A | ||||||||||||
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