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

Definitions

• the present invention relates to the electrolytic deposition of platinum, iridium, as well as their alloys, the properties of the thin layers obtained being readily reproducible and such that, in particular when they are deposited on titanium or metals or alloys having a similar anodic behavior, electrodes are obtained which, when used as anodes in electrolysis, have a long life and low overvoltage.
• Metals suitable for the manufacture of such structures are metals which are covered with films of their oxides under these electrolysis conditions, such as titanium, zirconium, niobium, tantalum, and tungsten, as well as their alloys. These metals are sometimes referred to as film-forming metals.
• Such thin layer coatings of platinum, iridium and alloys of these metals can be obtained by various well known methods, among which there may be cited as examples: cathode sputtering, painting with metallizing compositions, and electrolytic coating.
• the properties of the thin layer coatings obtained by these various methods are not identical with respect to their resistance to chemical, electrochemical and mechanical action, which resistance determines the life of the anodes thus produced, or with regard to the overvoltages with respect to the anodic products produced, which overvoltages must, of course, be as low as possible and must not increase in the course of time.
• the platinum and iridium are introduced in the form of halometallic acids or salts of said acids, or other complex combinations such as those of the metal amines, for instance, to which it has frequently been proposed to add numerous adjuvants, some of which are intended to impart special properties to the thin layer coatings of platinum or iridium obtained. 7
• the present applicants have particularly studied the electrolytic deposition of platinum, iridium and alloys of these metals from the corresponding bromometallic acids and salts of said acids in order during the course of manufacture, involving rechargings of baths, to obtain a series of anodes, thin layer coatings of constant, desired properties, and particularly thin layer coatings of alloys of these metals in the desired proportions, and particularly in the proportions previously known to be best.
• the use of electrolytic baths containing halogens for the depositing of the metals of the platinum series has been known, as a matter of fact, for a long time, and more recently the advantage of using baths containing bromine has been mentioned, particularly with regard to the depositing of iridium.
• the baths proposed are not capable of being used in true industrial fashion as a result of their initial composition and also due to the unfavorable evolution of this composition during use which results in an accumulation of bromide ions and cations, which makes it impossible to obtain thin layer coatings of platinum or iridium and their alloys having the desired properties and to obtain their deposition at constant speed.
• bromide ion presence which results either from the intentional addition of hydrobromic acid or of bromide to the baths, or from metal deposition operations, has the effect of decreasing the rate of deposition of the iridium, while the rate of deposition of the platinum is less affected, the effect on the baths containing both metals is intermediate.
• an object of the present invention to provide baths and methods for the deposition of thin layer coatings of platinum or iridium and their alloys which do not encounter the disadvantages of the prior art.
• the resulting thin layer coatings are uniform in thickness and resistance to chemical, electrochemical and mechanical action, and which resulting products, when used as anodes, provide low overvoltages.
• the platinum and iridium compounds which are easiest to use are bromoiridic and bromoplatinic acids, as well as the ammonium salts of these acids, which salts, however, scarcely make it possible to obtain baths of more than 5 g./ 1. (grams per liter) of the metals.
• This concentration is sufiicient to obtain a rather high rate of deposition, a concentration of less than 0.1 g./l. of these metals still making it possible to obtain thin layers of good quality with substantial speed.
• the concentration of platinum and/or iridium may vary from 0.1 g./l. to 60 g./l.
• the baths proposed by the present invention are formed on the basis of compounds which give primarily in aqueous solution brornoiridic and bromoplatinic ions as well as possibly ammonium and the cations of alkaline metals, and one or more of the acids previously mentioned as being of low complexing powder.
• These acids include nitric, sulfuric, perchloric and bromic acids.
• Perchloirc acid is preferred.
• the quantity of these acids added to the baths is preferably between 0.05 and 1 equivalent per liter of bath, values of between 0.1 and 0.5 being particularly well suited, the quantity selected being related to the concentration of metals in the bath. In any event, the amount of acid added should not be too high in order to avoid excessive liberation of hydrogen during the deposition operation.
• the proportions of the various ions and their concentrations are advantageously maintained at the desired values by the periodic or continuous addition of the desired compounds, the elimination of the disturbing ions being effected also periodically or continuously.
• This elimination is efit'ected in the case of the cations, for instance, in acid exchange resin columns, and the elimination of the bromide ions preferably by a strong bubbling of gas, in practice air, after their oxidation to the state of bromine.
• This oxidation can be carried out in a circulation outside the platinum and/ or iridium electrolytic deposition cell, by oxygenated water or ozone, for example, by the electrochemical oxidation in an annexed cell on an insoluble anode, or, even better, on the anode of the metal deposition cell itself.
• the electrolytic baths of the present invention may serve to deposit platinum and/or iridium on any substrate which is a conductor or made conductive on its surface, at times by depositing intermediate layers in order to avoid these substrates being attacked by said baths.
• the examples which follow have been limited to deposition on titanium due to the great advantage of the anodes which are formed of this metal and covered with nonattackable conductive thin layers, the metals anodically similar to titanium and particularly tantalum giving identical results as to their electrolytic properties in solutions of alkaline halides.
• Other metals which may be employed as substrates include other filmforming metals, such as zirconium, niobium, tungsten, etc., as recited hereinabove, or their alloys.
• EXAMPLE 1 The purpose of this example is to show the very strong influence of the concentration of BF ions on the rate of deposition of iridium.
• a series of titanium electrodes was coated with thin layers of iridium by electrolysis, using a current density of 0.3 amp./dm. (ampere per square decimeter), at a temperature of 75 C., without agitation, from a number of bromoiridic acid solutions containing 4 grams of metal per liter with increasing quantities of hydrobromic acids. To all these solutions perchloric acid was added so as to achieve a concentration of 0.1 N.
• Table 1 summarizes the results obtained with respect to the rate of deposition, that is to say, the thickness in microns of metal deposited per hour, as a function of the Br/ Ir ratio, that is to say, the ratio of the number of Branions coming from the hydrobromic acid added, to the number of iridium atoms present.
• EXAMPLE 3 This example describes the manufacture of a titanium electrode coated with iridium and its use as an anode.
• EXAMPLE 4 This example is intended to show the stability of the baths in accordance with the invention.
• the bath tested is similar to the bath of Example 3 and differs only by the amount of iridium present therein which corresponds here to 7.35 grams per liter of ammonium bromoiridate. This bath is maintained for 2 hours at 75 C. and does not form any sludge. A deposit of a thickness of 0.95 micron is carried out with this bath in the same general fashion as in Example 3, giving, in the electrolysis of sodium chloride solutions, results similar to those obtained with the deposition of the preceding example.
• EXAMPLE 5 This example concerns a platinizing bath which contains 0.75 grams per liter of ammonium bromoplatinate and the concentration of which is 0.35 N in perchloric acid. On a sanded titanium cathode there is obtained, with this bath maintained in agitation, a thin layer of platinum of a thickness of 0.45 micron Within 15 minutes, with a current density of 0.35 amp./dm.
• This electrode used as an anode for the production of chlorine from a brine containing 300 g./l. of sodium chloride and a pH of 4, maintained at 90 C., shows a potential of 1.09 volts referred to a calomel electrode for a current density of 100 amp./ dmf".
• EXAMPLE 6 This example describes the production of a series of mixed platinum/iridium thin layer coatings in which these metals are present in different proportions.
• Two master solutions of platinum and iridium are prepared by separately dissolving 1.5 grams of ammonium bromoplatinate in one liter of water and 1.1 grams of ammonium bromoiridate in one liter of water. By means of these stock solutions there are then prepared five baths of different Pt and Ir contents, and perchloric acid is added thereto so as to obtain a concentration of 0.2 N in said acid.
• EXAMPLE 7 This example concerns the continuous manufacture of a series of 12 electrodes of industrial dimensions intended for the electrolysis of sodium chloride brines so as to obtain chlorine and for which it is desired to obtain thin metal layers in which the proportion of iridium is substantially 20%.
• Solution A of platinum.-440 grams of ammonium bromoplatinate are dissolved in 20 liters of water in the presence of a strong cationic resin in acid form, whereupon this solution is passed over a column of the same resin so as to assure an elimination which is as complete as possible of the NH ions. After rinsing the ion exchange resin column, there are finally obtained 23 liters of solution of 5.2 g./l. of platinum which is concentrated by distillation under reduced pressure, to 60 g./l. of platinum.
• the initial solution used for the electrolysis is obtained by bringing to 10 liters the mixture of 100 ml. of Solution A, ml. of Solution B, and 100 ml. of a 10 N solution of perchloric acid.
• the Ir/ Pt ratio of this solution of 0.7 which corresponds substantially under the electrolysis conditions used to a proportion of 20% iridium in the metallic thin layers obtained.
• Each deposition is carried out at a temperature of 75 C. with a strong bubbling of air assuring the entrainment of the bromine formed on the anode by oxidation of the Br ions, as well as the agitation and homogenization of the baths.
• the current density is 1.4 amp./dm.
• the electrolysis times are about 5 minutes, which makes it possible to obtain platinum/iridium thickness of about 0.5 micron corresponding to about 10 grams.
• this amount of deposited platihum/iridium as well as the water lost by evaporation is substantially compensated for by adding 200 ml. of a solution resulting from the mixing of 1850 ml. of Solution A with 850 ml. of Solution B.
• the iridium content of the thin layers obtained is sufficiently uniform and varies from about 18 to 21%; the anodes thus obtained give satisfaction in an industrial diaphragm electrolysis cell intended for the production of chlorine and caustic soda solution.
• Baths which are aqueous and acidic and substantially bromide-ion free, for the deposition by electrolysis of platinum and/ or iridium, characterized by the fact that they are formed of compounds of platinum and/or iridium giving in aqueous solution primarily the bromoiridic and bromoplatinic anions, and of at least one acid selected from the group consisting of nitric, sulfuric, perchloric and bromic acids, and in which the platinum and/or iridium concentrations are between about 0.1 gram and 60 grams per liter and the said acid is present in an amount of between about 0.05 and 1 equivalent per liter of bath.
• Baths according to Claim 1 also containing a member selected from the class consisting of ammonium ions and cations of the alkaline metals.

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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)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Electrolytic Production Of Metals (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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• 1971
  • 1971-12-02 FR FR7143265A patent/FR2161825B1/fr not_active Expired
• 1972
  • 1972-11-22 NL NL7215792A patent/NL7215792A/xx not_active Application Discontinuation
  • 1972-11-29 BE BE792066D patent/BE792066A/xx not_active IP Right Cessation
  • 1972-11-30 AT AT1018772A patent/AT324062B/de not_active IP Right Cessation
  • 1972-11-30 SE SE7215615A patent/SE398895B/xx unknown
  • 1972-11-30 NO NO4395/72A patent/NO133372C/no unknown
  • 1972-11-30 US US00310884A patent/US3841980A/en not_active Expired - Lifetime
  • 1972-11-30 IT IT54386/72A patent/IT973814B/it active
  • 1972-11-30 BR BR8440/72A patent/BR7208440D0/pt unknown
  • 1972-12-01 JP JP11998772A patent/JPS5332345B2/ja not_active Expired
  • 1972-12-01 CH CH1756472A patent/CH552681A/fr not_active IP Right Cessation
  • 1972-12-01 GB GB5565172A patent/GB1399500A/en not_active Expired
  • 1972-12-01 SU SU1858839A patent/SU541441A3/ru active
  • 1972-12-01 CA CA158,427A patent/CA1015689A/en not_active Expired

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