Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/10—Electrodes, e.g. composition, counter electrode
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

• This invention relates to improvements in and relating to electrodes for electrolytic purposes and is more particularly concerned with the production of soluble silver anodes for use in the electrodeposition of silver.
• Electrolytic anodes as at present used, generally consist of an annealed sheet or strip of silver having a predetermined hardness below 40 VPN and of a particular shape designed to ensure as uniform as possible a dissolution of the anode throughout the whole periphery of the sheet or strip. It has also been the custom to fabricate the anodes from sheet or strip having crystals of a uni form size and to use silver of a relatively high state of purity.
• Silver anodes fabricated in the manner referred to above, have not proved entirely satisfactory in practice, as consistency in performance of the anodes cannot be ensured, one anode functioning satisfactorily, whilst another, although made in the same manner from the same material, behaving entirely unsatisfactorily due to what is known as shedding.
• Shedding which term is used in the art to mean the falling away from the anode of coarse or fine powdered silver, detrimentally affects the performance of a plating operation and anodes, which are subject to this characteristic in use, cannot be regarded as eflicient.
• the relative coarseness or fineness of the particles shed is, in no way, determinative of the total weight of the fall-out of either type, which may occur in practice, as a greater Weight of fine particle fall-out than of coarse particle fall-out is a not infrequent occurrence.
• the object of this invention is to overcome the disadvantages hitherto associated with the manufacture of silver electrolytic anodes and to provide a novel method of manufacture of anodes which will ensure consistently reproducible performance from anode to anode.
• the invention provides a method of making a silver electrode intended for electrolytic purposes which includes the steps of melting silver of about 99.98% purity, treating the molten silver with a reducing agent so as to reduce any oxygen present in the initial silver, forming the so treated silver into a billet of desired electrode shape and heat treating the shaped electrode at a temperature above 400 C. for a period of not less than 2 hours to effect homogenisation of silver crystals within the electrode structure.
• the invention further provides a method of treating a silver electrode to reduce to a minimum the tendency of said electrode to shed in use which comprises the steps of reducing the oxygen content of said electrode so as to provide an oxygen-free, or substantially ogygen-free electrode and then heat-treating the said electrode to effect homogenisation of the crystals thereof.
• the silver should preferably contain less than 0.0015% by weight of oxygen.
• Electrodes embodying the invention are preferably made by a continuous casting procedure, although other methods, such as extrusion, may, if desired, 'be employed. It will, however, be found that the casting method has the advantages of facilitating the control of the oxygen content as required and of producing a structure of interlocking crystals which tends to assist in the avoidance of shedding.
• the crystal homogenising step consists in an annealing treatment, the temperature and duration of which do not appear to be critical and may be varied over relatively wide ranges.
• the homogenising step may advantageously comprise annealing the silver at a temperature within the range of from about 400 C. up to 950 Cpfor a period which may vary from about 2 hours up to about 16 hours.
• the annealed silver should then be cooled to below 200 C., before exposure to air, and then quenched in water.
• Silver of about 99.98% purity is melted under a carbon cover by placing small pieces of charcoal on the surface of the melt and the molten silver is stirred with a graphite rod, so as to remove as far as possible any oxygen, which may have been present in the original silver.
• Thermolten silver at a temperature of :1090 C. is poured into a con- ;tinuous casting machine and thesolidified metal, on issuing from the mould, is rapidly quenched by a water-spray to reduce, to an absolute minimum, the risk of oxygen pick-up from the atmosphere.
• the actual temperature of pouring may Vary from the above figure, dependent on the particular typeof casting machine used to carry out the casting operation.
• an inert atmosphere may be admitted, and which is then placed in an annealing furnace.
• a protective atmosphere of pure dry nitrogen is used, but if desired, carbon dioxide or argon may be used instead.
• the silver is annealed to effect homogenisation of the crystals at a temperature of 750 C. for a period of 2 hours and is then quenched in water or allowed to cool.
• Electrolytic silver anodes in accordance with this invention, will be found to be highly satisfactory in use under normal plating conditions and to be free, in use, from shedding or to exhibit shedding characteristics to a minimumextent; V
• silver anodes treated in accordance with the teaching of this invention when testedunder conditions normally liable to cause severe shedding and which are, therefore, not employed in normal plating practice, namely, in use in an electrolyte of the following composition:
• theimproved silver anodes of the invention will have a greatly improved operating life and the user may select any anode from any given batch of such anodes with the knowledge that it will offer the same satisfactory performance as will any of the others of the batch.
• the invention is intended to include within its scope silver electrodes, such as electrohas been described, it is to be understood that modifications may be made thereto. without departing from the scope of the invention.
• the electrode need not be made by a continuous casting process, but an extrusion process may be used instead.
• a method of making a Silver electrode intended for electrolytic purposes which includes the steps of melting silver of about 99.98% purity, treating the molten silver with a reducing agent so as to reduce any oxygen present in the initial silver, forming the so treated silver into a billet of desired electrode shape and heat treating the shaped electrode at a temperature above 400 C. for a period of not less than 2 hours to effect homogenisation of silver crystals within the electrode structure.
• a method according to claim 1 wherein the reducing agent is a carboniferous material is a carboniferous material. 6.
• a method of making a silver electrode which comprises the steps of melting silver of about 99.98% purity in the absence of air and in the presence of carboniferous material, thereby removing oxygen, casting the molten silver and quenchingthe molded metal with a water-spray,
• a method according to claim 7 in which the an-. nealing treatment consists in heating the electrode from 400 to 950 C. for a period of from about 2 hours up to about 16 hours and is then quenched.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)

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Cited By (2)

Citations (2)

• 0
  • GB GB1054875D patent/GB1054875A/en active Active
• 1965
  • 1965-04-07 US US446391A patent/US3331709A/en not_active Expired - Lifetime
  • 1965-04-07 DE DEJ27854A patent/DE1285826B/de active Pending
  • 1965-04-09 BE BE662304D patent/BE662304A/xx unknown

Patent Citations (2)

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