US3841983A - Surface preparation process for recoating of used coated metallic electrodes - Google Patents

Surface preparation process for recoating of used coated metallic electrodes Download PDF

Info

Publication number
US3841983A
US3841983A US00348115A US34811573A US3841983A US 3841983 A US3841983 A US 3841983A US 00348115 A US00348115 A US 00348115A US 34811573 A US34811573 A US 34811573A US 3841983 A US3841983 A US 3841983A
Authority
US
United States
Prior art keywords
anode
electrode
coated
percent
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00348115A
Other languages
English (en)
Inventor
R Itai
H Kanai
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Japan Carlit Co Ltd
Original Assignee
Japan Carlit Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Japan Carlit Co Ltd filed Critical Japan Carlit Co Ltd
Application granted granted Critical
Publication of US3841983A publication Critical patent/US3841983A/en
Priority to US05/621,021 priority Critical patent/USRE28849E/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F5/00—Electrolytic stripping of metallic layers or coatings

Definitions

  • ABSTRACT OF THE DISCLOSURE A surface preparation process for use in recoati g of used metallic electrodes coated with one or more platinum group metals, one or more iron group metals, or chemical compounds thereof, which comprises using said metallic electrode(s) as anod (s) and passing a current between said metallic electrode(s) and a steel cathode(s) in an aqueous solution of sulfuric acid, nitric acid, perchloric acid, salts thereof, chlorates or persulfates, or a mixture solution thereof, and then dipping said metallic electrode(s) into an aqueous solution of hydrofluoric acid or hydrochloric acid.
  • This invention relates to a surface preparation process for use in recoating of used metallic electrodes comprising a conductive substrate coated with one or more platinum group metals, an iron group metal, or chemical compounds thereof. More particularly, the invention relates to a surface preparation process for recoating of used metallic electrodes(s), which comprises using said metallic electrode(s) as anode(s) and passing a current between said electrode(s) and steel cathode(s) in an aqueous solution of sulfuric acid, nitric acid, perchloric acid, salts thereof, chlorates or persulfates, or a mixture solution thereof, and then dipping said metallic electrodes in an aqueous solution of hydrofluoric acid or hydrochloric acid.
  • coated metallic electrodes as anodes in an electrolytic bath consisting of an aqueous solution of alkali metal chlorides has recently been proposed.
  • Said coated metallic electrodes consist of a combination of corrosion resistant metals, such as titanium, zirconium, tantalum or niobium as a conductive substrate metal and the coating thereon comprises one or more of platinum group metals, iron group metals, or chemical compounds thereof, for example oxides.
  • Said coated anodes show excellent chlorine overvoltage characteristic, have dimensional stability and can be produced at relatively low cost.
  • the acid solution method has disadvantages in that more than 10 percent by weight of the metallic substrate is lost and, also, the parts of the surface of the metallic substrate from which the coating has separated, are attacked by the acid and become rough, thereby making the surface of the metallic substrate unsuitable for recoating.
  • Another object of the present invention is to provide a method which removes the conductive coating from used coated metallic electrodes rapidly and with a minimum of damage to the metallic substrate.
  • a further object of the present invention is to provide a method for removing the conductive coating from used coated metallic electrodes as well as the oxides of the substrate metal from its surface, thereby providing a metallic substrate surface to which a new conductive coating will adhere firmly.
  • the remaining conductive coating can be easily and effectively removed from used coated metallic electrodes without substantial damage to the metallic substrate by using the coated metallic electrodes as an anode, and by passing a current of about 1 to A./dm. of anode current density between the anode comprising the metallic substrate coated with one or more platinum group metals, iron group metals, or chemical compounds thereof, and steel cathodes in an electrolyte consisting of about 5 to 70 percent by weight of an aqueous solution of sulfuric acid, nitric acid, perchloric acid, salts thereof, chlorates or persulfates, or of a mixture solution thereof, at a temperature of about 0 to 50 C., for a period of time suflicient to effect removal of said coating, thereafter lightly rubbing the surface of thus treated electrode with a soft cloth and/ or rinsing with water.
  • the resulting electrode substrates are dipped into an about 5 percent by weight aqueous hydrofluoric acid solution or an about 8 to 17 percent by weight aqueous hydrochloric acid solution for a few minutes, whereby the surface of the metallic substrate is made suitable for application of a new conductive coating.
  • the figure shows a graph of the relation between bath voltage and time for passing a current between a coated metallic electrode as an anode and steel cathodes.
  • metallic electrodes coated with one or more platinum group metals, an iron group metal and a mixture thereof includes an anode for electrolysis; said anode is composed of corrosion-resistant metals, such as titanium, zirconium, tantalum and niobium, coated with one or more platinum group metals, such as ruthenium, rhodium, iridium, platinum, and palladium, iron group metals, such as iron, cobalt and nickel; or oxides thereof.
  • sulfuric acid, nitric acid, perchloric acid, salts thereof, chlorates or persulfates includes sulfuric acid; sulfates, such as sodium sulfate, potassium sulfate, lithiurn sulfate and ammonium sulfate; nitric acid; nitrates, such as sodium nitrate, potassium nitrate, lithium nitrate, ammonium nitrate; perchloric acid; perchlorates, such as sodium perchlorate, lithium perchlorate, ammonium perchlorate; chlorates, such as sodium chlorate, potassium chlorate, lithium chlorate; and persulfates, such as potassium persulfate and ammonium persulfate.
  • Aqueous solutions of the above acids and salts are used to attain the purpose of the invention, and said aqueous solutions may be employed eifectively either separately or in combination. Furthermore, an amount of 0.1 to 3 percent by weight of hydrogen peroxide may be added to said aqueous solutions as an oxidation accelerator.
  • the concentration of the aqueous solutions of said acids and salts may vary depending on the kinds of acids and salts, but may generally be in the range of about to 70 percent by weight. If the concentration of said aqueous solutions is above 70 percent by weight crystals are apt to be deposited. On the other hand, if the concentration of the aqueous solutions is below 5 percent, the bath voltage and time required for passing a current are difficult to control and an increase in the bath voltage results in an increase in the electric power consumption.
  • the anode current density is within the range of about 1 to 100 A./dm. and preferably, of about 3 to 60 A./dm.
  • an anode current density in the range of about to 60 A./dm. is the most suitable for operation of this invention; when metallic electrodes coated with iron group metals or oxides thereof are used as the anode, and anode current density in the range of about 3 to 20 A./dm. is most desirable in the process of the present invention.
  • the temperature of the aqueous solution of said acids and salts during the current passage may range from about 0 to 50 C., but can normally be room temperature.
  • the period of time during which the current is passed varies depending on the temperature of the aqueous solution, the anode current density and the state of the coated metallic electrode; generally said period may fall in the range of about 20 minutes to 24 hours.
  • the current density is high and the temperature of the aqueous solution is low, the current is passed for relatively a short period. Meanwhile, if a longer period of current passing is preferred, then lower anode current densities and somewhat higher temperature may be required.
  • the bath voltage rises gradually until near the end of treating the coated metallic electrodes when it rises rapidly. During this period, the coating on the substrate metal is gradually broken and becomes brittle. If the bath voltage rises too rapidly, the electric current is disconnected, and the electrodes are removed from the electrolyte; the current should be disconnected before the break-down voltage of the substrate metal(s) of the electrode(s) is reached.
  • the final voltage at which current should be disconnected may vary depending on the type of coating on the conductive substrate, the type and the concentration of the aqueous solution(s), the anode current density, and the solution temperature, but usually the final voltage is set in the range of 6 to 15 volts, being chosen on the basis of practical experience.
  • the coating remaining on the substrate metal is made very brittle and it can then be stripped from the substrate metal with a minimum of damage to the substrate metal.
  • the mechanism by which the nature of the coating is changed is not clear, it is considered that oxides present in the coating change to a higher oxidation state, whereby said oxides are less corrosion-resistant.
  • conventional electrolytic treatments by which the oxidized surface of the substrate metal is electrolytically removed or polished away to prepare the surface of metal for coating are essentially different from the present invention in respect of action and mechanism.
  • electrolytic polishing aqueous solutions of phosphates, caustic alkali or the like are employed as typical treating agents, but none of such treating agents is used in the process of the present invention.
  • EXAMPLE 1 The coated metallic electrode comprising a titanium substrate having a ruthenium oxide coating thereon which was to be cleaned was used as an anode, and a current was passed between said anode and steel cathodes, in 50 percent by weight of an aqueous solution of sodium chlorate at 60 A./dm. of anode current density, for 30 minutes. During this treatment, the bath temperature rose from C. to C. Bath voltage rose gradually from 5.5 volts, and after 25 minutes from the start of the treatment, began to rise rapidly and was 7.5 volts at the end of the treatment. (FIG. 1 is referred to.) The anode was removed from the bath, and rinsed with Water and dried.
  • the Weight loss on the substrate while the current was passed was determined to be 0.1 percent. Thereafter, the thus treated metallic electrode was dipped into 5 percent by weight of an aqueous solution of hydrofluoric acid for 3 minutes to complete stripping of the coating. The weight loss of the substrate during this treatment was 1.6 percent. After the former treatment, the coating remaining on the surface of the substrate was completely stripped by dipping into the hydrofluoric acid solution and by rinsing with water, and the surface of titanium substrate was seen to be the same as that of an original substrate.
  • EXAMPLE 2 The coated metallic electrode comprising a titanium substrate having a platinum oxide coating thereon which was to be cleaned was used as an anode, and a current was passed between said anode and steel cathodes, in 5 percent by weight of an aqueous solution of potassium nitrate, at 10 A./dm. of anode current density, for 12 hours. During this treatment, the bath temperature was to C. Bath voltage was constantly maintained at around 4.1 volts, but after about 11 hours from the start of the treatment, the bath voltage began to rise gradually and rose to 11.0 volts at the end of the treatment.
  • the surface of the resulting metallic electrode was rubbed with a soft cloth and dipped into 5 percent by weight of an aqueous solution of hydrofluoric acid for 5 minutes to apply a new conductive coating.
  • the weight loss on the substrate during these treatments was determined to be 2.0 percent. It was found that the newly coated metallic electrode had a uniform and intimately bonded coating comparable to an original electrode.
  • a coated metallic electrode comprising a tantalum substrate having a magnetite coating thereon which had been used as an anode for producing a chlorate by electrolysis for a long period of time, and which began to show signs of an increase in bath voltage of electrolysis, was used as an anode and a current was passed between said anode and steel cathodes in 62 percent by weight of an aqueous solution of sodium perchlorate, at 3 A./dm. of anode current density, at 50 C. of a bath temperature, for 3 hours. The bath voltage at the end of this treatment was 8.2 volts. The weight loss of the substrate metal after dipping the treated metallic electrode into 17 percent by weight of an aqueous solution of hydrochloric acid for 2 minutes, was 0.8 percent by weight.
  • the coated metallic electrode which was to be cleaned was used as an anode. It was comprised of a titanium substrate having an iridium oxide coating thereon. A current was passed between said anode and steel cathodes, in a mixture solution of percent by weight of an aqueous solution of sodium sulfate, 10 percent by weight of an aqueous solution of sulfuric acid and 2 percent by weight of an aqueous solution of hydrogen peroxide, at 2-5 A./dm. of anode current density, at to C. of a bath temperature, for 2 hours. The weight loss of the substrate metal after clipping the treated metallic electrode into 5 percent by weight of an aqueous solution of hydrofluoric acid for 6 minutes was 2.6 percent by weight. A new iridium oxide coating was applied to the cleaned titanium substrate.
  • EXAMPLE 5 A recoated metallic electrode obtained by treatment according to Example 1 was employed as an anode for electrolysis of an aqueous solution of sodium chloride. The results obtained are given in Table 1. The recoated metallic electrode was similar to the originally coated metallic electrode in appearance and bath voltage characteristics. From these results, it was theoretically determined that a metallic electrode recoated after cleaning by the method according to the present invention would have a long life, while a metallic electrode recoated after cleaning by treatment only with an aqueous solution of hydrofluoric acid would have a short life.
  • the coating which remained on the substrate metal could easily be removed from said substrate metal by simple electrochemical means according to the present invent-ion.
  • the treatment according to the present invention may be automated.
  • the weight loss of the substrate metal was as little as less than 3 percent during the cleaning treatments according to the present invention.
  • the metallic electrode recoated after cleaning by the method according to the present invention was similar to an originally coated metallic electrode in appearance and bath volt-age characteristics and also had a long life.
  • a surface preparation process for recoating of a used coated metallic electrode coated with one or more platinum group metals or iron group metal oxides comprising using said electrode as an anode and passing a current at about 1 to A./dm. of anode current density between said anode and steel cathodes, in an electrolytic bath containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50 C., for a period of time suflicient to effect removal of coating remaining on said used electrode.
  • a surf-ace preparation process wherein a current is passed at about 3 to 60 A./dm. of anode current density.
  • a surface preparation process wherein a current is passed at about 10 to 60 A./dm. of anode current density in case the metallic electrode used as an anode is coated with a platinum group metal.
  • a surface preparation process wherein a current is passed at about 3 to 20 A./dm. of anode current density in case the metallic electrode used as an anode is coated with an iron group metal oxide.
  • a surface preparation process for recoating of a used coated metallic electrode coated with one or more platinum group metals or iron group metal oxides comprising using said electrode as an anode and passing a current at about 1 to 100 A./dm. of anode current density between said anode and steel cathodes, in an electrolytic bath containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50 C., for a period of time suflicient to effect removal of any remaining coating, thereafter lightly rubbing the surface of the thus treated electrode with a soft cloth and/or rinsing with water, and dipping the resulting electrode substrate into an about 5 percent by weight aqueous hydrofluoric acid solution or an about 8 to 17 percent by weight aqueous hydrochloric acid solution for a few
  • a surf-ace preparation process for recoating of a used coated metallic electrode coated with one or more platinum group metals comprising using said electrode as an anode and passing a current at about 10 to 60 A./dm. of anode current density between said anode and steel cathodes, in an electrolytic 'bat-h containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50 C., for a period of time suflicient to effect removal of any remaining coating, thereafter lightly rubbing the surface of a treated electrode with a soft cloth and/or rinsing with water, and dipping the resulting electrode substrate into about 5 percent by weight of an aqueous solution of hydrofluoric acid for a few minutes.
  • a salt selected from the group consisting of a s

Landscapes

  • 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)
  • Electrochemical Coating By Surface Reaction (AREA)
US00348115A 1972-08-28 1973-04-05 Surface preparation process for recoating of used coated metallic electrodes Expired - Lifetime US3841983A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US05/621,021 USRE28849E (en) 1972-08-28 1975-10-09 Surface preparation process for recoating of used coated metallic electrodes

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP8528172A JPS53386B2 (enrdf_load_stackoverflow) 1972-08-28 1972-08-28

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US05/621,021 Reissue USRE28849E (en) 1972-08-28 1975-10-09 Surface preparation process for recoating of used coated metallic electrodes

Publications (1)

Publication Number Publication Date
US3841983A true US3841983A (en) 1974-10-15

Family

ID=13854171

Family Applications (1)

Application Number Title Priority Date Filing Date
US00348115A Expired - Lifetime US3841983A (en) 1972-08-28 1973-04-05 Surface preparation process for recoating of used coated metallic electrodes

Country Status (3)

Country Link
US (1) US3841983A (enrdf_load_stackoverflow)
JP (1) JPS53386B2 (enrdf_load_stackoverflow)
GB (1) GB1406568A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0482565A3 (en) * 1990-10-22 1992-09-23 Union Carbide Coatings Service Technology Corp. Electrolytic process for stripping a metal coating from a titanium based metal substrate
US6440279B1 (en) 2000-12-28 2002-08-27 Alcoa Inc. Chemical milling process for inert anodes
US20080150139A1 (en) * 2006-12-21 2008-06-26 Jae Hong Kim Semiconductor Device and Method of Manufacturing the Same

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS51108809A (ja) * 1975-03-20 1976-09-27 Hitachi Maxell Jikikaadonoseizoho
JPS5640032Y2 (enrdf_load_stackoverflow) * 1976-12-20 1981-09-18
CN109891002B (zh) * 2016-11-22 2021-03-12 旭化成株式会社 电解用电极

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0482565A3 (en) * 1990-10-22 1992-09-23 Union Carbide Coatings Service Technology Corp. Electrolytic process for stripping a metal coating from a titanium based metal substrate
US6440279B1 (en) 2000-12-28 2002-08-27 Alcoa Inc. Chemical milling process for inert anodes
US20080150139A1 (en) * 2006-12-21 2008-06-26 Jae Hong Kim Semiconductor Device and Method of Manufacturing the Same
US7781318B2 (en) * 2006-12-21 2010-08-24 Dongbu Hitek Co., Ltd. Semiconductor device and method of manufacturing the same

Also Published As

Publication number Publication date
JPS53386B2 (enrdf_load_stackoverflow) 1978-01-07
JPS4940282A (enrdf_load_stackoverflow) 1974-04-15
GB1406568A (en) 1975-09-17

Similar Documents

Publication Publication Date Title
US4033837A (en) Plated metallic cathode
US3841983A (en) Surface preparation process for recoating of used coated metallic electrodes
US3554881A (en) Electrochemical process for the surface treatment of titanium,alloys thereof and other analogous metals
EP0063540B1 (en) Recoating of electrodes
USRE28849E (en) Surface preparation process for recoating of used coated metallic electrodes
US3463707A (en) Electrodeposition of lead dioxide
US3684577A (en) Removal of conductive coating from dimensionally stable electrodes
US3087874A (en) Electropolishing of titanium base alloys
US3761313A (en) Stripping of coated titanium electrodes
US2389131A (en) Electrodeposition of antimony
US5141563A (en) Molten salt stripping of electrode coatings
DE3815585C2 (enrdf_load_stackoverflow)
US2325660A (en) Electrodeposition of manganese and cathode therefor
US3573100A (en) Reconstitution of electrodes
US4132606A (en) Process for the manufacture of electrodes
US3440149A (en) Stable lead anodes
US4189357A (en) Method of treating a substrate material to form an electrode
US3412000A (en) Cathodic protection of titanium surfaces
CA1055882A (en) Process for the electrolytic recovery of gallium and/or alkali metals
JPS586788B2 (ja) 二酸化鉛被覆電極の再生法
US4802962A (en) Treatment of cathodes for use in electrolytic cell
US3841978A (en) Method of treating a titanium anode
US2154027A (en) Electrolytic device and method of making same
US3632490A (en) Method of electrolytic descaling and pickling
US2561222A (en) Electrolytic method of stripping nickel, chromium, copper, zinc, cadmium, silver, tin, and lead electrodeposits from ferrous basis metals, and compositions for use therein