US3837879A - Removing of worn coating from metal electrodes - Google Patents

Removing of worn coating from metal electrodes Download PDF

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Publication number
US3837879A
US3837879A US00245192A US24519272A US3837879A US 3837879 A US3837879 A US 3837879A US 00245192 A US00245192 A US 00245192A US 24519272 A US24519272 A US 24519272A US 3837879 A US3837879 A US 3837879A
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United States
Prior art keywords
bath
coating
molten salt
metal
support
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Expired - Lifetime
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US00245192A
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English (en)
Inventor
G Sluse
G Joannes
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Solvay SA
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Solvay SA
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/28—Cleaning or pickling metallic material with solutions or molten salts with molten salts
    • C23G1/32—Heavy metals

Definitions

  • ABSTRACT A method including immersing a coated electrode into a molten salt bath including essentially at least one bisulphate or pyrosulphate of an alkali metal or ammonium, at a temperature between 300 and 500 C, and water-rinsing the so-treated electrode after cooling thereof.
  • the present invention relates to a chemical method for removing worn coatings of electrodes for use in electrolysis, including (a) an electroconductive metal support resistant to corrosion under the conditions ruling in the electrochemical cell; and (b) a conductive coating, fixed on the support, which is also resistant to electrochemical attack and promotes the electron exchange between the support and ions of an electrolyte.
  • metal electrodes having a support made of titanium or tantalum allows to avoid these disadvantages.
  • the metal electrodes When the metal electrodes are taken out of service, they still retain an appreciable amount of the original coating, which often comprises noble metals, their oxides or other relatively inert materials rather difficult to remove by conventional chemical or electrochemical means. If it is desired to deposit new coatings on the surface of such supports and ensure their adherence, any trace of worn coating must disappear. But if the etching of a titanium or tantalum surface does not set any problem, it is not the case with metal electrodes taken out of service on account of the important chemical inertia of the support by anodic protection, resulting from the presence of noble metal, in a quantity ever so little.
  • Another object is to provide the easy recovering of the removed coating in order to provide its reutilization and exploitation.
  • a further object is to give the entire metal support its initial surface condition without subsequent treatment such as a conventional etching more or less harmful to the support metal.
  • the present invention relates to a method for rapidly and completely removing worn coatings from electrodes including an electroconductive coating fixed on an electroconductive metal support, without substantially damaging the support, such electrodes being adapted to be used in electrochemical processes and both support and coating being resistant to electrochemical corrosion under the conditions ruling in an electrochemical cell.
  • the coating promotes an electron-exchange between the support and ions of an elec trolyte in contact with the electrode.
  • the method includes the steps of immersing the worn electrodes in a molten salt bath which includes essentially at least one bisulphate or pyrosulphate of an alkali metal or of ammonium, at a temperature between 300 and 500C, cooling the electrodes and water-rinsing the so-treated electrodes.
  • electroconductive metal support resistant to electrochemical corrosion in the conditions ruling in the cell we generally mean a support at least superficially made of a film-forming metal such as titanium, tantalum, niobium, zirconium and tungsten or an alloy mainly constituted at least by one of such metals.
  • This support may optionally contain a core of a more conductive metal or alloy, such as copper, aluminum, or alloys thereof.
  • the nature of the conductive coating, set on the support is not critical for the method according to the invention, which allows to remove a large range of conductive coatings and particularly coatings containing, as active material promoting the electron exchange between the support and the electrolyte, at least one metal of the platinum group in metal form, in alloy and- /or in combination, especially in oxide state.
  • metal of the platinum group we mean platinum, iridium, rhodium, osmium, ruthenium and palladium.
  • Such coatings comprise for example, ruthenium and titanium dioxides, iridium-platinum alloys or stoichiometric compositions such as 2IrO WO They are rapidly removed by the method of the invention which besides allows their easy recovering: a molten salt bath containing an adequate quantity of coating material is allowed to cool and an aqueous solution is then made thereform.
  • the coating material generally insoluble, is easily separated by a convenient technique, such as filtration or centrifugation and may, afterwards, be reutilized as electrode coating or assigned to any different use.
  • the immersion duration in the molten salt bath depends on the temperature and the composition of the bath, on the nature of the coating, its thickness and crystallinity. It is possible to operate in a wide range of temperatures lying between 300C and 500C. Even if a temperature lower than 300C is sufficient to keep the bath in molten state, it is inconvenient to work below such temperature, if the maintenance of the required immersion term within reasonable limits is desired for removing all the coating. Likewise, it is preferred not to exceed substantially 550C in order to avoid any ignition risk for the metal support, as well as to avoid an important reduction of the bath volume by evaporation after some hours of use. An immersion from 15 to 60 minutes allows to treat any coating at temperatures compatible with the treatment.
  • the removing of the coating is generally carried out by keeping the pieces for 30 minutes in the bath.
  • any bisulphate or pyrosulphate of an alkali metal or ammonium suitable for the process of the invention, any bisulphate or pyrosulphate of an alkali metal or ammonium, optionally a mixture of two or more of them, and optionally in mixture with a minor proportion of one or more salts of an alkali metal or ammonium, especially sulphate, sulphite, bisulphite, pyrosulphite, dithionite, thiosulphate, sulphide, sulfhydrate.
  • alkali metal we mean lithium, sodium and potassium.
  • Baths with low melting point such as lithium bisulphate LiHSO, (M.P. 120C ammonium bisulphate Nl-LJ ISO (M.P.
  • the process according to the invention presents the appreciable advantage of leaving the metal support practically undamaged and ready to receive a new so adherent coating and with as favorable electrochemical properties as the former, after its emersion from a molten salt bath, cooling and water rinsing to dissolve the salt, and optionally a light etching in diluted oxalic acid.
  • the following examples 1-4) are given by way of illustration of the results obtained carrying out the process according to the invention.
  • the molten salt bath consists of ammonium bisulphate NH HSO (MP. 147C).
  • Several coats of a liquid composition were painted on the titanium, each coating being followed by thermal treatment.
  • the first coating consisted of a solution of RuCl .3H O and TiCl in isopropylic alcohol; the thermal treatments were carried out between 380 and 525C.
  • the second one consisted of a solution of H PtCl .6l-l O and H IrCl .xH O in isopropylic alcohol; the thermal treatments were carried out between 350 and 400C.
  • the agressivity of the bath was measured with regard to titanium of the uncoated strip and to the coating of the two other strips. This agressivity is given by the penetration depth (microns) for titanium and by the elimination ratio (percent) of the initial coating for the two coated strips.
  • the determination for the first of two strips was realized by spectrography and by fluorescence X, when only this last technique has been applied to the last strip where the elimination rates of Pt and Ir were separately determined. The results are set forth in Table 1. Under the conditions of this test, the molten bath of NH,HSO showed an unimportant agressivity with regard to Ti, whereas it removed the whole coating of RuO Ti0 and an average of 90 percent of the Pt lr coating.
  • the metal support After treatment in the molten salt bath and water rinsing, the metal support presents an homogeneous and rough surface suitable for receiving a coating by painting.
  • Four coats of a solution of RuCl .3H O and TiCl in isopropylic alcohol were applied onto the so treated titanium strips. After the fourth coating, the coated strips were heated between 380 and 525C.
  • the thus obtained coatings of RuO TiO of approximately 10 grams per square meter, adhered tightly to the underlying support and passed successfully the test consisting of attempting to tear off such coating with an adhesive tape applied under pressure.
  • the tested strips used as anodes in a cell with mercury-cathode for the electrolysis of a brine saturated with sodium chloride and chlorine at 80C, under an anode-cathode potential difference kept constant, the tested strips present excellent electrochemical characteristics such as shown in Table 2.
  • the molten salt bath consists of potassium pyrosulphate X 5 0 (MP. higher than 300C).
  • Example 1 The three strips of Example 1, a W strip uncoated and a Ti strip with a coating of 2lrO -WO of 4.6 g/m obtained by painting several coats of a solution of WCl and H lrCl in dimethylformamide and last thermal treatment during 5 hours at 475C, were immersed in such bath kept at 425C.
  • the agressivity of the bath was measured with regard to titanium and W on the two uncoated strips and to the coating of the three other strips. This agressivity is given (see Table l) by the penetration depth (microns) for titanium and W, and by the elimination ratio (percent) of the intial coating for the three coated strips. The elimination ratio of W and It were determined separately (by fluorescence X) for the last strip.
  • the molten bath of K 5 0 is practically inactive with regard to Ti and its agressivity with regard to W is unimportant. Moreover, it removes the whole coating of RuO TiO more than percent (average) of the coating of Pt lr and some 92 percent of noble metal included in the coating 2lrO WO After treatment in the molten salt bath and water rinsing, the metal support presents an homogeneous and rough surface suitable for receiving a coating by painting.
  • Example 2 Used as anodes, under the same conditions as in Example l, the so treated and coated strips of Ti also present excellent electrochemical characteristics, as shown in Table 2.
  • the molten salt bath consists of sodium pyrosulphate Na s- O, (MP. 401C).
  • Example 2 The four Ti strips of Example 2 were immersed for 30 minutes in this bath kept at 450C. After emersion from the bath of molten salt, cooling, water rinsing and drying, the agressivity of the bath was determined with regard to Ti, on the uncoated strip and to the coating on the three other strips. This agressivity is given (see 6 Table l) by the depth of penetration (microns) for Ti Although higher than those for the baths of precedand the elimination ratio (in percent) of initial coating ing examples, the agressivity of the molten salt of on the three coated strips, as in the preceding example. KHSO, with regard to Ti remains in allowable limits,
  • the metal support presents a homogeneous and After treatment in the bath of molten salt and water, rough support promoting the depositing of a coating by rinsing the metal support presented a homogeneous l0 painting.
  • the elimination rate is comprised between 5 9 and from the bath of molten salt, cooling, water-rinsing and 71 percent of the initial coating, following the determidrying of said strips, the agressivity of bath was deter- 30 nation technique, this being clearly below the 99-100 mined with regard to Ti on the uncoated strip and with percent elimination obtained for this type of coating, regard to coating on the two other strips.
  • a method for rapidly and completely removing, without substantially damaging the support, worn coatings from electrodes which include an electroconductive coating fixed on an electroconductive metal support, said electrodes being adapted to be used in electrochemical processes and both support and coating being resistant to the electrochemical corrosion under the conditions ruling in an electrochemical cell, said coating promoting an electron exchange between the support and ions of an electrolyte in contact with the electrode, said method comprising the steps of immersing the worn electrodes in a molten salt bath which consists essentially of at least one bisulphate or pyrosulphate of an alkali metal or ammonium, at a temperature between 300 and 500C, cooling said electrodes, and water-rinsing the so-treated electrodes.
  • bath of molten salt comprises substantially ammonium bisulphate as active substance.
  • a method according to claim 1, wherein said bath of molten salt is substantially constituted by potassium bisulphate.
  • a method according to claim 1, wherein said bath of molten salt is substantially constituted by an equimolar mixture of potassium and sodium pyrosulphates.
  • said bath of molten salt contains further at least one sulphate of an alkali metal or ammonium.
  • a method according to claim I wherein the duration of immersion is 30 minutes and the temperature of the molten salt bath is comprised between 400 and 500C.
  • said film-forming metal is titanium, tantalum, niobium. zirconium, or tungsten or an alloy mainly constituted by at least one of said metals.
  • said conductive coating contains at least one metal of the platinum group, and/or an alloy, and/or a compound of at least one metal of this group.
  • a process for recoating a worn electrode which electrode includes an electroconductive coating fixed on an electroconductive metal support having at least its outer layer made of a film-forming metal or a filmforming metal alloy, said electrode being adapted to be used in electrochemical processes and both support and coating being resistant to the electrochemical corrosion under the conditions ruling in an electrochemical cell, said coating promoting an electron exchange between the support and ions of an electrolyte in contact with the electrode, said method comprising 1. rapidly and completely removing, without substantially damaging the support, the coating on the support by a. immersing the worn electrode in a molten salt bath which consists essentially of at least one bisulphate or pyrosulphate of an alkali metal or ammonium, at a temperature between 300 and 500C,

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  • Chemical & Material Sciences (AREA)
  • Metallurgy (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Electrochemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
US00245192A 1971-04-21 1972-04-18 Removing of worn coating from metal electrodes Expired - Lifetime US3837879A (en)

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AT (1) AT313670B (en(2012))
BE (1) BE781798A (en(2012))
CH (1) CH547358A (en(2012))
DE (1) DE2213528A1 (en(2012))
FR (1) FR2133704B1 (en(2012))
GB (1) GB1360915A (en(2012))
IT (1) IT950329B (en(2012))
LU (1) LU63028A1 (en(2012))
NL (1) NL7204810A (en(2012))

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4049513A (en) * 1975-03-17 1977-09-20 Erco Industries Limited Treatment of cell anodes
US5141563A (en) * 1989-12-19 1992-08-25 Eltech Systems Corporation Molten salt stripping of electrode coatings
WO2003106737A1 (en) * 2002-06-17 2003-12-24 De Nora Elettrodi S.P.A. Methods for the reactivation of new and used electrolyser structures
CN109440131A (zh) * 2018-11-02 2019-03-08 江苏安凯特科技股份有限公司 一种纳米结构的光催化电极制备方法及应用

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4246083A (en) * 1978-08-31 1981-01-20 Johnson, Matthey & Co., Limited Removal of surface material

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2847374A (en) * 1956-06-12 1958-08-12 Kolene Corp Metal processing
US3174491A (en) * 1963-10-23 1965-03-23 Kolene Corp Molten salt spray apparatus for descaling stainless steel
US3293159A (en) * 1961-08-30 1966-12-20 Hooker Chemical Corp Process for producing a fused reducing bath for descaling
US3615815A (en) * 1969-03-03 1971-10-26 Horizons Research Inc Metal cleaning process
US3684577A (en) * 1969-02-24 1972-08-15 Diamond Shamrock Corp Removal of conductive coating from dimensionally stable electrodes
US3721626A (en) * 1969-02-03 1973-03-20 Valcovny Plechu N P Descaling method and composition of alkali metal hydroxide

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB851719A (en) * 1957-01-14 1960-10-19 Ici Ltd Descaling of titanium and zirconium after heat treatment
US3560259A (en) * 1969-12-04 1971-02-02 Bell Telephone Labor Inc Method of reclaiming tantalum from tantalum substrates having oxides of tantalum thereon

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2847374A (en) * 1956-06-12 1958-08-12 Kolene Corp Metal processing
US3293159A (en) * 1961-08-30 1966-12-20 Hooker Chemical Corp Process for producing a fused reducing bath for descaling
US3174491A (en) * 1963-10-23 1965-03-23 Kolene Corp Molten salt spray apparatus for descaling stainless steel
US3721626A (en) * 1969-02-03 1973-03-20 Valcovny Plechu N P Descaling method and composition of alkali metal hydroxide
US3684577A (en) * 1969-02-24 1972-08-15 Diamond Shamrock Corp Removal of conductive coating from dimensionally stable electrodes
US3615815A (en) * 1969-03-03 1971-10-26 Horizons Research Inc Metal cleaning process

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4049513A (en) * 1975-03-17 1977-09-20 Erco Industries Limited Treatment of cell anodes
US5141563A (en) * 1989-12-19 1992-08-25 Eltech Systems Corporation Molten salt stripping of electrode coatings
WO2003106737A1 (en) * 2002-06-17 2003-12-24 De Nora Elettrodi S.P.A. Methods for the reactivation of new and used electrolyser structures
CN109440131A (zh) * 2018-11-02 2019-03-08 江苏安凯特科技股份有限公司 一种纳米结构的光催化电极制备方法及应用

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LU63028A1 (en(2012)) 1972-12-11
IT950329B (it) 1973-06-20
CH547358A (fr) 1974-03-29
GB1360915A (en) 1974-07-24
DE2213528A1 (de) 1972-10-26
BE781798A (en(2012)) 1972-10-09
FR2133704B1 (en(2012)) 1974-12-20
FR2133704A1 (en(2012)) 1972-12-01
NL7204810A (en(2012)) 1972-10-24
AT313670B (de) 1974-02-25

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