Classifications

• • 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
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
  • C25C7/02—Electrodes; Connections thereof

Definitions

• a method for the surface treatment of aluminum electrodes for the electrolytic production of zinc characterized in that it substantially consists in dipping said electrodes, before their use, into a bath comprising an aqueous solution of at least one soluble lead salt.
• the preferred soluble lead salts are lead fluosilicate and lead fluoborate.
• the present invention relates to a method for the surface treatment of aluminum electrodes used for the production of zinc by electrolysis, in order to eliminate or at least reduce to a minimum the detrimental effect of fluorine present in the electrolytic solution.
• the invention also relates to the aluminum electrodes thus treated.
• the phenomenon of adhesion is attributed to the pickling action that the fluorine present in the electrolyte ex-' erts on the surface of the aluminum in the starting period of the electrolysis; that is, when said surface is not yet completely covered by the depositing zinc.
• the pickling action consists in destroying the oxide film that exists on the surface of the aluminum and that hinders the adhesion of the zinc deposit.
• an object of this invention is to provide a method for the surface treatment of aluminum cathodes such as to eliminate in all cases, or at least to reduce to a minimum, the harmful effects of fluorine, as described above.
• Another object of this invention is to provide a cheap method, capable of easy fulfillment, for the treatment of aluminum cathodes.
• the various soluble lead salts that may be used may be mentioned merely by way of example lead fluosilicate and lead fluoborate.
• the lead salt solution is acid and this acidity is imparted by the presence therein of at least one acid corresponding to the lead salt used, and preferably selected from the class consisting of fluosilicic and fluoboric acid.
• the dipping times may vary Within a wide range, depending on the desired effect, for instance, from 5 to 500 seconds. For reasons of maximum productivity, preference will be given to dipping times as short as possible.
• the concentration of lead (Pb ions) in the treating bath may vary within rather wide limits; thus, for instance, use can be made of a bath having a lead concentration between 0.05 and 5 g./l., in the presence or absence of free fluosilicic acid or free fluoboric acid in a concentration between 1 and 10 g./l.
• the layer of lead cement thus produced is only slightly adherent and does not cover the aluminum surface in a uniform and continuous way, but merely spotwise.
• the lead cement layer sets up a kind of cushion between the aluminum and the zinc forming thereon during the electrolysis of the zinc solution, thereby hindering the direct contact between the two metals (aluminum and zinc) and thereby facilitating their subsequent separation.
• the protective action of this lead cement layer is extremely effective Whatever the content of fluorine in the electrolyte may be.
• the quantity of lead that, on completion of the treatment according to the present invention, remains adhering to the aluminum cathode varies, of course, depending on the concentration of Pb' in the bath and on the dipping time.
• the layer of lead cement on the electrodes is not detrimental to the depositing of the zinc, the overvoltage of hydrogen on lead being about the same as that on zinc or aluminum.
• the corrosion of the aluminum cathode caused by the method of treatment according to this invention is quite irrelevant. In fact it has been found that for an aluminum electrode having 1 sq. m. of total immersed surface and for a treatment every 48 hours, in one year a loss of about g. of aluminum occurs based on a total weight of the immersed part of 5-6 kg. Thus, the treatment does not significantly affect the normal average life of the aluminum electrodes.
• the set of electrodes is carried to the manually or automatically operated stripping station, Where the zinc deposits are stripped from the aluminum cathodes; subsequently the cathodes are washed with water and again arranged in the electrolytic cells.
• the dipping into the treating bath according to this invention is made after the stripping and before the waterwashing. Since the dipping treatment only takes a few seconds or at most a few ten seconds, it affects the electrolytic cycle to a quite negligible extent.
• EXAMPLE 1 The feeding solution contained 50 ing/l. of fluorine. Three cathodes of each cell were treated according to the present invention by dipping them for 120 seconds into a solution containing: lead-0.5 g./l.; free fluosilicic acid-1.8 g./l.
• the cathodes were then washed with a jet of water and subsequently employed in the electrolysis.
• the dipping treatment was repeated after every three strippings.
• EXAMPLE 2 The feeding solution contained 50 mg./l. of fluorine. Three cathodes of each electrolysis cell were treated according to this invention by keeping them immersed for seconds in a solution containing: lead-0.1 g./l.; free iflllOSiliClO acid-1.3 g./1.
• the cathodes were then washed with a jet of water and subsequently employed in the electrolysis. This treatment was carried out on alternate days.
• EXAMPLE 3 The feeding solution contained l5 mg./l. of fluorine. Three cathodes of each electrolysis cell, after having been washed with water, were treated according to this invention by dipping them for seconds into a solution containing: lead-0.5 g./l.; free fluosilicic acid-l5 g./l.
• the cathodes were washed with a jet of Water and were then employed in the electrolysis.
• the stripping of the deposited zinc from the pre-treated cathodes was easily carried out.
• the stripping from the non-pre-treated cathodes of the same cells was definitely more diflicult.
• a method for the surface treatment of aluminum electrodes for the electrolytic production of zinc wherein said electrodes, before their use, are dipped into a bath comprising an aqeuous solution of at least one soluble lead salt, and thereafter using said electrodes as a cathode in a cell during the electrolytic production of zinc.
• soluble salt is selected from the class consisting of lead fiuosilicate and lead tfluoborate.
• a method according to claim 5, wherein the acid is selected from the class consisting of fluosilicic and rfluoboric acid.
• An aluminum electrode for the electrolytic production of zinc having a discontinuous, spot-wise surface layer of lead, wherein said lead layer ranges between about 0.02 to 0.2 g. of lead per square meter of the treated electrode surface.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Electrolytic Production Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=11216059

Family Applications (1)

Country Status (4)

Cited By (2)

• 0
  • BE BE759731D patent/BE759731A/fr unknown
• 1970
  • 1970-11-30 FR FR7042995A patent/FR2099031A5/fr not_active Expired
  • 1970-11-30 US US93893A patent/US3689385A/en not_active Expired - Lifetime
  • 1970-12-01 CA CA099597A patent/CA926815A/en not_active Expired

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