EP0321536B1 - Verfahren zur anodischen passivierung von kupfer in einer umgebung von geschmolzenen fluoriden, anwendung zum schutz von kupferteilen von fluor-elektrolyseanlagen - Google Patents

Verfahren zur anodischen passivierung von kupfer in einer umgebung von geschmolzenen fluoriden, anwendung zum schutz von kupferteilen von fluor-elektrolyseanlagen Download PDF

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Publication number
EP0321536B1
EP0321536B1 EP88905883A EP88905883A EP0321536B1 EP 0321536 B1 EP0321536 B1 EP 0321536B1 EP 88905883 A EP88905883 A EP 88905883A EP 88905883 A EP88905883 A EP 88905883A EP 0321536 B1 EP0321536 B1 EP 0321536B1
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EP
European Patent Office
Prior art keywords
copper
current
value
current density
bath
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
EP88905883A
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English (en)
French (fr)
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EP0321536A1 (de
Inventor
Patrick Germanaz
Sylvie Lamirault
Gérard Picard
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.)
Comurhex pour La Conversion de lUranium en Metal et Hexafluorure SA
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Comurhex pour La Conversion de lUranium en Metal et Hexafluorure SA
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    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/60—Constructional parts of cells
    • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/34—Anodisation of metals or alloys not provided for in groups C25D11/04 - C25D11/32

Definitions

  • the present invention relates to a method of passively anodizing copper pieces in the middle of molten fluorides forming an adherent protective layer with a high recovery rate; this process is particularly, but not exclusively, applicable to the protection of copper parts used in electrolysers for the production of fluorine.
  • a bath of molten fluorides which is generally a mixture of hydrogen fluoride and alkali metal fluorides and / or ammonium.
  • the anodes made of carbonaceous material are immersed vertically in the bath and are supplied with electric current by current leads usually made of copper.
  • the copper anode junction which represents a weak point, is usually carried out at the top of the anode, in this case the copper current supply and the Copper-anode junction are partially immersed in the bath and are subjected to the action. of the bath and the bubbles of fluorine released at the anode.
  • a passivation of the copper occurs on the one hand due to the soaking in the bath of liquid fluorides, on the other hand by anodization during the tensioning of the electrolysis cell, but the properties of the layer obtained are very insufficient for effective protection of copper.
  • a dissolution of the copper thus occurs, leading to the deterioration of the slow and regular copper-anode contact, necessitating the stopping and refurbishing of the electrolysis cell, in particular the repair of the current leads and the change of the anode. This refurbishment takes place approximately once a year.
  • the copper-anode junction can also and advantageously be carried out from below.
  • the copper current leads pass through the total thickness of the bath before being connected to the feet of the anodes. It is then necessary to isolate them to avoid their dissolution; one can for example make sheathing resistant to the bath.
  • a device of this kind is described in patent SU 193,454, which describes a cladding of the current leads effected by magnesium and the protection of the copper-anode contacts by a chemically inert insulator (fluorinated hydrocarbon). Such protections are difficult to implement and use expensive products.
  • KF-x HF will mean a mixture where the number of moles d 'HF is exclusively equal to or close to 2) for the electrolytic production of fluorine, currently limits the development and development of more efficient fluorine electrolyzer.
  • the Applicant has continued its research, the main object of which is to obtain a durable and effective passivation of copper in a liquid fluoride bath using a process that is simple to implement.
  • this passivation must durably and effectively protect the copper under the conditions encountered during the electrolytic production of fluorine; it must in particular resist the action of the KF, xHF electrolysis baths, the fluorine produced and the electrolysis current.
  • Another object is the obtaining or the controlled development of a protective layer of copper in the middle of molten fluorides which is tight and which has a strong adhesion to the copper substrate and a high recovery rate of said substrate.
  • Another object is to obtain an electrically insulating layer.
  • Another object is to obtain a layer which is thin while having, thanks to the strong cohesion of the particles which constitutes it, good mechanical characteristics, in particular resistance to abrasion, friction, impact ...
  • Another object of the invention is to use an electrochemical process which allows this passivation to be carried out in the tanks and on the production site, opening up the production of said tanks.
  • Another object is to avoid the slow dissolution of copper and the degradation of the copper-anode bonds during the electrolysis of liquid fluoride baths and particularly of the KF, xHF bath.
  • the invention is a method of passively anodizing parts in copper in KF medium, xHF (x close to 2) liquid making it possible to obtain an adherent protective layer, mechanically and electrically resistant, with a high recovery rate of the copper substrate, characterized in that said copper parts, once immersed in the KF, xHF liquid bath, are subjected to an anodic current of low surface density, calculated relative to the immersed copper surface, less than 0.1 A / dm2, this current being maintained either at a constant value depending on the time, or at a variable value. This treatment is applied for a variable duration which is always greater than a limit value dependent on the value of the anodic current density.
  • the bath consists of a liquid KF, xHF mixture, the HF content of which is preferably between 38 and 42.5%; this mixture is usually used as a bath for the electrolytic production of fluorine.
  • the bath should be liquid; it is advantageous to operate under such conditions (of temperature and of concentration) that the vapor pressure of HF does not exceed 50 mm of mercury, or that there is not more than 7% (weight) of HF driven by gases. Thus, it is advantageous to operate at a temperature between 85 and 105 ° C.
  • Battelle describes anodization intensities greater than a floor value (for example 0.4 A / dm2, itself significantly higher than the maximum intensity prescribed by the applicant.
  • the conditions of formation (in particular of nucleation, of growth, etc.) of the passivating layer, described by Battelle are very different and provide said layer with properties, for example of homogeneity of adhesion density, also very different.
  • These operating conditions cannot therefore be used to predict the conditions for the formation of a protective layer in a KF, xHF medium, meeting the requirements of the applicant, a layer which must be resistant to bathing, to the release of fluorine and to electrical conditions during electrolysis, and which is also adherent, compact and solid over time.
  • a direct voltage is applied between the copper part to be protected and a cathode of any conductive material, for example steel, also immersed in the bath.
  • This voltage as well as the shape, location, spacing, etc. of the cathode are such that the current density at all points of the surface to be protected is uniform and maintained at a low value.
  • the low current density applied to the surface to be protected can be maintained at a constant value as a function of time, and throughout the duration of the treatment, in this case the anodization treatment is said to be in constant mode; it can also have a variable value in this case the processing is said to be variable mode.
  • the duration processing increases exponentially and becomes prohibitive;
  • the quality of the protective layer formed practically does not change any more when the duration of treatment is excessively extended.
  • the current density must be less than 0.1 A / dm2, but preferably less than 0.05 A / dm2 and more particularly less than 0.025 A / dm2.
  • the duration of treatment practically but not limited to, it does not exceed 20 h and preferably 15 h, and consequently we avoid using, in constant mode, a current density less than 0.01 A / dm2.
  • the treatment time is generally greater than 0.5 h but for current densities of the order of 0.05 A / dm2, it is d use of treatment times between 2 and 4 h.
  • the curve in Figure 1 gives an illustration of what may be the relationship between the current density (plotted on the ordinate) and the processing time (plotted on the x axis) to obtain the same protective layer in the case where the current density (or intensity) is kept constant during the treatment, for a KF, xHF bath, containing 40.5% by weight of HF.
  • the current density applied is variable as a function of time, while remaining within the limits described above.
  • the values of the current densities used during each anodization sequence can be constant or variable, they can be the same or be different from one sequence to another; the durations of each anodization sequence can be the same or be different; the durations of each relaxation sequence may be the same or be different and are independent of the durations of the anodization sequences.
  • some anodizing sequences may have current densities of less than 0.01 A / dm2.
  • variable embodiment of the invention makes it possible to reduce the total duration of the treatment compared to the so-called constant mode and also makes it possible to reduce the value of the current density used with each anodization sequence.
  • the method according to the invention makes it possible to obtain a durable and efficient passivation of copper in molten fluoride baths by obtaining a protective layer formed essentially of a mixed copper fluoride, which appears to have a high level. covering the copper substrate, great compactness in the arrangement of the elementary particles, strong adhesion and high resistivity. This layer thus avoids the anodic dissolution of copper. These properties are all the more marked the lower the current density and the longer the treatment time.
  • the leakage current passing through the protective layer formed using a given voltage applied on either side of said layer.
  • it is measured, the part being immersed in a conductive bath, for example the passivation bath, by applying a DC voltage between said part and another plunging electrode.
  • a passivated copper piece according to the prior art, by simple dipping in a KF, xHF liquid bath, has a leakage current of 25 mA / dm2 at 5V.
  • a part passivated according to the method of the invention in this same type of bath has a leakage current not exceeding 5 mA / dm2 at 10 V, and usually close to or less than 3 mA / dm2 at 10 V.
  • the protective layer is also mechanically resistant, moreover it is very thin so that it does not alter significantly the dimensions of the passivated parts, nor their geometry.
  • the method according to the invention is applicable to the passivation of all kinds of copper parts to be subsequently used in the medium of fluorides, molten or in aqueous solution.
  • Copper parts passivated using the process according to the invention offer very good resistance to chemical corrosion in all media containing fluorides, in particular molten fluoride baths and more especially baths containing at least fluoride. hydrogen and an alkali or ammonium fluoride. Because the protective layer has good adhesion and significantly improved mechanical properties, it is possible to use the passivated parts in a calm or agitated, homogeneous or heterogeneous environment.
  • the process finds its particular field of application in the passivation and protection of copper parts, in particular current supply bars to the electrodes, installed in fluorine electrolysers using liquid baths KF, xHF as electrolyte, thanks to the quality improved layer that resists bathing, fluorine and current well.
  • the fact that these parts are under tension does not alter their resistance to corrosion.
  • the very good quality of the passivation obtained allows in the application to the electrolysis of fluorine to increase the lifespan of said copper parts up to at least five years, and to implement new cell technologies.
  • electrolysis in particular the supply of the anodes from the bottom knowing that copper parts passivated according to the process can be immersed and energized without problem.
  • a copper disc of type Cu a 1 with a diameter of 35 mm, with a total surface area of 0.2 dm2 is subjected to an anode voltage such that the intensity is kept constant at a value of 3 mA (0.015 A / dm2) for 12 h 30 min. , with a steel cathode identical to the anode, in a KF, xHF bath containing 40.5% by weight of HF, at 95 ° C. After treatment, the leakage current observed at a voltage of 10 V is 3.5 mA / dm2.
  • the leakage current observed at 10 V is only 2.9 mA / dm2, while the treatment time is only 10 h.
  • the leakage current observed at a voltage of 10V is 1 mA / dm2, which results in corrosion of 0.12 mm per year.

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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)
  • Electrolytic Production Of Metals (AREA)
  • Electroplating Methods And Accessories (AREA)

Claims (7)

  1. Verfahren zur passivierenden Anodisierung von Werkstücken aus Kupfer in flüssigem KF, xHF (x nahe 2)-Medium, das das Erhalten einer haftenden, mechanisch und elektrisch beständigen Schutzschicht mit hohem Bedeckungsgrad des Kupfersubstrats ermöglicht,
    dadurch gekennzeichnet,
    daß die Werkstücke nach Eintauchen in das flüssige KF, xHF (x nahe 2)-Bad einem anodischen Strom einer bezüglich der zu behandelnden eingetauchten Kupferoberfläche berechneten Oberflächendichte unter 0,1 A/dm² ausgesetzt werden, wobei dieser Strom auf einem als Funktion der Zeit konstanten Wert oder einem variablen Wert gehalten und während einer variablen Dauer angelegt wird, die stets über einem vom Wert des anodischen Stroms abhängigen Grenzwert und derart ist, daß man eine Schutzschicht erhält, die einen 5 mA/dm² bei 10 V nicht übersteigenden Leckstrom aufweist.
  2. Verfahren nach dem Anspruch 1,
    dadurch gekennzeichnet,
    daß die Oberflächenstromdichte vorzugsweise unter 0,05 A/dm² ist.
  3. Verfahren nach irgendeinem der Ansprüche 1 und 2,
    dadurch gekennzeichnet,
    daß der anodische Strom auf einem konstanten Grenzwert von 0,1 A/dm² gehalten wird und die Anlegedauer des Stroms wenigstens 0,5 h ist.
  4. Verfahren nach irgendeinem der Ansprüche 1 und 3,
    dadurch gekennzeichnet,
    daß die anodische Stromdichte während der Behandlung auf einem konstanten Wert gehalten wird.
  5. Verfahren nach irgendeinem der Ansprüche 1 bis 4,
    dadurch gekennzeichnet,
    daß die anodische Stromdichte einen im Lauf der Behandlung variablen Wert hat.
  6. Verfahren nach dem Anspruch 5,
    dadurch gekennzeichnet,
    daß man Folgen einer Anodisierung mit von Null abweichender Stromdichte mit Relaxationsfolgen mit Nullstromdichte abwechseln läßt, wobei der Wert der Stromdichte der Anodisierungsfolgen vorzugsweise von einer Folge zur nächsten sinkt.
  7. Schutzschicht von Kupferwerkstücken, die gemäß irgendeinem der Ansprüche 1 bis 6 erhalten wurde,
    dadurch gekennzeichnet,
    daß der durch diese Schicht hindurch gemessene Leckstrom unter 3 mA/dm² bei 10 V ist.
EP88905883A 1987-06-26 1988-06-23 Verfahren zur anodischen passivierung von kupfer in einer umgebung von geschmolzenen fluoriden, anwendung zum schutz von kupferteilen von fluor-elektrolyseanlagen Expired - Lifetime EP0321536B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8709574 1987-06-26
FR8709574A FR2617200B1 (fr) 1987-06-26 1987-06-26 Procede d'anodisation passivante du cuivre en milieu de fluorures fondus. application a la protection de pieces en cuivre des electrolyseurs fluor

Publications (2)

Publication Number Publication Date
EP0321536A1 EP0321536A1 (de) 1989-06-28
EP0321536B1 true EP0321536B1 (de) 1993-08-04

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Application Number Title Priority Date Filing Date
EP88905883A Expired - Lifetime EP0321536B1 (de) 1987-06-26 1988-06-23 Verfahren zur anodischen passivierung von kupfer in einer umgebung von geschmolzenen fluoriden, anwendung zum schutz von kupferteilen von fluor-elektrolyseanlagen

Country Status (8)

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US (1) US4892630A (de)
EP (1) EP0321536B1 (de)
JP (1) JP2680393B2 (de)
CA (1) CA1323596C (de)
DE (1) DE3882948T2 (de)
FR (1) FR2617200B1 (de)
WO (1) WO1988010328A1 (de)
ZA (1) ZA884547B (de)

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SU658187A1 (ru) * 1975-09-23 1979-04-25 Предприятие П/Я А-7186 Способ электрохимического оксидировани меди
JPS5927398A (ja) * 1982-08-04 1984-02-13 株式会社東芝 警報告知装置
JPS60211093A (ja) * 1984-04-06 1985-10-23 Fuji Photo Film Co Ltd 導電材料の電解処理方法及び装置
JPS60221591A (ja) * 1984-04-17 1985-11-06 Central Glass Co Ltd フツ素の製造方法

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Publication number Publication date
FR2617200B1 (fr) 1991-07-12
ZA884547B (en) 1989-03-29
EP0321536A1 (de) 1989-06-28
WO1988010328A1 (fr) 1988-12-29
JPH01503631A (ja) 1989-12-07
US4892630A (en) 1990-01-09
JP2680393B2 (ja) 1997-11-19
FR2617200A1 (fr) 1988-12-30
CA1323596C (fr) 1993-10-26
DE3882948D1 (de) 1993-09-09
DE3882948T2 (de) 1993-12-16

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