Process for the passivating anodization of copper in a medium of

Details Process for the passivating anodization of copper in a medium of Process for the passivating anodization of copper in a medium of

1989-02-23

1990-01-09

Tufariello, T. M.

Chemistry: electrical and wave energy

Processes and products

C25D 1102

Patent

active

048926302

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns a process for the passivating anodisation of copper parts in a medium of molten fluorides forming an adherent protective layer with a high covering rate; the process can be used in particular but not exclusively for the protection of the copper parts used in electrolysers for the production of fluorine.


STATE OF THE ART

The process for producing fluorine by electrolysis uses a bath of molten fluorides, which is generally a mixture of hydrogen fluoride and fluorides of alkali metals and/or ammonium. The anodes of carbonaceous material are immersed vertically in the bath and are supplied with electrical current by current supply members which are usually of copper. The copper-anode junction which represents a weak point usually occurs at the top of the anode, in which case the copper current supply member and the copper-anode junction are partially immersed in the bath and are subjected to the action of the bath and the fluorine bubbles which are given off at the anode. Passivation of the copper occurs on the one hand by virtue of immersion in the bath of liquid fluorides and on the other hand due to anodisation when the electrolysis cell is put under voltage, but the properties of the layer obtained are highly unsatisfactory for providing effective protection for the copper. The copper is thus dissolved, resulting in a slow, regular deterioration in the copper-anode contact, which requires the electrolysis cell to be stopped and renovated, in particular requiring the current supply members to be restored and the anode changed. That renovation operation is effected approximately once per year.
The copper-anode junction may also advantageously be made at the bottom. In that case the copper current supply members pass through the total thickness of the bath before being connected to the base portions of the anodes. It is then necessary for them to be insulated, to prevent dissolution thereof; it is possible for example to provide sheaths which are capable of resisting the bath. An arrangement of that kind is described in SU-patent No. 193 454 which describes sheathing for the current supply members which is effected by means of magnesium, and protection for the copper-anode contacts by means of a chemically inert insulating agent (fluorinated hydrocarbon). The use of such protection arrangements is a delicate matter and they involve the use of products which give rise to problems.
However, the document `Electrodeposition and surface treatment` I (3)--1973, pages 256-265 (Battelle) discloses a treatment for the anodic passivation of copper in a liquid KF-HF bath. To form the passivating layer, that document describes a constant anodic passivation current of at least 0.4 A/dm.sup.2 in an equimolecular KF-HF bath at 245.degree. C., the time for which that current is applied decreasing in proportion to an increasing current; for a passivation period of greater than about 60 minutes, it is noted that the value of the passivation current is still between 0.4 and 0.45 A/dm.sup.2 (FIG. 2), in other words 0.4 A/dm.sup.2 represents a minimum asymptotic value of the passivation current.
That document also discloses anodic passivation of the copper in an anhydrous HF bath at 20.degree. C., in which case the minimum asymptotic value of the anodisation current is about 0.15 A/dm.sup.2.
The difficulty involved in significantly reducing corrosion of the copper and preventing deterioration in the copper-anode contacts in liquid KF-x HF baths (throughout the description the expression KF-x HF will means a mixture in which the number of moles of HF is exclusively equal to or close to 2), for the electrolytic production of fluorine, constitutes at the present time a limit on improving and developing fluorine electrolysers with higher levels of performance.


OBJECT OF THE INVENTION

Thus the applicants continued their research, the main object of which is to provide for durable and effective passivation of copper in a bath of liquid fluorides by means of a process which is simple

REFERENCES:
Electrodeposition and Surface Treatment, vol. 1, No. 3, 1972/1973 pp. 2535.
Chemical Abstracts, vol. 91; No. 2, 1979, p. 413, 11360x.

Affiliated with

Also associated with

Rating

Process for the passivating anodization of copper in a medium of does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for the passivating anodization of copper in a medium of, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the passivating anodization of copper in a medium of will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-144064