DE2048600B2 - Process for improving and maintaining the anode activity in electrodeposition - Google Patents

Description

The finding concerns a method for improvement and maintaining the anode activity in the electrodeposition with the aid a rubbing agent acting on the anode surface. The increasing decrease in anode activity such processes are generally based on the formation of an oxide layer or one Coating of a different material on the anode surface, which leads to an increase in the electrical resistance of the system leads. This layer can be made of reactive substances that affect the Support the dissolution of the anode, deplete it or enrich it with by-products of the reaction that this hampers the dissolution of the anode. It can also be used at times Formation of a space charge coming through a layer that is concentrated on the metal ions of the anode is. The cause can also be the inactivity of the anode material. In some cases show the problem is caused by uneven dissolution or activity of the anode.

So far, the solution to this problem has been through the use of a complex-forming substance (active Anions) to help dissolve the anodes. However, many of these substances are corrosive, and many of them reduce the current yield considerably. It also occurs with many substances decomposition over time, especially at elevated temperatures. Higher temperatures and higher stirring speeds for the electrolyte have also been attempted. New ones emerge Problems arise, namely evaporation of the electrolyte, but this does not solve the problem at hand will. Even with increasing the electrode ratio one got no further, because with it the probability of polarization is reduced, but constructive ones are different Opportunities in large-scale industry because of the investment and space required.

Finally, according to FR-PS 667 687 a construction is known in which with the help of brushes Anode surface is processed. It was found, however, that even with this there was no significant activation the anode surface was to be reached.

The invention now relates to a method for improving and maintaining the anode activity

ίο participated in the electrolytic metal separation With the help of a rubbing agent acting on the anode surface. It is characterized in that during electrolysis the anode of the action of a rubbing agent in the form of a pad, which hard particles fixed at a distance from each other, contains, exposed in relative motion to each other, fresh electrolyte is continuously supplied to the anode through the support. Preferred as a base one endless tape or one disc of one

2u permeable material. The permeable material is expediently an open fabric.

"Activation of the anode surface" means the removal of the polarization layer and a layer of reaction products from the anode and the dislocation of the atoms in the anode surface to such an extent that it increases activity. The atomic dislocation by the invention Treatment of the anode surface leads to the generation of defects that favor the activity

represent in a substantially uniform manner such as complete or partial dislocations, holes, voids by impact, branching, lattice disturbances and the like in addition to increasing the defect concentration and this leads to the removal of any adhering layer which hinders the activity of the anode Method according to the invention for roughening the anode surface and thus increasing the effective anode area.

The abrasive for the process of the present invention is a plurality of small, hard, relatively inflexible particles which are fixed substantially at a distance from one another and are held generally perpendicular to the anode surface by a permeable support. The particles also have a plurality of surfaces which are parallel and largely associated with the anode surface. In the method according to the invention, a relative movement takes place between the anode surface and the rubbing agent during the electrolysis. In addition, sufficient pressure is applied to the friction means in a direction perpendicular to the anode surface to thereby bring about a mechanical activation of this surface Particles come into action at extremely short time intervals, for example in the range between 3.8 · 10 ~ ^T to 6.1 10 " ² s. Fresh electrolyte is fed to the anode surface at the same speed as it is carried along by the abrasive has surfaces parallel to the anode surface, whereby these surfaces can be the edges of the particles. These surfaces wipe fresh electrolyte over them. The electrolyte reaches these surfaces through the permeability of the substrate of the abrasive agent or through the corresponding supply of electrolyte ζ the work surface between the Medium and the Ar

üdenflUche. This is to avoid excessive concentrations flush away cations or undesired reaction products.

According to the process according to the invention, it is possible to maintain the essentially uniform Anode activity without the known disadvantages. Another feature of the invention The process consists in the fact that a rapid movement of the electrolyte takes place directly on the anode surface.

In the method according to the invention under pressure, both perpendicular and parallel to the ariod surface in a regulated manner a permeable base attached, spaced apart, relatively inflexible small Particles are applied in such a way that they contact any precipitate formed on the anode surface. It is necessary to put sufficient pressure on the backing to leave a weak scratch pattern arises on the anode surface. This scratch pattern can be seen with the naked eye. In any case however, it must be recognizable at a magnification of 10 OG or less. Is it to low, sufficient anode activation is not achieved. The scratches can be caused by metal removal develop. However, it is preferred to choose particles of such hardness that the metal atoms are dislocated on the anode surface and not so much an actual erosion is the cause of the formation of the Scratch is.

By using smaller, relatively inflexible, non-conductive ones Particles are not covered by them for any appreciable length of time on any part of the anode surface. These Particles are generally randomly distributed over and bound with the help of a resin adhesive on at least the side of the pad touching the anode surface and preferably each other in small increments Distances fixed, e.g. 142 to 3.2 mm. Given that it can be an accurate and regular distribution of the particles on the substrate can also be used, but this is generally one unnecessary complication.

The term "particle" is not just about completely separate and individual three-dimensional body, but also around larger body with a variety of tips, cutting, Projections or the like, such as a relatively hard resin coating on a fibrous material, the coating being a Has a plurality of irregularly arranged elevations and generally referred to as uneven must become. The particles preferably touch or at least substantially influence the whole Surface of the anode. Their size can vary over a wide range, e.g. B. They can be a middle one Have a diameter between 0.25 μm and 3.2 mm. In general, however, the size will be between 23 µm and 0.5 mm for best results. the Particles can be broadly defined as hard; i.e., they have a Knoopsclie hardness about 10, but hardness as such is not critical; but one should not use a product that is opposite the anode in question is too abrasive.

The pressure to be applied should depend on the hardness of the particles; in general it is true that for softer particles a greater contact pressure perpendicular to the anode surface is required than with harder particles Particle.

The abrasive is preferably for the elec trulyt permeable and has a continuous porosity in the order of at least 6, ' Sheffield Units (measured on a Sheffield Porosimeter using a 63.5 mm Rin ges), The base material is also preferably at least somewhat compressible and deformable, se that there are irregular surfaces of the anodes and their deposits, if necessary, to invest

ίο can. As already indicated above, the backing material having a plurality of thin-walled surfaces extending between the particles, which cause the electrolyte to wipe across the work surface. These areas can be the

is edges of the particles themselves; at the preferred Embodiment, however, these are small chambers or pores of regular or irregular shape, whose function is like a bucket elevator, in which small amounts of electrolyte over the anode surface be distributed. The most diverse products were used as permeable underlay materials, z. B. open-meshed networks to which the particles are glued, sandpaper-like structures in compressed or non-compressed form, open-cell foam sheets in which the activating Particles attached in or on the cell walls, sponge-like materials containing the particles, or the like

Various products can be used as a rubbing agent, e.g. B. in the sense of the US reissue 21 852, namely an open-mesh net with glued abrasive grain, according to US Pat. No. 3,020,139 non-woven Sheets with a large number of hard particles, fixed along the fibers with the aid of an adhesive of the webs, according to US Pat. No. 3,256,075, a sponge which contains sponge particles impregnated with hard resin contains, according to US Pat. No. 3,334,041, a sandpaper or abrasive cloth with perforations through which the Electrolyte can flow. The latter product must be used in the method according to the invention modified to be non-conductive.

The mode of movement of the abrasive across the anode surface can vary widely, i. H..

it can be linear and / or rotating, e.g. B. a rotating means, which during its rotational movement also performs a back and forth movement. The only requirement is that there be relative movement takes place in the required order of magnitude between these two objects. In In the same way, the relative movement can obviously also be achieved in that a movable Anode and a stationary friction means or both parts are movably arranged.

Simultaneous wiping over the anode and the electrodeposited surface of the cathode with abrasive agent has proven to be useful. It was found that the activation accelerated one Causes dissolution of the anode and thereby a sludge formation on the anode in particular at the Tin refining is prevented. In some cases, the anode can also be activated with a different speed than the treatment of the cathode may be desirable. While the simultaneous treatment of the cathode and the anode is preferred, the abrasive Agents are only in contact with the anode surface. The Beweaunese speed can also

if varied widely, at higher speeds the depolarizing effect becomes at higher Current densities favored.

There are also a large number of possible variations in terms of the abrasive that can be used, both in shape and size Composition. The requirements for the substrate and the hard particles were dealt with. Any non-conductive fiber material that can withstand erosion by the electrolyte and results in a porous base is suitable. However, non-fibrous products such as foamed or spongy material. The non-conductive particles are also not critical, so that various materials such as resin particles, abrasives, ceramic particles, glass powder, walnut shells or the like can be used.

The electrolyte is preferably used at room temperature, e.g. B. 20 ° C, but can also be at Working temperatures up to boiling point.

The distance between the electrodes can range from very small on the order of 25 µm up to Such electrode spacings are sufficient, so that only that caused by current strength and resistance Voltage drop is a limitation.

The pressure applied to the abrasive at the anode can vary, depending by the hard particles and the system, it can be kept relatively constant or during operation can be changed within limits, nus the requirement for scratching on the one hand and the Avoidance of undue material removal on the other hand.

A wide variety of electrode materials can be used according to the method according to the invention, namely from insoluble in the electrolyte to slightly soluble. So you can z. B. in sulfuric acid, Lead or zinc anodes, in molten cryolite aluminum anodes, in salt solutions graphite or Platinum anodes and for use in fuel cells anodes made of z. B. Use nickel in potassium hydroxide as an electrolyte.

In the method according to the invention, no corrosive or complex-forming ions are required, it operates at normal temperatures and does not require a high electrode ratio. the rapid movement of the abrasive causes rapid movement of the boundary layers on the anode surface and thus leads to the avoidance of excessive cation concentrations. Furthermore there is no need for anode bags, which are often required to collect particles falling from the anodes due to uneven anode dissolution. The anode dissolves over the entire surface area evenly, insofar as this is treated within the meaning of the method according to the invention will. As stated above, according to the invention, less pure anode material can be used, such as with usual procedures.

The method according to the invention will now be explained in more detail with reference to the figures.

Fig. 1 shows schematically the process according to the invention applied to copper refining;

F i g. Fig. 2 schematically shows a detailed view of a rubbing means which can be used according to the invention;

3 shows the weight loss in a diagram (Anode activity) of an anode made of pure tin, treated according to the invention in comparison to FIG Activity of the same anode by a common method;

FIG. 4 shows a diagram similar to FIG. 3, only that here the anode is made of a tin alloy 0.1% antimony and 0.04% copper;

Fig. 5 shows the dependence of voltage and current intensity at different current densities in Within the scope of the method according to the invention on einci pure tin anode;

6 is a similar diagram to FIG. f and shows the relationships in a known method;

F i g. 7 and 8 show the situation in the sense of FIG. 5 and 6, but here with a tin alloy mil 0.1%> antimony as anode.

In the case of the FIG. In the process illustrated in FIG. 1, the tub 10 contains the electrolyte 11. A sacrificial anode made of impure metal 12 is movably mounted in the electrolyte in contact with a rubbing agent in the form of an endless belt 14. A cathode 13 made of the metal to be deposited is initially in contact with the other side of the strip 14; During operation, however, as shown in FIG. 1, the band 14 is located between the anode Xl and the deposited layer of the pure metal 18 on the cathode 13 and in contact therewith. The edge 14 runs over deflection rollers 15, 16 and the drive roller 17. The tape and its rollers are mounted in such a way that they can be pulled away from the cathode surface 13 as the deposition 18 increases.

During operation, the abrasive belt rubs both over the surface of the electrodeposited Metal than over the surface of the anode and thus supports its rapid dissolution. F i g. FIG. 2 shows, in a considerable enlargement and idealized, part of a device that can be used according to the invention abrasive agent and the fixation of the hard particles in the substrate. In the non-woven web

z. B. made of non-conductive fiber material such as polyethylene terephthalate, the individual fibers 25 are fixed at their points of contact with an adhesive 26. A multiplicity of small hard particles 27 are located on the fibers 25 and in the sense of this embodiment adhered by the binder 26. At least some of the fibers 25 extend relatively parallel to the anode surface 29, as shown in the thread piece 28, and thus form thin-walled cells, with the help of which electrolyte is passed over the work surface (for reasons of clarity, here the particles 27 shown some distance from the anode surface 29; during operation, however, takes place actually touch instead).

The process according to the invention is explained in more detail using the following examples.

example 1

A bar made of raw copper, about 96% Cu, with a rectangular cross-section is used in the sense of FIG. 1 applied as an anode. The abrasive was a nonwoven sheet about 1.59 mm thick. Contains aluminum oxide, grain size 37 iim, which is bonded with a synthetic resin adhesive. This train was made on both sides of a 20/20 nylon fabric,

as it is known as reinforcement inserts, laminated to form a continuous abrasive belt approximately 15.25 cm wide. This tape runs between the anode and the

Instead of the copper cathode, you can also use the usual cathodes made of corrosion-resistant steel, brass or the like. Apply. This whole arrangement was immersed in a sulfuric acid copper sulfate solution, at Electrolysis formed a precipitate of highly pure, healthy copper on the cathode.

Example 2

In order to show the activating effect of the method according to the invention for anodic surfaces, identical anodes made of pure tin were used together with conventional copper cathodes in a tin electrolyte. This contained 284 g / l SnSO ₄ . One of these anodes was treated according to the invention, while such a treatment was omitted for the other anode. The results are shown graphically in Figs.

In all experiments the cathode was a copper plate, 1.29 dm ² , and the anode made of pure tin had an anode area of 1.61 dm'- '. The electrolysis was carried out under the following working conditions:

I found improvement in the activity of the anode in the process according to the invention.

This can be seen even more clearly from FIGS. 5 and 6, where the voltage is plotted against the current intensity is. F i g. 5 relates to the method according to the invention case 1 and FIG. 6 to the known Procedure case 2. The curves show that the influence on the activation of the anode surface was to reduce the polarization time, so that for

ίο a given current density the required voltage at the beginning and at the end of the experiment was almost the same. In case 2, the voltage at the end of the experiment was at the higher current density, namely 308 A / dm ² , more than twice the initial voltage.

122 or 90S or 615 A / dm ² 5 min

Anode current density

EIcktrolysis time

Room temperature

The electrolysis tub was through a fiberglass diaphragm divided into a cathode chamber and an anode chamber in each case was assigned to the anode a disk with a rubbing means is arranged, which is at a peripheral speed was driven by 75.3 m / min in order to achieve sufficient bath movement. In case 1 according to the invention, the disk just touched the anode surface and stroked it there. The disk was one with a diameter of 76 mm and a width of 19 mm, made of a nylon fabric 15 den, on which with the help of a resin adhesive silicon carbide abrasive grain, Grain 37 µm, was fixed. Wattmeter readings were used to determine the load on the drive motor for the disc in each experiment to reproduce.

In case 2 the disk ran a short distance (3.17 mm) from the anode surface in order to ensure the same stirring effect in the solution as in case 1, but without wiping contact as in case 1. The anodes were determined before and after the electrolysis after 1 minute and at the end of the test, i.e. after 5 minutes. The current density was kept constant in each test. Parallel tests were carried out and the mean values of the weight loss of the anodes after 5 minutes as a function the current density is determined. Case 1
Case 2

FaIU
Case 2

Current density
A / dm2

122
122

308
308

Voltage V at the beginning | at the end

3 3

8.4 35

3 13

10.6 14.6

From this comparison and FIGS. 5 and 6 it can be seen that a rapid depolarization the anode takes place by the activation according to the invention.

Example 3

Example 2 was modified in that as the anode a tin alloy with 0.1 ^η, antimony and 0.04 Ό ⁰ Zo copper was used.

Current density
A / dm ² Weight loss
e case 1 V2 0.4 Case 2. 122
308 0.4
0.9 case 1 308 0.3 Case 2

These values have been used for a diagram in FIG. 4.

case 1
Case 2

case 1
Case 2

Current density
A'dm ^:

Voltage V at the beginning at the end

122 3.4 4.6 122 12.0 11.4 308 15.8 14.9 308 34.0 14.4

FaM
Case 2

FaM
Case 2

Current density
A'dm ²

122
122

308
308

Weight loss

in practice

0.4 0.3

0.92 0.4

theoretically g

0.368

0.92

From the above list goes the essential increase "the dissolution rate and follow-See F i 2. 7 for case 1 and F i g. 8 for case 2.

Example 4 ^F

The arrangements in the sense of FIG. 1 were used to produce pure copper. The cathode was also pure copper, the electrode areas were 1.61 cm ² each. In place of the endless belt of the device according to FIG. 1, this time a porous disk was used in the sense of the example, diameter 76 mm, non-woven nylon backing with silicon carbide abrasive grain, grain

37 (im, disk speed 315 rpm, electrolyte 21OgZIH ₂ SO ₄ and 4SgZICuSOj in distilled water. 2 l of electrolyte were required for each experiment. Electrolysis time 5 min at room temperature. In this case the current was kept constant at 5 A. For comparison, the disk was used at the same running speed, but 3.17 mm away from the electrode surfaces. The voltage at the beginning and end of the experiment and the weight loss of the anodes were determined again. Case 1 according to the invention, Case 2 for comparison.

case 1
Case 2

Voltage V
at the beginning | at the end

12.0
50.0

11.0
25.0

Weight loss
G

0.5
0.7

Example 5

Example 4 was modified by using a 51X279 mm copper plate as the cathode and the pane only touched the anodic surface. The anodes were made of impure, blistered material Copper. The following average values resulted from several Paraüclversuche:

1 Instep
initially ung V
at the end Weight
loss
G case 9.5 8.0 0.60 case 25.5 20.3 0.55

From Examples 4 and 5 it can be concluded that that at the higher current density a lower voltage is obviously required for the anodic Dissolution of the copper (regardless of whether it is pure or vesicular) when the anode is treated according to the invention becomes opposite only to a bath movement. In the method according to the invention, the was average voltage according to example 5 around 8 V, whereas more than 20 V in the comparison test were needed.

The process according to the invention also leads to a saving in energy, because in the process according to the invention the product UI is around 40 W, whereas around 100 W had to be used in the comparative experiment. The energy required for activation according to the invention was about 1 W (the wattmeter that was connected in series with the drive motor for the disk showed 57 W for the method according to the invention and 56 W for the comparison method, where only the electrolyte was stirred).

Comparative experiments

To show that brushes, e.g. B. in the sense of FR-PS 667 687, and those used according to the invention abrasive means to completely different experiences lead, the following experiments were carried out.

The test arrangement was in one row: a rigidly mounted anode and a rotatable one above it Shaft a mounting plate with which the vertical cathode was in contact. The kahode and anode were essentially

10

gen over. The mounting plate was used on the one hand to: the rubbing agent according to the invention and, on the other hand, a brush in the sense of the state of the art to record.

The electrolyte was obtained by adding 8,500 _{parts by weight of NiSO 1} -g H ₂ O, 800 parts of H ₃ BO ₃ and 4 parts of saccharin to the 20,000 parts by weight of water. Working temperature of the electrolyte 65 ± 5 ° C; Anode Nickel sheet with an area of about 12.9 cm ² facing the cathode, mounting plate: polyvinyl chloride disc - 0 178 mm, thickness 12.7 mm - which had 108 bores with a diameter between about 3.8 and 6.35 mm over the outer area . These bores were used to allow the electrolyte appropriate access to the anode surface facing the cathode. Speed of rotation of the shaft 2100 rpm, so that there is a surface speed of the abrasive in the center of the cathode

ao of about 50 m / 's.

Cathode: Corrosion-resistant steel rod, Ø 12.7 mm.

1. Invention abrasive agent:

Needle felt (XU 94 Kendall Company) made of nylon

a.5 fibers 6 den, 210 g / m- ', thickness 2.68 mm. This felt was given away by roller application with a mixture of 1170 parts of polyurethane resin (40% solids content) and 500 parts of silicon carbide abrasive grain (grit 1000). The curing of the binder was carried out in 3 hours at 121 ° C and 50 ". 'I> relative humidity and then for 5 hours at 121 ⁰ C. From this material, a disk having a diameter of 178 mm was cut out and mounted on the Montaceplattc.

2. Additional holes were drilled in the mounting plate for the state-of-the-art brush, namely diameter 4.8 mm, depth 4.8 mm; it became bent tufts of nylon fibers - 200 den, length at least 63.5 mm - applied

and these tufts fixed in the mentioned holes with the help of a binder and then on a Sheared even length of 36.5 mm. This brush had a relatively constant bristle density over the entire work surface.

The brush was brought into a slight contact pressure against the anode surface facing the cathode (about 0.7 g / cm ² ).

3. The brush gave a satisfactory, glossy metal deposit at a nominal current density of 50 A / dm ^2, corresponding to an effective current density of about 35 A / dm ³ . At a nominal current density of 75 A / dm ² , the deposit was vesicular and the corners broke out when the thickness resulted in ^{an effective current density of 35 A / dm 2.} At 100 A / dm ² , only a burnt, green-colored deposit was obtained, which was completely unusable.

Under the same working conditions were obtained with the erfindiingsgemäß applied material up to nominal current densities of 200 A / dm ^ä corresponding RMS current densities of 130 A, 'dm-' high-gloss coatings.

If one now compares the results with brushes and abrasives used according to the invention, this shows in terms of the rate of deposition and thus the economic viability of the process eanz considerable differences.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. Process for improving and maintaining the anode activity in electrolytic Metal deposition with the help of a rubbing agent acting on the anode surface, characterized in that the anode surface of the action during the electrolysis of the rubbing agent in the form of a pad, the hardc-particles at a distance from one another contains fixed, is exposed in relative movement to each other, the anode through fresh electrolyte is continuously supplied to the base. 2. The method according to claim 1, characterized in that the base is an endless one Tape or a disc of a permeable material is used. 3. Process according to claim 2, characterized in that that an open fabric is used as the permeable material. 4. The method according to claim 1 to 3, characterized in that the rubbing agent is additionally paints the cathode on the other side.