DE2929305C2 - Process and device for the continuous electrodeposition of manganese on steel - Google Patents

Description

Since Bunsen succeeded in 1854. Using manganese electrolytically from an aqueous solution of manganese chloride To deposit a platinum anode, the electrolytic recovery of manganese has considerable Progress made Aqueous solutions of manganese sulphate come in as electrolytes Ammonium sulfate and aqueous solutions of manganese chloride containing ammonium chloride in Question. These electrolytes can also contain various additives. So far there are over 300 publications and patents on the electrowinning of manganese have been published.

These publications all relate to the electrolytic production of vu: i manganese, in which manganese ores are dissolved, leached and electrolyzed. More recently, attempts have been made to produce metallic manganese by electrolysis of neutral or weakly acidic manganese salt solutions at a current density of several amperes per dm ² using a diaphragm between the anode and the cathode.

Up to now there is no method for the continuous electrodeposition of manganese on steel known. The reasons for this include the following. Manganese is a very active element and it is the last Metal in the electrochemical series, which from an aqueous solution to electrochemical Paths can be separated. Impurities in the electrolyte, especially cations, interfere, as a result of which it becomes practically impossible to use metallic manganese as an anode material. Therefore it is necessary to use an insoluble anode. The supply or replenishment of manganese ions in the electrolyte is of great importance. In contrast to the electrolytic refining of metallic manganese, the Electroplating of manganese can be done without a diaphragm. This requires development new electroplating conditions and methods.

When manganese is electrodeposited in a sulphate or chloride bath, it forms on the plated Surface a thin oxide skin which, depending on the type of paint used, can deteriorate

Adhesion of the paint film can lead.

Steel electroplated with manganese has changed according to the environment also its appearance, and it forms brown rust, which not only deteriorates appearance, but also increased corrosion and deteriorated paint adhesion leads

Steel coated with manganese often shows a brown, blue color immediately after electroplating or purple color, but no metallic sheen, ι ο The hue and thickness of the colored film depend on the electroplating conditions and the washing conditions after electroplating. When using an electrolyte consisting mainly of manganese sulfate The color and thickness of the electrolyte bath increase in color and thickness Voltage between the electrodes increases. The presence of a thick colored film on the with Manganese electroplated surface prevents satisfactory results from being achieved afterwards chemical conversion treatment, in particular a phosphate treatment. That's why it is required the colored film before the chemical Remove conversion treatment.

While it is possible to make the colored film by treating it with an acidic solution with a to remove pH below 1.8, but it forms again immediately afterwards. If the stained film with a chromic acid solution, a manganese coating with a metallic sheen is obtained. this however, this is the exception.

However, this treatment has the disadvantage that the used chromic acid solution can only be released into the waste water after a pretreatment in order to avoid environmental pollution. The used chromic acid solution must be subjected to a reduction treatment. Another disadvantage of chromic acid treatment is that if manganese-coated steel sheet is treated on one side, the result of the subsequent phosphate treatment ₆ is worsened by the contact of the steel surface with the chromic acid solution.

The invention is therefore based on the object of a method for the continuous electroplating of Manganese on steel using an insoluble anode in an electrolyte bath without a diaphragm in which manganese-plated steel is obtained, which has the above-mentioned defects and disadvantages does not have.

Another object of the invention is to provide an apparatus for carrying out the continuous To provide electroplating of manganese on steel.

These objects are achieved by the invention. The invention relates to what is set out in the claims marked items.

In the method of the invention, the steel is continuously electroplated with manganese in an electrolyte bath using an insoluble anode and without a diaphragm, the amount of cations that are electrochemically more noble than manganese being limited in the bath and / or a reaction product from the bath is separated that is formed in the electrolyte bath. In this way a high current yield is achieved. Manganese (II) ions are fed into the manganese electrolyte bath by a process in which metallic manganese is in an aqueous solution or an electrolyte with a pH of at most 5.0 is resolved. In another embodiment, manganese (II) ions are fed into a sulfate or chloride bath for manganese electroporation by a process in which manganese sulfate or manganese chloride is dissolved in an aqueous solution or an electrolyte with a pH of at most 7.0 will.

The drawings are explained below

F i g. 1 to 3 show the influence of the change in the concentration of bath constituents on the cathode current yield in a manganese sulfate bath, an ammonium sulfate bath and an ammonium rhodanide bath.

F i g. 4 shows the relationship between the cathode current density and the cathode current efficiency in FIG Electroplating of steel strip that moves through the electrolyte bath at different speeds to be led.

F i g. 5 shows the relationship between the electrode spacing and the current efficiency of the same baths.

F i g. 6 schematically shows an embodiment of the invention.

F i g. 7 to 9 show examples of the manga n (II) ion supply device according to the invention.

The invention is described below with reference to a drawing explained in more detail

It is known that cations other than the metal ions to be electroplated are present in an electrolyte bath are present, deposited with the electrodeposition, thereby reducing the quality of the deposition suffers. At the same time, the deposition of the contaminating cations has a strong influence on the Deposition of the desired metal. This is particularly the case with manganese. It is therefore of of the utmost importance to determine the limit values of the individual cations in the electrolyte bath and the To control or limit amounts of these cations in the electrolyte bath. Examples of these disruptive Cations are chromium, zinc, tin, iron, "cadmium, cobalt, nickel, lead, arsenic, antimony, copper and" Silver ions.

It is also very difficult to use metallic manganese as the soluble anode in the electroplating of manganese to use. Furthermore, this is inconvenient in technical electroplating. This is why it is technically advantageous to use insoluble anodes. In this case, however, the oxidation occurs Manganese ions near the anode, which interferes with the electroplating. To prevent oxidation of the To avoid manganese ions, additives are incorporated into the electrolyte bath that inhibit oxidation. By Using these additives it is possible to electroplate manganese without a diaphragm perform. It is also possible, in contrast to the Electrorefining of manganese to achieve rapid and even deposition of manganese.

However, these additives change with formation during electrolysis or electroplating various reaction products that accumulate in the 3ad. For the successful implementation of the continuous liciien Electrodeposition of manganese it is therefore important to also prevent the formation of these reaction products to control or limit in the electrolyte bath.

Sulfur or selenium compounds are used as oxidation inhibitors, in particular sulfur compounds, such as rhodanide and thiourea, the usual sulfate or chloride baths for electroplating of manganese can be added.

The control of the basic constituents of the electrolyte bath requires, for example, a control of their concentration ranges, a limitation of the cations introduced into the electrolyte bath as impurities and a control of the change in the bath composition, in particular the formation of reaction products during electroplating. Unless these factors are successfully controlled, continuous galvanic deposition of manganese on steel is not possible. These factors are based on the chemical activity of manganese, and their influence is evident in extensive studies and attempts to develop a technically feasible process for continuous electroplating? of manganese on steel

In the continuous electroplating of manganese using an insoluble anode is it is crucial. Manganese (II) ions as a source of manganese

/'.1/"UItKHVII. I-'IC /. <Ι um vt / M ιτιαιι ^ ηιΐ ^ ii; iwmn iMiriif flat two procedures are carried out.

In the first process, metallic manganese is dissolved in the electrolyte bath, while in the home / wide process a manganese salt, such as manganese sulfate, is dissolved. Man earchlond <de M.ingancarbonat. is dissolved in the electrolyte bath. The choice of the manganese source for manganese (II) ions depends on the type of electrolyte bath. It is more practical to first prepare the manganese source in a separate manufacturing container. and then feed the electrolyte produced in this way into the electrolyte bath, as the manganese source can be easily dissolved in the electrolyte bath. This beruh ': on th ^e fact that the bath composition: m F.lektropi.ittierbehälter and other factors. v.ie de "pH value and the bath temperature, controlled ·. <. grounding. To stabilize the deposition of Manga" is ¹ , it is preferable to set the pH value in the range of 2 Ts »'jin / L and the bath temperature on a who! of at most 50 "C. The current density should preferably be in the range of 20 to 300 A / dm ² i: e. In practice, the electroplating container is usually a container with means for circulating the electrolyte. This enables a considerable increase in the current density, which in turn results in high electroplating speeds.

The control of the amount of impurities that are brought into the electrolyte bath, as well as the Reaction products are described in more detail below.

The interfering cations get into the ElektroKtbad from the base material to be electroplated. the electrolyte circulation system, the conductive roller and the chemicals added to the electrolyte bath. The limit amounts of the individual cations are explained below, in most cases these interfering cations are not present alone. It is desirable to keep the amount of these cations as low as possible The limit values for these cations are given below:

Cr
F-ί

A convenient control of the amount of these Cations ">; 2πη achieved by the following process

Zn MXl ρρΠ- - Sn iOO ppm CD I I'll) - Co I") Ph IiMl As 50 C ■; M I Aa 50

will. In any case, it is important to set the amount of this Keep cations within the allowable limits.

The following methods are available for separating the disruptive cages:

a) The cations are precipitated and separated using a sulfide such as hydrogen sulfide;

b) the cations are by adding an alkaline earth metal Hi metallsalz.es separated;

c) the free cations are reduced during electro plating by adjusting the pH value so as high as possible (pH 6 to 8).

It is also useful to separate these cations from the circulatory system of the electrolyte bath. this is expediently carried out by filtering the electrolyte in the circulatory system, for example in a storage container for the preparation of the electrolyte bath to the cations

happen in a separate precipitation tank.

The reaction products that accumulate in the electrolyte bath are very complex substances, mainly carbonates, sulfates, various Nitrogen compounds, colloidal sulfur and minor amounts of gaseous hydrocarbons. Hydrogen and nitrogen oxides exist. These reaction products have a decisive influence on the continuous electroplating of manganese.

■ Some of these reaction products can be the same Way how the interfering cations are separated. so that the influence of these reaction products in is decreased to some extent. Additionally you can The following methods are used to completely separate the reaction products, whereby a continuous electroplating of manganese enables:

(a) Separation using an adsorptic medium. like activated carbon;

(b) Separation by cleaning using ion exchange diaphragms or reverse osmosis membranes and

(l) Separation by heating and boiling the F. electrolyte bath.

Of these three methods mentioned, methods (a) and (b) are very effective, but there are also method (c) gives satisfactory results. It is therefore

■ possible, not just the amount of interfering cations. but also to keep the reaction products forming and accumulating in the electrolyte bath within limits by a get.yTiete combination of the methods listed above.

; ■ It is also necessary to check the pH of the

Electrolyte bath that occurs during electroplating

descends, steer. This can be done in a simple manner

Addition of aqueous ammonia solution take place. As stated above, it is for

-r, successful continuous galvanic deposition of manganese on steel is crucial to control the amount of cations, which are edier than manganese, in the electrolyte bath as well as the formation of reaction products that accumulate in the electrolyte bath. If the

-5 Electroplating of manganese is carried out on steel strip passing through the at high speed Eiektropiattiervorrichtung runs, the Eiektropiattierung must be carried out in several electroplate containers

because the amount of electricity available in a single electroplating tank is limited is. Continuous electroplating in multiple electroplating vessels can be technically successful plating with zinc, chromium and nickel can be carried out. These electroplating methods are suitable however, does not opt for the electroplating of manganese for the reasons mentioned above, namely because Mangen itself is a very active metal that is light oxidized, especially immediately after electroplating. This oxidation of manganese depends on the im Electrolyte bath from existing impurities. For this reason, a multi-layer plating in a plurality of electroplating containers avoided.

In the case of a single container electroplacing isi. As already stated, the amount of current available is limited, so that it is not possible to carry out the electroplating at high speed continuously at a current density of 40 A / dm ² , a pH of 2.0 and a constant bath temperature of 45 "C.

From Fig. 1 it can be seen that the cathode current efficiency can be improved with an increasing increase in the manganese sulfate concentration up to 60 g / liter can, but it remains constant even if the manganese sulfate concentration increases over 60 g / liter will. It can also be seen from FIG. 2 that the cathode current efficiency increases with increasing concentration of ammonium sulfate increases to 50 g / liter, but then remains constant even if the ammonium sulfate concentration rises above 50 g / liter. It can also be seen that if the concentration is unnecessarily increased strong of manganese sulfate and ammonium sulfate

ι, losses of electrolyte occur on the steel strip adheres while it is being transported.

F i g. 3 shows that a high constant current efficiency can be achieved if the concentration of the Ammonium rhodanide in the bathroom to a value above

»Jtaiiiuiatit, uuii.ii / .uiiiiiicm.

Therefore, it is important for a technical process to increase the electroplating speed by arranging a Increase plurality of electroplating vessels. In this case, however, it is necessary to prevent the oxidation of the To prevent manganese coating between the electroplating vessels. After extensive research has been found according to the invention that it is very useful if the to be electroplated Base material with the electrolyte is kept moist the entire time, while the base material is transported through the electroplating tank, for example by spraying on the electrolyte the steel or by immersing the steel in the electrolyte. The rapid and continuous electroplating Manganese on steel can therefore be carried out successfully if the surface of the steel is in wet condition while the steel is transported from one electroplating container to the next will.

It has already been mentioned above that it is a technical process for continuous electroplating of manganese using an insoluble anode is advantageous not to have a diaphragm use. It has been found experimentally that it is very important to control the bath composition and prevent oxidation of the manganese coating between the electroplating containers.

These experiments are explained in more detail below.

First of all, the conditions for achieving an optimal cathode current yield must be determined be to a steel strip electroplated with the required amount of manganese at the highest possible speed using a rectifier which is normally only a specific one has limited capacity.

As a manganese electrolyte bath, there are various baths, e.g. B. a sulfate and a chloride bath in question. It Tests were carried out to determine the cathode current yield in connection with a bath which mainly contains manganese sulphate, ammonium sulphate and ammonium rhodanide

The F i g. 1 to 3 show the influence on the cathode current yield as a function of the concentration of the individual components, namely manganese sulfate, ammonium sulfate and ammonium rhodanide, in an experiment using an electrolyte bath of 120 g / liter of manganese sulfate, 75 g / liter of ammonium sulfate and 60 g / liter of ammonium rhodanide ^ UgfUIICt (lllSlClgl. TTCtlll UlC I \ Ulfr.LtllldtlUII UCl ammonium rhodanide in the electrolyte bath is below 30 g / liter, the electrolyte becomes muddy due to the formation of black-colored deposits on the surface of the anode. The pH value is another important factor in sludge formation Electrolyte Unless the pH is 8.0 or less (acidic), a stable and transparent bright red electrolyte cannot be obtained, on the other hand, when the pH is lower than 2.0, metallic deposition does not occur Manganese, therefore the pH range from 2.0 to 8.0 is considered to be the most favorable range.

Continuous electroplating was made based on the above test results of manganese on steel strip with a continuously operating electroplating device. Fig. 4 shows the relationship between the cathode current density and the cathode current efficiency at Using various feed speeds of steel strip that is in an electroplating bath an insoluble anode made from an alloy of 95% lead and 5% tin in an electrolyte plating bath with 140 g / liter manganese sulfate. 60 g / liter ammonium sulfate and 30 g / liter ammonium rhodanide at a pH of 2.0 and a bath temperature of 50 ° C is electroplated.

From Fig. 4 it can be seen that the cathode current yield increases sharply with increasing current density up to about 20 A / dm ² and remains almost constant above this value and thus shows only a slight tendency to improve the current density even if the current density from 50 A / cm ² to 200 A / dm ^{2 is} increased, so the current yield is only slightly improved. Uniform electroplating can therefore be carried out if the cathode current density on the steel strip is kept at a value of at least 20 A / dm ² .

With regard to the importance of the distance between the electrodes, i. H. the distance between the steel strip cathode and the anode, further experiments were carried out on the relationship of the electrode spacing and to investigate the current yield at different feed rates. The results are summarized in Fig.5. The tests were carried out with an electrolyte bath of 120 g / liter Manganese sulfate 75 g / liter ammonium sulfate and 40 g / liter ammonium rhodanide at a pH value of 25 and carried out a bath temperature of 50 ° C

ίο

At each of the feed speeds of 50 m / min, 100 m / min and 150 m / min, the cathode current efficiency is greatly improved when the electrode spacing is 50 mm or less. A smaller electrode gap results in a better current efficiency, but the electrode spacing is limited by the condition avoid contact of the anode with the transported zm fast feed speed steel band. Due to the currently prevailing technical possibilities, it is possible to shorten the electrode spacing to about 5 mm. It is possible that this distance can be narrowed even further in the future.

The experiments described above were carried out with a sulphate bath. However, the method according to the invention is not limited to sulfate baths, but can also be applied satisfactorily to electrolyte baths of various compositions, such as a uiurfuuau mainly containing manganese chloride

äöiVic DauCT ΓΠϊί VCrSCiiiCuCrfCn MCHgCr

at most 5.0 must be adjusted to manganese (II) ions to be able to supply. Above this value, the supply of manganese (II) ions is not sufficient, which for Supplementation of the deposited amount of manganese is required.

The supply of manganese (II) ions from metallic manganese can be carried out in a chloride bath in the same way 300 g / liter of manganese chloride, 200 g / liter of ammonium chloride and 2 g / liter of ammonium rhodanide can be achieved, for example, when the pH is adjusted to a value not higher than 5.0 with hydrochloric acid.

Table I.

Additives such as sulfur and selenium compounds and glycerine.

Also, electroplating containers placed horizontally or vertically can be used with similar results be used.

The following is a method of supplying manganese (II) ions in continuous electroplating explained by manganese by the method according to the invention.

When using metallic manganese as a source of manganese (II) ions, the manganese is in a zone low pH, namely in an acidic zone, and the resulting manganese (II) ions are fed to the electrolyte bath. In contrast to the case when a manganese salt is used, it takes place no accumulation of anions because no further anions are formed, so that the bath composition remains practically constant over the entire time during the electroplating.

The feed rate is also high because manganese is used in metallic form. That's why it can Electrolyte bath can be kept stable for a long time, and it is only necessary to do so during electroplating to supplement the amount of manganese (II) ions consumed.

However, if the pH of the electrolyte bath rises above 5.0, this is not advantageous because the The rate of dissolution of the metallic manganese decreases. Therefore it is important to keep the pH value at one Set a value of at most 5.0. This is from the results of the experiment outlined below evident.

It becomes an electrolyte bath by dissolving 50 g / liter of manganese sulfate, 80 g / liter of ammonium sulfate and 60 g / liter of ammonium thiocyanate produced. The pH value is adjusted to a certain level with sulfuric acid Value set The base material is cold-rolled steel strip (JiS G3141 SPCC) with a thickness of 03 mm, a width of 5 cm and a length of 10 cm used

Manganese (II) ions are produced by dissolving metallic manganese in a separate container and added to the electrolyte bath.The electroplating container has a capacity of 1 liter, and the electroplating is carried out for 3 hours at a current density of 20 A / dm ² and a bath temperature of 30 durchgn ⁰ C with an anode made of carbon results the results are summarized in Table I. It can be seen that the pH-value to a value of

pi! -Won clos Moliillnodiidtiunii I train 6.0 unfavorable measurement structure i; short absclieiduni! s ς '.!'. • s »!. 5.3 despl. 5.0 mite M '. * schichlunp 4.5 descl. 4.1 the same 3.0 desul. 2.5 descl.

The metallic manganese used to produce manganese (II) ions is usually in the form of

tn dandruff, but it can also be used in powder form. The metallic manganese will usually obtained by electro refining, and it is usually available in the form of plates that do so are brittle in that they are broken into smaller pieces

ii can be. Preferably that has used metallic manganese with a grain size of 1 to 50 mm. The speed of dissolution decreases with the smaller Grain size too. In terms of the work required to crush the metallic manganese, the Plate form, however, more advantageous than powder form.

The following explains the method in which manganese sulfate or manganese chloride -> ls source for Manganese (II) ions is used. When using a sulphate bath, manganese sulphate is of course used, while manganese chloride is used when using a chloride bath. These salts stand out due to the high rate of dissolution, the supply of manganese (II) ions is easy to carry out, and that Electrolyte bath is easy to control because the bath composition does not vary in terms of ions changes.

In practice, the pH of the electrolyte causes the manganese sulfate or manganese chloride in it is solved, no difficulties, but the resulting manganese coating is less than satisfactory Quality if the pH value is 2.0 or lower. It is therefore advisable to adjust the pH value to a Set value above 2.0. The electroplating can even be carried out in the alkaline range, but the manganese salts are then subject to hydrolysis and in the strongly alkaline range precipitation occurs. The upper limit of the pH is therefore 8.0.

A typical sulphate bath essentially contains manganese sulphate, ammonium sulphate and ammonium rhodanide, while a typical chloride bath in the aqueous manganese chloride, ammonium chloride, and potassium rhodanide contains To supplement the manganese (II) ions, it is therefore advisable to add manganese sulfate to the sulfate bath

not to use manganese chloride for the chloride bath.

When using Manfc'ane carbonate as a source for Manganese (II) ions, the manganese carbonate is brought into solution in the strongly acidic pH range and the Electrolyte bath supplied. Carbonic acid forms from the carbonate anion and escapes from the solution. on In this way, there is no accumulation of anions in the electrolyte bath, and the bath composition changes not worth mentioning. In this case too, the electrolyte bath is over ι during the electroplating stable for a long period of time, and it is only necessary to replenish the consumed manganese by supplying To supplement manganese (II) ions.

Raising the pH to above 2.5 is inexpedient because the rate of dissolution of the Manganese carbonate becomes less. The pH should therefore be at most 2.5, which is evident from the following The test results communicated can be seen.

The experiment is carried out as follows: The lwt vuirsj

sulfate, 80 g / liter ammonium sulfate and 60 g / liter AmmonL: -nrhodanid produced. The pH value is adjusted to a certain value by adding sulfuric acid. Cold-rolled steel strip (JIS G3141 SPCC) 0.8 mm thick, 5 cm wide and 10 cm long is electroplated as the base material. Manganese (II) ions are produced by dissolving manganese carbonate in a separate container and feeding the solution into the electrolyte bath. A container with a capacity of 1 liter is used as the electroplating container. The electroplating is 3 hours at a current density of 20 A / dm ² and a bath temperature of 30 ⁰ C with an anode made of carbon conducted feeds the results are summarized in Table II. From the table it can be seen that the pH value should be adjusted to a maximum of 2.5 for a satisfactory supply of manganese (II) ions. At a value above 2.5, the supply of manganese (II) ions cannot take place quickly enough to replenish the amount of manganese deposited.

The following is the apparatus for continuous electroplating of manganese on steel and the Device for the supply of manganese (II) ions explained.

As insoluble electrodes for electroplating manganese, electrodes made of platinum, carbon, lead and ferrite can be used. During the continuous electroplating, manganese (II) ions are deposited in the Electrolyte bath consumed in an amount equal to the deposited amount of metallic manganese is equivalent to

Various investigations have been carried out on how manganese (II) ions are appropriate for the electrolyte bath are fed. First of all, the type of manganese source depends on the supply of manganese (II) ions to the Electrolyte bath from the pH zone, namely a low pH zone and a high pH zone into which the Manganese ion source is fed within the pH range required for the electroplating of manganese is suitable in the pH range from 2.0 to 3.0 metallic manganese granules are used as a source of manganese ions, while in the pH range from 3.0 to 7.0 water-soluble manganese salts such as manganese sulfate are used will. The necessary to dissolve the metallic manganese granulate to manganese (II) ions The rate of dissolution depends on such factors as the pH and the temperature of the bath in which the metallic manganese is dissolved, the grain size

the amount of metallic manganese and the contact between the solution and the metallic manganese.

The dissolution of the water-soluble manganese salts, such as manganese sulfate, is facilitated by increasing the Temperature of the dissolving liquid and by stirring. However, it is necessary to find an unfavorable one Effect of the anions of the manganese salts on the electroplating conditions after the dissolution of the Avoid salts. For these reasons, carbonates are preferred.

For the reasons outlined above, it is necessary to adjust the concentration of the manganese (II) ions in the electrolyte bath to determine manganese (II) ions automatically from the device to the electrolyte bath Feed supply of manganese ions. The concentration of the manganese (II) ions in the electrolyte bath changes due to the deposition of metallic manganese on the base material, the entrainment of Electrolyte through the steel and through evaporation of \ ν »ςςρΓ from the electrolyte. To determine the Several measuring devices are required to change the ion concentration: For example, one measuring device to determine changes in the bath volume in the plating device, such as a bath level measuring device, a measuring device for determining changes in the concentration of all salts in the Electrolyte bath, for example an electromagnetic concentration detector, and a measuring device for measuring changes in the concentration of sulfate ions or chloride ions during the precipitation of Manganese (II) ions in the electrolyte bath, like a pH meter. With the help of these measuring devices it is possible precisely determine the changes in the manganese (II) concentration in the electrolyte bath and the supply of Manganese controlled by a control mechanism that automatically turns the feed mechanism on controls certain working conditions based on the detected concentrations. So it is possible to automatically concentrate on a certain area by closing the supply line to the device that supplies the manganese ions.

An embodiment will be described below with reference to FIG the device for the electrodeposition of manganese on steel according to the invention explained.

A steel strip 1 is continuously coated with manganese in a horizontally arranged electroplating vessel. The steel strip is first cleaned and passes through the rollers 2 into the electroplating container 3, which is equipped with an insoluble electrode 4 parallel to the steel strip 1. Excess electrolyte on the steel strip is separated off by the squeegee rollers 5. The steel strip is then washed with water and passed into a subsequent treatment stage. The insoluble electrode usually consists of lead, carbon, titanium or platinum. When electroplating manganese in a sulphate bath, a lead electrode with several percent tin, antimony, etc. of an electrode made of pure lead is preferred because in this case electroplating can be carried out in a wider temperature range. The electrode made of the lead alloy results in a uniform deposition up to the usual bath temperature of 60 ⁰ C, while when using an electrode made of pure lead, the deposited amount of manganese drops when the bath temperature is 40 ⁰ C or higher

a pump P \ fed into the Elektroplattierbehalter 3 where the electrolyte from a öf ^f voltage enters the tank 3 8

The device 9 for supplying manganese ions consists of a pump P>, which feeds the electrolyte from the storage container 6 to dissolve the manganese source 10, and, if necessary, a control device 14 which is connected to measuring devices 15 and 16 which operate the pump Pz. The electrolyte supply system as well as the manganese dissolution system are controlled by the above-mentioned control device and an electrolyte control mechanism, which is described below, and are kept under desired operating conditions.

The electrolyte flows from the electroplating container 3 back into the storage container 6. In the continuous electroplating using such an electrolyte cycle system, the amount of manganese (II) ions in the electrolyte decreases. The change in the manganese (II) ion concentration is determined by a pH measuring device 15, which is immersed in the electrolyte in the EleKiroplauierbehäUer.The change in the concentration of free acid and the change in the salt concentration is determined by an electromagnetic concentration measuring device 16. The determined values are fed into the control device 14, in which the changes in the manganese (II) ion concentration are calculated. If the manganese (II) ion concentration is too low, a control system of the device for supplying manganese, for example the pump Pi, which is related to the device for the manganese source, is actuated so that the electrolyte from this storage device is operated at a certain flow rate flows off and electrolyte flows into the reservoir 6 so that the manganese (II) ion concentration is kept at a certain value.

Within the device 9, which supplies manganese ions, the manganese source 10 is in contact with the Electrolyte brought and dissolved to the electrolyte with the required amount of manganese (II) ions add to. The replenished electrolyte is put back into the Reservoir returned

If the pH value is adjusted to the range from 2.0 to 3.0, metallic manganese granules are expediently used as the source of manganese. The grain size of the manganese granulate is expediently a maximum of 5 cm, corresponding to a rate of dissolution to achieve the feed rate of the base material.

Electroplating is usually done at a constant bath temperature. The electrolyte will therefore chilled. With continuous electroplating at a bath temperature of 40 to 60 ° C, the Amount of electrolyte due to evaporation of the water and the entrainment of electrolyte through the Base material. This decrease in the amount of electrolyte is determined by a level measuring device 11, the is arranged in the storage container 6 If the surface of the electrolyte sinks, it opens by the control device 13, a valve 12 through which the required amount of water is fed to bring the fluid level back to normal. Also the concentrations of free acid and Manganese (II) ions in the set total amount of the electrolyte have changed compared to the concentrations before the setting. These changes are used by the pH meter and the above mentioned control device, and the The supply of free acid and the supply of manganese (II) ions are automatically controlled by dissolving the manganese source required total amount of electrolyte and the required concentration of manganese (II) ions the control devices 13 and 14 kept at the required value. The following is the manganese (II) feeder

ίο the invention explained

In Fig. 7, an embodiment of the device is shown schematically. The device consists of a manganese carbonate supply device 101, a manganese carbonate dissolving container 107, which is equipped with a pH meter 106 is equipped, an electrolyte reservoir 105, which is also equipped with a pH meter 106 is equipped and which are connected to an electroplating container 102 by lines that are connected to Pumps 103 and filters 104 on different ones

are equipped in sections and thus form a circulatory system. For the supply of manganese (II) ions to the Electropiaitier container using manganese carbonate is this through the supply device 101 placed in the dissolving container 107. The manganese Carbonate is brought into solution in the container 107, the pH value being adjusted to a value of 2 $ or lower by the pH measuring device 106. The pH value is adjusted by adding hydrochloric acid or by using a chloride bath Addition of sulfuric acid when using a sulphate bath. As the pH of the electroplating bath decreases during continuous electroplating, the addition of these acids can be small. In the dissolving tank 107 wi; td electrolyte with low

ji pH value fed from the electroplating container 102 The electrolyte supplemented with manganese (H) ions with a pH value of at most 2.5 is used by means of einet Circulation pump 103 fed into the storage tank 105 In the storage tank 105, the bath assembly is Composition checked and the pH value adjusted to a certain value The pH value setting takes place, for example, with aqueous ammonia solution to a pH of 2.5 to 6.0. This setting serves to maintain a constant pH value in the electroplat to maintain the animal container, otherwise the The pH value of the electrolyte decreases over time The electrolyte in the storage container 105 flows through there: Filter 104 and is fed into the electroplating tank 102 by means of the circulation pump 103. To this Way, it is possible to use manganese (II) ions in the galvanic deposition of manganese on steel to be supplied on a technical scale. This is for the technical production of manganese-coatedir Steel of great advantage.

According to the in F i g. 8 is the embodiment shown in the central part of the dissolving tank 107 a network IW is provided to keep small pieces of metallic manganese withhold appropriate amount. The metallic manganese is dissolved during the pH of the in

μ circulated electrolyte to a value of voi 5.0 or less set by means of the pH meter 106 will. The dissolution is carried out as follows

First of all, the metallic manganese that is present on the Network is held back, partially disbanded. Tue <

resulting finer particles of the metallic Man goose fall through the network 108 and are de Filter membrane 109 retained and go into solution. Almost the largest part of the egg used

Manganese goes into solution.

The other parts of the embodiment shown in Fig.8 are the same as those of the embodiment shown in Fig.7.

After the in F i g. 9, an agitator 110 is arranged in the dissolving container 107, to speed up the dissolution of the manganese. Furthermore, a filter membrane 109 is similar to that in FIG. 8th embodiment shown provided. Other parts are similar to that in FIG. 7 embodiment shown.

The examples illustrate preferred embodiments of the invention.

example 1

A 0.8 mm thick cold-rolled steel strip (JIS G3141 SPCC) is continuously filled with manganese electroplated under the conditions given below. Changes in the deposition of the Manganese are traced during the plating treatment.

Bath composition and plating conditions:

Manganese sulfate 120 g / liter

Ammonium sulfate 60 g / liter

Ammonium rhodanide 50 g / liter

PH value
anode

Bath temperature
Current density

2.5

Lead-tin alloy
35 ° C
20 A / dm *

The electroplating is done in a cell, in which the electrolyte is continuously circulated. To adjust the pH value is aqueous ammonia solution fed. Furthermore, manganese sulfate is used as a manganese (II) source at intervals admitted. The current yield is achieved when using a filter canister with activated charcoal and without one Filter container determined. The results are given below.

Current efficiency at the beginning of the plating:

With filter container 56%

Without filter canister 56%

Current yield after passing 300,000 coulombs per liter of electrolyte:

With filter container
Without filter container

55% 38%

Current yield after passing 300,000 coulombs per liter of electrolyte:

With cleaning container with membrane
reverse osmosis 56%

With cleaning tank with ion exchange membrane 55%

It can be seen from the results that high ίο current yields can be achieved with continuous electroplating if obtained during electroplating the electrolyte with a reverse osmosis membrane or an ion exchange membrane.

Example 3

The electroplating is carried out according to Example 1, however, 300 ppm iron (II) and zinc (II) ions are added to the electrolyte in order to reduce the influence of this Detect ions on the electroplating. Furthermore, hydrogen sulfide gas becomes in the impure electrolyte blown in or ammonium sulfide solution is added to the electrolyte to reduce its influence on the Determine electroplating. The electrolyte is passed through filter cloths during the cycle filtered. The results are summarized below

Current yield after passage of 50,000 coulombs per liter of electrolyte:

Without the addition of sulfide 35%

With the addition of ammonium sulfide 53%
With the addition of hydrogen sulfide 55%

From the results it can be seen that the adverse influence of interfering cations by Addition of a sulfide can be canceled.

Example 4

The electroplating is carried out according to Example 1, but the electrolyte is 120 ppm Iron (II) ions, 60 ppm Cu and 50 ppm Ni ions were added to reduce their influence on the electroplating to investigate. Furthermore, the impure electrolyte is mixed with 5 g of calcium carbonate, barium carbonate or strontium carbonate offset to determine their influence in the continuous electroplating. The electrolyte is filtered through filter cloths during the cycle. The results are summarized below.

It can be seen from the results that the current efficiency remains constant when in electroplating the electrolyte is filtered through an adsorbent such as activated carbon.

Current yield after passage of 100,000 coulombs per liter of electrolyte:

Without the addition of an alkaline earth metal carbonate 33%

With the addition of an alkaline earth metal carbonate 53%

Example 2

The electroplating is carried out according to Example 1, but instead of the filter container with Activated carbon a cleaning container with a membrane for reverse osmosis or a cleaning container used with an ion exchange membrane. The results are summarized below:

so From the results it can be seen that the The unfavorable influence of the cations can be eliminated by adding an alkaline earth metal salt.

Example 5

h> The electroplating is carried out according to Example I, however, the electrolyte contains 150 ppm iron (II) ions. 300 ppm zinc ions, 10 ppm chromium ions. 10 ppm lead ions and 5 ppm tin (II) ions

offset to their influence on the electroplating determine. Furthermore, the pH of the impure electrolyte is gradually changed to avoid the influence of the Determine change in pH. The electrolyte is passed through filter cloths during the cycle filtered. The results are summarized below

Current yield after passage of 50,000 coulombs per liter of electrolyte:

pH 2.5
pH 3.2
pH 4.5
pH 6.0
pH 8.0

35%
34%
35%
51%
520/0

It can be seen that steel can be continuously electroplated with manganese when electroplating carried out at a pH of 6 to 8 and the electrolyte is filtered.

Example 6

Electroplating is carried out as in Example 1, except that a heating tank is used in place of the filter tank with activated carbon and a cooling tank after the heating tank is used to heat and cool the electrolyte before it is fed into the electroplating tank. It is the change of manganese deposition in the course of time is determined in this case, the temperature of the electrolyte, ^ he enters the Elektroplattierbehälter, set to a value of at most 40 ⁰ C. The results are summarized below

Current yield after passage of 200,000 coulombs per liter of electrolyte:

Without heating the electrolyte 39%

With heating of the electrolyte 52%

From the results, it can be seen that in the continuous electroplating of manganese, there is very much it is effective to heat the electrolyte in order to obtain a constant current yield.

Example 7

The electroplating is carried out according to Example 1 using 3 separate electroplating containers performed to the effect of air on the plated base material between the electroplating containers to investigate.

The bath composition is the same as in Example 1. The electroplating is carried out under the same conditions as in Example 1, but the current density is 40 A / dm ² and the bath temperature is 25 ° C, and the electrolyte is mixed with 10 ppm iron (H) ions, 50 ppm zinc ions and 5 ppm tin ions are added.

The electroplating is done on two different eo Ways done: In the first method, the steel band that is between the electroplating containers runs, wetted with the electrolyte, while in the second method the steel strip between the electroplating containers is not wetted with the electrolyte, but is half dry. After electroplating the amount of manganese deposited and the current efficiency from the amount of current passage certainly. The results are summarized below

Current yield after passage of 5,000 coulombs per liter of electrolyte:

With a moistened surface
between the electroplating tanks 55%
With a dried surface
between the electroplating tanks 46 "/ o

The results show that it is important to prevent the oxidation of the deposited manganese between the Electroplating containers to prevent a high current yield when using a plurality of To achieve electroplating tanks.

Example 8

The electroplating is done in the same way as in Example! 7 methods are carried out for The supply of manganese (II) ions examined Metallic manganese and manganese carbonate are called manganese I) source used Since the pH of the electrolyte bath drops during electroplating, the pH value is continuously determined Manganese carbonate and metallic manganese are separated supplied to keep the manganese (II) concentration in the electrolyte bath constant. Be for this purpose Manganese carbonate and metallic manganese are dissolved in separate dissolving tanks, and the solutions are fed into the electroplating tank by means of a circulation pump. A filter tank is inserted into the circuit arranged with activated carbon to prevent the entry of impurities into the electrolyte. on In this way, the electroplating of the manganese could be carried out continuously with an almost constant current efficiency can be achieved even after the passage of 200,000 coulombs per liter of electrolyte. It Turde stated that Manganese (II) ions can be supplied continuously from metallic manganese or manganese carbonate.

Example 9

Electroplating is carried out in the same manner as in Example 7. There are also methods investigated for the supply of manganese (H) ions. In this example a chloride bath of the following composition is used:

35

40 manganese chloride

Ammonium chloride

Potassium rhodanide

Electroplating Conditions:

Current density

Bath temperature

PH value

350 g / liter

200 g / liter

2 g / liter

50 A / dm *

20 ⁰ C

4.5

A carbon electrode is used as the anode. Manganese chloride is used as a manganese (II) source used. As the pH of the electrolytic bath decreases during electroplating, manganese chloride becomes fed while the pH is continuously determined to maintain a constant manganese (II) concentration to maintain in the electrolyte bath. The manganese chloride is in a separate dissolution level

dissolved in the container, and the solution is fed into the circuit of the Electroplating tank fed in by means of a circulation pump. A filter tank is also added to the circuit switched on with activated carbon to prevent contaminants from entering the electrolyte bath. During the passage of 150,000 coulombs per liter of electrolyte there are changes in the current yield The results show that the current efficiency is determined immediately after the start of electroplating up to the passage of 150,000 coulombs ι ο between 85 and 90% It was also determined that instead of manganese chloride, metallic manganese is also used to supply manganese (II) ions can be. In this case, however, it is preferable to lower the pH to 2 to 3 in order to reduce the metallic Manganese easier to bring into solution.

Example 10

Electroplating in a bath is as follows Composition carried out: 150 g / liter of manganese sulfate, 80 g / liter of ammonium sulfate and 60 g / liter Ammonium rhodanide.

Electroplating Conditions:

PH value

Bath temperature

Current density

Electrode gap

3.0
50 ⁰ C

80 A / drn ² at a feed speed of 120 m /
min
20 mm

The current efficiency was 67%.
Example 11 20

Electroplating Conditions:

30th

35

The electroplating is carried out in a bath of the following composition: 120 g / liter of manganese sulphate, 70 g / liter of ammonium sulfate and 30 g / liter of ammonium rhoyanide.

PH value

Bath temperature

Current density

Electrode gap

2.2
47 ° C

160 A / dm ³ at a feed speed of 160 m / min
5 mm

The current efficiency was 78%.
Example 12

The electroplating is carried out in a bath of the following composition: 350 g / liter MnCb · 4 H2O, 200 g / liter ammonium chloride and g / liter potassium rhodanide.

Electroplating Conditions:

PH value

Bath temperature

Current density

Electrode gap

6.2
26 ° C

25 KIc.-; '. ¹ at a Vorschubgeschwind ¹ ness of 40 m / min
40 mm

The current efficiency was 93%.
Example 13

The electroplating is carried out in a bath of the following composition: 300 g / liter manganese sulfate, 150 g / liter ammonium sulfate and 10 g / liter sodium selenate (Na ₂ SeO ₄ ).

Electroplating Conditions:

pH 7.2

Bath temperature 41 ⁰ C

Current density 25 A / dm ²

Distance between electrodes 45 mm

The current efficiency was 78%.

In addition 5 sheets of drawings

Claims (15)

Patent claims: 1. A method for the continuous electroplating of manganese on steel using an insoluble anode in an electrolyte bath without a diaphragm, characterized in that the electroplating at a cathode current density of at least 20 A / m ² and a distance of at most 50 mm between the anode and the To limit the amount of cations to be electroplated, which are electrochemically more noble than manganese, the electrolyte bath is either mixed with a sulfide or with an alkaline earth metal salt or its pH value is adjusted to 6 to 8, the precipitated cations as well as some of those in the electrolyte bath accumulating reaction products are removed by filtration and manganese (II) ions are continuously added to the electrolyte bath by dissolving metallic manganese, manganese sulfate, manganese carbonate or manganese chloride 2. The method according to claim 1, characterized in that that the sulfide used is hydrogen sulfide or ammonium sulfide and the filtration using a filter cloth and activated carbon 3. The method according to claim 1, characterized in that the alkaline earth metal salt is calcium, Barium or strontium carbonate is used 4. The method according to claim 1, characterized that manganese (II) ions can be obtained by dissolving metallic manganese in an aqueous solution or supplies an electrolyte with a pH of 5.0 or less 5. The method according to claim 1, characterized in that Maiigan ( ⁷ ;.) - ions are supplied by dissolving manganese sulfate in an aqueous solution or an electrolyte with a pH of at most 7.0 6. The method according to claim 1, characterized in that manganese (II) ions are dissolved by dissolving of manganese chloride in an aqueous solution or an electrolyte with a pH of at most 7.0 feeds. 7. The method according to claim 1, characterized in that manganese (II) ions are dissolved by dissolving of manganese carbonate in an aqueous solution or in an electrolyte with a pH of a maximum of 24 supplies 8. The method according to claim 1, characterized in that that one also cleans the electrolyte bath "> o by means of an adsorbent. 9. The method according to claim 8, characterized in that there is activated carbon as the adsorbent used. 10. The method according to claim 1, characterized in that the electrolyte bath is also used cleans by means of membrane filtration 11. The method according to claim 10, characterized in that an ion exchange membrane or a membrane for reverse osmosis is used for membrane filtration 12. The method according to claim 1, characterized in that the electrolyte is circulated and thereby for the separation of gases contained in the electrolyte and for the stabilization of the f> Electrolyte heats up and cools down 13. The method according to claim 1, characterized in that that the electroplating is carried out in a plurality of electroplating cells and keeps the steel moist on its way from one cell to the next 14. Device for carrying out the method according to claims 1 to 13, characterized by a device for supplying a manganese source, the is provided with a control device and together with a measuring device for determination the manganese concentration, the pH value and the amount of the electrolyte bath is working 15. The device according to claim 14 for supplying manganese (II) ions into a manganese electroplating bath, characterized by a manganese source supply device, a dissolving tank for the manganese source, which is equipped with facilities for storing the manganese source and a pH meter has an electrolyte storage container with a pH meter and an electroplating container, wherein the electrolyte reservoir with the electroplating container through a line to Circulation of the electrolyte is connected which is provided with a pump and a filter