DE1048755B - - Google Patents

Description

C2SÜ

The invention relates to bath compositions and a method for electrodeposition of Iron coatings. It is particularly suitable for using machine parts that are worn or for other reasons Undersized, subjected to severe operating conditions and those parts that require dimensionally accurate machine reworking to the Bring the prescribed level, but without being limited to these applications. That Base metal on which the iron can be deposited according to the invention can itself Be iron or steel, copper or brass, but also other materials, provided they are electrically conductive are or can be made electrically conductive.

Numerous processes for the galvanic deposition of iron precipitates are from the literature known. The electroplating baths consist of an aqueous solution of iron sulfate or iron chloride or a mixture of both, which can contain various additives. In iron sulphate baths there is one movement of the bath is desirable in order to prevent the precipitate from growing in nodular form and to achieve an economical high throughput in production. Usually the anode constantly moved in the bathroom or set the goods in rotating motion. Furthermore, temperature and The composition of the sulfate bath and the current density are carefully monitored. Still they are Coatings not as good as those made in ferric chloride baths.

In iron chloride baths, however, temperatures of around 100 ° C must be used. For example, those parts that are not to be galvanized must be covered. The covers required for this are not stable at the temperatures in question. Furthermore, chloride baths are very corrosive, so that extensive precautions must be taken to protect the tubs and auxiliary devices. Neither iron sulfate nor iron chloride baths nor mixtures of the two can be used to produce uniformly reliable coatings that are later to be subject to severe operating conditions under normal operating conditions. All baths show a considerable tendency towards oxidation and form insoluble ferric compounds in considerable quantities. In addition, the iron coatings from a sulfate or chloride bath or a mixture thereof tend to become brittle. Although the brittleness can be reduced by subsequent heat treatment, the results of this treatment are not always uniform and the temperatures must sometimes be so high that the hardness of the coating suffers. Next with each of the baths is the adhesive bath and method of electroplating
Deposition of iron coatings

Applicant:

Dr. Henderik van der Horst

and engineering firm "Lernet Chromium"

H. van der Horst N.V.,

Hilversum (Netherlands)

Representative: Dipl.-Ing. W. Mouths, patent attorney,
Frankfurt / M., Börsenstr. 17th

Claimed priority:
V. St. v. America January 16, 1953

John Poor, Portville, NY (V. St. A.),
has been named as the inventor

strength of the iron coating, at least under the usual manufacturing conditions, is too low and uncertain than that the known processes for producing coatings would come into question, those so high Compressive and tensile loads are subjected, as they are common in today's mechanical engineering. From this it turns out that, at least for industrial production, the known ones are poorly suited are.

Iron baths are also known which contain BF ₄ ions, more than 6.5 g of Cl ions, NH ₄ ions and divalent iron.

The BF ₄ ions are present in such a large excess in this known iron bath that considerable amounts of salt-like substances accumulate on the surface of the anode or the bag surrounding it, which thus becomes impermeable to the electrolyte. The anode surface becomes ineffective, so that the divalent iron of the anode cannot get into the solution. This significantly reduces the amount of precipitation. The ineffectiveness of the anode surface also does not take place uniformly over the entire surface, so that the amounts deposited on the various parts of the cathode also become unequal.

In contrast, the bath according to the invention contains a precisely limited range of BF ₄ ions and a total content of acid ions that is weight-wise

809 729/235

3 4

moderately least 2V2iache of BF ₄ -Ionenmenge _pH value 2-5 below by means of direct current

amounts to. Worked using iron anodes.

This achieves essential advantages. So iron as a long-distance connection in the bathroom is up to one

it was found that z. B. the formation content of 1.5 g / l practically harmless at a

However, thick galvanic deposits with a bath of the 5 concentration of more than about 3 g / l tend to be

known composition therefore not possible for the precipitates to become rough,

is because the large BF ₄ ion concentration exceeds the above- If the required for the preparation of the bath

mentioned harmful influence increases and substances additionally contain harmful metals, they are in

nor the formation of substantial amounts of borofluorine purified in a known manner. Still some should

Hydrogen Acid. Then io foreign metals get into the bath, so they can un-

rod-shaped crystals, which alternate with ahn- are made harmful by z. B. steel wool in

borrowed formed metal crystals settle. Such bags in the bathroom or in a special cleaning

Precipitation is immersed with the baths of known composite tanks. Also by using

there is no ductility whatsoever, even after auxiliary cathodes have been dumped, some

prolonged heat treatment. Remove the precipitates and 15 foreign metals,

crumble into powder when bent. It could also be the presence of various organic

be measured that the with baths of substances in the bathroom is undesirable. Substances that z. B. the

known composition have a tendency to buffer the bath and the deposit

had warped severely during the heat treatment. Preventing the stanchions also helps containment

measured values of products with baths 20 of coal or coal compounds in the

were made according to the invention, showed only trains. This is undesirable when z. B. by means of

about the tenth part. Coating the worn surfaces of heavily used

The bath according to the invention is for use in machine parts back to their original

measurements are to be brought to the large-scale production of modern electroplating companies. Such substances too

well suited. The coating or precipitate is therefore in a known manner except for harmless ones

good adhesion even when removing large amounts of chips. It is best to take the bath during

is exposed. Furthermore, the coating is tight throughout the entire electroplating process through a filter and

and easy to work with. Under »Edit«, activated carbon should be circulated to if necessary

a cutting shaping is understood. To keep it as pure as possible. But if the bathroom has some

According to the working method, the coating can be hard or has not been used for 3 °, it should be

are soft, brittle or ductile and are also cleaned during operation,

can, if it has become too brittle, by after- The proportion of boron fluoride BF ₄ should not be below 10 g / l

following, per se known heat treatment are ductile bath solution. At very low concentrations

and toughened without losing its hardness, the coatings become rough, and at concentrations

suffers significantly from it. It is smooth, and the bath tends to precipitate below about 10 g / l

loan free of porous bodies and of \ ^r erunreini- trunks in undesirable amounts and

as well as fine-grained. Even with increasing the anode attack is too low for certain purposes.

Layer thickness does not increase the grain size significantly- This is especially true if the components are used to produce

worth, so that even thick coatings in cross section supply relatively hard coatings

are even. 40 are. For quantities above about 100 g / l, the iron

The bath temperature is advantageously low. The anode is badly attacked. A quantity of current density can be set relatively high, of 30 g / l, gives adequate protection against the BiI, without the need for excessively high temperatures or long-distance connections and, with a concentration, vigorous movement of the bath. With a concentration of 50 g / l, advantages are no longer achieved. A slight bath movement, e.g. B. by pumping, 45 The provided in the bath solution NH ₄ ions can be useful. The various factors hold back the formation of remote compounds or elements of the process can hold back in their oxidation of ferrous compounds. More important sizes with a relatively large margin, however, is that harder and finer-grained ones are over-set, and those of them that generate pulls. It will therefore tend to produce relative change during the process, do 50 hard coatings applied. In such a case, it is so slow that the process can nevertheless easily be controlled by the motor prior to coatings on the inner walls. cylinders.

For the galvanic deposition of iron over- The amount of Cl ions should not be less than about

puffs using a bath according to the invention amount to 6.5 g / l solution; their impact grows with them

Iron or steel anodes are used. At 55 of concentration. At 10 to 14 g / l they get

to prevent the coatings forming on the anodes from developing a fine-grained structure that

Sludge contaminates the workpiece, is left tough and relatively ductile between being left to around 315 ° C.

A porous partition wall in front of this and the anode. The greater the concentration, the greater the ductility

see, preferably from a known per se, the coatings are still on. At concentrations above

bag placed around the anode. At several 60 about 26.5 g / l solution increases the presence of

Anodes can be provided for each a bag or Cl ions can significantly increase the current density at which

a common bag for one group of anodes. Let it gain coatings in spite of the presence

acidic, divalent iron, chlorine or chlorine of NH ₄ ions up to a concentration of about

and baths containing sulphate and boron fluoride ions 13.5 g / l are not too high for certain purposes

\ 'used with the characteristic that they have internal stresses as the main constituents. At a concentration

component bivalent iron and chlorine ions removal of about 89 g / l without the presence of NH ₄ -

hold, whereby the quantities of two and SO ₄ ions to be used in the bath (with the exception of such SO ₄ ',

valuable iron more than 10 to 120 g / l, chlorine and that with a small amount of a wetting agent

Boron fluoride, boron fluoride which has come more than 26 g / l) and at a _pH value of about 3.4

ions 10 to 100 g / l. The greatest stretchability appears to be achieved at a 70.

For most purposes, a concentration of 100 g / l solution has proven itself.

SO ₄ ions cause a number of effects in the bath composition. They inhibit the influence of the Cl ions with respect to the formation of relatively soft coatings, ie they produce harder coatings than is otherwise possible, they increase the conductivity of the bath to a small extent, and together with BF ₄ ions increase it they attack the secondary anode. If much of the iron in the bath is ferrous sulfate, they reduce the rate of long-distance link formation. In the baths treated here, however, the coating-hardening effect and the effect increasing the anode attack predominate, and both grow with the concentration.

They are primarily used in the baths of the invention to form hard coatings. In concentrations of about 155 g / l and above, however, they have an undesirable effect on the dissolution of the iron in the anode, especially if the bath operates continuously for a long period of time. It is therefore expedient to use the concentration of SO ₄ ions, if at all, up to a maximum of 155 g / l, a concentration of 138 g / l being particularly suitable.

The presence of Sodium Lauryl Sulphate reduces the tendency of the bath to spray and contributes to the Prevent the formation of porous deposits. Instead of or together with sodium lauryl sulphate Other sodium salts of sulfuric acid fatty alcohols or mixtures of these salts or others can also be used equivalent wetting agents are used. Very small amounts of z. B. about 0.1 g / l Solution.

In general, the higher the bath temperature, the higher the current density at the cathode. in the in general, the temperature range between about 55 and 70 ° C is most suitable for all purposes and the range between 57 and 63 ° C is particularly preferable.

The current densities at the anode and cathode can differ considerably from one another. At a bath temperature of around 57 ° C, a current density of 16 A / dm ² at the anode generates considerable polarization.

As the cathode current density increases, the coating becomes harder, more brittle and rougher, and all the more so tensions arise.

Current densities of about 13 A / dm ² at the cathode represent the upper limit, even for extremely thin coatings. On the other hand, the lower limit is in the order of magnitude of about 0.54 A / dm ² . Since the formation of a layer of a certain thickness takes longer, even with a lower current density, a current density of about 4.3 A / dm ^{2 is} generally sufficient as a guideline for all purposes.

The higher the _pH value of the bath is, the greater is the formation of long-distance connections. Thus, in any case, the maximum _pH value is given; he is 5. At a lower _pH value, such as below 2, the coatings become brittle and tend internal stresses. The range of permissible Ph "values is therefore between 2 and 5.

Taking into account all circumstances are therefore used for Eisengalvanisierung bath temperature 57-66 ° C, cathode current densities of about 4.3 A / dm ² and p _H values from 3 to 3.8 recommended. For hard, tough coatings which are machinable without any particular difficulty, and are exposed to those heavy loads, at the same temperature and current density is a _pH value from 3.3 to 3.7 advisable. Produce within these areas - as a general rule ■ - the lower p _H values, the greater extensibility, the higher p _H values, the greater hardness after heat treatment.

In the proposed temperature and current density, the softest and most ductile coatings are obtained directly from a bath containing no NH ₄ - or SO contains ₄ ions (except as existing content in the wetting agent) and a _pH value of about 3, 2 to 3.5 has.

Iron coatings according to the method of the invention can either be relatively soft and ductile or harder, with internal stresses, and even quite brittle prepared depending on the choice of the individual ions and their concentrations, the p _H -value, the temperature of the bath and the cathode current density.

The aqueous solution of the various components can be prepared in various ways. The only important thing here is that boron fluoride ions are removed from the other components (with the exception of those such as Ferrous compounds that accompany the boron fluoride as a cation) are in the solution. In this way, the boron fluoride ions prevent the formation of insoluble ones or difficult to dissolve long-distance connections. For preparing and cleaning the bath it is recommended like proceed as follows.

About half of the required amount of water is heated to 48 to 66 ° C in order to accelerate the dissolution of the salts. Then the amount of ferroboron fluoride (Fe (BF ₄ ) ₂ ) corresponding to the boron fluoride ions is added. After dissolution, as much sulfates and chlorides are added as is necessary for the ion concentration. Up to 75% or more of the finished bath is added to the water, which has been preheated to 48 to 66 ° C., and the mixture is stirred well while avoiding stirring in air.

Once all the salt is dissolved, steel wool is added to bring the _pH value of the solution to 4 or higher. Usually 5 to 10 g per liter of solution is sufficient. The purpose of this addition is also to precipitate impurities that have come into the solution with the salts, to reduce any remote compounds present in ferrous compounds and to neutralize the acid contained in the salts. The reaction with the steel wool can be accelerated if the solution is kept at a temperature of 48 to 66 ° C; at a temperature of 54 ° C. or more, the reaction is completed overnight. Considerable gas evolution occurs, which results in spraying. Spraying can be reduced by adding a little wetting agent (approx. 0.04 g / l solution).

As soon as the _pH value increased to 4 or higher, the solution are added 3 to 5 g / l activated charcoal and an equal amount of filter aid and stirred, until the absorbed impurities.

This can take 3 hours or more. At the same time as this cleaning process, the wetting agents are also removed. It is then filtered. Then the intended amount of wetting agent is dissolved in a little hot water and added to the filtered bath solution. Then the remaining water is added and carefully stirred. If necessary, concentrated sulfuric acid (H ₂ SO ₄ ) is added in order to lower the pjj value to 3.3 to 3.7. Before use, the bath is electrolytically allowed to work for a few hours in order to improve its properties.

Claims (1)

Under the working conditions described, there is only a slight loss of ion concentration due to the electroplating process. When the concentration of boron fluoride ions falls to about 30 g / l, ferroboron fluoride can be added to the bath. If the Pij value is simultaneously higher than necessary, hydrofluoric acid (H B F4) can be added instead. A lack of sulfate ions can e.g. B. can be remedied by adding ferrous sulfate. If the ferrous sulfate concentration becomes too high, it can be reduced in the manner already described. If ferrous sulfate crystallizes out, ammonium ion can be lost at the same time, if such is present in the bath. Therefore, when the concentration drops, it can e.g. B. can be improved by adding ammonium chloride. Loss of Cl ions can be achieved by adding z. B. be balanced by ferrous chloride or by adding ammonium chloride, if the bath contains NH4 ions. The pH value should be determined and corrected at least once a day. While long-distance connections are formed by atmospheric oxidation on the one hand, the electroplating process on the other hand reduces the ferric compounds to ferrous compounds. Concentration consequently tends towards a certain fixed value. As soon as this value becomes too high, it can be reduced. The concentration of ferric compounds should be determined every few days and corrected as often at least until a mean value has been set and the range of fluctuation of the concentration has been determined and an equilibrium value has been determined and a periodic or constant correction has been made. If the bath is prepared and treated as prescribed, the concentration of metallic iron can be neglected. Example 1 To produce a soft, noticeably ductile coating, a bath of the following composition is produced: -BF4 45.5 g / l - Cl 89.2 g / l iron as Fe "84.9 g / l sodium lauryl sulfate 0.2 g / l water To fill up to 1 1, delay the circuit by about 5 minutes. After immersion or taking the delay into account, direct current is applied. It can also be useful to use a small current with a low current density of about 1.1 A / dm2 for about 10 With or without such a bias current, the current is set to a current density at the cathode of 4.3 A / dm2 and left until the precipitation on the workpiece has reached the desired strength are used for a long time for the same work piece or one after the other for a number of workpieces, it is filtered and cleaned frequently or constantly during electroplating, the components are added from time to time and the pH is corrected agile, the water replenishes. When the desired thickness of the coating has been reached, the workpiece is removed from the bath and rinsed with water. If the coating is not as tough and ductile as expected, the piece is heated in an oven to 315 ° C and left at that temperature for three hours or more. It is then taken out of the oven and exposed to room temperature to cool. Example 2 For the production of a relatively hard coating, e.g. B. on the inner wall of an engine cylinder, the bath should be composed as follows: -BF4 45.4 g / l -NH4 6.75 g / l -Cl 13.25 g / l -so, 35 138.2 g / l iron , as Fe "94.9 g / l sodium lauryl sulfate ... 0.2 g / l water to make up to 1 1 To make up the bath use: Fe (BF4), 60g / l FeSO, 7H2O 400 g / l 45 Zum Prepare the bath: Fe (BF4), 60 g / l FeCl2-4H2O 250 g / l wetting agent 0.5 g / l water to make up to 1 1 The bath is prepared, cleaned and, if necessary, brought to a pH value of 3.2 to 3.5 with hydrochloric acid. In the electroplating tank, the bath is kept between 57 and 60 ° C. Steel with the designation SAE 1020 with a low carbon content is used as the anode. the anodes are given such a surface compared to the surface to be electroplated that with a cathode current density of 4.3 A / dm2 at the anode a current density of less than 13 A / dm2 is established As is known, the immersed active part is surrounded by a porous bag, and at least the part that is immersed in the bath is freed of dirt, oil, scale, etc. from the belt. The item is immersed in the bath within about 5 minutes. It can be advantageous to add the one-NH4Cl 20 g / l wetting agent 0.5 g / l water to make up to 1 liter. The bath is prepared in the manner described in Example 1 and under the same conditions at a pH of 3.3 up to 3.7 galvanized. If, in the examples, the components of the bath are specified to within a fraction of a gram, this is not to be understood as indicating that the concentrations are particularly critical in the individual case; Rather, this is due to the fact that readily available salts were used in round amounts by weight to make up the baths. The concentrations of the constituents and the metal iron in the bath can vary considerably in each case. Ρ.Λ T KNT A "SlMItICH E: 1. Bath for the galvanic deposition of iron coatings from acidic, divalent iron, Solutions containing chlorine or chlorine and sulphate and boron fluoride ions, characterized in that that it contains divalent iron and chlorine ions as its main constituent, the applicable Amounts of divalent iron more than 10 to 120 g / l, chlorine and boron fluoride ions more than 26 g / l, of which boron fluoride ions 10 to 100 g / l, 2. Bath according to claim 1, characterized in that in the presence of chlorine and Sulphate ions the amount of chlorine ions is more than 6.5 g / l. 3. Bath according to claim 1 and 2, characterized in that it additionally contains 3.5 to 13.5 g / l NH ₄ ions. 4. Bath according to claim 1 to 3, characterized in that there is no more than 3 g / l ferric ions contains. 5. Bath according to claim 1 to 4, characterized in that there is also more than about 0.1 g, preferably contains about 0.2 g / l sodium lauryl sulfate. 6. Bath according to claim 1 to 5, characterized in that it contains about 45 g of BF ₄ ions, about 89 g of Cl ions, about 85 g of iron in divalent form and about 0.2 g of sodium lauryl sulfate per liter of solution. 7. Bath according to claim 1 to 5, characterized in that there are about 45 g of BF ₄ ions, about 6.75 g of NH ₄ ions, about 13.25 g of Cl ions, about 138 g of SO ₄ ions, about Contains 95 g of iron in divalent form and about 0.2 g of sodium lauryl sulphate per liter of solution. 8. A process for the electrodeposition of iron coatings using a bath as claimed in claim 1 to 7, characterized in that it is carried out at a _pH value 2-5 by DC using iron anodes. 9. The method according to claim 8, characterized in that at bath temperatures between Room temperature and about 71 ° C, preferably between 57 and 63 ° C, is carried out. 10. The method according to claim 8 and 9, characterized in that an anode current density of less than about 16 A / dm ² , preferably less than about 13 A / dm ² , is used. 11. The method according to claims to 10, characterized in that a cathode current density of less than about 11 A / dm ² , preferably about 4.3 / dm ² , is used. Considered publications:
German Patent No. 252 875;
U.S. Patent Nos. 2,523,160, 2,524,010;
»Galvanotechnik (formerly P f anh au ser)«, 1949, pp. 103/104, 204 to 206 and 952 to 954. 1 809 729/235 1.59