DE2447897A1 - CHROME-CONTAINING GALVANIC BAEDER - Google Patents

Description

, PAT E N TA N WA LI F

DR.-1 NG. VO N K REIS LE R DR.-l ■ \ 'G. SC KD * l WAL ·>

DR.-ING. TH. MEYER DR. FUES D I PL CHEf / .. ALEK VOhS KREIS LER D1PL.-CHEM. CAROLA KELLER DR.-ING. KLÖFSCH D1PL.-ING. SELTING

COLOGNE 1, DEICHMANNHAUS 2 A A 7 8 9 /

Cologne, 7.1-197 ² * Kl / Ax

International Lead Zinc Research Organization, Inc., 292 Madison Avenue, New York, HY 10017- (USA).

Electroplating baths containing chromium

The invention relates to electroplating baths containing three-part chromium ions, and methods for electrolytic baths Separation of chromium from these baths.

Solutions of hexavalent chromium are used as the electrolyte in common chrome plating baths. The disadvantages of these solutions are well known. In recent years, therefore, the possibilities of chrome plating baths containing chromium in the trivalent form have been investigated as an alternative to chrome plating baths in the hexavalent form. Among other things, an organic, preferably egg, aprotic buffer, in particular dimethylformamide (DMi ¹ ), was included in the trivalent chrome-plating baths during this development. Some aspects of this development are set out in U.S. Patent No. 3,772,170. The addition of these buffers to trivalent chrome-plating baths leads to considerable improvements compared to earlier attempts, but this method of operation has disadvantages which make it difficult to carry out on an industrial scale. The buffers used are quite expensive, so that improved performance must be bought at the expense of higher material costs Also, since the buffers are preferably aprotic, they can cause conductivity degradation

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of the bath. In addition, since many of the common ion-supplying materials (which, among other things, are used to increase are added to the conductivity) are less soluble in buffer-water \ mixtures than in buffer-free systems, the increase in conductivity achieved by the inclusion of these materials may be limited. Reduced conductivity leads to increased heat generation. In the case of high buffer concentrations, cooling can be used of the bath under the operating conditions. In addition, the buffered trivalent chromium electrolytes the disadvantage of a relatively limited deposition area and a relatively small one Have opacity. These disadvantages stand with the pH-V / erti at which the buffered solutions can be used, in connection. It is known that in order to achieve a good deposition area, the highest possible pH value is required preferable. Unfortunately, the chromium will precipitate if the pH is not kept relatively low.

It has now been found that by adding hypophosphite ions to trivalent chrome plating baths either as In addition to an organic buffer or as a replacement for this buffer, an electrolyte is formed that contains many of these Mitigates or eliminates disadvantages.

The invention accordingly relates to an aqueous chromium plating bath, the dissolved trivalent chromium ions and hypophosphite ions preferably in at least about one Contains 0.08 molar concentration, and also preferably ammonium ions in an at least 0.2 molar Concentration are present.

The invention also includes the electrolytic deposition of chromium-containing coatings on workpieces a method in which one places an anode and a cathode in a chromium plating bath according to the invention and allows a current to flow between anode and cathode in such a way that

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that chromium is deposited on the cathode «,

The exact concentration limits of hypophosphite ion that can be used have not yet been established, but the improvements up to a 2 molar concentration are remarkable. At higher concentrations, the improvement with increasing concentration is small. Furthermore, normal hypophosphite salts are generally not sufficiently soluble. A range from 0.5 to 2.0 molar is preferred for the hypophosphite ion. It is believed that the compound that forms the hypophosphite ion is not critically important, provided that the ion is not associated with materials that would have an adverse effect on the performance of the chrome plating bath. Sodium hypophosphite, for example as a monohydrate (WaKpPO _2. HpO), and hypophosphorous acid are suitable as suppliers of hypophosphite ions. When sodium hypophosphite is used, the molar concentration related to the hypophosphite ion is in the range from about 10 to 200 g / l, a range from about 50 to 150 g / l being preferred.

The addition of hypophosphite to trivalent chrome plating baths has a remarkable expansion of the deposition area, particularly the luster deposition area of the electrolyte. The known trivalent chrome-plating baths buffered with DMF have

Typical gloss deposition ranges from 125 to 3000 λ / τη By using hypophosphite either in addition to DMF or as a replacement for DMF or other organic buffers, electrolytes with gloss deposition ranges from 30 to 10000 A / m can be formed. The expansion of the deposition area is a significant step forward compared to the known trivalent chromium plating baths.

Another effect on the electrolyte is that in the presence of the hypophosphite ion, the deposition of chromium at low current densities with relatively

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high efficiency and "takes place at high current densities with relatively low efficiency. This effect can be such that" in the electrodeposition of chromium on workpieces shaped to give a wide range of current densities, the rate of deposition is almost uniform and independent can be on the current density. Actual separation efficiency is a complex puncture of many parameters of both the electrolyte and the working conditions. Typical numbers based on trivalent chromium are 2.5? Ό at 5000 A / m and Q ^u / o at 500 A / m, but these numbers can be varied within wide limits by changing the hypophosphite concentration or the concentration of other components of the electrolyte . With electrolytes containing hypophosphite, overall efficiencies in the range from 3 to 16 $, based on the trivalent chromium ion, can generally be achieved. These efficiencies result in deposition rates that are as good as those achievable with the best hexavalent chromium baths available. The yields are significantly lower than can be achieved by adding DMI ¹ (or another organic buffer) in high concentrations, but this is more than offset by an improvement in the separation efficiency. In this connection it should be noted that when comparing the current yields it is important to make a correction for the valence of the ion to be deposited in order to enable a true comparison.

The degree to which the improved separation performance is realized depends, among other things, on the concentration of the Hypophosphites off. As stated earlier, the improvements are at concentrations less than about 0.08 molar barely noticeable. At concentrations up to about 0.5 molar there is a shift in the threshold current density

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for chromium to lower fourths (from about 125 A / m "at the concentration zero) "up to about 90 A / m., By further increasing the hypophosphite concentration, the deposition area becomes even lower Current densities (optimally only 30 A / m) extended. As a result of the reduced efficiency at high current densities and a subsequent reduction in the disadvantageous high deposition rate at high density the tendency for the deposition to burn is also reduced. This latter effect is more pronounced at the high pH values that are set in the electrolyte by the buffering effect of the hypophosphite. The mode of operation of the invention as a puncture or as a function of the pH is described below received in more detail. Burning can be prevented completely when using chromium concentrations of less than about 0.9 molar in the presence of optimal hypophosphite concentrations is being worked on.

The mechanism by which the hypophosphite is so large Brings about improvement in the deposition of chromium is not yet fully understood. Currently it will be for believed likely that there were three separate but related effects. Lower phosphorous Acid is a weak acid, so the presence of the hypophosphite ion reduces the pH of the Electrolytes is increased. According to previous experience, an increase in the pH value of the electrolyte is known advantageous. Up to now, however, such an increase in the pH value in DMF baths would have resulted in the precipitation of the Chromium as complex hydroxides resulted from the solution. Prevents the presence of the hypophosphite ion this is very surprising. The conclusion to be drawn from this is that there is some sort of complex between the trivalent chromium ion and hypophosphite ion, which is stable at relatively high pH values (up to pH 7),

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is formed .. The stabilizing effect is also made from A later observation apparently shows that chromi salts, which are normally only dissolved with difficulty can be dissolved in water at approximately neutral pH in the presence of the hypophosphite ion. in the in general, the pH must be well in the acidic range in order to achieve dissolution. It is also used to dissolve of chromium (IIl) sulfate in water (or even aqueous acid) generally necessary to heat the mixture, to get a reasonably fast resolution. Chromium (III) sulfate dissolves in the presence of hypophosphite ions easy without heating.

The third way in which the Hypophospb.it the chromium deposition seems to influence is related to the actual electrode processes, their course in the electrolytic deposition of chromium is assumed. It is believed that the deposition of chromium metal, from solutions of trivalent chromium, is a two-step process Process is. The trivalent chromium ion becomes a divalent state and then a metallic one Chrome reduced. The speed and ease of chromium deposition is believed to be due to concentration determined by divalent chromium ions. Under normal circumstances, divalent chromium tends to to convert back into trivalent chromium through oxidation and thereby slow down the overall reaction. the Presence of the hypophosphite appears to stabilize the divalent chromium with respect to trivalent chromium and also to accelerate the formation of divalent chromium from trivalent chromium by electrons in the solution. It is believed that this is related to the activity of hypophosphite as a reducing agent, although it appears that there is no pure consumption of hypophosphite during the electrolysis. It appears from this that the hypophosphition

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not just trivalent Chrpm against high pH and bivalent chromium stabilized against oxidative reversal, but that also in the suspected complex of trivalent chromium Chromium and hypophosphite the trivalent chromium stabilizes the hypophosphite against oxidation causes.

As mentioned earlier, 'electrolytes can be trivalent Chromium, which contain hypophosphite, can be used at much higher pH values than was previously possible with DMF baths was possible. The electrolytes according to the invention enable the electrolytic deposition of chromium or chromium alloys in the pH range from 0.5 to 7 »whereby a range of 1.5 to 3.5 is preferred for chromium. The previously known baths were essentially open restricted to a pH of 1 to 3. This improvement in the applicable pH range is important because it is a Expansion of the deposition area made possible and also by reducing the acid attack on the base metal at the beginning of the electrodeposition process can be valuable. :

The concentration of trivalent chromium ions in the electrolyte is less important than in previous systems. In general, the concentration is 1.75 molar chromium ion-0,5-bis, preferably 0.7 to _{1} 3-o} molar Since Chrcm salts are relatively expensive, the chromium concentration is kept as low in practice, as practically is possible in order to keep the capital expenditure for the production of the bath minimal and to reduce the amount discharged with the workpieces. Reducing the loss through discharge with the workpieces is particularly important in the case of decorative chromium deposits, since the discharge can be up to 5 times the weight of the deposited metal. The presence of the hypophosphorus ions makes the rate of deposition of metallic chromium relatively independent

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on the concentration of trivalent chromium ions. this is important when the electrodeposition of alloys or the deposition of mixed precipitates from electrolytes containing mixed cations is taken into account.

The particular compound that supplies the chromium ions is not critically important, provided, of course, that sufficient solubility can be achieved; and other components that have adverse effects on the Electrolytes have not to be introduced. In general, dps can be in the form of its chloride, in the form of chromium other halide salts, in the form of sulphate, in the form of salts of phosphorusoxy acid, salts with organic acids or salts or complexes with other anions can be used. The salts can be normal, complex or be basic, although it should be noted that a pH adjustment may be necessary. The trivalent chromium ions can in situ by the action of an acid (e.g. hydrochloric acid, sulfuric acid or phosphoric acid) on the metal, its oxides (except CrO ^) or hydroxides are formed.

Other compounds that produce trivalent chromium ions are: 1) chromic acid, which is reduced with hydrogen peroxide, 2) a 57% basic solid salt (ie a solid salt containing 57% by weight Cr ₂ O) while the remainder consists of a neutral salt, e.g. CrCl-z) or 3) basic salts, e.g. a 57% basic solid salt in a sufficient amount of acid to form a solution of the neutral salt (e.g. a 57% basic solid salt in enough hydrochloric acid to form a CrCl ^ solution). In general, the basic salts can contain from 0% to 57% basic solids.

The preferred and optimal ranges for the concentrations of hypophosphite and trivalent chromium are generally coordinated so that a relatively low concentration of trivalent chromium

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ions have a low hypophosphite concentration and for high concentrations of trivalent auromions .a high hypophosphite concentration is appropriate. Molar ratios of trivalent chromium to hypophosphite are suitable in the range of 0.16 "to 5, however Ratios in the range from 0.7 "to 1.7" are preferred.

As mentioned earlier, the anions present in the electrolyte are not essential. Since the bathroom has no DMF or similar Requires buffer, the possible range of anions is expanded somewhat. However, as the hypophosphite one is moderately strong reducing agent, it can be assumed that anions with strong oxidizing properties are detrimental Have effects. For example, the nitrate and nitrite anions are none of the common anions preferred anions. The preferred anions include the Halidaniouen, especially chloride, bromide and Iodide anions, sulfate and phosphate anions of the most varied Art. Small amounts of other anions can arise as a result of the inclusion of various additives which will be discussed below should also be present. In contrast to DMF baths, which are preferably with a If essentially uniform anions are operated, hypophosphite baths can readily contain mixtures of anions tolerate. It is believed that by using a uniform anion in hypophosphite baths, no essential Advantage from the technical point of view is achieved.

Organic buffers can advantageously be added to the hypophosphite baths according to the invention. As with The known trivalent chromium baths prefer organic buffers, which have a strongly electronegative oxygen atom and are also preferably aprotic. Dimethylformamide is particularly preferred. For the For purposes of the invention, the organic buffers disclosed in U.S. Patent 3,772,170 can be used are described and defined. DMF (or another

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Buffer) is an optional component of the baths according to the invention and is usually present in concentrations of up to about 95 % of the electrolyte. However, the concentration must not be so high that the solubility of other components of the electrolyte is limited and thereby unusable concentrations are obtained. Since these organic buffers are relatively expensive, their concentration is preferably kept as low as possible. The necessity of using the buffers depends on the relative purity of the starting materials, in particular the compound which supplies the chromium ions. When the starting materials are relatively impure and contain materials that could otherwise have an adverse effect on the performance of the electrolyte, an organic buffer, particularly DMF, can be beneficial as it prevents substantial degradation of the performance of the electrolyte. The currently Commercial grade chromium (III) chloride available contains impurities in fairly high concentrations so that DMF can be added to the bath to improve performance, or rather to prevent deterioration in performance. The concentration required for this depends of course on the amount and type of impurities, but for commercial types of chromium (III) chloride are generally 1 to 40%, preferably 20 to 35% by volume of DMF, based on the total electrolyte, suitable. Chromium (III) sulfate is currently available in such a pure form that an organic buffer in the electrolyte is not absolutely necessary to make the process feasible. However, these buffers are optional components of sulfate baths.

During operation, the electrolytes according to the invention maintain significantly larger amounts of gaseous To form hydrogen than the previous systems of DMF

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Type. This is particularly so in electrolytes of the Pall, which Contains little or no organic buffer. The inclusion of ammonium ions increases stability and conductivity of the electrolyte improved «To achieve a substantial effect, an approximately 0.2 molar concentration is required of the Aiiimoniumion necessary. The concentration can be increased to about 6 molar to get the effect ' increase. A concentration range from 1 to 4 molar is preferred. The ammonium ion can be used as a halide or Sulphate salt or as a mixture of salts or can be formed in situ by reaction of ammonia dt acid.

Because the separation efficiency at high current densities is low, it is usually advantageous to add boric acid or a borate to the electrolyte »If no boric acid or no borate is present, the yield can drop to near zero at high current densities, with the possibility of uncovered places at high current densities results. Boric acid or borate increases the overall efficiency the deposition in such a way that this possibility is eliminated. The minimum concentration to achieve a considerable Effect is about 0.03 molar. Usable improvements are made up to a concentration of about 1 molar achieved. A range from 0.5 to is preferred 1 molar, in particular about 0.75 molar. Boric acid is on Reason of their ability to increase the separation efficiency improve, a normal component in technical electrolytes. In the method according to the invention are on Due to the increased pH value, the concentrations of boric acid or borate are significantly higher than in known baths possible. ;

As usual with the well-known trivalent chrome baths, can also the electrolyte according to the invention salts, especially halides and especially chlorides of alkali and alkaline earth metals such as sodium and calcium can be added. These additives improve the performance of the

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Bades in terms of deposition area, current efficiency and Opacity o The concentration of this component is usually 0.5 molar or more. Due to the proportionate little benefit from the presence of these compounds compared to the action of the hypophosphite are achieved, these additions are considered optional and not particularly preferred.

Additions of surface-active compounds can be advantageous for the baths according to the invention. Until now were mainly used in farmers of trivalent chromium Cation-active type surface active compounds are used. The other types were made because of the propensity for Formation of dull deposits or black spots is not preferred. The electrolytes according to the invention are in much less sensitive in this regard, so that cation-active, amphoteric and non-ionogenic types of surface-active Connections are usable, tlach the previous ones Findings can completely eliminate the previous disadvantage of the anion-active compounds in the baths according to the invention will. It is believed that this increased tolerance is a result of the effects made possible by the invention higher pH levels.

Examples of suitable surface-active compounds are:

Cation-active type: Oetyltrimethylammonium bromide, substituted Unidiazolines, etc.

Anion-active type: sodium lauryl sulfate, sulfonated

Castor oil, etc.

Non-ionic type: higher fatty alcohols, ethers and epoxies. Amphoteric type: higher fatty amino acids.

The surface-active compounds are generally added in concentrations of 5 to 50 ppm. A possible one Another advantage of adding a suitable

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Surfactant can be achieved is that there is splashing of the bath as a result of the above mentioned increased hydrogen development can decrease.

Other levelers and gloss substances can also add to the electrolyte are added according to the invention, but their presence is not critically important, and that with the advantages achieved by them are much lower than with the known systems.

I can add certain phthalates to the electrolyte have an advantageous effect especially in deposition systems with mixed cations. Di-n-alkyl phthalates, e.g. Di-n-pentyl phthalate and di-n-butyl phthalate improve the Current density range over which stainless chromium alloys (especially Cr / Pe, Cr / Ni and Cr / Fe / Ni alloys) can be deposited from mixed electrolytes. Di-n-pentyl phthalate is particularly advantageous (DPP). The role of phthalates is uncertain, but when it comes to separating out chromium-iron alloys, they extend it Area in which stainless precipitates are deposited. A certain lower limit of concentration, which is effective in the electrolytes according to the invention does not seem to exist. Improvements will be made until the Saturation detected. It is convenient to use a saturated solution in the presence of a small amount of a liquid Use phthalates to ensure constant satiety. Various other additives, e.g. Cetj ^ ltrimethylammoniumbromid, can also be beneficial when used in conjunction with the hypophosphite.

The temperature range within which the electrolytes of the invention can be used in accordance with is, the temperature range for the known electrolytes of trivalent chromium similar "is preferably at or near room temperature, _o h. worked in the range of 25 + 5 ° C. The practical maximum temperature depends on

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the anions present in the Baa. In the case of chloride baths, the working maximum is around 35 ° O, but sulfate baths up to 55 ° G can be used. In general, systems that do not contain organic buffer (DMF) operate at higher temperatures than systems that contain organic buffers. It is typical of the electrolytes according to the invention is that it essentially ⁺ Lich higher conductivities than the known electrolytes from DMF-type, and this has the double advantage of reducing the voltage requirement and a reduction in the heating by electrical resistance at a given total current amount. The best. Electrolytes according to the invention are "able to work at ambient temperature or in the vicinity of ambient temperature essentially at thermal equilibrium. There is thus largely no longer any need to intentionally cool the system from the outside.

The electrolyte according to the invention also enables the direct galvanic chrome-plating of reactive substrates viie zinc, aluminum and brass, without previously plating the substrate with copper or winding, as is the case with common baths, in which the chromium is deposited from the hexavalent form, is necessary because of their Higher typical working pH values are hypophosphite baths insofar as the known direct plating baths, in which the Chromium is deposited from the trivalent form, superior to an acid attack to a lesser extent than the base metal subject to «A certain acid attack takes place, however, if not a thin protective layer of chrome is applied to the base metal. This can be done by immersing the workpiece live in the bath and / or working with a high initial current density will.

An important minor feature of the invention is the ability the formation of alloy deposits through the use of a suitable mixture of cations in the elec-

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trolytes. Of "particular interest are chromium-iron,
Chromium-nickel and chromium-iron-nickel systems <> The dynamics of such "binary and ternary systems are complicated and not yet fully understood. As far as they are, however
Influence the composition of the deposit formed on the cathode, the following factors appear to be important: At hypophosphite concentrations of similar molarity to the chromium (III) ion and at concentrations of the latter above 0.8 molar, the rate of deposition of chromium is from an electrolyte of constant composition completely independent of the current density and also of any other cations that are simultaneously deposited on the cathode. In a given
The actual amount of chromium metal deposited on the cathode is thus constant over time. This is neither
in the case of iron noph, in the case of nickel, it is Pal ₀ The rate of deposition of these two metals is a point of concentration. The punctures that connect the concentration and deposition rate are direct but not linear. By changing the concentrations of
Iron and / or nickel in mixed plating baths can make G-round metals with a precipitate of predetermined
Composition to be coated. In hypophosphite baths, the dependence of the rate of deposition of iron and / or nickel on the current density is considerably lower than in the known systems. It is thus possible to apply precipitates with an approximately constant composition regardless of the current density. However, this compensating effect is not as pronounced with iron and nickel as with chromium, so that here a certain change in the composition of the deposit occurs with the current density.

In binary systems, for example chromium-iron or chromium-nickel systems, the chromium content of the generally increases
deposited alloy with increasing current densities

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at the expense of the other component. In ternary systems, i.e. chromium-iron-nickel systems, the situation is more complicated, however, the results obtained so far indicate that the chromium content increases with increasing current density largely at the expense of the iron increases while the proportion of nickel in the final precipitation, expressed as a fraction of the total precipitationa, approximately remains constant. The data available are due to the apparent relatively high deposition rates of iron not unambiguous. Higher deposition rates of the nickel can definitely do one reveal much stronger replacement of nickel by chromium.

It is a feature of binary and ternary separation systems in hypophosphite electrolytes that local fluctuations in the composition are smaller and therefore stainless precipitates containing iron are formed over a much wider range of current densities can be. Stainless plating has been formed at current densities of only 50 A / m, but it is so It is to be expected that this area will be expanded in the course of further development work. The exact reasons for this improvement is unknown, but it may be due to the fact that the function of deposition rate is made uniform depending on the current density in the presence of hypophosph.ite. The improvement of the area in which stainless deposits are deposited can be achieved by adding Phthalates, especially DPP, can be increased.

Since the iron (III) ion is an oxidizing agent, it interferes the deposition of chromium metal from solutions of chromium (III) ions. Furthermore, any EiSe ^ j (IIl) -IOn would Endeavor to oxidize the hypophosphite. Therefore, any iron that is suitable for the chromium bath is preferably used of the invention is added, added in a lower valence level. Generally the iron is called

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Iron (II) salt added.

The concentration of any iron added "is generally 0.05" to 2.5 moles, preferably 0.1 to 1 mol and the concentration ■ of the optionally added nickel 0.05 to 1 mol, preferably 0.1. up to, 0.5 moles. The exact concentration of iron and / or Nickel depends on the desired composition of the alloy to be deposited.

As well as the known electrolysers containing trivalent chromium, the electrolyte according to the invention can be used to form coatings containing inert, finely divided material. The material in Porm of particles having a diameter of usually have α and 100 5 M or less or whiskers having a length generally of 3 to 6 mm and a diameter, is ο.dgl during electrodeposition bath by moving the air with . y na electrolyte suspended. A chromium deposit (or an alloy deposit with another metal), in which the particles or whiskers are embedded, is deposited on the cathode. The particles or whiskers used can be larger than indicated above if the solution is agitated appropriately. Typical inert substances that are suitable for this application are, for example, aluminum oxide, yiter oxide, zirconium diboride, molybdenum disulfide and tungsten carbide. The addition of these materials makes the electrolytically deposited surface layer harder and more wear-resistant than would otherwise be the case.

The electrolytes according to the invention can be mixed by mixing of the components and then adjusting the pH. Based on normal chromium (III) salts, Sodium hypophosphite and preferably ammonium salts of mineral acids, optionally together with boric acid, a surface active compound or others

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Additions of the type described above, by dissolving these constituents in water or mixtures of water and organic buffers, generally an electrolyte is obtained, the natural pH of which is in the preferred range for electrolytic deposition. However, the pH of each mixture depends on the exact nature of the starting materials. The pH can be easily adjusted by adding mineral acid or caustic alkali (or ammonia) as required. The surprising finding has been made that at hypophosphite concentrations of more than about 1 mole and concentrations of trivalent chromium of 0.8 moles or more, an increase in the pH of the solution above 7 results in the mixture solidifying or gelling . The tar-like material formed in this way can be crushed into fine granules, which can be dissolved again in the calculated amounts of acid, the plating bath being obtained again. This tarry pesticide enables convenient transportation and storage of the electrolyte and constitutes a further feature of the invention. Heretofore, the exact nature of this solid is unknown, although it is believed that its overall composition can be determined.

In addition to this gel, the invention comprises one of the mixture the mass of the components of the electrolyte, dio, when dissolved in water, aqueous acid or aqueous alkali, or in mixtures thereof with an organic buffer forms a solution suitable for use as an electrolyte according to the invention. Typical for a such mixture is the following composition:

Trivalent chromium ion (Cr): 25 to 100, preferably

35 to 70 parts by weight.

Hypophosphite ion (H _p PO ~): 5 to 130, preferred

40 to 100 parts by weight

Ammonium ion (NHh ⁺ ): 3 to 100, preferably

20 to 70 parts by weight

The weight ratio of chromium ion to hypophosphite ion should be 0.16 to 4, preferably 0.6 to 1.4, and that

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The weight ratio of chromium ion to ammonium ion is 0.5 to 7, preferably 1 to 4. The concentrations of Chromium, Hypopho- spb.it and ammonium ion are here as ions and of course not expressed in terms of the type of materials actually used. The types of connections which are actually used are listed below:

Chromium (III) chloride hexahydrate CrCl ₃ c6H ₂ O

Sodium hypophosphite monohydra _{-NaH 2} PO _{9 .H 2} O

Ammonium chloride MH.Cl

Boric acid B (OH.)

Surface active compound Cetyltrimethylammonium bromide (cetavlon)

150 to 500, preferably 200 to 400 parts by weight

10 to? .00, preferably 50 to 100 parts by weight

50 to 170, preferably 55 to 110 parts by weight

to 65, preferably 30 to 65 parts by weight

up to 0.5 part by weight

The proportions of trivalent chromium ion to hypophosphite ion and from trivalent chromium ion to ammonium ion should be in the above ranges.

Chromium (II ±) sulfate nonahydrate Cr ₂ ZS0 ₄ "7 ₃ .9H ₂ 0

Sodium hypophosphite as NaH ₂ PO ₂ .H ₂ O

Ammonium u If at
Boric acid as

100 to 400, preferably 150 to 300 parts by weight

10 to 200, preferably 50 to 150 parts by weight

30 to 200, preferably 50 to 150 parts by weight

to 65, preferably from 30 to 65 parts by weight

Cetyltrimethylammonium bromide up to 0.5 part by weight

Here, too, should be the proportions of trivalent Chromium ion to hypophosphite ion and from trivalent chromium ion to ammonium ion within the above ranges lie.

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By dissolving these quantities in V / water or in a water-water-DMF mixture (Volume ratio of Wasper to DMF, for example 50:50) up to a volume of 1000 parts a chrome bath is obtained according to the invention.

The electrolytes according to the invention have a high stability over long operating times. In tests, baths worked flawlessly at more than 30 Ah / l. The electrolyte solutions are not stable under all storage conditions. Maintains at pH values during storage of 'less than 1.5 the current efficiency increases and at pH values above 3j5 to fall. The solid masses described above are believed to last indefinitely.

The stability of the electrolytes during long periods of operation is another indication that neither the hypopnosphite During the electrolysis, the decomposition products of the hypophosphite that are formed are quickly consumed are harmful. The electrolytes according to the invention can be used for long periods of time v / ground by simply adding more trivalent chromium ions (and other precipitates forming ions) to the electrolyte ^ th together with V / ater as needed and, if necessary, small amounts of acid or alkali may be added to maintain the pH. Losses due to discharge with the workpieces by adding bath components replaced.

Pie from the electrolyte and precipitates deposited by the method according to the invention are darker in color than the precipitates deposited from the hexavalent chromium form. They appear to be a little darker than is normal for the previously known systems that work with trivalent chromium. Dupernell tests at 0.25 yes have shown that the precipitate is highly microporous. Coatings of chromium and chromium-iron, chromium-nickel and chromium-iron-nickel produced according to the invention are extremely resistant to concentrated hydrochloric acid, and the

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Complete dissolution of even a 0.25 m thick layer can take up to 30 minutes. Alloy ^Q coatings may need to be heated to achieve complete dissolution. Thicker layers gradually darken in color and become darker as the deposition time increases finally black. The method according to the invention can be used to deposit chromium and chromium alloys on all common 3-round metals such as iron, steel and nickel as well as more difficult substrates such as aluminum, copper, brass and zinc. It has been observed that the connection of chromium on nickel deposits with excessive brightening or incompletely activated nickel deposits dissolves. This type of dissolution of the connection between the chromium deposit and the substrate can be switched off, for example

by brief cathodic treatment at 1500 A / m in 10% sodium cyanide and then good Rinse before the chromium is deposited.

The electrolyte and the electroplating process according to the invention avoid the difficulties which was previously connected with the evolution of chlorine at the anode was. There is now no longer any need to be special To use anodes or a separate anolyte or catholyte. According to the invention can be advantageous Graphite anodes are used <, a feature that applies to this Bad is more pronounced than with the previous trivalent chromium systems, the stronger hydrogen evolution is on the cathode, especially when the organic buffer concentrations are low or no organic buffer is present »This is an inconvenience, but not a disadvantage, since the evolution of gaseous forms. !! hydrogen does not appear to have any influence on the deposition characteristics or on the precipitates formed. The spraying of the surface due to the evolution of hydrogen can be switched off by,

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as already mentioned, a surface-active compound is added to the electrolyte.

The invention is further illustrated by the following examples.

Example 1 ■

A chrome bath of the following composition was made:

1 mole of CrCl ₅ ο6H ₂ O

1 mole of NH ₄ Cl

1 mole of NaH ₂ FO ₂ .H ₂ O

1 mol B (OB) 300 g DMI ¹ V / water to make up to 1

Per electrolyte had the following properties: pH 3

2 Deposition range 75 to 6000 A / m Hull cell voltage 18 V Hull cell current 10 A

The samples were plated in a bath containing the electrolyte for 2 minutes at 25 C, with the following Precipitations were obtained:

Current density,

A / nr 100 450 800 1500 2500 4000 6000

Thickness, pi 0.1 0.28 0.25 0.24 0.30 0.25 0.20

The results show that the thickness distribution is almost independent of the current density.

Example 2

An electrolyte was made from the following components:

0.8 moles of CrCl ₃ ο 6 H ₃ O

1.5 moles of NH ₄ Cl -

0.75 moles of NaII ₂ PO ₂ .H ₂ O

0.75 moles of B (OH) ₃

200 g DMi ¹ ... .. _ '_ _

509816/1 1

Water to make up to 1 1

The electrolyte had the following properties: pH .2.5

Deposition range .50-10000 A / m Hull cell voltage 13 V. Hull line current 10 A

The samples were plated for 2 minutes at 25 ° C with the following results:

Current density, A / m ² 100 450 800 1250 2400 5000 Thickness, jam 0.15 0.30 0.35 0.33 0.30 0.20 These results show that this bath was much more efficient than that in Example 1 called bath, but still formed an essentially uniform precipitate.

Example 3

An electrolyte of the following composition was prepared:

0.8 moles of CrCl ₅ ο 6 H ₂ O

1.5 moles

0.75 moles

0.75 moles ₂₂₂

150 g DMF

V / water to make up to 1 1 10 ppm cetyltrimethylammonium bromide

This gave a bath with the following properties:

pH 1.8

Deposition range 60 to 5000 A / m

Hull cell voltage 12 V

Hull cell stream. 10 A

The samples were stored for 2 minutes at 25 ° C with the following results plated:

Current density, A / m ² 150 300 600 1000 2000 4000

Thickness, / in 0.1 0.15 0.25 0.25 0.20 0.15

5 0 9 816/1109

Example 4

An τ Olli G aqueous sulfate bath was made up of the following 3 constituents share ηernesteilj

0.5 mol (3r ₂ {SO ₄ 5 ₃ .9H ₂ O <1 mol

2 MdI (1H ₄ ) ₂ SO ₄ (4 »oil

1 M.

Water ζ or tof filling to a total of 1 liter

A bath with the following properties was thus obtained pH 2.5

Abscheidrnssbereiuih 5ö bi ^ 5DO0 A / m

Hall-2ellenspannari _J g 1Ό T

10 A

Protes were plated 2 times at 25 ° C., with "precipitates having the following properties being cooled: current density, A / m ² 100 400 1000 3000 3000 thickness, at 0.1 0 _a 28 0.33 0.30 0.20

Example 5

An electrolyte according to the invention was made without boric acid the following components':

0.8 moles of OrGl ₃ . 6H ₂ O

1.5 moles IH ₄ Eq

0.8 moles of UaH ₂ PO ₂ .H ₂ Q

200 E DME

Water. To fill up to 1 1

This gave a bath with blow-drying properties PH 2.0

ADseneidungslaerelDn 60-5000 A / m ² Hull cell oltage 12 T

Hull cell flow 10 A

Samples were plated for 2 minutes at 2 ₅ ° G with results:

5 0 9 81B / 11Ü 9

2 4 / f 7 8 9 7

Current density, A / m ² '100 250 600 1000 2000 4000 Thickness, around 0.1 0.12 0.24 0.24 0.15 0.06

The thicknesses were determined coulometrically by stripping off the chrome down to the nickel base.

Example 6

A completely aqueous chloride electrolyte of the following Composition was made:

0.8 moles of CrCl ₃ ο6H ₂ O

1.5 moles of NH ₄ Cl

0.8 mol NaH ₂ P0 ₂ oH ₂ 0

0.8 moles of B (OH) ₃

Water to make up to 1 1

The bath was adjusted to pH 2.5 with ammonia. It had a deposit area on a nickel-plated Hull cell plate from 60 to 4000 A / cm ^. The HuIl cell voltage was 10 V, the Hull cell current was 10 A, determined coulometrically.

Current density, A / m ² 150 250 500 1000 3000 4500 thickness, around 0.15 0.16 0.20 0.20 0.25 0.20

Example 7

An electrolyte of the following composition was prepared:

CrCl ₃ -6H ₂ O 370 g H ₂ O 500 g PeCl ₂ -4H ₂ O 50 g DMP 500 g ^NH 4C1 50 g DPP saturated B (OH) ν 2 g NaH ₉ PO ₀ -H ₀ O different

~ cad.

This solution had a pH of 1.5. Electroplating tests were carried out at 25 ° C to determine how increasing amounts of HaH ₂ PO ₂ affect the deposition efficiency and the composition of the precipitate. The results are given in Table 1.

509816/1109

24 47.8 9

Ialie lie 1

pp current time composition efficiency, ^

"density, sec. in φ

¹ A / m £ ___ £ e Cr Pe Cr Fe + C r

0 300 300 80.0 20.0 23.0 9.0 32.0

O 1500 150 4-2.0 58.0 13.5 30.5 44.0

10 300 300 91.0. 9.1 18.0 4.5 22.5

10 1500 150 44.0 56.0 11.5 23.0 34.5

50 300 300 76.0 24.0 15.0 8.0 23.5 50 1500 150 52.5 47.5 11.5 16.5 28.0 125 300 300 62.5 37.5 11.5 11.0 22.5 125 1500 150 70.5 29.5 12.0 8> 5 20.5

As these results show, an increase in the concentration of sodium hypophosphite has an increase in the separation efficiency of chromium at low current densities and a reduction in the separation efficiency of chromium at high current densities. The overall effect is that the metal deposition rates are almost constant with changing current density and the composition of the alloy precipitate over the entire deposition area essentially evenly ifct,

Example 8

The experiment described in Example 7 was repeated, except that no DPP was used in the electrolyte and 400 g of DME ¹ and 600 HpO were added. The pH was 1.5. The results are given in Table 2.

509816/1 109

- 2'Ί -

24 * 7897

'fafaelle 2

Current density,
A / mg

TIME ₃

ZaasaKEmemsetzum efficiency ,, ■ $ Fs Gr. Fe Cr ' Pe-KQr

I500,
300

300
150 ©

300 Sl ₃ O 9.0

15 © 68.5 3I ₃ 50

300 97.0 3 * 0

180 69 ₃ ® 3I ₃ O

300 95.5 ^, 5

150 .71 * 6

3Ü0 77.0

15 ©% 3 * 0 5? * ©

300 62 * 5 57.5

15 © 41.5

7.0

8.0

32 ₃ ©

0.5

11 * 0 © ₃ 5 11.5

13 ₃ 5 B ₃ 5 22 ₃ 0

■ 8 ₃ ©% ₃ 0 12 ₃ 0

I ₃ O 15.5 22 ₃ 5

7 * © B ₃ 5 15 * 5

This Urneibinlssce selgeicij äaiß! Bei äl-esem El-ektrclyiteita with stelgeiiader -Hypop] b © .spl3ltk (D.nze: ntratIo: n üeT ifleders-ßhlages sow-oihl "bei äaoJaer, StroEidlellate als

: low current fill rate rises, "

Example 9 .

Electrolyte - according to the invention with the toigee 2 ^; ias ffle; nsetz; amg was twistedeaa ziiar AibseHaeMiiaing ^ oira Cühroffl ~ Hel £ el- umd -'Gihroin-JIskel-EIseua — ieglerssriiiem:

37 © g

MH ₄ Eq

500 pounds 500 g

Uac3a elmer A ^ sciheldiiaiQgsdaoer ^ © m 4 ampere-Staandein was a Bull Eelleaaplate plated. The quality of the leather

509816 / moa

Hit was bad. He showed numerous black ones Stripes and two different areas: at high current densities a chrome-rich area and at low current densities Current densities a nickel-rich area.

The addition of 25 g / l sodium hypophosphite had a significant improvement in the appearance of the boiler impact Episode. Precipitation was of good quality and uniform, but had a limited area «The Metal deposition took place above 500 A / m. By Increasing the hypophosphite concentration, this threshold current was decreased until at one concentration of 100 g / l a separation at 150 A / m ^ was achieved. By adding 15 ppm of cetyltrimethylammonium bromide

the threshold current density was further reduced below 100 A / m.

The metal deposition efficiency and composition of the precipitate formed from this electrolyte are listed in Table 3 below is low (less than 15/0, but shows the composition only changes slightly with current density.

Table 3 also shows the effect of adding 100 g / l FeClp.4HpO to the electrolyte to form a ternary system can be seen. Good quality rainfall was obtained, and the area where none

Rust formation took place, extended to 50 A / m. This electrolyte has metal deposition efficiencies approaching 50? A. The precipitation is predominant made of iron, however, it is to be expected that a precipitate will result from a corresponding change in the composition with a composition similar to 18/8 stainless steel.

509816/1109

g / 1

' Tabel

Flow time density A / m ²

O 300

0 1500

100-300

100 1500

Together-

Sec. Fe

Ki

Yield,

Gr Fe M Cr Fe + ILi + Cr

300- - 27.0 73.0 2.5 12.0 14.5

150-23.5 76.5-2.0 10.5 12.5

300 86.0 5.0 9.0 32.0 2.0 5.5 39.5

150 75.5 3.5 21.0 36.0 1.5 14.5 52.0

5098 1 6/1 1 0Θ

Claims (12)

P, a te η t, a η s ρ return 1) Eleittrolytiösung for the electrolytic deposition of chromium on a base ^ characterized by a content of trivalent chromium ions, hypophosphite 'ions and water. . - ■ 2) electrolyte solution according to claim 1, characterized in that it contains hypophosphite ions in one concentration of at least about 0.08 moles and trivalent ohrociones at a concentration of at least about 0.5 moles. 3) electrolyte solution according to claims 1 and 2, characterized in that it contains hypophosphite ions in a concentration of at least about 0.5 mol, preferably of about 0.5 Ms 2.0 mol. '■ 4) electrolyte solution according to claims 1 Ms 3, characterized in that it contains trivalent chromium ions a concentration of about 0.5 to 1 ^ 75 moles, preferably contains from about 0.7 to 1.3 mol » 5) electrolyte solution nac i to claims 1 to 4 »characterized in that the ratio of trivalent chromium ions to Hypophosphitionsn about 1.6: 1 to 5: 1 _f preferably about 0.7 1 to 1.7: 1. 6) electrolyte solution according to claims 1 · to 5, characterized characterized in that they have ammonium ions in a concentration of at least 0.2 mol, preferably of about Contains 1 to 4 moles. : 7) electrolyte solution according to claims 1 to 6, characterized in that it contains boric acid in one concentration of at least 0.03 mole, preferably from about 0.5 to 1.0 mole. 5 0 9 8 16/1109 8) electrolyte solution according to claims 1 to 7, characterized in that it contains an aprotic organic buffer which contains a strongly electrqnegative oxygen atom in a concentration of at least V /> _t preferably from about 1 to 40 $ of the total electrolyte solution. ; 9) electrolyte solution according to claims 1 to 8, characterized characterized in that it contains dimethylformamide as a buffer. 10) electrolyte solution according to claims 1 to 9 for the electrolytic deposition of chromium-iron iron ions, characterized in that they contain iron (II) ions in a concentration of about 0.05 to 2.5 mol _3, preferably of about 0, Contains 1 to 1.0 moles. 11) electrolyte solution according to claims 1 to 9 for the electrolytic deposition of chrome-nickel alloys, characterized in that they contain nickel ions in a concentration of about 0.05 to 1.0 mol, preferably contains from about 0.1 to 0.5 mol «, 12) electrolyte solution according to claim 11 for the electrolytic Deposition of. Chromium-iron-nickel alloys, characterized in that they contain iron (II) ions at a concentration of about 0.05 to 2.5 moles. Process for applying chromium-containing layers to a substrate by electrolytic means, characterized in that, that an electrolyte of claims 1 to 12 is used. ; 5 0 9816/1 1:09