DE2657012A1 - Trivalent chromium plating bath - contg. iron, cobalt nickel or manganese for improved quality at high current densities - Google Patents

Abstract

A trivalent Cr plating bath contains 30-150 ppm of Fe, Co, Ni or Mn. The trivalent Cr is in the form of a water soluble complex from which Cr can be electrodeposited. The added metals prevent the formation of greyish deposits at high current densities.

Description

Galvanic chrome bath

The invention relates to galvanic chrome plating. In particular concerns the invention electroplating from aqueous galvanic baths, the trivalent Chromium included.

The potential value of solutions containing trivalent chromium as an electrolyte for galvanic chromium deposition has been recognized for many years been. However, it was faced with practical application difficulties until recently nor the economic introduction of such galvanic chrome systems for decorative purposes, which are based on trivalent chrome. All commercially available Process for decorative galvanic chrome plating based on hexavalent chrome, which has some very serious drawbacks. However, there have been some significant ones recently Advances in the use of trivalent galvanic preparations Chromium made, especially with regard to a preparation in the U.S. Patent 3,954,574 and is a significant economic Had success.

In practice, the decorative appearance of precipitation that from galvanic baths with trivalent chromium, occasionally due to certain defects, such as streakiness, fogging or banding in certain cases Current densities are corrupted. In the Belgian patent 843 718 certain Defects described which, as was found, are traces of the presence of metal, such as those of iron, copper, zinc and nickel in the electrolyte.

It has now been found that even when these metals are practical are eliminated from the electrolyte, a slight grayish discoloration of the chromium deposits is observed at high current densities. Surprisingly, it was found that improved chromium deposits can be obtained under these circumstances, if the solution very small traces of certain metals within a certain concentration range contains.

The invention therefore relates to a galvanic chrome bath with trivalent Chromium, which, in addition to the usual additives, contains 30 to 150 ppm (parts per million parts) of metal, selected from the group consisting of iron, cobalt, nickel and manganese. The galvanic Chromium bath containing trivalent chromium is preferably one that has at least contains a water-soluble complex with trivalent chromium, which is capable of is to electrodeposit metallic chromium. Particularly preferred are complexes which contain carboxylates and halides. Such complexes can be pre-formed or be formed in situ in the bath. Particularly preferred are those baths that have a trivalent chromium salt, a formate, a bromide and Contain ammonium, as described in U.S. Patent 3,954,574.

Alternatively, and less preferably, the baths can be designed in this way be that they contain a preformed complex with trivalent chromium, where other ingredients glycolic acid or oxalic acid and a halide, such as a bromide, Are fluoride or, preferably, chloride, as is essentially the case in the United States patents 3,706,639, 3,706,640, 3,706,641 and 3,729,392, or it is around a bath of the same type, which also contains ammonium. Preferably the baths according to the invention contain a borate, such as sodium borate or boric acid, a chloride and / or sulfate and an alkali metal such as sodium or potassium usually such baths also contain a wetting agent. Baths according to the invention are preferred essentially free of hexavalent chromium. Usually they have a pH value between 1 and 4.

When using solutions according to U.S. Patent 3,954,574, the solution can contain bromide ions, formate or acetate ions and any boron ion, which can be the only type of anion. However, such solutions are inconvenient quite elaborate. Therefore, the solution preferably contains only so much bromide that practically the formation of hexavalent chromium is prevented, sufficient Amount of formate that the chromium is kept in the complex and a sufficient amount Borate that a buffer effect is achieved, the rest of the anions needed for this is to compensate for the cation content of the solution, these anions being cheaper can be, as is the case with chlorides and / or sulfates.

For example, the solution optionally and preferably additionally contains halide ions to bromide ions, such as fluoride or preferably chloride ions. The total amount of halide including bromide and any iodide present and any fluoride and / or Chloride may be sufficient, together with the formate content and any borate content to represent practically the entire anion content of the solution.

This anion content is determined by the number of cation equivalents (including of the hydrogen ion) and is usually 4 to 6 molar. According to Another embodiment, which is preferred, can additionally contain sulfate ions to be available. According to one embodiment of the invention, the sulfate is in one smaller amount, based on halide, e.g. in the form of a smaller amount, based on chloride and / or fluoride. According to an alternative, the sulfate can be a represent a larger proportion of the inorganic ions and can, although less preferred to be present in place of chloride and fluoride. Preferably contains The solution also contains alkali metal ions, usually in the form of cations of the conductive Salts and / or some or all of the salts that are used to introduce the Serve anions, are present, these alkali metals preferably sodium or Are potassium. The solution can also contain alkaline earth metals, such as calcium or magnesium, contain.

The solutions according to the invention can also be smaller, but tolerable Contains quantities of other additives, such as wetting agents (e.g. alkali metal alkylbenzene sulfonates) or means for preventing foam formation, which are usually used in galvanic Metal deposition can be used.

The new solutions according to the invention can therefore be as follows Fabric types include: A. Trivalent Chromium This is an essential one Part of all solutions according to the invention. Quantities less than 0.1 molar or over 1.2 molar of trivalent chromium results in a considerable loss of opacity, and the concentration is preferably maintained within these limits and is most preferably between 0.2 and 0.6 molar. Preferably the Solution practically free of hexavalent chromium, and preferably the chromium is in of the solution practically present as trivalent chromium before electroplating is chrome-plated.

B. Bromides The bromide component is highly preferred. The bromide concentration should preferably be kept above 0.01 molar to prevent the formation of hexavalent Preventing chromium as well as preventing the chromium plating rate from slowing down will. The maximum concentration is not critical, but usually it is below 4 molar and preferably below 1 molar. With an economical and effective The procedure is usually a concentration of bromide between 0.05 and 0.5 molar needed. The preferred range is 0.05 to 0.3 molar. The best results are obtained when the bromide concentration is greater than 0.1 molar. Iodide works in a manner similar to bromide, however, results in the disadvantage that free iodine, which during the chrome plating would be formed, only in an amount of 0.03 wt .-% is soluble in water compared to 4 wt% for bromine. Hence attempts Using iodide in place of bromide leads to unacceptable precipitates of Iodine. Iodide is also too expensive to use economically in place of bromide. It however, it is possible in principle to use a smaller amount of the bromide to be replaced by iodide, which is why the reference to bromide does not exclude bromide, which contains traces of iodide.

C. Carboxylates The carboxylates are highly preferred ingredients of the baths according to the invention, formates being most preferred. Usually the ratio of formate to chromium should not exceed 3: 1 on a molar basis, in order to avoid unacceptably heavy deposits of the corresponding chromium salt. If the proportion is below 0.5: 1, the hiding power of the metal coating is inappropriately reduced. The quantitative ratio of formate to chromium is preferably between 2: 1 and 1: 1.

Acetate works in a similar way to formate but gives one much slower chrome plating speed. To prevent the accumulation of With free halogen, acetate alone is not as effective as formate. However, it is possible Acetate as a partial substitute for formate up to about a third of the total amount To use carboxylic acid without producing a serious adverse effect.

Solutions that contain more than a third of the total carboxylic acid, are not competitive in practice with solutions based on formate alone, although they are still superior to such prior art electrolytes. Other less preferred carboxylates include glycolic acid, and also oxalic acid, albeit less preferred, other mono-, di-, poly-, hydroxy- and aldehyde-carboxylic acids, which are soluble in water and have no more than 10 carbon atoms. Examples these are citric acid, tartaric acid, glyoxalic acid, maleic acid, succinic acid and malonic acid.

D. Inorganic anionic complexing agents It is possible if also less preferred, at least part of the acting as a complexing agent Carboxylate by an inorganic anionic complexing agent for chromium, like hypophosphate, to replace.

E. Ammonia The presence of ammonium ions is strong in the present invention preferred. In general, if the ammonium concentration is below 0.1 molar there is a risk of the formation of hexavalent chromium. The upper limit is not critical, and ammonium can be present in amounts up to saturation, i.e. about 4 molar. Ammonium is preferably present in a concentration of at least 0.2 molar, most preferably 1 to 3 molar. These higher concentrations are therefore useful because chromium deposits get darker when the ammonium concentrations approaching the minimum, and also because of the presence of ammonium to it helps to reduce the consumption of formate. Carry both ammonium and formate helps to prevent the build-up of free bromine, but is at higher ammonium concentrations the amount of ammonium ion that is oxidized in this reaction is greater, resulting in savings with the more expensive formate. It is also possible, although not preferred, within within the scope of the invention some substituted ammonium compounds in the solution to be used, such as hydroxylamine, hydrazonium salts or alkylammonium salts. In absence however, of ammonium ions as such, these compounds usually do not give rise to any adequate opacity. Preferably are arylammonium ions or heterocyclic ones Ions, such as pyridinium ions, not available, as these tend to to inhibit the deposition of chromium.

F. Borate Although it is possible to obtain chromium from solutions according to the invention, Electroplating those containing no borate, it was not possible to achieve fully satisfactory To achieve results in practice when borate was absent. Concentrations below 0.1 molar results in an undesirably low opacity. The upper limit is not critical and is only determined by the solubility of borate in the system. General becomes however, preference is given to using 0.5 to 1 molar borate. The function of the borate is not quite transparent. The beneficial influence of borate can partly reduce the buffering effect can be attributed. However, other buffer salts, such as phosphates and citrates, are apparently relatively ineffective.

G. Conductive salts The use of conductive salts happens if necessary, but is generally preferred. The concentration of these salts is not critical and can between 0 and about 6 molar, depending on the solubility. Preferably lie the salts are present in amounts between 0.5 and 5 molar, e.g. 1 to 4 molar. Conductive salt is a term used in electrodeposition to to designate certain readily ionizable salts that are added to plating baths can be used to increase their electrical conductivity and thus the amount of electricity which is scattered in the bathroom to reduce. Typically, these are conductive salts Alkali metal or alkaline earth metal salts are stronger Acids found in are soluble in the solution. You should have a dissociation constant at least equal 10 2 have. Typical examples are the chlorides and sulfates of sodium and potassium.

H. Hydrogen Ions The best results are obtained when that Bad is a bit acidic. At low pH values (below 2) there is some loss opacity, which is no longer acceptable below a pH value of 1. if the pH is above 4, the rate of chromium plating is undesirably slow. An optimal pH value is between 2 and 3.5.

1. Chloride and / or fluoride The presence of these ions is expedient but preferred at least in the case of chloride. However, the amount is not critical. It can range from 0 to the maximum that is still permitted by solubility considerations is to fluctuate.

Chloride is generally in the bath in the form of the anion of the conductive salt (e.g. as sodium chloride) or as ammonium chloride, which is useful for Introduction of the ammonium ion, which is also required, or as chromium chloride, the possibly at least partially used to equip the bathroom with trivalent chrome is, and / or in the form of hydrochloric acid, which is useful for adjusting the pH of the bathroom is. The chloride content is preferably at least 1 molar, e.g. 1.5- up to 5 molar.

A particularly useful range is from 2 to 3.5 molar.

J. Sulphate This ion is useful, but preferred as a constituent.

The amount of sulfate is not critical and can, similar to that of the Chloride, fluctuate between 0 and the maximum amount that is still compatible with the solution is. In one type of bath, the amount of sulfate is less than the total amount of chloride. In another bath, however, the amount of sulfate is greater than the amount of halide and can be the predominant anion in the bathroom. Much like the chloride can the sulfate in the bath as an anion of the conductive salt or in the form of ammonium or chromium III salt or introduced as sulfuric acid. Use is particularly preferred of sulphate as a source of chromium in the form of chromium pickling liquors, which are made from basic chromium sulphate exist, and particularly useful in the form of a commercially available by-product and are an inexpensive source of trivalent chromium. Typical sulfate concentrations can be between 0 and 5 molar, preferably 0.5 to 4 molar, e.g. 0.6 to 3 molar, and most preferably 0.6 to 1.2 molar. Preferably the combined Concentrations of chloride and sulfate at least 1 molar, e.g. at least 2 molar and most preferably 2.5 to 4 molar.

K. Metals that can be deposited together These metals that can be deposited together with chromium Metals are essential components of the bath in the case of iron, cobalt and nickel and manganese. The latter are in the bath in a concentration of 30 to 150 ppm total present. They are usually in the form of their soluble chlorides or sulfates are used. Other metals that can be deposited with the chromium, such as copper, Zinc and lead, are preferably in amounts less than each 20 ppm, and preferably less than 30 ppm total.

L. Metals that cannot be co-deposited with chromium These metals are possibly, but preferably present. It is particularly preferred to alkali metals and in particular sodium and / or potassium in the bath in an amount of at least 0.5 molar up to 4 or 5 molar, depending on solubility, to be provided. The presence of sodium and / or potassium helps to increase the conductivity of the solution and also to improve the gloss density. Usually sodium and / or potassium come in one Amount of about 2 molar added at the beginning, but there is a tendency that it is These metals accumulate during the use of the bath, causing the concentration rises to the saturation value. Other alkali metals, such as lithium, alkaline earth metals, like calcium or magnesium, or other metal ions that are not out of solution with The chromium failing together can also be present. The amount of such Metals can fluctuate within very wide limits, provided they are not in the presence the other components fail. They are generally in the form of the conductive salt cation or the borate, formate and / or bromide salt present which are used, to provide this type of anion in the solution.

M. Surfactants These are optionally, but preferably in effective and tolerable amounts. Wetting agents and antifoaming agents in the entire technology of galvanic Plating used, and Many suitable examples are known to those skilled in the art. It can be any wetting agent that commonly used when plating with hexavalent chromium, according to the invention be used. However, since the solutions according to the invention are much less Have oxidative power than solutions with hexavalent chromium, it is possible and preferred Use the cheaper wetting agents, which are usually used for the less aggressive ones Plating solutions can be used. A fundamental limitation of the effectiveness the wetting agent results from the presence of free bromine in the solution. Surface active Agents that are easily brominated are therefore not recommended, such as

most nonionic surfactants.

The surfactants used in the present invention are typical cationic wetting agents such as those disclosed in British Patent 1,368,749 or preferably anionic, such as the sulfosuccinates, alkylbenzenesulfonates with 8 up to 20 aliphatic carbon atoms, such as sodium dodecylbenzenesulfonate, alkyl sulfates with 8 to 20 carbon atoms, such as sodium lauryl sulfate and alkyl ether sulfates, such as Sodium Lauryl Polyethoxysulfate.

If. the solution shows an undesirable tendency to foam it may also be possible to use compatible antifoam agents, e.g. fatty alcohols, like acetyl alcohol. The choice of surfactants for use in the solution according to the invention is routine work within ordinary skills of the specialist. The amount of wetting agent used corresponds to normal practice and is, for example, 0.1 to 10 parts per 1000 parts.

It is preferred that the solutions according to the invention essentially should consist of the aforementioned components. However, it is not excluded that smaller Amounts of other substances are present that interfere with the Solutions are compatible and the plating properties are not substantial affect. It is generally preferred that nitrate ions be substantially absent are present, as these lead to the deposition of chromium. Also is preferably none Sulphite ion present as this veil-like deposits in more than just small ones Can cause amounts. Other constituents of an organic or inorganic nature, which do not prevent the chromium deposition or which do not significantly reduce the opacity or create unacceptable toxicity issues. to be available. Whether a certain type of substance can be tolerated in the solution can be routinely determined by simple experimentation.

According to the invention, the baths are preferably made in such a way that as described in the aforementioned patents, however, include an additional 30 to 150 ppm of the metals iron, cobalt, nickel or manganese in the solution. Preferably the filler metal is iron or nickel and is most preferred the Ferriion. It is advisable to use a sufficient amount of an appropriate salt, e.g. ferric chloride or preferably ferric sulphate to the bath at any convenient stage added from its manufacture. Alternatively, the iron mixture can be mixed with any of the can be added to other components of the bath. For example, it is possible select a source from one of the other bath components, such as the chromium sulfate, which contains iron as an impurity, in sufficient quantity to produce the necessary Bringing out concentration in the bathroom. It is preferable to supplement the consumed Bad iron, cobalt, nickel or manganese added in the booster additions in an amount which is sufficient to keep the concentration within the stated limits keep. The concentration is preferably 40 to 100 nm, e.g. 0 ppm. If dt, concentration of iron, cobalt. Nickel or manganese greatly exceeds the specified limits, where plating defects arise, it can be eliminated by adding a hexacyanoferrate. e.g. as described in Belgian patent 843 718 , whereby it must be ensured that after the treatment the concentration of the mentioned metals is adjusted again as required in order to convert them into the inventively to bring characteristic concentration ranges.

The invention is further illustrated by the following examples.

Example 1 A galvanic chromium plating solution was prepared, the? O g / l chromium in the form of a commercially available chromium III sulfate and 32 g / l formic acid contained. The other ingredients were 75 g / l potassium chloride, 50 g / l boric acid, 10 g / l ammonium bromide and 90 g / l ammonium chloride according to US Pat. No. 3,954,574 of manufacture and chromium deposition at 0.5 amps per liter over 60 minutes iii the Hull cell coated a plate with the solution at 10 amps for 3 minutes. Gray bands could be detected at current densities above 400 ASF. The analysis the trace element solution showed 15 ppm iron, 10 ppm nickel and 1 to 2 ppm Copper and zinc. These metals came from traces, those in the other commercially available ones Ingredients templates.

There were now 25 ppm iron in the form of ferric chloride (FeCl3.6H3O), i.e. in an amount of 0.120 g / l, added and the solution again in the Hull cell to the Chrome plating used. The gray baths precipitate on the chrome disappeared and a clean disc with no tapes was obtained. The finally Analysis of the solution carried out showed that 40 ppm iron, 10 ppm nickel and 5 ppm Copper plus zinc were present.

Example 2 A working solution was prepared as above and used for Manufacture of chrome gloss coatings used. She got nickel. and iron contaminated, resulting in defective plating. Analysis of the solution showed that there were 110 ppm iron, 150 ppm nickel, 25 ppm zinc and 5 ppm copper, Then the solution would be treated with potassium ferrocyanide (K4Fe (CN) 6) in an amount of 1 m1 / l of a 20% by weight solution per 50 nFm of metals, i.e. in an amount of 6 ml / l, used. After a certain period of rejection, the deposited metals became filtered off and the solution analyzed again. It was 20 rpm in, 15 ppm nickel found, which means practically complete metal removal. The plating attempt in a Hull cell showed a trace of gray bands on the chrome-plated sheet metal, which began to develop at high current densities, and the work piece that had been chrome-plated in the electrolyte showed a pale gray appearance at the tips high current density. 25 ppm iron (as FeCl3.6H20) were added to the electrolyte, after which the gray bands and the gray markings on the workpiece immediately disappeared. The concentration of (nickel + iron) was in a concentration range of 40 to 100 ppm maintained by subsequent appropriate addition of iron to the make-up solutions.

Claims (4)

Claims Galvanic chromium bath, contained in an aqueous solution a complex of trivalent chromium among other common additives for decorative Purposes characterized in that it also contains 30 to 150 parts per million parts Contains iron, cobalt, nickel and / or manganese. 2. Chrome bath according to claim 1, containing as usual ingredients in addition trivalent chromium formate and / or its mixture with acetate, bromide, borate, sulfate and / or chloride, sodium and / or potassium ions, ammonium ions and a surface-active one Means, characterized in that it contains 30 to 150 parts per million parts of iron, Contains cobalt, nickel or manganese. 3. Method of refreshing a galvanic chrome bath with trivalent Chromium according to one of Claims 1 or 2 by adding appropriate salts, thereby characterized by having such an amount of a salt of iron, cobalt, nickel or manganese, especially iron (III) chloride or iron (III) sulfate, is added to the bath, that a concentration between 30 and 150 parts per million parts of said Metals in the bathroom is preserved. 4. Process for reconditioning a galvanic chromium bath containing trivalent chromium and an excess of iron, cobalt, nickel, copper, zinc and / or manganese by adding a water-soluble hexacyanoferrate complex salt to the bath, characterized in that the complex salt is only added in such an amount that the total concentration of iron, cobalt, nickel, copper, zinc and or Manganese reduced to a value of 30 to 150 parts per million parts in the bath with the total amount of zinc and copper below 20 parts per million and the total amount of iron, cobalt, nickel and / or manganese is greater than 30 parts per million parts.