CA1084441A - Chromium electroplating - Google Patents
Chromium electroplatingInfo
- Publication number
- CA1084441A CA1084441A CA256,190A CA256190A CA1084441A CA 1084441 A CA1084441 A CA 1084441A CA 256190 A CA256190 A CA 256190A CA 1084441 A CA1084441 A CA 1084441A
- Authority
- CA
- Canada
- Prior art keywords
- ferrocyanide
- bath
- solution
- plating
- excess
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/04—Electroplating: Baths therefor from solutions of chromium
- C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electroplating And Plating Baths Therefor (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
CHROMIUM ELECTROPLATING
ABSTRACT OF THE DISCLOSURE
Trivalent chromium electroplating baths which have developed characteristic faults due to accumulation of trace metal contaminants are treated with just sufficient of a water soluble ferrocyanide to restore the bath to normal working order. The presence of any excess of trace metal or of ferrocyanide may be detected by causing the solution to permeate upwardly through a water permeable medium and contacting separate parts of the solution in the water permeable medium with a soluble ferrocyanide and an iron salt respectively. Typically a test paper impreg-nated at either end with two salts is employed.
ABSTRACT OF THE DISCLOSURE
Trivalent chromium electroplating baths which have developed characteristic faults due to accumulation of trace metal contaminants are treated with just sufficient of a water soluble ferrocyanide to restore the bath to normal working order. The presence of any excess of trace metal or of ferrocyanide may be detected by causing the solution to permeate upwardly through a water permeable medium and contacting separate parts of the solution in the water permeable medium with a soluble ferrocyanide and an iron salt respectively. Typically a test paper impreg-nated at either end with two salts is employed.
Description
~08444~
The present invention relates to chromium electro-plating, and in particular to the maintenance of electroplating baths based on trivalent chromium.
Although the potential advantages of electroplating from solutions containing chromium in the trivalent state have been recognized for over fifty years, until recently a variety of practical difficulties have prevented the commercial adoption of any such solution. Chromium has therefore always been electroplated from baths containing the chromium in the hexavalent state, despite certain serious disadvantage of such baths~
Recently, however, various proposals have been made for overcoming at least some of the aforesaid difficulties.
One type of bath in particular, containing a trivalent chromium salt, a formate, a bromide and ammonium as essential ingredients is described in our U.S. Patent No. 3,954,574.
A process based on such a bath has recently been introduced commercially and is already gaining widespread acceptance ;
as a replacement for hexavalent chromium plating baths.
However, it has been discovered that some trivalent chromium plating baths, which work satisfactorily under laboratory or test conditions, sometimes develop plating defects after they have been installed commercially. In particular at least one, and usually a combination, of the following faults may occur:
A. A white haze at high current densities, which may, in severe cases, spread progressively to lower current densities.
B. A white band at the lower limit of the plating range, often accompanied by loss of adhesion at high current densities.
C. A white deposit at current densities of around 50 amps per square foot.
D. Brown or black smudges between about 100 and 200 amps per square foot.
~e have now discovered that the aforesaid faults, may, in many cases, be reduced or overcome by adding a small amount of water soluble ferrocyanide to the plating solution, w~enever the faults are observed.
~ ' :, . . . . . - , ,. , . . , -. ~ , ~ ., :: . . : , 'j ~ . .
' .. .. ' '. . . . :' ' ' ' .. " ' ' ' ' - ~08444~
Our invention therefore, according to one aspect, provides a method for the maintenance of an aqueous trivalent chromium electroplating bath which has begun to exhibit at least one of the aforesaid faults, which comprises adding thereto a sufficient amount of a water soluble ferrocyanide substantially to reduce or prevent said fault.
We have found that the invention is applicable to the maintenance of trivalent chromium electroplating baths generally. For example, it may be employed with baths of the type described in our aforesaid U.S. patent, or with baths containing glycollic acid such as are described in USP 3,706,636 to 643. The invention may also be used, for example, in combination with baths of the type described in BP 1,144,913, USP 3,021,267, USP 3,006,823, USP 3,069,333 and USP 3,111,464.
Generally speaking the baths contain a trivalent chromium salt, such as chromium chloride, sulphate or fluoride and a complexing agent such as a carboxylic acid, preferably a formate, or alternatively, for example, an acetate, glycollate or oxalate. Halides especially bromide are preferably present. The solution preferably contains alkali metal ions, for example sodium and/or potassium, and sulphate ions. Aprotic dipolar solvents such as dimethyl formamide may also be included but are preferably absent. Typically the pH of the bath is between 1 and 7, for example 1.5 to 5.
The ferrocyanide may be any ferrocyanide which is soluble in the bath, for example an alkali metal or ammonium ferrocyanide, for example sodium or potassium ferrocyanide.
The ferrocyanide may conveniently be added to the bath as an aqueous solution. The concentration of the ferrocyanide solution is not critical, and will normally be chosen according to the solubility of the particular ferrocyanide employed. For example using potassium ferro-cyanide we prefer to employ a solution containing about 20%
by weight ferrocyanide.
We have found that addition of ferrocyanide in amounts in excess of those required to eliminate the 4Q aforesaid faults, may cause a deterioration in the perfor-- . ' ' ~ .
.:
:
- ~08444~ ~
- mance of the bath. One way of avoiding this problem when the onset of any of the aforesaid faults is observed, is to add the ferrocyanide solution in small increments until the chromium deposit is satisfactory again. If a sufficient excess of ferrocyanide has accidentally been added to cause a significant deterioration, it is possible to remove the excess by adding a small amount of soluble cation such as copper, nickel, iron or zinc. In most plating shops this may conveniently be achieved by adding a small amount of nickel plating solution to the bath. The addition of metal ion should be made within 15 minutes preferably within l0 minutes of adding the ferrocyanide, in order to be fully effective, since on standing the excess ferrocyanide complexes with the chromium and is then difficult or impossible to precipitate with the added metal.
We believe that the aforesaid faults may be due to the accidental contamination of the bath by traces of metal cations, which are capable of codepositing with the chromium.
Our experiments have shown that fault A can be simulated by adding copper to the bath; similarly fault B appears to be associated with the presence of zinc, fault C with lead -and fault D with nickel or a mixture of nickel and iron.
It seems, surprisingly, that the ferrocyanide is capable of precipitating substantially all of the potentially harm-ful trace metals which are most commonly encountered in very low concentrations as contaminants in commercial practice, but without precipitating the chromium, which is a principal cationic constituent of the bath.
According to a preferred embodiment, therefore our invention provides a method of maintaining ~ trivalent chromium plating bath which exhibits plating defects associated with the codeposition with the chromium of trace metal contaminants, which method comprises analyzing the bath to determine the concentration of said trace metal contaminants in the bath and adding a water soluble ferro-cyanide in an amount sufficient to precipitate said contaminants.
Preferably the bath or any sample used for analysis should be filtered to remove any previously precipitated ~08444~
metal prior to the analysis.
The analysis of the bath may be carried out by any of the analytical techniques for quantitative determination of the trace metals which are well known in the art. Typically the bath may be analyzed by spectographic means, for example by spark ionization or atomic absorption. Alternatively polarographic means may be employed.
Usually it is only necessary to test for copper, zinc, iron and nickel, since these are the only metals which, in our experience, are likely to cause difficulties in practice. The invention is however applicable to the correction of plating faults due to the presence of other codepositable metals, including lead, cadmium, silver and gold, although significant contamination by such metals is unlikely to occur in practice.
The amount of ferrocyanide added is preferably substantially stoichiometric based on the trace metal contaminants present, or slightly less. Any substantial excess of ferrocyanide should be avoided. Addition of any effective quantity significantly less than the stoichiometric amount, while beneficial, may not entirely remove the plating fault. We have discovered that a good rule of thumb is to add 1 ml. of 20~ potassium ferrocyanide solution per litre of plating solution for every 50 ppm of trace metal contamination. In this way the bath can be relatively easily maintained in the face of at least the commonly encountered forms of contamination.
It is preferred to reduce any free halogen in the bath to halide prior to addition of the ferrocyanide, by addition of a reducing agent capable of converting halogen to halide, without adversely affecting the performance of the bath. One particularly suitable reducing agent for this purpose is ammonium formate, The proportion of formate is preferably sufficient to reduce all the free halogen in the solution. Typically 2 to 3 gms per litre of formate may ~e added, preferably as an aqueous solution.
The formate is preferably added with agitation, about 10 minutes prior to the ferrocyanide addition. Halogen is usually present in the bath immediately after plating.
, ' , .
Our invention further provides a rapid method for detecting the presence of harmful excesses of either the ferrocyanide or certain of the commoner metallic impurities, -so that appropriate remedial action can be taken without 5 delay. -According to one aspect of our invention there is provided a method of testing an aqueous solution such as a trivalent chromium plating bath which comprises contacting the solution with a water permeable medium, causing the solution to diffuse upwardly through the medium and contact-ing separate portions of the diffusing solution in the medium with a water soluble ferrocyanide salt and with a water soluble iron salt respectively.
Typically the contact between the diffusing solution and the two salts is ensured by impregnating separate parts of the medium with the two salts, the impregnated parts being disposed in such a way as to intercept separate por-tions of the diffusing solution. Preferably impregnated parts should be readily visible to an external observer so 2Q as to facilitate the detection of any colour changes.
The permeable medium is preferably a cellulosic material such as filter paper or chromatography paper.
However, any medium which is capable of causing aqueous solutions to diffuse upwardly therethrough, when its lower part is immersed, may in principle be employed. Preferably the medium is substantially colourless so as to permit observation of small colour changes.
According to a particular embodiment our invention provides a means for testing trivalent chromium plating baths comprising a water permeable medium, separate, exter-nally visible, parts of which are impregnated with a water soluble ferrocyanide salt and with an iron salt respectively.
Preferably the medium is a water permeable paper.
A particularly convenient form of test paper according to our invention comprises a strip of permeable paper such as filter paper, which can, for example, be rectangular or any similar convenient shape, a part at or near one end of which has been impregnated with the ferrocyanide and a part at or near the other end of which has been impregnated with . ~ .
, , :: - ~ . - .: .
: : . :
:
~08444~
the iron salt, preferably leaving an unimpregnated central part between the two impregnated parts. In use, such a paper mày be bent or folded about the unimpregnated part, so as to permit the latter to be contacted with the solution, leaving the two impregnated parts unimmersed. The solution diffused up each immersed arm of the paper, which separates out suspended solids, so enabling any colour change in either arm to be more readily detected.
Test papers according to the invention may conveniently be obtained by preparing rectangular strips of permeable paper and immersing the two ends of each strip respectively in solutions of the two salts, for sufficient ~-time to permit the two solutions to diffuse into separate, preferably non-overlapping parts of the paper. The paper may then be dried, for example in an oven.
The tests according to the invention may alternatively be performed using two separate test papers impregnated respectively with the two salts. If the medium is non-coherent or ~rittle in nature a suitable support means may be provided. For example, it is possible to perform the tests using a thin layer of silica gel supported on a plate, or in the case of po~dery or gelatinous media, to support the medium in a column (preferably of glass or similar transparent material).
The ferrocyanide salt is preferably an alkali metal or ammonium ferrocyanide for example tetra potassium ferrocyanide. The iron salt may be a ferric or preferably a ferrous salt, preferably of a mineral acid, for example a chloride, nitrate or sulphate.
3Q If a blue stain forms on contact between the solution being tested and the ferrocyanide, then the solution contains an excess of the metallic impurities, whereas a blue stain forming on contact bet~een the solution and the iron salt indicates an excess of ferrocyanide. Preferably an aliquot of trivalent chromium plating solution is taken and ferro-cyanide is added, stepwise, thereto. The solution is checked after each addition ~ith the test paper. The end point, in mls. ferrocyanide per litre of plating solution represents a maximum. In practice, preferably about 50%
~ ' 108444~ :
of this amount of ferrocyanide is added to the bath, followed by a further addition of e.g. 25%, if required.
The invention will be illustrated by the following Examples:
Example 1 A trivalent chromium plating solution which had been working satisfactorily developed a plating fault, giving dark smudges in the 100-200 ASF region. A sample of the solution was put into a 300 ml Hull Cell with circulatory cooling and a 10 amp 3 minute panel run. This panel showed black streaks between 100-200 ASF and from previous experience was diagnosed as being due to nickel and possibly iron contamination of the solution. It was established that some nickel plated components had been lost from plating jigs and had been dissolving in the electrolyte for some time. The electrolyte was analyzed spectroscopically for trace metals as follows:
Nickel 134 Copper 13 Iron 193 Zinc 26 Total Metals 366 A 20% w/v solution of potassium ferrocyanide (K4Fe(CN16.3H2O~ was prepared and 1 ml of this solution added per 50 ppm total metals perliter i.e. 7 ml per litre were actually added. The mixture was allowed to stand for 30 minutes and then used for plating components.
The black streaks were completely absent and normal plating performance was regained.
3Q Subsequent analysis of the electrolyte gave the following result:
~E~ % removal Nickel 20 85 Iron 98* (4 Copper 4 69 Zinc 8 69 *this figure will include a contribution from any excess reagent.
' ' : ~ ' . :--, :
,. - ~ , :~ . .. .: . :
.. . . ~
, , ': : , . , - los444l :'~` 9 Example 2 A similar electrolyte contaminated with iron, nickel, copper and zinc gave plating faults. In this case no trace metal analysis was available. Halogen was reduced by addition to the bath of 5 ml/litre of 55% w/w ammonium formate solution. The bath was agitated for 10 minutes, and then 20% potassium ferrocyanide was added in a step-wise fashion, beginning with 1 ml per litre of electrolyte and increasing the addition in 1 ml per litre steps, allowing 30 minutes reaction time between additions. Some improvement was noted after the addition of 3 ml per litre and fully satisfactory performance was achieved at 5 ml per litre. The precipitate of insoluble metal salts was allowed to remain in the bath and did not interfere with plating in any way, but the solution was filtered at the next shutdown to remove the precipitated metals.
Example 3 Test papers were each prepared by dipping one end of a rectangular strip of filter paper in 20% w/v solution of tetra potassium ferrocyanide and the other end is a 20% w/v solution of ferrous chloride. The solutions were each allowed to diffuse part way towards the centre of the strip, ~hich was then dried in an oven.
Example 4 A trivalent chromium plating solution, after working satisfactorily for several weeks, developed a fault which comprised the formation of dark smudges at current densities of between 100 and 200 amps per square foot. A test paper prepared according to Example 3 was folded across the unimpregnated central portion, which was dipped in the bath. The electrolyte diffused towards both ends of the paper and produced a blue stain near the ferrocyanide impregnated end, indicating the presence of metallic impurities.
35~ w/v aqueous solution of tetra potassium ferr~cyanide was added in 4 ml increments, allowing 30 minutes after each addition and then repeating the test. After the second addition, a blue stain was observed at the iron impregnated "
, . . . .
,--~ 10 end of the paper. 2 ml of 20% w/v ferrous chloride solution was added whereafter no stain was observed. Commercial plating was resumed and the bath functioned satisfactorily.
;, : . ~ .
'': '' 'i '"' ' ' . . :
The present invention relates to chromium electro-plating, and in particular to the maintenance of electroplating baths based on trivalent chromium.
Although the potential advantages of electroplating from solutions containing chromium in the trivalent state have been recognized for over fifty years, until recently a variety of practical difficulties have prevented the commercial adoption of any such solution. Chromium has therefore always been electroplated from baths containing the chromium in the hexavalent state, despite certain serious disadvantage of such baths~
Recently, however, various proposals have been made for overcoming at least some of the aforesaid difficulties.
One type of bath in particular, containing a trivalent chromium salt, a formate, a bromide and ammonium as essential ingredients is described in our U.S. Patent No. 3,954,574.
A process based on such a bath has recently been introduced commercially and is already gaining widespread acceptance ;
as a replacement for hexavalent chromium plating baths.
However, it has been discovered that some trivalent chromium plating baths, which work satisfactorily under laboratory or test conditions, sometimes develop plating defects after they have been installed commercially. In particular at least one, and usually a combination, of the following faults may occur:
A. A white haze at high current densities, which may, in severe cases, spread progressively to lower current densities.
B. A white band at the lower limit of the plating range, often accompanied by loss of adhesion at high current densities.
C. A white deposit at current densities of around 50 amps per square foot.
D. Brown or black smudges between about 100 and 200 amps per square foot.
~e have now discovered that the aforesaid faults, may, in many cases, be reduced or overcome by adding a small amount of water soluble ferrocyanide to the plating solution, w~enever the faults are observed.
~ ' :, . . . . . - , ,. , . . , -. ~ , ~ ., :: . . : , 'j ~ . .
' .. .. ' '. . . . :' ' ' ' .. " ' ' ' ' - ~08444~
Our invention therefore, according to one aspect, provides a method for the maintenance of an aqueous trivalent chromium electroplating bath which has begun to exhibit at least one of the aforesaid faults, which comprises adding thereto a sufficient amount of a water soluble ferrocyanide substantially to reduce or prevent said fault.
We have found that the invention is applicable to the maintenance of trivalent chromium electroplating baths generally. For example, it may be employed with baths of the type described in our aforesaid U.S. patent, or with baths containing glycollic acid such as are described in USP 3,706,636 to 643. The invention may also be used, for example, in combination with baths of the type described in BP 1,144,913, USP 3,021,267, USP 3,006,823, USP 3,069,333 and USP 3,111,464.
Generally speaking the baths contain a trivalent chromium salt, such as chromium chloride, sulphate or fluoride and a complexing agent such as a carboxylic acid, preferably a formate, or alternatively, for example, an acetate, glycollate or oxalate. Halides especially bromide are preferably present. The solution preferably contains alkali metal ions, for example sodium and/or potassium, and sulphate ions. Aprotic dipolar solvents such as dimethyl formamide may also be included but are preferably absent. Typically the pH of the bath is between 1 and 7, for example 1.5 to 5.
The ferrocyanide may be any ferrocyanide which is soluble in the bath, for example an alkali metal or ammonium ferrocyanide, for example sodium or potassium ferrocyanide.
The ferrocyanide may conveniently be added to the bath as an aqueous solution. The concentration of the ferrocyanide solution is not critical, and will normally be chosen according to the solubility of the particular ferrocyanide employed. For example using potassium ferro-cyanide we prefer to employ a solution containing about 20%
by weight ferrocyanide.
We have found that addition of ferrocyanide in amounts in excess of those required to eliminate the 4Q aforesaid faults, may cause a deterioration in the perfor-- . ' ' ~ .
.:
:
- ~08444~ ~
- mance of the bath. One way of avoiding this problem when the onset of any of the aforesaid faults is observed, is to add the ferrocyanide solution in small increments until the chromium deposit is satisfactory again. If a sufficient excess of ferrocyanide has accidentally been added to cause a significant deterioration, it is possible to remove the excess by adding a small amount of soluble cation such as copper, nickel, iron or zinc. In most plating shops this may conveniently be achieved by adding a small amount of nickel plating solution to the bath. The addition of metal ion should be made within 15 minutes preferably within l0 minutes of adding the ferrocyanide, in order to be fully effective, since on standing the excess ferrocyanide complexes with the chromium and is then difficult or impossible to precipitate with the added metal.
We believe that the aforesaid faults may be due to the accidental contamination of the bath by traces of metal cations, which are capable of codepositing with the chromium.
Our experiments have shown that fault A can be simulated by adding copper to the bath; similarly fault B appears to be associated with the presence of zinc, fault C with lead -and fault D with nickel or a mixture of nickel and iron.
It seems, surprisingly, that the ferrocyanide is capable of precipitating substantially all of the potentially harm-ful trace metals which are most commonly encountered in very low concentrations as contaminants in commercial practice, but without precipitating the chromium, which is a principal cationic constituent of the bath.
According to a preferred embodiment, therefore our invention provides a method of maintaining ~ trivalent chromium plating bath which exhibits plating defects associated with the codeposition with the chromium of trace metal contaminants, which method comprises analyzing the bath to determine the concentration of said trace metal contaminants in the bath and adding a water soluble ferro-cyanide in an amount sufficient to precipitate said contaminants.
Preferably the bath or any sample used for analysis should be filtered to remove any previously precipitated ~08444~
metal prior to the analysis.
The analysis of the bath may be carried out by any of the analytical techniques for quantitative determination of the trace metals which are well known in the art. Typically the bath may be analyzed by spectographic means, for example by spark ionization or atomic absorption. Alternatively polarographic means may be employed.
Usually it is only necessary to test for copper, zinc, iron and nickel, since these are the only metals which, in our experience, are likely to cause difficulties in practice. The invention is however applicable to the correction of plating faults due to the presence of other codepositable metals, including lead, cadmium, silver and gold, although significant contamination by such metals is unlikely to occur in practice.
The amount of ferrocyanide added is preferably substantially stoichiometric based on the trace metal contaminants present, or slightly less. Any substantial excess of ferrocyanide should be avoided. Addition of any effective quantity significantly less than the stoichiometric amount, while beneficial, may not entirely remove the plating fault. We have discovered that a good rule of thumb is to add 1 ml. of 20~ potassium ferrocyanide solution per litre of plating solution for every 50 ppm of trace metal contamination. In this way the bath can be relatively easily maintained in the face of at least the commonly encountered forms of contamination.
It is preferred to reduce any free halogen in the bath to halide prior to addition of the ferrocyanide, by addition of a reducing agent capable of converting halogen to halide, without adversely affecting the performance of the bath. One particularly suitable reducing agent for this purpose is ammonium formate, The proportion of formate is preferably sufficient to reduce all the free halogen in the solution. Typically 2 to 3 gms per litre of formate may ~e added, preferably as an aqueous solution.
The formate is preferably added with agitation, about 10 minutes prior to the ferrocyanide addition. Halogen is usually present in the bath immediately after plating.
, ' , .
Our invention further provides a rapid method for detecting the presence of harmful excesses of either the ferrocyanide or certain of the commoner metallic impurities, -so that appropriate remedial action can be taken without 5 delay. -According to one aspect of our invention there is provided a method of testing an aqueous solution such as a trivalent chromium plating bath which comprises contacting the solution with a water permeable medium, causing the solution to diffuse upwardly through the medium and contact-ing separate portions of the diffusing solution in the medium with a water soluble ferrocyanide salt and with a water soluble iron salt respectively.
Typically the contact between the diffusing solution and the two salts is ensured by impregnating separate parts of the medium with the two salts, the impregnated parts being disposed in such a way as to intercept separate por-tions of the diffusing solution. Preferably impregnated parts should be readily visible to an external observer so 2Q as to facilitate the detection of any colour changes.
The permeable medium is preferably a cellulosic material such as filter paper or chromatography paper.
However, any medium which is capable of causing aqueous solutions to diffuse upwardly therethrough, when its lower part is immersed, may in principle be employed. Preferably the medium is substantially colourless so as to permit observation of small colour changes.
According to a particular embodiment our invention provides a means for testing trivalent chromium plating baths comprising a water permeable medium, separate, exter-nally visible, parts of which are impregnated with a water soluble ferrocyanide salt and with an iron salt respectively.
Preferably the medium is a water permeable paper.
A particularly convenient form of test paper according to our invention comprises a strip of permeable paper such as filter paper, which can, for example, be rectangular or any similar convenient shape, a part at or near one end of which has been impregnated with the ferrocyanide and a part at or near the other end of which has been impregnated with . ~ .
, , :: - ~ . - .: .
: : . :
:
~08444~
the iron salt, preferably leaving an unimpregnated central part between the two impregnated parts. In use, such a paper mày be bent or folded about the unimpregnated part, so as to permit the latter to be contacted with the solution, leaving the two impregnated parts unimmersed. The solution diffused up each immersed arm of the paper, which separates out suspended solids, so enabling any colour change in either arm to be more readily detected.
Test papers according to the invention may conveniently be obtained by preparing rectangular strips of permeable paper and immersing the two ends of each strip respectively in solutions of the two salts, for sufficient ~-time to permit the two solutions to diffuse into separate, preferably non-overlapping parts of the paper. The paper may then be dried, for example in an oven.
The tests according to the invention may alternatively be performed using two separate test papers impregnated respectively with the two salts. If the medium is non-coherent or ~rittle in nature a suitable support means may be provided. For example, it is possible to perform the tests using a thin layer of silica gel supported on a plate, or in the case of po~dery or gelatinous media, to support the medium in a column (preferably of glass or similar transparent material).
The ferrocyanide salt is preferably an alkali metal or ammonium ferrocyanide for example tetra potassium ferrocyanide. The iron salt may be a ferric or preferably a ferrous salt, preferably of a mineral acid, for example a chloride, nitrate or sulphate.
3Q If a blue stain forms on contact between the solution being tested and the ferrocyanide, then the solution contains an excess of the metallic impurities, whereas a blue stain forming on contact bet~een the solution and the iron salt indicates an excess of ferrocyanide. Preferably an aliquot of trivalent chromium plating solution is taken and ferro-cyanide is added, stepwise, thereto. The solution is checked after each addition ~ith the test paper. The end point, in mls. ferrocyanide per litre of plating solution represents a maximum. In practice, preferably about 50%
~ ' 108444~ :
of this amount of ferrocyanide is added to the bath, followed by a further addition of e.g. 25%, if required.
The invention will be illustrated by the following Examples:
Example 1 A trivalent chromium plating solution which had been working satisfactorily developed a plating fault, giving dark smudges in the 100-200 ASF region. A sample of the solution was put into a 300 ml Hull Cell with circulatory cooling and a 10 amp 3 minute panel run. This panel showed black streaks between 100-200 ASF and from previous experience was diagnosed as being due to nickel and possibly iron contamination of the solution. It was established that some nickel plated components had been lost from plating jigs and had been dissolving in the electrolyte for some time. The electrolyte was analyzed spectroscopically for trace metals as follows:
Nickel 134 Copper 13 Iron 193 Zinc 26 Total Metals 366 A 20% w/v solution of potassium ferrocyanide (K4Fe(CN16.3H2O~ was prepared and 1 ml of this solution added per 50 ppm total metals perliter i.e. 7 ml per litre were actually added. The mixture was allowed to stand for 30 minutes and then used for plating components.
The black streaks were completely absent and normal plating performance was regained.
3Q Subsequent analysis of the electrolyte gave the following result:
~E~ % removal Nickel 20 85 Iron 98* (4 Copper 4 69 Zinc 8 69 *this figure will include a contribution from any excess reagent.
' ' : ~ ' . :--, :
,. - ~ , :~ . .. .: . :
.. . . ~
, , ': : , . , - los444l :'~` 9 Example 2 A similar electrolyte contaminated with iron, nickel, copper and zinc gave plating faults. In this case no trace metal analysis was available. Halogen was reduced by addition to the bath of 5 ml/litre of 55% w/w ammonium formate solution. The bath was agitated for 10 minutes, and then 20% potassium ferrocyanide was added in a step-wise fashion, beginning with 1 ml per litre of electrolyte and increasing the addition in 1 ml per litre steps, allowing 30 minutes reaction time between additions. Some improvement was noted after the addition of 3 ml per litre and fully satisfactory performance was achieved at 5 ml per litre. The precipitate of insoluble metal salts was allowed to remain in the bath and did not interfere with plating in any way, but the solution was filtered at the next shutdown to remove the precipitated metals.
Example 3 Test papers were each prepared by dipping one end of a rectangular strip of filter paper in 20% w/v solution of tetra potassium ferrocyanide and the other end is a 20% w/v solution of ferrous chloride. The solutions were each allowed to diffuse part way towards the centre of the strip, ~hich was then dried in an oven.
Example 4 A trivalent chromium plating solution, after working satisfactorily for several weeks, developed a fault which comprised the formation of dark smudges at current densities of between 100 and 200 amps per square foot. A test paper prepared according to Example 3 was folded across the unimpregnated central portion, which was dipped in the bath. The electrolyte diffused towards both ends of the paper and produced a blue stain near the ferrocyanide impregnated end, indicating the presence of metallic impurities.
35~ w/v aqueous solution of tetra potassium ferr~cyanide was added in 4 ml increments, allowing 30 minutes after each addition and then repeating the test. After the second addition, a blue stain was observed at the iron impregnated "
, . . . .
,--~ 10 end of the paper. 2 ml of 20% w/v ferrous chloride solution was added whereafter no stain was observed. Commercial plating was resumed and the bath functioned satisfactorily.
;, : . ~ .
'': '' 'i '"' ' ' . . :
Claims (6)
1. A method for the maintenance of an aqueous trivalent chromium electroplating bath which has begun to exhibit a plating fault which is selected from the group consisting of a white haze at least at high current densities, a white band at the lower limit of the plating range, a white deposit at current densities of around 50 amps per square foot and brown or black smudges at current densities between about 100 and 200 amps per square foot, which consists in adding thereto an amount of a water soluble ferrocyanide sufficient substantially to reduce said plating fault.
2. A method according to claim 1 wherein said water soluble ferrocyanide is selected from the group consisting of sodium, potassium and ammonium ferrocyanide.
3. A method according to claim 1 or 2 wherein any free halogen present in the bath is reduced to halide prior to the addition of the ferrocyanide
4. A method for the maintenance of an aqueous trivalent chromium electroplating bath which comprises determining the proportion of trace metal contaminants therein precipitable by ferocyanide and adding thereto sufficient of a water soluble ferrocyanide to precipitate said trace metals.
5. A method according to claim 4 wherein an excess of said ferrocyanide is added to said bath and said excess is subsequently removed by adding thereto sufficient of a trace metal to precipitate said excess.
6. A method according to claim 4 or 5 wherein any free halogen present in the bath is reduced to halide prior to the addition of the ferrocyanide.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000344047A CA1117405A (en) | 1975-07-03 | 1980-01-21 | Testing chromium electroplating baths |
| CA344,048A CA1127056A (en) | 1975-07-03 | 1980-01-21 | Means for testing chromium electroplating baths |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB28055/75A GB1558169A (en) | 1975-07-03 | 1975-07-03 | Chromium electroplating |
| GB28055/75 | 1975-07-03 | ||
| GB5180175 | 1975-12-18 | ||
| GB51801/75 | 1975-12-18 | ||
| KR7603197A KR800001242B1 (en) | 1975-12-18 | 1976-12-28 | Chromium electroplating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084441A true CA1084441A (en) | 1980-08-26 |
Family
ID=27258682
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA256,190A Expired CA1084441A (en) | 1975-07-03 | 1976-07-02 | Chromium electroplating |
Country Status (7)
| Country | Link |
|---|---|
| AU (1) | AU497515B2 (en) |
| BR (1) | BR7604381A (en) |
| CA (1) | CA1084441A (en) |
| DE (1) | DE2629879C3 (en) |
| ES (1) | ES449498A1 (en) |
| FR (1) | FR2319721A1 (en) |
| NL (1) | NL183660C (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2034354B (en) * | 1978-11-11 | 1982-12-01 | Ibm | Elimination of anode hydrogen cyanide formation in trivalent chromium plating |
| FR2529581A1 (en) * | 1982-06-30 | 1984-01-06 | Armines | ELECTROLYSIS BATH BASED ON TRIVALENT CHROME |
| US4432843A (en) * | 1982-07-29 | 1984-02-21 | Omi International Corporation | Trivalent chromium electroplating baths and processes using thiazole addition agents |
| WO2001096632A2 (en) * | 2000-06-15 | 2001-12-20 | Applied Materials, Inc. | A method and apparatus for conditioning electrochemical baths in plating technology |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE608806C (en) | 1932-04-01 | 1935-02-01 | Siemens & Halske Akt Ges | Process for eliminating the iron that accumulates in the chromium electrolyte |
-
1976
- 1976-07-02 CA CA256,190A patent/CA1084441A/en not_active Expired
- 1976-07-02 FR FR7620391A patent/FR2319721A1/en active Granted
- 1976-07-02 ES ES449498A patent/ES449498A1/en not_active Expired
- 1976-07-02 DE DE2629879A patent/DE2629879C3/en not_active Expired
- 1976-07-02 NL NLAANVRAGE7607319,A patent/NL183660C/en not_active IP Right Cessation
- 1976-07-05 AU AU15605/76A patent/AU497515B2/en not_active Expired
- 1976-07-05 BR BR7604381A patent/BR7604381A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU497515B2 (en) | 1978-12-14 |
| NL7607319A (en) | 1977-01-05 |
| DE2629879B2 (en) | 1979-12-13 |
| NL183660C (en) | 1988-12-16 |
| FR2319721B1 (en) | 1979-07-20 |
| AU1560576A (en) | 1978-01-12 |
| ES449498A1 (en) | 1977-11-16 |
| BR7604381A (en) | 1977-07-26 |
| NL183660B (en) | 1988-07-18 |
| FR2319721A1 (en) | 1977-02-25 |
| DE2629879A1 (en) | 1977-01-20 |
| DE2629879C3 (en) | 1980-08-14 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR810000219B1 (en) | Method of regenerating a chromium electroplating bath | |
| Molina-Holgado et al. | Voltammetric determination of lead with a chemically modified carbon paste electrode with diphenylthiocarbazone | |
| US4038160A (en) | Method of regenerating a chromium electroplating bath | |
| CA1084441A (en) | Chromium electroplating | |
| Pecsok et al. | Polarographic Characteristics of Vanadium Complexed with Ethylenediamine Tetraacetic Acid | |
| Dong et al. | A nafion/crown ether film electrode and its application in the anodic stripping voltammetric determination of traces of silver | |
| Kalcher | Voltammetry of hexacyanoferrates using a chemically modified carbon-paste electrode | |
| CA1117405A (en) | Testing chromium electroplating baths | |
| CA1127056A (en) | Means for testing chromium electroplating baths | |
| Hynek et al. | Spectrophotometric Determination of Aluminum in Ferrous and Nonferrous Alloys | |
| US4166719A (en) | Testing of aqueous solutions | |
| Ohzeki et al. | Enrichment and spectrophotometric determination of a trace amount of chromium (VI) as the diphenylcarbazide complex on a mixed resin prepared from finely divided anion and cation exchangers. | |
| JPH0410588B2 (en) | ||
| Ciszewski | Determination of thallium in bismuth by differential pulse anodic-stripping voltammetry without preliminary separation | |
| CN113358586A (en) | Novel method for measuring content of trace chloride ions in copper sulfate solution | |
| Jovanović et al. | Determination of low levels of cyanide with a silver/silver sulphide wire electrode | |
| JPS6024200B2 (en) | How to improve and maintain trivalent chrome plating solution | |
| Zanello et al. | Electrooxidation of chromium (III) in alkaline hydroxide solution at a platinum electrode | |
| GB1558760A (en) | Chromium electroplating | |
| Cox et al. | Voltammetric ion-selective electrode for chromium (VI) | |
| Liberti et al. | Aluminium (III)-iminodiacetic acid complexes in 0· M sodium perchlorate medium | |
| SU918339A1 (en) | Solution for compacting oxide coatings | |
| Jyo et al. | Response of a copper (II) ion-selective electrode in cupric buffers based on macrocyclic polyamines. | |
| Yamada et al. | Determination of trace mercury in the environmental water containing iodide by using cold-vapor atomic absorption spectrometry | |
| Napoli | Palladium complexes with triethylenetetraminehexa-acetic acid |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |