CA1121300A - Chromium electroplating - Google Patents
Chromium electroplatingInfo
- Publication number
- CA1121300A CA1121300A CA000267540A CA267540A CA1121300A CA 1121300 A CA1121300 A CA 1121300A CA 000267540 A CA000267540 A CA 000267540A CA 267540 A CA267540 A CA 267540A CA 1121300 A CA1121300 A CA 1121300A
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- Prior art keywords
- molar
- composition according
- bath
- iron
- salt
- 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.)
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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
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D23/00—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor
- E21D23/0004—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor along the working face
- E21D23/0034—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor along the working face comprising a goaf shield articulated to a base member
- E21D23/0039—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor along the working face comprising a goaf shield articulated to a base member and supported by a strut or by a row of struts parallel to the working face
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D23/00—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor
- E21D23/03—Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor having protective means, e.g. shields, for preventing or impeding entry of loose material into the working space or support
Abstract
CHROMIUM ELECTROPLATING
Abstract A tendency for grey discolouration at high current density in trivalent chromium plating solutions may be reduced by maintaining therein from 30 to 150 parts per million of iron or nickel.
Abstract A tendency for grey discolouration at high current density in trivalent chromium plating solutions may be reduced by maintaining therein from 30 to 150 parts per million of iron or nickel.
Description
l~Z~L300 The present invention relates to chromium electro-plating. In particular it relates to electroplating from aqueous trivalent chromium plating baths.
The potential value of solutions containing trivalent chromium as electrolytes for chromium plating has been recognized for many years. However, practical difficulties have, until recently, prevented the commercial introduction of any decorative chromium electroplating system based on trivalent chromium. All commercial decorative chromium plating has been based on hexavalent chromium, which has some very serious drawbacks. Recently, howeverS certain significant advances have been made in respect of triva-lent chromium plating compositions, in particular a com-position described and claimed in our U.S. Patent Number 3,954,574 which has had substantial commercial success.
In practice, the decorative appearance of deposits obtained from trivalent chromium plating baths may some-times be marred by certain faults such as streakiness, haze or bands at certain current densities. In ~elgian Patent Number 843,718, there are described certain faults which it has been discovered are due to the presence in the electrolyte of traces of metals such as iron, copper, zinc and nickel~ We have now found that even when these metals are substantially eliminated from the electrolyte, a slight greyish discolouration of the deposits at high current densities is observed. Surprisingly we have now discovered that an improved deposit may be obtained when the solution contains very small traces of certain metals, within a particular range of concentration.
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Our invention provides a trivalent chromium electroplating bath comprising from 30 to 15~ ppm of metals selected from iron and nickel. The trivalent chromium plating bath is preferably a bath containing at least one water soluble complex of tri-valent chromium capable of electrodepositing chromium metal.
Particularly preferred are complexes comprising carboxylates and halides. Such complexes may be preformed or formed in situ in the bath. Particularly preferred are baths con-taining a trivalent chromium salt, a formate, a bromide, and ammonium, substantially as described in the specification of our aforesaid U.S. Patent.
Alternatively and less preferably the baths may be of the type containing a preformed complex of trivalent chromium, with glycollic acid or oxalic acid and a halide such as bromide, fluoride or preferably chloride substantially as described in the specification of USP 3,706,639, USP 3,706,640, USP 3,706,641 and USP 3,729,392 or a bath of the same type additionally con-taining ammonium. Preferably baths according to our invention contain a borate, such as sodium borate or boric acid, chloride 20 and/or sulphate, and alkali metal such as sodium or potassium.
Customarily a wetting agent is also included. Baths according to our invention are preferably substantially free from hexa-valent chromium. Typically they have a pH of between 1 and ~.
Where solutions according to our aforesaid U.S. Patent are 25 employed, the solution may contain bromide, formate ~or acetate) and any borate ion which may be present, as the sole anion species, but such solutlons are undesirably expensive. Preferably, there-fore, the solution contains only sufficient bromide to prevent substantial formation of hexavalent chromium, sufficient formate ~ to be effective !, ~,, ' ' , 3(~
in complexing the chromium and sufficient borate to be effective as a buffer, the remainder of the anions required to balance the cation content of the solution comprising cheaper species such as chloride and/or sulphate.
For example the solution optionally and preferably contain~ halide ions in addition to bromide, such as fluoride, or preferably, chloride. The total amount of halide including the bromide and any iodide which may be present as well as any fluoride, and/or chloride may optionally be sufficient, together with the formate and any borate to provide essentially the total anion content of the solution. The latter is determined by the number of equiva-lents of cation (including hydrogen ion) and is typically from 4 to 6 molar. Alternatively, and preferably, there may additionally be present some sulphate ion. In one embodiment, the sulphate is present in a minor proportion based on the halide, e.g. a minor proportion based on the chloride and/or fluoride. Alternatively the sulphate may comprise a major proportion of the inorganic ion and, less preferably, may be present in place of chloride and fluoride. Preferably the solution also contains alkali metal ions, usually provided as the cations of the conductivity salts, and/or of some or all of the salts used to introduce the anion species, which alkali metals are preferably sodium or potassium. The solution may also contain alkaline earth metals such as calcium or magnesium.
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The solutions of our invention may additionally contain minor, compatible amounts of additives, such as wetting agents (e.g. alkali metal alkyl benzene sulphonates) or antifoams which are commonly used in plating technology.
Our novel solutions may therefore comprise some of the ollowing species.
A.Trivalent Chromium This is an essential ingredient of all the solutions of the invention. Proportions of less than 0.1 molar or more than 1.2 molar trivalent chromium result in significant loss of covering power, and the concentration is preferably maintained within these limits, most preferably between 0.2 and 0.6 molar. Preferably the solution is substantially free from hexavalent chromium and preferably the chromium in the solution is substantially all present as trivalent chromium before plating.
B. Bromide -This is a strongly preferred ingredient. The concen-tration of bromide should preferably be maintained above 0.01 molar, to avoid formation of hexavalent chromium, and lowering of the plating rate. The maximum concentration is not critical, but is typically less than 4 molar and preferably less than 1 molar. Economic and effective operation normally requires a concentration of bromide between 0.05 and 0.5. The preferred range is from 0.05 and 0.3 molar. Best results are obtained when the concentration of bromide is greater than 0.1 molar. Iodide functions in .c a similar fashion to bromide, but suffers from the dis-~ ,s, ~
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advantage that free iodine, which would be formed during plating is only soluble to the extent of 0.03% w/w in water compared with 4~ for bromine. Consequently attempts to use iodide in place of bromide lead to unacceptable precipitation of iodine. Iodide, is, moreover, too expensive to use economically in place of bromide. However, it is possible in principle, to replace a minor part of the bromide with iodide, and references herein to bromide do not exclude bromide containing traces of iodide.
10 C. Carboxylates This is a strongly preferred ingredient, formate being most strongly preferred. Typically the proportion of formate to chromium should not exceed 3 : 1 on a molar basis, to avoid unacceptably severe precipitation of the corresponding chromium salt. If the proportion is less than 0.5 : 1 the covering power is undesirably reduced. Preferably the pro-portion of formate to chromium is between 2 : 1 and 1 : 1.
Acetate functions similarly to formate but gives a very much lower plating speed. Acetate alone is not as effective as formate in preventing ~he accumulation of free halogen. It is possible, however, to use acetate as a partial replace-ment for formate up to about a third of the total weight of carboxylic acid without serious adverse effect. Solutions containing acetate as moxe than a third of the total car-boxylic acid are unlikely to be commercially competitivewith solutions based on formate alone, although they are superior to prior art electrolytes. Other less preferred carboxylates include glycollic acid, oxalic acid and also less preferably other mono, di, poly, hydroxy and aldehyde . .
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6a carboxylic acids which are soluble in water and have not more than 10 carbon atoms. Examples include citric, tartaric, glyoxalic, maleic, succinic and malonic acids.
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D. Inorganic ~nionic Complexants It is possible though less prefer~ed to replace at least part o~ the carboxylate complexant by an inorganic anionic complexant for chromium such as hypophosphite.
5 E. Ammonia !~ The pressence of ammoniumlis strongly preferred for our invention. Generally if the concentration of ammonium is less than 0.1 molar, there is a risk of forming hexavalent chromium. The upper limit is not critical and ammonium may 10 be present in amounts of up to saturation, i.e. about 4 molar.
Preferably the ammonium is present in a concentration of at least 0.2 molar, most preferably from 1 to 3 molar. These higher concentrations are desirable because deposits tend to be darker at ammonia concentrations near the minimum and also 15 because the presence of ammonium helps to reduce consumption of formate. Both ammonium and formate contribute to pre-venting the buildup of free bromine, but at higher ammonium concentration, the proportion of ammonium oxidised in this reaction is greater, with consequent economies with the 20 more expensive formate. It is also possible, though not pre-ferred, within the scope of this invention to include some substi'tuted ammonium compounds such as hydroxylamine, hydra-zonium or alkyl ammonium components in the compositions.
i~ s However, in the absence of ammonium itae~ they do not 25 normally provide ade~uate covering power. Preferably aryl-ammonium or heterocyclic ions such as pyridinium are abs~nt sence they tend to inhibit deposition of chromium.
~130~) F. Borate Although it is possible to plate chromium from solutions of our invention which do not contain borate, we have not been able to obtain what we consider fully satisfactory results, commercially, in the absence of borate. Concentrations below 0.1 molar result in undesira-bly low covering power. The upper limit is not critical and is determined only by the solubility of borate in the system, but generally we prefer to employ from O.S t~ 1 molar borate. The functionof the borate is obscure. Its beneficial effects may be in part due to its buffering action. However, other buffer salts, such as phosphates and citrates appear relatively ineffective.
11 G. _ nductivity Salts These are optional but generally preferred. The con-centration is not critical and may vary between zero and about 6 molar according to solubility. Preferably they are present in proportions between 0.5 and 5 molar, e.g. 1 to 4 molar. Conductivity salts is a term used in the plating art to d.~note certain readily ionisable salts which may be added to plating baths to increase their electrical con-ductivity and so reduce the amount of power dissipated in the bath. Typically they are alkali metal or alkaline earth metal salts of strong acids which are soluble in the solution. They should have a dissociation constant at least equal to 10 . Typical examples are the chlorides and sul-phates of sodium and potassium.
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H. Hydrogen Ion .
Best results are obtained when the bath is somewhat acidic. At low pH values (below 2) there is some loss of covering power which becomes unacceptable below pH 1. If the pH is above 4 the rate of plating tends to be undesira-bly slow. Optimu~ pH is between 2 and 3.5.
I. Chloride and/or Fluoride This is optional, but at least in the case of chloride, preferred. The amount is not, however, crticial. It may vary from zero up to the ma~imum permitted by solubility considerations. Chloride is generally introduced into the bath as the anion of the conductivity salt (e.g. sodium chloride), as ammonium chloride, which is a convenient means of introducing the ammonia requirement of the bath, as chromic chloride which may optionally be used to supply at least part of the chromium requirement, and/or as hydro-chloric acid, which is a convenient means of adjusting the pH of the bath. Preferably the chloride content is at least - 1 molar e.g. 1.5 to 5 molar. A particularly convenient range is 2 to 3.5 molar.
J. Sulphate This is an optional but preferred ingredient. The amount of sulphate is not critical and may, like that of the chloride, vary between zero and maximum amount which is compatible with the solution. In one type of bath the amount of sulphate is less than the total chloride. In a different type of bath, however, the proportion of sulphate is greater than the proportion of halide, and may be the predominant anion in the bath. Like .
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the chloride, the sulphate may be introduced into the bath as the anion of the conductivity sal-t, or of the ammonium or chromium salts or as sulphuric acid. Particularly preferred is the use of sulphate as the source of chromium in the form of chrome tanning liquors which are a basic chromi~n sulphate and which, being a commercial by~product are a particularly con-venient and cheap source of trivalent chromium. Typical sul-phate concentratlons may be between 0 and 5 molar preferably 0.5 to 4, e.g. 0.6 to 3, most preferably 0.6 to 1.2 molar.
Preferably the combined chloride and sulphate concentrations are at least 1 molar, e.g. at least 2 molar most preferably from 2.5 to 4 molar.
K. Co-depositable Metals These are an essential inyredient of the bath in the case 15 of iron and nickel. The latter are present in the bath in a concentration of from 30 to 150 ppm t:otal. They are normally introduced as their soluble chlorides or sulphates. Other co-depositable metals such as copper, zinc and lead are preferably pr~sent in proportions of less than 20 ppm each and more pre-20 ferably less than 30 ppm total.
L Non Co-depositable Metals These are optionally but preferably present. In partic-ular it is preferred to include alkali metals and especially sodium and/or potassium in the bath in a proportion of at least ~5 0.5 molar up to 4 or 5 molar according to solubility. The presence of sodium and/or pctassium helps the conductivity of the solution and also improves the throwing power. Typically the sodium and/or potassium are added in a proportion of about
The potential value of solutions containing trivalent chromium as electrolytes for chromium plating has been recognized for many years. However, practical difficulties have, until recently, prevented the commercial introduction of any decorative chromium electroplating system based on trivalent chromium. All commercial decorative chromium plating has been based on hexavalent chromium, which has some very serious drawbacks. Recently, howeverS certain significant advances have been made in respect of triva-lent chromium plating compositions, in particular a com-position described and claimed in our U.S. Patent Number 3,954,574 which has had substantial commercial success.
In practice, the decorative appearance of deposits obtained from trivalent chromium plating baths may some-times be marred by certain faults such as streakiness, haze or bands at certain current densities. In ~elgian Patent Number 843,718, there are described certain faults which it has been discovered are due to the presence in the electrolyte of traces of metals such as iron, copper, zinc and nickel~ We have now found that even when these metals are substantially eliminated from the electrolyte, a slight greyish discolouration of the deposits at high current densities is observed. Surprisingly we have now discovered that an improved deposit may be obtained when the solution contains very small traces of certain metals, within a particular range of concentration.
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Our invention provides a trivalent chromium electroplating bath comprising from 30 to 15~ ppm of metals selected from iron and nickel. The trivalent chromium plating bath is preferably a bath containing at least one water soluble complex of tri-valent chromium capable of electrodepositing chromium metal.
Particularly preferred are complexes comprising carboxylates and halides. Such complexes may be preformed or formed in situ in the bath. Particularly preferred are baths con-taining a trivalent chromium salt, a formate, a bromide, and ammonium, substantially as described in the specification of our aforesaid U.S. Patent.
Alternatively and less preferably the baths may be of the type containing a preformed complex of trivalent chromium, with glycollic acid or oxalic acid and a halide such as bromide, fluoride or preferably chloride substantially as described in the specification of USP 3,706,639, USP 3,706,640, USP 3,706,641 and USP 3,729,392 or a bath of the same type additionally con-taining ammonium. Preferably baths according to our invention contain a borate, such as sodium borate or boric acid, chloride 20 and/or sulphate, and alkali metal such as sodium or potassium.
Customarily a wetting agent is also included. Baths according to our invention are preferably substantially free from hexa-valent chromium. Typically they have a pH of between 1 and ~.
Where solutions according to our aforesaid U.S. Patent are 25 employed, the solution may contain bromide, formate ~or acetate) and any borate ion which may be present, as the sole anion species, but such solutlons are undesirably expensive. Preferably, there-fore, the solution contains only sufficient bromide to prevent substantial formation of hexavalent chromium, sufficient formate ~ to be effective !, ~,, ' ' , 3(~
in complexing the chromium and sufficient borate to be effective as a buffer, the remainder of the anions required to balance the cation content of the solution comprising cheaper species such as chloride and/or sulphate.
For example the solution optionally and preferably contain~ halide ions in addition to bromide, such as fluoride, or preferably, chloride. The total amount of halide including the bromide and any iodide which may be present as well as any fluoride, and/or chloride may optionally be sufficient, together with the formate and any borate to provide essentially the total anion content of the solution. The latter is determined by the number of equiva-lents of cation (including hydrogen ion) and is typically from 4 to 6 molar. Alternatively, and preferably, there may additionally be present some sulphate ion. In one embodiment, the sulphate is present in a minor proportion based on the halide, e.g. a minor proportion based on the chloride and/or fluoride. Alternatively the sulphate may comprise a major proportion of the inorganic ion and, less preferably, may be present in place of chloride and fluoride. Preferably the solution also contains alkali metal ions, usually provided as the cations of the conductivity salts, and/or of some or all of the salts used to introduce the anion species, which alkali metals are preferably sodium or potassium. The solution may also contain alkaline earth metals such as calcium or magnesium.
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The solutions of our invention may additionally contain minor, compatible amounts of additives, such as wetting agents (e.g. alkali metal alkyl benzene sulphonates) or antifoams which are commonly used in plating technology.
Our novel solutions may therefore comprise some of the ollowing species.
A.Trivalent Chromium This is an essential ingredient of all the solutions of the invention. Proportions of less than 0.1 molar or more than 1.2 molar trivalent chromium result in significant loss of covering power, and the concentration is preferably maintained within these limits, most preferably between 0.2 and 0.6 molar. Preferably the solution is substantially free from hexavalent chromium and preferably the chromium in the solution is substantially all present as trivalent chromium before plating.
B. Bromide -This is a strongly preferred ingredient. The concen-tration of bromide should preferably be maintained above 0.01 molar, to avoid formation of hexavalent chromium, and lowering of the plating rate. The maximum concentration is not critical, but is typically less than 4 molar and preferably less than 1 molar. Economic and effective operation normally requires a concentration of bromide between 0.05 and 0.5. The preferred range is from 0.05 and 0.3 molar. Best results are obtained when the concentration of bromide is greater than 0.1 molar. Iodide functions in .c a similar fashion to bromide, but suffers from the dis-~ ,s, ~
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advantage that free iodine, which would be formed during plating is only soluble to the extent of 0.03% w/w in water compared with 4~ for bromine. Consequently attempts to use iodide in place of bromide lead to unacceptable precipitation of iodine. Iodide, is, moreover, too expensive to use economically in place of bromide. However, it is possible in principle, to replace a minor part of the bromide with iodide, and references herein to bromide do not exclude bromide containing traces of iodide.
10 C. Carboxylates This is a strongly preferred ingredient, formate being most strongly preferred. Typically the proportion of formate to chromium should not exceed 3 : 1 on a molar basis, to avoid unacceptably severe precipitation of the corresponding chromium salt. If the proportion is less than 0.5 : 1 the covering power is undesirably reduced. Preferably the pro-portion of formate to chromium is between 2 : 1 and 1 : 1.
Acetate functions similarly to formate but gives a very much lower plating speed. Acetate alone is not as effective as formate in preventing ~he accumulation of free halogen. It is possible, however, to use acetate as a partial replace-ment for formate up to about a third of the total weight of carboxylic acid without serious adverse effect. Solutions containing acetate as moxe than a third of the total car-boxylic acid are unlikely to be commercially competitivewith solutions based on formate alone, although they are superior to prior art electrolytes. Other less preferred carboxylates include glycollic acid, oxalic acid and also less preferably other mono, di, poly, hydroxy and aldehyde . .
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6a carboxylic acids which are soluble in water and have not more than 10 carbon atoms. Examples include citric, tartaric, glyoxalic, maleic, succinic and malonic acids.
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D. Inorganic ~nionic Complexants It is possible though less prefer~ed to replace at least part o~ the carboxylate complexant by an inorganic anionic complexant for chromium such as hypophosphite.
5 E. Ammonia !~ The pressence of ammoniumlis strongly preferred for our invention. Generally if the concentration of ammonium is less than 0.1 molar, there is a risk of forming hexavalent chromium. The upper limit is not critical and ammonium may 10 be present in amounts of up to saturation, i.e. about 4 molar.
Preferably the ammonium is present in a concentration of at least 0.2 molar, most preferably from 1 to 3 molar. These higher concentrations are desirable because deposits tend to be darker at ammonia concentrations near the minimum and also 15 because the presence of ammonium helps to reduce consumption of formate. Both ammonium and formate contribute to pre-venting the buildup of free bromine, but at higher ammonium concentration, the proportion of ammonium oxidised in this reaction is greater, with consequent economies with the 20 more expensive formate. It is also possible, though not pre-ferred, within the scope of this invention to include some substi'tuted ammonium compounds such as hydroxylamine, hydra-zonium or alkyl ammonium components in the compositions.
i~ s However, in the absence of ammonium itae~ they do not 25 normally provide ade~uate covering power. Preferably aryl-ammonium or heterocyclic ions such as pyridinium are abs~nt sence they tend to inhibit deposition of chromium.
~130~) F. Borate Although it is possible to plate chromium from solutions of our invention which do not contain borate, we have not been able to obtain what we consider fully satisfactory results, commercially, in the absence of borate. Concentrations below 0.1 molar result in undesira-bly low covering power. The upper limit is not critical and is determined only by the solubility of borate in the system, but generally we prefer to employ from O.S t~ 1 molar borate. The functionof the borate is obscure. Its beneficial effects may be in part due to its buffering action. However, other buffer salts, such as phosphates and citrates appear relatively ineffective.
11 G. _ nductivity Salts These are optional but generally preferred. The con-centration is not critical and may vary between zero and about 6 molar according to solubility. Preferably they are present in proportions between 0.5 and 5 molar, e.g. 1 to 4 molar. Conductivity salts is a term used in the plating art to d.~note certain readily ionisable salts which may be added to plating baths to increase their electrical con-ductivity and so reduce the amount of power dissipated in the bath. Typically they are alkali metal or alkaline earth metal salts of strong acids which are soluble in the solution. They should have a dissociation constant at least equal to 10 . Typical examples are the chlorides and sul-phates of sodium and potassium.
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H. Hydrogen Ion .
Best results are obtained when the bath is somewhat acidic. At low pH values (below 2) there is some loss of covering power which becomes unacceptable below pH 1. If the pH is above 4 the rate of plating tends to be undesira-bly slow. Optimu~ pH is between 2 and 3.5.
I. Chloride and/or Fluoride This is optional, but at least in the case of chloride, preferred. The amount is not, however, crticial. It may vary from zero up to the ma~imum permitted by solubility considerations. Chloride is generally introduced into the bath as the anion of the conductivity salt (e.g. sodium chloride), as ammonium chloride, which is a convenient means of introducing the ammonia requirement of the bath, as chromic chloride which may optionally be used to supply at least part of the chromium requirement, and/or as hydro-chloric acid, which is a convenient means of adjusting the pH of the bath. Preferably the chloride content is at least - 1 molar e.g. 1.5 to 5 molar. A particularly convenient range is 2 to 3.5 molar.
J. Sulphate This is an optional but preferred ingredient. The amount of sulphate is not critical and may, like that of the chloride, vary between zero and maximum amount which is compatible with the solution. In one type of bath the amount of sulphate is less than the total chloride. In a different type of bath, however, the proportion of sulphate is greater than the proportion of halide, and may be the predominant anion in the bath. Like .
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the chloride, the sulphate may be introduced into the bath as the anion of the conductivity sal-t, or of the ammonium or chromium salts or as sulphuric acid. Particularly preferred is the use of sulphate as the source of chromium in the form of chrome tanning liquors which are a basic chromi~n sulphate and which, being a commercial by~product are a particularly con-venient and cheap source of trivalent chromium. Typical sul-phate concentratlons may be between 0 and 5 molar preferably 0.5 to 4, e.g. 0.6 to 3, most preferably 0.6 to 1.2 molar.
Preferably the combined chloride and sulphate concentrations are at least 1 molar, e.g. at least 2 molar most preferably from 2.5 to 4 molar.
K. Co-depositable Metals These are an essential inyredient of the bath in the case 15 of iron and nickel. The latter are present in the bath in a concentration of from 30 to 150 ppm t:otal. They are normally introduced as their soluble chlorides or sulphates. Other co-depositable metals such as copper, zinc and lead are preferably pr~sent in proportions of less than 20 ppm each and more pre-20 ferably less than 30 ppm total.
L Non Co-depositable Metals These are optionally but preferably present. In partic-ular it is preferred to include alkali metals and especially sodium and/or potassium in the bath in a proportion of at least ~5 0.5 molar up to 4 or 5 molar according to solubility. The presence of sodium and/or pctassium helps the conductivity of the solution and also improves the throwing power. Typically the sodium and/or potassium are added in a proportion of about
2 molar initially, but tend to accumulate during use so that 30 the concentration may rise to saturation value. Other alkali - lOa -metals such as lithium, ..1.
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--ll--alkaline earth metals such as calcium or magnesium or other metal ions which will not plate out of the solution with the chromium may also be present. The amount of such metals may vary within very wide limits provided that they do not precipitate in the presence of the other components.
They are generally present incidentally, as the cation species of the conductivity salt, or of the borate, formate and/or bromide salts which may be used to provide those anions species in the solution.
10 M. Surface ~ctive ~gents . .
These are optionally but preferably present in effective and compatible amounts. Wetting agents and antifoams are used throughout plating technology and many suitable examples are well known to those skilled in the art. Any of the wetting agents commonly used in hexavalent chromium plating may be used in the present invention. However, since the solutions of the present invention are much less strongly oxidising than hexavalent chromium solutions it is possible, and preferred to use the cheaper wetting aqents commonlv employed in t~e less agqressive tYpes of plating solution. The principal restriction on the effectiveness of the wetting agents arises from the ~resence of the free bromine in the solution. Surfactants which are liable to bromination are therefore not recommended e.g. most non-ionic surfactants. The surfactants used according to ourinvention are typically cationic such as those described in B.P. 1 3~8,749 or preferably anionic e.g. sulphosuccinates, alkyl benzene sul~honates having from 8 to 20 aliphatic carbon atoms, such as sodium dodecYl benzene sulPhonate, ,.~' ~ , .
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' lla alkyl sulphates having from 8 to 20 carbon atoms such as sodium lauryl sulphate and alkyl ether sulphates such as sodium lauryl polyethoxy sulphates. If the solution has undesirable oaming tendencies l~Z~L3~)0 it is also possible, optionally, to include compatible anti-foams e.g. fatty alcohols such as ~ alcohol. The choice of surfactants for use in our solution is a routine matter easily within the ordinary competence o those skilled in the art. The amount of wetting ayent used is in accordance with normal practice, e.g. 0.1 to 10 parts per thousand.
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It is preferred that the solutions of our invention-s~ff~d-consist essentially of the foregoing species. However, we do not exclude the presence ~ minor amounts of other species which ara compatible with the solutions and which do not adversely affect the plating properties to a material extent. Generally it is preferred that nitrate ion be substantially absent, since it tends to inhibit deposition of chromium. Sulphite ion also is preferably absent, since it can cause hazy deposits in more than very small amounts. Other species, organic or inoryanic, which do not inhibit plating of the chromium or materially reduce covering power or create unacceptable problems of toxicity, may optionally be present. Whether any particular species can be tolerated in the solution may be routinely 20 determined by simple testing.
According to the present invention ~he baths are pre-ferably made up substantially as described in any of the afore-said specifications but including from 30 to 150 ppm of iron or nickel in the solution. Preferably the additional metal is 25 ferric iron. Conveniently a sufficient quantity of an appro-priate salt, e.g. ferric chloride, or preferably ferric sul-phate is added to the bath at any convenient stage in the preparation thereof. Alternatively the iron may be introduced in admixture with any of the other components of the bath. For 30 example, it is possible to select a source of one of the other ' ' Z~30~
bath components, such as chromic sulphate, which contains iron as an impurity, in sufficient quantity to provide the necessary concentration in the bath. Preferably, when replenishing the bath, iron or nickel is included in the replenishing additions in a quantity sufficient to maintain the concentration within the specified limits. Preferably the concentration is 40 to 100 ppm e.g. 50 ppm. If the concentration of iron or nickel should greatly exceed the specified limits, thus resulting in a plating fault, it may be reduced by addition to the bath of a hexacyano-ferrate salt, substantially as described in the specification of the aforesaid Belgian Patent, but ensuring that after treatment the concentration of the aforesaid metals is adjusted as necessary to bring it within the concentration limits characteristic of this invention.
The invention is illustrated by the following examples:-1. A chromium plating solution was prepared containing 20 gpl chromium, the chromium being supplied from commercial chromic sulphate, and 32 gpl formic acid, the other constituents being potassium chloride (75 gpl), boric acid ~50 gpl), ammonium bromide (10 gpl) and ammonium chloride (90 gpl) as described in our aforesaid U.S. Patent. After preparation and plating out at 0.5 amps per litre for 60 minutes a Hull Cell panel was run on the solution at 10 amps for 3 minutes. At current densities in excess of 400 ASF grey bands could be detected. Analysis of the solution for trace elements showed 15 ppm iron, 10 ppm nickel and 1 - 2 ppm of copper and zinc, these metals ~ ' ') OO
having arisen from traces present in the commercial grades used.
25ppm of iron was added as ferric chloride (FeC136H30) (i.e. 0.120 g per litre) and the solution re-run on the Hull Cell. The grey bands had disappeared and a clean non-banded panel was obtained. The inal analysis of the solution was 40 ppm iron, 10 ppm nickel, 5 ppm (Cu + Zn).
2. A working solution made up as above and used for pro-duction became contaminated with nickel and iron, leading to a plating fault. Analysis of the solution confirmed 110 ppm Fe, 150 ppm Ni, 25 ppm Zn, 5 ppm Cu. The solution was treated with tetrapotassium hexacyanoferrate (K4Fe(CN)6) at the rate of 1 ml/ litre of a 20~ w/v solution per 50 ppm metals i.e. 6 ml/l. After allowing time for the reaction to reach completion the precipitated metals were filtered off and the solution reanalysed. Results were 20 ppm Fe, 15 ppm Ni, showing virtually complete removal of metals.
A Hull Cell panel showed a trace of grey bands beginning to develop at high current densities and work plated in the electrolyte showed a faint greyish appearance at very high current density points. 25 ppm iron (as FeC136H20) was - added to the electrolyte, when the grey bands and the grey marks on work immediately disappeared. The concentration of (nickel + iron) was maintained in the concentration range 40 to 100 ppm thereafter by suitable additions of iron to the replenishing solutions.
..
~ .
, , ~ ' ' ' ' `
,
~,i ,,.~ .~., :
.
. -, 0~
--ll--alkaline earth metals such as calcium or magnesium or other metal ions which will not plate out of the solution with the chromium may also be present. The amount of such metals may vary within very wide limits provided that they do not precipitate in the presence of the other components.
They are generally present incidentally, as the cation species of the conductivity salt, or of the borate, formate and/or bromide salts which may be used to provide those anions species in the solution.
10 M. Surface ~ctive ~gents . .
These are optionally but preferably present in effective and compatible amounts. Wetting agents and antifoams are used throughout plating technology and many suitable examples are well known to those skilled in the art. Any of the wetting agents commonly used in hexavalent chromium plating may be used in the present invention. However, since the solutions of the present invention are much less strongly oxidising than hexavalent chromium solutions it is possible, and preferred to use the cheaper wetting aqents commonlv employed in t~e less agqressive tYpes of plating solution. The principal restriction on the effectiveness of the wetting agents arises from the ~resence of the free bromine in the solution. Surfactants which are liable to bromination are therefore not recommended e.g. most non-ionic surfactants. The surfactants used according to ourinvention are typically cationic such as those described in B.P. 1 3~8,749 or preferably anionic e.g. sulphosuccinates, alkyl benzene sul~honates having from 8 to 20 aliphatic carbon atoms, such as sodium dodecYl benzene sulPhonate, ,.~' ~ , .
, . ~
' lla alkyl sulphates having from 8 to 20 carbon atoms such as sodium lauryl sulphate and alkyl ether sulphates such as sodium lauryl polyethoxy sulphates. If the solution has undesirable oaming tendencies l~Z~L3~)0 it is also possible, optionally, to include compatible anti-foams e.g. fatty alcohols such as ~ alcohol. The choice of surfactants for use in our solution is a routine matter easily within the ordinary competence o those skilled in the art. The amount of wetting ayent used is in accordance with normal practice, e.g. 0.1 to 10 parts per thousand.
f~
It is preferred that the solutions of our invention-s~ff~d-consist essentially of the foregoing species. However, we do not exclude the presence ~ minor amounts of other species which ara compatible with the solutions and which do not adversely affect the plating properties to a material extent. Generally it is preferred that nitrate ion be substantially absent, since it tends to inhibit deposition of chromium. Sulphite ion also is preferably absent, since it can cause hazy deposits in more than very small amounts. Other species, organic or inoryanic, which do not inhibit plating of the chromium or materially reduce covering power or create unacceptable problems of toxicity, may optionally be present. Whether any particular species can be tolerated in the solution may be routinely 20 determined by simple testing.
According to the present invention ~he baths are pre-ferably made up substantially as described in any of the afore-said specifications but including from 30 to 150 ppm of iron or nickel in the solution. Preferably the additional metal is 25 ferric iron. Conveniently a sufficient quantity of an appro-priate salt, e.g. ferric chloride, or preferably ferric sul-phate is added to the bath at any convenient stage in the preparation thereof. Alternatively the iron may be introduced in admixture with any of the other components of the bath. For 30 example, it is possible to select a source of one of the other ' ' Z~30~
bath components, such as chromic sulphate, which contains iron as an impurity, in sufficient quantity to provide the necessary concentration in the bath. Preferably, when replenishing the bath, iron or nickel is included in the replenishing additions in a quantity sufficient to maintain the concentration within the specified limits. Preferably the concentration is 40 to 100 ppm e.g. 50 ppm. If the concentration of iron or nickel should greatly exceed the specified limits, thus resulting in a plating fault, it may be reduced by addition to the bath of a hexacyano-ferrate salt, substantially as described in the specification of the aforesaid Belgian Patent, but ensuring that after treatment the concentration of the aforesaid metals is adjusted as necessary to bring it within the concentration limits characteristic of this invention.
The invention is illustrated by the following examples:-1. A chromium plating solution was prepared containing 20 gpl chromium, the chromium being supplied from commercial chromic sulphate, and 32 gpl formic acid, the other constituents being potassium chloride (75 gpl), boric acid ~50 gpl), ammonium bromide (10 gpl) and ammonium chloride (90 gpl) as described in our aforesaid U.S. Patent. After preparation and plating out at 0.5 amps per litre for 60 minutes a Hull Cell panel was run on the solution at 10 amps for 3 minutes. At current densities in excess of 400 ASF grey bands could be detected. Analysis of the solution for trace elements showed 15 ppm iron, 10 ppm nickel and 1 - 2 ppm of copper and zinc, these metals ~ ' ') OO
having arisen from traces present in the commercial grades used.
25ppm of iron was added as ferric chloride (FeC136H30) (i.e. 0.120 g per litre) and the solution re-run on the Hull Cell. The grey bands had disappeared and a clean non-banded panel was obtained. The inal analysis of the solution was 40 ppm iron, 10 ppm nickel, 5 ppm (Cu + Zn).
2. A working solution made up as above and used for pro-duction became contaminated with nickel and iron, leading to a plating fault. Analysis of the solution confirmed 110 ppm Fe, 150 ppm Ni, 25 ppm Zn, 5 ppm Cu. The solution was treated with tetrapotassium hexacyanoferrate (K4Fe(CN)6) at the rate of 1 ml/ litre of a 20~ w/v solution per 50 ppm metals i.e. 6 ml/l. After allowing time for the reaction to reach completion the precipitated metals were filtered off and the solution reanalysed. Results were 20 ppm Fe, 15 ppm Ni, showing virtually complete removal of metals.
A Hull Cell panel showed a trace of grey bands beginning to develop at high current densities and work plated in the electrolyte showed a faint greyish appearance at very high current density points. 25 ppm iron (as FeC136H20) was - added to the electrolyte, when the grey bands and the grey marks on work immediately disappeared. The concentration of (nickel + iron) was maintained in the concentration range 40 to 100 ppm thereafter by suitable additions of iron to the replenishing solutions.
..
~ .
, , ~ ' ' ' ' `
,
Claims (20)
1. In a trivalent chromium electroplating bath, the improvement which comprises 30 to 150 parts per million total of at least one metal selected from iron and nickel in said bath, and at least one carboxylate complexant selected from formate and acetate.
2. An electroplating bath according to claim 1 containing at least 1 water soluble complex of trivalent chromium capable of electrodepositing chromium metal.
3. An electroplating bath according to claim 2 wherein the complex includes a halide.
4. A composition according to claim 3 wherein the halide comprises bromide.
5. A composition according to claim 1 also containing ammonium ion.
6. A composition according to claim 5 containing from 0.1 to 1.2 molar trivalent chromium, at least 0.01 molar bromide, a proportion of formate to trivalent chromium between 0.5:1.0 and 3.0:1.0 on a molar basis, and ammonium ion in a proportion of at least 0.1 molar.
7. A composition according to any one of claims 1 to 3 containing at least 0.1 molar borate.
8. A composition according to any one of claims 1 to 3 having a pH between 1 and 4.
9. A composition according to any one of claims 1 to 3 containing at least 1 molar chloride.
10. A composition according to any one of claims 1 to 3 containing at least 0.5 molar sulphate.
11. A composition according to any one of claims 1 to 3 also containing 0.5 molar sodium and/or potassium.
12. A composition according to any one of claims 1 to 3 also containing a wetting agent.
13. A composition according to any one of claims 1 to 3 also containing a glycolate.
14. A composition according to any one of claims 1 to 3 containing from 40 to 100 ppm of iron and/or nickel.
15. A composition according to any one of claims 1 to 3 containing not more than 20 ppm each and not more than 30 ppm total of copper, zinc and lead.
16. A method of maintaining a trivalent chromium electo-plating bath comprising adding thereto sufficient of a water soluble salt of a metal selected from iron, nickel and mixtures thereof to provide from 30 to 150 parts per million total of the cation of said salt in said bath.
17. A method according to claim 16 wherein said added salt is an iron salt.
18. A method according to claim 17 wherein said added salt is a ferric salt.
19. A method according to claim 18 wherein said added salt is a ferric chloride or sulphate.
20. A method of maintaining a trivalent chromium electro-plating bath containing an excess of iron, nickel, copper and/or zinc which comprises adding to said bath only sufficient of a water soluble hexacyanoferrate salt to reduce the concentration of iron, nickel, copper and/or zinc to a value of from 30 to 150 parts per million, wherein the total of zinc and copper is less than 20 ppm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7595/76A GB1544833A (en) | 1975-12-18 | 1975-12-18 | Chromium electroplating |
| GB51798/75 | 1975-12-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121300A true CA1121300A (en) | 1982-04-06 |
Family
ID=10461418
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000267540A Expired CA1121300A (en) | 1975-12-18 | 1976-12-09 | Chromium electroplating |
Country Status (5)
| Country | Link |
|---|---|
| BE (1) | BE849522A (en) |
| CA (1) | CA1121300A (en) |
| FR (1) | FR2335624A1 (en) |
| GB (1) | GB1544833A (en) |
| SE (1) | SE455104B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2071151B (en) * | 1980-03-10 | 1983-04-07 | Ibm | Trivalent chromium electroplating |
| FR2529581A1 (en) * | 1982-06-30 | 1984-01-06 | Armines | ELECTROLYSIS BATH BASED ON TRIVALENT CHROME |
| CN114411211B (en) * | 2022-01-20 | 2023-03-10 | 厦门市金宝源实业有限公司 | Stainless steel color imitation decorative chromium plating process |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2927066A (en) * | 1955-12-30 | 1960-03-01 | Glenn R Schaer | Chromium alloy plating |
-
1975
- 1975-12-18 GB GB7595/76A patent/GB1544833A/en not_active Expired
-
1976
- 1976-12-09 CA CA000267540A patent/CA1121300A/en not_active Expired
- 1976-12-13 SE SE7614000A patent/SE455104B/en not_active IP Right Cessation
- 1976-12-17 FR FR7638242A patent/FR2335624A1/en active Granted
- 1976-12-17 BE BE173364A patent/BE849522A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| SE455104B (en) | 1988-06-20 |
| FR2335624A1 (en) | 1977-07-15 |
| BE849522A (en) | 1977-06-17 |
| SE7614000L (en) | 1977-06-19 |
| FR2335624B1 (en) | 1980-04-04 |
| GB1544833A (en) | 1979-04-25 |
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