CA1123370A - Electroplating chromium and its alloys using chromium thiocyanate complex - Google Patents
Electroplating chromium and its alloys using chromium thiocyanate complexInfo
- Publication number
- CA1123370A CA1123370A CA292,140A CA292140A CA1123370A CA 1123370 A CA1123370 A CA 1123370A CA 292140 A CA292140 A CA 292140A CA 1123370 A CA1123370 A CA 1123370A
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- solution
- chromium
- salt
- iii
- ncs
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- 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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- 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)
- Chemically Coating (AREA)
- Manufacturing Of Magnetic Record Carriers (AREA)
Abstract
Method and Composition for Electroplating Chromium and its Alloys and the Method of Manufacture of the Composition ABSTRACT OF THE DISCLOSURE
A plating solution, the making thereof and the use for chromium plating is disclosed. The solution is an equilibrated essentially aqueous solution of a hexavalent thiocyanatochromium III complex wherein the ratio of the total chromium III to the total thiocyanate is about 1:6. A preferred and improved method of making the solution from a hexathiocyanatochromium salt is also disclosed.
A plating solution, the making thereof and the use for chromium plating is disclosed. The solution is an equilibrated essentially aqueous solution of a hexavalent thiocyanatochromium III complex wherein the ratio of the total chromium III to the total thiocyanate is about 1:6. A preferred and improved method of making the solution from a hexathiocyanatochromium salt is also disclosed.
Description
3'7~ ' Method an~ Composition for Electroplating Chromium and its Alloys and the Method of Manufacture of the Composition Using Chromium Thiocyanate Complex Related Applicatlons This application is related to our U.K. speclfication 1,431,639 naming Dona}d John ~arclay and William Morris Morgan as inventors and complete specification of which was published on April 14, 1976. This is also related to our copending Canadian application Serial No. 292,187, filed December 1, 1977, naming Donald John Barclay and William Morris Morgan as inventors, and entitled "Electroplating Chromium and Its Alloys".
Background of the Invention The above U.K. specification teaches a chromium, or chromium alloy electroplating solution, in which th~ source of chromium comprises an aqueous solution of a chromium (III) thiocyanate complex. Said specification further describes a process of plating chromium, or a chromium containing alloy, which process comprises passing an electroplating current between an anode and a cathode in said electroplating solution.
In a preferred form the chromium ~III) thioc~anate complex consists essentially of an aqueous solution of a chromium (III) aquo thiocyanate complex or mixture of complexes having the general formula:
~; .
~lZ33'7L) 1 [(H~0)6 nCrIII (NCS) n]3 n; where n = a positive integer
Background of the Invention The above U.K. specification teaches a chromium, or chromium alloy electroplating solution, in which th~ source of chromium comprises an aqueous solution of a chromium (III) thiocyanate complex. Said specification further describes a process of plating chromium, or a chromium containing alloy, which process comprises passing an electroplating current between an anode and a cathode in said electroplating solution.
In a preferred form the chromium ~III) thioc~anate complex consists essentially of an aqueous solution of a chromium (III) aquo thiocyanate complex or mixture of complexes having the general formula:
~; .
~lZ33'7L) 1 [(H~0)6 nCrIII (NCS) n]3 n; where n = a positive integer
2 from 1 to 6 (~ote: that the subscripts are always positive but
3 the superscript may be positive, negative or zero). Complexes o
4 this type are well known, see Inorganic Chemistry 9, 1024, (19707.
The plating from the solutions described in the above-.
6 mentioned speci~ications has many advantages over the conventional 7 methods of plating chromium from the highly toxic chromic acid 8 baths or from baths using toxic organic solvents. Most important 9 of these is the removal of the serious health hazard present 10 during plating and the fact that the effluent is easier and safer 11 to dispose of. This process is less expensive, is rll~re 12 efficient electrically, and the useful life of the processing 13 apparatus is much l~nger due to less corrosion. Significantly 14 the deposited chromium is micro-crack free and is capable of 15 being bent without cracking. H~wever, it has been found that the 16 appearance of the chromium deposits at low current densities is a l7 strong function of the ratio of the total concentration of 18 chromium III to total thiocyanate in the plating solution. For 19 example, at a total chromium III to total thiocyanate ratio of 1:2, 20 while bright chromium is being deposited at current densities in 21 the range 20mA/cm2 to 120mA/cm2, this quality falls off rapidly 22 below 20mA/cm2; and in fàct a black deposit is obtained at current 23 densities less than about 15mA/cm2. This can be deleterious when 24 plating complex shapes on which there is a wide range of current 25 densities. It is believed that reason for the black deposit is 2~ the incomplete deposition of chrom~um fro~ Cr(~2ol6 ~ at l~ current 27 densities. Previous attempts to plate chromium from this ion 28 resulted in nonmetallic deposits.
3,1Z33'70 Summary of the InVention The present invention provides a chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous equilibrated hexathiocyanatochromium (III) salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)6 is maintained low. The solution may optionally be further characterized by containing a highly ionizable salt to increase the electrical conductivity of the solution. As used herein the ratio of chromium III to thiocyanate in the solutions means the total chromium, both free ions and complexed ions, to the total thiocyanate, both free ions and complexed ions.
The present invention also provides a method of electroplating chromium comprising the steps of providing an aqueous equilibrated solution of hexathiocyanatochromium III
salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)63+ is maintained low, and passing an electric current between an anode and a cathode in said solution.
In one embodiment such a method is provided wherein the salt solution was equilibrated prior to use by being heated to an elevated temperature. Preferably the elevated temperature is about 80C and the solution is maintained at such temperature for about three hours. In some cases, an embodiment is provided further characterized by addition of a highly ionizable salt to increase the electrical conductivity of the solution.
This solution and method generally provides good plating at low current densities. This will allow good plating - 1~2337~
results with current densities even as low as 5mA/cm2 and up to 320 mA/cm2.
Description of the Preferred Embodiments According to the present invention a chromium III
thiocyanate complex or mixture of complexes preferably of the general formula [(H2O)6 CrIII(NCS)n]3 n wherein n is a positive intPger from one to six is employed in aqueous solution. The solution is so formed and equilibrated that the ratio of the total chromium III (both free and complexed ions) to the total thiocyanate (both free and complexed ions) is 1:6. This is accomplished by providing thiocyanate in sufficiently large excess whereby the equilibrium of the equation:
- 3(a) -33~tO
1 Cr(H2O)6 + n~NC.S) + [Cr(H2O)6 n(NCS)n] ~ n(H2O) 2 tends to the right so that the concentration of Cr(H2O)63+ is low and the deposition of black deposits is minimized. By this means 4 the range of practical current densities can be increased from
The plating from the solutions described in the above-.
6 mentioned speci~ications has many advantages over the conventional 7 methods of plating chromium from the highly toxic chromic acid 8 baths or from baths using toxic organic solvents. Most important 9 of these is the removal of the serious health hazard present 10 during plating and the fact that the effluent is easier and safer 11 to dispose of. This process is less expensive, is rll~re 12 efficient electrically, and the useful life of the processing 13 apparatus is much l~nger due to less corrosion. Significantly 14 the deposited chromium is micro-crack free and is capable of 15 being bent without cracking. H~wever, it has been found that the 16 appearance of the chromium deposits at low current densities is a l7 strong function of the ratio of the total concentration of 18 chromium III to total thiocyanate in the plating solution. For 19 example, at a total chromium III to total thiocyanate ratio of 1:2, 20 while bright chromium is being deposited at current densities in 21 the range 20mA/cm2 to 120mA/cm2, this quality falls off rapidly 22 below 20mA/cm2; and in fàct a black deposit is obtained at current 23 densities less than about 15mA/cm2. This can be deleterious when 24 plating complex shapes on which there is a wide range of current 25 densities. It is believed that reason for the black deposit is 2~ the incomplete deposition of chrom~um fro~ Cr(~2ol6 ~ at l~ current 27 densities. Previous attempts to plate chromium from this ion 28 resulted in nonmetallic deposits.
3,1Z33'70 Summary of the InVention The present invention provides a chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous equilibrated hexathiocyanatochromium (III) salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)6 is maintained low. The solution may optionally be further characterized by containing a highly ionizable salt to increase the electrical conductivity of the solution. As used herein the ratio of chromium III to thiocyanate in the solutions means the total chromium, both free ions and complexed ions, to the total thiocyanate, both free ions and complexed ions.
The present invention also provides a method of electroplating chromium comprising the steps of providing an aqueous equilibrated solution of hexathiocyanatochromium III
salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)63+ is maintained low, and passing an electric current between an anode and a cathode in said solution.
In one embodiment such a method is provided wherein the salt solution was equilibrated prior to use by being heated to an elevated temperature. Preferably the elevated temperature is about 80C and the solution is maintained at such temperature for about three hours. In some cases, an embodiment is provided further characterized by addition of a highly ionizable salt to increase the electrical conductivity of the solution.
This solution and method generally provides good plating at low current densities. This will allow good plating - 1~2337~
results with current densities even as low as 5mA/cm2 and up to 320 mA/cm2.
Description of the Preferred Embodiments According to the present invention a chromium III
thiocyanate complex or mixture of complexes preferably of the general formula [(H2O)6 CrIII(NCS)n]3 n wherein n is a positive intPger from one to six is employed in aqueous solution. The solution is so formed and equilibrated that the ratio of the total chromium III (both free and complexed ions) to the total thiocyanate (both free and complexed ions) is 1:6. This is accomplished by providing thiocyanate in sufficiently large excess whereby the equilibrium of the equation:
- 3(a) -33~tO
1 Cr(H2O)6 + n~NC.S) + [Cr(H2O)6 n(NCS)n] ~ n(H2O) 2 tends to the right so that the concentration of Cr(H2O)63+ is low and the deposition of black deposits is minimized. By this means 4 the range of practical current densities can be increased from
5 ~s low as 5mA/cm and up to 320mA/cm .
6 The advantage of a l:6 ratio of chromium III to thio-
7 cyanate is not only that it increases the practical range of
8 current densities, but also that the ion Cr(NCS)63 is stable and
9 is commercially available from hexathiocyanatochromium III salts, l0 such as K3 Cr(NCS)6; Na3 Cr(NCS)6; or (NH4)3 Cr(NCS)6. By ll equilibrating this ion, for example at 80C for three hours, the 12 required [Cr (H2O)6 n ~NCS)n]3 n species may be formed. It will be ~3 clear that the preparation of the ~hromium III aquo thiocyanate 14 ions by this technique is significantly easier t~han by the method 15 describ~d in the above-mentioned patent specification.
17 Another significant advantage of plating chromium from trivalent chromium thiocyanate electrolytes is the possibility of l9 adding organic species such as wetting agents. This is not 20 possible with chromic acid electrolytes since the organic material 21 is spontaneously oxidized. It has been found that adding wetting 22 agents such as TRITON-X (TRITON is a Trademark of Rohm and Haas 23 Company) or FC-98 (a trademark of the 3M Corporation), to the 24 aqueous chromium III thiocyanate plating solution improves the 25 appearance of the deposited chromium and extends the maxim~m ~urrent 26 density at which deposition can occur before gas streaming prevents 27 plating. Hull cell tests have shown that with the addition of 28 these wetting agents the range of current density for bright 29 deposits can be increased to between 5mA/cm and 170mA/cm2.
UK976018 _ 4 _ ~PP
.
~;,z33 ,0 .
1 It has also been found that the conductivity of 2 the platint.~ solution can be increased by adding salts such 3 as sodium perchlorate (NaC10~), sodium sulphate (Na2SO~) or 4 potassium sulphate (K2SO4).
Increasing the total chromium concentration in the 6-solution up to about 0.1~, while maintaining the 1`:6 ratio of 7 chromium to thiocyanate, improves the plating efficiency of.the 8 bath and.increases the maximum current. density at which bright 9 deposition occurs to 320m~/cm2.
Nickel or cobalt sulphate can be added to the solution 11 for plating chromium/nickel or chromium/cobalt alloys, as des-12 crihed in the above-mentioned U.~. specification.
13 The above-mentioned U.K. speci~ication 14 describes the use of an ion exchange membrane to separate the 15 anolyte from the bulk plating solution'.~ The purpose of this 16 membrane is to prevent the fall of solution pll during plating.
17 ~part from this pll change no dele-terious anode reactions have 18 been observed. ~ disadvantage.associated with the use of the 19 membrane is the hi~her volta~e required to overcome its resis-20 ~ance to currcnt flow and the resulting rise in bath tempera-21 ture. ~ccordingly ion exchange membranes have not been used in 22 thc plating ~rocess described'herèin.
23 Using a normal ratio of solution volume to electrode 24 surface area (no more than 100 cm2 electrode area per litre of 25 solution) and when plating parts with a normal bright chromium 26 thickness (say 0.3 to 0.5~m), the pH change during:a plating 27 cycle is not sufficient to affect plating. The p~l can be ad-~8 justed, periodically during use, by addition of small quantities - *M = moles per liter UK976018 _'5 _ 13LZ3~70 1 of sodium hydroxide solution. ~lternatively the p~l can be 2 maintained within the required limi-ts by automatic additions oE
3 sodium hydroxide solution.
4 The invention will now be described with reference -to 5 the following examples:
~ EX~MPLE I
7 A 0.05M aqueolls solution of chromium III aquo thio-8 cyanate complex ions prepared as described in the above-mentioned 9 U.K. patent specification, i.e., by heating sodium thiocyanate
17 Another significant advantage of plating chromium from trivalent chromium thiocyanate electrolytes is the possibility of l9 adding organic species such as wetting agents. This is not 20 possible with chromic acid electrolytes since the organic material 21 is spontaneously oxidized. It has been found that adding wetting 22 agents such as TRITON-X (TRITON is a Trademark of Rohm and Haas 23 Company) or FC-98 (a trademark of the 3M Corporation), to the 24 aqueous chromium III thiocyanate plating solution improves the 25 appearance of the deposited chromium and extends the maxim~m ~urrent 26 density at which deposition can occur before gas streaming prevents 27 plating. Hull cell tests have shown that with the addition of 28 these wetting agents the range of current density for bright 29 deposits can be increased to between 5mA/cm and 170mA/cm2.
UK976018 _ 4 _ ~PP
.
~;,z33 ,0 .
1 It has also been found that the conductivity of 2 the platint.~ solution can be increased by adding salts such 3 as sodium perchlorate (NaC10~), sodium sulphate (Na2SO~) or 4 potassium sulphate (K2SO4).
Increasing the total chromium concentration in the 6-solution up to about 0.1~, while maintaining the 1`:6 ratio of 7 chromium to thiocyanate, improves the plating efficiency of.the 8 bath and.increases the maximum current. density at which bright 9 deposition occurs to 320m~/cm2.
Nickel or cobalt sulphate can be added to the solution 11 for plating chromium/nickel or chromium/cobalt alloys, as des-12 crihed in the above-mentioned U.~. specification.
13 The above-mentioned U.K. speci~ication 14 describes the use of an ion exchange membrane to separate the 15 anolyte from the bulk plating solution'.~ The purpose of this 16 membrane is to prevent the fall of solution pll during plating.
17 ~part from this pll change no dele-terious anode reactions have 18 been observed. ~ disadvantage.associated with the use of the 19 membrane is the hi~her volta~e required to overcome its resis-20 ~ance to currcnt flow and the resulting rise in bath tempera-21 ture. ~ccordingly ion exchange membranes have not been used in 22 thc plating ~rocess described'herèin.
23 Using a normal ratio of solution volume to electrode 24 surface area (no more than 100 cm2 electrode area per litre of 25 solution) and when plating parts with a normal bright chromium 26 thickness (say 0.3 to 0.5~m), the pH change during:a plating 27 cycle is not sufficient to affect plating. The p~l can be ad-~8 justed, periodically during use, by addition of small quantities - *M = moles per liter UK976018 _'5 _ 13LZ3~70 1 of sodium hydroxide solution. ~lternatively the p~l can be 2 maintained within the required limi-ts by automatic additions oE
3 sodium hydroxide solution.
4 The invention will now be described with reference -to 5 the following examples:
~ EX~MPLE I
7 A 0.05M aqueolls solution of chromium III aquo thio-8 cyanate complex ions prepared as described in the above-mentioned 9 U.K. patent specification, i.e., by heating sodium thiocyanate
10 together with a chromium perchlorate solution. However, sufficient
11 excess sodium thiocyanate ~as used to result in a ratio of
12 chromium III to thiocyanate of 1:6. Sodium perchlorate ~.as added
13 to increase in the conductivity of the solution. A wetting agent,
14 TRITON-X was also added to the solution.
lS The composition of the platin~ solution comprised:
16 Chromium III....................... 0.05M
17 Thiocyanate........................ 0.30M
18 Boric ~cid......................... 50g~1itre ~sat~ration) 19 Sodium Perchlorate......... ,....... 100g/litre rrl~lToN-x....... ~ o~l~l/litre ~1 ~ brass plate was plated from the solution described above 22 usin~ a standard 267 mm Hull cell under the followin~ conditions:
23 ~node............ ..................Platinized titanium mesh 24 Cat~ocle........ ...................Brass Hull cell plate 2~ p~l. ............ ...................2.6 26 Temperature...... ...................20C
27 Total Current.... ...................4~
28 Cell Voltage..... ...................8.5V
29 Plating Time..... ...................2 minutes llZ3;3'7~
1 The cathode was found to be plated with a bright 2 c~lromium deposit from the 4m~/cm2 to the 170mA/cm2 positions on 3 a ~lull cell scale.
4 Below the 4mA/cm2 level there were interference colors 5 due to very thin chromium deposits followed by a bare brass area.
6 Above the 170m~/cm2 level deposition had been prevented b~ excessive 7 hydrogen ~as streaming. The pH of the solution after plating was 8 1.80. Thus ~right chromium of rich attractive color was obtained 9 over the whole of the plating current density ran`ge and no black 10 deposit was produced at low current densities.
11 EX~MPLE II
12 ~ solution was prepared as in Example I with 0.lM
13 chromium tIII) 14 The composition of the plating solutio~ comprised:
lS The composition of the platin~ solution comprised:
16 Chromium III....................... 0.05M
17 Thiocyanate........................ 0.30M
18 Boric ~cid......................... 50g~1itre ~sat~ration) 19 Sodium Perchlorate......... ,....... 100g/litre rrl~lToN-x....... ~ o~l~l/litre ~1 ~ brass plate was plated from the solution described above 22 usin~ a standard 267 mm Hull cell under the followin~ conditions:
23 ~node............ ..................Platinized titanium mesh 24 Cat~ocle........ ...................Brass Hull cell plate 2~ p~l. ............ ...................2.6 26 Temperature...... ...................20C
27 Total Current.... ...................4~
28 Cell Voltage..... ...................8.5V
29 Plating Time..... ...................2 minutes llZ3;3'7~
1 The cathode was found to be plated with a bright 2 c~lromium deposit from the 4m~/cm2 to the 170mA/cm2 positions on 3 a ~lull cell scale.
4 Below the 4mA/cm2 level there were interference colors 5 due to very thin chromium deposits followed by a bare brass area.
6 Above the 170m~/cm2 level deposition had been prevented b~ excessive 7 hydrogen ~as streaming. The pH of the solution after plating was 8 1.80. Thus ~right chromium of rich attractive color was obtained 9 over the whole of the plating current density ran`ge and no black 10 deposit was produced at low current densities.
11 EX~MPLE II
12 ~ solution was prepared as in Example I with 0.lM
13 chromium tIII) 14 The composition of the plating solutio~ comprised:
15 . Chromium (III)..................... 0.1 L6 Thiocyanate........................ 0.6M
17 Boric ~cid......................... 50g/litre (saturation) 18 Soclium Perchlorate..... ,.......... 100g/litre 19 TRITON-`X............... ~.......... 0.1ml/litre ~ brass ~lull cell cathode was plated ~rom this 21 solution in a standard 267mm Hull cell under the following 22 conditions:
23 ~node.............................. Platinized titanium mesh 24 Catl-ode........................... Brass ~ull cell pla-te p~....... ,........................ 2.6 26 Telnperature....................... 20C
27 Total Current...................... 5~
28 CFll Voltage....................... llV
29 Plating Time....................... 2 minutes UK97601~ _ 7 _ 1~233 ,~0 .
1 The cathode was found to be plated with a bright 2 chromium deposit from the IOmA~cm to the 320mA/cm2 positions.
3 Below lOmA/cm2 and above 320mA/cm2 a band o inter-4 ~erence colors faded out to bare brass. The deposit was slightly 5 darker in color than deposits plated ~rom 0.05M chromium solu-6 tions. The high current density limit was calculated from R. O.
7 Hull's formula given in the book, "Nickel and Chromium Plating", 8 (page 23) by Dennis & Such, published by Newnes-Butterworths.
9 Examples III to VI describe alternative methods of 10 preparing a solution containing Cr(NCS)6 ions.
12 A 0.05M aqueous solution of sodium hexathiocyanato-13 chromium tIII) (Na3Cr(NCS)6) was saturated with boric acid 14 (H3B03). The solution was then heated at 80C for three hours.
15 The solution was then cooled and lOOg/~tre NaC104 was added
17 Boric ~cid......................... 50g/litre (saturation) 18 Soclium Perchlorate..... ,.......... 100g/litre 19 TRITON-`X............... ~.......... 0.1ml/litre ~ brass ~lull cell cathode was plated ~rom this 21 solution in a standard 267mm Hull cell under the following 22 conditions:
23 ~node.............................. Platinized titanium mesh 24 Catl-ode........................... Brass ~ull cell pla-te p~....... ,........................ 2.6 26 Telnperature....................... 20C
27 Total Current...................... 5~
28 CFll Voltage....................... llV
29 Plating Time....................... 2 minutes UK97601~ _ 7 _ 1~233 ,~0 .
1 The cathode was found to be plated with a bright 2 chromium deposit from the IOmA~cm to the 320mA/cm2 positions.
3 Below lOmA/cm2 and above 320mA/cm2 a band o inter-4 ~erence colors faded out to bare brass. The deposit was slightly 5 darker in color than deposits plated ~rom 0.05M chromium solu-6 tions. The high current density limit was calculated from R. O.
7 Hull's formula given in the book, "Nickel and Chromium Plating", 8 (page 23) by Dennis & Such, published by Newnes-Butterworths.
9 Examples III to VI describe alternative methods of 10 preparing a solution containing Cr(NCS)6 ions.
12 A 0.05M aqueous solution of sodium hexathiocyanato-13 chromium tIII) (Na3Cr(NCS)6) was saturated with boric acid 14 (H3B03). The solution was then heated at 80C for three hours.
15 The solution was then cooled and lOOg/~tre NaC104 was added
16 to increase the conductivity of the solution. The wetting
17 agent TRITON-X was added.
18 The composition of the plating solution comprised:
19 Chromium (III)..................... 0.05M
Thiocyanate........................ 0.30M
21 Boric Acid......................... 50g/litre (saturation) 22 Sodium Perchlorate................. lOOg/litre 23 TRITON-X........................... O.lml/litre A 0.05M aqueous solution of sodium hexathiocyanato-26 chromium (III) (Na3Cr~NCS)6) was saturated with boric acid.
27 The solution was then reduced electrochemically on a mercury 28 electrode at a potential of -lOOOmV vs SCE ~Standard Calomel Electrode) to produce a /
~;~33 ~ ~
1 solution of chromium (II) thiocyanate complexes. This solution 2 w~s reoxidiz~d ~t -300mV vs SCE to p~oduc~ a mi~ture of 3 chromium (III) aquo thiocyanate complexes. (See Inorganic 4 Chemistry 9, 1028, 1970.) 100cJ/litre sodium perchlorate was 5 added to increase the conductivity of the solution. ~ _ 6 wetting agent TRITON-X was also added.
8 ~ 0.05M aqueous solution of potassium he~athio-9 cyanatochromium (III) (K3Cr(NCS)6) was saturated with boric 10 acid. The solution was then heated at 80~C for three hours.
11 The solution was then cooled and 100g/litre sodium sulphate 12 was added to increase the conductivity oE the solution. The 13 wetting agent TRITON-X was added.
14 The composition of the bath comprised:
Chromium (III)..................... ~0.05M
-lfi Thiocyanate........................ Ø30 17 Boric ~cid........................ .50g/litre (saturation~ ~
18 Sodium Sulphate.................... .100g/litre ~ ~, 1~ TRI~'ON-X................ O......... Ølml/litre EX~MPLE ~
21 ~ convellient way of providincl the electrolytes is a 22 concentrate o~ an aqueous solution of the chromium (III) thio-23 cyanate comple~ having the 1:6 chromium to thiocyanate ratio, ~_ which can be diluted to give the desired concentration of the 25 various ions.
26 While the invention has been particularly shown and 27 described with reference to preferred embodiments thereof, it 28 will be understood by those skilled in the art that various ~
29 changes in form and details may be made therein without departing ~2es 30 from the spirit and scope of the invention.
UK976018 _ 9 _
Thiocyanate........................ 0.30M
21 Boric Acid......................... 50g/litre (saturation) 22 Sodium Perchlorate................. lOOg/litre 23 TRITON-X........................... O.lml/litre A 0.05M aqueous solution of sodium hexathiocyanato-26 chromium (III) (Na3Cr~NCS)6) was saturated with boric acid.
27 The solution was then reduced electrochemically on a mercury 28 electrode at a potential of -lOOOmV vs SCE ~Standard Calomel Electrode) to produce a /
~;~33 ~ ~
1 solution of chromium (II) thiocyanate complexes. This solution 2 w~s reoxidiz~d ~t -300mV vs SCE to p~oduc~ a mi~ture of 3 chromium (III) aquo thiocyanate complexes. (See Inorganic 4 Chemistry 9, 1028, 1970.) 100cJ/litre sodium perchlorate was 5 added to increase the conductivity of the solution. ~ _ 6 wetting agent TRITON-X was also added.
8 ~ 0.05M aqueous solution of potassium he~athio-9 cyanatochromium (III) (K3Cr(NCS)6) was saturated with boric 10 acid. The solution was then heated at 80~C for three hours.
11 The solution was then cooled and 100g/litre sodium sulphate 12 was added to increase the conductivity oE the solution. The 13 wetting agent TRITON-X was added.
14 The composition of the bath comprised:
Chromium (III)..................... ~0.05M
-lfi Thiocyanate........................ Ø30 17 Boric ~cid........................ .50g/litre (saturation~ ~
18 Sodium Sulphate.................... .100g/litre ~ ~, 1~ TRI~'ON-X................ O......... Ølml/litre EX~MPLE ~
21 ~ convellient way of providincl the electrolytes is a 22 concentrate o~ an aqueous solution of the chromium (III) thio-23 cyanate comple~ having the 1:6 chromium to thiocyanate ratio, ~_ which can be diluted to give the desired concentration of the 25 various ions.
26 While the invention has been particularly shown and 27 described with reference to preferred embodiments thereof, it 28 will be understood by those skilled in the art that various ~
29 changes in form and details may be made therein without departing ~2es 30 from the spirit and scope of the invention.
UK976018 _ 9 _
Claims (19)
1. A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous equilibrated hexathiocyanatochromium (III) salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)63+ is maintained low.
2. A solution as claimed in Claim 1, further character-ized by containing a highly ionizable salt to increase the electrical conductivity of said solution.
3. A solution as claimed in Claim 2, in which the salt is selected from the group consisting of sodium perchlorate, sodium sulphate, and potassium sulphate.
4. A solution as claimed in Claim 1, 2 or 3 further characterized by a wetting agent.
5. A solution as claimed in Claim 1, in which the hexathiocyanatochromium (III) salt is selected from the group consisting of Na3Cr(NCS)6, K3Cr(NCS)6, and (NH4)3Cr(NCS)6.
6. The solution as claimed in Claim 5, characterized by containing boric acid.
7. A solution as claimed in Claim 5 or 6, in which 0.05M of the hexathiocyanatochromium III salt is present.
8. A method of electroplating chromium comprising the steps of providing an aqueous equilibrated solution of hexa-thiocyanatochromium III salt complex, the molar ratio of total chromium III to total thiocyanate being about 1:6, so that the concentration of Cr(H2O)63+ is maintained low, and passing an electric current between an anode and a cathode in said solution.
9. The method as defined in Claim 8, further characterized by said solution containing 0.05M of the complex.
10. A method as in Claim 8 wherein the plating solution salt is selected from the group consisting of Na3Cr(NCS)6, K3Cr(NCS)6, and (NH4)3Cr(NCS)6.
11. The method as defined in Claim 10, wherein the solution is saturated with boric acid.
12. The method as defined in Claim 10, wherein the salt solution was equilibrated by being heated to an elevated temperature.
13. The method as defined in Claim 12, wherein the elevated temperature is about 80°C and the solution is maintained at said temperature for about three hours.
14. The method as defined in Claim 8, wherein the salt is Na3Cr(NCS)6, and wherein the solution is electrochemically reduced during the plating and thereafter reoxidized.
15. The invention as defined in Claim 14, wherein the complex is prepared electrochemically on a mercury electrode.
16. A method as claimed in Claim 8, further characterized by addition of a highly ionizable salt to increase the electrical conductivity of said solution.
17. A method as claimed in Claim 16, in which the salt is selected from the group consisting of sodium perchlorate, sodium sulphate, and potassium sulphate.
18. A method as claimed in Claim 8, wherein said equilibrated solution further comprises a wetting agent.
19. The method as claimed in Claim 8, wherein said equilibrated solution further comprises a saturating amount of boric acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB52,594 | 1976-12-16 | ||
| GB52594/76A GB1571193A (en) | 1976-12-16 | 1976-12-16 | Electroplating chromium and its alloys |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1123370A true CA1123370A (en) | 1982-05-11 |
Family
ID=10464519
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,140A Expired CA1123370A (en) | 1976-12-16 | 1977-12-01 | Electroplating chromium and its alloys using chromium thiocyanate complex |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5395134A (en) |
| BE (1) | BE853930R (en) |
| CA (1) | CA1123370A (en) |
| CH (1) | CH627795A5 (en) |
| DE (1) | DE2723023A1 (en) |
| FR (1) | FR2374436A2 (en) |
| GB (1) | GB1571193A (en) |
| IT (1) | IT1115399B (en) |
| NL (1) | NL7704932A (en) |
| SE (1) | SE429563B (en) |
| ZA (1) | ZA773264B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IN153802B (en) * | 1978-11-11 | 1984-08-18 | Ibm | |
| GB2093861B (en) * | 1981-02-09 | 1984-08-22 | Canning Materials W Ltd | Bath for electrodeposition of chromium |
| GB8411063D0 (en) * | 1984-05-01 | 1984-06-06 | Mccormick M | Chromium electroplating |
| DE102006035871B3 (en) * | 2006-08-01 | 2008-03-27 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Process for the deposition of chromium layers as hard chrome plating, plating bath and hard chrome plated surfaces and their use |
| JP2011099126A (en) * | 2008-01-24 | 2011-05-19 | Okuno Chemical Industries Co Ltd | Trivalent chromium plating bath |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1431639A (en) * | 1974-12-11 | 1976-04-14 | Ibm Uk | Electroplating chromium and its alloys |
-
1976
- 1976-12-16 GB GB52594/76A patent/GB1571193A/en not_active Expired
-
1977
- 1977-04-19 FR FR7712637A patent/FR2374436A2/en active Granted
- 1977-04-22 SE SE7704661A patent/SE429563B/en not_active IP Right Cessation
- 1977-04-25 BE BE176993A patent/BE853930R/en not_active IP Right Cessation
- 1977-04-25 CH CH508777A patent/CH627795A5/en not_active IP Right Cessation
- 1977-05-05 NL NL7704932A patent/NL7704932A/en not_active Application Discontinuation
- 1977-05-21 DE DE19772723023 patent/DE2723023A1/en active Granted
- 1977-05-30 ZA ZA00773264A patent/ZA773264B/en unknown
- 1977-12-01 CA CA292,140A patent/CA1123370A/en not_active Expired
- 1977-12-02 IT IT30296/77A patent/IT1115399B/en active
- 1977-12-12 JP JP14825677A patent/JPS5395134A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2374436A2 (en) | 1978-07-13 |
| DE2723023A1 (en) | 1978-06-22 |
| SE429563B (en) | 1983-09-12 |
| JPS5621356B2 (en) | 1981-05-19 |
| NL7704932A (en) | 1978-06-20 |
| IT1115399B (en) | 1986-02-03 |
| CH627795A5 (en) | 1982-01-29 |
| FR2374436B2 (en) | 1980-02-01 |
| GB1571193A (en) | 1980-07-09 |
| SE7704661L (en) | 1978-06-17 |
| ZA773264B (en) | 1979-01-31 |
| JPS5395134A (en) | 1978-08-19 |
| DE2723023C2 (en) | 1988-01-07 |
| BE853930R (en) | 1977-08-16 |
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