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US4256548A
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Elimination of anode hydrogen cyanide formation in trivalent chromium plating
Assignee: International Business Machines Corp
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Filing: 1979-10-18
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Granted: 1981-03-17
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Expires: 1999-10-18
Abstract
Abstract Generation of hydrogen cyanide at the anode in a chromium (III) - thiocyanate plating bath, resulting from oxidation of thiocyanate anions, is prevented by an additive to the electroplating solution which oxidizes at the anode in preference to the thiocyanate, and whose reaction products will not adversely affect the cathode reaction. Such an additive is potassium iodide.
Inventors
- 👤 Donald J. Barclay
- 👤 James M. L. Vigar
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 09:00
CPC Classifications
C; C25; C25D; C25D3/00; C25D3/02; C25D3/04; C25D3/06
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
70 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of a chromium (III)-thiocyanate complex and which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen at the anode characterized in that the solution further comprises an additive which will undergo electrochemically reversible oxidation at the anode in preference to the thiocyanate oxidation.
Claim 2
Dependent Claim
70 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of a chromium (III)-thiocyanate complex and which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen at the anode characterized in that the solution further comprises an additive which will undergo electrochemically reversible oxidation at the anode in preference to the thiocyanate oxidation.
Claim 3
Dependent Claim
18 words
An electroplating solution as claimed in claim 1 in which the additive is a source of iodide ions.
Claim 4
Dependent Claim
18 words
An electroplating solution as claimed in claim 2 in which the source of iodide ions is potassium iodide.
Claim 5
Dependent Claim
18 words
An electroplating solution as claimed in claim 1 in which the additive is a source of ferrocyanide ions.
Claim 6
Dependent Claim
23 words
An electroplating solution as claimed in claim 1 in which the additive's oxidation potential at the anode is less than that of thiocyanate.
Claim 7
Dependent Claim
18 words
An electroplating solution as claimed in claim 5 in which the additive is a source of iodide ions.
Claim 8
Dependent Claim
103 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of chromium sulphate (Cr 2 (SO4) 3 .15H 2 O) and sodium thiocyanate (Na NCS), and which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen, characterized in that the solution comprises an iodide ion additive which will undergo oxidation at the anode in preference to thiocyanate oxidation, and further comprise a pH buffer, a constituent to impart conductivity to the solution, and a further buffer which supplies one of the ligands to the chromium complex.
Claim 9
Dependent Claim
103 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of chromium sulphate (Cr 2 (SO4) 3 .15H 2 O) and sodium thiocyanate (Na NCS), and which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen, characterized in that the solution comprises an iodide ion additive which will undergo oxidation at the anode in preference to thiocyanate oxidation, and further comprise a pH buffer, a constituent to impart conductivity to the solution, and a further buffer which supplies one of the ligands to the chromium complex.
Claim 10
Dependent Claim
38 words
An electroplating solution as claimed in claim 7 in which said pH buffer is boric acid (H 3 BO 3 ), said constituent is sodium chloride (NaCl), and said further buffer is glycine (NH 2 .CH 2 .COOH).
Claim 11
Dependent Claim
84 words
A process of plating chromium or a chromium alloy comprising passing an electric current between an anode and a cathode both of which are immersed in an electroplating solution in which the source of chromium comprises an aqueous solution of a chromium (III)-thiocyanate complex, in which process chromium or a chromium alloy is deposited on the cathode and an additive is provided which is electrochemically oxidized at the anode in preference to the oxidation of thiocyanate anions and is a source of iodide ions.
Claim 12
Dependent Claim
84 words
A process of plating chromium or a chromium alloy comprising passing an electric current between an anode and a cathode both of which are immersed in an electroplating solution in which the source of chromium comprises an aqueous solution of a chromium (III)-thiocyanate complex, in which process chromium or a chromium alloy is deposited on the cathode and an additive is provided which is electrochemically oxidized at the anode in preference to the oxidation of thiocyanate anions and is a source of iodide ions.
Claim 13
Dependent Claim
23 words
A process as claimed in claim 9 further comprising the step of chemically reducing the additive oxidation products back to the original additive.
Claim 14
Dependent Claim
24 words
A process as claimed in claim 10 in which the step of chemically reducing the additive oxidation products comprises adding hydrazine to the solution.
Claim 15
Dependent Claim
14 words
A process as claimed in claim 11 in which the additive is potassium iodide.
Claim 16
Dependent Claim
27 words
A process as claimed in claim 10 in which the step of chemically reducing the additive oxidation products comprises adding a source of sulphite to the solution.
Claim 17
Dependent Claim
39 words
A process as claimed in claim 13 comprising the further step of precipitating sulphate ions formed as a result of the chemical reduction step out of solution by adding barium hydroxide, barium chloride or barium carbonate to the solution.
Claim 18
Dependent Claim
14 words
A process as claimed in claim 14 in which the additive is potassium iodide.
Claim 19
Dependent Claim
77 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of chromium sulphate (CR 2 (SO4) 3 .15H 2 O) and sodium thiocyanate (Na NCS) which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen at the anode, characterized in that the solution further comprises a potassium iodide additive which undergoes oxidation at the anode in preference to thiocyanate oxidation.
Claim 20
Dependent Claim
77 words
A chromium or chromium alloy electroplating solution in which the source of chromium comprises an aqueous solution of chromium sulphate (CR 2 (SO4) 3 .15H 2 O) and sodium thiocyanate (Na NCS) which is susceptible to evolution of hydrogen cyanide as a result of the oxidation of thiocyanate anions to free thiocyanogen at the anode, characterized in that the solution further comprises a potassium iodide additive which undergoes oxidation at the anode in preference to thiocyanate oxidation.
Claim 21
Dependent Claim
47 words
An electroplating solution as claimed in claim 16 including boric acid (H 3 BO 3 ) functioning as a pH buffer, sodium chloride (NaCl) importing conductivity to the solution, and a glycine (NH 2 .CH 2 .COOH) buffer supplying one of the ligands of the chromium complex.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-03-16 | 1984-09-15 | 1985-03-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-03-16 | 1988-09-15 | 1989-03-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-03-16 | 1992-09-15 | 1993-03-17 | $7700.00 | Window Closed / Lapsed |