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US4851092A
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Process for electrolytically pickling chromium-containing stainless steel
Assignee: Andritz AG
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Filing: 1988-05-03
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Granted: 1989-07-25
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Expires: 2008-05-03
Abstract
Abstract In a process for the electrolytic pickling of chromium-containing stainless steel, pickling proceeds initially in an aqueous Na 2 SO 4 solution and subsequently in acid, preferably mixed acid. The CrO 4 2- formed is converted by the addition of reducing agent and acid as a function of the pH value and the redox potential to Cr 2 (SO 3 ) 3 or Cr 2 (SO 4 ) 3 . H 2 SO 4 serves as the acid and a substance is used as a reducing agent selected from the group Na x H y S z O v , wherein x=0 to 2, y=0 to 2, y=1 to 6 and v=2 to 6. The pH value is adjusted to less than three by the addition of acid.
Inventors
- 👤 Gerald Maresch
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 11:07
CPC Classifications
C; C25; C25F; C25F1/00; C25F1/02; C25F1/04; C25F1/06
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
71 words
Process for the electrolytic pickling of chromium-containing stainless steel, in which initially pickling proceeds in an aqueous Na 2 SO 4 solution and thereafter in acid, comprising the improvement of adding acid and a reducing agent to the aqueous Na 2 SO 4 solution in amounts regulated in accordance with pH value and the redox potential of the solution such that a pickling solution free of CrO 4 2- is attained.
Claim 2
Dependent Claim
71 words
Process for the electrolytic pickling of chromium-containing stainless steel, in which initially pickling proceeds in an aqueous Na 2 SO 4 solution and thereafter in acid, comprising the improvement of adding acid and a reducing agent to the aqueous Na 2 SO 4 solution in amounts regulated in accordance with pH value and the redox potential of the solution such that a pickling solution free of CrO 4 2- is attained.
Claim 3
Dependent Claim
27 words
Process according to claim 1, wherein the pH value of the solution is adjusted to less than 3 by the addition of H 2 SO 4 .
Claim 4
Dependent Claim
14 words
Process according to claim 2, wherein the pH is adjusted to 1.5 to 2.5.
Claim 5
Dependent Claim
33 words
Process according to claim 1, wherein the redox potential of the solution measured against a calomel electrode is reduced by 50 to 100 mV by the addition of acid and the reducing agent.
Claim 6
Dependent Claim
52 words
Process according to claim 1, wherein a compound of the formula Na x H y S z O v is used as the reducing agent, wherein x=0 to 2, y=0 to 2, z=1 to 6 and v=2 to 6; and wherein in the reaction Na 2 SO 4 is formed as well.
Claim 7
Dependent Claim
22 words
Process according to claim 1, wherein the Na 2 SO 4 concentration of the solution is adjusted to 100 to 250 g/l.
Claim 8
Dependent Claim
19 words
Process according to claim 6, wherein the Na 2 SO 4 concentration is adjusted to 170 to 200 g/l.
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) | 1992-07-24 | 1993-01-23 | 1993-07-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-07-24 | 1997-01-23 | 1997-07-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-07-24 | 2001-01-23 | 2001-07-25 | $7700.00 | Window Closed / Lapsed |