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US4753680A
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Process for the preparation of bright, color-pure iron oxide red pigments
Assignee: Bayer AG
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Filing: 1985-12-26
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Granted: 1988-06-28
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Expires: 2005-12-26
Abstract
Abstract A bright, color-pure iron oxide red pigment is produced by an improved process by precipitation of iron(II) salts in aqueous solution with an alkaline precipitating agent, oxidation at temperatures of from 20° C. to 100° C. and annealing of the resulting precipitation products under air to form iron oxide red pigments, wherein the improvement comprises before adding the alkaline precipitating agent, the iron(III) content of the aqueous solution is adjusted to 1 to 15 mol %, based on the total iron content of the iron salt solution.
Inventors
- 👤 Wilfried Burow
- 👤 Jurgen Wiese
- 👤 Gunter Buxbaum
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 17:48
CPC Classifications
C; C09; C09C; C09C1/00; C09C1/22; C09C1/24; C01; C01G; C01G49/00; C01G49/02; C01G49/06; C08; C08K; C08K3/00; C08K3/18; C08K3/20; C08K3/22; C01P; C01P2006/00; C01P2006/12; C01P2006/60; C01P2006/62; C01P2006/63; C01P2006/64
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
94 words
In an improved process for the preparation of bright, color-pure iron oxide red pigments by precipitation of iron(II) salts in aqueous solution with an alkaline precipitating agent, oxidating at temperatures of from 20° C. to 100° C. and annealing of the resulting precipitation products under air to form iron oxide red pigments, the improvement comprises adding the alkaline precipitating agent to said aqueous solution which contains Iron(II) salts and Iron(III) salts and wherein the content of Iron(III) is 1 to 15 mol %, based on the total iron content of the iron salt solution.
Claim 2
Dependent Claim
94 words
In an improved process for the preparation of bright, color-pure iron oxide red pigments by precipitation of iron(II) salts in aqueous solution with an alkaline precipitating agent, oxidating at temperatures of from 20° C. to 100° C. and annealing of the resulting precipitation products under air to form iron oxide red pigments, the improvement comprises adding the alkaline precipitating agent to said aqueous solution which contains Iron(II) salts and Iron(III) salts and wherein the content of Iron(III) is 1 to 15 mol %, based on the total iron content of the iron salt solution.
Claim 3
Dependent Claim
17 words
A process according to claim 1 wherein oxidation is achieved by an oxidizing agent which is air.
Claim 4
Dependent Claim
21 words
A process according to claim 1 wherein the iron(III) content is produced by oxidation with air at a pH below 3.
Claim 5
Dependent Claim
18 words
A process according to claim 1 wherein the iron(II) salts are sulphates, chlorides or a mixtures of both.
Claim 6
Dependent Claim
28 words
A process according to claim 1 wherein the alkaline precipitating agent is NaOH, NH 3 , Na 2 CO 3 , MgO, MgCO 3 or a mixture thereof.
Claim 7
Dependent Claim
19 words
A process according to claim 1 wherein precipitation is achieved with 0.5 to 1.3 equivalents of alkaline precipitating agent.
Claim 8
Dependent Claim
19 words
A process according to claim 6 wherein precipitation is achieved with 0.8 to 1.3 equivalents of alkaline precipitating agent.
Claim 9
Dependent Claim
34 words
A process according to claim 1 wherein prior to precipitation, a soluble aluminum salt is added to the solution in quantities of from 1 to 10 mol %, based on the total iron content.
Claim 10
Dependent Claim
34 words
A process according to claim 1 wherein prior to precipitation, a soluble phosphorous salt is added to the solution in quantities of from 1 to 5 mol %, based on the total iron content.
Claim 11
Dependent Claim
24 words
A process according to claim 1 wherein the precipitated iron oxide black is washed, dried, annealed at 700° to 1100° C. and then ground.
Claim 12
Dependent Claim
14 words
A process according to claim 10 wherein annealing is at 800° to 950° C.
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) | 1991-06-28 | 1991-12-28 | 1992-06-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-06-28 | 1995-12-28 | 1996-06-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-06-28 | 1999-12-28 | 2000-06-28 | $7700.00 | Window Closed / Lapsed |