US4376714A
Expired / Lapsed
US
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Process for preparing acicular iron oxide particles
Assignee: Eastman Kodak Co
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Filing: 1980-11-06
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Granted: 1983-03-15
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Expires: 2000-11-06
Abstract
Abstract This disclosure relates to a process for preparing acicular magnetic iron oxide particles by (a) adding an aqueous solution of a ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of the ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing these particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting the non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation. The ferrous salt solution is subjected to reducing conditions prior to and/or during the addition to the alkaline hydroxide solution to reduce contaminating ferric ions that are normally present to ferrous ions.
Inventors
- 👤 Bernard J. Pingaud
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 02:59
CPC Classifications
C; C01; C01G; C01G49/00; C01G49/02; G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70626; G11B5/70642; C01P; C01P2002/00; C01P2002/50; C01P2002/52; C01P2004/00; C01P2004/01; C01P2004/03; C01P2004/10; C01P2004/54; C01P2004/60; C01P2004/62; C01P2004/80; C01P2004/82; C01P2004/84; C01P2006/00; C01P2006/42
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
108 words
In a process for preparing acicular magnetic iron oxide particles comprising (a) adding an aqueous solution of ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of said ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing said particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting said non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation, the improvement wherein said ferrous salt solution is subjected to reducing conditions prior to or during said addition to reduce contaminating ferric ions present therein to ferrous ions.
Claim 2
Dependent Claim
108 words
In a process for preparing acicular magnetic iron oxide particles comprising (a) adding an aqueous solution of ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of said ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing said particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting said non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation, the improvement wherein said ferrous salt solution is subjected to reducing conditions prior to or during said addition to reduce contaminating ferric ions present therein to ferrous ions.
Claim 3
Dependent Claim
42 words
A process according to claim 1 in which said reducing conditions are provided by adding said ferrous salt solution to said alkaline hydroxide solution in the presence of a sufficient concentration of reducing agent to reduce said ferric ions to ferrous ions.
Claim 4
Dependent Claim
16 words
A process according to claim 2 in which said reducing agent is an inorganic reducing agent.
Claim 5
Dependent Claim
17 words
A process according to claim 3 in which said reducing agent is sodium sulfite or sodium hydrosulfite.
Claim 6
Dependent Claim
38 words
A process according to claim 3 in which said reducing agent is added to said aqueous solution of ferrous salt in a concentration in the range of about 10 to 100 meq. per mole of said ferrous salt.
Claim 7
Dependent Claim
18 words
A process according to claim 2 in which said reducing agent is a sulfite, hydrosulfite, dihydroxybenzene, or hydroxylamine.
Claim 8
Dependent Claim
27 words
A process according to claim 2 in which said reducing agent is added to at least one of said aqueous solutions of ferrous salt or alkaline hydroxide.
Claim 9
Dependent Claim
44 words
A process according to claim 2 in which said reducing agent is sodium sulfite, sodium hydrosulfite, hydroquinone or hydroxylamine hydrochloride and is added to said aqueous solution of alkaline hydroxide in a concentration in the range of about 2 to 12 meq. per liter.
Claim 10
Dependent Claim
21 words
A process according to claim 2 in which said stoichiometric excess is in the range of about 50 to 100 percent.
Claim 11
Dependent Claim
18 words
A process according to claim 9 in which said reducing agent is a sulfite, hydrosulfite, dihydroxybenzene or hydroxylamine.
Claim 12
Dependent Claim
27 words
A process according to claim 9 in which said reducing agent is sodium sulfite or sodium hydrosulfite and is added to said aqueous solution of ferrous salt.
Claim 13
Dependent Claim
19 words
A process according to claim 1 in which said stoichiometric excess of alkaline hydroxide does not exceed 250 percent.
Claim 14
Dependent Claim
16 words
A process according to claim 12 in which said alkaline hydroxide is an alkali metal hydroxide.
Claim 15
Dependent Claim
28 words
A process according to claim 13 in which said alkali metal is sodium or potassium and said reducing agent is added to said aqueous solution of ferrous salt.
Claim 16
Dependent Claim
17 words
A process according to claim 13 in which said ferrous salt is ferrous sulfate or ferrous chloride.
Claim 17
Dependent Claim
23 words
A process according to claim 12 in which said non-magnetic particles are dehydrated, reduced and oxidized to form magnetic gamma ferric oxide particles.
Claim 18
Dependent Claim
19 words
A process according to claim 1 including the additional step of doping said magnetic particles with doping metal ions.
Claim 19
Dependent Claim
21 words
A process according to claim 17 in which said doping metal ions are present in said aqueous solution of ferrous salt.
Claim 20
Dependent Claim
15 words
A process according to claim 17 in which said doping metal ions are cobalt ions.
Claim 21
Dependent Claim
28 words
A process according to claim 17 in which said doping metal ions are ions of cobalt, ferrous iron, nickel, chromium, zinc, cadmium, manganese, calcium, tin, samarium, or europium.
Claim 22
Dependent Claim
18 words
A process according to claim 20 in which said doping metal ions are ions of cobalt and calcium.
Claim 23
Dependent Claim
22 words
A process according to claim 1 in which said non-magnetic particles are dehydrated and reduced to form magnetic ferrous ferric oxide particles.
Claim 24
Dependent Claim
23 words
A process according to claim 1 in which said non-magnetic particles are dehydrated, reduced and oxidized to form magnetic gamma ferric oxide particles.
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) | 1986-03-14 | 1986-09-13 | 1987-03-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-03-14 | 1990-09-13 | 1991-03-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-03-14 | 1994-09-13 | 1995-03-15 | $7700.00 | Window Closed / Lapsed |