Claims
- 1. The process of making magnetic particles consisting essentially of the following steps:
- a. forming a suspension of acicular gamma ferric oxide in an aqueous solution of a salt of a metal selected from the group consisting of barium, strontium, lead and calcium, and a soluble trivalent iron salt, adding an alkali to form a precipitate and drying the resulting mixture of the precipitated decomposition products of said salts and acicular gamma ferric oxide,
- b. heating said dry mixture in an atmosphere containing oxygen at a temperature of at least 300.degree. F. to produce a magnetic particle having a core of acicular gamma ferric oxide and a coating comprising a mixture of an oxide of metal selected from barium, strontium, lead and calcium and trivalent iron oxide.
- 2. The process of claim 1 wherein quantities of the starting materials are selected to yield a product having the composition
- (MO).sub.x (Fe.sub.2 O.sub.3).sub.y (Fe.sub.2 O.sub.3).sub.z
- wherein M is the metal selected from barium, strontium, lead and calcium, (Fe.sub.2 O.sub.3).sub.y is the oxide formed by the trivalent iron salt and (Fe.sub.2 O.sub.3).sub.z is the gamma ferric oxide and wherein the ratio of x to z is from 0.04 to 0.2 and the ratio of x+y/z is from 0.1 to 0.4.
Parent Case Info
This is a continuation of application Ser. No. 945,276, filed Sept. 25, 1978, which is a continuation of Ser. No. 837,837, filed Sept. 29, 1977, both now abandoned.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4125474 |
Dezawa et al. |
Nov 1978 |
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Continuations (2)
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Number |
Date |
Country |
Parent |
945276 |
Sep 1978 |
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Parent |
837837 |
Sep 1977 |
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