Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1997-02-18
1998-06-23
Bonner, Melissa
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
423634, 423632, 252 6256, C09C 124, C09D 1700, C01G 4906, C01G 4908
Patent
active
057699372
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to high-purity .gamma.-Fe.sub.2 O.sub.3 pigments and Fe.sub.3 O.sub.4 pigments with a particle diameter of 2-100 nm, a saturation magnetization above 40 nTm.sup.3 /g, a remanence below 10 nTm.sup.3 /g, a Cr content below 40 mg/kg of pigment, a Cu content below 40 mg/kg of pigment and a C content below 100 mg/kg of pigment.
The invention additionally relates to processes for preparing these pigments, to aqueous suspensions which contain these pigments, and to the use of the pigments and suspensions in the medical sector.
Ferromagnetic iron oxide pigments are known to be usable in the medical sector in particular in the form of an aqueous suspension, as contrast agents in magnetic resonance imaging.
The pigments are known to be prepared by reacting an aqueous solution of iron salts with a base, adjusting the iron valency required in the pigment by using iron(II) and iron(III) salts or, if the iron valency is too low, by oxidative treatment of the solution, eg. with atmospheric oxygen. The precipitate is then separated off and washed and dried in a conventional way.
The iron salts used as starting compounds still contain, however, small amounts of salts of other metals such as chromium, nickel and copper. These impurities do not interfere with use for most purposes but are not physiologically acceptable if, like contrast agents, they are put directly into the bloodstream in the human body.
Furthermore, iron pigments suitable for magnetic resonance imaging must meet high demands in respect of ferromagnetic sensitivity, for which the level of the saturation magnetization at low remanence represents a measure, in order thereby to keep the dose of the agent as small as possible. Finally, these contrast agents should have particles as fine as possible so that they will dissolve faster in the blood and do not form any deposits which are difficult to break down on the blood vessel walls.
Contrast agents with these properties have not previously been available, and accordingly it is an object of the present invention to remedy this deficiency.
It is an object of the present invention therefore to prepare, in an industrially simple and economic manner, ferromagnetic iron oxide pigments which are suitable for medical purposes, in particular as contrast agents for magnetic resonance imaging, and which have a distinctly reduced content of impurities.
We have found that this object is achieved by .gamma.-Fe.sub.2 O.sub.3 pigments and Fe.sub.3 O.sub.4 pigments with an average particle diameter of 2-100 nm, a saturation magnetization above 40 nTm.sup.3 /g, a remanence below 10 nTm.sup.3 /g, a Cr content below 40 mg/kg of pigment, a Cu content below 40 mg/kg of pigment and a C content below 100 mg/kg of pigment.
We have additionally found a process for preparing these pigments, and the use of these pigments as contrast agents in magnetic resonance imaging.
It is necessary to employ the iron or an iron oxide in highly pure form as precursor for preparing pigments of this type. Precursors of this type can be obtained from iron compounds obtainable by simple chemical or physical purification, preferably distillation. Particularly suitable for this purpose are volatile iron compounds, in particular iron carbonyls such as iron pentacarbonyl.
Iron pentacarbonyl can be prepared and purified by distillation in a conventional way, as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A14, pages 595-601 , VCH Verlagsgesellschaft mbH, 1989.
Iron can be obtained in a conventional way from iron pentacarbonyl by thermal decomposition at 60.degree.-300.degree. C., preferably 150.degree.-250.degree. C. Suitable for preparing iron oxides from iron carbonyls are normally oxidative decomposition of iron pentacarbonyl with oxygen or an oxygen-containing gas.
Iron oxides of these types, some of which are commercially available, have a considerable content of non-ferromagnetic iron oxides such as .alpha.-Fe.sub.2 O.sub.3 with a large particle size which is unwanted for use
REFERENCES:
patent: 4631089 (1986-12-01), Rademachers et al.
Ullmann's Encyclopedia of Industrial Chemistry, vol. A14, 5th Ed. pp. 595-601, 1989 no month.
Kormann Claudius
Schlegel Reinhold
Schwab Ekkehard
BASF - Aktiengesellschaft
Bonner Melissa
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