GB1406503A - Magnetic materials - Google Patents

Abstract

1406503 Ferrites IMPERIAL CHEMICAL INDUSTRIES Ltd 1 Aug 1973 [11 Aug 1972] 37544/72 Heading C1J A ferrite comprises, in addition to its main components (defined), an additional modifying metal (defined) having a limited solubility in the ferrite, present in an amount in excess of that which can normally dissolve, this excess being present in significant proportions within at least part of the interior of the ferrite grains in addition to being present at the grain boundaries. The excess modifying metal when in the grain interior may either be in the form of a supersaturated solution or a precipitate. The main components may be Mn/Zn, Cu/Zn, Ni/Zn, or Ba. A suitable preparation involves co-precipitation (e.g. with ammonium carbonate or bicarbonate) of the metals as isomorphous salts (e.g. carbonates) and heating to form the ferrite, which may in turn be calcined, granulated, shaped and sintered to form a magnetic material. In a particular preparation an aqueous solution of the salts of the main components and additional modifying metal is mixed with an aqueous solution containing ammonium bicarbonate at least 30% in excess of that stoichiometrically necessary to precipitate the metal ions as carbonates which precipitated mixture is then heated (e.g. above 500‹ C.) to form the ferrite composition. The salts may be nitrates, sulphates or chlorides and precipitatable sols. (e.g. SiO 2 ) may also be included. In the examples Mn/Zn ferrites are prepared having as modifying metals of limited solubility, Ca, and also a modifying metal of much higher solubility namely Ti. Other modifying metals of limited solubility referred to in the case of Mn/Zn ferrites are Sr and Ba.