Protocol for the synthesis of Ba-hexaferrites with prefixed coercivities

Abstract The ferrite industry is one of the largest consumers of iron oxides, usually in the form of hematite from the roasting of steel pickling liquors or from mineral sources. In previous papers we have tested an oxidation process for obtaining magnetite and goethite from steel pickling liquors and two mathematical models have been proposed for synthesizing these two iron oxides. In this paper, the characteristics of magnetite and goethite are related with the coercivity of hexaferrites synthesized when the former are used as raw materials. Constant conditions were used for the ceramic method. Using goethite, Ba-hexaferrite is obtained only when the goethite is precipitated at the lowest oxidizer flow. When magnetite is used, a protocol with a statistically validated correlation is proposed for synthesizing hexaferrites with coercive fields between 230 and 450 kA/m. This correlation is valid for an oxidation process carried out at stirring speed of 1000 rev/min and with an air flow between 7.5 and 101/min. A second empirical correlation is proposed for obtaining final coercivities between 450 and 525 kA/m, for which it is necessary to increase the calcination time.