| 摘要 |
A ferromagnetic ferrite particularly one containing manganese and zinc contains 0.01-1 per cent by weight of calcium oxide in the boundaries separating grains forming the ferrite. Mn3O4 containing a small amount of CaO was prepared by heating carbonates of the metals in air at 950 DEG C. for 2 hours, or by coprecipitation of their oxalates. It was milled with specified proportions of Fe2O3 and ZnO, compressed, and heated for four hours in nitrogen containing oxygen to the extent which resulted in a small proportion of FeO in the finished ferrite as described in Specification 730,703 [Group XXXV]. In alternative methods, calcium carbonate was added to a mixture of the three other oxides. The heat treatment needed to produce a grain size in the ferrite resulting in optimum values of magnetic properties is discussed. Cavities formed in the ferrite were found in the boundaries with optimum grain size. |
