| 摘要 |
839,860. Magnetic compositions. PHILIPS ELECTRICAL INDUSTRIES Ltd. Aug. 7, 1956 [Aug. 10, 1955], No. 24172/56. Drawings to Specification. Class 38 (2). Ferromagnetic material suitable for use at frequencies of at least 50 mc/s. consists of simple and/or mixed crystals having a composition represented by the formula Ba 3 CO 2 Fe 24 O 41 of which up to one third of the Ba may be replated by Sr, Ca, and/or Pb. The crystals are hexagonal with a C-axis of about 52.3 Š and an A-axis of about 5.9 Š. The material is made by sintering in air or oxygen at a temperature not less than 1200‹ C., a mixture of oxides in suitable proportions, or of compounds such as carbonates, oxalates and acetates which convert to oxides on heating. The starting material may include preformed reaction products of two or more metal oxides, e.g. BaFe 12 O 19 having the structure of magnetoplumbite. The mixture is first ground in a ball mill with ethyl alcohol. The starting material may be presintered at 800-1100‹ C. reground, and, if desired, resintered several times. To facilitate sintering silicates or fluorides may be added, and an organic binder may be used when the material is pressed to its final shape. A number of examples of processes of manufacture exhibiting differences in detail are described, and properties of the products including values of their real permeabilities Á<SP>1</SP> are tabulated. For two examples curves are given showing variation of Á<SP>1</SP> and tan 8 = Á<SP>11</SP>/Á<SP>1</SP> with frequency (Figs. 1 and 2, not shown). |
