Improvements in methods of producing magnetic cores having hysteresis loops which approach rectangularity

摘要

828,185. Magnetic compositions. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct. 25, 1957 [Oet. 30, 1956], No. 33401/57. Drawings to Specification. Class 38 (2). A magnetic core having a rectangular hysteresis loop is made by sintering at 1350‹- 1450‹ C. in an atmosphere containing more oxygen than air, a shaped body containing 49-52% mol. Fe 2 O 3 , 14-40% mol. MgO, 9-35% mol. NiO, and 0.5-1.5% mol. CoO, the sintered body being treated in an alternating or direct magnetic field at a temperature between the Curie point and 150‹ C. The initial mixture containing oxides or compounds which convert to oxides on heating may be prefired at 750‹-1000‹ C., subsequently ground and compressed. The magnetic field may be applied while cooling the body from sintering or during reheating after sintering. The manufacture is described of a large number of bodies of differing compositions by grinding Fe 2 O 3 with carbonates of Mg, Ni and Co in ethyl alcohol, prefiring in air at 800‹ C. for 2 hours, regrinding, compressing into rings, sintering in oxygen at 1420‹ C., for 2 hours and cooling in a direct magnetic field of 100 Oersted after subsequent heating in air to 500‹ C. Squareness ratios are given for these compositions and also for cores having the composition 24.9% mol. MgO, 19.6% mol., NiO, 1.0% mol. CoO and 50% mol. Fe 2 O 3 after cooling from different temperatures in a direct magnetic field. Curves are given (Fig. 2, not shown), for one core to show that the rectangularity does not vary much over a range of values of magnetizing force despite changes in room temperature.