Effect of sintering enclosures and sintering parameters on the magnetic properties of a high permeability manganese-zinc ferrite

Manganese-zinc ferrite (Mn0.52Zn0.41Fe2.07O4) has been prepared by the mixed-oxide route. Specimens were in the form of toroids, pressed in the green state to 11.9 mm outside diameter and 5.9 mm inside diameter. To assess the effect of zinc loss, a variety of circular local sintering enclosures were employed. All specimens were initially sintered in air at 1390 degrees C for times of 7.5-16 h, After cooling to 1200 degrees C they were held for 4 h in atmospheres containing 0.0125-0.05% oxygen, Sintered products were single-phase, with density greater than or equal to 95% theoretical and a grain size of about 20 mu m. Use of a partial sintering enclosure led to a 45% increase in initial permeability mu(i), but use of a full enclosure led to a reduction in mu(i), Firing the samples at 1200 degrees C in an atmosphere containing 0.025% oxygen yielded near-stoichiometric samples, in which the initial permeability was maximized (about 10 200) over a wide range of temperatures 25-90 degrees C. The eddy current losses in such samples were twice as high as for samples sintered in an oxygen atmosphere containing 0.05 % oxygen.