Magnetic Materials Obtained from Silicate Melts in the System Fe<sub>2</sub>O<sub>3</sub>-MnO-Alkali Oxide-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>

Abstract

Most commercial products of ferrites are made by firing preformed powder mixtures of raw materials. This conventional method, however, is not adapted for obtaining products of the special shapes such as fiber and film. In this study we undertook to examine the possibility of obtaining magnetic materials from melted silicates containing Fe2O3 and MnO and of forming the melts into desired shapes by the ordinary glass-forming technique.The compositions of the melts studied were of 7.5-20% Fe2O3, 7.5-20% MnO (or CoO and NiO), 0-5% Li2O (or Na2O and K2O), 0-15% Al2O3, and 55-70% SiO2(mole). The raw materials were ferrous oxalate, manganese dioxide, cobaltic oxide, nickel oxide, lithium-, sodium- and potassium carbonates, aluminium hydroxide and potter's flint powders. Their mixtures to yield about 50 gram of melts were heated in sintered-alumina crucibles in an electric furnace at temperatures from 1300° to 1400°C. Their melting behaviors and the workability of their melts into shapes of fiber or plate during cooling were investigated. X-ray diffraction analysis and magnetic measurement were made on materials quenched in air.The results obtained are as follows:1) The melts of the compositions, 7.5-15% Fe2O3, 7.5-20% MnO, 0-5% Li2O (or Na2O and K2O), 5-15% Al2O3, 55-70% SiO2 (mole) were fluid at temperatures 1300°-1400°C, and were able to be formed into desired shapes during cooling.2) The intensity of magnetization of quenched specimens reached up to 18 gauss/g at the field of 10, 000 oersteds. Magnetization increased with increasing the content of Fe2O3 or Fe2O3+MnO, and decreased with increasing the content of Al2O3. The specimens of high Fe2O3 content saturated magnetically at a fairly weak magnetic field whereas the specimens of Fe2O3 content less than 15mole% did not saturate even at the field as strong as 5, 000-10, 000 oersteds. The followings are some examples of the composition which showed high magnetization and magnetic saturation at a weak magnetic field.3) Separation of fine crystallites of spinel-type ferrites was confirmed by X-ray analysis in some of quenched specimens containing high amount of Fe2O3. The average size of the crystallites estimated from the broadening of X-ray diffraction peaks was 60-150A.4) Reheating quenched specimen generally increased the intensity of magnetization and also accelarated magnetic saturation at weak magnetic field.