Strontium ferrite powders prepared from oily cold rolling mill sludge by solid-state reaction method

Oily cold rolling mill （CRM） sludge is one of the pollutants emitted by iron and steel plants. Recycling oily CRM sludge can not only reduce pollution but also bring social and environmental benefits. In this study, using oily CRM sludge as sources of iron oxide, the strontium ferrite powders were synthesized in multiple steps including vacuum distillation, magnetic separation, oxidizing roasting, and solidstate reaction. The optimal technological conditions of vacuum distillation and oxidizing roasting were studied carefully. To consider the effects of Fe203/ SrCO3 tool ratio, calcination temperature, milling time and calcination time on magnetic properties of prepared strontium ferrite powders, the orthogonal experimental method was adopted. The maximum saturation magneti- zation （62.6 mA-m2.g-1） of the synthesized strontium ferrite powders was achieved at the Fe203/SrCO3 mol ratio of 6, 5 h milling time, 1250 ~C calcination temperature, and 1 h calcination time. Strontium ferrite powders syn- thesis method not only provides a cheap, high quality raw material for the production of strontium ferrite powders, but also effectively prevents the environmental pollution.

Microstructure of pre-sintered permanent magnetic strontium ferrite powder

The microstructure and characteristics of pre-sintered strontium ferrite powder were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The present study shows that the pre-sintered strontium ferrite powder is provided with a certain particle size distribution, which results in high-density magnets. The strontium ferrite particle has a laminar hexagonal structure with a size similar to ferrite single domain. Ferric oxide phase due to an incomplete solid phase reaction in the first sintering is discovered, which will deteriorate the magnetic properties of ferrite magnet. In addition, the waste ferrite magnets with needle shape arranging along C axis in good order into the powders are found, which have no negative effects on finished product quality.

Tuning of magnetic properties of aluminium-doped strontium hexaferrite powders

M-type Al-doped strontium ferrite powders （SrA1xFe2n-xO19, n = 5.9） with nominal Al content of x = 0-2.0 are prepared by traditional ceramic technology. The phase identification of the powders, performed using x-ray diffraction, shows the presence of purity hexaferrite structure and absence of any secondary phase. The lattice parameters decrease with increasing x. The average grain size of the powders is about 300 nm-400 nm at Al3＋ ion content x = 0-2.0. The room- temperature hysteresis loops of the powders, measured by using vibrating sample magnetometer, show that the specific saturation magnetization （σs） value continuously decreases while the coercivity （Hc） value increases with increasing x, and He reaches to 9759 Oe （1 Oe = 79.5775 A/m） at x = 2.0. According to the law of approach saturation, Hc value increases with increasing Al3＋ ion content, which is attributed to the saturation magnetization （Ms） decreasing more rapidly than the magnetic anisotropy constant （Kl） obtained by numerical fitting of the hysteresis loops. The distribution of Al3＋ ions in the hexaferrite structure of SrAlxFe2n- xO19 is investigated by using 57Co Mtssbauer spectroscopy. The effect of Al3＋ doping on static magnetic properties contributes to the improvement of magnetic anisotropy field.