Investigation And Preparation Of The Core-nanoshell Composite Materials Doped With Rare Earth

In this paper, the core-nanoshell composite materials, that iron-rich hollow cenosphere as nuclear and ferrite doped with rare earth as core, were prepared by high-energy ball milling solid-state reaction method using iron-rich hollow cenosphere, rare earth and iron nitrate as main raw materials.When the hollow cenosphere in the higher content of iron, it is called iron-rich hollow cenosphere, which recovered from the thermal power plant fly ash, mainly chemical composition are Fe2O3 and Fe3O4, followed by SiO2 and Al2O3; iron-rich hollow cenosphere are strongly magnetic materials, which are density, mechanical strength, good stability, and the average particle size is less than 75μm.Rare earth with abundant magnetic properties are concerned at present, due to the unique 4f electronic structure of rare earth.which has a high magnetic moment, high magnetic anisotropy, high magnetostriction coefficient, high magneto-optical effects and low magnetic ordering transition temperature (called "four high and one low") and the complex structure of magnetic ordering and other characteristics, especially when the formation of rare earth complexes with other elements, the more abundant magnetic, electrical and optical properties will be reflected.The core-nanoshell composite materials doped with rare earth were prepared, influences of the process conditions (including the pretreatment of iron-rich hollow cenospheres, the milling time and the calcination temperature) on the phase structure, particle size and the morphology were studied. The key process conditions of preparing excellent performance composite materials were obtained:①when prepared the core-nanoshell composite materials by high-energy ball milling solid-state reaction method, the pretreatment of iron-rich hollow cenospheres was needed, which could remove surface impurities, and improve their compatibility and reactivity;②controlled milling conditions:When the milling rate was 200r/min, milling time was 30min, the spherical and well dispersed composite materials were received;③controlled calcination conditions:the precursor was preheated at 450℃for 1h, and then tempered at 800℃for 3h, which called two-step heat treatment, can prevent the formation ofα-Fe2O3 intermediate and improve product purity.Thermal analysis were studied by means of thermalgravimetric analysis-differential thermal analysis(TG-DTA). The phase and the sample size were determined by means of X-ray diffraction (XRD) and the Scherrer formula. Scan electron microscope(SEM) and energy dispersive (EDS) were used to examine the morphology and composition of material. Magnetic properties were measured by vibrating sample magnetometer(VSM). Some important results were concluded:the core-nanoshell composite materials with iron-rich hollow cenosphere as nuclear were obtained under the optimal conditions. On the one hand, can reduce the density of the composite; on the other hand, the formation of two-phase exchange coupled composite wrap layer between the cenosphere and ferrite doped with rare earth, obtaining the light, magnetic composites, moreover, providing a theoretical basis for further development of iron-rich hollow cenosphere.Compared to single-phase ferrite materials doped with rare earth, the magnetic properties of core-nanoshell composite materials had been greatly improved, such as the relative remanence of core-nanoshell composite materials doped with Sm increased 0,06 and the coercivity enhanced to 7.5KOe. In addition, high-energy ball milling solid-state reaction method doesn't use solvents, which have many features such as high selectivity, high yield and the simple process. This method is suitable for the promotion of industrialization, and has some practical value.