Thermal Instability and Microstructure of Strontium M-type Hexaferrite Nanoparticles Synthesized by Citrate Approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy （ IR ）, thermogravimetric analysis （ TG ）, differential scanning calorimetry （ DSC ）, X- ray diffraction（ XRD ） techniques, energy dispersive spectroscopy（ EDS ）, and transmission electron microscopy（ TEM ）. The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600℃ were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6℃ determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanopartieles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possibl α-Fe2O3 . The agglomerated particles with sizes less than 200 nm obtained at 800℃ were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanopartieles with sizes less than 100um cotdd take place at 900 ℃ . Up to 1000 ℃ , the phose transformotion to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α- Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of stroutium M-type hexaferrite , SrFe12-x□O19 （0≤x ≤0.5）.

Thermal instability and microstructure of strontium M-type hexaferrite nanoparticles synthesized by citrate approach

The dried gel of SrFe₁₂O₁₉, prepared by citrate approach, was investigated by means of infrared spectroscopy (IR), thermograimetric analysis (TG), differential scanning calorinetry (DSC), X-ray diffraction (XRD) techniques, energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600°C were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6°C determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanoparticles were decomposed into SrFeO_2.5 with an orthorthombic cell and Fe₂O₃ with a tetragonal cell as well as possible α-Fe₂O₃. The agglomerated particles with sizes less than 200 nm obtained at 800°C were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanoparticles with size less than 100 nm could take place at 900°C. Up to 1000°C, the phase transformation to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1 μm were composed of α-Fe₂O₃ and strontium M-type hexaferrite. The method of distinguishing γ-Fe₂O₃ with a spinel structure from Fe₂O₃ with tetragonal cells by using powder XRD method was proposed. Fe₂O₃ with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α-Fe₂O₃ as an additional phase appears in the calcinations is the cationic vacancy of strontium M-type hexaferrite,SrFe _l2-x▭_x O ₁₉(0⩽x⩽0.5). 3 Funded by Hi-tech Research and Development Program of China (863-2001AA339020) and Open Foundation of State Key Laboratory of Advanced Technology for Materials Synthesis and Processing (No. 2003 SJ-10)