Synthesis And Magnetic Properties Of Nanocrystal Barium Ferrite By Glycine-nitrate Process

Barium ferrite is a Permanent magnetic material with high magnetic anisotropy, high coercivity and excellent chemical stability, so it been widely used as permanent magnet, magnetic recording materials,tape and disk,high-performance nano-Ferrite absorbing agent. The micro-structure has great influence on magnetic properties for barium ferrite, when the particle size of barium ferrite reached its single-domain critical dimensions, the coercivity reached the maximum value. In order to obtain barium ferrite with small size and good single phase, various preparation methods had been developed in recent years, for example: ceramics, chemical co-precipitation method, sol-gel method, hydrothermal method and so on,The purpose of these preparation methods is to obtain the nano-sized barium ferrite under low sintering temperature, which could improve the magnetic properties of the permanent magnetic materials.The glycine - nitrate combustion method has been widely used to prepare materials of fuel cells, however, the preparation of nano-crystalline barium ferrite with glycine - nitrate combustion method has been reported hardly. First, the resulted powders with glycine - nitrate process dispersion, single crystallinity, narrow particle size distribution, and high purity; Secondly, the glycine - nitrate combustion method is easy to operate with short experimental period, because the reactants dispersed uniformly in the solutions, the atom could enter the lattice sites through short-proliferation or rearrangement, the fast react speed and low formation temperature of glycine - nitrate combustion method resulted in small particle size and uniform distribution, which were advantages of the sol-gel technology and low-temperature combustion synthesis technology respectivly. The purpose of this work is to prepare nano-fuel Barium ferrite particles: with glycine nitrate combustion method. Glycine works as a complexing agent of barium ferrite , in order to have better magnetic properties of samples, and get good single phase. The calcination temperature, metal ions ratio, holding time, glycine and the ratio of four metal ions were(1) The optimal stoiehiometry of metal ion (Fe/Ba )= 10.8.Antlfemimagnetie BaFe₂O₄ can be found in the sample with less iron, the coereiveforce of barium ferrite increased,.which can be explained by the pitining effect of BaFe₂O₄. BaFe₂O₄ and a-Fe₂O₃ can be found in the sample with more iron, the coereiveforce of barium ferrite decreased.(2). The optimal reaction temperature is 850℃.The resultant magnetic parameters of barium ferrite are Hc =5102Oe, Ms = 53.72emu/g,and the grain size is about 80-150nm;When the calcined temperature reached 950℃, the grain size is about 200-600 nm;and the coercive force decrease due to the formation of multidomain. The resultant magnetic parameters of barium ferrite are Hc = 4992Oe, Ms = 54.72emu/g, and the grain size is about 80-150nm.(3) The optimal holding time of heat treatment is four hours. Intermediate phases were observed when the holding time is less than four hours,Longer holding time will give an increase of the grain size and a decrease of the coercivity.(4) The optimal stoiehiometry of (G/N) is G/N = 3.5. when G/N = 2, the actual temperature of combustion is too low, a-Fe₂O₃ is generated at this low temperature, so pure barium ferrite phase is generated difficultly .When G / N = 2.5, G/N = 3, the magnetic parameters of barium ferrite dose not reach the best value. With grain size increasing, and larger than single-domain critical size, magnetic properties also increase. When G/N = 3.5, the grain size is in single-domain and is larger than the critical size, coercivity reached the maximum value .When G/N = 4,the grain size is about 300-600 nm, and the coereive force deerease due to the formation of multidomain.