Preparation Of Magnetic Nanocomposites And The Study Of The Magnetic Properties

The permanent magnetic nanocomposite with alkali-earth and rare-earth powders, magnetic fluid were firstly synthesized using novel techniques---sol-gel combustion synthesis method, sol-gel packing method and sol-gel process. Samples are using as compound absorber, medium of magnetic record, magnetic memory and lubricant. Based on theoretical analysis and experimental studies, the effects of the pH of solution, the kinds and amounts of complexing agents, the adding of dispersant, and the condition in heat treatment of the gel on crystal phase, particle size and magnetic properties of ultra-fine powders were firstly investigated systematically to clarify the optimum forming conditions.The thermal analyse of dried gel was carried out by means of differential thermal analysis (DTA) with a heating rate of 10℃/ min. The phase of the samples was determined by X-ray diffraction (XRD) and infrared spectrometer (IR). The microstructure was observed by scanning electronic microscope (SEM). Magnetic measurements were conducted by vibrating sample magnetometer (VSM). Some important results are summarized as follows:Ⅰ. Preparation of new pattern permanent magnetic nanocomposite and foundation of sol-gel packing method.1 On the base of clarifying the optimum forming conditions, BaFe12O19/γ-Fe2O3, SrFe12O19/γ-Fe2O3, SmFeO3/γ-Fe2O3 and NdFeO3/γ-Fe2O3 were prepared, which are new pattern permanent magnetic nanocomposite with small size (about 20nm), narrow size distribution and high magnetic properties. These four powders are not seen to report.2 Sol-gel packing method was founded, which combines sol-gel with liquid packing.this method can solve powder dispersing preferably.3 The permanent magnetic nanocomposite as compound absorber and medium of magnetic record is analyzed and studied.Ⅱ. The permanent magnetic nanocomposite powders with alkali-earth The permanent magnetic nanocomposite powders with alkali-earth BaFe12O19/γ-Fe2O3 and SrFe12O19/γ-Fe2O3 were synthesized by sol-gel combustion synthesis method1 The automatism combustion of the gel is correlation with the mol ratio of nitrate and citric acid. The ratio influence little on the structure of powders, but the magnetic properties will be improved when the amount of citric acid increase.2 The optimum forming conditions is gained, these small magnetic particles allow effective exchange coupling between hard and soft magnetic phases and result in the simultaneous enhancement of the magnetic properties.Ⅲ. The permanent magnetic nanocomposite powders with rare-earthThe permanent magnetic nanocomposite powders with rare-earth were synthesized by sol-gel packing method1 Sol-gel packing method can design and clipping the pit-shell composite particles in the structure and can improve the disperse of nano-powders. The (BH)max of its block is 221 kJ m-3.2 The permanent magnetic nanocomposite prepared by sol-gel packing method has less rare-earth than tradition quench quickly, mechanical alloying method, and the cost is depressed, which display enhancement of permanent magnetic and antisepsis properties. The tenacity property has been improved because the permanent magnetic nanocomposite contains soft magnetic.Ⅳ. Magnetic fluidThe magnetic fluid of Fe3O4 and CoFe2O4 were prepared, which take the coal oil, water and alkyl as the carrier liquid .1 Fe3O4 and CoFe2O4 magnetic particles were prepared by novel sol-gel process. The optimum parameter of prepared Fe3O4 and CoFe2O4 nanoparticles were determined. When the pH was about 7, the particles modified by the surfactant were scattered in the carrier liquid. The magnetic fluid was prepared. The factors, which influence magnetic fluid properties, such as type of surfactant, quantity of surfactant, modified temperature, modified time, pH, action of ultrasonic, centrifugal effect, were discussed. The density and the viscosity of magnetic fluid were also measured.2 The total iron—Fe[x] in the magnetic fluid was used to express the stability of magnetic fluid, The effects on the stability of magnetic fluid were discussed, such as the gravity, the centrifugal force, the depositing condition, then the effects on the magnetism of magnetic fluid were discussed.