Papers by Author: Zhi Dong Han

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Authors: Zhi Dong Han, Qing Rui Zhao, Li Min Dong, Ze Wu, Xian You Zhang
Abstract: Nano-size BaM hexaferrites (BaLa0.5Fe11.5O19) were synthesized in the presence of SiO2 nano- particles by sol-gel method. The X-ray diffraction (XRD) patterns of ferrites annealed at above 900°C manifested that all the species had hexagonal crystal structure and no diffraction peaks of SiO2 found. Compared with BaLa0.5Fe11.5O19 powders, those synthesized in the presence of SiO2 nano-particles presented in smaller powder size, as proved by scanning electron microscopy (SEM). As a result, SiO2 nanoparticles promoted the formation of more homogeneous and finer ferrite crystal while the structure of hexaferrites consisted with that synthesized without SiO2 nano-particles. Microwave absorbing properties were evaluated. As a result, BaLa0.5Fe11.5O19/SiO2 showed good microwave absorbing properties with the maximum absorption more than 20dB.
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Authors: Li Min Dong, Zhi Dong Han, Ze Wu, Xian You Zhang
Abstract: A novel ceramic synthesis technique, microwave-assisted process was investigated for the production of Barium Hexagonal ferrite (BaFe12O19) powders with improved physical properties. Compared to conventional syntheticroute, the new method significantly shortened synthetic steps and reaction time. This technique involves the reaction of stoichiometric amount of metal nitrates and appropriate dosage of citric acid at microwave oven and the whole process took only 15 min. The powders of BaFe12O19 were further investigated by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results showed that the formation temperature of M-type Ba hexaferrite is significant low, compared to conventional furnace heating. The X-ray diffraction analysis demonstrates that the phase purity of the microwave-processed samples were determined and compared with a conventionally processed material. SEM observations indicate that the size of the synthesized BaFe12O19 powders is small and uniform distribution. Thus, microwave irradiation is proved to be a novel, extremely facile, timesaving and energy-efficient route to the synthesis of BaFe12O19 powders.
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Authors: Li Min Dong, Yan Li Zhuang, Zhi Dong Han, Ze Wu, Xian You Zhang
Abstract: Green phosphor of La(BO3, PO4): Ce, Tb was synthesized by means of sol-gel method and conventional solid state method. The thermal formation process was characterized by thermogravimetric analysis (TG) and (DTA). The effects of synthesis method and conditions on the crystal and morphological structure were investigated by (XRD) and (SEM). The results revealed that La (BO3, PO4): Ce, Tb phosphors with monocline structure and high purity were successfully prepared by sol-gel method. Compared with solid state method, the products synthesized by sol-gel method presented well developed crystal structure, small particle size, narrow size distribution and high luminescent performances. The product synthesized at 1050°C for 2h had better emission intensity.
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Authors: Zhi Dong Han, Li Min Dong, Ze Wu, Xian You Zhang
Abstract: The paper aims at synthesizing La substituted BaM hexaferrites (BaLa0.5Fe11.5O19) in the presence of SiO2 nano-particles by sol-gel method. Effects of SiO2 nano-particles on the structure and particle size of hexaferrites are investigated by XRD and SEM. Magnetic properties of BaFe12O19, BaLa0.5Fe11.5O19 and BaLa0.5Fe11.5xO19/SiO2 are compared by vibrating sample magnetometer (VSM). The XRD patterns of BaLa0.5Fe11.5O19/SiO2 calcined at 1000°C manifest that all the species have hexagonal crystal structure and no diffraction peaks of SiO2 are found. Compared with BaLa0.5Fe11.5O19 powders, those synthesized in the presence of SiO2 nanoparticles present in smaller powder size, as proved by SEM. The results of VSM reveal that BaLa0.5Fe11.5O19 possesses much higher saturation magnetization than BaFe12O19. BaLa0.5Fe11.5xO19/SiO2 also shows higher saturation magnetization than BaFe12O19, but lower than BaLa0.5Fe11.5O19 because of addition of nano-SiO2.
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Authors: Li Min Dong, Zhi Dong Han, Ze Wu, Xian You Zhang
Abstract: Green-emitting Y3Al5O12: Tb phosphor materials have been widely studied because of their high luminescence efficiency and stability under the conditions of high irradiance with an electron beam. In this paper, Green-emitting phosphor of yttrium aluminum garnet (Y3Al5O12 or YAG) doped with Tb3+, Ce3+ and Gd3+ was synthesized by sol-gel method. By means of TG/DSC, XRD, and photoluminescence (PL) performance, the sintering condition and its influence on the powder’s emitting performance were studied. The experimental results showed that, Y2.8Tb0.12 Ce0.08-x GdxAl5O12 synthesized by sol-gel method was a kind of phosphor of good performance. When the value of x was set at 0.04, the best emitting performance was obtained. The Y3Al5O12: Tb, Ce, Gd particles had fine size, spherical shape, filled morphology, high crystallinity, and good brightness.
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Authors: Zhi Dong Han, Li Min Dong, Ze Wu, Lian Wei Shan, Xian You Zhang
Abstract: BaFe12O19 and La-Mn substituted M-type Ba hexaferrites were synthesized by sol-gel method and characterized by XRD, SEM and FTIR. The results showed that citric acid played an important role in the forming process of BaFe12O19. BaFe12O19, synthesized under lower citric acid and presintered at 450°C, showed improved hexagonal crystal phase. BaLa0.5Fe11.5O19 and Ba(MnLa)0.5Fe11O19 showed similar crystal structure to BaFe12O19 while Ba0.5Mn0.5Fe12O19 and Ba0.5Mn0.5La0.5Fe11.5O19 showed changed crystal constant. FTIR analysis proved the formation of new mental-oxygen bond in substituted hexaferrites.
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