Han Zhidong

Preparation and Sinterability of Mn-Zn Ferrite Powders by Sol-Gel Method

Abstract Mn-Zn spinel ferrites were synthesized by sol-gel method. Effects of calcined temperature on structure and particle size of MnZnFe 2 C 4 were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns indicate that the ultra fine Mn-Zn ferrite exhibits a spinel crystal structure. SEM images show that the powder fired at 900 °C for 2 h has an average diameter of 60 ∼ 90 nm. The particle size becomes larger with the increasing of calcined temperature and the distribution of particle becomes even more homogeneous. Sintering behaviors of synthesized ferrite powders depend on the powder characteristics and high temperatures have induced the good crystallization of particles.

Structure of BaLaxFe12-x O19/SiO2 Synthesized by Sol-Gel Method

Abstract M-type hexaferrites BaLa x Fe 12-x O 19 powders were synthesized by sol-gel method in the presence of SiO 2 nanoparticles. The X-ray diffraction patterns of BaLa x Fe 12-x O 19 /SiO 2 calcined at 1000 °C manifest that all the species have hexagonal crystal structure and no diffraction peaks of SiO 2 are found. The structure of BaLa x Fe 12-x O 19 seems uniform at different La doping dosage. Fourier transform infrared (FTIR) proves the co-existence of SiO 2 and ferrites in the products. The addition of SiO 2 nanoparticles promotes the formation of more homogeneous and finer ferrite crystal, as proved by scanning electron microscopy (SEM). Compared with BaLa 0.5 Fe 11.5 O 19 powders synthesized without SiO 2 nanoparticles, those synthesized in the presence of SiO 2 nanoparticles present in smaller powder size and similar structure.

The Dielectric Properties for Yttrium Doped SBT Thin Films Prepared by Sol-Gel Method

In this work, Sr0.5Ba0.5Ti1-zYzO3 (SBT) thin films were prepared on a Pt/SiO2/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by IR, XRD and TEM. The influences of Y on the microstructure and dielectric properties of Sr0.5Ba0.5Ti1-zYzO3 thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Increasing Y doping has a clear effect on the grain size of SBT. It is found that the proper Y doping content decreases dielectric loss for SBT thin films.

Preparation of Zn-Al hydrotalcite and its modification with sodium dodecyl sulfate and 2-carboxyethyl phenyl phosphinic acid

Zn-Al hydrotalcites were prepared by coprecipitation method with the Zn/Al molar ratio of 3:1, 2:1 and 1:1. Sodium dodecyl sulfate (SDS) and 2-carboxyethyl phenyl phosphinic acid (CEPPA) were adopted to modify hydrotalcite by coprecipitation method. The structure of Zn-Al hydrotalcites and the modified ones were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS). XRD results indicated that the layered structure of Zn-Al hydrotalcites was influenced by the Zn/Al molar ratio. The Absorption peaks of Organic groups were observed in FT-IR Spectroscopy of SDS-LDH and CEPPA-LDH, which proved successfully synthesis of SDS modified LDH and CEPPA modified LDH. The SEM and EDS results confirmed the existence of SDS and CEPPA in the modified products, which are consistent with FT-IR results. The successful intercalation of SDS and CEPPA increased the interlayer space of LDH, which makes modified LDH promising and preferable as flame retardants in nanocomposites.

Distribution of Al 2 O 3 in PE/EVA blends and the thermal conductivity of PE/EVA/Al 2 O 3 composites

This paper aims at dispersing nanoscale Aluminium oxide (Al₂O₃) in Polyethylene/Ethylene Vinyl Acetate copolymer blends (PE/EVA) to improve the thermal conductivity of the composites. Blends of PE and EVA were prepared at different PE/EVA ratio, and PE/EVA blends with co-continuous structure were obtained. PE/EVA/Al₂O₃ composites were prepared by dispersing different amount of Al₂O₃ into co-continuous PE/EVA blends. Scanning Electron Microscopy (SEM) was used to observe the morphology of PE/EVA/Al₂O₃ composites treated by selective solution extraction. The thermal conductivities and mechanical properties of PE/EVA/Al₂O₃ composites were investigated. SEM results indicated that Al₂O₃ was observed to selectively localize in PE phase. Moreover, the selective distribution of Al₂O₃ and the co-continuous structure of the composites were helpful in improving the thermal conductivity and mechanical properties, leading to a 20.9% increase of thermal conductivity of PE/EVA/Al₂O₃ composites in comparison to that of PE/Al₂O₃ composites.

Preparation of graphite nanosheets/TiO 2 composites and photocatalytic performance

Graphite nanosheets / Titanium dioxide composites (GN/TiO₂) were fabricated via sol-gel method which use tetrabutyl titanate as Ti source and different ratio of GN/TiO₂ were prepared. The composites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic properties of GN/TiO₂ composites were evaluated by using Methyl orange. XRD results indicate that the composites show distinct diffraction peaks of antase-type TiO₂ and graphite. TEM results proved the uniform dispersion of TiO₂ particles on the nanosheets of GN. The ratio of GN and TiO₂ exerted significant influences on the photocatalytic properties of the composites. GN/TiO₂ composite with GN and TiO₂ ratio of 1:0.15 expressed excellent photocatalytic properties.

Experimental Investigations on Yttrium Borate Phosphate Phosphors with Codoped Ce3+ and Tb3+ Ions

Abstract Green phosphor of Y(BO3, PO4): Ce, Tb was synthesized by means of sol-gel and conventional solid state methods. The thermal formation process was characterized by thermogravimetric analysis (TG) and differential thermal analysis (DTA). The effects of synthesis conditions on the crystalline and morphological structures were investigated using the X-ray diffraction (XRD) and Scanning Electronic Microsocpy (SEM). The results revealed that Y(BO3, PO4): Ce, Tb phosphors with the monocline structure and high purity were successfully prepared by the sol-gel method. Furthermore, the products synthesized by the sol-gel method showed a well developed crystal structure, small particle size, narrow size distribution, and high luminescent performance. The product synthesized at 1050 °C in 2 h had better emission intensity than the others.

Thermal degradation of polyethylene/layered double hydroxides nanocomposites

Mg-Al layered double hydroxide (LDH) was modified with sodium dodecyl sulfate (SDS) by regeneration method. Polyethylene/modified LDH composites (PE/SDS-LDH) were prepared by melt blending and solution mixing method. Maleated polyethylene (PEgMA) was used to improve the compatibility between LDH and PE. The dispersion of LDHs in PE matrix was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). Thermal degradation of PE/SDS-LDH composites was characterized by thermogravimetric analysis (TGA). The results reveal that PE/PEgMA/SDS-LDHs microcomposites were obtained by melt blending method and PE/PEgMA/SDS-LDHs nanocomposites were prepared by melt blending PE with SDS-LDH/PEgMA master-batch obtained by solution mixing. Due to the thermal decomposition of LDHs at much lower temperature than PE, the degradation of composites begins at low temperature regardless of the dispersion of LDH in PE. The initial degradation temperature corresponding to 5% weight loss of nanocomposites is higher than that of microcomposites. Compared with microcomposites, the nanocomposites present the higher temperature corresponding to the maximum thermal degradation rate and more residues at the end of thermal degradation, indicating the better barrier properties and charring effects of nano-dispersed LDH.

Pyroelectric 0.7BaO·0.3SrO·0.5Nb 2 O 5 ·0.5TiO 2 composite ceramics by Powder-Sol method

0.7BaO·0.3SrO·0.5Nb<inf>2</inf>O<inf>5</inf>·0.5TiO<inf>2</inf> (SBN/BST) composite ceramics were, for the first time, fabricated using a Powder-Sol (P-S) method with Nb<inf>2</inf>O<inf>5</inf> fine powder suspended in the barium strontium titanate (abbreviated as BST) sol solution. X-ray diffraction (XRD) investigations revealed that the tetragonal tungsten bronze (TTB) phase and perovskite phase were co-present in compositions. Scan electron microscope (SEM) investigations showed that the composite ceramic is homogeneous and fine-grained. The average grain size of BST and SBN phase is 200 nm and 3.0 µm, respectively. The room temperature relative dielectric constant is 2320 for this sample measured at 1 kHz and zero bias. The pyroelectric coefficient of the 0.7BaO·0.3SrO·0.5Nb<inf>2</inf>O<inf>5</inf>·0.5TiO<inf>2</inf> is found be 70 nc/cm²·°C in the room temperature.

Microwave-Induced Combustion Synthesis of Hexagonal Barium Ferrite Powders

A novel ceramic synthesis technique, microwave-assisted process was investigated for the production of Barium Hexagonal ferrite (BaFe^Oip) powders with improved physical properties. Compared to conventional synthetic route, 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 BaFe^Oy were further investigated by X-ray diffractometer (XRD), infrared spectroscopy (IR), 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.