Xianyou Zhang

Effect of Surface-treated Nano-silica on Thermal Behavior and Flame Retardant Properties of EVA/ATH composites

The effects of nano-silica with different surface treatment on thermal stability, flame retardant properties and mechanical properties of ethylene-vinyl acetate copolymer (EVA) /alumina trihydrate (ATH) composites are discussed by thermal gravimetric analysis (TG), limited oxygen index (LOI) and tensile properties. The results of TG show better thermal stability of composites with nano-silica. The maximal weight loss rate is obviously decreased with the addition of nano-silica. Furthermore, the composites with surface treated nano-silica possess better thermal stability and lower weight loss rate. More residues left at 600°C reveal that surface treated nano-silica can promote the charring of the composites. Thus, improved flame retardant properties of composites with surface treated nano-silica can be discovered as a result of much higher LOI value. Meanwhile, such composites also show improved tensile properties than EVA/ATH at the same loading levels of fillers.

Synthesis of hexagonal barium ferrite nanoparticle by sol-gel method

Abstract M-type Ba hexaferrites were successfully synthesized by sol-gel method. Several synthesizing factors, such as pH value, citric acid/metal ion ratio, and dispersion agent were mainly discussed. Fine and pure powders of BaFe12O19 were optimally synthesized under the conditions of the pH value is 7 and citric acid/metal ion ratio is 3. The X-ray diffraction analysis demonstrates that no impurity is observed in the synthesized powders after presintered at 450 °C and calcinated at 1100 °C. SEM observations indicate that the size of the synthesized BaFe12O9 powders is small and uniform distribution. It can also be learned from SEM that the co-synthesizing sol-gel method can be in favor of the formation of finer particles.

Fabrication and characteristics of strontium barium niobate/barium strontium titanate ceramics by powder–sol method

Abstract Barium strontium titanate (Ba 1- x Sr x TiO 3 , BST) and strontium barium niobate (Sr x Ba 1- x Nb 2 O 6 , SBN) are important ferroelectric materials with excellent pyroelectric, dielectric properties and faster response time of infrared radiation. SBN/BST composite ceramics with different mole ratios of Nb and Ti were fabricated using a powder-sol (P-S) method with Nb 2 O 5 fine powders suspended in the barium strontium titanate (BST in short) sol solution. The X-ray diffraction results indicate that three intermediate phases, i.e. TiO 2 , BaNb 2 O 6 and SrNb 2 O 6 , are developed during the formation of SBN-BST. Powders obtained from dried gels are calcined at 800 ? for 3 h. The Ti 2p spectra of only one spin-orbit doublet are observed, which indicates one 4+ chemical state in the composite ceramics. The binding energies of Nb element depend strongly on composition.

Effects of surface modification of nano-silica on the thermal degradation and combustion Behaviors of LLDPE

In this paper, nano-silica with and without surface modification was used to prepare linear low density polyethylene (LLDPE) /silica composites whose thermal stability and combustion behaviors were investigated by thermal gravimetric analysis (TG) and cone calorimeter (CONE), respectively. As a result of TG, composites with surface modified nano-silica possessed better thermal stability than that with pristine nano-silica. The results of CONE proved better combustion properties of composites with surface modified nano-silica by showing reduced heat release rate (HRR) and mass loss rate (MLR).

Microstructure and Microwave Properties for Barium Magnesium Niobate

Relaxor-type ferroelectric perovskites (Ba,La)(Mg,Nb)O3(BLMN) ceramics have been synthesized from oxides by sintering in airs using a conventional mixed oxide process. From the XRD patterns, it is found that the amount of the perovskite phase increases with the increasing amount of La2O3. Furthermore, by the X-ray photoelectron spectroscopy (XPS) analyzation, it is discovered that the amount of Nb4+ is increased as La2O3 dopants increase from 0 to 0.04. Microwave properties of ceramics was also discusses in relation to the microstructure and density.

Effects of Surface Modification of Nano-silica on Combustion Behaviors of LLDPE/ATH/silica composites

In this paper, nano-silica with and without surface modification was added into linear low density polyethylene (LLDPE) to prepare LLDPE/silica or LLDPE/Aluminun trihydrate (ATH)/silica composites. Effects of surface modification of nano-silica on the dispersibility of silica in LLDPE and combustion behaviors of composites were investigated by Transmission electron microscopy (TEM) and cone calorimeter (CONE). The results showed silica without surface modification was not well dispersed in LLDPE owing to the severe aggregation of silica particles and its poor compatibility with LLDPE. Improved dispersibility of surface modified silica was found because of its improved compatibility with LLDPE. Obvious decrease of peak-HRR value was observed. Well dispersed silica after surface modification, as proved by TEM, should be contributed to the decreased peak-HRR. Because the shapes of two curves were similar, it was concluded that the mechanistic reason for the decreased HRR come mainly from the physical effects of silica on the surface.

Synthesis and photoluminescence of Ce 3+ and Tb 3+ doped double phosphates KMLaPO 4 (M = Mg, Ca, Sr)

Rare earth luminescent materials have become the main materials in information display, light engineering and here we describe a new approach to prepare the KMLaPO<inf>4</inf>: Ce, Tb. We take the X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer to study the structure and the morphology and elemental component, TG-DTA also used to investigate the sinter process. Our results indicate that the substitute of K⁺ and M²⁺ to La³⁺ can not change the structure of monocline. The SEM shows flaky morphology with average size about 1µm. The optical results suggest that K<inf>x</inf>Mg<inf>x</inf>La<inf>0.6−x</inf>PO<inf>4</inf>: Ce, Tb has highest photoluminescence intensity (PL), and the PL increase with the concentration of K⁺ and M²⁺ ions.

Researched on microstructure and density of sintered ZnO non-linear resistors

Systematic researched have been made of the grain growth and density of sintered ZnO-based systems containing one or more additive oxides of the type Bi2O3, MnO2, and CoO. These samples were characterized using such techniques as scanning electron microscopy. The influence of the nature and amount of additive oxides and sintering temperature at 950 to 1350°C is discussed in relation to microstructure, breakdown voltage and the density present.

Electrohydrodynamic enhancement condensation of dielectric liquid on the horizontal enhanced tube

The enhancement of condensation heat transfer is of practical importance in many industries such as Heating, Ventilating and Air Conditioning, power, and aerospace. The present work is concerned with the electrohydrodynamic enhancement of external condensation on single commercial enhanced tubes. Future phases of this work will include applying the technique to practical heat exchangers and developing a prototype of electrohydrodynamic condenser. Single tube experiments were performed on enhanced tube. The green refrigerant was R-134a, with the electrohydrodynamic voltage in the range 0 to 25 kV, saturation temperature 298 to 318K, and heat flux 35kW/(m K). The results indicated that the external heat transfer coefficient significantly increased under the effect of electrical field. The optimum heat transfer enhancement was approximately 2.6-fold, with electrohydrodynamic power consumption lower than 1.5% of the test section heat transfer rate. Key word: electrohydrodynamic, Enhancement Condensation, dielectric liquid, heat transfer

Study on heat transfer effect of in electrohydrodynamic model pipe

An electrohydrodynamic (EHD) enhancement heat transfer model was designed and made. This model is divided into three parts, they are vaporization section, adiabatic section and condensation section. The insulating liquid was selected as working fluid and the copper wire which diameter is 1mm was selected as the high voltage electrode. The proper insulation coordination was designed as well. The temperature difference in the inlet and outlet of the coolant in the vaporization section and the condensation section, and the saturation vapor pressure in the model were measured under different dc high voltage and different tilt angle, that is, the vaporization section was placed higher than the condensation section. The experiment results indicate: Such EHD enhancement heat transfer technology can be practically employed in the refrigeration and the heat transfer projects, and has special reference value for the investigation of antigravity heat pipes.