He Ping Zhou

Morphotropic Phase Boundary Study of the BNT-BKT Lead-Free Piezoelectric Ceramics

A lead-free piezoelectric ceramic binary system based on bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)-bismuth potassium titanate (Bi0.5K0.5)TiO3 (BKT) was synthesized by conventional mixed-oxide technique. The XRD analysis showed that the rhombohedral-tetragonal morphotropic phase boundary (MPB) of the Bi0.5 (Na1-xKx)0.5 TiO3 system was in the composition range of x = 0.16 ~ 0.20. In addition, the piezoelectric properties of this system were also investigated. It was indicated that the piezoelectric properties are better with the compositions near the rhombohedral phase within the MPB than the compositions near the tetragonal phase.

Synthesis of Nano-Sized SrTiO3 Photocatalyst by Sol-Gel Method

A sol-gel processing technology was employed to synthesize fine SrTiO3 powder by using strontium nitrate (Sr(NO3)2) , butyl titanate (Ti(OC4H9)4) as precursors, citric acid (C6H8O6) as complexing agent and (ethylene) glycol (C2H6O2) as stabilizer. Prepared the precursors in liquid phase and then calcined the precursors to achieve nano-sized SrTiO3 powders. The microstructure and composition of the as-synthesized samples were characterized by X-ray diffraction (XRD), Scan Electron Microscopy (SEM), and the photocatalytic activity was studied. The results showed that all the SrTiO3 particles were identified as perovskite phase. The pH values, the content of the acetic acid, the heat treat temperature play important roles on the synthesis of the SrTiO3 photocatalyst. When the pH=1, n(Sr(NO3)2 ) : n(Ti(OC4H9)4) = 1 : 1, n(Sr(NO3)2 ) : n(C6H8O6)=1:1.7, the product has better rate of photodegradation for the Methylene Blue under the ultraviolet condition.

Study of Structural and Dielectric Properties of Ba0.6Sr0.4(ZrXTi1-X)O3 Ceramic

BaxSr1-xTiO3 [(BST), 0£x£1] is a solid solution ferroelectric material exhibiting a large dielectric constant non-linear change with an applied DC electric field. And Ba(ZrxTi1-x)O3 solid solution also has received much attention because of the good tunbality. In this paper, Ba0.6Sr0.4(ZrxTi1-x)O3 (x=0.15,0.20,0.25,0.30,) ceramic was obtained by traditional ceramic processing. The structural, surface morphological, dielectric properties, tunable properties of this material as well as the mechanism of their nonlinear dielectric constant under DC electric field were systematically examined. The Zr ions substitution of Ti ions has a strong effect on the grain sizes and the dielectric property. The results show that Ba0.6Sr0.4(ZrxTi1-x)O3 (x = 0.2, 0.25,0.3) ceramic is a promising candidate for the DC electric field tunable materials for microwave electronics application, because they exhibit high relative tunability (44%, 48%, 35%, respectively) as the strength of electric field is up to 1.5 kV/mm, and low dielectric loss (0.0026, 0.00044, 0.0015, respectively) at 100 kHz at room temperature. X-ray diffraction analyses indicated that the samples present perovskite phase. Scanning electron microscopy micrograph of sample indicated that the grain size decreased and density increased with Zr concentration increasing.

Effects of Fuel Content and Calcination Procedure on Phase Composition and Microstructure of LiMn2O4 Prepared by Solution Combustion Synthesis

Spinel LiMn2O4 was prepared by solution combustion synthesis. The effect of fuel content and calcination procedure on phase composition and microscopic structure of LiMn2O4 was studied. X-ray diffraction patterns showed that fuel content had no obvious influence on the grain size and phase purity of LiMn2O4. Higher calcination temperature led to higher phase purity, lager grain size, and better crystallization of resultant LiMn2O4. Below 600°C the effect of calcination time was inconspicuous, which became notable above 700°C. Scanning electron microscope images showed that nanocrystalline LiMn2O4 was obtained when the calcination temperature was lower than 600°C and the grain size increased at higher temperatures.

Particle Size Control in Sol-Gel Synthesis of Nano Hydroxyapatite

Sol-gel method is one of the most potential techniques for mass-production of nano hydroxyapatite. In this paper, particle size control techniques, including dripping speed control, addition of several dispersants such as ammonium citrate, castor oil and silane coupling agent, as well as usage of insoluble and water soluble starch additives, were investigated. The particle size and microstructures of as synthesized hydroxyapatite were studied by X-ray diffraction, Scanning electron microscopy and dynamic light scattering. The results indicated that all the control techniques had considerable effects on decreasing the crystallite size, and the starch additives also exhibited obvious effect on preventing the agglomeration of nano crystallites during the synthesizing process.

Study on Thermal Conductivity of SPS-Sintered Si3N4 Ceramics after Heat-Treatment

α-Si3N4 ceramics were sintered at a low temperature of 1773K by using a spark-plasma-sintering (SPS) method with different heating rates, and then they were further heat-treated at different temperatures from 1773K to 2273K, to study the effect of the heating rate of SPS on the microstructure and the thermal conductivity of Si3N4 ceramics after the heat-treatment. Results show that the heating rate of SPS has great influence on the phase transformation and the microstructure of the β-Si3N4, but it has little influence on the thermal conductivity of the ceramics. This proves that the thermal conductivity of the ceramics does not have an obvious relationship with the ratio and the size of the columnar β-Si3N4 grain.

The Influence of Bi3+ on the Sintering of Cordierite Glass Ceramic

The effects of Bi3+ addition on the sintering performance and microstructural evolution of cordierite were analyzed in this paper. Cordierite powders were prepared by sol-gel processing. As nucleating agent, the Bi3+ additive was found to promote the phase transition from µ-cordierite to α-cordierite and decrease sintering temperatures. The effect of Bi3+ on the activation of cordierite can be attributed to the nucleation of cordierite. The doping of Bi3+ increased the expansion coefficient and dielectric constant. Too much Bi3+ will inhibit the cordierite crystallization and encourage anorthite crystallization.

Preparation of (Ca+M) (M=Mg, Yb, Sr) Co-Doped α-SiAlON Powders by Combustion Synthesis

In this paper, α-SiAlON powders co-doped with (Ca+M) (M=Mg, Yb, Sr) were prepared by combustion synthesis. The effect of Ca incorporation on the phase composition and grain morphology of reaction products was discussed. The experimental results showed that Ca incorporation promoted the growth of rod-like α-SiAlON crystals in (Ca+Mg) and (Ca+Yb) systems. For (Ca+Sr) system, the addition of Ca assisted Sr into α-SiAlON crystal lattice and increased the relative content of α-SiAlON in reaction product.

Study on Phase Transformation and Microstructure Development of Yb α-SiAlON Ceramics Prepared by Pressureless Sintering

In this paper, single-phase Yb α-SiAlON ceramics were prepared by pressureless sintering and the densification, phase transformation as well as microstructure development were studied. It was demonstrated that the phase transformation could be completed at 1700 °C and elevated temperature was beneficial to grain growth. Additionally, effect of the addition of seed crystals prepared by combustion synthesis was discussed. From the experimental results, it was found that the added seed crystals facilitated the phase transformation and improved the microstructure development, resulting in the formation of elongated grains.

Effects of Technical Parameters on the Phase Composition and Microstructure of Yb α-SiAlON Prepared by Combustion Synthesis

In this paper, Yb a-sialon powders with elongated grains have been prepared by combustion synthesis. The effects of diluents, nitrogen pressure, adding a-sialon seeds and NH4F on the phase transformation and microstructure development of the samples are discussed systematically. The experimental results show that the addition of diluents, proper nitrogen pressure and additive NH4F can facilitate the nitridation of Si. It was also found that the added a-sialon seeds and NH4F are beneficial to the nucleation and growth of elongated grains.