Xiao Zhan Yang

Preparation and Properties of BN-SiO2 Composite Ceramics

A series of BN-SiO2 composite ceramics with high relative densities have been fabricated by hot pressing of a mixture of hexagonal boron nitride powder and silica sol. X-ray diffraction (XRD) results show that silica are distributed in the BN matrix as noncrystalline state. Microstructure of as-sintered composite ceramics is observed by scanning electron microscopy (SEM). The influence of the secondary phase on the mechanical properties is studied by varying the silica content from 10 wt% up to 40 wt%. Dielectric properties of composite ceramics are also measured from 1 MHz to 2.0 GHz.

Synthesis of Ordered Mesoporous Carbon Using MCM-41 Mesoporous Silica as Template

Mesoporous carbon with high surface area and ordered structure was synthesized via a nanocasting process using mesoprous MCM-41 silica as a template and sucrose as a carbon precursor. Sample was characterized by XRD, SEM, TEM and nitrogen adsorption. The results show that the templated carbon has a BTE surface area ∼1200 m2/g, a pore volume ∼1.0 cm3/g, and a bimodal porosity centered at around 4 nm and 46 nm.

Properties and Microstructure of Optically Transparent Polycrystalline Spinel

Fully transparent polycrystalline spinel(MgAl2O4)has been prepared by combined vacuum sintering and hot isostatic pressing. This paper investigated transparent polycrystalline spinel optical properties sintered in different atmospheres and discussed the effect of sintered processing parameters on the development of the microstructure and transmission properties. The optical transmittance of the specimen sintered at 1500°C following HIPed at 1800°C was nearly the same as that of single crystal spinel. The transmission properties of spinel can be improved with the increase of temperature and pressure of sintered/HIPed spinel. Specimens sintered in vacuum following HIP have higher transmittance than those sintered in air or in hydrogen.

Fabrication and Characterization of Porous Mullite Coating on Porous Silicon Carbide Support

Mullite powders of stoichiometric composition were synthesized by sol-gel process with TEOS and Al(NO3)3·9H2O as silicon and aluminum source. Homogeneous mullite powders were used as the starting materials to prepare the porous mullite coating on the porous silicon carbide support by repeated dip-coating method. XRD analysis revealed that the mullite precursor gels almost completely transformed to orthorhombic crystalline mullite at 1200°C. The average pore diameter and porosity of the porous mullite coating were about 4.5µm and 52.3%, respectively.

Preparation of Porous Wollastonite Ceramics for Filtration

Wollastonite powder was selected as a starting material with carbonate as pore-forming agent and binder added. The porous ceramics were prepared at different temperature by sintering method. The process includes batching, granulating, pressing molding, drying and sintering. It is discussed the influence of sintering temperature, dosage of binder, dosage of pore-forming agent, pressure of molding and holding time on the performance of porous ceramics. According to the principle of particles stack, the porous wollastonite ceramics for filtration with various diameters, shapes and porosity were fabricated by serial experiments. These products have 1 to 10 microns in pore size, 30.04 to 66.15% in porosity, 2.82 m2/g in specific surface area.

Preparation of TiO2 Nanocrystalline Films by Electrophoretic Deposition and their Application in Dye-Sensitized Solar Cells

TiO2 nanocrystalline films were prepared by electrophoretic deposition (EPD) under a pulseperiodic electric field. The EPD behavior of TiO2 nanocrystalline suspension was investigated. The uniform 9.2-μm-thick TiO2 film was obtained by reasonably controlling the EPD condition. A dye-sensitized solar cell, with the EPD TiO2 film as the photoanode, obtained about 4.1% of photon-to-electron conversion efficiency (η). Its Jsc, Voc and fill factor (ff) are 11.6 mA/cm2, 0.65 V and 0.55, respectively. The effect of TiCl4 modification on the photovoltaic property of the solar cell was also discussed.

Synthesis and Characterization of Regular Hexagonal NiCo2O4 Nanosheets

In this article, the spinel NiCo2O4 nanosheets with diameters of 100-200 nm were prepared by calcinations of co-precipitates, which were obtained by co-precipitation method. Different kinds of precipitants, including NaOH, KOH, Na2CO3 and ethanedioic acid aqueous solutions were investigated, and regular hexagonal nanosheets are synthesized only when the precipitant is strong KOH or NaOH solution. The morphology and structure of the hexagonal precursor particles and nanosheets were investigated, and the mechanism of the formation of hexagonal nanosheets is discussed.

Relation between Porosity and Permeability of Ceramic Membrane Supports

A membrane support provides mechanical strength to a membrane top layer to withstand the stress induced by the pressure difference applied over the entire membrane and must simultaneously have a low resistance to the filtrate flow. Due to their low thermal-expansion coefficient and good thermal-shock resistance as well as excellent mechanical and chemical stability at elevated temperatures, porous SiC ceramics have been widely used as catalyst supports and hot-gas or molten-metal filters. In this work, the influence of the particle size, sintering time and sintering temperature on the porosity and permeability of supports made by dry-pressing of micron-sized SiC powders is investigated. The present work presents a comparison of properties and performance data for samples made with different particle size. The effects of sintering time and temperature were analyzed in view of overall porosity and permeability. From calculations it becomes clear that optimum values exist for the material properties of the support.

Synthesis of Titanium Dioxide Nanotubes by Ion Exchange Approach

Nanotube-shaped powders had been synthesized successfully from commercial anatasetype titanium dioxide powder by ion exchange approach. All nanotubes were open-ended with 3~5 nm in inner diameter, 8~12 nm in outside diameter and 200~400 nm in length. EDS result revealed that the nanotube was only composed of Ti and O. XPS analysis showed that two peaks located at 458.5 and 464.2 eV were assigned to Ti4+ in titanium dioxide. The formation mechanism of titanium dioxide nanotubes was also discussed in this paper.

Preparation of Ni-Co Spinel Oxide by Alloy Oxidation Method

In this paper, NiCo2O4 spinel oxide was synthesized by the oxidation of Ni-Co alloy. The variables that affect the formation of spinel oxide include the Ni-Co ratio in the alloy, the oxidation temperature and time. 350°C is the upper oxidation temperature limit. And longer oxidation time is helpful. Surface roughness analysis shows that with the formation of NiCo2O4, the surface shows rougher.