Ting Xian Xu

Strength of Liquid-Phase-Sintering Cordierite Ceramics

The high dense pure cordierite ceramics and liquid-phase-sintering cordierite ceramics were prepared with the starting powder made by sol-gel progress. The porosities of them are less than 6.21%, and some can be up to 1.0% especially. The flexural strength of the sample can get to 167 MPa, which is greater than that of 103 MPa of pure cordierite ceramics. The composition, fracture behavior and microstructure of the liquid-phase-sintering cordierite ceramics are investigated. The result shows that the increased flexural strength is mainly attributed to the change in cell parameters of cordierite and the small grain size.

Preparation and Properties of Low-Temperature Sintered SrBi4Ti4O15/Ag Composites

Strontium bismuth titanate (SBTi) matrix composites containing Ag particles were synthesized by the conventional solid-state reaction method. The SBTi/Ag composites have been characterized by various techniques: x-ray diffraction, optical metallurgical microscope, scanning electron microscope and dielectric measurement. It is found that Ag doping significantly affect the physical properties of composites. By adding Ag particles to the SBTi matrix, the single-phase layered perovskite structure of the matrix is preserved and the sintering temperature of the system decrease from 1120°C of the single-phase SBTi to 950°C of the SBTi/Ag composites. With the increase of sintering temperature, the size of silver particles increase, but the SBTi grains have no significant growth. The SBTi/Ag composites show a significant change of the dielectric constant. By increasing Ag content, a gradual increase of the dielectric constant is observed and the dielectric loss of the SBTi/Ag composites remain unchanged when the temperature rangers from room temperature to 200°C, however, the Curie peak of dielectric constant is repressed, which has been interpreted based on the effective dielectric fields developed around conducting phases and the inhibition effect of nonferroelectric secondary phase to electro-strain.

Preparation and CO2 Gas Sensitive Properties of CuO-SrTiO3-Based Semiconductor Thin Films

CuO-SrTiO3-based thin films were prepared by novel sol-gel technology on Al2O3 substrates using Cu(NO3)2, SrCl2 and TiCl4 as the starting materials, critic acid and ethylene glycol as chelating agents. CO2 sensing properties of the films were investigated. Structure characteristics of the sol and asgrown thin films were analyzed by FT-IR spectrum, X-ray diffraction and SEM. The results reveal that the films consisted of CuO phase and SrTiO3 phase have nanocrystalline microstructure at 750°C for 40 min. The modified CuO-SrTiO3 thin films exhibit good resistance-temperature and gas sensitivity properties in a wide range of temperature. The films exposed to 6% CO2 show that sensitivity are 32, and response and recover time are within 2 s at 250 °C operating temperature.

Study on Stability of Nano-Al2O3 Aqueous Suspension

Al2O3 ceramic fillers were incorporated into polyetheretherketone (PEEK) to improve the mechanical property in order to suit its aerospace application. To get the high performance composite, it is important to control the dispersion of the nano-Al2O3 among the PEEK matrix. As a pre-fabrication process, the dispersion behaviors of the nano-Al2O3 particles in the liquid medium were studied. Thestability of suspensions was characterized by zeta potential, sediment volume, viscosity and TEM analysis. The mechanism of dispersing nano-Al2O3 aqueous suspension has been investigated including single-electronic stabilization, steric stabilization, and electrostatic stabilization. The highly dispersed and stabilized nano-Al2O3 aqueous suspensions were obtained at acidic condition (pH=3) with PEG-400 and tri-ammonium citrate (TAC).

Properties of Silicon Nitride Using Cordierite as Sintering Additives

Silicon nitride materials with low dielectric properties were prepared using nano and micron silicon nitride powders as raw materials and the green bodies were sintered with cordierite as sintering additive in flowing nitrogen. The additives of cordierite powders prepared by sol-gel method and solidstate reaction method could greatly decrease the sintering temperature. The dielectric constant of materials decreased as sintering temperature fell, whereas the strength showed relatively low as the low sintering temperature. XRD analysis showed the main phase of material was Si2N2O, which indicated that the Si3N4 could be integrated with SiO2. Porous structures were observed by SEM, showing compact sintering cannot be achieved at these temperatures, explaining the low strength.

Resistivity-Temperature Properties of La(TixMn1-x)O3 Ceramics

Samples of La(TixMn1-x)O3 (0.1 ≤ x ≤ 0.7) were sintered at different temperatures. The experimental results showed that the resistivity-temperature curves of the samples match NTC characteristic. The crystal structure was analyzed using X-ray diffraction and the microstructure was observed by scanning electron microscope.

Effect of Various Dispersants on the Gel-Casting of Silicon Nitride

A high solid loading of dispersed silicon nitride slurry was prepared with various dispersants, which allowed a stable silicon nitride suspension with sintering additives (cordierite) in alkaline regions to a solid content of 45 vol%. Gum arabic, PMAA-NH4, TMAH, PAA-NH4 and their composites were selected as dispersants. The results suggested that the composite dispersant which was obtained using PAA-NH4 and TMAH with the ratio in 4:1 was more effective in aqueous silicon nitride powder suspensions system than simplex dispersant. The green bodies derived exhibited a mechanical strength as high as 8.7MPa and SEM photos revealed that the green body also had a high homogeneity.

Study on Gas Sensing Properties of WO3 Thin Films

Tungsten oxide thin films were prepared by an inorganic-sol-gel dip-coating process, where the sol was obtained by adding citric acid, as chelating agent, to the ammonia solution of tungstic acid. The resultant thin films were a mixture of monoclinic and tetragonal phases of WO3 and, after being pretreated at 600°C and sintered at 650°C, the average grain size of the polycrystalline films was about 500 nm. The gas-sensing properties of WO3 thin films were tested at temperatures ranging from 500° to 600°C and in nitrogen gas containing 5vol% O2 or 5vol% H2. The WO3 sensors exhibited a good sensitivity and response speed at the temperature of 550°C.

Production of Si3N4 Whiskers in Solid Mixtures through Vapor-Solid Mechanism Using 2MgO 2Al2O3 5SiO2 as Sintering Additives

The production of silicon nitride whiskers in solid mixtures under nitrogen-containing atmospheres was investigated. Green bodies made of micron and nano silicon nitride powders with 2MgO×2Al2O3×5SiO2 as sintering additive were sintered at 1500~1560oC in flowing nitrogen-containing atmospheres. Resultantly whisker-like products were formed on the cold side of the graphite boat. X-ray diffraction analysis indicated that the formed whisker were α–Si3N4. The products were analyzed by transmission electron microscope. The morphologies of the resulting whisker were varied with sintering temperatures and atmospheres. Dislocation structures were observed on the edge of some whiskers. This suggested that the whisker growth proceeded through a vapor-solid (VS) mechanism. The mechanism of whiskers growth at different temperatures and atmospheres was discussed with a thermodynamic calculation based on a database software.

Preparation of SrBi2Ta2O9 Ferroelectric Thin Films by Liquid Source Misted Chemical Vapor Deposition Method Using Inorganic Salt Solution

A liquid source misted chemical vapor deposition (LSMCVD) system was used to deposit SrBi2Ta2O9 ferroelectric thin films on Pt/TiO2/SiO2/Si substrates using strontium nitrate, bismuth nitrate and fluorine tantalum acid as the starting ingredients. Citric acid, ethylene glycol, and ethylenediaminetetraacctic acid were employed as chelating agents to form homogeneous and stable sol. A density, homogenous, crack-free and c-axis oriented SrBi2Ta2O9 thin films were prepared successfully and the resultant thin film exhibits the ferroelectric properties of 2Pr of 3.8 C/cm2, 2Ec of 60kV/cm at ±3.5 V, respectively.