Ying Chun Zhang

Fabrication of Li2TiO3 Ceramic Pebbles by Gelcasting Method

Lithium titanate (Li2TiO3) ceramic pebbles are considered to be a candidate material of the tritium breeders for fusion reactor from the viewpoints of good tritium recovery, chemical stability and other excellent properties. In this study, fine grain and pure Li2TiO3 powders were prepared by solid-state method at 700°C using TiO2 and Li2CO3 as raw materials. Li2TiO3 pebbles were prepared by gel-casting method using acrylamide (AM) as organic monomer, N,N’-methylenebisacrylamide (MBAM) as cross-linker, ammonium citrate as dispersant, and isooctyl alcohol as defoamer. The effect of solid content, dispersant, pH and the ball milling time on the fluidity and dispersion of ceramics slurry were investigated, and the effects of sintering temperature and holding time were also discussed in present study. The sintered ceramic pebbles with diameter of 1.0 mm show a smooth surface, uniform grain size and perfect sphericity. The Li2TiO3 ceramic pebbles sintered at 1250°C for 8 hours had the highest density (> 90% of theoretical density) and crush strength.

Preparation of ZnNb2O6 Nano-Powders by Pechini Method

ZnNb2O6 ceramics with a columbite crystal structure, is a promising candidate for application in microwave devices. In this study, ZnNb2O6 nano-powders were prepared using Nb2O5 and Zn(NO3)2 as raw materials by Pechini method. The microstructure and crystal structure of ZnNb2O6 powders were investigated systematically using X-ray powder diffraction and SEM techniques. The effect of amount of citric and ethylene on the formation of sol-gel and the particle size of ZnNb2O6 powders were also investigated using orthogonal design. Finally, the optimum process parameters for synthesis ZnNb2O6 nano-powders were obtained in this study.

Microstructure and Microwave Dielectric Properties of Ba5(Nb1-xTax)4O15 (x = 0 ~ 0.5) Ceramics

The Ba5(Nb1-xTax)4O15 (x=0~0.5) solid-solution ceramics with hexagonal perovskite structure were prepared by solid-state oxide route. The phases and structure of the sintered ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of composition and sintering temperature on the bulk density, microstructure and microwave dielectric properties were also investigated. As the value of x increased from 0 to 0.5, the Q×f value increases from 36,049 to 49,493 GHz (at ~9GHz), whereas the dielectric constant (εr) decreases from 39.21 to 33.03 and the temperature coefficient of resonant frequency (τf ) decreases from 78.6 to 19.4 ppm/oC. The results indicate that the microwave dielectric properties of Ba5(Nb1-xTax)4O15 ceramics can be easily modified in a large range by changing the relative content of Ta to Nb.

Preparation and Characterization of Bi2Ti2O7 Microwave Dielectric Ceramics by Citrate Sol-Gel Method

Bi2Ti2O7 microwave dielectric ceramics were synthesized by a modified sol-gel method using citric acid as metal chelating agent. The thermal decomposition behavior of the as-prepared precursor was characterized by XRD technique. The effects of the amount of citric acid and the molar ratio of bismuth nitrate to tetrabutyl titanate on the crystal structure of Bi2Ti2O7 were also investigated. XRD results showed that well-crystallized Bi2Ti2O7 powders could be synthesized by calcining the precursor at 550 °C as the molar ratio of CA to Bi was 1:1. Moreover, non-stoichiometric ratio of Bi to Ti was required to form the pure Bi2Ti2O7 phase. However, Bi4Ti3O12 and Bi2Ti4O11 second phases were formed after sintering process. At 1150 °C, only the sample doped with 3 wt% Ho3+ showed a single pyrochlore structure, which exhibited good microwave dielectric properties with a high εr of 115.02, a Q × f of 1,515 GHz, and a τf of 30 ppm/°C.

Clay Minerals as a Feasible Additive to Stabilize Cadmium in Contaminated Soils

The adsorption behavior of clay minerals in cadmium contaminated soils has been studied in order to remedy soils contaminated with this metal in this work. The results show that Langmuir model best describes the adsorption of Cd2+, and the maximum sorption values of 8.45 mg/g for bentonite, 5.69mg/g for sepiolite and 10.57mg/g for attapulgite are obtained at pH 5-6. In addition, the effect of clay minerals amendment on a highly cadmium contaminated soil has been studied by means of pot experiments. The results indicate that the metal concentrations in shoot and root of plant decreased with addition of clay minerals to soil (1%), and the highest decrease value of metal concentrations is obtained in the soils added by attapulgite amendment.

Preparation of Li4SiO4 Ceramic Pebbles by Agar Method Using Li2SiO3 and Li2CO3 as Raw Materials

Lithium-containing ceramic pebbles, the likeliest tritium breeders in the future, are needed in the fusion reactor blankets. Currently, lithium orthosilicate (Li4SiO4) has been widely studied for tritium breeding pebble as it has 1250 °C melting temperature, 0.54 g/cm3 lithium concentration, and excellent tritium release performance. For simplifying reaction mechanism and the preparation technology to tailor the properties, the Li4SiO4 breeders were produced with an agar-gel technology using stable and cheap lithium metasilicate and lithium carbonate as starting materials. In addition, the solid (the prepared powder and ager) and liquid (deionized water) weight ration of the green pebble was also evaluated. The crush load, density, and open porosity achieved 36 N, 89.3% TD, and 4.5 %, respectively.

Synthesis of YAG Powders by Co-Precipitation Method

In this paper, yttrium aluminum garnet (YAG) powders were synthesized by the normal-strike co-precipitation method (adding precipitant solution to the metal nitrate solution). Aluminum nitrate (Al (NO3)3 9H2O) and yttrium nitrate (Y(NO3)3 6H2O) were used as raw materials and ammonium hydrogen carbonate (AHC) was used as the precipitant. The precursor was calcined at the temperature of 900-1200 °C for 2 hours. The crystal structure and microstructure of YAG powders were investigated and analyzed by XRD, FESEM, TG-DTA and laser particle size analysis. The results show that the concentration of metal ion and AHC have a significant effect on crystal structure of YAG powders, and pure YAG powders were obtained at 1000 °C when the concentration of Al3+ was 0.1 mol/L and the concentration of AHC was 1 mol/L. The average primary crystallites particle sizes were ranged from 50 nm to100 nm in diameter. nanosize YAG powders with excellent properties and good dispersity can be produced at the temperature of 1100 °C.

Effects of Ta5+ Substitution on Structure Transition and Microwave Dielectric Properties of Zn(Nb1-xTax)2O6 Ceramics

The crystal structure, phase relation, microstructure and dielectric properties of microwave dielectric ceramics comprised of Zn(Nb1-xTax)2O6 were investigated systematically using XRD, SEM and a network analyzer in this study. XRD results show that the Zn(Nb1-xTax)2O6 ceramics have the orthorhombic for all x values. However, two kinds of solid solutions phase regions based on columbite structure and ZnTa2O6 structure were observed. SEM results show that the growth of grains is restrained with increase of Ta content in Zn(Nb1-xTax)2O6 ceramics. The dielectric properties exhibited a significant dependence on the crystal structure and compositions of the ceramics. The dielectric constant (εr) of Zn(Nb1-xTax)2O6 ceramics increased with increasing Ta content. However, the quality factors (Q×f) of this system show a different trend, and decrease with increasing Ta content. At x=0.65, a zero temperature coefficient of resonant frequency ( τ f) can be realized in Zn(Nb1-xTax)2O6 ceramics system.

Corrosion Resistance Properties of Carbon Nanotube Reinforced Electroless Composite Coating

The carbon nanotube reinforced Ni-P matrix composite coating on 45# steel has been prepared by electroless plating method in this study. The microstructure and the corrosion properties of the composite coating were investigated systematically using SEM and a potentiostat. SEM results show that the carbon nanotube was uniform embedded in the crystal grains of Ni-P. The polarization curves indicate that the composite coating exhibit excellent corrosion resistance properties which is superior to that of the conventional Ni-P coating.

Effects of CuO Addition on the Microstructure and Microwave Dielectric Properties of MgTa2O6 Ceramics

MgTa2O6 powders with the tetragonal phase have been synthesized by mixed oxide method at 1100 °C when the molar ratios of MgO and Ta2O5 increase from 1:1 to 1.2:1. The microwave dielectric properties of sintered MgTa2O6 ceramics without additives at 1400°C for 6h, which consists of tetragonal and orthorhombic phases have been investigated. The results show that the ceramic possesses a dielectric constant of 27.5, a high Q×f value of 156000 GHz and a temperature coefficient of resonant frequency of 21.6 ppm/°C at 6-10 GHz. Different amounts of CuO has been used as sintering additives to lower the sintering temperature of MgTa2O6 ceramics. The effect of the CuO doping agent on the microstructure, densification and the microwave dielectric properties of MgTa2O6 ceramics has been studied using X-ray diffraction, scanning electron microscope and HP8720ES network analyzer. The results indicate that the 1-5 wt. % CuO dopant can lower the sintering temperatures of this materials dramatically. The second phase of CuTa2O6 was found in MgTa2O6 ceramics, which caused the deterioration of Q×f value of the ceramics.