Papers by Author: Zhi Wei Chen

Abstract: Lithium dizirconium phosphate (LiZr2(PO4)3) possesses good ionic conductivity owing to its unique framework structure and can be used as favorable anode material in Li-ion battery. LiZr2(PO4)3 is commonly prepared by solid phase reaction in which higher temperature is needed and pure LiZr2(PO4)3 without other phases is difficult to obtain in the final products. In this paper, low cost hydrothermal synthesis of pure (LiZr2(PO4)3) was studied. Effects of the hydrothermal conditions (molar ratios of Li+ to ZrOCl2, addition of HF, pH values of reaction system and hydrothermal temperatures) on the phase composition of the products were investigated. The results showed that pure LiZr2(PO4)3 was successfully prepared at lower temperature of 80°C for 24h with the addition of HF when the pH value was adjusted to 5.0 and the molar ratio of Li+ to ZrOCl2 was 0.5 with the concentration of ZrOCl2 as 0.6mol/L. The phases and purity of the final products were characterized by XRD analysis.

Abstract: The grain boundary character distribution (GBCD) and its effect on the corrosion resistance of copper and brass (H65, H80) after solid solution and cold-rolled annealing were investigated by means of static weight loss method, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Electron back-scattered diffraction (EBSD).The possible mechanism of the effect of proportion of low ∑ coincidence site lattice (ΣCSL) on corrosion resistance were discussed preliminary. The results show that the proportion of low ΣCSL of the three kinds of samples after cold rolling and annealing all increase obviously compared with samples in solid solution. The proportions of low ΣCSL( such as Σ3,Σ9 and Σ27 ) of H65 brass,H80 brass and copper increase in turn in the same heat treatment conditions. In addition, it can increase the grain boundary ratio of low ΣCSL up to 67.9% by cold rolling of 6% and annealing at 650°C for 10min; The corrosion experiments show that corrosion resistances of samples after heat treatment are much better than that in solid solution. In the three samples, the corrosion resistance of copper is the best and that of H80 brass is better than that of H65 brass. Key words: copper; brass; GBCD; corrosion resistance

Abstract: Two observation techniques of internal microstructure, including hole and second particle, of micron scale powders have been established and applied to frangible and tough powders. One is that powders were embedded in epoxy resin, sectioned by an ultramicrotome, then observed by using the transmission electron microscopy (TEM) in turn; another is that the fracture of powders were observed by using the scanning electron microscopy (SEM).

Abstract: Determination of particle size and shape factors of the corundum powders by SEM image analysis has been reported in our preceding work. However, the effect of sample preparation and image processing has not been investigated. In order to obtain appropriate images, samples was well-dispersed by vibrating particles manually up and down, and then thicker Pt coating was well sputter coated on the surface of samples; compared with the magnifications of 100 and 32, magnification of 50 was more reasonable; for distinguishing particles from image background properly, the gray threshold value of 70 was set to transform gray image to binary image; to decrease image noises, three image filters, i.e. Erosion Filter, Dilation Filter and Median Filter were investigated and the last one was the most effective. This method of sample preparation and image processing can be used in regular and irregular particles determination.

Abstract: Fused silica micro-powders with D₅₀ of 1.8μm were firstly prepared by ball milling. Effects of milling time on particle size distribution and microstructures of the powders were discussed. Then, the green compacts with volume density of 1.86g/cm³ was obtained by slip casting with lactic acid as dispersant. Effects of lactic acid content on apparent viscosity of the slurry, thickness and density of the green compacts were investigated. Finally, fused silica ceramics with thermal expansion coefficient of 0.56∙10^-6/°C, bending strength of 64MPa and volume density of 1.94g/cm³ were prepared.

Abstract: ALON ceramics with optimal mechanical and optical properties were obtained by cold isostatic pressing the as-prepared powders at 180 MPa and sintering at 1900°C under N2 atmosphere for 8h. Microstructures and IR transmittance of ALON prepared under different sintering conditions were studied systematically to discuss the effect of microstructures on mechanical properties and IR transmittance. In addition, IR spectra of transparent ALON test pieces in different thickness were collected. The results demonstrated that the bending strength decreased while IR transmittance increased with the increase of grain size of ALON ceramics; with the increase of thickness of ALON test piece, IR transmittance decreased and the scope of the decrease reduced with the increase of grain size of ALON ceramics.

Abstract: Nano-TiO2 coating film is one of the efficient photocatalysts. The particle size distribution of TiO2 has important influence on photocatalytic activity. A new method to determine the particle size distribution of TiO2 nano-film coated on ceramic was developed, by which the images of film acquired by Atom force microscope (AFM) were processed, and TiO2 particles contacted with others were separated and detected. The particle size distributions of two TiO2 nano-films were determined.

Abstract: The shape of inorganic powder particles, prepared by spray-drying process, is close to sphere, and the dry conditions have greater effect on the sphericity. The particle shape is normally described by words or shown by micrographs — these are qualitative and imprecise. In order to characterize the particle shape quantitatively, three shape factors, i.e. aspect ratio (M), roundness (R) and concavity (C), are proposed to describe the particle shape of the inorganic powders in different aspects. An image process method, that “holes” were filled and then particle clusters were separated, was developed and applied in scanning electron microscope (SEM) image in which some particles with “shadow” contact with each other. Mean shape factors, based on about 500 particles in 10 micrographs, are proposed to characterize the particle shape of the inorganic powders. The determination results of four inorganic powders show that cracking catalyst powders without silicon additive and produced after rebuilding of the spray-drying device are closer to spheres.

Abstract: Fully densitified 3Y-TZP (>98% of theoretical density) ceramic tools have been prepared by gelcasting and sintered with conventional pressureless at 1500 ~ 1600°C. The microstructure and mechanical properties as a function of sintering temperature were investigated. The experiment results indicate that the samples with a range of grain size from 300nm to700nm have high mechanical properties. With the sintering temperature rising, the hardness show no obvious change, the average value is 13.2GPa; while the bending strength have a trend of first increasing then decreasing. The optimal sintering temperature is 1550°C, the bending strength and the fracture toughness all reach the maximum, which is 947 MPa and 8.9MPa.M1/2.

Abstract: The integrated translucent alumina tube used in metal halide lamps have been fabricated by gelcasting process. The influence of sintering process, various sintering fluxes on the micro- structure was discussed. Furthermore, the relation between the luminance and the microstructure was also investigated. The results reveal that when the sintering temperature is 1750°C, the holding time is 6h, the compact product whose average grain size is about 20μm could be obtained; the triple dopant combinations of MgO, Y2O3, La2O3 can promote sintering and improve the microstructure more than double, single dopants and the contents of sintering flux are 99.6wt%Al2O3, 0.2wt%MgO, 0.1wt.%Y2O3 and 0.1wt.%La2O3 respectively; The transmittance increases with the pore decreaseing, the grain size enlarging and the degree of the surface finish improving, the average in line transmittance is about 40%.