Papers by Author: Jin Ye Niu

Abstract: Fused Quartz crucible with large scale was formed by gelcasting processing in this paper. Effects of dispersant, pH values and particle grading on solids content of slurries were discussed to increase the volume density of the green compacts and decrease the shrinkage and deformation during sintering. Effects of acrylamide content and the ratio of acrylamide to coupling agent on bending strength of the green compacts were investigated. Effects of the amount of initiator and curing temperature on the gelcasting processing were studied as well. The green compacts with solids content of 80% was obtained when the addition ratio of dispersant to Quartz powders was 0.3wt %, the ratio of Quartz powders in D50 of 1.9μm and 7.6μm was adjusted to 3:7, the addition ratio of acrylamide to Quartz powders was 1.0wt % and the ratio of acrylamide to coupling agent was 16:1. The bending strength of the sinterred produts was found to be 76.0MPa with volume density of 1.94 g/cm2. Fused Quartz crucible prepared under conditions mentioned above was 800mm in length, 800mm in width and 400mm in height.

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: 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: 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%.

Abstract: With AlN, Al2O3 and Al powders as starting materials, ALON powders were prepared by high temperature solid state reaction at 1650°C, 1750°C and 1850°C respectively. Nitrogen gas at 1atm was selected as reaction atmosphere. X-ray diffraction analysis and scanning electron microscope analysis were carried out for the as-prepared ALON powders. In this paper, single-component γ-ALON porous materials were obtained at temperatures below 1800 degree with void ratio more than 75%, which is prone to be grinded to powders less than 1μm and applicable for the preparation of transparent ceramics. Aluminum oxynitride spinel γ-ALON transparent ceramics were successfully obtained with the as-prepared ALON powders. The volume density of the transparent ceramics was 3.67g/cm2, which is 99.3 percent of the theoretical density of γ-ALON materials. The bending strength of the transparent ceramics was 296MPa and the transmittance was about 75% in the wavelength range of 1.2 to 5.3μm.

Abstract: Silicon nitride coatings were prepared by chemical vapor deposition (CVD) method. The effect of raw precursor materials (SiH4 and NH3) ratio, gas flow amount, reaction temperature, and reaction pressure and deposition time to the microstructure, chemical compositions and crystal structures of the silicon nitride coatings are investigated. The results suggest that when the SiH4 and NH3 are used as the precursors, Ar is used as the protect gas, H2 is used as the carrier gas, the flow amount of SiH4 and NH3 is 200 sccm and 1000 sccm, the reaction pressure is 100 Pa, the reaction temperature is 900 oC and the deposition time is 30 min, the silicon nitride coatings with high deposition rate (~ 85 Å/min), small grain size (~ 0.2 µm) and high density are obtained. XRD results of the obtained silicon nitride coatings suggest their phase structure is amorphous.