Papers by Author: Dao Yuan Yang

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Authors: Dao Yuan Yang, Hui Yu Yuan, Fen Ling Qian, Juan Wu, Kai Zhu, Rui Zhang
Abstract: After preparing samples (3mm long×4mm wide×36mm high) of Al2O3-MgAlON composites and sintered at 1500°C for 2 h in N2 atmosphere, samples’ cracks were carved by a Vickers hardometer’s pressing head on the center of the sample surface (4 mm×36 mm). Subsequently, the cracks were healed at 1000°C-1550°C for 6 h respectively. Effects of healing temperature on sample’s strength, crack healing dynamics and its molecular dynamics simulation were investigated. The results suggested that: the optimum range of cracks healing temperature was 1300°C-1550°C, and the healing process accelerated at 1300°C, meanwhile, the strength of samples increased significantly. Cracks completely healing finished at 1550°C. The dynamics equation of crack healing was lnν = -Q/kT+lnC. Through characterizing the crack healing rate with the recovering rate of sample’s strength, the diffusion activation energy Q = 4.264 × 10-30 J•K-1 and diffusion constant C=7.359 were claimed. The result of the molecular dynamics simulation suggested that cracks healing process was caused by diffusion could be divided into five stages: passivation of crack tips, formation of salient island, crack shrinkage, generation of secondary crack, and complete healing.
Authors: Fei Yuan, Dao Yuan Yang, Ting Wang, Zhan Li
Abstract: This study analyzed effects of different thickness(TH) and thermal conductivity of graphite mold on temperature, liquid phase percentage and conductive heat flux, the cooling process of fused cast AZS 33# refractory could be simulated by using COMSOL Multiphysics software. The results show that: when the graphite mold thickness increased, surface center temperature and liquid phase area of casting decreased gradually, but conductive heat flux increased gradually, the cooling rate of casting increased, which were helpful to form fine crystals near the casting surface. When using conventional graphite mold, the optimum thickness was less than 40mm, while using the high thermal conductivity graphite mold, the optimum thickness was 50mm. So the rapid and homogeneous cooling process of casting could reduce the possibility of material crack and obtain fine crystals structure of material; comparing with conventional graphite mold, high thermal conductivity graphite mold was more beneficial to achieve uniform and fast cooling process to improve the performance and passing rate of products.
Authors: Rui Zhang, Hai Long Wang, Hong Liang Xu, Hong Xia Lu, Dao Yuan Yang
Abstract: SiC-based boundary layer capacitors were prepared by hot pressing. XRD, TEM and the high-resolution TEM techniques were used to characterize the sintered samples. It was found that the width of the grain boundary within the SiC-based boundary capacitors was about 200 nm. Extremely high dielectric constant of >2,400,000 appeared in a wide temperature range from 590oC to 730oC, with the maximum of >2,900,000. The critical temperature was about 500oC. Space charge polarization was detected as the temperature increased. Nano grains in the boundary phase were observed, which might enhance the space charge behavior.
Authors: Dao Yuan Yang, Fen Ling Qian, Kai Zhu, Zhan Ling Lu, Rui Zhang
Abstract: Hexagonal MgAl2O4 spinel fibers were synthesized at 1500oC for 6h in nitrogen atmosphere. The structure and morphology of the fibers were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fibers grew via vapor- liquid- solid mechanism. The twin mechanism was suggested to play a key role in the formation process of the hexagonal fibers.
Authors: Hong Xia Lu, Zhang Wei, Rui Zhang, Hong Liang Xu, Hai Long Wang, De Liang Chen, Dao Yuan Yang
Abstract: Nano-Fe particles coating Al2O3 composite powders were prepared by heterogeneous precipitation method with nanometer -Al2O3 and Fe(NO3)3•9H2O as raw materials. The composite powders were analyzed by DSC-TG, XRD,SEM and Zeta potential. Results showed that Fe coating Al2O3 nanometer composite powders were obtained in the condition of being sintered at 500°C for 30min and reduced at 700°C for 1h in H2. The coating Fe nanometer particles are in the shape of sphericity with diameter about 30nm and the dispersion of the powders is uniform. Al2O3/Fe composite ceramics were obtained by hot-pressing (30MPa). The mechanical properties of the composite were investigated after hot press at different temperatures. With the increasing of Fe content in composite ceramics, the hardness of the composite is decreased. Fracture toughness of 10mol%Fe content is 5.62MPa after sintered at 1400°C, which is increasing 57% high than that of monolithic Al2O3 ceramics.
Authors: Hong Liang Xu, Hai Long Wang, Hong Xia Lu, Xiao Fang Liu, Dao Yuan Yang, Wen Bin Chen, Sheng Lin, Rui Zhang
Abstract: SiCw/3Y-ZrO2/A12O3 composites were prepared. The composite powders were prepared by a precursor method. Samples were conventionally sintered at 1500°C and 1580°C for 2h in air. The density, phases, microstructure, hardness of the SiCw/3Y-ZrO2/A12O3 composites were investigated. It was found that the relative density of the samples decreased as the increasing content of SiCw. The optimum mechanical properties may be obtained in the SiCw/3Y-ZrO2/A12O3 composites with 5 vol.% SiCw.
Authors: Juan Wu, Dao Yuan Yang, Kai Zhu, Rui Zhang
Abstract: Mullite- corundum ceramic was fabricated using bauxite and silica fume as raw materials by gel-casting process. The fluidity of the slurry, as well as strength, apparent porosity, pore size distribution, phase composition and microstructure of sintered specimen were studied. The results showed that: the slurry had low viscosity, good fluidity for casting if pH=9, dispersant 0.33wt% and solid content 60vol%; the strength of material came up to 165MPa even if the apparent porosity was about 30%; the samples were characterized by mullite 70%, corundum 22%, rutile 3%, glass phase only 5%, the size of majority grains was about 2μm, and most crystals with high melting point bonded directly; the average aperture was 264nm, the pore size distribution were divided into 2~30nm, 45~60nm and 1500~4000nm three regions. The distribution probability of nano- aperture was the largest, the volume of micron -aperture was the maximum, but all pores were less than 4μm in diameter, which suggested that the materials had micro porous characteristics. The microcrystalline, crystals combined directly and micro porous structure leaded to high strength of the refractory materials together.
Authors: Dao Yuan Yang, Min Xiao Ma, Ruo Yang Liu, Yue Chu, Yi Ming Yin, Luo Yuan Li, Guan Hui Wan
Abstract: Fused cast Zirconia-Alumina-Silica material (AZS) is the key refractory to glass furnace. In order to reduce production cost and optimize production process, the influences of riser position and riser size on temperature gradient, solidification time, residual melt modulus, solidification fraction, and cooling rate of cast system were studied by the finite element simulation method according to the brick size of 600 mm × 400 mm × 300 mm. It turned out that it would be more efficient in feeding when riser located at the center of maximum surface of a brick or when the height of riser is 250 mm-270 mm, while the volume ratio of brick to riser is 2.95-2.74, on condition that the size of riser upper surface is 450 mm × 450 mm and the bottom 150 mm×150 mm.
Authors: Kai Zhu, Dao Yuan Yang, Juan Wu, Rui Zhang
Abstract: Cordierite is an excellent material with good thermal shock resistance and used at high temperature for its low thermal expansion coefficient. Cordierite ceramics were prepared by using talc, alumina and kaolin clay as starting materials. The thermal expansion coefficient, phase composition and microstructure were studied and the results showed that: in order to get samples with low thermal expansion coefficient, the optimum chemical composition was a little rich in Al2O3 compared with the theoretical composition, the optimum sintering temperature was 1350°C, and adding 10% starch as pore-forming agent could effectively decreased the thermal expansion coefficient of the samples even to 0.8×10-6/°C. The samples contained majority of cordierite phase, with trace mullite and glass, the acicular cordierite crystals in samples developed very well and there were 10% starch powder used as pore-forming agent in formula. All these were the reasons to decrease the thermal expansion coefficient of cordierite material.
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