Papers by Author: Yao Li

Abstract: It is a typical and representative problem which coal mining has been causing serious damage in the Eastern Plains of China with high phreatic water level. Based on GIS technology, we analyzed the characters of cropland and coal resources, the results showed that the area of the overlapped areas of cropland and coal resources was 1.28 × 10⁵km², which accounted for 38.22% of the total arable land of the study area. Based on investigation and statistics, we investigated and forecast the farmland damage and analyzed the comprehensive treatment status in the typical region, the results showed that coal mining led to farmland subsided depth and perennial water, the recovery rate of cultivated land was between 50% and 70% in the treated area and more lower in the untreated area, the trend of arable land area continued to reduce would be hard to contain, the local governments faced unprecedented pressure on cultivated land protection.

Abstract: The process of Electron Beam-Physical Vapor Deposition (EB-PVD) preparing SiC coating by Electron Beam evaporating 3C-SiC ingot on stainless steel (SS) substrate was firstly discussed as a preliminary estimation from thermodynamic viewpoint. The results show that, with the temperature increasing from 2500 to 3400 K, the purity of SiC coating increases from 0.58 to 0.734.

Abstract: Quartzite microcrystallite glass ceramics is one of the most promising machinable ceramic materials due to its many outstanding properties. The density of quartzite microcrystallite glass ceramics is smaller than the aluminum alloy and its thermal conductivity approaches to the zirconia and its elastic module is also very small; All these advantages meet the requirements for structural components to work at higher temperature; Compressive properties of quartzite microcrystallite glass ceramics had been studied at room temperature and 500°C in this paper; The specimens had been aged at 1000°C for 5, 10, 20, 30 hours, respectively. Through SEM observations of the fracture surface of the specimens, the microstructural changes had been determined; The tests showed: the compressive property of the machinable glass ceramic declined as the ageing time increasing; but the compressive property of the specimen aged for 10 hours was inferior to that aged for 20 hours; Then compressive property declined as the ageing time increasing. The SEM observation indicated that with the extend of ageing time, the grains grew bigger and microporous and microcracks increased in the specimens; Comparing the compressive property at room temperature with that at 500°C, one found that the change of compressive property was very small when the ageing time was the same; With the extend of ageing time, the curve of the compressive property changed from smooth curves to broken lines.

Abstract: In the process of preparation of high silicon steel by EB-PVD, the effect of distance between ingot and substrate on the weight percent of silicon in the silicon steel was investigated through specially designed experiment. Energy dispersive spectroscopy (EDS), optical microscope (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD) were used to characterize the weight percent of silicon, microstructure, crystal grain size and phase of the high silicon steel. The experimental results show that the weight percent of silicon in the silicon steel decreases with increasing of the distance between ingot and substrate, when the distance is about 415 mm, high silicon steel can be fabricated by EB-PVD. The microstructure of the high silicon steel was composed of columnar crystal grain, the size of the crystal is about 25-50 μm. The material back to the substrate side is composed of B2 and exhibits strong {400} texture.

Abstract: Low-density xSiO2-(1-x)Al2O3 xerogels with x=0.9, 0.8, 0.7, 0.6 (mole fractions) were prepared by sol-gel and non-supercritical drying. Silica alkogels, which were the framework of binary composite materials, formed from tetraethyl orthosilicate (TEOS) by hydrolytic condensation with a molar ratio of TEOS: H2O: alcohol: hydrochloric acid: ammonia =1: 4: 10: 7.5×10-4: 0.0375. Aluminum hydroxide derived from Al(NO3)3·9H2O and NH4OH acting in the alcohol solution under the condition of catalyst. After filtrating and washing, the precipitation was mixed into silica sols to form SiO2-Al2O3 mixed oxide gels with different silicon and aluminum molar ratio. The structural change and crystallization of the binary xerogels were investigated after heat treatment at 600
for 2 h by the means of X-ray diffraction. Nitrogen adsorption experiment was performed to estimate specific surface area, porous volume and pore size distribution. The structural change of xerogels was observed by FT-IR spectroscopy. The resulting mixed xerogels possess of mesoporous structure which is characteristic of cylindrical pores, high specific surface area of 596-863 m2/g and a relatively narrow pore distribution of 2.8-30 nm. Al2O3 is introduced into the SiO2 phase and some of Al-O-Si bonds form.

Abstract: Low density SiO2-xZrO2 aerogels with x=35wt%, 65wt%, 75wt%, 90wt%, 95wt% were prepared by CO2 supercritical drying technique with tetraethylorthosilicate (TEOS) and zirconyl nitrate dihydrate (ZrO(NO3)2 .2H2O) by hydrolytic polycondensation under different chemical conditions. The prepared aerogels are performed by X-ray Diffraction (XRD), Transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR) and BET surface areas to characterize and analyze the morphology and pore structure of SiO2-ZrO2 aerogels. The results showed that the SiO2-ZrO2 areogels are the typical of nano mesopores and the average pore size is about 50 nm. The specific surface areas varied from 345.5 to 615.5 m2/g with (SBET)MAX = 615.5 m2/g with 20wt% Zirconia; Moreover a mass of Si-O-Zr bands formed in the aerogels and the formation mechanism of Si-O-Zr bands are also discussed.

Abstract: The thin film deposited by electron beam physical vapor deposition (EB-PVD) on rotating substrate was approached via a kinetic Monte Carlo (KMC) algorithm on a “surface” of tight-packed rows. The motivation is to study the surface morphology distribution of thin film along the substrate radial. Effective deposition rate model and effective incident angle model were established along the substrate radial. Two phenomena are incorporated in the KMC simulation: adatom-surface collision and adatom diffusion. The KMC simulations show that the surface roughness of thin film is small and the changing of surface roughness is small near the side of rotation axis, however, the surface roughness is big near the side of substrate edge, and the surface roughness increases quickly with the increasing of substrate radius when r>300 mm. The simulation results indicate that the effective incident angle is the main factor to cause the changing of surface roughness: the effective incident angle does not reach critical value and the deposition rate difference is small when the radius is less than 300 mm, so the surface roughness of thin film in the scope is small and its changing is small, but when r>300 mm, the effective incident angles increase sharply with radius increasing and all of them are above the critical value, which cause surface roughness of thin film to increase quickly. Experiments reveal that the KMC method can predict surface roughness distribution of thin film deposited by EB-PVD on rotating substrate.

Abstract: Silica xerogels were prepared by sol-gel process and non-supercritical drying. Two kinds of reinforcements, SiC whisker and short carbon fiber (CF), were chosen to control the shrinkage during drying process and improve the mechanical properties of xerogels. Microstructure and mechanical properties of samples were examined. It was found that the addition of SiC whisker could greatly improve the elastic modulus of silica xerogels, while short CF could prominently decrease the volume shrinkage ratio but could not improve the elastic modulus. Analysis showed that the difference between the two reinforcement mechanisms was caused by the interface and the size of the doped fiber and whisker.

Abstract: Highly Nano-porous SiO2-ZrO2 aerogels were manufactured with tetraethylorthosilicate (TEOS) and zirconyl nitrate dihydrate (ZrO(NO3)2 .5H2O) by the sol-gel method followed by supercritical drying technique. The prepared aerogels are performed by SEM, FT-IR and BET to characterize and analyze the morphology and pore structure of SiO2-ZrO2 aerogels. The results showed that:(i) The areogels are the typical of nano pores in the interval between 1

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