Papers by Author: Shuang Shii Lian

Abstract: Directional Casting of silicon is a cost effective process to grow multi-crystalline Si ingots for wafers of solar cells. An appropriate melting process of polycrystalline silicon is closely related to the material properties and the size of graphite susceptors. These parameters have great influence not only on the melting temperature of silicon melt but also on the efficiency of induction heating, impurity distribution, dendrite and the direction of crystalline grains, which ultimately affect the properties of the solar cells. Therefore, in order to obtain good quality and energy efficiency of growth of polycrystalline silicon, one needs to know how the temperature fields relate to the processing parameters such as different sizes and properties of graphite susceptors in the furnace. In this paper, the influences of different properties such as density, electrical conductivity, thickness of graphite susceptor and cooling base-plate on the temperature of silicon with induction heating have been studied. To have an optimized control of processing parameters, a finite element-based software was used to simulate the temperature distribution of silicon melt in a polycrystalline vacuum induction refining furnace. The simulation takes into account the interaction of the induced eddy current and the heat transfer coupling in the vacuum induction furnace. Some of the modelling results are summarized as follows: 1. The material properties of the graphite susceptor have great influence on the temperature distribution. 2. The higher the operating frequency of the current, the sooner it reaches the melting temperature. 3. Base-plate made of stainless steel 304 performs better than the copper base-plate for the control of temperature distribution. 4. There exists an optimal thickness of the graphite susceptor, and the rise of temperature is not linearly proportional to the thickness of the graphite susceptor.

Abstract: Nickel-free high nitrogen stainless steel has become more important due to its impressive mechanical and corrosion properties. In contrast to high pressure processes, melting plasma in a normal atmosphere is an alternative way of obtaining high nitrogen content at low cost. However, melting in such an atmosphere will bring some surface impurities, like sulfur and oxygen, into the stainless steel through the refractories or the materials themselves. Therefore, this research aims the relationship between the sulfur and nitrogen content, and their influence on biocompatibility. Thermo-Calc is first used to design the composition of Fe-Cr based austenitic nitrogen stainless steel, and melted with different melting techniques, including plasma and an induction melting furnace. The results indicate that the nitrogen content varies with different sulfur content. It is also found that α-Fe (Ferrite) plates are observed near the grain boundaries when the sulfur content reaches a certain level. Besides, the Sulfur content has an obvious influence on the biocompatibility rather than nitrogen contents.

Abstract: This paper presents the development of anode substrates of solid oxide fuel cells (SOFCs), prepared by rotating electrode powder-making equipment to improve the efficiency of cells and the coking issue that appears in traditional Ni-YSZ composite anodes when operated with hydrocarbon fuel. Combining the advantage of good electronic conductivity, leading less carbon residue of copper and high temperature oxidation resistance of Cr or Ni, the anode substrate is designed with Cu-Ni and Cu-Cr alloys so that the cells are able to work within the service temperature of 800-1000 C. To optimize the properties of conductivity, less carbon deposition and heat resistance, this research has invented substrates of copper-based dual metal composite alloys which are different from ordinary anode cermet powder made of nickel-ceramic composites. This new anode powder of dual metal alloys is made by rotating electrode powder-making equipment, with the powders being sintered to porous substrates. Experimental results show that the substrate has a good porosity and an electrical conductivity.

Abstract: A study of thermal field in induction melting with cold crucible and dual induction frequencies is presented in this paper. Numerical simulation was done by finite element based software COMSOL with use of multi-physical modeling. A method of superposing of magnetic vector potential is proposed to solve the complexity of dual induction frequencies. Different conditions of high and low frequencies were given in the calculation to find the effects on distribution of thermal fields. The computed temperature distribution was compared with the macro etched section of solidified ingots and the results showed that the orientation of dendritic grain structures follow to the similar direction of heat flow. This indicates that proper set of induction coils could enable more uniform thermal field distribution and attaining controlled solidification morphology in the ingots.

Abstract: This study is intended to reduce the difference of thermal expansion coefficient between metallic interconnector and solid electrolyte of SOFC (Solid Oxide Fuel Cell) without sacrificing of electrical conductivity. Fe-Cr alloys have been chosen as candidate materials due to its merit of low cost and high temperature oxidation resistance. Different amount of alloys element and compositions have been varied to optimize the properties by method of alloys design with aid of thermodynamics software Thermal-Cal. Phase diagrams of multi-components alloys have been drawn to predict the possible stable phases formed in the investigated metals. An arc melter and plasma melting furnace were used to melt the investigated alloys. The measurements of thermal expansion coefficients and electrical conductivities are carried out with TMA and ASR resistance instrument. The results indicate that the Fe-10Cr alloy exhibits the smallest thermal expansion coefficient among the alloys, while Fe-16Cr has a lowest electrical resistance .

Abstract: The slag from steel plants or incinerators was tried to be recycled and be reused as foam materials through plasma arc melting. The study was intended to investigate the making of foam slag with laboratory plasma melting facilities. The investigated materials consisted of different mixtures of Al2O3、SiO2 、FetO、CaO and Na2O, with the fluxes that were necessary to examine the capability of pore-formation in the solidified ingots. It has been found that the foam slag could be obtained with the proper compositions and conditions of arc heating. The dimensions and distributions of pores were studied and correlated with the temperatures and compositions of slag. The results showed that the sizes of pores inside the solidified ingots were in the range of 1~5 mm, and the thickness of slag was around 20 mm. As to the distributions of the pores in the ingots of slag, further improvement would be needed in the future.

Abstract: Synoviocyte is one of the cells in direct contact with the wear particles and the role of synoviocytes in the prosthesis loosening remains to be further understood. The purpose of the present study is to investigate whether particulate biomaterials cause synoviocyte dead or simply activate these cells. The activation of synoviocyte in response to particulate biomaterial exposure will be indicated with its phagocytotic ability. As to the effects of particulate biomaterials to apoptosis will be tested on rabbit synoviocytes, HIG-82 cells. The results demonstrate that the addition of cobalt particles would lead the HIG-82 cells to apoptosis and apoptosis accompanying caspase3 cleavage, which means that apoptosis of the HIG-82 cells resulted from the addition of cobalt particles might went through caspase-dependent pathway. On the other hand, exposing to nonmetal particles such as TiO2 and SiO2, particles did not provoke apoptosis of the HIG-82 cells. TiO2 particles activated the cells and were phagocytosed by the HIG-82 synoviocytes, no significant biological effects were found while the HIG-82 cells exposed to SiO2 particles.

Abstract: The refining of MG-silicon (MG-Si) is closely related to the cost and purity of solar-grade silicon (SoG-Si) as well as semiconductor-grade silicon (SeG-Si). Plasma arc refining of MG-silicon is one of the alternative and effective route to remove the impurities in silicon. In this study, a 60KW transfer-arc plasma melting furnace operated in105Pa was used to purify the MG-Si by different kinds of working gas, which was composed of 100%Ar, 95%Ar+5%O2, 95%Ar+5%H2, and 70%Ar+30%H2 respectively. During the processing, an optical spectrometer was used to monitor the changes of compositions. The experimental results show that the removal rate of impurities of aluminum, calcium, sodium, barium...etc. in silicon with plasma working gas containing oxygen, and hydrogen are higher than pure Ar plasma. Especially with 30% H2 plasma, the removal rate of the Na and Ba could reach 100% and the removal rate of Ca and Al could also achieve to 99.5% and 89.5% respectively. For the impurities of boron in the MG-Si, the elimination rate of hydrogen-mixed plasma could be as high as 76%.The in-situ monitoring of plasma refining is accomplished with the monochromators in the range of visible light’s wavelength. From the results of chemical analysis and optical spectrograph, it revealed that elimination rate of Fe and Al was higher in hydrogen-contained plasma arc than in pure Ar plasma, As to the refining of carbon, the hydrogen and oxygen mixed plasma arc are also efficient to reduce the carbon content in silicon, which could be decreased from 310 ppm to 60~70 ppm.