多晶硅铸锭涂层用高纯Si3 N4微粉的研究进展与展望

本文根据国内外高纯氮化硅微粉制备的研究情况,综述了硅粉直接氮化法、硅亚胺热分解法、气相反应法等几种氮化硅粉末的主要制备方法,介绍了各种制备方法在生产多晶硅铸锭涂层用氮化硅微粉的优缺点,并从产品质量、成本等角度分析比较了各种制备方法的特点,指出了制备多晶硅铸锭用氮化硅粉末的主要发展方向.     

Influence of Argon Gas Flow Rate on Oxygen and Carbon Impurities Concentration in Multicrystalline Silicon Grown by Directional Solidification Furnace: Numerical and Experimental Investigation

Silicon - The quality of the multi-crystalline silicon ingot mainly depends on the defects and impurity distribution. The impurities originate from the various furnace parts and feedstock. The...     

Effect of the Silicon Nitride Coating of Quartz Crucible on Impurity Distribution in Ingot‐Cast Multicrystalline Silicon

Multicrystalline silicon ingots were fabricated via the directional solidification method in a vacuum induction furnace using silicon nitride (Si₃N₄) as quartz crucible coating. The effect of Si₃N₄ coating on the impurity content, transference, and distribution in Si ingots was investigated. The results can be summarized as follows: The impurities contained in Si ingots, including Fe, Ca, Mn, Cu, P, and B, were found to decrease at varying degrees when the inner surface of the quartz crucible was coated with Si₃N₄. A mixed layer composted by Si₃N₄ and Si was observed on the surface of the Si ingot. This mixed layer provided microdefects for the nucleation of metallic impurities. The Fe and N contents in the Si/Si₃N₄ mixed layer changed with the same tendency, and FeSi₂ particles formed on the Si/Si₃N₄ crystalline boundary. Both Fe and Ca precipitated in the SiC particles near the Si ingot/Si₃N₄‐coating interface.     

Reduction of Carbon and Oxygen Impurities in mc-Silicon Ingot Using Molybdenum Gas Shield in Directional Solidification Process

Silicon - Transient global heat transfer simulations are done to analyse the impact of molybdenum shield on carbon and oxygen impurity formation in mc-silicon grown by Directional Solidification...     

我国多晶硅铸锭坩埚的现状与发展

本文总结了我国多晶硅锭坩埚生产现状,指出熔融石英材质坩埚仅能一次性使用,可反复使用的坩埚是发展方向,介绍了国内外可反复使用坩埚的主要生产技术.     

Thermodynamic Analysis of Dissolved Oxygen in a Silicon Melt and the Effect of Processing Parameters on the Oxygen Distribution in Single-crystal Silicon During Czochralski Growth

Silicon - The dissolved oxygen in a silicon melt at equilibrium at different temperatures and SiO partial pressures in Ar during Czochralski growth was subjected to thermodynamic analysis. The...     

Oxidation of Silicon, Silicon Carbide, and Silicon Nitride in Gases Containing Oxygen and Chlorine

Chlorine contamination accelerates the oxidation of silicon-based ceramics through the formation of volatile silicon chloride or silicon oxychloride species which degrade the protective character of the SiO₂ film. Accelerated attack may occur by active corrosion or formation of bubbles in the oxide layer. Si₃N₄ is much more resistant to this attack than either silicon or SiC. This resistance may be related to the presence of a thin silicon oxynitride layer below the SiO₂ scale which forms on Si₃N₄.     

Improving the Efficiency of Multicrystalline Silicon by Adding an ARC Layer in the Front Device

High efficiency multicrystalline solar cells must improve performance while replacing higher cost monocrystalline silicon with lower cost multicrystalline silicon. Composite silicon dioxide-titanium dioxide (SiO₂?TiO₂) films are deposited on a large area of 15.6×15.6 cm² textured multicrystalline silicon solar cells to increase the incident light trapped within the device. This is being achieved through new cell device structures that improve light trapping and energy conversion capability. These new structures depend on passivated thick and thin layers of silicon dioxide and titanum dioxide grown via wet and dry thermal oxidation. By replacing dry oxidation with wet oxidation the temperatures process can be lowered from 1050^°C to 850^°C to reduce both cycle time and wafer damage.     

Carbon Inclusions in Sintered Silicon Carbide

The carbon additions in the pressureless sintering of SiC are commonly used for the removal of SiO₂ layers on the starting powders. In practice, it is common to add more C than is necessary for stoichiometric removal to ensure a complete deoxidation. As a result, inclusions of excess free C are a general feature of the microstructure of sintered SiC. This phenomenon was studied by high-resolution Auger electron spectroscopy on ultra-high-vacuum-exposed fracture surfaces as well as by high-resolution transmission electron microscopy of B- and C-doped materials.     

Ablation Behavior of a Three-Dimensional Carbon/Silicon Carbide Composite Nozzle in an Ethanol/Oxygen Combustion Gas Generator

The ablation properties of a three-dimensional carbon/silicon carbide composite nozzle were investigated via hot-fire testing by an ethanol/oxygen combustion gas generator simulating combustion environments of the liquid rocket engine. The linear ablation rate at the nozzle throat was 0.250±0.023 mm/s, and the overall mass ablation rate was 0.246 kg/(m² s). The ablation in the divergent section, convergent section, and in the regions near the throat grew severe by degree. Ablation mechanisms of the composite nozzle were predominated by the oxidation of the composite, and volatilization of the silica scale derived from oxidation of silicon carbide resulted in further ablation of the nozzle.     

Effect of High Temperature Annealing on Crystal Structure and Electrical Properties of Multicrystalline Silicon by the Metallurgical Method

The defects of dislocations and grain boundaries (GBs) could significantly reduce the electrical properties of multicrystalline silicon (mc-Si) solar cells     

Comparison Between Carbon Nanotube and Carbon Nanofiber Reinforcements in Amorphous Silicon Nitride Coatings

Amorphous silicon nitride coatings were reinforced with carbon nanotubes and dense carbon nanofibers. These reinforcements were all fabricated with graphene layers oriented parallel to the fiber axis, and some of the nanofibers were also heat-treated at high temperature to improve graphitic ordering. The effectiveness of these reinforcements as toughening agents was then compared qualitatively by examining the fiber pull out lengths from fracture surfaces. With the dense nanofibers there was almost no evidence of pull-out, whereas the materials reinforced with multiwalled carbon nanotubes exhibited significant pull-out. Based on these results, the multiwalled carbon nanotubes appear to provide significantly more toughening than the dense nanofibers.     

Effect of Carbon and Silicon Carbide/Carbon Interlayers on the Mechanical Behavior of Tyranno-SA-Fiber-Reinforced Silicon Carbide-Matrix Composites

Several CVI-SiC/SiC composites were fabricated and the mechanical properties were investigated using unloading–reloading tensile tests. The composites were reinforced with a new Tyranno-SA fiber (2-D, plain-woven). Various carbon and SiC/C layers were deposited as fiber/matrix interlayers by the isothermal CVI process. The Tyranno-SA/SiC composites exhibited high proportional limit stress (∼120 MPa) and relatively small strain-to-failure. The tensile stress/strain curves exhibited features corresponding to strong interfacial shear and sliding resistance, and indicated failures of all the composites before matrix-cracking saturation was achieved. Fiber/matrix debonding and relatively short fiber pullouts were observed on the fracture surfaces. The ultimate tensile strength displayed an increasing trend with increasing carbon layer thickness up to 100 nm. Further improvement of the mechanical properties of Tyranno-SA/SiC composites is expected with more suitable interlayer structures.     

Preparation of Silicon Carbide Fiber from Activated Carbon Fiber and Gaseous Silicon Monoxide

Crystalline silicon carbide (SiC) fiber was produced by a new, simple procedure. Activated carbon fiber (ACF) was reacted with gaseous silicon monoxide and was converted to SiC fiber at elevated temperature and reduced pressure. The reaction was completed at temperatures as low as 1473 K. The reacted fiber consisted of submicrometer particles which were not observed in the original ACF. The SiC crystal size in the reacted fiber was approximately 30 nm. The microstructure of the fiber became dense after it was heat-treated in air at 1573 K or in nitrogen gas at 1873 K.     

Strength Distribution in Commercial Silicon Carbide Materials

Four types of commercial silicon carbide samples from different sources were characterized in terms of baseline strength and strength distribution (reliability). Four-point flexural strength of each material was determined on 30 test bars, 5.1 by 0.64 by 0.32 cm, for a reliable estimate of the Weibull modulus values. The results show that the average strength of these sintered silicon carbide samples ranged from 380 to 482 MPa (55 to 69 ksi) at room temperature and 307 to 470 MPa (45 to 68 ksi) at 1370°C (2500°F). Considerable variations in strength were found among specimens of each material. Baseline Weibull modulus values ranged from 8 to 11 at room temperature and 7 to 11 at 1370°C (2500°F). The strength scatter clearly reflected flaw variability, which must be minimized to improve reliability in sintered silicon carbide materials.     

Fabrication and Characterization of Three-Dimensional Carbon Fiber Reinforced Silicon Carbide and Silicon Nitride Composites

Three-dimensional (3D) carbon fiber reinforced SiC and Si₃N₄ composites have been fabricated using repeated infiltration of an organosilicon slurry under vacuum and pressure. Open porosity of the infiltrated body was reduced from 40% after the first infiltration to approximately 8% after the seventh cycle. Further reduction of open porosity to less than 3% was accomplished by hot-press densification. The maximum values of flexural strength and fracture toughness were, respectively, 260 MPa and 7.3 MPa·m^1/2for C/Si₃N₄ composites, and 185 MPa and 6 MPa·m^1/2 for C/SiC composite.     

Oxidation of Chemically-Vapor-Deposited Silicon Carbide in Carbon Dioxide

Chemically-vapor-deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO₂) at temperatures of 1200–1400°C for times between 96 and 500 h at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate-limiting kinetic mechanisms are discussed. Passive oxidation of SiC by CO₂ is negligible compared to the rates measured for other oxidants that are also found in combustion environments, oxygen and water vapor.     

Oxidation Kinetics of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen

The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen ( P _H2O= 0.1 atm) at temperatures between 1200° and 1400°C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al₂O₃ reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.     

Gas Chromatographic Fractionations of the Carbon and Oxygen Isotopes of Carbon Monoxide

Abstract

A high-precision gas chromatograph was used in conjunction with a quadrupole mass spectrometer and an on-line computer to study the fractionation of carbon and oxygen isotopes in carbon monoxide on silica and on finely divided nickel powder. Relative retentions were studied as a function of temperature using both natural abundances and isotopically enriched species. On silica, the values ranged from 0.99639 ± 0.00046 to 1.00152 ± 0.00089 for the ¹³/¹²C pair and from 1.00054 ± 0.00057 to 1.00162 ± 0.00039 for the ¹⁶O/¹⁸O pair. The values on nickel were greater, average values being 1.037 for the ¹²C/¹³C pair and 1.009 for the ¹⁶O/¹⁸O pair. The larger values on nickel compared to those on silica reflect the much stronger interaction.     

结晶器旋转对电渣重熔钢锭中元素分布的影响

采用自行设计的结晶器可旋转电渣炉,研究了旋转速率对电渣重熔钢锭中元素偏析度的影响. 结果表明,当结晶器旋转速率为0~28 r/min时,随其增加,元素的分布更均匀,C偏析度从0.26降至0.0545, Si偏析度从0.26降至0.06, Mn偏析度从0.17降至0.03, Cr偏析度从0.275降至0.066,原因是结晶器运动带动渣池运动,使渣池温度趋于均匀化,同时渣池运动也带动金属液滴在渣池中运动,使小液滴随机滴落于金属熔池中,而不是集中于金属熔池中心部位,因而促进熔池温度均匀分布,有利于形成浅平状熔池;但旋转速率过高对电渣重熔钢锭的凝固质量有害,当旋转速率从28 r/min增至35 r/min时,C偏析度从0.0545增至0.097, Si偏析度从0.06增至0.08, Mn偏析度从0.03增至0.076, Cr偏析度从0.066增至0.16,原因是渣池剧烈运动带动金属熔池运动,流动的液态金属冲洗两相区,将其中树枝晶周围的浓化溶质带走,使该区域溶质含量降低,导致元素偏析.