Kinetics Analysis of Boron Removal from Silicon through Reactions with CaO-SiO2 and CaO-SiO2-Al2O3 Slags

Metallurgical and Materials Transactions B - Different types of slags have been used to refine silicon, particularly for removing boron impurity from metallurgical grade (MG) silicon. Although a...     

CaO-SiO2-Na2O-CaF2-Al2O3-MgO渣系的结晶温度

通过差热分析仪测定了CaO-SiO2—Na2O-CaF2—Al2O3—MgO系连铸结晶器保护渣的结晶温度。在本实验渣系条件下，连铸保护渣的结晶温度随着渣中CaO／SiO2值、Na2CO3含量、CaF2含量和MgO含量的增加而升高，随着渣中Al2O3含量的增加而降低。化学成分通过改变粘度，来影响晶核形成速度和晶体成长速度，从而决定了连铸保护渣的结晶性能。结晶温度随着保护渣粘度的降低而升高。     

Stability of Fluorine-Free CaO-SiO2-Al2O3-B2O3-Na2O Mold Fluxes

Metallurgical and Materials Transactions B - B2O3 and Na2O are key components of fluorine-free mold fluxes for continuous casting, but both are highly volatile, which affects the flux stability....     

Electrically Enhanced Boron Removal from Silicon Using Slag

An approach to enhance silicon refining using slag has been developed. The enhancement of the process was carried out by applying electrical potential difference across the slag and the silicon phase. This resulted in a shift in the apparent equilibrium in favor of higher partition ratio for the impurities. The application of electrical potential difference also enhanced the mass transfer rate increasing the overall kinetics of the process. This has been demonstrated in laboratory experimentations for the removal of boron from silicon-boron melts using slag. A CaO-SiO₂-Al₂O₃ slag was reacted with Si-B melt at 1823 K (1550 °C). Electrical potential differences were applied through graphite rods immersed in each of the liquid phase. The results showed that the apparent B-partition ratio and the apparent slag mass transfer coefficient were increased by a factor of 1.2 and 1.4, respectively, when a potential difference of 3 V was applied to the phases. The technique has the potential to be used for improving the existing slag refining process by increasing the overall kinetics and the slag capacity to absorb the impurities.     

Reaction Mechanism and Kinetics of Boron Removal from Molten Silicon via CaO-SiO2-CaCl2 Slag Treatment and Ammonia Injection

Metallurgical and Materials Transactions B - To improve the boron-removal efficiency of metallurgical-grade silicon by increasing the reaction rate, a combined method with the...     

CaO-SiO2-Na2O-CaF2-Al2O3-MgO渣系的粘性活化能

采用CaO-Si02-Na20-CaF2-Al2O3-MgO渣系，通过测定粘度和粘性活化能，建立二次回归正交设计模型，借此研究了粘性特征与碱度、Na20含量、CaF2含量、Al2O3含量及MgO含量之间的关系，为设计开发连铸保护渣提供了理论依据。研究结果表明，粘性活化能随着渣中碱度、Na2C03含量和CaF2含量的增加而减小；Al2O3和MgO对粘性活化能的影响与碱度密切相关。连铸保护渣的粘度和粘性活化能具有相似的变化规律。     

Evaporation Removal of Boron from Metallurgical-Grade Silicon Using CaO-CaCl2-SiO2 Slag

In order to optimize the B removal during slag-refining process for solar-grade silicon production, a new process for the removal of B in molten Si was proposed based on the principle of oxidized chlorination and evaporation. B can be generated and evaporated in the form of B-containing gas on the basis of calculated vapor pressures of forming species in the BO_1.5-CaCl₂ slag at 1723 K (1450 °C). CaO-SiO₂-CaCl₂ slag was selected to remove B in molten Si. In the slag-refining experiments, compared with the binary systems of CaO-CaCl₂ and SiO₂-CaCl₂ slag, the ternary slag system CaO-SiO₂-CaCl₂ showed a better potential (86 pct) for B removal. Furthermore, the relationships among the removal efficiency, the estimated evaporative efficiency, and the partition ratio were all discussed.     

Phosphorus Capacity of CaO-SiO2-Al2O3-MgO-FexO Slag

The CaO-SiO2-Al2O3-MgO-FexO slag occurs in the production process of Corex ironmaking technology.Most of its metallurgical properties,especially the phosphorus property,are different from the slag produced from blast furnace or converter.In order to explore the dephosphorization ability of CaO-SiO2-Al2O3-MgO-FexO slag,its phosphorus capacity was measured at 1 673 Kby gas-slag-metal equilibrium technique.An iron crucible was used as the reaction vessel,Ag alloy with 0.2% P was used as the metal phase which equilibrated with CaO-SiO2-Al2O3-MgO-FexO slag,and a constant flow of CO-CO2-N2 gas was used to provide oxygen partial pressure in the experiment.The effects of MgO,FexO and basicity on slag phosphorus capacity were investigated by single factor test.The results show that the phosphorus capacity rises firstly and then decreases with increasing MgO content under the condition of basicity 1.3,FexO content of 2% and Al2O3 content of 12%.The phosphorus value reaches maximum as the MgO content is 8%.When the basicity of slag is 1.1,MgO content is 10%,and Al2O3 is 12%,the phosphorus capacity increases with the increase of FexO content.The phosphorus capacity rises linearly when the basicity is increased from 1.1to 1.5.     

Phosphorus Removal from Si-Fe Alloy Using SiO2-Al2O3-CaO Slag

Metallurgical and Materials Transactions B - Phosphorus removal from silicon using a combination of solvent and slag refining, with lower carbon footprint and lower energy requirement than the...     

基于IMCT理论的CaO-SiO2-MgO-Al2O3-Na2O渣系的脱硫热力学模型

 为了精确表征含Na2O渣系的脱硫能力，改善脱硫效果，基于熔渣离子与分子共存理论（IMCT）建立了CaO-SiO2-MgO-Al2O3-Na2O渣系结构单元的作用浓度计算模型和1 753 K时该渣系的脱硫热力学模型。并对渣系的总硫分配比及各自硫分配比的影响因素进行了讨论分析。理论结果表明，除LS， MgS外，随着Al2O3质量分数的增加，该渣系的脱硫能力明显下降，而MgO和Na2O质量分数的增加，对提高渣系的脱硫能力具有明显的促进作用。此外，少量的Na2O即可表现出很强的脱硫效果，这为含有Na2O的冶金二次资源在铁水脱硫过程中的应用以及铁水脱硫渣系的优化提供了必要的理论依据。     

Crystallization Behaviors of CaO-SiO2-Al2O3-Na2O-CaF2-(Li2O-B2O3) Mold Fluxes

The effects of basicity (CaO/SiO₂), B₂O₃, and Li₂O addition on the crystallization behaviors of lime-silica-based mold fluxes have been investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy, X-ray diffraction (XRD), and single hot thermocouple technique. It was found that the crystallization temperature of cuspidine increased with increasing the basicity of mold fluxes. The crystallization of wollastonite was suppressed with increasing the mold flux basicity due to the enhancement of cuspidine crystallization. The addition of B₂O₃ suppresses the crystallization of mold flux. The crystallization temperature of mold flux decreases with Li₂O addition. The size of cuspidine increases, while the number of cuspidine decreases with increasing mold flux basicity. The morphology of cuspidine in mold fluxes with lower basicity is largely dendritic. The dendritic cuspidine in mold fluxes is composed of many fine cuspidine crystals. On the contrary, in mold fluxes with higher basicity, the cuspidine crystals are larger in size with mainly faceted morphology. The crystalline phase evolution was also calculated using a thermodynamic database, and compared with the experimental results determined by DSC and XRD. The results of thermodynamic calculation of crystalline phase formation are in accordance with the results determined by DSC and XRD.     

Removal of phosphorus from CaO-SiO2-MgO-Al2O3-P2O5 melts to the gas phase

The behavior of phosphorus in CaO-SiO₂-MgO-Al₂O₃-P₂O₅ melts is studied experimentally, so as to determine the potential for the removal of phosphorus from oxide melts to the gas phase. To identify the factors that affect the removal of phosphorus from oxide melts to the gas phase, experiments are conducted with different basicity CaO/SiO₂ and with the injection of N₂, Ar, and CO + CO₂ mixture (with different CO/CO₂ ratios). It is established that the basicity is the main factor affecting the transfer of phosphorus from the oxide melt to the gas. When the basicity is 1.0 or less, phosphorus is removed from oxide melts. At higher basicity, no transfer of phosphorus from the oxide melt to the gas is observed. These findings are confirmed by calculations based on the theory of regular ionic solutions for acidic slag, at different basicity values. Calculations show that, when the basicity is 1.05 or less, the activity of SiO₂ exceeds that of CaO, and correspondingly SiO₂ displaces P₂O₅ from its strong compound with CaO. That creates favorable conditions for the transfer of phosphorus from the oxide melt to the gas.     

Oxidative Removal of Boron from Molten Silicon by CaO-based Flux Treatment with Oxygen Gas Injection

Oxidative removal of boron from molten silicon has been investigated at 1773 K (1500 °C) by CaO-based flux treatment with oxygen gas injection. Since oxygen gas is injected into the silicon melt after adding CaO- or CaCO₃-CaF₂ flux onto the melt, high oxygen partial pressure is maintained at the flux-O₂-Si interface and the removal of boron proceeds under nonequilibrium conditions. The experimental results clarified that the behavior of boron removal from molten silicon depends on the competition between the oxidation reactions of boron and silicon. On the basis of the results obtained, optimum operating conditions for boron removal by the flux treatment were examined from the viewpoints of initial flux composition, reaction time, oxygen gas flow rate, and orifice size of gas injection nozzle. By repeating the batch operation for 120 seconds three times under the optimum conditions determined in the present study, boron concentration in metallurgical-grade silicon could be reduced from 14 to 7.6 mass ppm efficiently.     

Distribution of Boron Between Silicon and CaO-MgO-Al2O3-SiO2 Slags

Production of solar-grade silicon through metallurgical refining methods can be less expensive than current production methods both in terms of energy use and capital cost. Slag refining is a potential metallurgical refining method for removal of boron from silicon. The distribution of boron between silicon and binary CaO-SiO₂ and MgO-SiO₂ slags, and between silicon and ternary CaO-MgO-SiO₂ and CaO-Al₂O₃-SiO₂ slags has been investigated in this work at 1873 K (1600 °C). The distribution coefficient of boron has been found to be between 2 and 2.5 in the binary CaO-SiO₂ and MgO-SiO₂ systems. It has also been found to be in the same range across the entire CaO-MgO-SiO₂ system. In these systems the distribution coefficient is unaffected by slag composition. The distribution coefficient has been found to decrease with increasing Al₂O₃ content in the slag in the ternary CaO-Al₂O₃-SiO₂ system.     

Removal of Boron from Silicon by Moist Hydrogen Gas

New and cheaper refining methods for production of metallurgical silicon are needed to meet the increasing demands for low-cost, high-quality silicon for the solar cell industry. One promising refining method for boron is moist hydrogen treatment. In this work, an evaporation unit has been used to produce wet hydrogen gas, which subsequently has been sparged on top of silicon melts. The effect of temperature and gas composition on boron removal has been studied. The main results show that boron is removed from liquid silicon and the removal rate is controlled by chemical reaction depending on $ p_{{{\text{H}}_{ 2} {\text{O}}}} $ and $ p_{{{\text{H}}_{ 2} }} $ . Water vapor treatment of molten silicon can alone remove boron. However, in combination with hydrogen gas, the removal rate is significantly increased. In addition, the rate of boron removal in silicon has been found to decease with increasing temperature.     

Viscosity of CaO-SiO2-Al2O3-MgO-B2O3 slags

The viscosity of CaO-SiO₂-Al₂O₃ slags with 8% MgO and 4% B₂O₃ is investigated over a broad range of composition, by means of a simplex-lattice experiment design. For slag of basicity 6–8 in the upper left region of the local simplex, with 15–25% Al₂O₃, 8% MgO, and 4% B₂O₃, the viscosity is high: 9.4–26.4 P over the range 1500–1530°C. Displacement of the slags of basicity 5–8 to the lower region of the local simplex ensures high fluidity in the given range of Al₂O₃ concentration: the viscosity is 1.5–6.1 P over the range 1500–1530°C.     

Structural Investigation of Phosphorus in CaO-SiO2-P2O5 Ternary Glass

Metallurgical and Materials Transactions B - The system of CaO-SiO2-P2O5 ternary glass is not only among the major constituents of steelmaking slags in iron and steel industry, but also play a...