Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na₂O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na₂O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na₂B₂O₄) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na₂O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas.     

Wettability of Silicon Carbide by CaO-SiO2 Slags

The wettability of silicon carbide by liquid CaO-SiO₂ slags that contain 47 to 60 wt pct SiO₂ was studied using the sessile drop wettability technique. The experiments were carried out in Ar and CO atmospheres. A small piece of slag was melted on SiC substrates under different heating regimes up to 1600 °C. It was found that the wetting is not significantly dependent on the temperature and the heating rate. However, the wettability is relatively high, and the wetting is higher for slags that contain lower SiO₂ concentrations. Moreover, the wettability between the slags and SiC is dependent on the gas phase composition, and it is higher in Ar than that in CO. When the SiO₂ concentration changes from 47 pct wt to 60 pct wt, the wetting angle changes from 20 deg to 73 deg in Ar and from 58 deg to 87 deg in a CO atmosphere. The formation and bursting of gas bubbles also was observed after some contact time, which indicates that the wetting system is a reactive type. However, microscopic studies indicated that no metal phase exists at the slag/silicon–carbide interface. Therefore, it was concluded that chemical reactions between the slag and SiC take place and that SiO₂ is slowly reduced to form CO and SiO gases. Based on the experimental data, the dependence of the Girifalco–Good coefficient on the slag composition and the relationship between the interfacial tension of CaO-SiO₂ slags and SiC also were estimated.     

On the Dissolution Behavior of Sulfur in Ternary Silicate Slags

Sulfur dissolution behavior, in terms of sulfide capacity (C _S), in ternary silicate slags (molten oxide slags composed of MO – NO – SiO₂, where M and N are Ca, Mn, Fe, and Mg), is discussed based on available experimental data. Composition dependence of the sulfur dissolution, at least in the dilute region of sulfur, may be explained by taking into account the cation–anion first-nearest-neighbor (FNN) interaction (stability of sulfide) and the cation–cation second-nearest-neighbor (SNN) interaction over O anion (oxygen proportions in silicate slags). When the Gibbs energy of a reciprocal reaction MO + NS = MS + NO is positive, the sulfide capacity of slags with virtually no SiO₂ or low SiO₂ concentration decreases as the concentration of MO increases. However, in some slags, as SiO₂ concentration increases, replacing NO by MO at a constant SiO₂ concentration may increase sulfide capacity when the basicity of NO is less than that of MO. This phenomenon is observed as rotation of iso-C _S lines in ternary silicate slags, and it is explained by simultaneous consideration of the stability of sulfide and oxygen proportions in the silicate slags. It is suggested that a solution model for the prediction of sulfide capacity should be based on the actual dissolution mechanism of sulfur rather than on the simple empirical correlation.     

Dissolution Behavior of Aluminum Titanate Inclusions in Steelmaking Slags

Metallurgical and Materials Transactions B - The current work investigates the dissolution path and mechanism of aluminum titanate inclusions in steelmaking slags using a high-temperature confocal...     

Reactions Between Liquid CaO-SiO2 Slags and Graphite Substrates

Metallurgical and Materials Transactions B - In this study, the spreading and infiltration behavior of liquid slag in contact with different grades of graphite was investigated. The wetting and...     

Investigation of the Viscosity and Structural Properties of CaO-SiO2-TiO2 Slags

The viscosity of CaO-SiO₂-TiO₂ slags was measured via the rotating cylinder method to reveal the effect of TiO₂ on viscous flow of the slags. Furthermore, the structure of the ternary slags and the role of Ti⁴⁺ were investigated by Fourier transform infrared and Raman spectroscopy techniques. The results are beneficial for a better understanding of the behaviors of Ti-bearing silicate slags. The TiO₂ additions lowered the viscosity and apparent activation energy of the slags. However, the degree of polymerization (DOP) of silicate network was found to be enhanced with increasing the TiO₂ content, which is suggested by the increase in mole fraction of Q ³ ([SiO₄]-tetrahedra with three bridging oxygens) and the decrease in Q ⁰. The Eq. [2] Q ² ? Q ¹ + Q ³ was appropriate to express the relationship of different Q ⁿ species. The introduction of Ti⁴⁺ into the silicate network as network formers increased the DOP but weakened the strength of slag structure at the same time. Besides, a large proportion of Ti⁴⁺ exists in the slag in the form of \( TiO_{4}^{4 - } \) monomers, resulting in a decrease of viscosity with increasing TiO₂ content.     

Effect of Chlorine on the Viscosities and Structures of CaO-SiO2-CaCl2 Slags

Metallurgical and Materials Transactions B - The viscosities of CaO-SiO2-CaCl2 (CaO/SiO2 = 1.12) slags were measured to elucidate the effect of chlorine with CaCl2 content from 0...     

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...     

An interacting pair model for alkaline binary and ternary liquid silicates: Application to the systems Na2O-K2O-SiO2 and Na2O-Cs2O-SiO2

Among all the available models describing the structure of molten silicates, that of Pelton et al. allows accurate fitting of the experimental data of the free energies in the binary systems MO-SiO₂ with M=Fe, Mn, Pb, and Ca. An extension to the ternary systems MO-M′O-SiO₂, where M and M′ are alkaline metals, is proposed. A statistical treatment of the configurations of the solution gives a meaning to the new parameters. The mixed alkaline effect is quite well shown by the application of the model to the ternary systems K₂O-Na₂O-SiO₂ and Cs₂O-Na₂O-SiO₂, in particular, in the calculation of the configurational entropy.     

Insight into the Relationship Between Viscosity and Structure of CaO-SiO2-MgO-Al2O3 Molten Slags

Metallurgical and Materials Transactions B - This article elucidates the quantitative relationship between viscosity and structure in a basic slag system of CaO-SiO2-MgO-Al2O3 and focuses on the...     

碱度对CaO-SiO_2-Al_2O_3-MgO-TiO_2渣系黏度的影响

针对重庆钢铁集团近年来增加澳矿使用量后,炉渣中Al2O3含量的增加对炉渣流动性的不利影响,对重钢高炉的炉渣性能进行了试验研究。以重钢高炉现场渣为基础,利用旋转黏度计测试了Al2O3质量分数为12%、Mg O质量分数为8%、Ti O2质量分数为5%、碱度为1.07~1.50时,Ca O-Si O2-Al2O3-Mg O-Ti O2渣系黏度变化情况;并测量了不同Ti O2含量时炉渣黏度变化情况。研究结果表明:在当前碱度范围内,随着二元碱度增加,炉渣黏度降低,当二元碱度超过1.35时,黏度降低趋势变平缓;炉渣中加入适量Ti O2能降低黏度,改善流动性。     

Messung der Aktivität der Sauerstoffionen in den flüssigen Systemen Na2O-SiO2 und K2O-SiO2

Erörterung der Anwendung von Festelektrolytzellen zur Ermittlung thermodynamischer Eigenschaften von Schlackenschmelzen. Verwendung einer Festelektrolytzelle zur Bestimmung der Schlackenbasizität durch Berechnen des negativen Logarithmus der Sauerstoffionenaktivität (pO-Wert) aus den EMK-Messungen an den flüssigen Systemen Na₂O–SiO₂ und K₂O–SiO₂ in Abhängigkeit von Zusammensetzung und Temperatur. Ermittlung der Kieselsäureaktivitäten der Schlacken. Aussagen über die Bildung von Anionenkomplexen.     

Viscosity Measurement and Structure Analysis of Cr2O3-Bearing CaO-SiO2-MgO-Al2O3 Slags

Metallurgical and Materials Transactions B - In this study, the effects of different Cr2O3 contents and optical basicity (denoted by Λ) on the viscosity and structure of the Cr2O3-bearing...     

Thermodynamic study of Na2O-SiO2 melts at 1300° and 1400 °C

The vapor pressures of Na above stirred Na₂O-SiO₂ melts in equilibrium with graphite and CO were determined at 1300° and 1400 °C using the transpiration technique. Compositions studied ranged from about 60 mole pct SiO₂ to close to SiO₂ saturation. Activities of components Na₂O and SiO₂ were calculated from the data. Log a_Na2_O (pure liquid as standard state) varies from about −8.7 and −8.5 at silica saturation to −6.3 and −6.1 at 40 mole pct Na₂O at 1300° and 1400 °C, and the molar Gibbs energy of mixing, ΔG _m, at the disilicate composition (X_Na2_O = 0.33) at each of these temperatures is −83.0 and −85.4 kJ, respectively. The Toop and Samis, Yokokawa and Niwa, and Lin and Pelton solution models for binary silicates were applied to the ΔG _m data at 1350 °C and parameters for the models were estimated to give best fits. All three models show good correspondence with the measured ΔG _m curve. The capabilities of the models in predicting activity data in this system have been compared. D. N. Rego, Formerly Graduate Student at Carnegie-Mellon University, G.K. Sigworth, Formerly with Carnegie-Mellon University,     

The sulfur partition ratio and the sulfide capacity of Na2O-SiO2 slags at 1200 °C

The sulfur partition ratio between carbon-saturated iron and Na₂O-SiO₂ slags and the sulfide capacity of these slags have been measured at 1200 °C. The two measurements are consistent with each other and the results are compared with other investigations. These slags have higher sulfide capacities and partition ratios than equivalent CaO-based slags and are thus attractive desulfurizers. Both the sulfide capacity and the partition ratio increase with increasing Na₂O. The activity coefficient of Na₂S has been calculated; it also increases with increasing Na₂O. The solubility of sulfur in a slag of 0.4 mole fraction Na₂O is estimated to be 5 pct.     

Wettability of Molten Steel／Na2O-Li2O-SiO2-B2O3 Slag System

Thewettability phenomenonbetweenmoltensteelandmetallurgicalslagisoneofthemostimpor tantsubjectsinsteelmakingprocess.Theformationofsteel slagemulsions ,andtheformationandelimina tionofnon metallicinclusionsinsteelaretypicalex amples.Theinterfacialtensionan…     

Potentiostatic polarization measurements on solid platinum-molten PbO-GeO2, PbO-SiO2, and Na2 O-SiO2 interfaces

Potentiostatic polarization measurements were carried out to investigate the mechanism of the charge transfer process on solid platinum-molten PbO-GeO₂, PbO-SiO₂, and Na₂O-SiO₂ interfaces over a temperature range of 900° to 1135°C in an atmosphere of air and argon-oxygen gas mixtures.     

稀贵金属铑物料溶解技术研究进展

稀贵金属铑物料的溶解是铑冶金领域不可或缺的环节,并且是公认的难题.铑物料溶解技术主要存在的问题在于:溶解周期长、溶解效率低、回收率低、试剂消耗量大、能耗高、操作过程复杂、返料多、环境污染严重等.铑的高效清洁溶解,保证铑的回收率一直是科研人员研究的重点,但大多数溶解技术仅处在实验室研究阶段,处理规模不大,工业化应用实施难度大.目前工业中应用的铑物料溶解技术主要是中温氯化-溶解法和硫酸氢钠(钾)熔融-溶解法,但也都存在不同程度的问题.通过对难溶稀贵金属铑物料的溶解技术研究进展情况进行较为全面的介绍;对各种溶解技术的关键技术进行分析;对各种溶解技术所存在的问题进行讨论,认为铑物料高效清洁的溶解新技术的研发及推广引用,是当前铑冶金领域迫切需要解决的问题;电化学溶解和微波溶解技术对环境污染较小,具有较大的发展潜力,但还需要在提高铑的溶解效率、保证铑的直收率等方面进行更为深入的研究;通过进一步深入系统了解和研究贵金属铑的性质,开发具有规模化、工业化应用的溶解新技术,实现铑物料的高效清洁溶解,提高铑的溶解效率,保证其回收率,是今后铑溶解技术发展的重要方向.