Oxygen pressure dependence of tracer diffusivities of Ca and Fe in liquid CaO-SiO2-FexO system

The tracer diffusivities of calcium and iron in a steel-making slag of 33 pct CaO-27 pct SiO₂-40 pct Fe₂O₃ by charge composition have been measured at 1360 to 1460°C as a function of temperature and oxygen pressure in the gas phase. The results expressed in cm²/s (in SI unit of m²/s, the following equation should be divided by 10,000) are given by $$D^{tr} = D_0 \left[ {P_{O_2 } } \right]^{1/\chi } \exp \left[ { - \frac{E}{{RT}}} \right](at 1360 to 1460^\circ C)$$ where for tracer diffusion of iron, D_o is 0.2,x is 8.5, andE is 26 kcal/mol (1.09 x 10⁴ J/ mol) and for tracer diffusion of calcium, D_o is 0.1,x is 12.5, andE is 28 kcal/mol (1.17 × 10⁴ J/mol). Prior to diffusion runs, the slag was equilibrated with the gas mixture of carbon monoxide and dioxide with an oxygen pressure of 10^?11 to 10^?8 atm. The diffusivity was measured by the instantaneous plane source method, using radioactive tracers of calcium and iron. The increase of the tracer diffusivities with the oxygen pressure was interpreted in relation to a probable increase of the divalent cation vacancies in the slag.     

CaO-SiO2-FeOx-MgO氧化物体系液相区及相关系计算

焚烧垃圾底灰的主要氧化物组分为SiO2、CaO、Al2O3、Fe2O3、Na2O和MgO,该六元体系相关系和热力学性质对于焚烧底灰渣化处理中玻璃相形成以及重金属低浸出具有重要影响.本文运用计算热力学理论及相图计算方法,对CaO-SiO2-FeOx-MgO四元氧化物体系的热力学性质进行了研究,获得了描述该四元系液相吉布斯自由能的模型参数,并依此计算了不同温度及氧分压下SiO2-FeOx-MgO、CaO-SiO2-FeOx和CaO-SiO2-FeOx-MgO体系液相区和高铁区域的相关系.计算结果表明温度及氧分压对上述3个氧化物体系的液相区及高FeOx区域的相平衡关系具有较大影响     

Oxygen pressure dependence of Cu2O-CuO-Gd2O3 phase diagram

The phase diagram of the Gd-Cu-O system has been investigated under various oxygen partial pressures by thermal analysis. In this system, only one ternary compound Gd₂CuO₄ exists stably, depending on the oxygen partial pressure. This compound decomposes to Gd₂O3 and Cu₂O under low oxygen partial pressure at high temperature. The incongruent melting and decomposition temperatures of Gd₂CuO₄ and the temperature of eutectic reaction have been investigated as a function of oxygen partial pressure. The present ternary system includes two invariant reactions:L + Gd₂O₃ ⇆ Gd₂CuO₄ + Cu₂O at 1376 K under 0.07 atm O₂ (7.09 kPa) andL⇆ Gd₂CuO₄ + CuO + Cu₂O at 1321 K under 0.42 atm O₂ (42.56 kPa). The thermodynamic properties of the system have also been considered.     

An assessment of the CaO-SiO2 system

An evaluation of the CaO-SiO₂ system has been made using a newly developed model, a two-sublattice model for ionic solutions. Two alternatives were tested. In the first one, three anions were assumed, O⁻², SiO₄ ⁻⁴, and SiO₃ ⁻². In the second one, SiO₃ ⁻² was omitted. A set of parameter values describing the Gibbs energy of the liquid phase and solid phases was fixed for each alternative by a computer-operated optimization procedure called PARROT. Satisfactory assessments were achieved over the whole phase diagram range with both alternatives. The main difference between them occurs at the monotectic point. A comparison between calculated properties and experimental data is given. Formerly Research Associate, Royal Institute of Technoloy     

Solubility of nitrogen in CaO-SiO2-CaF2 slag system

Equilibrium experiments between gas and slag were carried out to understand the thermodynamic behaviour of nitrogen in the CaO-SiO₂-CaF₂ slag system at 1600°C. The solubility of nitrogen in this slag system increased as the oxygen potential decreased and as the reaction temperature increased. The values of the nitride capacity have a minimum at about 2.0 slag basicity, having higher values in both more acidic and basic regions. This may be explained by two mechanisms for nitrogen dissolution; incorporated nitride ion and free nitride ion state. In slag with 2.0 basicity or less, MgO content increased the nitride capacity slightly. At higher slag basicity, however, nitride capacity decreased with MgO content. The effects of BaO to substitute CaO on nitride capacity showed similar behaviour as MgO. This complex relationship between basicity of slag and nitride capacity is explained by using optical basicity. It was found that nitride capacity and optical basicity had a close relationship even in the different basic oxide systems.     

Thermodynamic behaviour of carbon in CaO-SiO2 slag system

In order to understand the thermodynamic behaviour of carbon in steelmaking slag at high temperature, the carbon dissolution into CaO-SiO₂ slag system has been investigated including the effects of temperature and slag components on the carbon dissolution reaction. It was found that carbide solubility in the CaO-SiO₂ slag decreased with increasing oxygen potential to confirm the theoretical relationship of ?1/2, which reflected the ionic exchange reaction mechanism between carbon and oxygen ions. Carbide solubility in slag as a function of slag basicity for various slag systems appeared to confirm this mechanism. This reaction mechanism implied that the carbide dissolution proceeded due to the reaction of solid carbon and oxygen ions supplied from (CaO) in slag. The oxygen ion appears to be the driving force as it is influenced by the slag components as well as the temperature as shown in the concept of the carbide capacity of slag. The solubility of carbide in the CaO-SiO₂ slag increased with the addition of CaF₂; the role of CaF₂ for carbide dissolution into slag could be speculated to have complex effects on indirect increase in basicity in spite of (CaO) dilution. Substitution of CaO by MgO decreased the solubility of carbide in the CaO-SiO₂-MgO slag, possibly caused by the relatively low electro-negativity of MgO.     

Silicon-Oxygen equilibrium and nitrogen distribution between CaO-SiO2 slags and liquid iron

Silicon-oxygen equilibria in an Fe-0.003 ~ 27 mass pct Si alloy in equilibrium with the CaO-SiO₂ slags were studied in the temperature range of 1823 to 1923 K using a lime crucible. At the same time, nitrogen distribution ratios, L_N, between slag and metal were measured, and from these results and the reported values for activities of SiO₂, nitride capacities, , defined by (mass pct N). were evaluated. It was found that the values for L_N decreased, whereas those for increased with an increase in temperature. Activities of SiO₂ were determined using the values for L_N and obtained in previous gas-slag experiments. These values were compared with the previous results.     

Phase relations in the system CaO-SiO2-ZrO2 at 1573 K

Zirconia-based solid electrolytes with zircon (ZrSiC₄) as the auxiliary electrode have been suggested of sensing silicon concentrations in iron and steel melts. A knowledge of phase relations in the ternary system MO-SiO₂-ZrO₂ (M = Ca, Mg) is useful for selecting an appropriate auxiliary electrode. In this investigation, an isothermal section for the phase diagram of the system CaO-SiO₂ZrO₂ at 1573 K has been established by equilibrating mixtures of component oxides in air, followed by quenching and phase identification by optical miroscopy, energy disperse analysis of X-rays (EDAX) and X-ray diffraction analysis (XRD). The equilibrium phase relations have also been confirmed by computation using the available thermodynamic data on condensed phases in the system. The results indicate that zircon is not in thermodynamic equilibrium with calcia-stabilized zirconia or calcium zirconate. The silica containing phase in equilibrium with stabilized zirconia is Ca₃ZrSi₂O₉. Calcium zirconate can coexist with Ca₃ZrSi₂Og and Ca₂SiO₄.     

Oxidation state and activities of chromium oxides in CaO-SiO2-CrOx slag system

The activities of chromium oxides in a CaO-SiO₂-CrO _x slag system were determined with the electromotive force (EMF) method by equilibrating with metallic chromium at 1873 K. The effect of slag basicity on the activity coefficients of CrO and CrO_1.5 was analyzed. The results showed that increasing the slag basicity increased the activity coefficient of CrO; however, the effect on that of CrO_1.5 was not significant. The oxidation state of chromium in CaO-SiO₂-CrO _x slags was systematically investigated at both 1873 and 1863 K. It was found that divalent and trivalent chromium coexists in the slags. Divalent chromium oxide is favored, instead of trivalent chromium oxide, because of low slag basicity and low oxygen potential. It was concluded that the oxidation state of chromium in the slag system varied greatly from almost pure “CrO” to a composition corresponding to Cr₃O₄. In addition, the thermodynamic data in the slag system were assessed based on the regular solution model to mathematically describe the activities of chromium oxides in the slags. A group of model parameters were obtained. The calculated activities of chromium oxides were comparable to the measured data.     

CaO-SiO2-FeOx及CaO-SiO2-P2O5-FeOx渣系热力学性质的研究

CaO-SiO2-FeOx三元渣系和CaO-SiO2-P2O5-FeOx四元渣系是转炉脱磷用渣的主要子渣系,研究这两种渣系的热力学性质可为脱磷渣的高效利用提供理论依据。利于相图软件FactSage分别绘制了这两种渣系的相图,并分析了温度和氧分压对体系相平衡关系和液相线的影响规律。分析结果表明:升高温度会使这两种渣系的液相区扩大,初晶相稳定区域显著减小;降低氧分压会导致尖晶石固溶体相的初晶区消失,磷石英(SiO2)、伪硅灰石(CaSiO3)、α’-Ca2SiO4固溶体相减小。     

Distribution equilibria of Pb and Cu between CaO-SiO2-Al2O3 melts and liquid copper

The distribution equilibria of lead and copper between CaO-SiO₂-Al₂O₃ melts and liquid copper were measured at 1623 K under a controlled H₂-CO₂ atmosphere. The distribution ratios were plotted against the oxygen partial pressure, and reasonable oxide forms dissolved in the melts were estimated from the slopes of the plots. The activity coefficients of lead oxide (PbO) and cuprous oxide (CuO_0.5) increased with increasing slag basicity, defined by X _CaO/X _SiO2. The temperature dependence of the activity coefficients of lead oxide and cuprous oxide was also measured.     

Measurement of tracer diffusivities of Ca45 and Fe59 in silica saturated FeO-CaO-SiO2 melts with the porous frit technique

The tracer diffusivities of Ca⁴⁵ and Fe⁵⁹ in silica saturated FeO-CaO-SiO₂ melts have been determined, at 1600 °C, using the porous frit technique. The frits were made by sintering silica powder into quartz tubing. Diffusion occurred in a semi-infinite medium from a plane source of doped material with the same chemical composition. The tortuosity of each frit was determined by calibration with a resistivity cell. The diffusivity values obtained are about 2.0 · 10^?6 cm² s^?1 for Ca⁴⁵ and 1.0 · 10^?5 cm² s^?1 for Fe⁵⁹. The higher diffusivity of iron is possibly due to the different bonding by oxygen which causes a transition state in the jumps of Fe²⁺ ions from one site to the next.     

Activity model of CaO-SiO2-AleO3-V2O3 quaternary system

根据熔渣结构的分子离子共存理论建立了CaO-SiO2-Al2O3-V2O3四元系活度模型。应用该模型计算出的活度数据,对用钒氧化物矿代替钒铁直接合金化冶炼高速钢的工艺过程进行了热力学计算和分析。用此活度数据计算了Al作还原剂时渣的平衡成分。计算结果表明,渣中V2O3的质量分数极低,直接合金化的热力学条件好,钒的理论最大还原率高。通过计算钢中或渣中的各种还原剂还原渣中V2O3的ΔG和LV,表明在炼钢工艺常用的所有还原剂中,Al的还原能力最强。     

CaO-SiO_2-Al_2O_3-V_2O_3四元系活度模型

根据熔渣结构的分子离子共存理论建立了CaO-SiO2-Al2O3-V2O3四元系活度模型。应用该模型计算出的活度数据,对用钒氧化物矿代替钒铁直接合金化冶炼高速钢的工艺过程进行了热力学计算和分析。用此活度数据计算了Al作还原剂时渣的平衡成分。计算结果表明,渣中V2O3的质量分数极低,直接合金化的热力学条件好,钒的理论最大还原率高。通过计算钢中或渣中的各种还原剂还原渣中V2O3的ΔG和LV,表明在炼钢工艺常用的所有还原剂中,Al的还原能力最强。     

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...     

低氧分压条件下CaO-SiO_2-P_2O_5(10%)-FeO体系热力学性质的研究

以促进2CaO·SiO_2-3CaO·P_2O_5固溶体生成的非均相脱磷工艺被视为未来实现转炉少渣冶炼的重要手段,但目前相关渣系热力学性质的研究较少,不能为合理解释非均相渣脱磷的机理提供理论依据.为此,本文利用FactSage热力学软件绘制了低氧分压(1mPa)条件下CaO-SiO_2-P_2O_5(10%)-FeO体系及其子体系的热力学相图,分析了不同温度下相平衡关系及液相线的变化规律.研究结果表明:升高温度可使体系中液相区及Ca_3(PO_4)_2初晶区的范围扩大,但会导致α'-Ca_2SiO_4的初晶区缩小以及Ca_2Fe_2O_5等物相的消失;降低氧分压可使体系的液相区缩小,并向高FeO的方向收缩;CaO-SiO_2-P_2O_5(10%)-FeO体系中存在较大的α'-Ca_2SiO_4与Ca_3(PO_4)_2共存区,尤其是α'-Ca_2SiO_4,Ca_3(PO_4)_2与Ca_2Fe_2O_5的三相共存区可极大地促进2CaO·SiO_2-3CaO·P_2O_5固溶体的生成.     

CaO-SiO_2-10%La_2O_3-Nb_2O_5体系中特定成分范围内液相线分布

本文利用热丝法熔化性能测定仪对CaO-SiO_2-10%La_2O_3-Nb_2O_5四元渣系中特定成分范围内渣样的熔化温度进行测定,分别得到了1573、1623和1673K的液相线分布.同时通过热力学平衡实验以及扫描电镜(SEM)、能谱分析(EDS)等检测分析手段明确了相应区域内的初晶相,并对上述液相线进行修正.实验结果对含铌和稀土渣系热力学信息的进一步研究以及铌和稀土资源的综合利用具有实际意义.     

Thermodynamics of chromium oxides in CaO-SiO2-CaF2 slag

The distribution ratio of chromium between a CaO-SiO₂-CaF₂ slag and liquid silver under the oxygen partial pressure used in practical hot-metal dephosphorization treatment was measured at 1623 K. The distribution ratio was minimal when the basicity index of a slag, wt pct CaO/wt pct SiO₂, was about 2. The redox equilibrium between CrO (Cr²⁺) and CrO_1.5 (Cr³⁺) in the slag was also measured as a function of slag composition. The calculated activity coefficient of CrO had a maximum value at wt pct CaO/wt pct SiO₂=2, whereas that of CrO_1.5 decreased monotonously with the increase in slag basicity.     

Photon conductivity of metallurgical slags of the three component system CaO-SiO2-Al2O3

The measuring method proposed by Keene and Quinn has been further developed to investigate 3-component slags of the system CaO-SiO₂-Al₂O₃ at temperatures of 800–1600°C in the wavelength range of 550 to 850 nm. The results are presented with the aid of the complex refraction index, which embodies all information on the optical properties of the slags investigated, including photon conductivity and thermal emissivity. Comparison of the photon conductivities determined shows good agreement with the corresponding values of various types of glass cited in literature. The discontinuous pattern of the phonon conductivity curve in the melting range of 40% CaO-40% SiO₂-20% Al₂O₃ slag, as already found by Gammal and Li, is also evident from the data of the present investigation.     

Effect of Cr2O3 on properties of CaO-SiO2-FetO-MgO system and dissolution behavior of lime

The productivity of the chrome-containing semi-steel converter smelting process is directly affected by the slag-forming speed during the converter preliminary stage.The effects of Cr2O3 content on the physicochemical properties of the CaO-SiO2-FetO-MgO system,such as melting temperature,solidification behavior,mineral composition,and lime dissolution rate,were studied.The results showed that the slag was an amorphous phase at 1500 ℃.When Cr2O3 was added,Ca(Fe,Mg)Si2O6 and spinel were formed in the slag.With the increase in Cr2O3 content,the amount of spinel precipitation increased,and the dendritic Fe3O4 crystal gradually changed into the granular(Fe,Mg)(Fe,Cr)2O4 crystal.As the Cr2O3 content increased from 0 to 2.91 wt.％,the melting temperature of the slag rose,and the melting range of the slag expanded slightly,but the lime dissolution rate did not change.When the Cr2O3 content further increased to 9.09 wt.％,the melting temperature continued to rise,the melting range rapidly expanded,and the lime dissolution rate decreased.