Chemical behaviour of nitrogen in metallurgical slags

According to previous experimental work, nitride capacity C_N, in opposition to sulfide capacity C_S, decreases with increasing optical basicity of metallurgical slags. This tendency is also confirmed by the contradictory behaviour of the free energy changes of oxide-nitride and oxide-sulfide transformation reactions as a function of basicity. From the present metal-slag equilibrium studies, denitrogenation potentials P_N = %(N)/{%[N] · %[Al]} were obtained characterizing denitrogenation efficacy of slags at given compositions and temperatures. From these potentials, factors were derived which mark the effects of individual slag components. It was found that these factors feature the same basicity dependence as nitride capacities C_N and denitrogenation potentials P_N. The factors are increased, e.g., as less basic oxides are increasingly present in the slag phase in the order BaO → SrO → CaO → MgO.     

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.     

Nitrogen solution in BaO-B2O3 and CaO-B2O3 slags

The nitrogen solubility and nitride capacity of the BaO-B₂O₃ and CaO-B₂O₃ systems were measured at 1698 and 1773 K, respectively, using a gas-liquid equilibration technique. These systems were chosen because they have wide liquidus regions at the temperature of interest and were expected to show two types of nitride solution behavior. The nitride capacities of both systems showed minimum values with changing composition. This was explained by considering that nitrogen can dissolve into slag as “free nitride” at high basicities and as “nitride incorporated” with the network for acidic slags. The change of the nitride capacity with optical basicity and the activity of the basic component followed the predicted behavior for the proposed solution mechanism. The nitride capacity of the BaO-B₂O₃ system is considerably greater than for the CaO-B₂O₃ system because BaO is a more basic oxide than CaO. The activity of BaO in the BaO-B₂O₃ system was also measured by equilibration with liquid silver, at known oxygen potentials, and the activities show large negative deviations from ideal behavior.     

The sulphide capacity of CaO-SiO2-Al2O3-MgO(-FeO) smelting reduction slags

The effects of MgO and FeO contents on the sulphide capacity of Corex slags were investigated at 1773 K using gas/slag equilibrium technique as a fundamental study for stabilising Corex operational conditions. The gradual substitution of MgO for CaO at a fixed basicity [B = {(%CaO)+(%MgO)}/(%SiO₂)] decreased the sulphide capacities of CaO-SiO₂-Al₂C₃-MgO slags. The addition of FeO into the CaO-SiO₂-Al₂O₃-MgO slags at the fixed (%CaO)/(%SiO₂) ratio, MgO and Al₂O₃ contents significantly increased the sulphide capacities. The sulphide capacity decreased according to the increasing Al₂O₃ content at the fixed (%CaO)/(%SiO₂) ratio, MgO and FeO content. Based on the previously reported and present values of sulphide capacities, the sulphide capacity as a function of slag composition on the mole fraction base at 1773 K was expressed by the formula of log C_S = X_CaO – 3.89 X_SiO2 – 3.18 X_Al2O₃ – 0.55 X_MgO + 2.43 X_FeO – 2.61. In addition, the relationship between the sulphide capacity and optical basicity could be represented as the formula of log C_S = 12.51 A – 12.24 and the theoretical optical basicity of FeO was found be 0.94 from the correlation. The effect of FeO on the sulphur distribution ratio was estimated using the present sulphide capacity values and the oxygen activity in liquid iron, which could be determined with the help of Fe/FeO equilibrium. FeO activity in slag was well described by the quadratic formalism based on the regular solution model. The sulphur distribution ratio according to FeO content varies in an opposite way, compared with that of the sulphide capacity.     

The Effect of MgO on the Viscosity of the CaO‐SiO2‐20 wt%Al2O3‐MgO Slag System

The viscosities of CaO‐SiO₂‐20 wt%Al₂O₃‐MgO slags (CaO/SiO₂ = 1.0–1.2, wt%MgO = 5–13) were measured to estimate the effect of MgO on the viscous behaviour at elevated temperatures. The slag viscosity at 1773 K decreased with increasing MgO contents, which was typical of a basic oxide component at relatively low basicity (CaO/SiO₂) of 1.0. The FT‐IR spectroscopic analysis of the slag structure seems to verify this behaviour. However, an unexpected contradiction with the temperature dependence was observed above 10 wt%MgO and above CaO/SiO₂ of 1.2. Although the apparent activation energy was expected to decrease with additions of the basic oxide component MgO, the apparent activation energy increased. This unexpected behaviour seems to be related to the change in the primary phase field correlating to the phase diagram corresponding to the slag composition. Therefore, in order to understand the viscosity at both high Al₂O₃ and MgO, not only should the typical depolymerization of the slag structure with high MgO content be considered but also the primary phases of which the molten slag originates.     

CaO-SiO2-MgO-Al2O3-BaO渣系脱硫能力研究

为了探究温度、碱度（R）、MgO质量分数和BaO质量分数对高炉渣脱硫能力影响,以酒钢现场高炉渣实际成分为基准,选取分析纯化学试剂配制实验渣样,采用双层石墨坩埚法研究了含钡渣系的脱硫能力,并考察BaO对脱硫动力学条件的影响。研究结果表明,增大高炉渣碱度,提高渣中MgO质量分数均能使硫分配比增加,炉渣脱硫能力增强。渣中BaO质量分数由0增加到4%,硫分配比先逐渐升高后略有降低,BaO质量分数为35%左右时硫分配比达到最大值。BaO质量分数增加使得熔渣中硫的传质系数增大,脱硫速率明显提升。     

硫容量模型和在五元渣系CaO SiO2 MgO Al2O3 FetO中的应用

 硫容量和硫平衡分配比是衡量炼钢过程中渣系脱硫能力的重要指标。通过光学碱度模型和KTH模型计算了五元渣系CaO SiO2 MgO Al2O3 FetO的硫容量,并与文献的实验测定值进行了比较。结果表明用KTH模型计算的硫容量比用光学碱度模型计算的硫容量更接近实验值,因此KTH模型可用来预测不同组元渣系的硫容量。还详细研究了硫容量和硫平衡分配比的影响因素,结果表明硫容量随炉渣碱度和温度的增加而增加,硫平衡分配比随着钢液中铝、碳、硅含量的增加而增加。     

Carbon Solubility in the CaO-SiO2-3MgO-CaF2 Slag System

The carbon solubility in the CaO-SiO₂-3MgO-CaF₂ slag system at 1773 K (1500 °C) was investigated under CO/Ar and CO/N₂ gases. Higher extended basicity [(CaO + MgO)/SiO₂) increased the carbon solubility in the slag as the activity of free oxygen ions ( $ \varvec{a}_{{{\mathbf{O}}^{2 - } }} $ ] promoted the reaction of the free carbide mechanism. Higher CaF₂ also resulted in higher carbon dissolution into the slag as fluorine ions interact with the bridged oxygen (O⁰) in the melt structure to increase the activity of the free oxygen ions in the melt. Structural information obtained from the Fourier transformed infra-red (FT-IR) and Raman revealed a depolymerization of the network structure as the simpler structural units of NBO/Si = 4 increased and the Si-O-Si bending vibrations decreased with higher basicity and CaF₂ content. This correlated well with higher free oxygen ions (O^2?) in the slag system and subsequently higher carbon dissolution. A correlation of the theoretical optical basicity (Λ_th) with the logarithm of the carbon content in slag showed a relatively similar trend and an increase of carbon was observed with higher optical basicity.     

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.     

Study on phosphate and sulphide capacities of CaO-CaCl2 slags

Experiments were carried out at 1175–1350°C to study the phosphate capacity of CaO-CaCl₂ slags and the sulphide capacity was calculated according to the correlation between the two capacities. At 1200°C the logarithm of the phosphate capacity increased from 24.5 to 26.5 with increasing CaO mole fraction from 0 to 0.22 in the slags and it decreased with increasing temperature. Sulphide capacity increased both with increasing CaO mole fraction and temperature. A good linear correlation was found between slag carbonate capacity and phosphate capacity as well as sulphide capacity. Optical basicity was used to evaluate the property of the CaO-CaCl₂ slag in the present study. The value of optical basicity of CaCl₂ is established as 0.63. The correlations of optical basicity with above mentioned three capacities were found to be linear.     

Slag-foaming phenomenon originating from reaction of titanium-bearing blast furnace slag: effects of TiO2 content and basicity

ABSTRACT

The foaming behaviour originating from the reduction of iron oxide in molten CaO–SiO₂–MgO–Al₂O₃–TiO₂ slag was studied at 1500°C with the aid of a real-time foaming process monitoring system. The effect of TiO₂ content and binary basicity on the slag foaming were investigated. It was found that the TiO₂ content has a significant influence on the foaming degree, while the basicity of the slag has a smaller influence. The foam-generation time, foam duration, and foam-elimination time greatly increased with increasing TiO₂ content, while they slightly increased with increasing basicity. Furthermore, the source of gas and the effect of physical properties of the slag on the foaming behaviour were also discussed. This study can provide a guideline for the utilisation of high-ratio titanium-bearing magnetite ore in the blast-furnace iron-making process, which is seriously affected by the slag-foaming problem.     

高Al2O3含量的高炉渣熔化性能研究

以首钢现场高炉渣为基础渣样,采用三角锥试样变形法,在高Al2O3含量的条件下研究了炉渣二元碱度、Al2O3含量及MgO含量对高炉渣熔化性能的影响.结果表明：三角锥试样变形法可以使炉渣试样的熔化变形过程更明显,特征温度的判断也更加准确;炉渣二元碱度（1.0～1.25）以及Al2O3含量（15％ ～ 22％）增加均会使炉渣熔化性温度出现较为明显的升高;适当地增加MgO含量可以在一定程度上改善炉渣的熔化性能.     

The solubility of water vapour in CaO‐SiO2‐Al2O3‐MgO slag system

The solubility of water vapour in the CaO‐SiO₂‐Al₂O₃‐MgO quaternary slag system was measured using an inert gas fusion technique with thermal conductivity detection. The slags were equilibrated with argon‐water vapour mixture corresponding to 0.157 bar of water vapour pressure at 1873 K. The slag solubility of water vapour is proportional to the square root of vapour pressure. Since the hydroxyl capacity of slag, C_OH shows an independence on the relative amount of CaO or MgO in slag, the contributions of CaO and MgO on the hydroxyl capacity are equivalent on a molar basis. Whereas, Al₂O₃ shows a better effect on the hydroxyl capacity than SiO₂. A linear relationship between hydroxyl capacity and slag basicity in logarithmic scale was obtained with the slope of 1/2, confirming the water vapour dissolution reaction into a basic slag as (O^2‐) + H₂O(g) = 2(OH^?). The correlation between hydroxyl capacity and slag components was derived in terms of their contributing weight factors. The measured values of C^'_OH agree well with the calculated ones using the interaction energies of α_H‐Al = ?38300 and α_H‐Mg = ?22700 J determined with the aid of the regular solution model. In addition, the correlation between hydroxyl capacity and sulphide capacity was empirically derived as a formula of logC_OH = 1/2logC_S + (4.38 ± 0.25) through the thermodynamic expression of both capacities by virtue of the common oxygen ion activity.     

Thermodynamics of nitrogen in CaO-SiO2-AI2O3 slags and its reaction with Fe-Csat. melts

The solubility of nitrogen as the nitride ion in CaO-SiO₂-Al₂O₃ slags in equilibrium with N₂-CO gas mixtures and carbon was measured at 1823 K. The nitride capacity (C _N3-) was calculated to compare the nitrogen contents measured under different nitrogen and oxygen potentials.C _N3- decreased with increasing basicity and by replacing SiO₂ with A1₂O₃. The nitrogen partition ratio between carbon saturated iron and the slag was measured in CO gas at one atmosphere at 1823 K. By comparing the partition ratios with the corresponding nitride capacities measured by the gas-slag experiments, it was concluded that the oxygen partial pressure at the slag-metal interface was controlled by the Fe-FeO reaction. A new definition of nitride capacity was proposed based on the reaction between nitrogen and the network former,i.e., SiO₂ or A1₂O₃. This capacity could consistently explain the experimental results. Empirical equations were derived to estimate the activity coefficients of silicon and aluminum nitrides in the slags. On leave of absence from the Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Sendai, Japan.     

Effect of FeO and CaO on the Sulfide Capacity of the Ferronickel Smelting Slag

The effect of FeO and CaO on the sulfide capacity in MgO-SiO₂-FeO based slags equilibrating with Fe-Ni alloys at 1773 K and 1873 K (1500 °C and 1600 °C) was investigated. The sulfide capacity in the MgO-SiO₂-FeO and MgO-SiO₂-CaO-FeO slags increased with higher FeO content and higher temperatures due to an increase in the activity of O^2? and a decrease in the activity coefficient of sulfide ion in slag. The sulfide capacity of the MgO-SiO₂-CaO-FeO slag also increased with an increase in the CaO content due largely to the increase in the activity of O^2?. Furthermore, CaO and FeO seem to be more effective than MgO in increasing the sulfide capacity in the MgO-SiO₂-CaO-FeO slag system. In addition, the comparison of the experimental results with the theoretical estimate using the modified empirical optical basicity showed relatively good linear agreement.     

Influence of refining slag composition on cleanness and fatigue life of 60Si2MnA spring steel

The influence of basicity and Al₂O₃ content of LF refining slag on T.[O] (total oxygen) as well as type, number and size of non-metallic inclusions in Al killed 60Si2MnA spring steel was investigated. The results showed that with the increase of slag basicity R(CaO/SiO₂) or the decrease of Al₂O₃ content in slag, the T.[O], number and size of non-metallic inclusions decreased significantly. On the one hand, as the slag basicity increased, inclusions in steel were transformed from Al₂O₃–SiO₂–CaO–MgO quaternary system to Al₂O₃–SiO₂–CaO–MgO–CaS quinary system, which made the formation of voids between inclusions and steel matrix to decrease. Furthermore, thermodynamic calculations showed that CaS could only form in steel (R?≥?3.4). Al₂O₃–SiO₂–CaO–MgO came close to the compositions of the low melting point area, while Al₂O₃–SiO₂–CaO–MgO–CaS deviated from this. On the other hand, as the Al₂O₃ content in slag increased, Al₂O₃–SiO₂–CaO–MgO–CaS came close to the compositions of the low melting point area. In conclusion, the cleanness and fatigue life of 60Si2MnA spring steel had been improved by the increase of slag basicity or the decrease of Al₂O₃ content in slag.     

Optimization of BF Slag for High Cr2O3 Vanadium-titanium Magnetite简

In order to clarify the slag system of high Cr2O3 vanadium-titanium magnetite smelting in BF （blast furnace）, the melting properties of slag samples prepared by analytically pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high Cr2O3 vanadium-titanium magnetite was obtained, which contained 10% MgO, 8% TiO2 and 15% Al2O3, with the binary basicity being 1.15. In addition, the effects of basicity, MgO, TiO2 and A12 03 on slag melting properties were investigated by single factor test, and the results showed that, with increasing the basicity or TiO2 content, melting temperature （Tin） increased, whereas initial vis- cosity （r/0） and high temperature viscosity （r/h） decreased. With increasing the MgO content, Tm decreased firstly and then increased. With increasing the Al2 O3 content, Tm increased, and η0 and r/h decreased firstly and then increased.     

The influence of MgO,K2O,Na2O and gas pressure on slag foaming behaviour under reducing conditions

Using a photoelectric measuring technique to determine the foaming behaviour of iron oxide-containing slag, investigations were carried out into the influences of magnesium oxide and the alkali oxides K₂O and Na₂O on melt foaming behaviour under reducing conditions. An MgO content of just a few percent intensifies the foaming action of acidic and self-fluxing melts. This behaviour is also induced by a relatively low addition of alkali oxide. If the magnesium oxide and alkali oxide addition is further increased, slag volume growth during foaming declines. With basic compositions, both the magnesium oxide and the alkali oxides may reduce the volume increase of the foaming slag. Overall, melts undergo maximum foaming under conditions of medium basicity and in the medium temperature range. Alkali oxides promote the phenomenon of melt resolidification often observed in the tests. Tests with different furnace gas pressures up to max. 3 bar reveal that foaming volume of the melt increases with rising gas pressures.     

Thermodynamics of nitrogen in CaO-SiO2-AI2O3 slags and its reaction with Fe-Csat. melts

The solubility of nitrogen as the nitride ion in CaO-SiO₂-Al₂O₃ slags in equilibrium with N₂-CO gas mixtures and carbon was measured at 1823 K. The nitride capacity (C _N3-) was calculated to compare the nitrogen contents measured under different nitrogen and oxygen potentials.C _N3- decreased with increasing basicity and by replacing SiO₂ with A1₂O₃. The nitrogen partition ratio between carbon saturated iron and the slag was measured in CO gas at one atmosphere at 1823 K. By comparing the partition ratios with the corresponding nitride capacities measured by the gas-slag experiments, it was concluded that the oxygen partial pressure at the slag-metal interface was controlled by the Fe-FeO reaction. A new definition of nitride capacity was proposed based on the reaction between nitrogen and the network former,i.e., SiO₂ or A1₂O₃. This capacity could consistently explain the experimental results. Empirical equations were derived to estimate the activity coefficients of silicon and aluminum nitrides in the slags. On leave of absence from the Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Sendai, Japan.     

A Study of Some Elemental Distributions Between Slag and Hot Metal During Tapping of the Blast Furnace

This paper investigates the distribution of elements between slag and hot metal from a blast furnace through calculation of distribution coefficients from actual production data. First, samples of slag and hot metal tapped from a commercial blast furnace were taken continually at 10‐minute intervals for a production period of 68 hours. Distribution coefficients of manganese, silicon, sulphur and vanadium were then calculated from the results of the sample analyses. A major conclusion drawn from examination of the results was that the behaviour of the studied elements was as could be expected when approaching the equilibrium reactions from thermodynamic theory. The distributions of the elements in the slag‐metal system showed clear tendencies which did not appear to be influenced by the operational conditions of the furnace. For example, for manganese, vanadium and sulphur, it was found that a higher basicity led to a decreased distribution coefficient L_Mn and L_V, but an increased L_S, which is according to theory. Another observed relationship was that slag basicity increased with an increased carbon content in the hot metal, which indicated that SiO₂ was reduced to [Si] when the oxygen potential decreased. Furthermore, it was found that sulphur and silica behaviour likened that of acidic slag components, while the manganese oxide and vanadium oxide behaviour was similar to that of basic slag components.