CaO In Slag Research Articles

Electrochemical behaviour of titanium-bearing slag relevant for molten oxide electrolysis

A containerless approach was used to investigate the electrochemical behaviour of TiO2−SiO2−Al2O3−MgO−CaO slags in their molten state. Iridium was used in a three-electrode configuration to perform a combination of electrochemical techniques inside a modified thermal imaging furnace. The real-time visualization during experimentation and the post-mortem microscopy analysis confirmed the direct production of an Ir−Ti−Si alloy and the evolution of oxygen during electrolysis. Thermodynamic properties of the slag were predicted with FactSage and were consistent with experiment. The results justify the use of this method to better characterize the potential of these systems as a secondary source of materials.

The influence of MgO/ZrO2/Al2O3 refractories on the refining process of Ti-containing steel based on kinetic study

Ti-containing steel is widely used in various industries, and its refining process has a significant impact on performance. The influences of refractories on the refining process were studied by the interaction between refining slag and Ti-containing steel in this paper. During the refining process with MgO and ZrO2 crucible, the content of MgO and ZrO2 in the refining slag respectively increase, and they also appear in the inclusions. MgO refractory can promote the reaction between CaO in slag and molten steel, but Al2O3 and ZrO2 refractories cannot. Al2O3 refractory significantly increases the Al2O3 content oin the inclusions by affecting the slag-metal-inclusion reaction. A kinetic model for simulating the reaction of the refractory-slag-metal-inclusion system was established, and it can be applied to predict the composition variations of the slag, the steel, and the inclusions during the refining process. According to the model and experimental results, it is obvious that MgO, Al2O3 and ZrO2 refractories have different mass transfer with refining slag. The mass transfer coefficients of all three refractories were obtained in current research (kMgO = 1.0 × 10-4 m/s, kAl2O3 = 2.0 × 10-4 m/s and kZrO2 = 1.1 × 10-4 m/s).

Effect of Vanadium and Titanium on Desulfurization of CaO Slag in Liquid Iron

The possibility of vanadium and titanium participating in the CaO desulfurization reaction has been evaluated. The desulfurization products of CaO which were added to liquid iron containing vanadium–titanium in lab conditions were observed. At the early stage of adding CaO, titanium and sulfur ware agglomerated on the surface of CaO particles. The particles were composed of CaO, TiO2, and CaS. However, vanadium oxide was not detected. It was proposed that the titanium rather than the vanadium could react with CaO and sulfur. The desulfurization kinetics experiment showed that the high titanium content in liquid iron reduced desulfurization velocity, while vanadium had little effect on the desulfurization. The reason for this was that the TiO2 which surrounded the CaO particle impeded the mass transfer of sulfur. The vanadium and titanium had a little influence on the final sulfur content of CaO desulfurization. The theoretical discussion of these phenomena was carried out. The controlling reaction of final sulfur content was (CaO) + [S] + [C] = (CaS) + CO(g).

Determination of Nitrogen Content in the Slags of CaO — Al2O3 System by Kjeldahl Method

Due to the expansion of the nomenclature of steel grades in the industry and the development of new special alloys with increased strength and corrosion-resistant properties, both in the metallurgical industry and in welding, researchers are very interested in the dissolution of nitrogen in metals and slag. Gas permeability of slag is one of the reasons for the appearance of gases in both the base metal and the weld metal. It is determined by two properties: solubility and mass transfer of gases in slag. In addition, in real conditions, the process of dissolving gases in slag is influenced by the transmission of gases by convection and the initial content of gases in the slag. The transfer of gases to the metal through slag is observed mainly in electroslag processes and welding under flux when there is no direct contact of molten metal with a gas phase. To evaluate the nitrogen permeability of the slag and the mechanism of nitrogen solubility in the high alloys it is necessary to have a reliable, highly sensitive and economical method of gas analysis of nitrogen in metals and slags.
 A review of nitrogen determination methods in steels is presented. The method of analysis of nitrogen in slags of the CaO — АL2O3 system by the Kjeldahl method was tested. The results of the analysis of slag compositions of the CaO — АL2O3 system allowed us to conclude that it is possible to use the Kjeldahl method (determination of nitrogen content in steels) for the determination of nitrogen content in slags. This technique and installation can be recommended for use by metallurgists and welders as a reliable, simple and inexpensive method for nitrogen content analysis in metals and slags.

Interaction of Pure Alumina Refractory with FeO–SiO2 and FeO–SiO2–CaO Slags Relevant to the Novel Flash Ironmaking Technology

Interaction of alumina (Al2O3) refractory with FeO–SiO2 and FeO–SiO2–CaO slags relevant to the flash ironmaking technology (FIT) is investigated in this work. It is shown that for slags relevant to FIT, the interaction process can be described by a kinetic model based on counter diffusion of only Fe2+ and Al3+ cations through hercynite (FeAl2O4) formed as a result of the interaction. The diffusion of Si4+ and Ca2+ ions through FeAl2O4 can be neglected, and the only effect these cations have is that they affect the activity of iron oxide (FeO) at the slag–FeAl2O4 boundary. Analyses of reacted samples using X‐ray diffraction (XRD), scanning electron microscopy–energy dispersive X‐ray spectroscopy (SEM–EDX), and electron probe microanalyzer (EPMA) show that the proposed model appropriately describes the growth of FeAl2O4 with the parabolic rate law being obeyed for both FeO–SiO2 and FeO–SiO2–CaO slags in the temperature range of 1200–1400 °C. The values of effective diffusivity () are calculated independently from experiments with FeO–SiO2 and FeO–SiO2–CaO slags agreed with each other, with the activation energy values in the two cases being 246 and 253 kJ mol−1, respectively. These values of and activation energy are in good agreement with the corresponding values obtained previously from Fe–Al2O3 and FeO–Al2O3 systems.

Study on the Iron Production Process through the Analysis of By‐Products Found at Jiǔdiàn Iron Production Site, China

Jiǔdià n iron production site in China is a relic smelting site, which in the past produced pig iron. In this study, scientific analysis of the smelting furnace and collected slag was conducted to reveal some aspects of the ancient Chinese smelting technique. A 3D model of the smelting furnace showed a narrow lower part and an upper section which increased in diameter upwards. Although the smelting furnace relic does not include the upper part and its complete shape cannot be predicted, the remaining part suggests that the furnace had a larger diameter in the central part compared to the upper and lower parts. Most of the collected slag was completely vitrified. Long prismatic fayalite was observed in the matrix of some samples. The iron particles contained phosphorus, which could not be discharged during smelting work. In addition, as the CaO/SiO2 ratio was 0.42 or lower in the results of the content analysis, no CaO slag former had been added. However, the ratio of CaO/SiO2 to Al2O3/SiO2 did not have a constant trend. This needs to be investigated in a further study. Key words: Smelting furnace, Slag, Indirect smelting method, Slag former

Aluminum, titanium and oxygen control during electroslag remelting of stainless steel based on thermodynamic analysis

Experimental investigation and thermodynamic calculation were carried out to study the effect of slag on alloying elements during electroslag remelting with developing a thermodynamic model to control titanium and aluminum in ingot. The thermodynamic model based on ion and molecule coexistence theory and conservation law of element atoms was established to analyze the change in aluminum and titanium along the height of ingot. The results show that low CaO slag is suitable for electroslag remelting of metal containing high titanium-to-aluminum ratio. As electroslag remelting process consists of slag temperature-rising and temperature-stable periods, TiO2 should be added into water-cooled copper mold during temperature-rising period in order to keep the thermodynamic equilibrium between titanium and aluminum, and the amount of TiO2 is the difference value calculated by the reaction between titanium and alumina at 1477 and 1677 °C.

The Integration of Plant Sample Analysis, Laboratory Studies, and Thermodynamic Modeling to Predict Slag-Matte Equilibria in Nickel Sulfide Converting

The Kalgoorlie Nickel Smelter (KNS) produces low Fe, low Cu nickel matte in its Peirce–Smith converter operations. To inform process development in the plant, new fundamental data are required on the effect of CaO in slag on the distribution of arsenic between slag and matte. A combination of plant sample analysis, high-temperature laboratory experiments, and thermodynamic modeling was carried out to identify process conditions in the converter and to investigate the effect of slag composition on the chemical behavior of the system. The high-temperature experiments involved re-equilibration of industrial matte-slag-lime samples at 1498 K (1225 °C) and P(SO2) = 0.12 atm on a magnetite/quartz substrate, rapid quenching in water, and direct measurement of phase compositions using electron probe X-ray microanalysis (EPMA) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). A private thermodynamic database for the Ca-Cu-Fe-Mg-Ni-O-S-Si-(As) system was used together with the FactSage software package to assist in the analysis. Thermodynamic predictions combined with plant sample characterization and the present experimental data provide a quantitative basis for the analysis of the effect of CaO fluxing on the slag-matte thermochemistry during nickel sulfide converting, in particular on the spinel liquidus and the distribution of elements between slag and matte as a function of CaO addition.

Study on Formation Mechanism of CaO-SiO2-Based Inclusions in Saw Wire Steel

Attempts were made to elucidate the formation mechanism of CaO-SiO2-based inclusions in saw wires by both laboratory experiments and industrial trials. The key point was to make clear the origin of CaO in such oxide inclusions. Probable origins of [Ca] in steel were first discussed, which can be taken into steel from the steel-slag reaction or ferrous alloy. As a result, slag-steel chemical reaction equilibrium was carefully evaluated at 1873 K (1600 °C) to classify the changes of dissolved aluminum ([Al]), total magnesium (Mg), and total calcium (Ca) in steel and the caused composition variations of inclusions. With the rise of slag basicity from 0.5 to 1.8, [Al] was remarkably increased from 0.00045 to 0.00139 mass pct, whereas Mg varied in the range of 0.00038 to 0.00048 mass pct. By contrast, Ca was constantly kept below 0.00003 mass pct. Accordingly, Al2O3 and MgO in inclusions witnessed obvious rises from 5 to 23 mass pct and from 2 to 8 mass pct, respectively. By contrast, inclusions were free of CaO when slag basicity was below 1.5. With slag basicity further increased to 1.8, CaO witnessed a negligible rise to only 1.0 mass pct on average. This phenomenon agreed well with thermodynamic calculations, which revealed that chemical reaction between steel and CaO in slag (for example, between [Si] and CaO) was weak to hardly supplying sufficient [Ca] to steel to increase CaO in inclusions. Ca contained in ferrous alloys as contaminations was not the cause of CaO-SiO2-based inclusions, either. The industrial trial results indicated that CaO-SiO2-based inclusions have been readily produced in short time just after BOF tapping. Also, a percentage of them changed slightly with the proceeding of refining. Based on the good agreement of laboratory, industrial, and thermodynamics calculations results, it can be reasonably concluded that CaO-SiO2-based inclusions in saw wire were exogenous particles from entrapped/emulsified top slag, but not products of slag-steel-inclusion chemical reactions.

Separation of boron from metallurgical grade silicon by a synthetic CaO-CaCl2 slag treatment and Ar-H2O-O2 gas blowing refining technique

Abstract Boron separation from metallurgical grade silicon (MG-Si) is still a puzzle for metallurgical route. A purification method to MG-Si using a synthetic CaO-CaCl2 slag (no SiO2 addition) treatment combined with an Ar-O2-H2O gas blowing technique was studied. The mechanism of boron separation from silicon using the synthetic CaO-CaCl2 slag treatment and the Ar-O2-H2O gas blowing was analyzed and elaborated. The results showed that the intermediate product SiO2, generated by the O2 gas blowing, was combined into silicate with CaO slag reagent. Boron in silicon can be separated by both gaseous borides HBO, BOCl and borate CaO·B2O3. It was found that the boron separation can be further improved by separating soluble boron in the refined silicon using the acid leaching treatment. The total separation efficiency of boron in MG-Si reached 94.5% using the combined slag treatment and gas blowing refining technique followed an acid leaching treatment to the refined silicon.

Viscosity and structure evolution of the SiO2-MgO-FeO-CaO-Al2O3 slag in ferronickel smelting process from laterite

The SiO2 fractions in laterite-nickel ores are quite high, thus certain amount of lime should be used as fluxing material to achieve good fluidity and desulfurization capacity in industrial smelting process. However, this operation leads to an additional cost of lime. In addition, the increase of slag volume decreases the effective furnace volume. To avoid such problem, partial reduction of FeO has been suggested. Therefore, the high SiO2, low MgO and FeO and very little CaO slag is formed, which was less studied in the previous literature. Therefore, the viscosity and slag structure are investigated in the present study through FT-IR and Raman analysis methods. Experimental results show that the slag is a mixture of liquid and solid phases under the experimental temperature. The FT-IR and Raman spectra show that the fractions of the complex polymerization structure decrease significantly with the increase of FeO content and slag basicity, resulting in the decrease of apparent viscosity.

A Dynamic Flux Dissolution Model for Oxygen Steelmaking

A modified model for prediction of flux dissolution in oxygen steelmaking process is presented in this study. The aim of this paper is to introduce a procedure for simulating the amount of dissolved lime with respect to the saturation concentration of CaO by coupling the existing thermodynamic and kinetic models simultaneously. The procedure is developed to calculate the saturation concentrations/solubility of CaO in slag using thermodynamic models namely FactSage™, Cell Model, and Thermo-Calc™. Total amount of dissolved lime is evaluated by integrating solubility values in the rate equation of lime dissolution over time taking into account the effects of physical properties and temperature of slag and particle size of flux additions and validated against industrial data available in literature. Comparison between measured and calculated undissolved lime shows a good agreement between them using any thermodynamic models even though there are some differences in the predictions of saturation concentration of CaO in slag. It has been shown that two distinct control mechanisms for lime dissolution in BOF slags exist and consideration of the free lime-controlled mechanism is essential for accurate prediction of dissolution rate of lime in slag.

Viscosity measurements of the SiO2–K2O–CaO system relevant to biomass slags

The present study delivered the measurements of viscosities in SiO2–K2O–CaO system which is important for many applications including biomass slags. The rotational spindle technique was used in the measurements in the composition range of 49.8–78.2mol% SiO2 and 7.7–29.5mol% K2O and temperature range of 997–1601°C. Molybdenum crucibles and spindles were employed in all measurements in ultrahigh purity argon. Analysis of the quenched sample by Electron Probe X-ray Microanalysis (EPMA) after the viscosity measurement enables the composition and microstructure of the slag to be directly linked with the viscosity. The increase of SiO2 concentration has been proved to significantly increase both viscosity and activation energy. The replacement of CaO by K2O was found to decrease viscosity and activation energy of the SiO2–K2O–CaO slags. The viscosities of the industrial biomass slag are compared with the synthetic slags. Predictions of the viscosity from several models are also compared with the experimental data from the present study and literatures.

Thermodynamic design of electroslag remelting slag for high titanium and low aluminium stainless steel based on IMCT

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of stainless steel with high titanium and low aluminium contents. The CaO in slag has great effect on the activities of TiO2 and Al2O3, and thermodynamic analysis was applied to investigate the CaO behaviour based on the ion and molecule coexistence theory of slag. The thermodynamic analysis results show that the increases as CaO content in slag decreases, which is better for preventing loss of titanium caused by its reaction with the alumina in the ESR slag. The slag with low CaO content at low temperature is suitable for ESR of 1Cr21Ni5Ti.

Influence of Basicity and MgO on Fluidity and Desulfurization Ability of High Aluminum Slag

AbstractThe viscosity of experimental slag, which was mixed based on the composition of a practical blast furnace slag, was measured in this paper. The influence of Al2O3and MgO content, basicityR2=w(CaO)/w(SiO2) on the fluidity of slag was studied. The stepwise regression analysis in SPSS was used to reveal the relationship between sulfur distribution coefficientLSand slag composition as well as furnace temperature. The results show that increasing of MgO up to 12% can decrease the slag viscosity. Thew(MgO) should be controlled below 8% when there is 20% Al2O3in the slag. Temperature of hot metal and content of CaO in slag are the two dominant factors on the desulfurization capacity of slag.

Corrosion of high alumina refractories by Al2O3-CaO slag: thermodynamic and kinetic approaches

The corrosion of refractories results from reactive transport, namely, transport of slag through the open porosity of refractory and chemical reactions of the impregnated medium. The transport involves either diffusion or penetration, depending on the properties of the corrosive slag and the microstructure of the refractory material. In addition, the chemical reactions of dissolution and precipitation of new phases are highly numerous and complex. The mechanisms of corrosion are well-described in the literature. However, the corrosion kinetics is not well-known. This paper focused on the corrosion of high alumina refractories by Al2 O3 -CaO slag. The transport properties of the refractory material were assessed by a capillary rising test. Corrosion tests associated with XRD and SEM-EDS analyses were performed for a better understanding of the kinetics. The aim of this study is to predict the corrosion wear of refractories.

Effect of Boric Acid on the Properties of Magnesium Slag Powder

This paper studies about the boric acid affect on magnesium slag powder properties. The certain content of 0.05% to 3.0%(weight ratio) boric acid and magnesium slag was sufficiently mixed, the mixed powder is putted into a 20 × 20 × 20mm mold, and using 13 tf pressure to press the powder. The molded sample was placed in a muffle furnace, sintering at different temperatures (1000 °C ~ 1200 °C) and different holding times (1h ~ 6h), when holding time is reached, the sample was cooled naturally. Samples were analyzed. The sintered samples using XRD to study phase analysis and using EDS to research elemental composition and doing SEM for microstructure analysis. The results showed that: the main components of magnesium slag CaO, MgO, Fe2O3, Al2O3, β-C2S, γ-C2S and so on. Magnesium slag with certain content of boric acid, with the sintering temperature, the acid content and the holding time increases, the conversion rate of the β-dicalcium silicate change into γ-dicalcium silicate in magnesium slag is decreases. Without adding boric acid the suppress square material magnesium slags are mess into powder, magnesium slag joined with certain content of boric acid still be a square material, and suppression of the sample becomes more dense.

Relationship between structure and viscosity of CaO–SiO2–Al2O3–MgO–TiO2 slag

Structure of the CaO–SiO2–Al2O3–MgO–TiO2 slag was studied by molecular dynamics simulation at 1773K. Additionally, part of viscosities were measured for quantitatively establishing the relationship between the structure and viscosity with varying basicities and TiO2 additions. Role of TiO2 as basic oxide was verified and it can be inferred that the structure of TiO2 is relatively similar to MgO compared to CaO. In addition, distribution of three different types of O was presented from which it can be obtained that nonbridging oxygen preferentially localized beside Si rather than Al. Moreover, parameter αM was proposed to estimate charge-balancing capability of M for [AlO4] (where M denotes Ca2+, Mg2+, Ti4+) along with the average values of αCa, αMg and αTi equaling to 1.731, 1.282 and 1.092, respectively, suggesting that Ca2+ is preferentially compensated for [AlO4] than Mg2+ and Ti4+. Therefore, TiO2 and MgO have a prominent effect on depolymerizing the framework of the slags than CaO in slags containing high Al2O3. Finally, the natural logarithm of the measured viscosities exhibit a linear dependence on the fraction of Q4 for Si, indicating that the degree of polymerization for Si is still the principal factor which affects the viscosity despite the complicated composition.

Effect of the Composite of Fly Ash and Slag on Alkali-Silica Reaction

The study used the method of accelerated mortar bar test to study alkali aggregate reaction (ASR) with sandstone aggregate. Both fly ash and slag can inhibit the expansion of mortar bar. Results show that 50% slag can inhibit ASR reluctantly, but 10% fly ash and 20% slag can inhibit ASR very well, and the inhibitory effect of fly ash is far better than slag. Because of the high content of CaO in slag, it has inhibit and promote aspects, when the ASR is fierce, slag can inhibit ASR, otherwise slag can promote ASR.

Dissolution behaviour of lime in vanadium extraction slag

During the converter vanadium extraction process, phosphorus cannot be removed from hot metal due to the absence of CaO in the slag. In order to lower the phosphorus content and produce CaO-containing vanadium slag, which could be directly used in a subsequent roasting process, lime dissolution in FeOx–SiO2–V2O3–TiO2 slag was investigated using a rotating disk/cylinder technique. Kinetics of dissolution were correlated with the Levich–Cochran equation for a rotating disc and used to determine the effective diffusivity of lime. The results show that dissolution rates were several times greater than previous studies in the BF/BOF slag system and were strongly dependent on the rotation speed, indicating mass transfer to be the rate-limiting step. The diffusivity of CaO in slag was calculated from the dissolution rate and solubility data, and was inversely proportional to the viscosity of the slag. The effects of temperature and revolution speed on the dissolution of lime were analysed and discussed.