Fluoride Evaporation and Melting Characteristics of CaF2–CaO–Al2O3–MgO–Li2O–(TiO2) Slag for Electroslag Remelting

Ju, Jiantao; Ji, Guangheng; Tang, Chenmei; An, Jia-liang

doi:10.1002/srin.202000111

Cited by 11 publications

(3 citation statements)

References 33 publications

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“…The vapour pressure of LiF was much higher than that of CaF 2 in lithium-containing slags. When gaseous species with different vapour pressures exist, the species with higher vapour pressure vaporise preferentially 14 , 28 . Consequently, LiF is the major component that leads to the fluoride loss in Li 2 O-containing slag, and CaF 2 is the main volatile product in the L0 slag.…”

Section: Kinetics Of Evaporationmentioning

confidence: 99%

“…The most common approach for developing low-fluoride slags is to control the CaO/Al 2 O 3 mass ratio and substitute a small amount of oxides for CaF 2 to keep the physicochemical properties stable. Several oxides including Na 2 O, B 2 O 3 , and Li 2 O are considered as potential substitutes for CaF 2 12 – 14 . Among them, a small addition of Li 2 O could effectively regulate the viscosity and melting temperature of the slags; thus, the partial substitution of CaF 2 with Li 2 O retains the performance of the slags.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

Tang

et al. 2020

Sci Rep

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The isothermal kinetics of fluoride evaporation from CaF 2-cao-Al 2 o 3-Mgo-tio 2-(Li 2 O) slag with varying Li 2 O content were investigated in the temperature range 1743-1803 K by thermogravimetric analysis. Thermodynamic calculations and viscosity measurements were applied for studying the evaporation mechanism of fluoride. The results showed that the evaporation ratio increases with increasing Li 2 O content and temperature. The volatile constituents from the molten slags, mainly LiF and CaF 2 , were detected and their concentrations calculated. The fluoride evaporation is primarily affected by the vapour pressure of LiF and CaF 2 , viscosity of the slags, and melt-component activities under given experimental conditions. On the other hand, mass transfer of the gas is not the ratecontrolling step that affects fluoride evaporation from the slags. The activation energy for fluoride evaporation gradually decreased from 193 ± 11 to 113 ± 3 kJ mol −1 as the Li 2 O content in the slags increases from 0 to 5.48 wt%. These results hold great theoretical significance for developing lowfluoride slags for electroslag remelting. The slags in electroslag remelting (ESR) process serve as a heat source, a barrier to the atmosphere, and a medium for liquid metals refining 1-5. To perform the intended functions, the slags must have some well-defined properties such as low electrical conductivity and suitable viscosity at remelting temperature 6,7. The traditional ESR slags are CaF 2-CaO-Al 2 O 3-based slags with a high CaF 2 content, and an additive such as MgO, TiO 2 or SiO 2 is commonly used to meet specific material requirements. However, fluoride evaporation from high CaF 2-content slags is a potential health-and safety hazard. Furthermore, it would alter the chemical composition and cause changes in the metallurgical properties of the slags 8-11. Therefore, it is important to develop low-fluoride slags and study their effect on fluoride evaporation during the ESR process. The most common approach for developing low-fluoride slags is to control the CaO/Al 2 O 3 mass ratio and substitute a small amount of oxides for CaF 2 to keep the physicochemical properties stable. Several oxides including Na 2 O, B 2 O 3 , and Li 2 O are considered as potential substitutes for CaF 2 12-14. Among them, a small addition of Li 2 O could effectively regulate the viscosity and melting temperature of the slags; thus, the partial substitution of CaF 2 with Li 2 O retains the performance of the slags. Several works reported by Shi et al. 15 have researched the effect of Li 2 O on the viscosity of CaF 2-CaO-Al 2 O 3-MgO slags, which suggested that the viscosity of slags decreased with Li 2 O content increasing from 0 to 4.5 wt%. Kim et al. 16 measured the viscosity of CaO-Al 2 O 3-12 wt% Na 2 O-12 wt% CaF 2-based slags and concluded that the addition of Li 2 O depolymerized the large aluminate structures and decreased the slag viscosity. Additionally, Liu et al. 17 studied the effect of Li 2 O on the properties of CaF 2-CaO-Al 2 O 3-SiO 2-Na 2 ...

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Section: Kinetics Of Evaporationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

Tang

et al. 2020

Sci Rep

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“…It is well known that some slag constituents have higher vapor pressure in the molten state than the rest of the slag [19]. For example, much attention was dedicated to CaF 2 evaporation from the slags [20][21][22]. Some pioneering works on CrO 3 [23,24] and V 2 O 5 [25,26] volatilization from steelmaking slags are relatively well addressed in the literature.…”

Section: Introductionmentioning

confidence: 99%

Two Potential Ways of Vanadium Extraction from Thin Film Steelmaking Slags

et al. 2023

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During the steelmaking process, a great amount of slag is generated as a by-product. Vanadium-bearing steelmaking slags are classified as hazardous and require special handling and storage due to the toxicity of vanadium pentoxides. At the same time, such slags are valuable sources for the recovery of vanadium. The present work reviews the investigations on vanadium recovery from CaO-SiO2-FeO-V2O5 thin film slags under the neutral and oxidizing conditions in the temperature range 1653 K to 1693 K (1380 °C to 1420 °C) using Single Hot Thermocouple Technique (SHTT). The slag samples were analyzed by SEM/EDX. The results indicated that vanadium pentoxide evaporation can be up to 17.73% under an oxidizing atmosphere, while spinel formation under an argon atmosphere was detected in the conditions of thin film slags.

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Effect of the Slag Composition on the Process Behavior, Energy Consumption, and Nonmetallic Inclusions during Electroslag Remelting

Schneider

Wiesinger

Gelder

et al. 2022

steel research int.

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Electroslag remelting (ESR) is a well-established secondary refining process for many steels and Ni-base alloys with highest requirements regarding material properties. The main purposes are a dense solidification of ingots with a low degree of segregation as well as the reduction of medium-sized and especially complete removal of large nonmetallic inclusions (NMI). The specific energy consumption of ESR is documented in the range from 880 to over 2000 kWh t À1 . [1][2][3][4][5][6][7] Rising requirements regarding sustainability, emission control, and environmental protection have triggered new awareness for this topic. [4,8,9] Besides plant geometry and design, the customarily CaF 2 -based slag plays the key role in the heat generation and energy consumption of ESR. Key properties are the melting point as well as the electrical and thermal conductivity. [2,10] Other factors such as fill ratio and the amount of slag, or the melt rate can also have a strong effect. [4,8,[11][12][13][14][15][16] According to Holzgruber, [16] rising fill ratios up to 0.4 lead to a reduction in specific energy consumption due to a better heat transfer into the electrode and less radiation losses at the free slag surface. A further increase in fill ratio surprisingly resulted in a reversed trend due to changing immersion depths. Results from Li et al., [14] both laboratory scale and industrial size, demonstrate the strong effects of fill ratio (0.24 and 0.6) and electrical conductivity on the specific energy consumption with values below 1000 kWh t À1 at higher fill ratios combined with low or no CaF 2 -containing slags. CaF 2 -free slags in Brückmann and Schwerdtfeger [17] confirmed their particular advantage in specific energy consumption with values below 1000 kWh t À1 .There are only few reports of systematic research on energy consumption in ESR on the industrial scale. A recent investigation with a wider variation of slags is documented in refs. [5][6][7], and confirms an almost linear increase with electrical conductivity. A similar but less pronounced increase is reported in Jäger and Kühnelt [18] for slag composition with a wide variety of CaF 2 contents and a significantly higher fill ratio. A recent summary on the different effects of the fill ratio and the electrical conductivity on the specific energy consumption can be found in Schneider et al., [4] indicating that the energy consumption data from laboratory scale

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Fluoride Evaporation and Melting Characteristics of CaF₂–CaO–Al₂O₃–MgO–Li₂O–(TiO₂) Slag for Electroslag Remelting

Cited by 11 publications

References 33 publications

Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

Two Potential Ways of Vanadium Extraction from Thin Film Steelmaking Slags

Effect of the Slag Composition on the Process Behavior, Energy Consumption, and Nonmetallic Inclusions during Electroslag Remelting

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