CaO CaF2 Research Articles

Effect of MgO Content and CaO/Al2O3 Ratio of CaF2–CaO–Al2O3–MgO Slag on the Oxidation Behavior of Mg in Mg-Containing GH3128 Alloy

Effect of MgO Content and CaO/Al2O3 Ratio of CaF2–CaO–Al2O3–MgO Slag on the Oxidation Behavior of Mg in Mg-Containing GH3128 Alloy

Electrochemical Extraction of Fe–Si Alloy Form SiO2–CaO–CaF2–FeOx Slags by Molten Oxide Electrolysis

Electrochemical Extraction of Fe–Si Alloy Form SiO2–CaO–CaF2–FeOx Slags by Molten Oxide Electrolysis

Effects of TiO2 and CaO/Al2O3 on Melting Characteristics, Surface Tension, and Structure Electroslag‐Remelting‐Type Low‐Fluorine Slag

The influence of TiO2 and CaO/Al2O3 on the surface tension of CaF2–CaO–Al2O3–SiO2–MgO–TiO2 low‐fluorine slag system is determined by pulling method, and the melting characteristics of the slag system are determined by differential scanning calorimetry . It is found that the surface tension decreases with the increase of temperature. With the increase of TiO2 from 7% to 16%, the surface tension decreases from 2.97 to 0.71 N m−1, the Tend decreases from 1683 to 1648 K, and the activation energy decreases gradually. When the CaO/Al2O3 increases from 0.9 to 1.8, both the surface tension and Tonset show a minimum value, the surface tension is 2.286 N m−1, the Tonset is 1498 K, and the crystallization phase is formed during the melting process. The main reason TiO2 affects the structure is the substitution of Ti4+ for Al3+ in the [AlO4]5− structure to form the Ti2O64− structure, which leads to depolymerization of the Q2 and Q3 polymerization degree and thus the slag system structure, while CaO/Al2O3 affects the slag polymerization degree by influencing the amount of bridging oxygen. Finally, the surface tension is characterized using each structure to derive a relationship between structure and surface tension.

Effect of MgO content and CaO/Al2O3 ratio on melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag for electroslag remelting

During electroslag remelting (ESR), high MgO contents are typically added to CaF2–CaO–Al2O3 slag to control magnesium content in iron- and nickel-based alloys. The melting temperature and viscosity of ESR slag are pivotal for energy consumption, production efficiency, smooth operation, and ingot quality. However, there is currently a notable scarcity of research on the melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag with high MgO levels. Thus, the melting temperatures and viscosity of CaF2–CaO–Al2O3–MgO slags with varying MgO contents and CaO/Al2O3 (C/A) ratios were investigated. The results show that as the MgO content increases from 7.83 % to 13.18 %, the final precipitation content of the MgO phase significantly increases, resulting in an increase in the melting temperature from 1306 °C to 1319 °C. With the increase in the C/A ratio from 0.86 to 1.16, the precipitation completion temperatures of the Ca12Al14F2O32 and MgO phases significantly decrease and the MgAl2O4 phase transforms into the CaO phase. Hence, the melting temperature decreases from 1329 °C to 1314 °C. Further increasing the C/A ratio to 1.40, the final precipitation content of the CaO phase increases, resulting in a decrease in the melting temperature from 1314 °C to 1282 °C. Moreover, as the MgO content and C/A ratio increase, the slag viscosity exhibits different change trends within various temperature ranges. This depends on which of the depolymerization of the slag structure and the precipitation and clustering of the MgO phase has a greater effect on the slag viscosity.

A comparative Monte Carlo simulation study on shielding features of the CaF2–CaO–B2O3–P2O5–SrO–Ta2O5 glass system against X-ray by GEANT4 and MCNPX codes

Regarding to their unique physical and mechanical features, glasses and glass–ceramics are suitable materials for shielding purposes. The present study evaluates the shielding properties of the CaF2–CaO–B2O3–P2O5–SrO–Ta2O5 glass system using Monte Carlo GEANT4 and MCNPX codes for X-ray radiations with an energy range of 20 to 100 keV. MAC values of the Ta0, Ta1, Ta2, Ta2.5, and Ta3 samples of the CaF2–CaO–B2O3–P2O5–SrO–Ta2O5 glass were computed using Phy-X/PSD, GEANT4, and MCNPX codes and compared. According to the results, the programs have good compatibility with each other. For instance, in the energy of 40 keV and for the Ta2 sample, GEANT4 and MCNP codes are 1.445765406 and 1.517801204 cm2/g, respectively, indicating 7.419529525 and 2.829628418% differences with 1.562 cm2/g obtained using the Phy-X/PSD software. According to recent estimations, the Ta3 sample of the CaF2–CaO–B2O3–P2O5–SrO–Ta2O5 glass system can be selected as the best shield compared with the other samples.

Effect of CaO/Al2O3 on electrical conductivity, viscosity and structure of electroslag remelting-type TiO2-bearing slag

The composition of electroslag has a great influence on the remelting behaviour, and the electrical conductivity and viscosity of slag directly affect the energy consumption and the surface quality of the alloy. The electrical conductivity and viscosity of CaF2–CaO–Al2O3–SiO2–MgO–TiO2 slag system with different CaO/Al2O3 (0.9–1.8) were measured by a high-temperature physical property measuring instrument, and the structure of the slag was analysed by FTIR and Raman spectroscopy. The results showed that the electrical conductivity increased from 0.027 to 0.071 S · cm−1 and viscosity decreased from 0.58 to 0.27 Pa s with the temperature rising from 1733 to 1823 K. The activation energy of each slag system increases and then decreases. The higher the temperature, the stronger the ion mobility in the melt. There is an inflection point for electrical conductivity and viscosity when the CaO/Al2O3 is 1.2. With the increase of Ca2+ and the conversion of free O2−, [AlO6] and [AlF6] to Q2, Q3 and Q4, the decrease of melt degree of polymerisation (DOP) leads to the decrease of carrier diffusion ability. As DOP of Q2, Q3 and Q4 continue to increase, the electrical conductivity begins to decrease and the viscosity increases. The linear equations of viscosity and electrical conductivity are established according to the experimental results.

Study on properties of CaF2–CaO–Al2O3–MgO–B2O3 electroslag remelting slag for rack plate steel

Abstract The loss of boron (B) in the rack plate steel during the electroslag remelting process has a significant impact on its mechanical properties. Therefore, it is necessary to design appropriate slags to suppress the loss of B. CaF2–CaO–Al2O3 phase diagram was calculated to determine the basic slag. The influence of MgO and B2O3 on the performance of the basic slag was studied to determine the optimal amount of MgO addition. The equilibrium reactions between rack plate steel and the 50.48 mass% CaF2–24.81 mass% CaO–24.71 mass% Al2O3–2 mass% MgO-y mass% B2O3 (y was 1–10) slag were studied to examine the variation in B content in the steel. Results indicate the presence of a temperature-qualified eutectic point in the CaF2–CaO–Al2O3 phase diagram. With an increase in MgO content in the slag, the melting temperature of the basic slag initially decreases and then increases, while the electrical conductivity decreases. On the other hand, B2O3 reduces the melting point of the slag and increases the equilibrium B content in the steel. The 50.48 mass% CaF2–24.81 mass% CaO–24.71 mass% Al2O3–2 mass% MgO-y mass% B2O3 (y was 5–7) slag can achieve the target range of B content in the steel, and its viscosity meets the requirements of electric slag remelting.

Investigation on surface tension of CaF2–CaO–SiO2 (–MgO–Al2O3) melts

In this work, the surface tension of CaF2–CaO–SiO2 melt with high CaF2 contents was measured by pulling cylinder method at 1773 K. The effects of CaF2 content, basicity, and the addition of MgO and Al2O3 on the surface tension were also investigated by considering the change in the melt structure. It was observed that as the CaF2 content increased from 30 to 80 mass%, there was no further depolymerizing effect on the silicate structure of the melt, maintaining a constant basicity of 1. However, the surface tension of the melts decreased from 397 to 325 mN/m due to the surface-active effect of CaF2. With the increase of basicity from 0.5 to 3, the surface tension of the melt initially increased from 342 mN/m to a maximum value of 390 mN/m, then decreased to 368 mN/m. The maximum value occurred at a basicity of 2. Furthermore, at constant basicity, the addition of MgO from 0 to 10 mass% led to a decrease in the surface tension of the melt decreased from 358 to 326 mN/m. Similarly, with the basicity ranging from 1 to 3, the addition of 10 mass% Al2O3 resulted in a decrease in the surface tension of the melt.

Dissolution kinetics and reaction mechanism of Al2O3 in molten CaF2–CaO–Al2O3 slag

Dissolution kinetics and reaction mechanism of Al2O3 in molten CaF2–CaO–Al2O3 slag

Radioluminescence characteristics of Eu2O3 ions activated CaO/CaF2 + La2O3 + P2O5 scintillating glasses

The novelty of this research is to prepare phosphate glasses (10CaO/CaF2 + 20La2O3 + 69P2O5) with the effect of 1 mol% Eu2O3 and the incorporation of 10 mol% CaO (or) CaF2, focusing attention on their structural and optical features, together with their influence in the ultimate scintillation spectral response. When CaO (oxide, OE glass) content is replaced by CaF2 (fluoride, FE glass), changes in density and molar volume measurements are observed, including a decrease in the bands of OH groups in the IR spectral range (2500–4000 cm−1). The results of the optical absorption (OA) of glasses showed various peaks in the ranges of 350–600 nm (UV–Visible) and 1800–2400 nm (NIR). The phonon energies of the OE (1219 cm−1) and FE (1210 cm−1) glasses from the Raman spectra are in good agreement with the value (1222 cm−1) obtained from the excitation (PLE) spectra (7F0 →5D2) of Eu3+ ions. From the emission (PL) spectra of glasses, the surrounding environment of Eu3+ ions is evaluated with respect to (Ω2,4,6) intensity parameters and asymmetric (R/O) ratio. Moreover, the OE and FE glasses emit the highest red-emitting 5D0 → 7F2 transition (∼612 nm) under UV light and X-ray radiations. The decay time due to Eu3+ emission is 2.217 ms for OE glass and 2.329 ms for FE glass. In addition, spectroscopic parameters and (x, y) color coordinates are calculated for both glasses fabricated in this work. Furthermore, temperature-dependent luminescence was studied from 10 K to 550 K and found to high in FE glass. The integrated scintillation efficiencies of OE and FE glasses are about 17 % and 18 % of commercial BGO scintillating crystal.

Viscosity and surface tension of CaF2–CaO–Al2O3-based slag with varying SiO2 and B2O3 contents for ESR of rotor steel

Viscosity and surface tension of CaF2–CaO–Al2O3-based slag with varying SiO2 and B2O3 contents for ESR of rotor steel

Oxidized pellets production from stainless steel solid wastes: induration characteristics and harmful elements migration behavior

Stainless steel solid wastes (SSSW) treatment and recycling has attracted wide attention in recent years because of more stringent environment laws and regulations. Recycling of SSSW through carbothermal reduction of chromite (SRC)-electric furnace (EF) process is favorable to the effective treatment of SSSW and recovery of valuable elements. In this paper, SSSW are used to manufacture sufficiently strong oxidized pellets with the coexistence of chromite concentrates for ferrochrome production based on the SRC-EF process. The induration characteristics and harmful element migration behavior during oxidation of pellets are investigated and revealed. It is found that the oxidized pellets made from 100% SSSW possess low mechanical strength. Increasing the ratio of chromite concentrate from 0% to 80% can significantly improve the pellet strength from 460 N/pellet to 1868 N/pellet when preheating at 1000 °C for 12min and roasting at 1275 °C for 15min. Oxidized pellets made from SSSW and chromite are mainly dominated by the solid-phase consolidation due to the recrystallization of iron-rich spinel phases and sesquioxide derived from oxidation of ferrous oxides. In addition, slag bonding of CaO–CaF2–SiO2–FeO system also plays an important role in the consolidation of oxidized pellets. As for pellets made from 32% SSSW and 68% chromite concentrate, 39.96% F, 91.06% S, 66.73% Cl can be removed from the pellets when preheating at 1000 °C for 12 min and roasting at 1275 °C for 15 min.

Effect of CaF2 and CaO/Al2O3 ratio on evaporation and melting characteristics of low-fluoride CaF2–CaO–Al2O3–MgO–TiO2 slag for electroslag remelting

ABSTRACT The present study focuses on the evaporation of fluoride from low-fluoride CaF2–CaO–Al2O3–MgO–TiO2 slag with varying CaF2 content and CaO/Al2O3 mass ratio and the melting characteristics of the slag. Moreover, thermodynamic and kinetic calculations are made to reveal the fluoride evaporation mechanism. The results show that the gaseous substance evaporated from the slag is mainly CaF2. The calculated vapour pressure in a sequence is CaF2 > MgF2 > AlF3 > AlOF. Furthermore, with the increase in CaF2 content from 15 to 30 wt-%, the evaporation of fluoride increases from 0.934 to 1.047%, and the melting temperature drops from 1480 to 1443°C. With the increase in the CaO/Al2O3 mass ratio from 0.8 to 1.4, the weight loss increases from 0.92 to 1.95% and then decreases to 1.70%, and the melting point drops from 1460 to 1324°C. The slag evaporation is controlled by the Valensi reaction mechanism, and its mechanism function is G(α) = α+(1−α)ln(1−α), which belongs to two-dimensional diffusion.

Oxidation behavior of boron in 9CrMoCoB steel by CaF2–CaO–Al2O3–SiO2–B2O3 electroslag remelting (ESR) type slag

The laboratory-scale experiments between the CaF2–CaO–Al2O3–SiO2–B2O3 slag and 9CrMoCoB steel were carried out in alumina and magnesia crucibles at 1823 K to investigate the oxidation behavior of boron (B) during the electroslag remelting (ESR) process. The activities of SiO2 and B2O3 in the slag and the activities of Si and B in the molten steel were calculated by the ion and molecule coexistence theory (IMCT) and the Wagner formalism, respectively. The results showed that both SiO2 and B2O3 have a significant influence on the equilibrium B content. The calculated content of B was in good agreement with the experimental value when the SiO2+B2O3 content in the slag is more than 3.3 wt%. The temperature had little influence on the equilibrium B content when the SiO2, B2O3 and CaO content were in the ranges of 3–5 wt%, 0–1 wt%, and 20–30 wt%, respectively. However, the Si is more prone to oxidation than is B as the temperature increases, indicating that more SiO2 should be added in the slag to reduce the oxidation of Si. From the 80 tonnes industrial tests, the distribution of B and Si content along with the radial direction of the remelted ingot was almost uniform, which is in line with the calculated B content (approx. 30 ppm) under conditions of the Si content in the liquid steel and the (%B2O3)/(%SiO2) ratio are 0.07% and 0.05, respectively, at 1973 K.

Kinetic study on the reaction between Incoloy 825 alloy and low-fluoride slag for electroslag remelting

Abstract A kinetic model for the reactions between the low-fluoride slag CaF2–CaO–Al2O3–MgO–Li2O–TiO2 and Incoloy 825 alloy was proposed based on the two-film theory. The applicability of the model was verified to predict the variation of components in the slag–metal reaction process. The results show that the controlling step of the reaction 4[Al] + 3(TiO2) = 3[Ti] + 2(Al2O3) is the mass transfer of Al and Ti in the liquid alloy and the controlling step of the reactions 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3) and [Si] + (TiO2) = [Ti] + (SiO2) is the mass transfer of SiO2 in the molten slag. With increasing TiO2 content in the slag from 3.57% to 11.27%, the Al content in the alloy decreased whereas the Ti content increased gradually. The Si content continued to decrease during the slag–metal reaction. Soluble oxygen in the alloy reacts with Al, Ti, and Si, resulting in a decrease of the oxygen content in the alloy. The variations of TiO2 content were in good agreement with the calculated results by the kinetic model whereas the measured results of Al2O3 and SiO2 in the slag were lower than the calculated results, which is mainly due to the volatilization of fluoride.

Influence of SeO2 on in vitro bioactivity and antibacterial activity of CaF2–CaO–B2O3–P2O5–SrO glass system

In vitro bioactivity studies (in SBF) and antibacterial activity studies (against S. aureus and E. coli bacteria) of SeO2 doped CaF2–CaO–B2O3–P2O5–SrO glasses were performed as a function of SeO2 content. X-ray diffraction and scanning electron microscopic studies indicated the formation of Se-HAp crystalline layer on the samples after immersing in SBF. Infrared and Raman spectral studies further established the deposition of hydroxyapatite layer on the surface of these samples. The thickness of HAp layer deposited on the samples is found to be dependent on the content of SeO2 dopant; this is assessed by measuring weight loss of the glasses due to dissolution in SBF and by measuring the variation of pH and the chemical analysis of the left-over fluid as functions of SeO2 content. The studies indicated the maximal content of hydroxyapatite is deposited on the surface the glasses doped with 4.0 mol% of SeO2. The studies on antibacterial effect against E. coli and S. aureus of the glasses indicated the maximal inhibition of bacteria in the samples doped with 4.0 mol%. This is ascribed to the presence of maximal concentration of [SeO3]2- ions (confirmed by IR and Raman studies) in this glass sample. Overall, the results of bioactivity of SeO2 doped bioglasses indicated that the presence of SeO2 not only enhanced bioactivity potential but also facilitated increase of antimicrobial activity.

Fluoride vaporization and crystallization of CaF2–CaO–Al2O3–(La2O3) slag for vacuum electroslag remelting

The vaporization and crystallization of CaF2–CaO–Al2O3 slags with different La2O3 contents for electroslag remelting were investigated by various analytical methods. The results show that the main volatiles from investigated slag within 7.4 wt% La2O3 content at 1723 K are CaF2 and AlF3. The weight loss of CaF2–CaO–Al2O3-(La2O3) slags decrease with increase of La2O3 content in both thermo gravimetric experiment and vacuum condition. The addition of La2O3 within 7.4 wt% reduces the viscosity and breaking temperature of investigated slag, and the change of viscosity is not the main reason to inhibit the fluoride vaporization. The vapor pressure of CaF2 and AlF3 at 1723 K decreases with increase of La2O3 content because of the changes in component activity. Thus, fluoride vaporization becomes weakened. The crystalline phases of CaF2–CaO–Al2O3 slag are 11CaO·7Al2O3·CaF2 and CaF2, while the crystalline phases of slag within 7.4 wt% La2O3 content are (CaLa)Al3O7, La(AlO3) and CaF2. The La2O3 addition can decrease the crystallization temperature of CaF2 and prevent the precipitation of 11CaO·7Al2O3·CaF2.

The impact of Nb2O5 on in-vitro bioactivity and antibacterial activity of CaF2–CaO–B2O3–P2O5–SrO glass system

This work consists of in vitro bioactivity (in SBF) and antibacterial studies (against S. aureus and E. coli bacteria) of Nb2O5 doped bioactive glasses. X-ray diffraction and scanning electron microscopy investigations indicated deposition of Nb-HAp (hydroxyapatite) crystalline layer on the samples after exposing to SBF. The spectroscopy investigations also indicated the deposition of HAp layer on these samples. The magnitude of HAp deposited on the glasses found to be relying on concentration of Nb2O5 dopant; this conclusion was drawn by determining weight loss of the glasses due to exposure to SBF and also by assessing the variation of pH of the remnant fluid as functions of Nb2O5content. The studies further indicated the maximal content of hydroxyapatite was deposited on the surface the glasses doped with 4.0 mol% of Nb2O5. The antibacterial studies (against E. coli and S. aureus bacteria) of these glasses indicated the maximal killing effect of bacteria of the samples admixed with 4.0 mol% of Nb2O5. This result is attributed to the occupancy of maximal fraction of Nb ions in NbO6 structural units (confirmed by IR and Raman spectroscopic results) in this sample that paved the way for easy disintegration of the glass and to act on the bacteria. Overall, the results of bioactivity studies of Nb2O5 doped bioglasses indicated that the Nb2O5 not only enhanced bioactivity potential but also exhibited antimicrobial activity.

Gamma Ray Shielding Properties of Yb3+-Doped Calcium Borotellurite Glasses

This research work aims to investigate the radiation shielding ability of a Yb3+-doped calcium borotellurite glass system. The system has the basic composition of CaF2–CaO–B2O3–TeO2–Yb2O3 but is denoted as TeBYbn for simplicity. The effect of increasing the TeO2 content in the glasses from 10 to 54 mol% was investigated, with five different chosen compositions and densities. The Phy-X/PSD program was used to investigate the mass attenuation coefficient (µ/ρ) of the samples. The mass attenuation coefficients were theoretically determined by using an online software for the calculation of shielding parameters. Other parameters were then calculated and analyzed, such as the linear attenuation coefficient (µ), transmission factor (TF), radiation protection efficiency (RPE), effective atomic number (Zeff), and mean free path (MFP). TeBYb5, the glass with the greatest TeO2 content, was shown to have the greatest µ/ρ; however, at greater energies, the differences between the values are practically negligible. µ was shown to increase with density, such as from 0.386 cm−1 to 0.687 cm−1 for TeBYb1 and TeBYb5 at 0.284 MeV, respectively. The least TF was found for samples with a thickness of 1.5 cm, proving an inverse correlation between the thickness of the sample and the TF. The HVL and TVL of the glasses decreased as the density of the samples increased, which means that TeBYb1 is the least effective out of the investigated glasses. The five samples proved to have a lower MFP than some other shielding glasses, demonstrating their capabilities as radiation shields. Based on the calculated parameters, TeBYb5 indicated the greatest photon attenuation ability.

In-vitro bioactivity and antibacterial properties of CaF2‒CaO‒B2O3‒P2O5–SrO glass system-influence of Ta2O5

In vitro bioactivity studies (in SBF) and antibacterial activity studies (against S. aureus and E. coli bacteria) of Ta2O5 doped CaF2‒CaO‒B2O3‒P2O5‒SrO glasses were investigated. XRD and SEM studies indicated formation of Ta-HAp crystalline layer on the samples after immersing in SBF. The studies indicated the maximal content of hydroxyapatite is deposited on the surface of the glasses Ta2.5. Antibacterial effect against E. coli and S. aureus showed that the samples doped with 2.5 mol% of Ta2O5 are more efficient in killing the bacteria. Such maximal effect is attributed to the presence of the largest concentration of TaO6 groups that have acted as modifiers in this glass sample.