Papers by Keyword: Calcium Fluoride

Abstract: Solid lubricant is an environment-friendly alternative to liquid lubricants, which can be applied in extreme environmental conditions like high temperature and pressure where liquid lubricants fail. In this work, an attempt was made to synthesize calcium fluoride, a solid lubricant material from scrap eggshell powder by using the ion exchange method. The prepared eggshell powder was treated with 40% concentric hydrofluoric acid and was manually mixed using a mortar and pestle. The synthesized CaF₂ powder was characterized by using SEM and XRD. The degree of Crystallinity was calculated from the XRD data by using Origin Pro and Excel software. The Crystallinity of the prepared CaF₂ powder was found to be 78.01%. The crystal size of the synthesized CaF₂ powder was calculated using Scherer’s formula. The crystal size was found to be between 9–22 nm ranges. The synthesized calcium fluoride XRD intensity peaks were matching exactly with the JCPDS card of the standard CaF₂ powder, confirming the presence of CaF_2.

Abstract: We present here a study on the electrical and structural properties of p-type PbTe films doped with CaF₂. The layers were grown by molecular beam epitaxy on freshly cleaved (111) BaF₂ substrates. The doping level was monitored by the CaF₂ solid source cell temperature (T_CaF2), which varied from 500 to 1150 °C. The films with low doping level, T_CaF2 ≤ 1010 °C, exhibited flat surfaces with crystalline quality close to the undoped PbTe sample. In contrast, samples with high levels of doping (T_CaF2 > 1010 °C) presented CaF₂ agglomerates on the surface and a worse crystal quality. The hole density at 77 K versus T_CaF2 oscillated between 1.3 × 10¹⁷ and 3.6 × 10¹⁷ cm^-3 and did not exhibit a systematic behavior as the fluoride supply is raised. The results indicate that CaF₂ is not an effective p-type dopant for PbTe, due to the abscence of a resonant level close to the valence band or to compensation of extrinsic dopant levels.

Abstract: In this paper, a direct co-precipitation method was used to prepare antimony-doped calcium fluoride nanopowders (NPs). The effects of reaction concentration, reaction medium and lanthanum doping on the properties of calcium fluoride NPs were investigated via a control variable method and the best preparation conditions was identified. The structural analysis of the powder materials prepared in this work were carried out by XRD, SEM, ICP and other test methods. By analyzing the experimental data, we found that the best performance of Eu-doped CaF₂ NPs can be acquired under the reaction concentration of 1 mol/L in aqueous solution. In the same time, the NPs possess a high degree of dispersion with an average diameter of 22 nm, which is beneficial to the preparation of transparent Eu³⁺: CaF₂ ceramics with excellent up-conversion luminescence. The results show that the grain size, the crystallinity of the NPs and the amount of Eu infiltration have a decreasing tendency with the increasing reaction concentration, while the degree of agglomeration of the NPs can be enhanced by increasing the reaction concentration.

Abstract: Preparation of the tundish coverture fluxes by the blast furnace slag can recycle utilization of solid wastes discharged from iron and steel industry. Calcium fluoride and magnesia can play an important role for the basic performance of tundish coverture fluxes. The impact on the melting temperature, viscosities and surface tension of the tundish coverture fluxes from the content of calcium fluoride and magnesia were studied. The results showed that: When the content of CaF₂ increased from 10% to 25%, the melting temperature, the viscosity and the surface tension were decreased by 50°C, 0.3 Pa·S and 0.039 N/m respectively. The viscosity was brought down of 0.02 Pa·S, the surface tension was increased by 0.03 N/m, and the difference between the lowest and highest melting temperature was about 3°C when the content of MgO changed from 5% to 11%.

Abstract: To reduce the pollution caused by employing CaF₂ as fluxing agent in metallurgical flux, boron sludge is used as fluxing agent to substitute for CaF₂. The melting temperatures of CaO-SiO₂-Fe₂O₃-boron sludge system were investigated. The melting temperature of CaO-SiO₂-Fe₂O₃-boron sludge slag system is increased with the increase of ω (CaO)/ω (SiO₂) at first, and then fluctuates at about 1430°C. Moreover, the melting temperature of CaO-SiO₂-Fe₂O₃-boron sludge system is decreased with the increase of boron sludge content at first and then increased, 7% content of boron sludge has the best fluxing effect and the melting temperature is1445°C. As a conclusion, the fluxing effect of boron sludge is close to CaF₂, boron sludge may be considered to substitute for CaF₂.

Abstract: The melting temperature of CaO-SiO₂-B₂O₃-(boron mud, CaF₂) slag system was investigated. The slag melting temperature was measured by using the hemisphere method. The results indicate that B₂O₃ has a significant fluxing effect on the slag system. When 1%-11% B₂O₃ was employed as fluxing agent, the melting temperature of the slag changed from 1525°C to 1200°C. When the content of B₂O₃ is 5% and the range of basicity is 1.5~3.5, the melting temperature of the slag increases with the increase of the basicity. However, when boron mud or CaF₂ was added to the slag, the melting temperature of the slags decreased with the increase of addition at a fixed B₂O₃ content (5%) and a fixed basicity (R=2.5). Furthermore, the melting temperature of the slag system which contains CaF₂ is lower than the slag system which contains boron mud.

Abstract: CaF₂/AG25 (CFA) hybrid sorbent formed by hybrid reaction with activated calcium fluoride of low cost and anionic dye wastewater-Acid Green 25 (AG25) was used for the treatment of cationic dye wastewater. The adsorption of two cationic dyes methyl violet (MV) and Neutral Red (NR) from aqueous solutions was examined using a batch sorption technique. The effects of time, pH, ionic strength and temperature on the adsorption were also examined. It exhibited a faster adsorption to cationic dyes and hardly affected in pH over 3.5, ionic strength low 0.04 mol/L and temperature between 20 oC and 60 oC. The adsorption behavior of the NR and MV on CFA is in good agreement with the Langmiur isotherms model with the correlation coefficients of R 0.9948 for NR and 0.9992 for MV and the maximum adsorption capacity of NR (39.22 mg/g) and MV (48.78 mg/g). Finally, this sorbent was used in treatment of two practical cationic dye wastewaters with satisfactory results.

Abstract: A new hybrid material of CaF2/ABB6B (CFAB) was developed by the template-free hybridization of acid brilliant blue 6B (ABB6B) with CaF2. The composition and structure of the material were determined and characterized. In contrast to conventional sorbents, the hybrid material contains lots of negative charges as the basis of specific adsorption. The efficient removal of cationic dyes of victoria blue B (VBB), ethyl violet (EV) and basic brilliant blue BO (BBBO) indicates that it has an improved adsorption capacity and selectivity with a short removal time less than 5 min; while the hybrid sorbents fit the Langmuir isotherm model. Instead of using ABB6B reagent, an ABB6B-producing wastewater was reused to prepare the cost-effective sorbent, and the equilibrium adsorption capacities of which reached 46.29 mg•g-1, 24.81 mg•g-1 and 30.40 mg•g-1 for VBB, EV and BBBO, respectively. The sorbent was then used to treat the actual wastewater samples with satisfactory results of over 96% decolonization and 82% COD-decreasing. This work has developed a simple and eco-friendly method for synthesizing a practical and efficient sorbent. The results shown that the hybrid adsorption material has ideal decolorization and COD lowering efficiency and a good application prospect in dye industrial wastewater treatment.

Abstract: AlN powders were prepared via carbothermal reduction-nitridation of nonhydrolytic Al₂O₃ gels. The XRD results showed that only AlN phase formed when the sample was calcined at 1450 °C in N2 flow of 80 ml/min, which was lower than that using Al₂O₃ powders as starting materials. The AlN powders were near-spherical particles and their particle size was around 400 nm. The effect of the CaF₂ addition on the synthesis of AlN powders was aslo investigated. The results showed that the synthesis temperature of AlN powders colud decrease to 1400 °C, when 3wt% of atalytic agent CaF₂ was added. Meanwhile, the particles size of AlN powders decreased, but their size distribution became wide range.

Abstract: Objective: This study aimed to investigate fluoride release, flexural strength and surface characteristics of three orthodontic acrylic resins (A) blended with (1) sodium fluoride powder (NaF), (2) calcium fluoride powder (CaF2), and (3) glass ionomer cement powder (GIC). Material & Methods: Acrylic resin was blended with NaF, CaF2 , and GIC to make orthodontic acrylic plates. Each sample group was divided into subgroups at fluoride concentrations 5%, 10% and 20%. The acrylic resin was cured in a round stainless steel mold and kept in a bottle with 10 ml. deionized water then kept in an incubator at 37oC. The deionized water, changed every day, was tested for fluoride release up to six mo by Orion machine. For the flexural strength test, the samples were cured in a stainless steel mold, 64 mm. long, 10 mm. wide and 3.3 mm. high according to standard of ISO 20795-2 and testing was done up to 6 mo in deionized water. Scanning electron microscope determined surface characteristics after being blended. Results: Fluoride release was observed from orthodontic acrylic plates blended with NaF, CaF2 and GIC. The results of the A-NaF and the A- CaF2 group decreased fluoride level greatly at day 2, but the A-GIC group was observed at day 7. The A-NaF group and the A-GIC group could not detect fluoride level after mo 4 and 2, respectively. The A-CaF2 group found greater long term fluoride release than the A-NaF and the A-GIC group especially at 20% concentration (up to six mo). Significant differences (p<0.05) of fluoride release level (ppmF) among the A-NaF, A-GIC, and A-CaF2 groups at 5% concentration in every time point from day 1 to the mo 5, but not significant in mo 6 similar to the 10% concentration comparison. Whereas, comparing the 20% concentration among groups, significant differences (p<0.05) were found between groups in all periods of time (from the day 1 to mo 6). When comparing the different concentrations of 5%, 10%, and 20% in each group, significant differences (p<0.05) were found in every concentration at every time period of the A-GIC group from day 1 to mo 2, in the A-CaF2 group from day 1 to mo 6 and in the A-NaF group from day 1 to mo 4. Conclusion: Fluoride release was observed from orthodontic acrylic plates blended with NaF, CaF2 and GIC. The longest duration of fluoride release from orthodontic acrylic plates was found in the CaF2 group followed by the NaF and GIC groups. The flexural strength in every group decreased over time. This result implied that the flexural strength decreased during fluoride release. The acrylic surface was seen to be porous in every period of the fluoride release process.