CaF2 Content Research Articles

Experimental analysis on tribological behavior of Co/TiC/CaF2/Y2O3 composite coating developed by plasma transferred arc (PTA) cladding technique on AZ91D Mg alloy substrate

Abstract In this study, Co/TiC/CaF2/Y2O3 composite coating was fabricated on AZ91D Mg alloy by plasma transferred arc cladding (PTA) technique. The composite coating was fabricated with parameters as PTA current of 40 A and scan speed of 150 mm/min. The coating powders consisted of Co (60 wt. %) and Y2O3 (1 wt. %), with varying amounts of TiC (ranging from 34 wt. % to 19 wt. %) and CaF2 (ranging from 5 wt. % to 20 wt. %). An investigation on the effect of TiC and CaF2 content on the mechanical and wear performance of Co/TiC/CaF2/Y2O3 composite coatings has been conducted. Characterization of the coatings such as microstructure, elemental analysis, and phase analysis were investigated by scanning electron microscopic (SEM) with energy dispersive x-ray spectroscopic (EDX), and x-ray diffraction (XRD) respectively. Results showed that the phase constituents in the coatings were TiC, CoO, CoTi, Co2Y3, YTiO3, CoYC, TiO2, and CaF2. The maximum average microhardness of the clad layer was about 1162HV0.05, while the average microhardness of AZ91D Mg alloy substrate was about 68HV0.05. Based on this study, it has been found that the coating has 17 times more hardness than the AZ91D Mg substrate. Also, it can be concluded that the coating has nearly 37 times higher wear resistance than the AZ91D Mg alloy substrate.

Efficient Fluoride Recovery from Wastewater Using Mesoporous Ca-based Nanomaterials Derived from Municipal Solid Waste Incineration Fly Ash via Fluidized Bed Crystallization

This study introduces an innovative approach utilizing mesoporous Ca-based nanomaterial (MCN) derived from municipal solid waste incineration (MSWI) fly ash as carriers in a fluidized bed crystallization (FBC) process for the recovery of fluoride from semiconductor wastewater. The transformation of nonporous MSWI fly ash into mesoporous structures was achieved through facile treatments, including ultrasonic-assisted leaching with ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA–Na) and surface modification with sodium silicate, enhancing surface functionalities and active site formation. The resulting MCN exhibited a significant surface area of 222.0 m2/g, ideal for fluoride recovery. When tested with synthetic wastewater, the recovery efficiency and crystallization ratio of fluoride using MCN in the FBC system reached 99.0% and 93.3%, respectively. Further investigation revealed that the unique surface properties and large surface area of the MCN promoted the crystallization of fluoride-containing precipitates, resulting in homogeneously nucleated cubic CaF2 crystals and facilitating layer-by-layer crystal growth. Testing the FBC process with real semiconductor wastewater resulted in a crystallization efficiency of 94.5%, with the CaF2 content in the recovered precipitates reaching 84.3±0.7%. These findings highlight the potential of MCN as an innovative carrier for fluoride recovery, demonstrating a novel and environmentally friendly method for converting waste into valuable materials. This study offers a promising solution for treating fluoride-contaminated wastewater, with high potential to revolutionize industrial wastewater management and promote a circular economy.

Effect of CaO–Al2O3–SiO2–MgO(–CaF2) refining slag system on inclusions in silicon–manganese deoxidized spring steel

In order to make the refined slag match various grades of spring steel, high-temperature equilibrium experiments were conducted in the laboratory to study the effect of CaO–Al2O3–SiO2–MgO refining slag with varying basicity, Al2O3 content, and CaF2 additives on inclusions containing Al (Al2O3) in silicon–manganese-deoxidised steel. The results show that the control effect of low basicity refining slag on inclusions is better than that of high basicity slag. The soluble aluminium increases with the increase of the basicity of steel slag and the Al2O3 content in inclusions is positively correlated with the Al2O3 content in slag. When the relative adsorption capacity of the refined slag is 6 × 10−3, the area density of Al-containing inclusions in steel is at a low level. Low basicity slag with low Al2O3 is good, and it is more suitable for producing high-end spring steel. To produce middle- and low-end spring steel, the refining slag system with a basicity of about 2–2.5, Al2O3, MgO, and CaF2 content is about 10% can be used. Among them, a small amount of CaF2 improves the liquidity of steel liquid, improves its relative adsorption capacity to Al-containing inclusions, and can control the production of Al-containing inclusions in the steel.

Effects of CaF2 and La2O3 on the phase structure of rare earth in CaO–SiO2–La2O3–CaF2 slags

The rare earth in the rare earth slag can be separated and enriched by heating and melting the rare earth slag and then slowly cooling crystallisation. In this process, it is of great significance to study the effect of chemical composition on the crystallisation of rare earth phase in slag and the effect of slag viscosity on crystal growth. The rare earth slag melt samples were prepared according to the main chemical composition of rare earth slag by using an analytical pure reagent. The effects of CaF2 and La2O3 contents on the phase structure and morphology of rare earth phase in CaO–SiO2–La2O3–CaF2 slags were studied by SEM-EDS and XRD. The relationship between the viscosity of the slag and the crystal growth behaviour was studied by measuring the melt viscosity with the cylinder rotation method. The results show that the rare earth in CaO–SiO2–La2O3–CaF2 slags exists in the form of CaLa4(SiO4)3O. The change of CaF2 and La2O3 content has no effect on the structure of rare earth phase, but the size of rare earth crystal phase changes obviously. With the increase of CaF2 and La2O3 content, the size of rare earth crystal phase increases gradually. CaF2 and La2O3 can reduce the viscosity transition temperature of slag melt and increase the crystallisation temperature range of rare earth phase to promote crystal growth.

Insights into the crucial role of pH to achieve the dual goals of efficient fluoride removal and resource recovery from the photovoltaic manufacturing wastewater

Fluoride-containing wastewater arose from the rapid development of photovoltaic manufacturing, and caused many environmental and health concerns. Chemical precipitation is commonly applied for fluoride removal, in which pH plays a crucial role while lacking systematic and in-depth research. In this study, the effect of pH on fluoride removal was investigated from both theoretical and experimental views, and the recovered precipitates with pH control were characterized. Theoretical analysis illustrated the quantitative relationship between reaction rate and pH, which indicated an optimal pH of about 8 for fluoride removal. This result was further validated by the batch and continuous experiments. In the batch experiments, the highest fluoride removal efficiency of 99.00 ± 0.01 % and lowest fluoride residual of 19.93 ± 0.16 mg/L were achieved at pH 8.00. In the continuous experiments, the fluoride residual was controlled under 10 mg/L with a fluoride removal rate of 2298.3 ± 0.5 kg F/(m3·d) in the optimal pH range of 6.95 to 8.47. The precipitate characteristics in terms of morphology, elements composition, and crystallization property showed a close correlation with reaction pH. Furthermore, a multidimensional system involving CaF2 content, precipitant saving, particle size, crystallinity, and fluoride residual was established to assess the fluoride removal and precipitate recovery with pH control. A neutral condition was recommended to achieve the above dual goals. This work provided systematical and deep insights into the pH role in fluoride removal and precipitates recovery, and could offer guidelines for the development of industrial fluoride-containing wastewater treatment.

Preparation and cutting performance of (W,Ti,Ta)C/CaF2 nano-self-lubricating cermet tool material via spark plasma sintering

To improve the machining surface integrity of HT250 gray cast iron, (W,Ti,Ta)C based nano-self-lubricating cermet tools containing nano CaF2 were successfully prepared by spark plasma sintering (SPS). When the content of nano CaF2 was 5 vol%, the flexural strength, hardness, and fracture toughness of (W,Ti,Ta)C/CaF2 nano-self-lubricating cermet tool were 1134 ± 39 MPa, 18.97 ± 0.22 GPa and 8.52 ± 0.33 MPa·m1/2, respectively. The cutting experiments were carried out by minimum quantity lubrication (MQL), and the effects of nano CaF2 content and MQL on cutting performance were studied. The cermet tool with 5 vol% nano CaF2 had the optimized cutting performance under MQL conditions, with cutting forces FX, FY, and FZ reduced by 20.5%, 37.9%, and 33.3%, respectively, cutting temperature decreased by 34.8%, and tool life increased by 16.7%. The solid-liquid dual lubrication cutting method combined with the solid lubrication CaF2 and MQL effectively reduced the thickness and oxidation degree of the work hardening layer. The optimized surface roughness of the workpiece after machining was 0.89 ± 0.05 μm, which is 27.6% lower than that of dry cutting.

Formation mechanism of large-sized CaO-SiO2-CaF2-Al2O3-MgO composite inclusions in super 304H stainless steel rods

Employing silicon deoxidation in the production of Super 304H stainless steel, large-sized CaO-SiO2-CaF2-Al2O3-MgO (CSFAM) composite inclusions are frequently observed in the rods, posing a substantial threat to product quality. This study delves into an analysis of the constituent phases of these large-sized inclusions, identifying the coexistence of liquid phase and spinel phase. Leveraging industrial experiments, systematic sampling of Super 304H stainless steel, and a comprehensive analysis involving dynamic and thermodynamic calculations, this study investigates the formation mechanism underlying such inclusions. The composition of inclusions in the sample before AOD tapping mirrors that of the slag, with high CaF2 content, indicating that they come from slag entrapment. Through kinetic calculations, it is indicated that the time of existence of the liquid film during the ascent of these inclusions is significantly longer than the collision time. This suggests that they are not easily removed and tend to persist in the steel. Despite LF refining, the predominant types of inclusions remain unchanged, and the decrease in temperature leads to the precipitation of solid-phase MgO within the inclusions. Solubility calculations for solid-phase MgO show a rising trend with temperature. Post-casting, MgO and Al2O3 content in inclusions increase, the solid-phase MgO region disappears, and in the subsequent cooling process, inclusions precipitate the stable spinel phase (MgAl2O4). Solubility calculations for solid-phase MgAl2O4 show a temperature-dependent increase. After the completion of casting, the steel ingot undergoes a deformation process through rolling, leading to the transformation of inclusions into large-sized, elongated, composite CSFAM inclusions.

Enhancing mechanical strength of Sr-based oxyfluoride glasses in glass ionomer cement through phase separation

Glass-ionomer cements (GICs) are used in various applications in clinical restorative dentistry. In this study the effect of CaF2 content of the glasses on microstructure, thermal and mechanical behaviors of the synthesized glass ionomer cements was investigated. The results showed that by adding CaF2 at expense of SrF2 the first exothermic temperature (TE) of the glass was reduced from 735 to 704 °C and the compressive strength was increased from 42.0 ± 1.29 MPa to 60.3 ± 1.5 MPa as well. These substitutions led to extending of liquid-liquid phase separation in the glass. The enhancement of mechanical properties demonstrated through the process of annealing glass powder at temperatures below half of the glass transition temperature. This technique contributes to the improvement of mechanical properties by decreasing the residual stress and fostering the separation of amorphous phases. The formation of phase separation appears to be a significant factor in improving the mechanical properties of the oxyfluoride cements.

Kinetic Investigation of the Deep Desulfurization of 5 wt% Si High-Silicon Austenitic Stainless Steel

Given the demand for extremely low sulfur content in 5 wt% Si high-silicon austenitic stainless steel (SS-5Si), smelting utilizes a slag composition of CaF2-CaO-Al2O3-MgO-SiO2 with a basicity of 1 to 3, Al2O3 content ranging from 2.04 to 9.61%, and CaF2 content between 20.8 and 31.62%. Experiments designed to investigate the sulfur content in molten steel at temperatures of 1773 K, 1823 K, and 1873 K over durations of 1, 5, 10, 15, and 30 min, under varying slag compositions, corroborated with a theoretically derived model hypothesizing a “rate-controlling” step in mass transfer, revealed that the mass transfer of sulfur within the molten steel was determined to be the rate-controlling step (RCS) in the (CaO) + [S] = (CaS) + [O] reaction kinetics, and the variability of the mass transfer coefficient of sulfur, kS,m, in the molten steel ranged from 1.04 × 10−5 m∙s−1 to 2.24 × 10−5 m∙s−1. Based on the temperature dependency of kS,m, the apparent activation energy for the desulfurization reaction was estimated to be 96.03 kJ/mol. Considering the slag components, the binary basicity, denoted as R, exerted an overriding influence on the process of desulfurization. At a basicity of 1, the sulfur content within the liquid steel was reduced, from 22 ppm to 11 ppm within a time span of 30 min. In contrast, an increase in the basicity to a value of 3 showed a significant consequence: over an identical temporal duration of 30 min, the sulfur content was drastically reduced to 2.2 ppm. By contrast, an initial surge in desulfurization rates is observed within the first five minutes, attributable to relatively lower concentrations of Al2O3 and higher levels of CaF2. Subsequently, these parameters exert no significant influence on the kinetics of the desulfurization process.

Thermodynamic Analysis of the Oxidation Behavior of Cerium in High‐Speed Steel during Electroslag Remelting

Cerium loss is difficult to be avoided during the electroslag remelting (ESR) process. To reduce the cerium loss in high‐speed steel during the ESR process, the present study investigates the thermodynamics of cerium oxidation in cerium‐containing high‐speed steel based on the thermodynamic calculation and laboratory‐scale steel–slag reaction experiments. The results show that the reactions between [Ce] and (Al2O3), as well as [Ce] and (MgO) contribute to the cerium loss in the steel. Increasing the contents of CaF2 and MgO in the slag, the activities of Al2O3 and Ce2O3 show a slightly decreasing trend. The addition of CaO and Ce2O3 significantly reduces the Al2O3 activity but enhances the Ce2O3 activity. MgO activity shows an insignificant change with the contents of CaO and Ce2O3, while it decreases with adding Al2O3 and CaF2. Reducing Al2O3 content and enhancing Ce2O3 content in the slag are feasible to increase the cerium yield in the steel. With increasing Al2O3 content from 16.93 to 26.92 wt%, the cerium yield decreases from 8.4% to 6.0%. Increasing Ce2O3 content from 3.98 to 11.01 wt% enhances the cerium yield from 6.0% to 16.9%. The actual soluble Ce content in equilibrium with slag is almost less than 0.001 wt%.

Control of Aluminum and Titanium Contents in the Electroslag Remelting of ATI 718PlusTM Alloy.

The burning loss of Al and Ti elements in superalloys during electroslag remelting has become a prevalent issue. And the existing slag system is not suitable for smelting the ATI 718PlusTM alloy. Therefore, it is imperative to develop a new slag system for smelting the ATI 718PlusTM alloy. To mitigate this issue, a thermodynamic model of the oxidation reaction of Al and Ti at the slag and alloy interface was established based on the ion and molecule coexistence theory (IMCT). The thermodynamic model was used to investigate the correlation between the equilibrium content of Al and Ti, slag composition, smelting temperature, and initial Al and Ti content of the electrode. The results indicate that while increasing the smelting temperature can effectively inhibit the burning loss of Al, it will exacerbate the burning loss of Ti. Increasing CaO and Al2O3 contents can inhibit the Al burning loss, while an increase in the TiO2 content can inhibit the Ti burning loss. Although an increase in the MgO content results in the burning loss of Al, its impact on the Al is minimal. The burning loss of Al and Ti was not affected by the change in the CaF2 content. The high Al content in ATI 718PlusTM makes it prone to burning loss of Al during the electroslag remelting. The combustion loss of Al can be reduced by increasing the Ti content in the electrode or adding a suitable amount of aluminum powder to the slag system. The accuracy of the model had been validated through experimental verification.

High temperature tribological response of Fe-2Cu-0.8C-CaF2 self-lubricating composites at high speeds

In this work, Fe-2Cu-0.8C-CaF2 self-lubricating composites with calcium fluoride solid lubricant (3 □ 12 wt.%) were examined for their friction and wear at 5 and 10 m/s, at 500 °C. Addition of CaF2 decreased density and hardness of composites. During sliding, materials gained weight due to oxidation. Compared to the base matrix (Fe-2Cu-0.8C), composites showed lower weight gain and lower coefficient of friction. Increase in porosity with CaF2 content increased oxidation resulting in higher weight gain and increased friction due to wear debris abrasion. Increase in speed reduced weight gain due to higher material loss. Adhesion was the dominant wear mechanism in base matrix; delamination and wear debris abrasion in composites. Temperature rise at sliding surfaces was theoretically estimated. Increase in speed increased temperature, which reduced friction due to softening and shearing of solid lubricant. Composite with 3 wt.% CaF2 showed least surface damage and 6 wt.% showed lowest coefficient of friction, i.e., lower by 16% and 10% at 5, 10 m/s than base matrix. Tribological response of the composites to a broad range of applied parameters, viz. speed, load and temperature taken from earlier works and present work is briefly summarized. The study suggests the dominant role of CaF2 content and the wear debris in altering the tribological response. Further, the stability of the developed composites at high temperature and high load conditions was also established. The study suggests that the developed composites could serve high-load and high-temperature applications for heavy machinery such as bearings, shafts and gears.

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.

Investigation of the effect of P2O5 and CaF2 on the crystallization behavior of La2O3-bearing calcium–silicate–aluminum slags using the single hot thermocouple technique

The effects of P2O5 and CaF2 components of rare earth (RE)-bearing slags on their crystallization behavior were investigated using single hot-thermocouple technique (SHTT). The time temperature transformation (TTT) diagram exhibited single-nose curves within the examined slag composition range, in agreement with the individual CaLa4(SiO4)3O-type phase detected by an isothermal crystallization experiment in a furnace. Additionally, an increase in the P2O5 content shortened the incubation time and increased the nucleation rate of the columnar CaLa4(SiO4)3O-type phase in the 1350–1150 °C temperature range, while an increase in the CaF2 content had the opposite effects on the incubation time and nucleation rate. The sizes of the CaLa4(SiO4)3O-type phases in the slags with CaF2 were larger than those in the slags with P2O5, as verified by both in situ SHTT images and the crystallization experiment. The continuous cooling transformation (CCT) diagram suggested that an increase in the P2O5 content increased the initial crystallization temperature, whereas an increase in the CaF2 content decreased it. An analysis of the isothermal crystallization kinetics revealed that the columnar CaLa4(SiO4)3O-type phase exhibited phase diffusion-controlled growth. An increase in the P2O5 content tended to decrease the crystallization activation energy, while an increase in the CaF2 content increased the activation energy.

Influence of CaF2 on the spectroscopic studies of Dy–Eu co-doped fluoroborate glass for lighting applications

To investigate novel glass materials applicable to W-LED, we designed and prepared a series of glasses with varying compositions. The compositions of the glasses were (64-x)B2O3–15Al2O3–10Na2O–10Bi2O3-xCaF2-0.5Dy2O3-0.5Eu2O3 (x = 0, 5, 10, 15, 20, 25). The glasses were synthesized using the melting quenching method. The effect of CaF2 on the structural feature of fluoroborate glass was studied by infrared spectroscopy analyses. Determination of fluorine content in glass by 19F NMR inversion spectroscopy. The absorbance of glass increased as the CaF2 content increased in the visible and ultraviolet light ranges. The optical band gap of the prepared glasses was obtained from the absorption spectrum, which confirmed the existence of nonbridging oxygen (NBO) in the glass network structure. The fluorescence lifetime of the glass increases with increasing CaF2 content, and the quantum yield of the glass first increases and then decreases. In addition, fluoroborate glass had a lower Urbach energy, indicating that its network structure was relatively uniform and stable. In contrast, the increase in Urbach energy is due to the substitution of CaF2, leading to more defects. By adjusting the excitation wavelength and CaF2 content, the color temperature (1598–3346 K) and color rendering index (36–63) of fluoroborate glass can be effectively adjusted. These results show that the prepared Dy/Eu co-doped fluoroborate glasses have a potential application in white lighting.

Preparation of oily sludge-derived glass-ceramics by low-temperature melting with addition of CaF2

Oily sludge (OS), a hazardous waste that generated in the process of petroleum exploration, utilized as raw material in this study for preparation of high value-added glass-ceramics. The effect of CaF2 addition and temperature on the melting behavior, crystallization mechanism, physical-chemical properties and heavy metals leaching of glass-ceramics was highlighted. The results indicated that the obtained parent glass demonstrated completely amorphous structure at 1200 °C when CaF2 content was 4 wt%. The addition of CaF2 improved crystallinity of glass-ceramics, which further improved the glass-ceramics properties. Comparing the properties of OC-1200-830 with OCF4-1030, it was observed that the density increased from 2.27 g/cm3 to 2.60 g/cm3, compressive strength increased from 56.43 MPa to 122.00 MPa, bending strength increased from 6.16 MPa to 11.41 MPa, acid resistance increased from 92.8% to 96.8%, alkali resistance increased from 94.6% to 98.2%, and water absorption reduced from 0.19% to 0.12%. The leaching concentrations of heavy metals in the glass-ceramics were below than the thresholds required in GB 5058.3–2007, China. The theoretical energy consumption of glass-ceramics melted at 1200 °C was 30.84%–41.37% lower than that melted at 1500 °C, which demonstrated that the glass-ceramics prepared in this study have cost advantages.

Purification mechanism of fluoride-containing sludge from different sources by hydrometallurgy

The rapid development of electronic technology and the new energy industry accelerates the production of fluoride-containing sludge (FCS), mainly composed of CaF2. Meanwhile, fluorite is suffering shortage. Therefore, recycling FCS is a win-win way. In this study, the components of four FCS from different factories were analyzed and their mechanism of purification by hydrometallurgy was explored. The results showed that the components of FCS1 and FCS2 from different semiconductor factories were similar, and their main content was CaF2. FCS3 from a liquid crystal display (LCD) factory contained a large amount of Ca3(PO4)2 and FCS4 from a solid center contained many NaNO3, leading to different purification mechanisms. Research on acid leaching for impurity removal indicated that H2SO4 acid was not suitable for purifying FCS1, HCl acid dissolved a large amount of CaF2 and HF acid was the best. After the organic matter was removed by 500 °C calcination, the CaF2 content in the solid product reached about 90 % by 2 mol/LHF purifying FCS1 and FCS2. After HF acid leaching FCS3, the solid product contained a large amount of bonded water, therefore, only after calcination can the CaF2 content reach 96.9 %. FCS4 was purified by the calcination-HF acid leaching process of FCS1 to obtain 94.3 % CaF2 content, but it can also obtain 90.3 % CaF2 content by simple washing to remove a large amount of NaNO3 in it. To sum up, according to the fluorite grade standard and FCS compositions, different processes can be selected to purify the sludge as a fluorite substitute for the needs of different industries. Finally, the industrial process flowchart was provided, and operating costs were accounted for.

Crystal formation in Eu3+ - Doped oxyfluorophosphate glass-ceramics for luminescence thermometry

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO3 - (25-x) CaO – x CaF2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF2 at the expense of CaO reduces Ω2 and Ω4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%.The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω6 while reducing Ω4, as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1.

Thermodynamic behavior of bioactive glass in relationship with high fluorine content

Fluoride (F) is important for enhancing illogical activity of bioceramics. To increase fluoride content of derived Hench bioactive glass (BaG), bioactive fluorosilicate glasses (BaG-Fx) were synthesized by using melting method and characterized using different physico-chemical analyses. Fluoride-containing BaGs were synthesized at a temperature of 1350°C. Structural and thermal effect of calcium fluoride (CaF2) insertion into the glass network in the BaG: SiO2–CaO–Na2O–P2O5 quaternary system was studied. Indeed, the incorporated amounts of fluorine (CaF2) (from 5% to 20% by mass) induced significant physico-chemical changes. Through the structural study by X-ray diffraction (XRD), the amorphous character of our fluorosilicate glasses is proven. Infrared (IR) spectroscopy proved the incorporation of fluorine into the glass matrix. In the microstructural framework, we revealed the morphological changes of the glass powders as a function of the CaF2 content. These results were confirmed by Brunauer, Emmett and Teller (BET) measurements. Through Differential Scanning Calorimetry (DSC) thermal analysis we established the impact of fluoride ions on the structural dynamics and thermodynamic properties of these newly developed bioactive glasses. Accordingly, it was possible for the first time to incorporate as much as 20 wt% of CaF2 in BaG respecting the conditions of bioactivity and biodegradability required by Hench. After detailed analyses of the transformation entropies of BG-Fx as a function of the added CaF2 content, it can be stated that the intermolecular movements within the fluorosilicate network are more limited as a function of the added CaF2 amount. This slows down the ion exchange phenomena and subsequently the dissociation of the material in vitro, which can be anticipated to occur after implantation in vivo.

A novel strategy to prevent hydrogen charging via spontaneously molten-slag-covering droplet transfer mode in underwater wet FCAW

Underwater wet welding is widely used in offshore platform maintenance, oil pipeline repair and wreck salvage operations. A high diffusible hydrogen content is recognized as one of the critical reasons behind the reduction in the reliability of underwater wet welded joints. In this study, the entry route of hydrogen during underwater wet flux-cored arc welding of 304 stainless steel at a depth of 0.5 m was first confirmed experimentally using an in-situ X-ray imaging system. The hydrogen charging was deemed to dominantly occur when pendant droplets were formed due to the extremely high temperature of molten metal and the absence of slag coverage. This resulted in 13.51 mL/100 g of diffusible hydrogen remaining in the droplet and 9.42 mL/100 g in the deposited metal. To prevent hydrogen charging, an unprecedented molten-slag-covering droplet transfer mode was developed by reducing the CaF2 content and maintaining the CaF2/TiO2 to an appropriate ratio in the flux, through which the molten slag spontaneously covered the droplet, electric arc and molten pool completely during the entire welding process and the entry of hydrogen was successfully blocked and the diffusible hydrogen content was reduced to the same level as that achieved via onshore welding (3.26 mL/100 g).