Ca2SiO4 Phase Research Articles

Carbothermal Reduction of Stainless Steel Dust and Laterite Nickel Ore: Slag Phase Behavior Regulation and Self-pulverization Control Mechanism

Stainless steel dust is a type of high basicity iron containing solid waste from the iron and steel smelting industry. In this study, the carbon-containing composite briquettes were prepared by adding low basicity laterite nickel ore and stainless steel dust, and the valuable metals Fe, Cr, and Ni were recovered by carbothermal reduction. The results show that the addition of laterite nickel ore into CBSL (carbon containing composite briquette of stainless steel dust and laterite nickel ore) effectively improves the recovery of metal Fe, Cr and Ni and the self-pulverization rate of reduction slag. The reduction temperature is 1450°C, the reduction time is 30 min, the FC/O (molar ratio of fixed carbon to oxygen) is 1.0, and the laterite nickel ore addition is 6%, the recoveries of metal Fe, Cr and Ni are 92.1%, 90.1% and 91.6%, respectively, and the self-pulverization rate of the reduction slag reaches 91.5%. The Ca2SiO4 phase content of the reduced slag at high temperature is 71.8%, and the reduced slag system is located in the orthosilicate Ca2SiO4 region of the phase diagram, which effectively improves metal recovery, enables efficient separation of the reduced product and reduces energy consumption for subsequent processing.

Samarium doped calcium silicate derived from agro-food wastes and their structural, optical and luminescent properties

Samarium doped calcium silicates (Ca2−xSiO4:xSm3+, (x(%) = 0.25, 0.50, 0.75, 1.00) are synthesized using cost effective natural resources such as rice husk ash and egg shell powder through solid-state reaction method. The structural, optical, and photoluminescent properties of the as-prepared samples are reported. X-ray diffraction and Rietveld refinement results confirm that monoclinic- Ca2SiO4 phase is stabilized at room temperature in agro-food waste derived phosphors. Differential thermal analysis data provides information about the phase transformations. Scanning electron microscope images show that the synthesized samples have spherical morphology. Ca2SiO4 related vibrational bands appear in the Fourier transform infrared spectrum. Optical band gap of these phosphors is found to lie in the range 3.56–3.67 eV. Agro-food wastes inherently contain titanium in trace amounts thus, the photoluminescence emission spectrum consists of bands linked to both samarium and titanium ions. Presence of titanium makes these phosphors inherently luminescent. CIE co-ordinates of these phosphors lie in the bluish-green region. These results suggest that agro-food wastes have excellent potential of being used as precursors for synthesizing visible light emitting phosphors. Moreover, present study paves the way for effectively utilizing agro-food wastes for synthesizing environment friendly and cost-effective phosphors.

Luminescent properties of CaSiO3: Ce3+: A preliminary study

Rare-earth-activated CaSiO3 was synthesized through co-precipitation technique. Variation of Ca:Si ratio (x) resulted in formation of γ- Ca2SiO4 and β- Ca2SiO4 phases with significant effect on the Ce3+ luminescence. The average fluorescence lifetime of the Ce3+ ions for x = 1, 1.43 and 2 were found to be 33.5, 34.3 and 36.5 ns respectively. The quantum efficiency of the stoichiometric phosphor was 64%. The phosphor exhibits appreciable OSL sensitivity (62% of that of the Al2O3: C) for x = 2.

Highly improved biological and mechanical features of bioglass-ceramic/ gelatin composite scaffolds using a novel silica coverage

In the present study, mechanical and chemical properties of the bioglass-ceramic/gelatin composite scaffolds were investigated. The reinforcing particles were synthesized using the sol-gel method in SiO2–CaO–P2O5 systems. The composite scaffolds were also fabricated through solvent casting and freeze-drying routes. The effect of the chemical composition of the synthesized particles and temperature of the heat treatment process on the mechanical and chemical properties of the bioglass containing scaffolds were investigated in detail. Two different coverages, namely gelatin-glutaraldehyde and silica, were utilized for covering the composite scaffolds. According to the X-ray diffraction results, heat-treating the particles at 1100 °C caused the crystallization of the Ca3(PO4)2 phase. Based on the three-point flexural test results, the final mechanical strength of the gelatin-glutaraldehyde-covered scaffolds ranged between 2 and 4 MPa. Covering the composite scaffolds with the silica coverage remarkably increased the final strength values ranging between 12 and 18 MPa. The in vitro cell-based experiment results indicate the cytocompatibility of the scaffolds when they are incubated with dental pulp stem cells. Also, the presence of the silica coverage on the scaffolds increased the viability of the stem cells in comparison with the gelatin-glutaraldehyde-covered scaffolds. Furthermore, evaluation of the bioactivity behavior of the scaffolds showed that the Ca2SiO4 phase was formed on the surface of the samples from 7 to 21 days of immersion in simulated body fluid (SBF). The morphology of the mineralized phase on the surface of the scaffolds changed from Cauliflower to rod-like nodules by changing the type of scaffold coverage from gelatin-glutaraldehyde to silica after immersion in SBF media. Altogether, the bioglass-ceramic/gelatin composite scaffolds could have a promising role in bone tissue engineering application.

Dysprosium doped and titanium activated calcium silicates for cool white light emitting diode derived from natural resources

An environment friendly and cost-effective method is presented to utilize natural resources to synthesize Ca3−xSi2O7:xDy3+,x(%)=0.00, 0.25, 0.50, 0.75, 1.00 cool white light emitting diodes by solid-state synthesis technique. The structural, morphological and luminescent properties of the synthesized phosphors have been studied using various experimental techniques. X-ray diffraction confirms that doping of dysprosium (Dy3+) enhances the volume fraction of Ca2SiO4 phase with respect to Ca3Si2O7 phase, upto x(%)=0.50. As indicated by the scanning electron microscope images all samples show partial liquid phase sintering. Fourier transform infrared spectroscopy shows the presence of bands corresponding to the vibrational modes of Si–O and O–Si–O units present in Ca3Si2O7 and Ca2SiO4 phase. Diffuse reflectance spectra results produce optical band gap values between 3.67- 3.79 eV. Along with the characteristic emission bands of Dy3+, the photoluminescence spectra contains additional bands due to trace titanium ions naturally found in the agriculture and food wastes. Commission International de’Eclairage coordinates (CIE) coordinates are in the white region of the CIE diagram, suggesting that this is an effective method of utilizing agriculture and food wastes for synthesizing cool white light emitting diodes.

In situ synchrotron X-ray diffraction study of the electrochemical reduction of SiO2 in molten CaCl2

In situ synchrotron X-ray diffraction was used to investigate the electrochemical reduction of SiO2 to Si in molten CaCl2 at 1123 K for the first time. The present technique enabled direct determination of intermediate products at high temperature, without cooling and washing treatments. Based on the diffraction data, the Ca2SiO4 phase was detected inside the electrode, but not at the electrode edge. These results were explained by the presence of different concentrations of O2− ions in molten CaCl2 permeating different regions of the electrode.

Effect of B2O3 addition on mineralogical phases and leaching behavior of synthetic CaO\u2013SiO2\u2013MgO\u2013Al2O3\u2013CrOx slag

Boron oxide is frequently applied in modification of stainless steelmaking slag to mitigate the disintegration of slag. In this work, the effect of B2O3 on mineralogical phases and hexavalent chromium leaching behavior of synthetic CaO–SiO2–MgO–Al2O3–CrOx slag was investigated. Di-calcium silicate, merwinite, spinel, akermanite, and matrix phase were observed as main minerals in slags by scanning electron microscope (SEM) equipped with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD) techniques. It was found that 2% B2O3 addition is sufficient to eliminate the disintegration of synthetic slag by suppressing the phase transition to γ-Ca2SiO4. The size of spinel phase increases with increasing B2O3, which could be well interpreted by enhanced Ostwald ripening. The amount of Ca2SiO4 phase in slag was reduced by addition of B2O3; however, excess B2O3 (> 2%) addition would significantly increase chromium concentration and overall chromium distribution in Ca2SiO4 phase. Leaching results according to US-EPA-3060A method indicated that excess boron oxide addition (> 2%) leads to a significant increase of hexavalent chromium leaching concentrations and should be avoided for stabilizing stainless steel slag.

Formula omitted] and inherent [formula omitted] activated [formula omitted] near white light emitting phosphors synthesized from agro-food waste ashes

Rice husk ash and egg shell powder wastes have been used to synthesize Dy3+ activated Ca2SiO4 value-added and cost-effective phosphors, by solid-state reaction method. The structural, morphological and optical properties of Ca2−xSiO4:xDy3+ (x = 0, 0.0025, 0.0050, 0.0075 and 0.0100) have been investigated. Energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy results indicate the presence of high amount of silica and calcium along with the presence of some trace elements like titanium, iron, sodium, magnesium aluminium, potassium and sulfur. X-ray diffraction (XRD) analysis shows that increasing the doping concentration of Dy2O3 to x = 0.0100 results in monoclinic Ca2SiO4 phase. Further, XRD also confirms the presence of minor CaFeO3 phase. Diffuse reflectance spectra show that optical band gap for the synthesized samples lies in the range 3.40–3.50 eV. Luminescence spectra contains the typical emission bands of Dy3+ corresponding to F49/2−HJ6, J = 15/2, 13/2. Additionally, there are some extra bands in the luminescence spectra indicating the presence of TiO2 in the agro-food wastes. Trace elements inherently present in the agro-food wastes not only act as stabilisers of the monoclinic phase at room temperature but also result in photoluminescence in the visible region. CIE coordinates are close to the white light region, indicating that these phosphors can find use in cost-effective and environmentally viable solid-state lighting applications.

Synthesis of a Ca3SiO5–Ca2SiO4–Ca3Al2O6 cement system with rapid setting capacity by spray‐pyrolysis coupled with sol–gel method

A modified mineral-trioxide-aggregate (mMTA) with rapid setting capacity was newly synthesized by spray-pyrolysis following a sol-gel reaction. Its faster setting capacity and initially higher compressive strength compared with Portland cement (PC) were evaluated. The precursor solution of the mMTA was prepared through condensation following hydrolysis among Ca(NO3 )2 ·4H2 O, Si(OC2 H5 )4 , and Al(NO3 )3 ·9H2 O under nitric acid. The mMTA powder was then synthesized by spray-pyrolysis at 1500°C. The particle shape was spherical with an average particle size of 0.8 ± 0.3 μm, while PC particles were irregular and 3.9 ± 3.0 μm in size. The mMTA consisted of mostly Ca3 SiO5 , Ca3 Al2 O6 , and partial Ca2 SiO4 phases, while the PC comprised mainly Ca3 SiO5 , Ca2 SiO4 , and partial Ca3 Al2 O6 phases. The final setting times of mMTA and PC measured under 95% relative humidity were about 11 min and 3 h, respectively. The early stage of setting in mMTA was dominated by the rapid formation of hexagonal-plate-like Ca3 Al2 O6 ·6H2 O crystals, while that in PC was dominated by needle-like calcium-silicate-hydrate gels and columnar-shaped Ca(OH)2 crystals. The late stage of setting in mMTA was dominated by calcium-silicate-hydrate gels and Ca(OH)2 crystals, while that in PC was dominated by Ca3 Al2 O6 ·6H2 O crystals. The compressive strengths of mMTA and PC after 30 min of setting were 4.5 and 0.2 MPa, respectively. The results suggest that mMTA has potential to be used as a filling material for accidental pulp-exposure or pulpal floor perforation cases that require rapid setting capacity and initial good strength. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1440-1451, 2019.

Thermodynamics of the CaO–SiO2–VOx system at 1873 K under the oxygen partial pressure of 6.9×10−11 atm

AbstractBased on the phase equilibria of the CaO–SiO2–VOx system determined experimentally at 1873 K and the oxygen partial pressure of 6.9×10−11 atm, the isothermal section diagram of the system was constructed. Aside from the simple oxides SiO2 and V2O3, three complex crystal phases CaV2O4, Ca2SiO4 dissolving V2O3, and CaVO3 dissolving SiO2 were found in the present investigated composition range. The solubility of V2O3 in Ca2SiO4 phase can reach 5 mass %, and the CaVO3 phase dissolves about 5% mass SiO2. Furthermore, the thermodynamic activities of VOx and SiO2 in the determined single liquid region were measured by equilibrating the melts with liquid copper. The activity coefficient of SiO2 decreases linearly with the increase in the basicity of the melts and is almost irrelevant to the total content of vanadium oxides. The activities of vanadium oxides increase slightly with the increase in the basicity but are mainly determined by the total content of vanadium oxides in the melts. With the increase in the basicity, the activity coefficient of VO1.5 increases almost linearly, whereas those of VO2 and VO2.5 decrease gradually.

Synthesis and fluorescence properties of Ca2SiO4:Dy3+ phosphor for solid state lighting application

The series of Dy3+ doped Ca2SiO4 phosphors were successfully prepared by solid state method at 1200 °C. The Ca2SiO4 was verified to be in a pure Ca2SiO4 phase by X-ray diffraction analysis. Moreover, scanning electron microscopy (SEM) and EDAX was investigated for morphological and content present in the as-prepared sample. On the SEM analysis, the average particle size was in the range of 2–10 µm. The photoluminescence (PL) emission for various excitation (λex = 326, 350, 366 and 388 nm) indicated that the emission under 350 nm was optimum. The PL intensity of 485 nm (blue) corresponding to 4F9/2 → 6H15/2 was higher than 575 nm (yellow) corresponding to 4F9/2 → 6H13/2. The CIE color coordinates were found to very close to the standard white color coordinates (x = 0.33, y = 0.33). Which clearly indicate that the Ca2SiO4:Dy3+ phosphor can be used as a potential candidate for the solid state application.

Adsorption and immobilization of actinides using novel SiO2–ZrO2-calcium alginate aerogels from high level liquid waste

The novel SiO2–ZrO2-calcium alginate aerogels were prepared by Sol–Gel process with phase separation method for investigating the adsorption and immobilization performance of the plutonium and minor actinides from high-level liquid waste (HLLW). The materials contained porous network structure with high surface area (233.44–481.08 m2/g) and pore volume (0.50–1.26 m3/g). The aerogels were superior adsorbents for the removal of plutonium and minor actinides, the maximum adsorption capacity and adsorption rate (35 °C, 75 rpm) reached 231.5 mg/g and 99.2%. For all the waste forms, SiO2, ZrO2 and Ca2SiO4 phases were simultaneously observed in the matrix. Moreover, Ce entered into Ca sites of Ca2SiO4 and Zr sites of ZrO2. The substitution of Ca and Zr by Ce in the Ca2SiO4 and ZrO2 implies a promising disposal measure of actinides.

Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu(2+) and Ce(3+)/Li(+)-Activated Ca1.65Sr0.35SiO4 Phosphors.

Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the αL′-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2–x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250–450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs).

The firing steps and phases formed in Mg–Zr–Al refractory dolomite-based materials

Due to the open pore microstructure, MgO–CaZrO3 refractory composites are considered useful materials in various industrial applications. However, the reactivity of the MgO limits its utilization in acid conditions. The chemical inertness and more balanced mechanical properties of MgAl2O4 in comparison with MgO bring forward CaZrO3–MgAl2O4 refractories as promising alternative materials.The present study was carried out in order to determine the feasibility of using Argentine dolomites in the preparation of CaZrO3–MgAl2O4 by solid state reaction. The thermal and structural changes which occur during the firing of the batches up to 1425°C were studied by the combination of diffractometric and infrared spectroscopic data at the most remarkable reaction steps. The study of phase changes within the investigated thermal range allowed establishing the main differences in the composition of the mixtures in each firing step. According to these results, the final product is composed mainly by MgAl2O4, CaZrO3, and Ca2SiO4 phases and the optimal synthesis temperature would be 1425°C. According to SEM microscopy, the existence of ceramic bonding between CaZrO3 and MgAl2O4 could be confirmed.

Single-phase silicocarnotite synthesis in the subsystem Ca3(PO4)2–Ca2SiO4

In the last years, the addition of silicon to hydroxyapatite and tricalcium-phosphate materials is being widely studied, due to the well-known influence of silicon on bone formation. Silicocarnotite (Ca5(PO4)2SiO4) presents a structure type carnotite, very close to hydroxyapatite, with a wide range of Ca2+, SiO44− and PO43− solid solutions. These characteristics make silicocarnotite attractive as potential biomaterial.In this work, the synthesis of silicocarnotite has been studied by a simple and economical method. The formulation and thermal treatment have been designed based on the information supplied by the Ca3(PO4)2–Ca2SiO4 phase diagram. Single-phase silicocarnotite material has been obtained from stoichiometric mixtures of tricalcium phosphate and dicalcium silicate. In order to optimize the synthesis conditions, a two-stage heating was used: heating at 1550°C/2h and subsequent annealing at 1400°C/4h. Mineralogical and microstructural characterizations of the obtained material have been determined by X-Ray Diffraction, Fourier Transform Infrared Spectrometry–Attenuated Total Reflection and Micro-Raman and Scanning electron microscopy.

Preparation and luminescent properties of Ca2Si(O4-xNx)：Eu2+ green-emitting phosphors

A nitrogen-contained solid solution Ca2Si(O4-xNx):Eu2+ green phosphors was successfully synthesized using the method of mixing Ca-Si-O xerogel precursor with Si3N4 powders in a non-reducing atmosphere (pure nitrogen). The structure, morphology, and luminescent properties of the phosphors are characterized by X-ray diffraction (XRD), \text {scanning} electron microscopy (SEM) and photoluminescence (PL) spectra. Results show that the Ca2Si(O4-xNx):Eu2+ is obtained and especially the reduction of Eu3+ to Eu2+ occurs when the mixture of Si3N4 and precursor is calcined at 1100℃ in pure nitrogen atmosphere. XRD results show that the crystalline structure of N-contained solid solution Ca2Si(O4-xNx):Eu2+ is consistent with that of βup -Ca2SiO4 phase. The phosphors can be efficiently excited at a wavelength of 270–400 nm and shows a single intense broadband emission (450–600 nm). Significantly, the red-shift (501 nm to 504 nm) of emission peak occurs and the luminescent intensity is improved significantly with increasing N concentration. With increasing Eu2+ concentration, luminescent intensity of the phosphors increases continuously and reaches a maximum value at the concentration of 0.25 mol% Eu2+. Then the luminescent intensity decreases significantly and the concentration quenching effect appears when Eu2+ concentration is above 0.25 mol%.

Effect of B2O3 on phase compositions of high Ti bearing titanomagnetite sinter

The phase compositions of high Ti bearing titanomagnetite sinter with different contents of B2O3 were studied at 1623 K under an oxygen partial pressure of 5×10−3 atm. The results showed that B2O3 mainly gathered in Ca2SiO4 phase and formed 2CaO.xSiO2.2/3(1−x)(B2O3) phase. The appearance of B2O3 can restrain the precipitation of CaTiO3 and 2CaO.xSiO2.2/3(1−x)(B2O3) and promote the amount of Fe bearing mineral phase in the current experimental condition. In addition, the shape of CaTiO3 changed from bulk to strip type with the increase in B2O3 content. The formula of silicoferrite of calcium and aluminium changed from 1·6CaO.4·9Fe2O3.Al2O3.1·8SiO2 to 2·5CaO.5·9Fe2O3.Al2O3.2·6SiO2, and the formula of dicalcium (boron) silicate changed from 2CaO.SiO2 to 2CaO.0·33SiO4.0·45B2O3 when B2O3 content was from 0 to 2·0 mass-% in the sinter. The change of phase compositions with the addition of B2O3 in the sinter will be beneficial for improving its metallurgical properties.

Effect of TiO2 on equilibrium phase sinter at oxygen partial pressure of 5×10−3 atm

The effect of TiO2 content on the phase compositions of sinter was conducted under reaction equilibrium at oxygen partial pressure of 5×10−3 atm. The results showed that TiO2 mainly existed in the phase of perovskite. With the increase in TiO2 content, the content of secondary hematite phase increased and the ratio of hematite and magnetite in the sinter phase decreased. Meanwhile, the ratio of perovskite and Ca2SiO4 increased and the increased level of perovskite was larger than that of the Ca2SiO4 phase. The volume fraction of the phase silico-ferrite of calcia and alumina decreased from 44·9 to 41·5%, and the chemical formula of silico-ferrite of calcia and alumina changed from 4·7CaO.9·2Fe2O3.Al2O3.2·3SiO2 to 1·6CaO.4·9Fe2O3.Al2O3.1·8SiO2 when the percentage of TiO2 was from 0 to 12 mass-% in the sinter.

Influence of SiO2 modification on phosphorus enrichment in P bearing steelmaking slag

In order to effect enrichment of phosphorus in the converter slag, phosphorus enrichment was researched by slag modification with SiO2. The SiO2 modification process was evaluated thermodynamically, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that n2CaO.SiO2–3CaO.P2O5 (nC2S–C3P) solid solution is generated by the reaction of Ca3(PO4)2 phase in the slag with precipitated Ca2SiO4 phase at 1623 K, and Ca2SiO4 in the solid solution is reduced with increasing SiO2; hence, the phosphorus content in the solid solution is increased. If the addition of SiO2 is excessive, the amount of Ca2SiO4 precipitation in the slag is decreased remarkably (and even disappeared), CaSiO3 phase is generated and the generation of nC2S–C3P solid solution is reduced, which is not favourable to phosphorus enrichment. Through magnetic separation, the non-magnetic fraction was increased by 10–74·68% compared with the original slag. The distribution ratio of P2O5 was increased from 2·71 to 5·48. As 84·57% of the phosphorus in the slag is in the collected non-magnetic substances, the work demonstrates that most of the phosphorus is able to be effectively recycled.

In situ fabrication and wettability of Ca2SiO4/CaTiO3 biocoating by laser cladding technology on Ti–6Al–4V alloy

Wetting is the first and foremost event when a biomaterial is implanted into the biological system. Hence, it is very essential to investigate the wettability of a biomaterial before further biological studies. A textured coating with different relative amounts of Ca2SiO4 and CaTiO3 was in situ fabricated by varying laser scan speed. The wettability of different coatings was investigated. The results indicate that the relative amount of Ca2SiO4 phase increased with decreasing laser scan speeds and reached the highest value of 48·17±2·10 mJ mm−2, and the geometrically textured topography with a surface roughness of 9·17 μm was obtained at a laser scan speed of 2 mm s−1. The microstructure in the coating can be characterised as fine dendrites. Surface energy values varied with the relative amount of Ca2SiO4 phase. The coating obtained at the laser scan speed of 2 mm s−1, which contains more relative amount of Ca2SiO4, presents the highest surface energy, indicating most desirable wettability. This resulted in an increase in contact angle in simulated body fluid solution for improved wettability. The microhardness presented a gradient distribution from the coating surface (1072 HV) to the substrate (260 HV).