CaO Phase Research Articles

Experimental determination of the 1300 °C and 1400 °C isotherms for CaO–SiO2–TiO2-10 wt% Al2O3 system in air

Phase equilibrium relations for the CaO–SiO2–TiO2-10 wt%Al2O3 system were studied at 1300 °C and 1400 °C by a high temperature equilibration and quenching method, with the purpose of extending the equilibrium phase information for the TiO2-containing slag systems. Equilibrium phase assemblies and phase compositions were analyzed by Scanning Electron Microscopy (SEM) equipped with an X-ray Energy Dispersive Spectroscopy (EDS). The equilibrium solid phases of perovskite CaO·TiO2, wollastonite CaO·SiO2, rutile TiO2, silica SiO2 and sphene CaO·SiO2·TiO2 were confirmed to coexist with a liquid phase. Based on the experimental results, the 1300 °C and 1400 °C isotherms were constructed in the CaO–SiO2–TiO2-10 wt% Al2O3 quasi-ternary phase diagram. Significant discrepancies were found between the present results and the simulated results by FactSage and MTDATA databases, as well as the results from previous literature.

Identification of Phase CaCO3/MgO in Bangkalan Dolomite Sand as An Antibacterial Substance

Dolomite sand has several ingredients such as CaCO3 and MgO which have the potential as an antibacterial substance. The making of this antibacterial substance uses the heating/calcination method of dolomite powder with a variation of holding time from 0.5 to 2.5 hours at a temperature of 700°C. The nanoparticles produced from the calcination process were then characterized by XRD to identify the formed phase. This study aimed to determine the effect of holding time on phase formation on dolomite. The results of this study are identified as forming four phases namely calcite (CaCO3), periclase (MgO), calcium hydroxide (Ca(OH)2) and lime (CaO) with different percentages in each variation of holding time. The Ca(OH)2 and CaO phases include the impurity phase with a lower percentage than the CaCO3 and MgO phase percentages. The most dominant phase is CaCO3 and the MgO phase formed optimally at 1 hour holding time with a percentage of 47.1% CaCO3 and 35.9% MgO.

Insights and utility of cycling-induced thermal deformation of calcium-based microporous material as post-combustion CO2 sorbents

On the quest of finding ideal sorbent for post-combustion CO2 capture, calcium-based sorbent seems to have the potential, but often it cannot sustain its reactivity, especially after repeated cycle of sorption. This work aims to unravel the controlling factors in carbonation reaction and thermal-induced deformation of skeleton pore network that limits the CO2 absorptivity of calcium-based sorbent. Through precise measurement of CO2 absorption activity using TGA/DSC and a series of characterization, this study paves the way for the development of next-generation CaO sorbent that has high CO2 uptake capacity and thermal stability. Key findings include CaO particles with severe point defects contribute to fast CO2 absorption activity. The transformation from CaCO3 phase to CaO phase from organic precursor is 4 times higher than the inorganic precursor. Decomposition of calcium formate is thermally stable regardless of calcination temperature. Citrate-based structure precursor is able to produce homogeneous nanosized CaO particle. Shifting of reaction controlling regime from fast carbonation reaction to diffusion limited stage happened at Thiele modulus of 1.35. Lastly, first stage of fast carbonation reaction will take place at CaO sorbent’s surface with proximate zero activation energy and second stage of slow carbonation reaction is controlled by high activation energy of ion diffusion behavior in CaCO3 ionic crystals at product diffusion layer. Future research direction can focus on reproducing long periodical citrate-like structural precursor using sol-gel method to mimic the behavior of calcium formate and calcium citrate to form nano-sized CaO particles with thermally stable crystal structure.

Development of CaO-based adsorbents loaded on charcoal for CO2 capture at high temperature

CaO-based adsorbents have the potential to be used for CO2 capture at high temperature. However, CaO-based adsorbents exhibit a sharp decay in CO2 uptake capacity over multiple cycles, owing to the sintering of CaO particles. In this paper, a series of charcoal supported CaO-based adsorbents were developed to improve the CO2 capture performance of CaO using three different methods: physical mixing, wet impregnation and sol-gel method. The influences on CO2 capture of CaO loading and carbonation temperature are also included. The morphology and structural properties of the adsorbent were investigated by means of electron microscopy, nitrogen adsorption and XRD. It is found that the novel sorbent with an optimal mass ratio of CaO to charcoal of 4:1 prepared by the sol-gel method exhibits an initial capture capacity of 15.1 mmol g−1 and maintains a capacity of 8.0 mmol g−1 after 15 cycles of carbonation (600 °C) and calcination (650 °C), around 60% higher than that of sol-gel CaO. The CaC-4 possesses a porous stucture with a high surface area of 63.6 m2·g−1 and a pore volume of 0.166 cm3·g−1, making CO2 diffusion easier. The XRD analysis displays that crystalline size (26 nm) of the CaO phase in CaC-4 is much smaller than that of the reference bulk CaO (96 nm), reflecting that charcoal can effectively inhibit the growth of CaO crystalline. Furthermore, the introduction of charcoal derived from biomass pyrolysis will improve the economic viability of the CO2 capture process.

Polytypism in calcium oxide compound: Mechanical and dynamical evidence of structural stability

Bulk calcium peroxide (CaO2) was synthesized in 1941, where experiments assigned a tetragonal ‘calcium carbide’ phase. However our first-principles calculations of thermodynamic and dynamical properties evidence that the tetragonal calcium carbide phase of CaO is unstable. Therefore we revisit here the stability of the Ca–O system at ambient pressure by using evolutionary methodology for crystal structure prediction. Besides the well-known rocksalt phase of CaO, unexpected new hexagonal nearly thermodynamically stable, and unstable tetragonal calcium carbide phases have been discovered at ambient conditions. Computed elastic constants and phonon reveal that all polytype phases of CaO are mechanically stable; whereas rocksalt and hexagonal (tetragonal) are dynamically stable (unstable). Furthermore, the electronic, mechanical and dynamical properties of rocksalt, hexagonal and tetragonal structures of Ca–O system are examined in relation with calcium oxide polytypes.

Effect of CaO-FeO-MnO system solid solution on the hydration activity of tri-component f-CaO in steel slag

The ingredients and formation mechanism of calcium iron manganese phase were confirmed and analyzed to comprehend further the hydration activity of tri-component f-CaO in four type steel slags. BSE-EDS analysis indicates that the tri-component f-CaO in four type steel slags was a phase of CaO·aFeOx·bMnOy system and the mean values of nFe/nCa, nMn/nCa and (nFe + nMn)/nCa were focused on nearby 0.12, 0.08 and 0.2, respectively. According to the relevant element ratio, the simply simulated experiments of tri-component f-CaO were conducted that the CaO-FeO-MnO system finite solid solution and a new crystalline phase of Ca2Fe2O5 were formed. The formation mechanism of CaO-FeO-MnO system finite solid solution was described briefly. By means of SEM-EDS, the microstructure of synthetic tri-component f-CaO was observed, and the analyses of XRD/TG-DTA and thermodynamic theory were applied to the hydration activity. The results show that the hydration percentage of tri-component f-CaO was about 80% after autoclaved for 3 h, and more than two times that of after hydrated at ambient temperature for 36 h. The CaO-FeO-MnO system solid solution was one of the critical factors which causes the poor hydration activity of tri-component f-CaO. This theoretical investigation will lay a foundation for building materials and solid waste fields.

Phase compositions and microwave dielectric properties of Sn-deficient Ca2SnO4 ceramics

The phase compositions and low-permittivity microwave dielectric properties of Ca2Sn(1−x)O(4−2x) (0 ≤ x ≤ 1.0) ceramics were investigated through a solid-state reaction at 1350 °C-1450 °C for 5 h. A small Sn-deficiency is beneficial to inhibiting a CaSnO3 second phase and forming a Ca2SnO4 single phase with excellent microwave dielectric properties (εr = 9.9, Q × f = 120,100 GHz, and τf = −45.6 ppm/°C) in the Ca2Sn(1−x)O(4−2x) (x = 0.02) ceramics. With an increase in x from 0.04 to 1.0, the amount of CaO phase increased, and the Ca2SnO4 phase decreased gradually. Finally, a CaO pure phase (εr = 10.6, Q × f = 229,600 GHz, and τf = −37.5 ppm/°C) was obtained at x = 1.0.

Physical, mechanical and in vitro evaluation of a novel cement based on akermantite and dicalcium phosphate dihydrate phase

Magnesium containing calcium silicates have recently shown that they are promising materials for various biomedical application with potential use in the form of bulk ceramic, composite scaffold or coatings on metallic substrates. A novel akermanite (AK; Ca2MgSi2O7)/dicalcium phosphate dihydrate (DCPD, CaHPO4. H2O) cement mixture was tested in this work in order to produce an alternative AK/DCPD biocement for orthopedic applications. For comparison, we have prepared two cements mixed with 2.5 wt% NaH2PO4 solution (labeled as NaH2PO4 cement) and with the solution composed of organic 2.5 wt% citric acid a 2.5 wt% trisodium citrate (citrate cement) respectively. The results demonstrated only a partial dissolution of AK, regardless of the type of liquid used. On the other hand, the DCPD was completely hydrolyzed much faster in the citrate cement. The final hydration product was an amorhous quarternary phase of CaO–MgO–SiO2–P2O5 composition with the remaining unreacted akermanite embeded in the cement matrix. The highest early compressive strength was observed in the citrate cement (33 MPa), but much lower value was measured in NaH2PO4 cement (7 MPa) after 1 d setting. Different cell responses have been observed when the cells were cultured on the surfaces of cement substrates. While the NaH2PO4 cement demonstrated high proliferation activity of osteoblast, the citrate cement showed strong cytotoxic cell response, probably as a result of higher concentration of citrates on the cement surface, which can negatively affect the attachment and proliferation of osteoblastic cells.

Thermal behavior of perlite concrete used in a sodium-cooled fast reactor

In this study, the thermal behavior of the perlite concrete used in a sodium-cooled fast reactor was investigated for obtaining information on a plant simulation system for safety assessment. The thermal stability and kinetic behavior of multistep thermally induced processes of perlite concrete were examined using thermoanalytical techniques and other complementary methods. The partially overlapping thermal decomposition process comprising seven reaction steps was characterized by kinetic deconvolution analysis based on a cumulative kinetic equation by determining the contribution and all kinetic parameters for each component reaction step. The thermal decomposition product was a mixture of amorphous and crystalline phases located in a CaO-rich region in the SiO2–CaO phase diagram. The softening or melting of the decomposition product was initiated at approximately 1520 K. The significance and reliability of the results obtained were discussed on the premise of their practical uses for the safety assessment.

Analisis Komposisi Fasa dan Parameter Unit Sel Kristal Hasil Kalsinasi Suhu Tinggi Abu Cangkang (Paguroidea) dengan Metode Rietveld

Quantitative analysis by data refinement of the Rietveld method for calcium-based catalyst samples from hermit crabs (Paguroidea) ash has been successfully carried out. The results of the improvement showed that the samples of hermit crab shell calcined at 900 ° C gave different phase compositions and unit cell parameters due to the influence of calcination times 2, 3 and 4 hours. 2 hours is a single phase CaCO3 calcite, 3 hours are multiphase CaCO3 calcite and CaO, while a 4 hour sample is a single phase CaO . The reliability value (R) of the improvement results, R P , R wp , R exp and GoF = χ 2 gives good and acceptable results

Nano indentation Analysis of Multi Stage Spark Plasma Sintered Hydroxyapatite-Calcium Titanate Biocomposite

Despite being highly bioactive and biocompatible, some of the limitations like poor fracture toughness, lack of electrical conductivity and antimicrobial properties restrict the use of monolith hydroxyapatite (HA) as bone replacement material. In this paper, we address one such issue and will demonstrate how CaTiO3 (CT) addition enhances physical properties like strength, fracture toughness etc. Therefore, the strategy in the current research is to develop dense HA-CT biocomposites using innovative multi-stage spark plasma sintering (MSSPS) technique (at 50 MPa, 1200oC, 5 min), that can mimic the function and properties close to that of natural bone. Fine scale microstructural characterization using TEM reveals the presence of twins in CaTiO3 grains and the grain size of HA is around 1-2 µm. Phase analysis using x-ray diffraction analysis revealed an absence of α and β-tricalcium phosphate (Ca3(PO4)2) or CaO phase which is also supported by Fourier transformed infra-red spectroscopy. Elastic modulus of 46-135 GPA is obtained using nanoindentation. Based on the available empirical models, it has been observed that the experimentally measured density hardness, and elastic modulus match reasonably well with that of the natural cortical bone.

Dielectric response on ultraviolet light irradiation of Ba0.85Ca0.15Zr0.1Ti0.9O3 based ceramics

Ba0.85Ca0.15Zr0.1Ti0.9O3-based ceramics with doping of Ca3Co4O9, CaMn0.98Nb0.02O3, and Zn0.98Al0.02O were fabricated. CaO and CaCO3 secondary phase were observed in all doped ceramics. These phases caused vacancies of Ca ions, which became associated with oxygen vacancies induced by ultraviolet light, leading to the formation of a defect dipole. The defect dipoles enhanced the photo-induced dielectric properties. The maximum enhancement was about 60% with Ca3Co4O9 doping while other ceramics did not show significant change. The results here suggested that the ultraviolet light-induced dielectric properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramic may be largely tunable by Ca3Co4O9 addition and could be an alternative material for light sensors.

Evolution behaviour of nonmetallic inclusions in Ti-bearing 11Cr stainless steel with calcium treatment

ABSTRACTNonmetallic inclusions formed during the Ti-stabilized stainless steelmaking process can induce the clogging in the submerged entry nozzle during continuous casting. To investigate the formation mechanism of nonmetallic inclusions in Ti-stabilized stainless steel, steel specimens were taken at different stages in industrial trials. The characteristics of inclusions and the chemical compositions of steel were analysed. After 10 min of Al deoxidation, the main type of inclusions in samples was irregular MgO·Al2O3. With titanium addition after calcium treatment, the irregular dual phase CaO–TiOx–Al2O3–MgO inclusions were formed. The steel compositions of most samples were located in or close to the Al2O3–TiOx liquid oxide phase field. According to experiment and thermodynamic results, the solid CaTiO3 and/or CaO·2Al2O3 inclusions were formed during titanium addition when the molten steel contained more than 20 ppm calcium. The effect of the initial calcium content on the formation of Ca–Al–Ti–O inclusions during titanium addition was discussed.

Performance characteristics of collapsible CaO-SiO2 based ceramic core material via layered extrusion forming

An additive manufacturing method, named layered extrusion forming (LEF), was adopted to fabricate collapsible ceramic cores. Green samples were first fabricated using CaCO3 and SiO2 powders as precursor materials and aqueous polyethylene glycol solution-silica sol as a composite binder and then calcined at 1100 °C − 1300 °C for 2 h. The effect of CaO-SiO2 molar (C/S) ratio on the performance characteristics of green and sintered samples was investigated. The results showed that the slurries exhibited a pseudoplastic behavior for different C/S ratios, and the linear shrinkage of the green samples showed a slight increase with decreasing C/S ratio. After sintering, the reduction of C/S ratio obviously decreased linear shrinkage and bending strength, whereas strengthened the hydration resistance. The microstructure analysis demonstrated that the porosity was increased with decreasing C/S ratio, thereby weakening the bending strength. The ceramic cores samples were constituted by Ca2SiO4 and CaO phases. The existence of the Ca2SiO4 improved the hydration resistance, leading to relative lower collapsibility. The sintered samples with a C/S ratio of 2.45 obtained a superior collapsibility in water, especially in the higher water temperature, which is significant for industry applications.

Triethanolamine as an efficient cosolvent for biodiesel production by CaO-catalyzed sunflower oil ethanolysis: An optimization study

Triethanolamine was applied as an efficient ?green? cosolvent for biodiesel production by CaO-catalyzed ethanolysis of sunflower oil. The reaction was conducted in a batch stirred reactor and optimized with respect to the reaction temperature (61.6-78.4?C), the ethanol-to-oil molar ratio (7:1-17:1) and the cosolvent loading (3-36 % of the oil weight) by using a rotatable central composite design (RCCD) combined with the response surface methodology (RSM). The optimal reaction conditions were found to be: the ethanol-to-oil molar ratio of 9:1, the reaction temperature of 75?C and the cosolvent loading of 30 % to oil weight, which resulted in the predicted and actual fatty acid ethyl ester (FAEE) contents of 98.8 % and 97.9?1.3 %, respectively, achieved within only 20 min of the reaction. Also, high FAEE contents were obtained with expired sunflower oil, hempseed oil and waste lard. X-ray diffraction analysis (XRD) was used to understand the changes in the CaO phase. The CaO catalyst can be used without any treatment in two consecutive cycles. Due to the calcium leaching into the product, an additional purification stage must be included in the overall process.

Effect of Cooling Rate on Phase and Crystal Morphology Transitions of CaO⁻SiO₂-Based Systems and CaO⁻Al₂O₃-Based Systems.

The phase and crystal morphology transitions of two typical types of mold fluxes were investigated fundamentally using differential scanning calorimetry (DSC) and confocal scanning laser microscopy (CSLM) techniques. For the traditional CaO–SiO2–CaF2-based mold flux, different cooling rates can change the phases and the crystal morphologies. Faceted cuspidine and CaSiO3 are co-precipitated when the cooling rate is less than 50 °C·min−1. The phases transform from Ca4Si2O7F2 and CaSiO3 to Ca4Si2O7F2 at the cooling rate of 50 °C·min−1. Cuspidine shows four different morphologies: faceted shape, fine stripe, fine stripe dendrite, and flocculent dendrite. The crystalline phases of CaAl2O4 and Ca3B2O6 are co-precipitated in the CaO–Al2O3-based mold flux. Neither the phases nor the crystal morphologies change in the low cooling rate range (5 °C·min−1 to 50 °C·min−1). With decreasing temperature, the morphology of CaAl2O4 firstly becomes dendritic, and then the dendritic quality gradually changes to a large-mesh blocky shape at the cooling rates of 100 °C·min−1, 200 °C·min−1, and 500 °C·min−1. Different cooling rates do not show an obvious impact on the morphology transition of CaAl2O4. The strong crystallization ability and large rate of crystallization affect the control of the heat transfer of the CaO–Al2O3-based mold flux during casting. The big morphology difference between primary crystals of the CaO–SiO2–CaF2-based mold flux and the CaO–Al2O3-based mold flux is probably one of the biggest factors limiting lubrication between the CaO–Al2O3-based mold flux and high-Al steel during casting.

Sorption-enhanced reforming of tar: Influence of the preparation method of CO2 absorbent

To remove tar and produce environment-friendly H2, one of the promising routes is the sorption-enhanced steam reforming (SESR) process, in which the CO2 sorbent is a key element. We prepared the CO2 sorbents with Ca12Al14O33 as carrier with various methods. Their characterizations were examined, and the sample prepared by solgel (SG) method showed the strongest CaO and Ca12Al14O33 phases and the most excellent pore structure among all the samples. Then, a thermogravimetric experiment was conducted, and the results showed that the sample prepared by sol-gel (SG) method had the best CO2 adsorption capacity and excellent long-term cyclic stability. Finally, the sorbent was used into the steam reforming experiments of tar. Under the action of the sorbent, the reforming reaction was enhanced in-situ, with the H2 yield and concentration improved obviously, and especially, H2 concentration can reach over 98.85%.

Expansibility of cement paste with tri-component f-CaO in steel slag

Steel slag used as binding materials often shows volumetric instability because of the existence of f-CaO (free calcium oxide). According to the composition analysis of steel slag, the tri-component f-CaO (CaO·aFeO1.5·bMnO2) was synthesized. The single phase CaO and some solid solution phases were detected in the tri-component f-CaO by XRD. The single phase CaO was found to be completely hydrated at room temperature after 18 h. The solid solution phase could not be hydrated at room temperature, while it could be hydrated partly via a boiling treatment. The hydration activity of CaO in the solid solution phase was lower than that of the single phase CaO. The f-CaO was mixed into Portland cement to study the expansibility by autoclave test. The single phase CaO had no contribution to the expansion when the content was not more than 1%. The solid solution phase in f-CaO was the main cause of the expansion. The relationship between the autoclave expansion rate and the f-CaO content conformed to the exponential equation. For the tri-component f-CaO, the smaller the molar ratio of Ca to Mn and Fe was, the more solid solution phase was present and the greater was the expansibility.

Photoluminescent properties of nanocrystalline Sm3+-doped CaO–CeO2system synthesized by an auto-igniting combustion synthesis technique

This study investigates the optical properties of samarium-doped microstructured and nanostructured CaO–CeO2mixed solutions. Conventional solid state method and auto-igniting combustion synthesis were used for the preparation of the samples. The as-prepared samples were characterized using X-ray diffraction, Fourier Transform Infrared spectroscopy, Transmission Electron Microscopy, UV-Visible spectroscopy and photoluminescence spectroscopy. A mixed phase formation with phases of CaO, CeO2and Ca(OH)2was observed form X-ray diffraction studies. The transmission electron microscopic studies have shown that the average particle size of the as-prepared powder was in the range of 30–40 nm. A blueshift is observed in the bandgap of the nanocrystalline samples. Strong orange–red emission was observed for Sm[Formula: see text]-doped samples and the chromaticity values were calculated using CIE chromaticity diagram.

Effects of oxygen atmosphere, FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

ABSTRACTThe mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO2–MgO–Al2O3–FetO–P2O5 slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO2 (w(CaO)/w(SiO2))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa2SiO4-Ca3(PO4)2 (thereafter nC2S-C3P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO4 phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC2S-C3P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeOx content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeOx content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.