System CaO Research Articles

Incorporation of calcium in glasses: A key to understand the vitrification of sewage sludge

AbstractThe quantity of sewage sludge generated daily by wastewater treatment plants represents a major environmental problem and a financial burden for plant operators. Valorization strategies focusing on reusing sewage sludge as a raw material are currently developed. Vitrification can help us reduce the volume of waste and binds the components in the structure of chemically stable glasses and glass‐ceramics. In this study, the vitrification of sewage sludge inside a basaltic rock has been simulated by producing glasses and a glass‐ceramic from basalt enriched in calcium that lie between the stability fields of pyroxene and melilite in the system CaO–MgO–SiO2–Al2O3. CaO addition causes the oxidation of the melt at above the liquidus, increases the crystallization temperature, decreases the melting temperature, and improves the microhardness of the glasses. Glass‐ceramic processes improves the properties of the Ca‐doped basalt glass. The microhardness of the glass (8.2 GPa) and the glass‐ceramic (8.6 GPa) and leaching tests (in the ppb range) place both the glass and the glass‐ceramics at the high end of the mechanical properties and chemical resistance of ceramic tiles for the building industry.

A Reappraisal of Peridotite Solidus Phase Equilibria from 6 to 14 GPa in the System CaO–MgO–Al2O3–SiO2

AbstractExperimentally determined isobaric invariant melting phase relations from 6 to 14 GPa in the system CaO–MgO–Al2O3–SiO2 (CMAS), involving the crystalline phases forsterite + orthopyroxene + clinopyroxene + garnet and liquid, are reported. Experiments were conducted using a multianvil device with stepped lanthanum chromite heaters in the pressure cells. At a fixed pressure, the five-phase assemblage identified above can exist only at a single temperature. As such, these isobaric invariant points correspond to the solidus of model garnet peridotite in this part of the composition space in the studied system, as is the case at lower pressures in some previous studies. The solidus of model peridotite is univariant in pressure–temperature space, has a positive Clapeyron slope, and the isobaric invariant solidus temperatures, at 6, 8, 10, 12, and 14 GPa, are 1965 °C, 2090 °C, 2200 °C, 2280 °C, and 2320 °C, respectively. Over the investigated pressure range, orthopyroxene is in reaction relation with the liquid, with the fusion reaction taking the form forsterite + clinopyroxene + garnet = orthopyroxene + liquid. The compositions of liquids reported here do not seem to depend on orthopyroxene being present in the experiments. Compositionally, liquids here are fairly magnesian and siliceous, and have lower alumina and lime concentrations than at lower pressures with the identical crystalline phase assemblage in the system CMAS. In contrast to some previous studies, in this study, there is no evidence of maximum and minimum normative forsterite concentration of the isobaric invariant liquid at around 8 and 12 GPa, respectively, nor of a substantial curvature in the track of liquid compositions, when such liquids coexist with the above-mentioned four-phase crystalline phase assemblage. Instead, here, with increasing pressure from 6 to 14 GPa, liquids at the isobaric invariant points (defining the univariant solidus) become progressively (quasi-linearly) enstatite-normative. This experimental observation on liquid compositions from the present study might be important for future work aimed at investigating the chemistry of liquids derived from partial fusion of anhydrous peridotite at pressures, and corresponding depths in Earth, greater than investigated here.

Interfacial reactions between titanium–copper melt and crucible oxides

Interfacial reactions of various cold isostatic pressed oxide crucibles (calcia, yttria-stabilized zirconia, and yttria) with Ti–5wt% Cu alloy at 1680 °C for 15 min melting in an argon environment have been investigated to estimate the corrosion resistance. Predicting thermodynamic analysis results indicate that oxide refractories based on calcia, zirconia, and yttria, can be used for melting titanium–copper alloy. However, significant differences between experimental results and those thermodynamic analysis results in the ZrO2–12 wt% Y2O3 and CaO systems were identified. The surface observations and element distribution made on cross-sections perpendicular to the interface using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) show that obvious interfacial reactions between alloy melt and ceramics in ZrO2–12 wt% Y2O3, and CaO systems occur at experimental temperature, while yttria shows the most superior stability with the most desirable features of interface properties of metal and crucible, and the product of dissolved Y2O3 was still found in the metal. Meanwhile, the interaction between the ZrO2 oxide and the Ti–5 wt% Cu melt can be effectively reduced by the addition of Y2O3. The high apparent porosity of the crucible results in low resistance to erosion caused by Ti–5Cu melt. Moreover, the reduction of calcia causes the boiling of the melt. These results would provide the basis for designing a new refractory for the melting of titanium–copper alloy.

Visualization of Slag Data for Efficient Monitoring and Improvement of Steelmaking Slag Operation in Electric Arc Furnaces, with a Focus on MgO Saturation

Frequent slag sampling and analysis is still the most common method used to investigate and improve slag operation in electric arc furnaces (EAFs) for low-alloyed carbon steelmaking. An MgO saturation diagram for EAF slags was derived from phase equilibrium calculations in the system CaO–MgO–FeO–SiO2–5%Al2O3 to provide monitoring and interpretation of the slag data with respect to control of MgO saturation, FeO reduction, dissolution from the MgO-based refractory lining, and unusual losses of repair mixes. Examples from 14 industrial EAFs are given.

The Beneficial Mechanical and Biological Outcomes of Thin Copper-Gallium Doped Silica-Rich Bio-Active Glass Implant-Type Coatings

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs®BG alkali-free SBG system (mol%: SiO2—38.49, CaO—36.07, P2O5—5.61, MgO—19.24, CaF2—0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (~600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (RRMS < 1 nm) and hydrophilic (water contact angle of ~65°). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs®BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of ~53 MPa, Lc3 critical load value of ~4.9 N, hardness of ~6.1 GPa and an elastic modulus of ~127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays.

Diamond resorption and immiscibility of C-O-H fluid in kimberlites: Evidence from experiments in H2O – CO2 – SiO2 – MgO – CaO system at 1–3 GPa

Kimberlites are the deepest sourced magmas emplaced at the Earth's surface. They provide a “window” into the processes at the base of the subcratonic mantle. A better understanding of the origin, composition, and emplacement mechanisms of kimberlites is hampered by uncertainties in the contents of the two main volatiles, H2O and CO2. Diamond dissolution in H2O and in CO2 fluids produces distinct resorption features offering an opportunity to determine the composition of the magmatic fluid in kimberlites. Here we examined the relationship between H2O:CO2 ratio of the fluid and the style of diamond resorption by conducting experiments in C-O-H fluid saturated with silicates with variable H2O:CO2 ratios at the conditions of kimberlite ascent of 1–3 GPa and 1150–1350 °C. Our results showed that the geometry of etch pits on diamond and the resorption style evolve consistently as bulk CO2 content of the fluid changes from 0 to 50 to 50–90 and 90–100 mol%. The fluid composition at the run conditions was monitored by entrapment of synthetic fluid inclusions in olivine and quartz. The inclusions demonstrated the existence of a fluid miscibility gap at 1–3 GPa and 1250 °C with two fluid endmembers, an aqueous and a carbonic phase, which H2O:CO2 ratio at 1 GPa determined with confocal Raman microscopy is (H2O)0.62(CO2)0.38 and (H2O)0.12(CO2)0.88 respectively. Hence, diamond resorption morphology depends on the proportions of the end-member aqueous and carbonic fluids, which vary with the bulk composition of the fluid. The different density and ability of aqueous and carbonic fluids to dissolve silicates (olivine) would promote their separation in the rising magma column. Concentration of the lower density aqueous fluid towards the tip of the propagating dyke would facilitate more efficient fracturing of the country rocks and faster ascent of the kimberlite magma causing explosive eruption. We propose that preferential attachment of aqueous fluid bubbles would help to increase the buoyancy of olivine xenocrysts and possibly diamond in the kimberlite magma offering a mechanism for transporting the heavy mantle cargo.

Experimental study and thermodynamic optimization of the ZnO–FeO–Fe2O3–CaO–SiO2 system

Liquidus phase equilibrium experimental data from the present study for the ZnO-“Fe2O3”-CaO-SiO2 system in air, combined with phase equilibria and thermodynamic data from the literature on the ZnO-“Fe2O3”-CaO system in air and ZnO-“FeO”-CaO-SiO2 system in equilibrium with metallic Fe, have been used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in the ZnO–FeO–Fe2O3–CaO–SiO2 system. The modified quasichemical model is used for the liquid slag phase; spinel (Fe,Zn,Ca)tetr (Fe,Zn,Ca,Va)oct2O4, melilite Ca2(Fe2+,Fe3+,Zn)(Fe3+,Si)2O7 and olivine (Fe,Zn,Ca)I(Fe,Zn,Ca)IISiO4 are described with compound energy formalism; lime and wustite (monoxide) (Ca,Fe,Zn)O, zincite (Zn,Fe,Ca)O1+x, calcium-zinc ferrites Ca2Fe2O5-“CaZnO2” and CaFe4O7-“ZnFe4O7”, α- and α′-dicalcium silicate (Ca,Fe,Zn)2SiO4 and tricalcium silicate (Ca,Fe,Zn)3SiO5 and silicoferrite of calcium (SFC) Ca9Fe46SiO80–Ca12Fe40Si4O80 are described within Bragg-Williams formalism; for other phases, previous assessments have been adopted. The phase diagrams are back calculated with the optimized model parameters. Present study is a part of research program on the characterization of the multicomponent PbO–ZnO–FeO–Fe2O3-“Cu2O”-CaO-SiO2 system.

CaO doped ZnO–Bi2O3 varistors: Grain growth mechanism, structure and electrical properties

In this study, the impact of CaO doping on the microstructure, phase and electrical properties of the ZnO–Bi2O3 system was studied. The powder was synthesized by the solution combustion route. Reduction in the crystallite size of ZnO from 23 nm to 17 nm of the powder sample with CaO doping was noted. Conventional sintering was used to consolidate the powders. Solid state reacted compositions revealed, from X-ray diffraction, formation of two phases (a) Ca4Bi6O13 at 750 °C and (b) Ca0.89Bi3.11O5.56 at 900 °C. An increase in density from 4.21 to 5.45 gcc−1 and a decrease in grain size from 4.50 to 1.54 μm with increasing CaO doping were also observed. A grain growth mechanism in the ZnO–Bi2O3–CaO system was proposed. The breakdown field increased up to 1 wt % CaO (27 kV cm−1) and after that decreased. Impedance spectroscopic investigation, in the temperature range of 100300 °C and frequency range of 0.1 Hz -1M Hz, exhibited two relaxations. These were attributed to defects formed. The two-stage activation energy of conductivity was noticed, which was similar to that observed in complex ZnO varistor systems.

Carbonate melts in the hydrous upper mantle

Carbonatite compositions resulting from melting of magnesian calcite + olivine + clinopyroxene were experimentally determined in the system CaO–MgO–SiO2–CO2–H2O as a function of temperature and bulk H2O contents at 1.0 and 1.5 GPa. The melting reaction and melt compositions were found to be highly sensitive to H-loss or -gain during experiments. We hence designed a new hydrogen-trap technique, which provided sufficient control to obtain consistent results. The nominally dry solidus temperatures at 1.0 and 1.5 GPa are 1225–1250 °C and 1275–1300 °C, respectively. At 1.0 GPa, the solidus temperature decreases with H2O increasing to 3.5 wt% (1025–1050 °C), then remains approximately constant at higher H2O concentrations. Our nominally dry solidus temperatures are up to 140 °C higher than in previous studies that did not take measures to limit hydrogen infiltration and hence suffered from H2O formation in the capsule. The near-solidus anhydrous melts have 7–8 wt% SiO2 and molar Ca/(Ca + Mg) of 0.78–0.82 (XCa). Melting temperatures decrease by as much as 200 °C with increasing $${\text{X}}_{{{\text{H}}_{{2}} {\text{O}}}}$$ in the coexisting COH-fluid. Concomitantly, near-solidus melt compositions change with increasing bulk H2O from siliceous Ca-rich carbonate melts to Mg-rich silico-carbonatites with up to 27.8 wt% SiO2 and 0.55 XCa. The continuous compositional array of Ca–Mg–Si carbonatites demonstrates the efficient suppression of liquid immiscibility in the alkali-free system. Diopside crystallization was found to be sensitive to temperature and bulk water contents, limiting metasomatic transformation of carbonated upper mantle to wehrlite at 1.0–1.5 GPa to < 1175 °C and < 7 wt% bulk H2O.

Size of metal drops formed on a bubble of reducing gas at oxide melt barbotage

To estimate the size of the drops formed on individual bubbles of the reducing gas during the oxide melt barbotage, a metal phase formation model was used. This model includes the following stages: formation of bubbles upon injection of gas into the melt; metal recovery on the bubbles surface and its concentration in the form of drops in stern. Equations are presented that make it possible to estimate the limiting sizes of a gas bubble (Rкрп) and drops (rкрк) moving in oxide melt without crushing. Using the densities (p, kg/m3) and surface tension (σ, mJ/m2) of B2O3 - CaO (1) and B2O3 - CaO - CuO (2) melts in the temperature range of 1373 - 1673 K, described by the equations σ1= 87,0 + 0,242T, p1 = 3,2610-3 - 0,91T, σ2= 10,8 + 0,178T, p2 = 3,1910-3 - 0, 70T, respectively , the critical dimensions of a gas bubble (Rкрп)moving in an oxide melt without crushing were calculated. In B2O3 - CaO - CuO melt, critical radius of the bubble varies from 0.047 to 0.053 m depending on temperature, and for the B2O3 - CaO system these values are 0.06 - 0.081 m. Using a technique with thermodynamic equilibrium calculations that allows to describe the features of oxide melt barbotage by various reducing gases, we determined the change of the copper oxides content in B2O3 - CaO - CuO melt depending on the amount of CO introduced at different temperatures. Based on the obtained data, the amount of copper formed during the interaction of Cu2O in the melt with a single CO bubble wascalculated depending on the content of copper oxide and the amount of CO in the bubble. The correlation dependences of the drop size on the content of Cu2O in the melt (CCu O, %), temperature (T, K) and the amount of CO in the bubble (nCO , mol) were obtained by statistical data processing methods.

Assessing the chromium mobility in ashes through SiO2–Al2O3–Fe2O3–CaO system: The role of composition

Given the millions of coal-fired power stations worldwide and the generalization of co-firing technologies in the near future, the aqueous extraction experiments were taken to study the effects of oxides on Cr mobility in ashes through SiO2–Al2O3–Fe2O3–CaO system. The results identify that both the component and the species of Cr in samples are vital factors to govern the fate of Cr during combustion. Although Cr-oxide hardly reacts with Al2O3, SiO2, and mixtures at 900 °C, the immobilization of Cr in Si–Al glass is ascribable to the heat-driven phase transformation of Cr-rich clay. The strong capture of Cr-oxide by CaO leads to the primary extraction of active Cr with the high toxicity and mobility; however, the opposite effect is found by Fe2O3. But the interactions of Al-/Si- oxides with others can trigger some changes in Cr mobility, wherein there is the lowest mobility of Cr in the case of Cr entering into the structures of Fe-rich SiO2/Si–Al glass during combustion. Thus, without regard to the sample source, it is effective to reduce the environmental risk of Cr in ashes through raising SiO2 and reducing MCaO/MFe2O3 < 5/4 prior to combustion.

Osteogenic properties of manganese-doped mesoporous bioactive glass nanoparticles.

Mesoporous bioactive glass nanoparticles (MBGNs) based on the SiO2 -P2 O5 -CaO system have demonstrated promising properties for the local delivery of therapeutically active ions with the aim to improve their osteogenic properties. Manganese (Mn) has been identified as a candidate ion for local application in bone tissue engineering applications. It remains unknown how SiO2 -P2 O5 -CaO-based MBGNs influence human bone marrow-derived mesenchymal stromal cells (BMSCs) in terms of viability, proliferation, and differentiation and how these features can be modified by the addition of Mn to the MBGNs' composition. Therefore, in this study, MBGNs (composition in mol%: 50 SiO2 , 40 CaO, 10 P2 O5 ) and its Mn-doped derivate 5Mn-MBGNs (composition in mol%: 50 SiO2 , 35 CaO, 10 P2 O5 , 5 MnO) were applied to a culture of BMSCs in two different concentrations. With increasing concentration, 5Mn-MBGNs supported osteogenic differentiation and enhanced the upregulation of genes encoding for extracellular matrix proteins but also negatively influenced cell viability and proliferation. When applied in lower concentrations, MBGNs showed not only viability- and growth-enhancing effects but also significant pro-osteogenic features-however, these positive properties deteriorated with increasing concentration. Two major conclusions can be drawn from this study: (a) supplementation with Mn enhances the osteogenic properties of MBGNs in a dose-dependent manner and (b) MBGNs constitute an attractive vector for therapeutically active ions since it exhibits an intrinsic pro-osteogenic potential that can be improved and/or modified by incorporation of therapeutically active ions. Future studies should focus on the evaluation of further candidate ions that are known to influence osteogenic differentiation positively.

Structure Sensitive Properties of System B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;- CaO Melts

Boron oxide-based systems on structure and properties are similar to silicate systems, but they are more fusible and so are widely used in modelling various metallurgical processes. This paper presents the results of viscosity, electrical conductivity, surface tension and density measurements of the B2O3–CaO system with a content of 25–45% CaO in the temperature range above the liquidus temperature. To measure viscosity, vibration viscometry was used. Electrical conductivity was measured via the contact method using an alternating current bridge. Surface tension and density were measured using the lying drop method. The obtained results were used to describe the structure of borate melts.

Mechanism and Kinetics of the Carbothermic Reduction of Metals in the FeS–Ni3S2–CaO System

The reduction of metals by carbon and carbon monoxide in the FeS–Ni3S2–CaO system on continuous heating to 1250°C is studied using thermogravimetric and differential thermal analyses combined with mass spectrometry of gases. The formation of the oxysulfides CaFeSO and Ca3Fe4S3O6 along with sulfide phases is revealed in the FeS–CaO and FeS–Ni3S2–CaO systems on heating in an inert atmosphere. The chemism of the carbothermic reduction of sulfides FeS, Ni3S2, and Fe4.5Ni4.5S8 in a mixture with calcium oxide is determined. The reduction products are shown to be calcium sulfide and metals, and an additive of calcium oxide inhibits the evolution of sulfur-containing gases. The reduction of nickel sulfide by carbon and carbon monoxide is activated if iron sulfide is introduced into a reaction mixture along with calcium oxide. Iron sulfide favors the formation of intermediate iron–calcium oxysulfides with enhanced reactivity. In the temperature range from 750 to 1170°C, the experimental data on the carbothermic reduction of metals in the FeS‒Ni3S2–CaO system are described by a one-step Avrami–Erofeev model, in which the process is determined by the step of nuclei formation and growth. The kinetic parameters of the process are found to be E = 520 kJ/mol, log A = 18.2 s–1, and n = 0.87 (E is the activation energy, A is the preexponential factor, and n is the reaction order). The data obtained are useful for the development of technologies for the direct isolation of valuable metals from sulfide raw materials.

Fixation of borate-anions in lamellar AFm-phases in the system CaO–Al2O3–B2O3–H2O at 20 ​°C, 40 ​°C and 50 ​°C

Synthesis of boron containing lamellar calcium aluminum hydroxy salts were performed at different relative humidities and the behaviour and properties of the lamellar phases were investigated. The following AFm compound could be synthesized in pure form and their properties were determined:AFm-phase: 3CaOAl2O3CaHBO3.nH2O.With excess boron an Ettringite-compound AFt with the following composition is coexisting in the investigated system:Ettringite-phase: 3CaOAl2O32Ca[B(OH)4]2Ca(OH)2·30H2O.The incorporation of boron in the interlayer of LDH-phases under the influence of OH-ions at different temperatures were investigated. Carbonate was excluded by using a glove box to get definite lattice parameters. Different boron containing AFm-phases, using pure phase compositions in the system OH-lamellar AFm phase and the boron containing AFm phase, were synthesized. The solid solution between the so called compounds Monoborate and Monohydroxide at different temperatures and different relative humidities, with careful control of the different water contents of the lamellar phases, was investigated. Boron contents in solution and the uptake in the interlayer of the AFm-phases was studied [13]. The uptake of boron from pure solutions and the newly formed relevant phases with AFm structure and at higher boron contents of the ettringite structure were determined.

Preparation and Characterization of Akermanite/Merwinite Scaffolds for Bone Tissue Repair

The ceramics in the system CaO–MgO–SiO2 has recently attracted a great deal of attention because they display a good in vitro bioactivity and have potential use as bone implants. Biphasic calcium-magnesium-silicate ceramics were prepared by a sol-gel method. The dried gel with chemical composition 3CaO.MgO.2SiO2 was thermally treated at 1200 °C for 2 hrs. The structural behavior of the synthesized ceramics was examined by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Merwinite crystalline phase and akermanite phase were recognized. Then, porous akermanite/merwinite scaffolds were prepared to utilize polymer sponge method and evaluated by employing SEM. Furthermore, bone marrow stromal cells (BMSC) adhesion and proliferation on the scaffolds were evaluated by MTT assay test. Differentiation of the cells was assessed by measuring alkaline phosphatase (ALP) activity. The results demonstrated that BMSC adhered and spread well on akermanite scaffolds and proliferated with the increase in the culture time, and the differentiation rate of osteoblasts on scaffolds was comparable to that on blank culture plate control. Thus, the obtained results presented that the akermanite/merwinite scaffolds deserve attention for bone tissue engineering applications.

Calculation and analysis of temperatures and compositions eutectics binary and ternary sections of systems CаО—CoO—Al2О3 and ВаО—СоО—Al2О3

This study focuses on the calculation and analysis of temperatures and compositions of eutectics binary and ternary sections of CaO—CoO—Al2O3 and BaO—СoO—Al2O3 systems with the aim of possibility establishing of developing compositions of calcium­aluminate and barium­aluminate refractory cements with the use of spent aluminum­cobalt­molybdenum catalyst without additional processing. The temperatures and compositions of eutectic binary and ternary sections of the CaO—CoO—Al2O3 and BaO—CoO—Al2O3 systems were calculated. The temperatures and compositions of eutectics in binary sections of the systems were calculated using the Epstein—Howland formulas, and for three­component sections, by solving a system of nonlinear equations. The calculation results and characteristics of binary and ternary eutectic sections of the three­component systems CaO—CoO—Al2O3 and BaO—СoO—Al2O3 were presented. The graphic images of liquidus and solidus surfaces of the optimal regions were given. It was found that, composite materials based on these systems can be used to obtain binding materials with an operating temperature above 1250 C. The most suitable areas to get heat­resistant special purpose binders with increased operational temperature have been determined.

Application of phase equilibrium studies of CaO–SiO2–Al2O3–MgO system for oxide inclusions in Si-deoxidized steels

In the steelmaking process, the compositions of the oxide inclusions could be modified by refining slags to a large extent. The chemistries of the oxide inclusions and refining slags can be described by the system CaO–SiO2–Al2O3–MgO. Phase equilibria and liquidus temperatures in this system have been experimentally investigated in the composition and temperature ranges related to the oxide inclusions and refining slags by means of high-temperature equilibration, quenching and electron probe X-ray microanalysis. Isotherms in the interval of 20 °C between 1260 and 1560 °C were determined in the primary phase fields of wollastonite, anorthite, spinel, and melilite. Effects of the mass ratio of (Al2O3+SiO2)/((Al2O3+SiO2)+(CaO + SiO2)) and MgO content on the liquidus temperatures have been discussed to assist inclusion control. To obtain the lowest liquidus temperature of Al2O3–SiO2–CaO–MgO system inclusions, refining time ought to be properly controlled.

Phase equilibria in the system CaO–SiO2–Nb2O5–La2O3 at 1473 K with pO2=10−15.47 atm

Phase equilibria in the CaO–SiO2–La2O3–Nb2O5 system are important for the utilization of Nb and Rare Earth resources. In the present work, phase equilibria in the CaO–SiO2–La2O3–Nb2O5 system at 1473 K in H2 (pO2 = 10−15.47atm) were studied by the equilibrium experiment. SEM, EDS and XRD analysis were employed to identify the equilibrium phase relations. The isothermal spatial phase diagram of the CaO–SiO2–La2O3–Nb2O5 system and the isothermal section of CaO–SiO2–Nb2O5-(5%, 10%) La2O3 pseudo-ternary system were constructed. A total of eight equilibrium phase regions were determined, including Liquid + CaNb2O6+CaSiO3+LaNbO4 region, Liquid + CaNb2O6+SiO2+CaSiO3 region, Liquid + CaSiO3+CaNb2O6 region, Liquid + CaSiO3+SiO2 region, Liquid + CaNb2O6+SiO2 region, Liquid + CaSiO3 region, Liquid + SiO2 region and Liquid + CaNb2O6 region. Additionally, the influence of pO2 on equilibrium composition and temperature was also investigated considering its significant effect on phase equilibria in the slag system with variable valence elements. The results indicated that higher external pO2 can increase the equilibrium O content in a slag system, while higher equilibrium temperature corresponds to higher equilibrium pO2. Besides, the relationship between phase equilibria shown in the traditional slag system and in the related generalized alloy system was also revealed. The present experimental data can help further study on Nb-bearing and RE-bearing slag systems, and the theoretical conclusions will help the development of thermodynamic models.

Mineral–melt partition coefficients and the problem of multiple substitution mechanisms: insights from the rare earths in forsterite and protoenstatite

A trace element may substitute into a mineral by more than one substitution mechanism, complicating the thermodynamic description of its partition coefficients. In order to understand this phenomenon better, the mineral/melt partition coefficients for all 14 rare earth elements (REE) plus Y and Sc were measured experimentally for coexisting forsterite and protoenstatite in the system CaO–MgO–SiO2 ± Al2O3 ± TiO2 at 1406 °C and atmospheric pressure. For both phases, the results show these large trivalent cations (REE3+) replace Mg2+ on octahedral sites, but with charge-balance achieved by two different mechanisms: (1) cation vacancies (2 REE3+ + vacancy = 3 Mg2+); and (2) substitution of Al for Si (REE3+ + Al3+ = Mg2+ + Si4+). The overall REE partition coefficient is the sum of the partition coefficients for each substitution mechanism. Because the stoichiometric control is different for each mechanism, the relative importance of the mechanism varies with melt composition, including the activities of both silica and alumina in the melt ($${{a}}_{{{\text{SiO}}_{ 2} }}^{\text{melt}}$$ and $${{a}}_{{{\text{AlO}}_{ 1. 5} }}^{\text{melt}}$$). The coexistence of forsterite and protoenstatite fixes the silica activity, allowing the effect of $${{a}}_{{{\text{AlO}}_{ 1. 5} }}^{\text{melt}}$$ to be separated from that of $${{a}}_{{{\text{SiO}}_{ 2} }}^{\text{melt}}$$. The relative importance of the two mechanisms depends strongly on the identity of the REE for forsterite, but not for protoenstatite. The results are used to test the lattice strain model: the two substitution mechanisms in forsterite imply different values for the Young’s modulus in the Brice equation, despite the fact that the REE3+ cations likely occupy the same crystallographic site in both mechanisms, casting doubt on the physical basis of the lattice strain theory. Comparison with literature data confirms earlier observations that the activity coefficients of REE2O3 in silicate melts decrease with increasing SiO2 content of the melt, but the effect decreases with increasing atomic number, from La to Lu, and is almost negligible for Sc. The influence of melt composition should apply to the mineral/melt REE partition coefficients of all other minerals. Recognizing that observed mineral/melt partition coefficients are often the sums of contributions from multiple substitution mechanisms, each with its own dependence on both crystal composition and the stoichiometric control from the melt composition, will improve parameterizations of the mineral/melt partition coefficients of other rock-forming minerals. Partition coefficients for Na, Al, Ca, Ti, and Zr are also reported.