Ions In CaO Research Articles

Molecular dynamics analysis of the microstructural behavior of fluoride ions in CaO–SiO2-based and CaO–Al2O3-based slag systems

To further clarify the structural behaviour of F− in CaO–SiO2–CaF2–MgO and CaO–Al2O3–CaF2–MgO slags, the microstructure of F ions in slags with different CaF2 contents was resolved by molecular dynamics simulation. The results showed that no stable coordination structure was formed between Si and F, and no chemical bond could be formed; while Al and F and Ca and F could form relatively stable structures, both of which could be bonded. With the increase of CaF2 content, the average distance between Si–Si and Al–Al atom pairs increases, and CaF2 plays the role of network diluent. F− ions are mainly coordinated with Ca2+, and there is a dynamic equilibrium between Ca2+ and coordination anions (O2− and F−) in both systems, and the total coordination number is maintained between six and seven, which is distributed in the network structure in the form of Ca–F clusters. As F− replaces the position of O2− in the Ca–O structure, Ca2+ ions in the silicate slag system are not sufficient to balance the negative charge, and the charge balance can only be maintained by sharing the O2− at the top angle, leading to more interconnected silicate network structures, resulting in a shift in the oxygen type in the melt and the appearance of more highly polymerised Qn structural units. In aluminates, the electrically neutral [AlO3F]4− tetrahedral structure is formed as F replaces O atoms in [AlO4]5− tetrahedra, where the released O atoms are absorbed by other [AlO4]5− tetrahedra to form unstable highly coordinated Al. However, since the formed [AlO3F]4− tetrahedral structure is neutral, it can, together with Ca2+, balance the Al–O network structure with negative charges, making the system contain a large amount of Al–O–Al bridging oxygen structure and the effect of CaF2 in reducing viscosity is diminished.

Multi‐ion diffusion model and application to solid dissolution in CaO–Al2O3–SiO2 melts

AbstractA general multi‐ion diffusion model for liquid slag is developed for silicate melts by combining the tracer diffusivities of ions and chemical potentials from the CALculation of PHAse Diagrams thermodynamic database. For the demonstration of the model, the tracer diffusivities of Ca, Al, Si, and O ions in CaO–Al2O3–SiO2 melts were optimized as functions of temperature and composition using available isotope experimental data. The present model successfully simulates liquid‐junction diffusion in the CaO–Al2O3–SiO2 system and the dissolution of solid SiO2 and Al2O3 particles in CaO–Al2O3–SiO2 melts. Furthermore, the model can be readily expanded to multicomponent systems, making it potentially applicable to refractory dissolution in liquid slag and various other diffusion‐controlled high temperature processes involving liquid oxide melts.

Electroreduction mechanism and electrodeposition of ferric ions in CaO–SiO2–Al2O3–Fe2O3 slags at 1773 K

ABSTRACT The reduction mechanism for electrodeposition of ferric ions (Fe3+) in molten oxide slags and the influence of different conditions on electrolysis of molten Fe2O3-containing CaO–Al2O3–SiO2 slags under constant current were investigated. Cyclic and square wave voltammetric analyses showed that the electrochemical reduction of Fe3+ in the molten slags involved reduction to Fe2+ and then Fe2+ reduction to Fe. When constant-current electrolysis was performed between a molybdenum cathode and a graphite anode, an iron-rich metallic phase formed at the cathode. Both the current efficiency and electrolysis rate increased with electrolysis current at a constant temperature. The current efficiency and electrolysis rate of high-calcium slag were higher than those of high-silicon slag.

Effect of Na Ions on Melt Structure and Viscosity of CaO–SiO<sub>2</sub>–Na<sub>2</sub>O by Molecular Dynamics Simulations

Molecular dynamics (MD) simulations have been used to study the effect of Na ions on the structure properties of CaO–SiO2–Na2O melts. The short-range structure and medium-range structure of CaO–SiO2–Na2O in this study are consistent with existing data. The replacement of Ca2+ with Na+ in CaO–SiO2–Na2O melts has almost no effect on the degree of polymerization and distribution of bond angles of Si–O tetrahedron. From micro perspective, Na ions enhance the mobility of CaO–SiO2–Na2O melts by multiple ways. Firstly, the modification effect of Na+ on the melt network structure is weaker than that of Ca2+, the Si–O tetrahedron around Na+ is sparser than Ca2+, which is more conducive to ions movement. Secondly, the diffusion capacity of Na+ is much greater than other ions in CaO–SiO2–Na2O system, which the overall diffusion capacity of the system can be improved by adding more Na+. Thirdly, since Na+ has only one charge, there is no electrostatic restraint on the depolymerized tetrahedron which happened in multivalent charges such as Ca2+, so that the mobility of CaO–SiO2–Na2O is stronger than that of CaO–SiO2. The micro changes provide an explanation for the improvement of macro liquidity.

Luminescent properties and energy transfer of CaO:Ce3+, Mn2+ phosphors for white LED

We have synthesized yellow–orange CaO:Ce3+,Mn2+ phosphors by solid-state reaction. Photoluminescence properties and energy transfer mechanism from Ce3+ to Mn2+ ions have been investigated. The Ce3+ activated phosphors exhibit strong absorption in the range of 250–490nm and a yellow emission centered at 554nm. When Mn2+ ions were codoped, CaO:Ce3+,Mn2+ phosphors exhibit yellow emission band of Ce3+ as well as orange emission band centered at 600nm of Mn2+. We observed an efficient energy transfer from Ce3+ to Mn2+ ions in CaO:Ce3+,Mn2+, which was verified from the lifetime decay curves and was discussed by Dexter׳s energy transfer theory. The critical distance of the energy transfer from Ce3+ to Mn2+ ions has also been calculated to be 12.3Å by spectral overlap methods following Dexter׳s theory and by concentration quenching mechanism to be 15.2Å. Moreover, by combining the synthesized phosphors and InGaN blue chip (460nm), warm-white light has been created.

Activating Nonreducible Oxides via Doping.

Nonreducible oxides are characterized by large band gaps and are therefore unable to exchange electrons or to form bonds with surface species, explaining their chemical inertness. The insertion of aliovalent dopants alters this situation, as new electronic states become available in the gap that may be involved in charge-transfer processes. Consequently, the adsorption and reactivity pattern of doped oxides changes with respect to their nondoped counterparts. This Account describes scanning tunneling microscopy (STM) and photoelectron spectroscopy (XPS) experiments that demonstrate the impact of dopants on the physical and chemical properties of well-defined crystalline oxide films. For this purpose, MgO and CaO as archetypical rocksalt oxides have been loaded either with high-valence (Mo, Cr) or low-valence dopants (Li). While the former generate filled states in the oxide band gap and serve as electron donors, the latter produce valence-band holes and give rise to an acceptor response. The dopant-related electronic states and their polarization effect on the surrounding host material are explored with XPS and STM spectroscopy on nonlocal and local scales. Moreover, charge-compensating defects were found to develop in the oxide lattice, such as Ca and O vacancies in Mo- and Li-doped CaO films, respectively. These native defects are able to trap the excess charges of the impurities and therefore diminish the desired doping effect. If noncompensated dopants reside in the host lattice, electron exchange with surface species is observed. Mo ions in CaO, for example, were found to donate electrons to surface Au atoms. The anionic Au strongly binds to the CaO surface and nucleates in the form of monolayer islands, in contrast to the 3D growth prevailing on pristine oxides. Charge transfer is also revealed for surface O2 that traps one Mo electron by forming a superoxo-species. The activated oxygen is characterized by a reinforced binding to the surface, an elongated O-O bond length, and a reduced barrier for dissociation, and represents an important intermediate for oxidation reactions. The charge-transfer processes described here are quenched if Li is inserted into the oxide lattice, neutralizing the effect of the extra electrons. The specific behavior of doped oxides has been explored on a mechanistic level, i.e. on thin-film model systems at ultrahigh vacuum and low temperature. We believe, however, that our results are transferrable to realistic conditions and doping might thus develop into a powerful method to improve the performance of nonreducible oxides in surface-catalyzed reactions.

Model for diffusion coefficient estimation of calcium ions in CaO–Al2O3–SiO2 slags

As a common component in metallurgical slag, CaO plays an important role in desulphurisation, dephosphorisation and absorption of non-metallic inclusions. In order to better understand the mechanism of the slag/metal reactions, the diffusion dynamics of calcium ions in CaO–Al2O3–SiO2 slags were studied. It was found that there was almost a linear relation between the logarithms of pre-exponential factor and diffusion activation energy. By combining the relation between the diffusion activation energy and the optical basicity corrected in the CaO–Al2O3–SiO2 slags, a simple model used to estimate the diffusion coefficient of calcium ion is proposed. The estimated values of the CaO–SiO2 and CaO–Al2O3–SiO2 systems agree well with the experiment data, with a mean deviation of 35·3 and 22·5% respectively.

Characterization and photoluminescence properties of some CaO, SrO and CaSrO2 phosphors co-doped with Eu3+ and alkali metal ions

CaO:Eu3+, M+ (Li+ or Na+ or K+), SrO:Eu3+and CaSrO2:Eu3+ powders were prepared by combustion synthesis method and the samples were further heated to ∼1000°C to improve the crystallinity of the materials. The structure and morphology of materials were examined by X-ray diffraction and scanning electron microscopy. The morphology of CaO:Eu3+ and co-doped with alkali metal ions powders was very similar. Small and coagulated particles of nearly cubical shapes with small size distribution having smooth and regular surface were formed. The surface morphology of SrO and CaSrO2 materials was not smooth and coagulated particles of irregular shapes with different sizes were observed. The characteristic emissions of Eu3+ had strong emission at 614 and 620nm for 5D0→7F2 with other weak transitions observed at 580, 592, 654, 705nm for 5D0→7Fn transitions where n=0, 1, 3, 4 respectively in all host lattices. Photoluminescence intensity followed the order as in CaO>CaSrO2>SrO lattices. A remarkable increase of photoluminescence intensity was observed by the co-doping of alkali metal ions particularly K+ ions in CaO:Eu3+.

Electron spin resonance of diluted solid solutions of MnO2 in Y2O3

Abstract Electron spin resonance spectra of Mn 2+ in diluted solid solutions of MnO 2 in Y 2 O 3 have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn 2+ ions in sites with two different symmetries were observed, as well as Mn 2+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn 2+ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C 2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn 2+ ions of 0.53 nm, of the same order as that of Mn 2+ ions in CaO.

Ionic properties of oxygen in slag

As an attempt to determine the fundamental properties of slags, and atomic structures the fractions of oxygen ions in CaO–SiO 2 and CaO–AlO 1.5 were measured. Samples of CaO–42.6 mol% SiO 2∼ CaO–64.8 mol% SiO 2 and CaO–28.7 mol% Al 2 O 3∼ CaO–44.7 mol% Al 2 O 3 were equilibrated at 1873 K and then quenched. The amount of oxygen ions of the samples was estimated by measuring areas of the Gaussian functions fitted to the binding energy of electrons in 1s-shell of oxygen using X-ray photoelectron spectroscopy (XPS) of these as prepared samples. The viscosity, sulfide capacities, and water solubility reported by others were analyzed with the experimental results and the ratio of activity coefficients was formulated as a function of composition.

Calculations of off-centre displacements of divalent substitutional ions in CaO, SrO and BaO from model potentials

Abstract The problems of representing the polarizability of oxygen in potential models for oxides are discussed. Simple shell-model interionic potentials for MgO, CaO, SrO, BaO, MnO, FeO, CoO and NiO are proposed and the parameter fitted to the dielectric constants and lattice spacings. The oxygen polarizability and interactions are taken to be the same in all cases. Model predictions of cohesive energies, elastic constants and phonon dispersion are tested against experiment and found to be reasonably satisfactory for such an oversimplified model. Defect energies are calculated for Mg2+, Mn2+, Fe2+, Co2+ and Ni2+ substitutional impurities in CaO, SrO and BaO host crystals. Off-centre minima displaced in 〈111〉 directions are found in all cases in SrO and BaO, although SrO: Mn2+ is marginal: in CaO all the impurities studied remain on-centre. For systems which have been investigated experimentally these predictions show good agreement.

Charge-transfer satellites in the x-ray photoelectron spectra of 3d° and 4d° metal oxides

O(2p)-metal (d) charge-transfer satellites in core level spectra of 3d° metal ions in CaO, Sc2O3, TiO2 and V2O5 and 4d° ions in SrO, Y2O3, ZrO2 and Nb2O5 have been reported. A systematic increase in the satellite separation is noticed going from CaO to V2O5 and from SrO to Nb2O5.

The Cr2+:CaO Jahn-Teller system

Acoustic paramagnetic resonance from Cr2+ ions in CaO has been observed at frequencies close to 9 GHz and detailed results have been obtained with the magnetic field H directed along the (111) direction. With this direction for H, the peaks in the APR spectrum are expected to arise from those Cr2+ ions occupying zero-strain sites as the Hamiltonian displays C3i symmetry. An analysis of the data obtained is given and it is shown that the results can be fitted to a multimode Jahn-Teller model. Values for the basic crystal-field parameters and an energy-level diagram for zero-strain sites are obtained.

Energy of the First Excited Electronic Level (s) ofFe2+in CaO

The electron-spin recovery time $\ensuremath{\tau}$ has been observed for low concentrations of ${\mathrm{Fe}}^{2+}$ ions in CaO in fields of about 1800 G from 1.3 to 4.1 K; line broadening at 8.9 GHz has been measured from 7 to 15 K. The temperature dependence of $\ensuremath{\tau}$ and the linewidth give the energy of the first excited state (s) to be 23.9 \ifmmode\pm\else\textpm\fi{} 1.5 ${\mathrm{cm}}^{\ensuremath{-}1}$, indicating strong orbital reduction, probably due to dynamic Jahn-Teller distortions. The observed bottleneck generated at 9, 18, and 700 GHz by pulse saturation at 9 GHz is consistent with earlier observation of intrinsic spin-lattice relaxation of ${\mathrm{Fe}}^{2+}$ at similar concentrations in MgO.

EPR Studies of Impurities in Electron‐Irradiated CaO

AbstractThe EPR spectrum of Mn4+ ions in CaO has been observed in single crystals containing Li+ or Na+ ions. Electron irradiation of such crystals results in Mn4+ being converted to Mn2+, a concomitant reaction being the formation of [Li]° and [Na]° trapped hole centres. Several other paramagnetic species are produced by the irradiation including atomic hydrogen, [Li]− and [Li+H]+ centres. The spin Hamiltonian parameters which describe the EPR spectra of these impurity centres are reported and discussed. Optical or thermal bleaching of the [Li]° or [Na]° centres above 77 K results in the annihilation of Mn2+ and [Li2+H]+ centres: atomic hydrogen and the [Li] centres are less readily bleached by these treatments.

2S [formula omitted] -states of Pb 3+-ions in CaO and ZnO

EPR-spectra of Pb 3+-ions in CaO and ZnO are studied at 1.6 K. The g-values and the reduction of the hyperfine interaction constants A are correlated with the partial electron transfer to the ligands.

Jahn-teller effects in the electron spin resonance spectra of ions with spin 1

A study is made of the effects of the dynamic Jahn-Teller effect on the electron spin resonance ofS′=1 ion in a cubic lattice. The idea that the ion and its near neighbours form a molecule which is almost decapled from the rest of the lattice is not used and the ion is coupled directly to all the lattice modes. The resulting many-body problem is treated using Green function methods, the emphasis being placed on deriving an expression for the intensity of the spin resonance line. It is found that the spectrum consists of two overlapping lines, in agreement with some of the experimental results available for .S′=1 ions in CaO and MgO.

Co-Ordination state of aluminium ions in CaO–Al2O3–SiO2 glasses

Co-Ordination state of aluminium ions in CaO–Al2O3–SiO2 glasses