Spinel Solid Solution Research Articles

Synthesis, magnetic and structural properties of (1-x)LiFe5O8–(x)LiZn2.5Ti2.5O8 spinel solid solutions

Compounds with the spinel structure present a technologically important class of materials. Spinels show a great variety of magnetic and magnetoelectric phenomena owing to the facile entrance of transition metals in the cationic sublattices. One of such examples is lithium ferrite LiFe5O8 with high ferrimagnetic phase transition temperature and cationic order-disorder transformations. The latter are important as they influence the crystal symmetry, which is crucial for physical properties. In this work we synthesize a series of (1-x)LiFe5O8–(x)LiZn2.5Ti2.5O8 (0≤x≤1) solid solutions and characterize them with various experimental and theoretical methods. The solid solutions experience a series of concentrational phase transformations between atomically ordered (P43(1)32) and disordered (Fd3¯m) phases. The variation with concetration x of Fe3+ occupancies in cationic sublattices is studied using Mössbauer spectroscopy. The Mössbauer and magnetic measurements reveal sharp suppression of magnetic properties at x≥0.5 when the number of Fe3+ ions in the A-sublattice vanishes. The magnetic behaviour in the studied series of solid solutions is confirmed by Monte Carlo calculations with magnetic exchange interactions determined using the density functional theory.

Modulation of solid solution in MgxMn1−xAl2xFe2(1−x)O4 spinel ceramics for multifunctional devices

AbstractSolid solution modulation is an ideal method for combining the advantages of different parent compounds while mitigating their disadvantages. Here, we investigated the thermal sensitivity, magnetic properties, and microwave absorption of MgxMn1−xAl2xFe2(1−x)O4 (0.2 ≤ x ≤ 0.8) spinel solid solution ceramics for application in multifunctional devices. The electrical transport and magnetic properties can be modulated by adjusting the solution ratio. The ceramics exhibit negative temperature coefficient characteristic. The B‐values from 5065–8056 K, suggesting accurate temperature measurements over a wide temperature range. As a type of soft magnetic material, it has a narrow hysteresis loop and high resistivity. Vector network analyzer studies indicate Mg0.2Mn0.8Al0.4Fe1.6O4 could be a candidate for microwave absorption in S‐band. This study successfully extends the applicability of MgxMn1−xAl2xFe2(1−x)O4 ceramics for high‐temperature thermistors and also confirms potential for multifunctional device.

Phase equilibria of SiO2–Al2O3–Fe3O4-5 wt.% CaO system at 1400 °C in air relevant to the production of continuous basalt fibers: Emphasis on spinel solid solution phase

A long-term foundational study aimed at developing a thermodynamic database for continuous basalt fiber systems is in progress. In this work, the equilibrium phase relations of the SiO2–Al2O3–Fe3O4-5 wt.% CaO system at 1400 °C in air atmosphere were determined experimentally using the equilibrium-quenching technique. Subsequent analyses were conducted using Electron Probe Micro-Analysis (EPMA), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) to validate the experimental results and further investigate the microstructural characteristics. The results revealed a single liquid region and three distinct two-phase regions as Liquid-Cristobalite, Liquid-Mullite solid solution, and Liquid-Spinel solid solution. Additionally, two three-phase regions were identified as liquid-cristobalite-mullite solid solution, and liquid-mullite solid solution-spinel solid solution. This work contributes to a deeper understanding of the phase behavior during the melting of basalt ore systems, which is crucial for optimizing their production and enhancing their applications.

Unlocking Cr3+-Cr3+ Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability.

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) hold promising potential as next-generation compact, portable, and intelligent NIR light sources. Nonetheless, the lack of high-performance broadband NIR phosphors with an emission peak beyond 900 nm has severely hindered the development and widespread application of NIR pc-LEDs. This study presents a strategy for precise control of energy-state coupling in spinel solid solutions composed of MgxZn1-xGa2O4 to tune the NIR emissions of Cr3+ activators. By combining crystal field engineering and heavy doping, the Cr3+-Cr3+ ion pair emission from the 4T2 state is unlocked, giving rise to unusual broadband NIR emission spanning 650 and 1400 nm with an emission maximum of 913 nm and a full width at half-maximum (fwhm) of 213 nm. Under an optimal Mg/Zn ratio of 4:1, the sample achieves record-breaking performance, including high internal and external quantum efficiency (IQE = 83.9% and EQE = 35.7%) and excellent thermal stability (I423K/I298K = 75.8%). Encapsulating the as-obtained phosphors into prototype pc-LEDs yields an overwhelming NIR output power of 124.2 mW at a driving current of 840 mA and a photoelectric conversion efficiency (PCE) of 10.5% at 30 mA, rendering high performance in NIR imaging applications.

Study on High‐Temperature Reactions of MgO Refractory with Ti‐Bearing Al‐Killed Steel

To understand the interaction behaviors between MgO refractory and Ti‐bearing Al‐killed steel grades, laboratory experiments are conducted at different times using different steel grades containing different Ti contents (w[Ti] = 0–0.2%). The results show that when MgO refractory reacts with Ti‐free Al‐killed steel, an MgO–Al2O3 spinel‐reacted layer can be detected at the steel‐refractory boundary. In the case of Ti‐bearing Al‐killed steel, an MgO–Al2O3–TiOx system‐reacted layer is formed at the edge of MgO refractory, and the thickness of the layer and the TiOx content in the layer increase with the increase of reaction time and the dissolved Ti content in steel. Thermodynamic calculations indicate that the MgO–Al2O3–TiOx system layer is a spinel solid solution, and is the stable phase in Ti‐bearing Al‐killed steel. In addition, the melting point of the reacted layer declines with the increase of TiOx. Therefore, the corrosion of MgO refractory by Ti‐bearing steel grades is more serious than that by conventional steel grades, and it also leads to the formation of MgO–Al2O3–TiOx system macroinclusions in steel.

Influence of kaolin and red clay on ceramic specimen properties when galvanic sludge is incorporated to encapsulate heavy metals

This study presented the influence of two types of clay: kaolin (Kao) and red clay (RC) on the chemical and physical properties of ceramic specimens when galvanic sludge (GS) is incorporated to encapsulate heavy metals. Samples were obtained of GS from the industrial district of Manaus – Amazonas State, Brazil, and kaolin (Kao), and red clay (RC) from the Central Amazon. A fourth sample was prepared by mixing GS, Kao, and RC in the ratio 1:1:8 (GS + Kao + RC). This mixture was ground, and ceramic specimens were prepared, and heat treated at 950 °C and 1200 °C for three hours for phase detection, compressive strength, leaching of Fe, Ni and Cr metals and life cycle assessment. Galvanic sludge, Kao, and RC were also, and heat treated to at 950 °C and 1200 °C for three hours, obtaining GS950, GS1200, Kao950, Kao1200, RC950, and RC1200. The samples were submitted to XRF, XRD, Rietveld refinement, Mössbauer spectroscopy, TG/DTG/DSC, and SEM. The results show that the formation of nickel oxide and a spinel solid solution of the type Fe3+{Fe1-y3+,Fe1-x2+,Nix2+,Cry3+}O4 (in which [] = tetrahedral site, {} octahedral site) occurs in GS1200, which is caused by sulfate decomposition to SO2. At 1200 °C, heavy metals are encapsulated, forming other phases such as nickel silicate and hematite. Life cycle assessment was used to verify the sustainability and value of GS in clay for making bricks, and it indicated that the production of ceramics is feasible, reduces the use of clays, and is sustainable.

High‐Throughput Study of the Phase Constitution of the Thin Film System Mg–Mn–Al–O

The increasing importance of recycling makes the recovery of valuable elements from slags interesting. The concept of engineered artificial minerals aims at the formation of phase(s) with a high content of the to‐be‐recovered element(s) from slags of pyrometallurgical recycling processes. For this, understanding the phase constitution of the slag systems, such as the spinel‐forming subsystem Mg–Mn–Al–O from Li‐ion battery recycling, is of great importance. Herein, the phase constitution is investigated using a thin film materials library (ML) that covers the composition space (Mg14−69Mn11−38Al14−74)Ox. High‐throughput energy‐dispersive X‐ray spectroscopy and X‐ray diffraction confirm the formation of the spinel solid solution phase for a wide composition space. The Mn oxidation state is shown to be a mixture of Mn2+ and Mn3+ by analyzing Mn 2p3/2 spectra from X‐ray photoelectron spectroscopy. For one measurement area of the ML containing equal atomic amounts of Mg, Mn, and Al, transmission electron microscopy shows columnar spinel grains with Mg, Mn, and Al evenly distributed. Based on these results, it is suggested that the high likelihood of spinel formation in slags can be influenced by controlling the Mn oxidation state to allow the formation of desirable engineered artificial minerals for Li recovery.

Monitoring Structural Changes during Electrochemical Cycling of Solid-Solution Spinel Oxide MgCrVO4.

Rechargeable magnesium-ion batteries (MIBs) hold significant promise as an alternative to conventional lithium-ion technology driven by their natural abundance and low-cost, high-energy density, and safety features. Spinel oxides, including MgCrVO4, have emerged as a prospective cathode material for MIBs due to their promising combination of capacity, operating potential, and cation mobility. However, the structural evolution, phase stability, and processes of Mg mobility in MgCrVO4 during electrochemical cycling are poorly understood. In this study, we synthesized a single-phase, solid solution of spinel oxide MgCrVO4 and employed operando X-ray diffraction to couple physical properties with structural changes during cycling. Our results revealed a two-phase reaction mechanism coupled with a solid-solution-like reaction, highlighting the complicated transformation between two distinct phases in the MgCrVO4 lattice during Mg (de)intercalation. Rietveld refinement of the operando data provided valuable insights into the mechanism of the Cr/V-based spinel oxide, shedding light on the transition between the two phases and their roles in Mg-ion (de)intercalation. This study contributes to a deeper understanding of the structural dynamics in multivalent cathode materials and sets the stage for the development of advanced Mg-ion cathodes with enhanced performance and stability.

Enhanced energy transfer and near-infrared luminescence by crystal field regulation in Zn3Ga2GeO8:Cr3+,Yb3.

Near-infrared (NIR)-emitting phosphors with broadband absorption from ultraviolet to visible light have been considered significant spectral converter materials for solar cells. In this work, NIR phosphor Zn3Ga2GeO8 (ZGGO):Cr3+,Yb3+ spinel solid solutions were synthesized using the classical high-temperature solid-state method. With an increase in the doping concentration of Cr3+ ions in ZGGO:Cr3+,Yb3+, a more distorted octahedron appeared around Cr3+ ions, which increased crystal field splitting. This process was accompanied with a broadening of NIR emission from Cr3+ 4T2 → 4A2 transition and enlarged the overlap area between the absorption spectrum of Yb3+ and the emission spectrum of Cr3+, resulting in an efficient energy transfer between Cr3+ and Yb3+. In the case of high-concentration Cr3+ doping, the near-infrared luminescence intensity of Yb3+ was more than 8 times that of low-concentration doped Cr3+. Therefore, it is proposed that the Cr3+,Yb3+ co-doped ZGGO phosphor is a potential spectral convert materials for silicon-based solar cells and thereby improves photovoltaic conversion efficiency.

Boosting broadband short-wave infrared emission to achieve near-unity quantum efficiency via bridging Cr3+-Ni2+ in spinel solid-solutions towards light-emitting diode applications.

Recently, short-wave infrared (SWIR) phosphor-converted light-emitting diodes (pc-LEDs) have garnered increased attention due to their widespread applications in night vision, biological imaging, and non-destructive testing. Nevertheless, the currently used SWIR phosphors suffer from poor thermal stability and low quantum efficiency. In this study, a finely tuned spinel-based solid solution, Mg0.5Zn0.5Ga2O4, is prepared to host Ni2+ to induce SWIR emission. Cr3+ is codoped as a sensitizer to bridge Cr3+ and Ni2+ ions, significantly enhancing blue light absorption and facilitating energy transfer (ET) to Ni2+ ions. The champion SWIR phosphor exhibits a broadband emission centered at 1304 nm with a full width at half maximum (FWHM) of 250 nm, achieving a near-unity internal quantum efficiency (IQE = 97.7%) and a good thermal stability (70.7%@423 K). The fabricated SWIR pc-LED device delivers a high SWIR output power of 39.9 mW at 360 mA, enabling its application in non-destructive imaging and testing.

Cu-Al spinel oxide as a sustained release catalyst for methanol steam reforming: Enhancing the catalytic performance via surface reconstruction

Cu-Al spinel oxide as a sustained release catalyst gradually releases active metal Cu during the methanol steam reforming reaction, whose catalytic behavior depends strongly on the surface structure of the catalyst. In this context, Cu-Al spinel solid solution is synthesized by a solid phase ball milling method, followed by treating with acidic and basic solutions in order to modulate the surface composition and structure, thereby to further improve the catalytic performance. Nitric acid is effective for the removal of both surface dispersed Cu and Al oxide species, whereas sodium hydroxide is only effective for the removal of Al oxide species, and ammonium hydroxide shows the weakest effect, removing a very small amount of Cu and Al species. Accompanying with the loss of Cu and Al species, the catalyst surface undergoes structural reconstruction, showing a redistribution of Cu species. Consequently, the copper releasing behavior varies drastically. The catalytic testing results show that the nitric acid and ammonium hydroxide treated catalysts present improved activity, where in the former also shows better stability. Sodium hydroxide treatment has a negative effect on the sustained releasing catalytic performance. In combination with the characterization results of the tested catalysts, it is found that both the copper particle dimension and the microstructure strain of sustained released copper play important roles in the catalytic performance. The findings of this report provide a practical method for the improvement of the sustained releasing catalysis.

Synthesis, Electrochemical Properties and Crystal and Electronic Structure Changes in Charge/Discharge Process of Spinel Type Cathode-Materials Mg1.33-Y(V1.67-x+yMnx)O4 for Magnesium Secondary Batteries

Attention has therefore focused on rechargeable batteries using multivalent cations, which are expected to offer even higher energy densities than lithium ion batteries. One topic that has attracted attention is rechargeable batteries using Mg as a carrier. The advantage of using Mg is that it has a low electrode potential with a high capacity.Although previous research into Mg rechargeable battery cathode materials started with a report by Aurbach1) et al., and included chevrel compounds, these have had problems in terms of battery voltage and cycle properties. In spinel-type Mg1+yCo2-x-yMnxO4, charge and discharge capacities were reported to increase by substituting Mn2). V is thought to have high reversibility due to having a broad mixed atomic valence. The authors synthesized Mg1.33V1.57Ni0.1O4, and reported that the discharge capacity after 14 cycles was 160 mAh/g and the capacity retention rate was high3). Furthermore, the authors investigated the spinel solid solution αMgCo1.5Mn0.5O4-(1-α)Mg(Mg0.33V1.57Ni0.1)O4 as a new cathode material and evaluated its battery properties, and as a result found that the initial discharge capacity at α = 0.3 was 180 mAh/g with the discharge capacity maintained after 60 cycles4 ). However, the substitution products need to be investigated in order to improve the discharge potential of the Mg-V system and enhance the cycle properties.The present study investigated the synthesis of a new spinel type cathode material Mg1.33-y(V1.67-x+yMnx)O4 by substituting Mn into Mg1.33V1.67O4 and different Mg content in order to increase the charge-discharge capacity and improve the cycle properties. The crystal and electronic structures and charge-discharge properties depending on the amount of Mn substitution and Mg content, and the structural changes accompanying charging and discharging.Mg1.33-y(V1.67-x+yMnx)O4 was synthesized by a solid -phase method under high vacuum atmosphere. The product was assigned to the spinel structure with space group Fd-3m from the powder X-ray diffraction. Synthesized materials of uniform composition were confirmed from elemental mapping by STEM-EDS. Charge and discharge cycle tests showed that the deliverable discharge capacity depends on the cycle number, Mn composition, and working temperature. The charge and discharge cycle tests showed the discharge capacity increased with repeated cycles. Mg1.33V1.57Mn0.1O4 showed the largest discharge capacity of 256 mAh/g at 13th cycles while the initial capacity was only 73 mAh/g at 90°C. The local structure was analyzed based on EXAFS spectra at the V K-edge for the pristine and electrode materials, and the results suggested that Mg1.33V1.57Mn0.1O4 had the smallest lattice distortion due to Mn at 16d sites, and XAFS spectra at the V K-edge indicated the significant change in the oxidation state of V during the charge/discharge cycles. The particularly stable crystal structure and large contribution of charge compensation by V may jointly contribute to the superior charge-discharge property of Mg1.33V1.57Mn0.1O4 5).Moreover, we investigated the different Mg, Mn content sample. Mg1.25(V1.55Mn0.2)O4 showed an increase in capacity from the first discharge capacity 71mAh/g to 199mAh/g after 34 cycles at 90℃ (Fig.1). The change in crystal structure due to charging and discharging was investigated. Focusing on the magnitude of M(16d)-O6 octahedral strain, the strain after 10th discharge is significantly reduced, so it is considered that the structure was stabilized by repeating the cycles and contributed to the improvement of the cycles characteristics. The electronic structure was analyzed by MEM, which showed that the electron density between the 16d-32e sites was higher and the covalent bond was higher than that of the diffusion sites after charge and discharge. From this, it is considered that the host structure was stabilized by charge and discharge, which contributed to the increase in charge and discharge capacity. From the result of XANES, it revealed that V is trivalent to tetravalent and Mn is divalent. Furthermore, from the results of EXAFS, it was clarified that the amount of reduction was larger in Mg1.25(V1.55Mn0.2)O4, especially in charge and discharge, because the amount of change in the distance between V and O was larger. Acknowledgements This work was supported by JST ALCA-SPRING Grant Number JPMJAC1301, Japan.We are deeply grateful for the cooperation of Dr. T. Honma and Dr. H. Ofuchi of JASRI for the XAFS analyses (SPring-8, BL14B2), Dr. K. Osaka of JASRI for the measurement of the synchrotron X-ray diffraction (SPring-8, BL19B2). References 1) D. Aurbach, et al., Adv. Mater., 19, 4260 (2007).2) Y. Idemoto, et al., J. Power Sources, 482, 228920 (2021).3) Y. Idemoto, et al., J. Power Sources, 455, 227962 (2020).4) Y. Idemoto, et al, Electrochemistry, 90(2), 027002(2022).5) Y. Idemoto, et al, J. Electroanal. Chem., 928, 1107064 (2023). Figure 1

Structural Characterization and Electrochemical Performance of Spinel Oxide Cathodes for High Voltage Mg-Ion Batteries

Non-aqueous Mg-ion batteries are a class of next generation batteries that promise high energy densities as an alternative to Li-ion batteries. Materials discovery and development is therefore required to fulfill this promise. MgCrMnO4 solid-solution oxide spinel with suitable redox voltages and facile Mg2+ mobility has been identified as a promising candidate for practical, high voltage cathodes in Mg-ion batteries. Here, we discuss the development of this solid-solution spinel oxide class as a cathode material, novel synthesis methods of these oxide spinels, as well as their electrochemical performance. Mg-Cr-Mn spinel oxides with varying Cr and Mn content were synthesized via conventional sol-gel methods, urea co-precipitation, and layered double hydroxide precursors. High-resolution synchrotron XRD and solid-state nuclear magnetic resonance (NMR) spectroscopy characterization along with electron microscopy indicated that different synthetic routes resulted in structural and morphological differences. This in turn lead to differences in electrochemical performance: overpotentials on charge or discharge, reversibility, and deliverable capacity. Electrochemical results in Mg-ion full cells indicate improved performance (lower overpotentials, higher reversibility, and increased capacity) for MgCrxMn2-xO4 cathodes synthesized via urea co-precipitation. To the best of our knowledge, full cells testing these Mg-Cr-Mn spinel oxide cathodes have not been previously reported.

Low-dose X-ray induced long afterglow NIR luminescence from Cr3+ doped Zn1–xCdxGa2O4 spinel solid solutions

The low-dose X-ray induced long afterglow near infrared (NIR) luminescence from Cr3+ doped Zn1–xCdxGa2O4 spinel solid solutions was investigated. The structure analysis shows the good formation of Zn1–xCdxGa2O4 spinel solid solutions, which possesses a cubic spinel structure with Fd3m space group. The formation of Zn1–xCdxGa2O4 spinel solid solutions induces the obvious increase of long afterglow near infrared luminescence excited by low-dose X-ray. When the content of doped Cd2+ reaches 0.1, the low-dose X-ray induced long afterglow NIR luminescence is the maximum. More importantly, only 5 s X-ray irradiation can induce more than 6 h NIR afterglow emission, of which the afterglow luminescent intensity is still 5 times stronger than the background intensity after 6 h. The thermoluminescent results show that under the 5 s exposure of X-ray, the trap density of Zn0.9Cd0.1Ga2O4:Cr3+ is much higher than that of ZnGa2O4:Cr3+. The replacement of Cd2+ ions with large radius at Zn2+ sites causes the increase of defects and dislocations, which results in the obvious increase of trap concentrations. And the addition of high-z number elements Cd2+ would enhance the X-ray absorption of the solid solutions, which thus can be easily excited by low-dose X-ray. Zn0.9Cd0.1Ga2O4:1%Cr3+ solid solution is a potential candidate of low-dose X-ray induced long afterglow luminescent materials.

Flash sintering improves the densification and mechanical properties of high entropy oxides used in anodic applications

High entropy oxides (HEOs) have multi-cation disordered chemical structure that makes it suitable as anode for battery applications. (Mg0.2Ti0.2Zn0.2Cu0.2Fe0.2)3O4 has spinel structure with outstanding electrochemical performance because of its configurational entropy stabilized structure. However, its cyclability is poor because of its pulverization during charging-discharging cycles. Its hardness can be improved with better densification but sintering at higher temperatures (∼1200 °C) results in disintegration into different phases (phase separation). With the help of flash sintering, higher densification could be achieved with phase purity of spinel solid solution. The hardness of flash sintered specimens was found to be higher than that of conventionally sintered specimens of equivalent density, suggesting a better neck formation with flash sintering. The role of current density was investigated on density and hardness since porosity and strength both are important for anode applications. The uniform distribution of particles is confirmed by EDS analysis and the underlying mechanism for the ultrafast densification of the Reaction sintered HEOs has been discussed.

Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags

The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu1+Fe3+O2) from a spinel solid solution (magnetite, Fe3O4) and understand why cuprospinel (CuFe2O4) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe2+6.89Cu2+0.86Co0.13Mg0.15Si0.02)8.05 (Fe3+15.52Al0.41Ti0.01Cr0.01)15.95O32, and (Cu1+0.993Co0.002Mg0.002)0.997(Fe3+0.957Al0.027Ti0.005Si0.004)0.993O2, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling.

Influence of composition on the emission properties of impurities in solids: Case study of Mg1-xZnxAl2O4:Cr3+ with the spinel structure

The importance of structural disorder of crystal lattice for the formation of the optical properties of impurity ions is studied by evaluating the optical properties of Cr3+ impurity ions in Mg1-xZnxAl2O4:Cr3+ (x = 0; 0.25; 0.50; 0.75; 1.0) spinel solid solutions. It is demonstrated that the gradual replacement of Zn by Mg, which transforms the normal spinel ZnAl2O4 into the inverse spinel MgAl2O4, leads to an enhancement of the Cr3+ red emission. In addition, the Cr3+ decay rate (inverse to the emitting excited state lifetime) increases linearly when Zn is gradually replaced by Mg. These observations are explained by the lifting of the parity selection rule due to the random distribution of the Zn and Mg cations in the second coordination sphere around the emitting ion, which lowers the local symmetry at the impurity ion site. The strategy of deliberately creating disorder in the crystalline lattice is a successful way of increasing brightness and decreasing the excited state lifetime of the impurity ions, which can be applied for improving emission properties of the phosphor materials used in solid state lighting.

Corrosion mechanisms of Al2O3-SiC-C refractory castables by iron and slag based on post-mortem analysis of industrial samples

The Al2O3-SiC-C or ASC castables are used in the main runners of blast furnaces. Most of the papers published to date focus on laboratory corrosion tests because access to the post-mortem samples of ASC castables is difficult. However, investigation of post-mortem samples is crucial in reducing the wear of ASC castables. The main runner is divided into the turbulence, middle, and non-turbulence zones. The microstructures of post-mortem samples located in working linings of different zones were investigated by SEM/EDS technique. The thermodynamic simulations were carried out in different systems, such as slag/refractory and iron/refractory, using the FactSage software. The SEM/EDS results showed the formation of phases with low melting points, such as gehlenite and anorthite, together with spinel solid solutions in the matrix and calcium dialuminate near the alumina aggregates. The thermodynamic simulations showed that slag and iron tend to react with alumina and silicon carbide, respectively.

The phase evolution of resin‐bonded Al2O3‐Al refractory containing magnesia under N2‐blowing

AbstractPhenolic resin‐bonded Al2O3‐Al‐MgO refractories were prepared from sintered alumina and aluminum as raw materials, adding 3 wt%, 9 wt% and 15 wt% high‐purity magnesia. The green samples were treated at 200°C and heated at 1300°C and 1600°C in a nitrogen atmosphere. The results showed that the phases after heating at 1300°C were α‐Al2O3, spinel solid solution (MgAlON), Al4O4C, Al4C3 and unreacted aluminum. The phases after heating at 1600°C were α‐Al2O3, spinel solid solution (MgAlON), Al4O4C, Al4C3, (Al2OC)x(AlN)1‐x solid solution, Al8O3N6, and unreacted aluminum, with a tendency to shift from Al‐O‐C to MgAlON with increasing MgO content. MgAlON was obtained by in situ synthesis of MgO, Al2O3, Al, and N2 at 1300°C. With sufficient magnesia, the stability of Al4O4C and Al4C3 decreases at 1600°C, and AlON is formed with better stability and can be solubilized into MgAlON. That is, when magnesia was added to the phenolic resin‐bound Al2O3‐Al composite under a nitrogen atmosphere, more stabilized MgAlON was formed.

Continuous degradation of plasticizer bisphenol A by catalytic Cu(FexAl2-x)O4@sediment ceramic membranes combined with peroxymonosulfate activation

The Cu(FexAl2-x)O4-embeded sediment ceramic membranes (CuFeAl@SCMs) were fabricated by the low-temperature sintering technology and further employed in a dead-end filtration device for continuous bisphenol A (BPA) degradation with peroxymonosulfate (PMS) activation. Results showed that using river sediment as precursor decreased the fabrication temperature for ceramic membranes (900 °C). The Al-doping Cu(FexAl2-x)O4 spinel solid solution was the predominant product phase, and the membrane with 42 wt% spinel content (CuFeAl@SCM-42) exhibited the highest BPA degradation efficiency (98.3%). SO4∙- and ∙OH were identified as the involved and primary reactive oxygen species (ROS). The density functional theory (DFT) calculations illustrated the forming mechanisms of SO4∙- and ∙OH. Furthermore, the DFT results confirmed that Al doping could enhance the adsorption energy and the electron transfer rate between the spinel and PMS, which encouraged PMS activation for BPA degradation. The outstanding performance of BPA degradation was observed in different pH, PMS content, transmembrane pressure, anions, natural organic matter (NOM) and water matrices, which revealed the excellent practicability, stability and recyclability of the prepared CuFeAl@SCM-42 in complex water environment. Therefore, this study demonstrated the possibility of using dredged river sediment to fabricate the superior catalytic ceramic membranes for wastewater treatment under a low-temperature sintering scheme.