MgAl2O4 Spinel Research Articles

Transformation of refractory ceramic MgAl2O4 into blue light emitting nanomaterials by Sr2+/Cr3+ activation

The current research aims at manipulation of physical properties of spinel MgAl2O4 by substitution of Sr2+ cations at tetrahedral and Cr3+ at orthogonal-sites. Synthesized materials were studied by XRD, TGA, SEM, EDX and UV–visible, diffuse reflectance and photoluminescence spectroscopy. A series of Sr2+ and Cr3+ doped derivatives with the general formula Mg1-xSrxAl2-yCryO4 (where x, y = 0.2, 0.4, 0.6, 0.8 and 1.0) have been produced and investigated using the co precipitation technique. Although strain in the cubic crystal structure of magnesium aluminate spinel was seen upon doping due to Sr2+'s higher cationic radius, the structure remained reserved (spinel) for low dopant concentration (x, y = 0.2, 0.4, 0.6). The behavior of activator ions Cr3+ in these derivatives is supposed to be altered due to change in site occupancy. Due to presence of antisites defects activator ions; structural, optical, thermal, electrical properties of MgAl2O4 material were modified.

Er‐Doped MgAl2O4 Nanofilms Enabling Highly Efficient Near‐Infrared Electroluminescence from the Silicon‐Based MOS Devices Fabricated by Atomic Layer Deposition

AbstractEr3+‐doped polycrystalline MgAl2O4 (MAO:Er) spinel nanofilms are deposited via atomic layer deposition, and the metal‐oxide–semiconductor light emitting devices are fabricated. The crystallinity and morphology of the MAO:Er nanofilms are explored by modifying the annealing temperatures, Al2O3/MgO ratios and Er2O3 dopant cycles. The similar electroluminescence (EL) emissions peaking at 1530 nm indicates the identical crystal field environment for the doped Er3+ ions. The concentration quenching is verified to occurs via the energy transfer among the neighboring Er3+ ions. The optimal device (800 °C‐annealed, Al2O3/MgO ratio close to stoichiometry, Er3+: 1.85 mol%) yields the highest external quantum efficiency of 28%, the power efficiency of 0.32% and the optical power density of 14.62 mW cm−2. The smooth MAO:Er spinel nanofilms with the low refractive index and high resistance ensure the highly efficient light extraction and the generation of energetic electrons for the impact excitation of Er3+ ions. The trap‐assisted tunneling under operation electric field dominates the conduction mechanism for the EL emissions. The estimated decay lifetime of 1154.4 µs and a large‐stimulated emission cross‐section in the order of 10−15–10−14 cm2 are revealed from the EL emissions. Intense near‐infrared emissions from these Si‐based MAO:Er devices have great potential in the optoelectronic applications.

N-Decorated Main-Group MgAl2O4 Spinel: Unlocking Exceptional Oxygen Reduction Activity for Zn-Air Batteries.

The development of economical and efficient oxygen reduction reaction (ORR) catalysts is crucial to accelerate the widespread application rhythm of aqueous rechargeable zinc-air batteries (ZABs). Here, a strategy is reported that the modification of the binding energy for reaction intermediates by the axial N-group converts the inactive spinel MgAl2O4 into the active motif of MgAl2O4-N. It is found that the introduction of N species can effectively optimize the electronic configuration of MgAl2O4, thereby significantly reducing the adsorption strength of *OH and boosting the reaction process. This main-group MgAl2O4-N catalyst exhibits a high ORR activity in a broad pH range from acidic and alkaline environments. The aqueous ZABs assembled with MgAl2O4-N shows a peak power density of 158.5mWcm-2, the long-term cyclability over 2000h and the high stability in the temperature range from -10 to 50°C, outperforming the commercial Pt/C in terms of activity and stability. This work not only serves as a significant candidate for the robust ORR electrocatalysts of aqueous ZABs, but also paves a new route for the effective reutilization of waste Mg alloys.

Formation of carbon with a diamond-like lattice during the production of spinel MgAl2O4 by a combustion synthesis

Magnesium aluminate spinel (MAS) containing a carbon impurity was prepared by self-propagating high-temperature synthesis (SHS). Periclase MgO, alumina Al2O3, fuel Al powder, 2 wt% boron, and oxidizer Mg(NO3)2·6H2O were used as starting reagents for MAS synthesis. The phase composition of original boron and synthesized products, the structure and surface morphology of the samples were investigated. EDS analysis and elemental mapping confirmed that the impurity detected as crystals formed during the synthesis was carbon. IR spectroscopy showed that the carbon detected in the synthesized product has a diamond-like lattice similar to that of detonation diamonds. The analysis of gases evolved during combustion was performed. A proton‑boron reaction is shown to take place during fast self-propagating high-temperature synthesis of spinel. The probable mechanisms of carbon formation in the synthesis products are proposed using the experimental data.

Sol-gel combustion synthesis and near-infrared luminescence of Ni2+-doped MgAl2O4 spinel phosphor

Near-infrared phosphor converted light-emitting diode (NIR pc-LED) has many advantages over traditional NIR light sources, and has broad application prospects in night vision surveillance, non-destructive testing, bioimaging, and other fields. Phosphors are typically synthesized by the high-temperature solid-phase method as chunks or large granules, which need to be ground to small particles for practical application. This process introduces surface defects and reduces the luminous efficiency of phosphors. In this work, near-infrared phosphors composed of spinel MgAl2O4:Ni2+ with particle size less than 100 nm was synthesized in high-purity by sol-gel combustion method using nitrate salts with citric acid were used as raw materials. Under 365 nm excitation, MgAl2O4:Ni2+ phosphors emit broadband near-infrared luminescence of 1000–1600 nm with a width at half maximum of 237 nm. The optimal Ni2+ doping concentration was determined to be 1.5 mol% and the optimal sintering temperature was 1200 °C. The thermal activation energy of this phosphor was found to be 0.409 eV and the phosphor had good luminescence thermal stability. An NIR pc-LED device was assembled from the phosphor and commercially available near-ultraviolet LED, which showed a current-dependent increased of NIR luminescence up to 160 mA and an efficiency drop appeared with further increase of the current, suggesting a thermal dependent quenching may have occurred. On the other hand, the output of NIR luminescence increased nearly linearly with the increased of current when a 360 nm laser diode was used as the excitation light source, indicating the NIR phosphor has a very high fluorescence saturation threshold. Our study provides the utility for the sol-gel method in the preparation and the potential application of the nanoscale NIR-II phosphor materials.

Production, stability and properties of ultrafine MgAl2O4 (spinel) particles stabilized Mg–3Ca alloy foams

The present work reports the synthesis and mechanical behavior studies of Mg–3Ca alloy foams stabilized by ultrafine MgAl2O4 (spinel) particles. The MgAl2O4 particles was created in-situ in the Mg–3Ca alloy melt through the reaction of Mg, Al and O. Foaming was done by adding dolomite (CaMg(CO3)2) as blowing agent in the melt. The foaming behaviour was studied for different MgAl2O4 content in Mg–3Ca and holding times (10 and 15 min). The study reveals that the presence of MgAl2O4 significantly influences the foaming behavior of Mg–3Ca alloy resulting in equiaxed cell structure, uniform cell size distribution, higher expansion in comparison to the Mg–3Ca alloy foam which contains only MgO and CaO. An in-depth phase and microstructural analysis were performed to investigate the particles present in the gas-solid interface of the foam that contributes to foam stabilization. The quasi-static compression studies of foams exhibited better compressive strength (≈3–11 MPa) and energy absorption capacity (≈1.3–5.7 MJ/m3) in comparison to the Mg foams reported in the literature. The ductility of the Mg foams was also measured and compared with that of existing aluminium foams.

TiB2 effects on the AlMgB14–TiB2 ceramics structure and properties

This paper studied titanium diboride (TiB2) effects on the structure and properties of AlMgB14 ceramics. AlMgB14–TiB2 samples with 30 wt% and 50 wt% TiB2 were obtained by the self-propagating high-temperature synthesis. The addition of 30 wt% TiB2 did not significantly change the phase composition of the AlMgB14 ceramics, which remained comparable with the initial powder mixture composition. However, increasing the TiB2 amount to 50 wt% resulted in the MgAl2O4 spinel phase appearance. The addition of TiB2 significantly increased the microhardness of AlMgB14 from 7 GPa to 19.9 GPa, compared to the initial material, and also increased its flexural strength to 314 MPa.

Effects of Binary Oxide Coated MWCNTs Toward Tailoring the Mechanical, Thermo-Mechanical, and Microstructural Properties of Pressureless Sintered MgAl2O4 Spinel Ceramic Composite

Effects of Binary Oxide Coated MWCNTs Toward Tailoring the Mechanical, Thermo-Mechanical, and Microstructural Properties of Pressureless Sintered MgAl2O4 Spinel Ceramic Composite

The annealing kinetics of the F-type defects in MgAl2O4 spinel single crystals irradiated by swift heavy ions

The annealing kinetics of the F and F+ color centers induced in MgAl2O4 single crystals under irradiation by 156-MeV 132Xe and 2.25-GeV 197Au ions are precisely measured via relevant optical absorption bands and analyzed in terms of the diffusion-controlled reactions between two pairs of anion Frenkel defects which determine thermal stability of irradiated material. It is demonstrated that two types of mobile oxygen interstitials (neutral and charged ones) are involved into recombination process with very different activation energies, which are practically independent on radiation fluencies.

Key features of nano NixMg1-xAl2O4 spinel for biogas bi-reforming: CO2 activation and coke elimination

Using green and sustainable biogas as raw material to produce syngas (H2/CO≈2) suitable for direct synthesis of green methanol has attracted wide attention, but developing efficient catalysts with high activity/stability remains a big challenge. A series of MgAl2O4 spinel catalysts (denoted as NixMg1-xAl2O4) is designed and applied in biogas bi-reforming. The nano NixMg1-xAl2O4 catalysts were comprehensively characterized by Raman, SEM, HR-TEM, H2-TPR, CO2-TPD, etc. The CO2 activation was verified by in situ CH4-TPSR/CO2-TPO, and the key role of NixMg1-xAl2O4 in coke removal behavior mechanism was further confirmed. Due to the efficient CO2 adsorption/activation and strong metal–support interaction, nano NixMg1-xAl2O4 shows excellent catalytic stability to inhibit sintering and carbon deposition. At reforming conditions of 750 °C, a weight hourly space velocity (WHSV) of 32,400 mL gCat−1 h−1, the Ni0.4Mg0.6Al2O4 catalyst exhibits excellent CH4/CO2 conversion of 91/51 % are achieved, followed by slight decrease after 40 h, and remain basically stable for the next 40 h.

Sol-gel synthesis, characterization, and electrochemical evaluation of magnesium aluminate spinel nanoparticles for high-capacity hydrogen storage

In this research, we successfully synthesized magnesium aluminate (MgAl2O4) spinel nanoparticles using a sol-gel process, with stearic acid serving as a capping agent. The synthesis process involved calcination at 900 °C for 4 h, resulting in the formation of nanoparticles with an average crystallite size of approximately 12 nm, as determined through Debye–Scherrer analysis and X-ray diffraction (XRD) data. The optical band gap was measured as 2.84 eV using Diffuse Reflectance Spectroscopy (DRS) analysis. Additionally, we found the mean pore size of the nanoparticles to be 20.2 nm through Brunauer–Emmett–Teller (BET) analysis. We characterized the resulting powders using various techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Vibrating Sample Magnetometry (VSM). We conducted electrochemical investigations utilizing the Chronopotentiometry (CP) technique. The electrochemical analysis demonstrated that MgAl2O4 spinel nanoparticles exhibit a noteworthy hydrogen storage capacity of 4000 mAh/g, highlighting their potential as promising candidates for hydrogen storage applications. This comprehensive study underscores the successful synthesis, thorough characterization, and exceptional electrochemical performance of MgAl2O4 spinel nanoparticles, firmly positioning them as valuable materials for advancing hydrogen storage technologies.Graphical

Grain-size effect on Cr3+ and F-centres photoluminescence in nanophase MgAl2O4 ceramics

Photoluminescence (PL) spectroscopy of transparent MgAl2O4 spinel ceramics with grain size between 100 and 300 nm was studied at 7 K temperature in the near-IR-VUV range of spectrum with synchrotron radiation excitation. The PL spectra were composed of optical transitions from spatially different regions of the ceramics, which analysis evidenced grain size effect on the emission line-shapes and intensities. In particular, emission of impurity Cr3+ ions, being structured in the crystalline bulk, became broad-band in the grain boundary regions, which was associated with respectively strong and weak local crystalline fields. It was observed that (i) excitons and F centres transfer energy to Cr3+ and (ii) Cr(2Eg)/Cr(4T2g) and F-centres/Cr3+ PL intensity ratios underwent a linear dependence on the grain size.

Al‐Cu‐Fe alloys in the solar system: Going inside a Khatyrka‐like micrometeorite (KT01) from the Nubian Desert, Sudan

AbstractA recently described micrometeorite from the Nubian desert (Sudan) contains an exotic Al‐Cu‐Fe assemblage closely resembling that observed in the Khatyrka chondrite (Suttle et al., 2019; Science Reports 9:12426). We here extend previous investigations of the geochemical, mineralogical, and petrographic characteristics of the Sudan spherule by measuring oxygen isotope ratios in the silicate components and by nano‐scale transmission electron microscopy study of a focused ion beam foil that samples the contact between Al‐Cu alloys and silicates. O‐isotope work indicates an affinity to either OC or CR chondrites, while ruling out a CO or CM precursor. When combined with petrographic evidence we conclude that a CR chondrite parentage is the most likely origin for this micrometeorite. SEM and TEM studies reveal that the Al‐Cu alloys mainly consist of Al metal, stolperite (CuAl), and khatyrkite (CuAl2) together with inclusions in stolperite of a new nanometric, still unknown Al‐Cu phase with a likely nominal Cu3Al2 stoichiometry. At the interface between the alloy assemblage and the surrounding silicate, there is a thin layer (200 nm) of almost pure MgAl2O4 spinel along with well‐defined and almost perfectly spherical metallic droplets, predominantly iron in composition. The study yields additional evidence that Al‐Cu alloys, the likely precursors to quasicrystals in Khatyrka, occur naturally. Moreover, it implies the existence of multiple pathways leading to the association in reduced form of these two elements, one highly lithophile and the other strongly chalcophile.

A novel dual-strengthening technology combining external second phase nanoparticle method and hot compression deformation process in micro-alloyed medium carbon steel

Herein, a novel dual-strengthening technology that combines the external second-phase nanoparticle addition method with the hot compression deformation tests was carried out to investigate the effects of surface-modified nanoparticles (NPs) and deformation conditions on the characteristics of inclusions and the evolution of microstructure in the micro-alloyed (MA) medium carbon steels. The results revealed that the inclusions in the steels were divided into single phase inclusions and composite phase inclusions. With the addition of NPs, Al2O3 inclusions were replaced by MgAl2O4 spinel, and the composite inclusions mainly consisted of TiN–VN, MgAl2O4–TiN and MgAl2O4–TiN–MnS inclusions, and the same types of inclusions became significantly smaller in size. According to the EDS results, some of the inclusions acted to induce ferrite nucleation, and the MgAl2O4–TiN–MnS composite inclusion was more favorable for the nucleation of acicular ferrite (AF). The deformation induced ferrite (DIF) started to form at the deformation temperature of 750 °C and the maximum stress peak in the NPs-bearing steel was 516 MPa, which was 28.4% higher than that in the original steel. The proportion of ferrite increased as the deformation temperature decreased. The dispersed NPs contributed to the ferrite nucleation and the grain refinement as the inclusion-modifying agent, which improved the material properties, and the relevant strengthening mechanisms were explained.

Synthesis and characterisation of mesoporous MgAl2O4 hollow spheres as a high-value product in a waste recovery strategy

Micrometre-scale hollow sphere-shaped MgAl2O4 powders were synthesised using a spray-drying method, followed by calcination. An aqueous solution of mixed Mg2+ and Al3+ salts, derived from aluminium slag and serpentine tailings, served as a source of magnesium and aluminium. The secondary raw materials were subjected to acid leaching, and the refined leachates were used to prepare a spray-dried MgAl2O4 precursor, which was heat-treated at temperatures ranging from 550 °C to 1100 °C for 1 h. Characterisation of the resulting MgAl2O4 spinel powders was performed using various physicochemical techniques, including thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical adsorption using N2 (BET). The prepared MgAl2O4 spinel demonstrated several unique properties, including ultrafine particles with a uniform distribution (1–5 μm) and minimal particle agglomeration, high sintering activity (beginning at 550 °C), high purity, high specific surface area (110 m2 g-1/750 °C), and open porosity with a narrow pore size distribution (3–7 nm). These properties make the prepared MgAl2O4 spinel a highly valuable product for waste recovery strategies. The simplicity, efficiency, and cost-effectiveness of this process also predispose it to large-scale production of functional mixed metal oxides of various compositions for use in industries such as energy storage, sensing, and 3D printing fillers.

EFFECTS OF BINARY OXIDE COATED MWCNTS TOWARD TAILORING THE MECHANICAL, THERMO-MECHANICAL, AND MICROSTRUCTURAL PROPERTIES OF PRESSURELESS SINTERED MgAl2O4 SPINEL CERAMIC COMPOSITE

This study presents a performance evaluation of MgAl-binary oxide-coated multi-walled carbon nanotubes (MWCNTs) as a reinforcement phase in a magnesium aluminate spinel MgAl2O4 ceramic composite system fabricated using a pressureless sintering technique. The physical properties, including porosity, bulk density, and flexural strength of spinel composites were evaluated in the temperature range of 1500 – 1600 ?C. The results reveal the coated MWCNTs architecture's promising influence on the composite system's property enhancement. The developed thin-film coating on the MWCNTs favors enhanced dispersibility with better matrix-reinforcement interfacial connectivity, thereby improving the mechanical and thermo-mechanical performance of the composites.

Solid-State Reaction Synthesis of MgAl2O4 Spinel from MgO-Al2O3 Composite Particles Prepared via Electrostatic Adsorption.

This paper presents the formation of magnesium aluminate spinel using composite particles prepared via electrostatic adsorption (ESA). Scanning electron microscopy (SEM) images confirmed the presence of Al2O3-MgO composite particles. A mixture of Al2O3 and MgO raw materials was also prepared by using the conventional bead-milling method for comparison. The samples sintered at elevated temperatures were characterized through X-ray diffraction, SEM, and relative density measurements. Additionally, the lattice parameter and strain of the samples were determined using the Nelson-Riley function and the Williamson-Hall equation. A pure spinel phase formed in the ESA-derived sample sintered at 1400 °C, while the MgO structure remained in the conventionally prepared sample sintered at 1600 °C. The densities of samples sintered at 1450 °C or higher exceeded 90%. The lattice strain of the prepared samples was inversely proportional to the sintering temperature, attributed to the formation of large grains at higher temperatures. However, the sample sintered at 1600 °C for 8 h exhibited the highest strain of 0.0074 because the crystals grew in a certain direction.

Photocatalytic Degradation of Polyethylene Plastics Using MgAl2O4 Nanoparticles Prepared by Solid State Method

In this study, MgAl2O4 nanoparticles with different calcination times were synthesized for photocatalytic applications. Different analyses techniques such as XRD, SEM, EDX, UV-visible, and FTIR were performed to investigate the structural, chemical, optical, and mor-phological properties of the synthesized nanoparticles. XRD analysis revealed the formation MgAl2O4 spinel structure. UV-Visible measurements indicate that MgAl2O4-2 nanoparticles had a narrower energy gap compared to MgAl2O4-1 and MgAl2O4-3. Results of SEM analysis revealed that the synthesized MgAl2O4 nanoparticles consist of small aggregated particles with (40-60 nm) particles size. EDX measurements con-firmed the formation of MgAl2O4 nanoparticles without any impurities. The photocatalytic performance was evaluated by the photodegradation of polyethylene plastics using MgAl2O4 nanoparticles under UV irradiation. The FT-IR measurements before and after the degradation of polyethylene plastics confirm the formation of new functional groups as a result of photodegradation processes.

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.

Highly efficient MnOx catalysts supported on Mg-Al spinel for low temperature NH3-SCR

Selective catalytic reduction (SCR) has been extensively employed in industries for the removal of NOx while it is still a challenge to develop novel low-temperature catalysts. The redox and acid sites on the catalyst are often preconditions that cooperate in the SCR reaction. In this study, a series of MnOx supported on MgAl2O4 spinel catalysts (denoted as Mn/MAS) were successfully prepared by incipient wetness impregnation method for low-temperature SCR of NOx with ammonia. The effects of the calcination temperature of MAS support and Mn loading on catalyst structure and performance were examined. The Mn0.12/MAS-700 catalyst showed the best low-temperature denitrification performance, with more than 80% conversion of NO at 150–300 °C and higher than 60% N2 selectivity. Moreover, the denitrification efficiency remained at nearly 90% in the presence of H2O. The physicochemical properties of the catalysts were determined using various characterization methods, and the corresponding results found that the higher concentration of Mn4+ and surface chemisorption oxygen enhanced the low-temperature activity of the catalysts. The addition of Mn species increased the surface acidity of weak acid centers which promoted the catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) revealed that the Eley-Rideal mechanism was introduced mainly at 100 °C on the Mn0.12/MAS-700 catalyst. This work provides new inspiration into the effect of Mn species, and the synergistic role of active components Mn and MAS support in the SCR reaction.