Magnesium Aluminate Spinel Research Articles

Force rheological polishing of polycrystalline magnesium aluminate spinel using agglomerated diamond abrasive

The high hardness and polycrystalline structure of polycrystalline magnesium aluminate spinel (PMAS) present significant challenges in achieving high-precision processing, particularly during polishing. Issues such as low processing efficiency and grain effects can compromise processing accuracy, surface quality, and optical performance. To address these challenges and enhance both polishing efficiency and surface quality, this study employed agglomerated diamond (AD) abrasives and single crystal diamond (SCD) abrasives in force rheological polishing (FRP). The experimental results revealed that the lowest surface roughness (Sa) and optimal selective material removal were achieved using 25 μm AD abrasives, particularly those agglomerated with 0.2 μm SCD abrasives. This approach reduced Sa from 146.1 nm to 4.6 nm, peak-to-valley height difference (Sz) from 1329 nm to 69.3 nm and achieved a material removal rate (MRR) of 228.8 nm/min. Conversely, polishing with 1 μm SCD abrasives resulted in poorer selective material removal, with Sz decreasing from 1265.1 nm to 280.9 nm and Sa decreasing from 138.3 nm to 27.6 nm, although it exhibited the highest MRR of 323.64 nm/min. The superior polishing results obtained with AD abrasives, compared to SCD abrasives of the same size, can be attributed to the polycrystalline-like structure of AD abrasives, which exhibit more micro cutting edges. Additionally, the surface and subsurface damage after polishing with AD abrasives was analyzed. The results indicated that material removal of PMAS using AD abrasives was effective in FRP, resulting in minimal lattice distortion. This study provides both theoretical and experimental foundations for polishing PMAS using larger-sized AD abrasives in FRP.

Enhancement of strength and thermal shock resistance of MgO‐MgAl2O4 ceramic filters with microporous MgO powder: Effect of α‐Al2O3 micro‐powder content

AbstractIn this work, MgO‐MgAl2O4 ceramic filters were fabricated from microporous MgO powder and α‐Al2O3 micro‐powder, in which microporous MgO powder was prepared using Mg(OH)2 as initial raw material. With the α‐Al2O3 micro‐powder content increased from 0 to 15 wt%, the tight packing and reaction sintering between MgO microparticles and Al2O3 microparticles promoted the formation and growth of magnesium aluminate spinel necks, reduced the apparent porosity of ceramic filter skeletons, decreased the pore size, and improved the strength of the filters. When the α‐Al2O3 micro‐powder content further raised to 20 wt%, the thermal mismatch between MgO microparticles and spinel microparticles caused a small amount of crack generation, which lowered the strength of the filter. Besides, after introducing the α‐Al2O3 micro‐powder, more spinel necks were produced due to a small amount of MgO solid dissolved in the spinel lattice during the thermal shock test, which enhanced the thermal shock resistance of the filters. When the α‐Al2O3 micro‐powder content was 15 wt%, the filter had excellent comprehensive performance, the bulk density and apparent porosity of the filter skeleton were 3.09 g/cm3 and 10.7%, and the compressive strength before and after thermal shock test was 3.48 and 3.70 MPa, respectively.

Synthesis of Eu3+ doped magnesium aluminate spinel via combustion method: Investigation of thermodynamics, crystal structure, microstructure, and luminescence properties

AbstractIn the current research, the rare earth‐doped magnesium aluminate (MgAl2O4:Eu3+) spinels were produced by the combustion synthesis method. The employment of thermodynamic calculations revealed that the combustion approach is a proper way to synthesize MgAl2O4:Eu3+ material by urea fuel, although this procedure was fulfilled at 500°C, the final temperature will be around 2030°C. The x‐ray and FT‐IR spectra confirmed the successful formation of spinels, while it was shown that the calcination procedure results in a significant increase of crystallinity. On the other hand, it was interestingly seen that the addition of large amounts of Eu3+dopant (10 wt%) suppresses the crystallinity. The MAUD calculations interestingly revealed that the increase of Eu3+ dopant from 1 to 10 wt% leads to the increase of MgO and Al2O3 impurities. The related microstructural evaluations revealed that the particle size of the synthesized powders is mostly less than 40 nm which shows the superiority of combustion synthesis over other commercial methods. Also, the broadening of XRD peaks confirmed the formation of nano‐sized powder. The photoluminescence (PL) characterizations showed that doping of MgAl2O4 with 7 wt% Eu3+ brings the most intensive emission properties at the wavelengths of 592 and 617 nm.

The effect of MnO2 additive on the microstructure and mechanical properties of magnesium aluminate spinel

AbstractIn this study, varying amounts of MnO2 up to 5 wt.% were added to magnesium aluminate spinel (MA) bodies using a solid‐state sintering method at 1200–1600°C. The effect of MnO2 addition on the phase composition, microstructure, distribution of elements, and ionic valence of MA was investigated via X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy, respectively. The results showed that Mg2+ ions in MA crystals were replaced by Mn2+ ions, resulting in the formation of the (Mg1‐xMnx)Al2O4 solid solution. The distorted crystal structures promoted the sintering reactions, and the mechanical characteristics of MA were greatly improved by the solid solution strengthening process. When the additive amount of MnO2 was 5 wt.% and the sintered temperature reached at 1600°C, excess manganese ions hardly dissolved into the lattice of MA. And these ions were only distributed at the grain boundaries of MgAl2O4, forming a “barrier” that hindered the migration and diffusion of particles, thereby suppressing the sintering process and weakening the mechanical strength of MA.

Additive manufacturing of alumina refractories by binder jetting

In this work, refractory components based on alumina were produced by binder jetting using a large-scale 3D printer. The formulation contained several particle fractions up to a grain size of 3 mm, equal to the printer resolution. The binder system contained fine dead burnt magnesia, milled citric acid and reactive alumina, which were added to the aggregate mixture to create the powder bed. Deionized water was deposited from the printer's nozzles and triggered the binding reaction between the magnesia and citric acid. After 24 h, the printed samples were removed from the powder bed, dried and sintered at 1600 °C for 5 h. Reactive alumina contributed to the in situ creation of magnesium aluminate spinel at high temperature. The samples were characterized in terms of Young's modulus of elasticity, bending and compressive strength in 2 directions (parallel and perpendicular to the printing direction). The broken parts were used to investigate physical properties such as the open porosity and bulk density. The microstructure was studied by means of computed tomography. Finally, powder samples were used to determine the phase composition at different stages of production by means of XRD.

Quantitative analysis of grain boundary segregation and fracture behavior in Ca-doped magnesium aluminate spinel

Quantitative analysis of grain boundary segregation and fracture behavior in Ca-doped magnesium aluminate spinel

Transparent Magnesium Aluminate Spinel Ceramics Reinforced by Alumina Nanofibers

Transparent Magnesium Aluminate Spinel Ceramics Reinforced by Alumina Nanofibers

Synergistic effect of YAG particulate reinforcement on microstructural and thermo-mechanical properties of pressureless sintered MgAl2O4 spinel ceramic composites

Yttrium aluminum garnet (YAG) powders, synthesized through a partial wet chemical process, exhibit controlled morphology, high phase purity, and uniform homogeneity etc. This process involves the precipitation of aluminum ions onto Y2O3 particles. The transformation process of the Al-compound/Y2O3 precursor structure leads to the direct crystallization of pure YAG at 900 °C, passing through an intermediate stage where hexagonal YAH phase forms. A comprehensive study was conducted on the impact of preformed YAG as a reinforcing phase on the densification, mechanical, and thermo-mechanical properties of MgAl2O4-YAG composite, sintered under pressureless sintering in temperature range of 1500 °C–1600 °C. The inclusion of YAG particulate up to 5.0 wt% significantly enhances the densification, hardness, fracture toughness, flexural strength and high-temperature mechanical behavior of magnesium aluminate spinel (MAS) ceramics, however, increasing the YAG content beyond 5.0 wt% causes a reduction in these properties. The optimized addition of YAG particulate contributes to reducing the average grain size and refining the microstructure of the spinel ceramic matrix.

EELS Quantification of Ca and Y Segregation Behaviors in Magnesium Aluminate Spinel

EELS Quantification of Ca and Y Segregation Behaviors in Magnesium Aluminate Spinel

Electrochemical and statistical study of Nickel ion assessment in daily children intake samples relying on magnesium aluminate spinel nanoparticles

Lately, children's daily consumption of some products, such as cereals and candies, has been rising, which provides a compelling rationale for determining any metallic substances that may be present. Monitoring the concentration of certain metals, like nickel, in these products is necessary due to medical issues in humans when consumed regularly. So, in this work, a novel and highly selective carbon paste as a Ni(II) ion-selective sensor was prepared and investigated using ceramic magnesium aluminum spinel nanoparticles as the ionophore and tritolyl phosphate (TOCP) as a plasticizer. A modified co-precipitation method was used to synthesize the spinel nanoparticles. X-ray diffraction, scanning electron microscope with EDAX, transmission electron microscope, and BET surface area were used to determine the phase composition, microstructure, pores size, particle size, and surface area of the synthesized nanoparticles. The spinel nanoparticle was found to have a nano crystallite size with a cubic crystal system, a particle size ranging from 17.2 to 51.52 nm, mesoporous nature (average pore size = 8.72 nm), and a large surface area (61.75 m2/g). The composition ratio of graphite carbon as a base: TOCP as binder: spinal as ionophore was 67.3:30.0:2.7 (wt%) based on potentiometric detections over concentrations from 5.0 × 10−8 to 1.0 × 10−2 mol L−1 with LOD of 5.0 × 10−8 mol L−1. A measurement of 29.22 ± 0.12 mV decade−1 over pH 2.0–7.0 was made for the Nernstian slope. This sensor demonstrated good repeatability over nine weeks and a rapid response of 8 s. A good selectivity was shown for Ni(II) ions across many interferents, tri-, di-, and monovalent cations. The Ni(II) content in spiked real samples, including cocaine, sweets, coca, chocolate, carbonated drinks, cereals, and packages, were measured. The results obtained indicated no significant difference between the proposed potentiometric method and the officially reported ICP method according to the F- and t-test data. In addition to utilizing ANOVA statistical analysis, validation procedures have been implemented, and the results exceed the ICP-MS methodology.

Atomistic structures and stabilities of MgAl2O4 surfaces under processing conditions: A first-principles thermodynamics study

Surfaces, in contacting ambient environments, are of particular importance for controlling sintering, thin-film growth, and catalytic activity of oxides. Magnesium aluminate spinel (MgAl2O4), an essential oxide for both functional and structural ceramics, has attracted considerable attentions across diverse scientific fields. Nonetheless, a central challenge in rationally manipulating the properties of MgAl2O4 lies in the atomistic understanding of its surface structures under processing conditions. This study presents comprehensive first-principles calculations of MgAl2O4 (110) and (111) polar surfaces with/without off-stoichiometries. We predict from a thermodynamic model the dependence of surface stabilities on critical processing parameters, namely the oxygen partial pressure (PO2) and temperature (T). The findings indicate that at typical sintering temperatures, the non-stoichiometric (110) surface transits from Al/Mg-rich to O-rich with increasing PO2. In contrast, the non-stoichiometric (111) surface stably terminates in a Mg-rich configuration at low PO2, gradually shifting to Al-rich and then to Mg/O-rich as PO2 increases. The correlation between surface off-stoichiometry and stability is elucidated through electronic structure analysis. The investigation offers fundamental insights into surface structures and physicochemical behavior of MgAl2O4, thereby facilitating the rational processing control of complex oxides for applications in catalysis and electronics.

Oxidation and corrosion resistance of resin-bonded magnesia-based refractories reinforced by CaB6 addition for secondary refining

Excellent properties are required for refractories used for secondary refining because of the harsh service conditions. The current study investigated the effect of calcium boride (CaB6) on the properties of magnesium oxide (MgO)‒based refractories. The sample with 0.4 wt% CaB6 exhibited excellent properties. It possessed the highest bulk density indicating that a suitable content of CaB6 can increase the compactness of the refractories. The in-situ formation of aluminum oxycarbonitride (Al3CON) at high temperatures in the MgO-based refractories was from the reaction of Al, Al4C3, AlN, and Al2O3 due to the addition of Al powders, which endowed them with high strength. The refractory containing 0.4 wt% CaB6 also exhibited the highest hot modulus of rupture (HMOR) of 26.6 MPa, which was around 2.5 times the strength of commercial MgO‒CaO bricks and 1.5 times that of the samples without CaB6 addition. In addition, it exhibited the best oxidation resistance revealed by the minimum thickness of the decarbonization zone, because the addition of CaB6 promoted the formation of a dense magnesium aluminate spinel (MgAl2O4, MA) layer between the oxidized and non-decarburized zone in the refractories, thereby promoting the resistance of the samples to oxidation. It also exhibited excellent thermal shock resistance, and the residual strength ratio reached 76.6 %. The corrosion depth of the sample containing 0.4 wt% CaB6 was 9.8 % that of the MgO‒CaO bricks. This work indicates a potential alternative for producing high‒performance resin‒bonded MgO-based refractories with CaB6 in secondary refining furnaces.

Effect of alumina sol on the preparation of magnesia‐alumina spinel foam ceramics by foaming‐sol method

AbstractIn this work, magnesia‐alumina spinel foam ceramics were prepared by foaming‐sol method using magnesia alumina spinel as raw material, anionic surfactant potassium oleate (PO) as foaming agent, and alumina sol as curing agent. The curing mechanism and the effect of alumina sol content on the stability of foam slurry and the properties of foam ceramics were investigated. In the foam slurry, the alumina sol can react with PO, so magnesia‐alumina spinel can be fixed in the foam structure through the gel network to improve the stability of the foam slurry. The gelation process reduces the viscosity of the foam slurry. The pores of magnesia‐alumina spinel foam ceramics sintered at 1500°C are mostly closed pores and the average pore was 29.7–42.1 µm. With the increase of alumina sol content, the bulk density of magnesia‐alumina spinel foam ceramics increased from 1.3 to 1.9 g/cm3, the cold compressive strength from 8.8 to 22.7 MPa, and the thermal conductivity from .417 to .806 W·m−1·K−1(350°C).

Study on the effect of size and density of micropores on transparent ceramic damage induced under intense laser irradiation

The increasing utilization of transparent ceramics in laser systems, particularly the magnesium aluminate spinel (MgAl2O4) transparent ceramic, has positioned it as the primary candidate for high energy laser system exit windows. Nevertheless, the increased energy and power of laser output necessitate higher standards for the laser-induced damage threshold in transparent ceramics. Residual micropores within transparent ceramics pose a potential source of damage. In this study, we employed the post-annealing process to effectively modulate the density and size of micropores. We first established the relationship between the density and size of micropores and laser damage threshold, which described the damage morphology of transparent ceramic in detail. Subsequently, we developed a multi-physical field coupled kinetic model of laser damage in micropores, providing a quantitative analysis of how factors such as micropore size and density influence the damage morphology of transparent ceramic surfaces when subjected to laser irradiation. Using time-resolved pumping and probing technology, we conducted in situ detection of laser damage caused by micropores, enabling detailed examination of damage kinetic behavior. Ultimately, this study elucidated the physical mechanism behind micropore-induced transparent ceramic damage. This has significant implications for enhancing the anti-laser damage performance of transparent ceramics in high-intensity laser systems.

Effect of pH on the chemical composition, morphology, and densification of magnesium aluminate spinel nanopowder synthesized by the coprecipitation method

Effect of pH on the chemical composition, morphology, and densification of magnesium aluminate spinel nanopowder synthesized by the coprecipitation method

Magnesium aluminate spinel transparent ceramics with high optical and mechanical performance by Y3Al5O12 sintering additive

AbstractHigh‐quality magnesium aluminate spinel (MAS) transparent ceramics were successfully fabricated using Y3Al5O12 (YAG) as the sintering additive. The influence of the YAG content on the sintering behavior, microstructure, and optical properties of the MAS transparent ceramics was systematically investigated. A 4 mm‐thick sample with 0.01 wt.% YAG hot isostatic pressed at 1600°C achieved the highest in‐line transmittance of 84.0% at 400 nm and the flexural strength of the sample was as high as 347.3 MPa, which represents the highest‐performing reported MAS transparent ceramics that were sintered with oxide additives.

Preparation and properties of cordierite-based multi-phase composite far-infrared emission ceramics by fine-grained tailings

In this paper, cordierite ceramics with high far-infrared emission properties are synthesized by a high-temperature solid-phase method using molybdenum tailings and vanadium-titanium magnetite tailings. The microstructure, physical properties and far-infrared emission mechanism of ceramics are investigated. The results show that the ceramics synthesized with 10 wt% molybdenum tailings and 30 wt% vanadium-titanium magnetite tailings have a flexural strength of 67 MPa, a bulk density of 2.531 g/cm3 and a maximum far-infrared emissivity of 0.958 when the sintering temperature is 1200 °C. The crystal phase of the ceramic are 21.4 % cordierite and 58.7 % magnesia-alumina spinel. In the sintering process, the Fe3+ in vanadium-titanium magnetite tailings doped into the cordierite to substitute the Mg2+, which has the similar ionic radius with Fe3+, to form a substitutional solute. Ionic substitution causes the lattice parameters of cordierite larger, reducing the symmetry of the lattice vibrations and leading to lattice distortion. In addition, the composition of a large amount of magnesia-aluminum spinel is attributed to the far-infrared emission properties of ceramics.

Tailoring tactics for preparation of superior thermal insulation materials from blast furnace ferronickel slag: Control of sintering temperature

Blast furnace ferronickel slag (BFFS) was converted to thermal insulation materials by sintering of its mixture with 15 wt% fly ash cenosphere (FAC) from 1000 °C to 1200 °C. The influence of sintering temperature on the phase compositions, microstructures, and properties of the materials was investigated based on both thermodynamic and experimental analyses. It was demonstrated that increasing sintering temperature from 1000 °C to 1200 °C led to linear increases of contents of diopside (CaMgSi2O6; y = 0.039T – 21.5, where y and T denote the content and temperature, respectively), anorthite (CaAl2Si2O8; y = 0.0504T – 46.54), and magnesium aluminate spinel (MgAl2O4; y = 0.043T – 30.86) in the thermal insulation materials. Meanwhile, there existed linear decreases of contents of akermanite (Ca2MgSi2O7; y = -0.0352T + 66.18) and gehlenite (Ca2Al2SiO7; y = -0.0914T + 129.96), which could form a solid solution above 1100 °C, suppressing the expansion associated with the generation of magnesium aluminate spinel. Along with the phase transformation, the macroporous structure was also identified. By sintering at 1100 °C for 2 h, an optimal high-quality thermal insulation material with apparent porosity of 46.04%, water absorption of 42.12%, bulk density of 1.35 g/cm3, linear shrinkage of 0.82%, compressive strength of 6.83 MPa, thermal conductivity of 0.31 W/(m·K) at 25 °C and 0.42 W/(m·K) at 800 °C, and refractoriness of 1259 °C could be obtained.

Study on magnesia alumina spinel heat storage ceramics for solar thermal power generation

AbstractSolar thermal storage ceramic materials use photothermal power generation technology to store heat energy, which is an important way to use clean energy and reduce carbon emissions. In this paper, MgAl2O4 ceramics were prepared by pressureless sintering with fused magnesia and α‐Al2O3 as the primary raw materials and TiO2 as the additive. The phase composition, microstructure, physical properties, thermal shock resistance, and thermal physical properties of MgAl2O4 thermal storage ceramics were studied. The results show that the main crystalline phase of B4 is MgAl2O4 and the secondary crystalline phase is MgTi2O5. Ti4+ is dissolved into MgAl2O4 lattice, which distorts the lattice, reduces activation energy, and promotes sintering. The sample B4 (69.73 wt% α‐Al2O3, 30.27 wt% fused magnesia, and 7 wt% TiO2) sintered at 1510°C had the best comprehensive physical properties, and its bending strength and bulk density were 89.41 MPa and 3.27 g/cm3, respectively. After 30 thermal shock cycles, the bending strength of the sample B4 is slightly lost. The thermal stress generated during the expansion and contraction of the grain volume led to the decrease of the bending strength. From room temperature to 1000°C, the specific heat capacity of sample B4 is .44–1.25 J/(g·K). The heat capacity increases with the increase of temperature, and the heat storage density increases. The heat storage density is 1218.75 kJ/kg (1000°C). Heat capacity increases with temperature due to intensified lattice vibration at high temperatures. Therefore, magnesia alumina spinel ceramics show great potential in solar thermal energy storage.

Effect of Yb2O3 Addition and Sintering Temperature on the Densification Behavior of Magnesium Aluminate Spinel Powder

The effect of Yb2O3 and sintering temperature on the densification behavior of magnesium aluminate spinel powder was studied. Results showed that Yb2O3 was beneficial to the sintering densification of MgAl2O4. When the content of Yb2O3 was 3 wt%, the relative density of magnesium aluminium spinel (MAS) was 98.54%, and the microstructure was more compact. The maximum hardness was 21.48 GPa, and the second phase Yb3Al5O12 appeared in the 3 wt% Yb2O3 samples. The mechanism of Yb2O3 in promoting the sintering densification of MAS is due to the appearance of Yb3Al5O12. When the sintering temperature is 1700°C, the relative density of MAS reaches a maximum of 98.54%, the hardness also reaches a maximum value of 21.48 GPa, and the grain size is more uniform. When the temperature exceeds 1700°C, the relative density and hardness of MAS decrease. The best sintering aid content and temperature synergistically worked to promote the densification and increased the hardness of MAS.