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Keywords = magnesium aluminates

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19 pages, 5407 KiB  
Article
Prediction of Reduction Recovery of Iron and Vanadium Oxides in Low-Grade Vanadium–Titanium Magnetite Based on Response Surface Model
by Xueting Jiang, Hao Wu and Aijun Deng
Metals 2025, 15(6), 595; https://doi.org/10.3390/met15060595 - 27 May 2025
Viewed by 465
Abstract
In this study, the effects of reduction temperature and time on the reduction rates of iron and vanadium oxides in low-grade vanadium–titanium magnetite (VTM) were investigated. Based on the results of physical experiments, both the response surface method (RSM) and central composite design [...] Read more.
In this study, the effects of reduction temperature and time on the reduction rates of iron and vanadium oxides in low-grade vanadium–titanium magnetite (VTM) were investigated. Based on the results of physical experiments, both the response surface method (RSM) and central composite design (CCD) were used to fit the prediction model of the reduction rate of iron and vanadium oxides in low-grade VTM. The results of the RSM prediction model show that under the condition of a sufficient reducing medium, affected by the high-temperature products, such as silicates and magnesium aluminates, the reduction rate of iron and vanadium oxides in low-grade VTM will first increase and then decrease. This indicates that a single factor cannot maximize the reduction efficiency of metal oxides. The results of the RSM prediction model show that the correlation fitting coefficient and correction fitting coefficient of the model are greater than 99% and 98%, respectively. The F-value is 150.05 and 176.19, respectively, and the p-value is less than 0.0001. This indicates that the RSM prediction model has high accuracy and reliability. After parameter optimization of the RSM prediction model, when the reduction temperature is 1446 °C~1498 °C and the reduction time is 43 min~60 min, the maximum reduction rates of iron oxide and vanadium oxide in iron ore can reach 92.93% and 69.20%, respectively. The study of reaction kinetics shows that the reduction processes of iron and vanadium oxides in VTM are controlled by three-dimensional diffusion conditions. The apparent activation energies of the reactions are 86.76 kJ/mol and 90.30 kJ/mol, respectively. Full article
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14 pages, 3148 KiB  
Article
Liquid Structure of Magnesium Aluminates
by Viviana Cristiglio, Irina Pozdnyakova, Aleksei Bytchkov, Gabriel J. Cuello, Sandro Jahn, Didier Zanghi, Séverine Brassamin, James W. E. Drewitt and Louis Hennet
Materials 2024, 17(24), 6173; https://doi.org/10.3390/ma17246173 - 17 Dec 2024
Viewed by 888
Abstract
Magnesium aluminates (MgO)x(Al2O3)1−x belong to a class of refractory materials with important applications in glass and glass–ceramic technologies. Typically, these materials are fabricated from high-temperature molten phases. However, due to the difficulties in making measurements [...] Read more.
Magnesium aluminates (MgO)x(Al2O3)1−x belong to a class of refractory materials with important applications in glass and glass–ceramic technologies. Typically, these materials are fabricated from high-temperature molten phases. However, due to the difficulties in making measurements at very high temperatures, information on liquid-state structure and properties is limited. In this work, we employed the method of aerodynamic levitation with CO2 laser heating at large scale facilities to study the structure of liquid magnesium aluminates in the system (MgO)x(Al2O3)1−x, with x = 0.33, 0.5, and 0.75, using X-ray and neutron diffraction. We determined the structure factors and corresponding pair distribution functions, providing detailed information on the short-range structural order in the liquid state. The local structures were similar across the range of compositions studied, with average coordination numbers of n¯AlO4.5  and n¯MgO5.1 and interatomic distances of rAlO=1.761.78 Å and rMgO=1.931.95 Å. The results are in good agreement with previous molecular dynamics simulations. For the spinel endmember MgAl2O4 (x = 0.5), the average Mg-O and Al-O coordination numbers gave rise to conflicting values for the inversion coefficient χ, indicating that the structural formula used to describe the solid-state order-disorder transition is not applicable in the liquid state. Full article
(This article belongs to the Section Materials Physics)
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25 pages, 5747 KiB  
Article
Potential for the Recovery of Selected Metals and Critical Raw Materials from Slags from Polymineral Zn–Pb Ore Metallurgy—Part I
by Magdalena Cempa, Paweł Lejwoda, Klaudia Karabela, Anna Pieprzyca, Henryk Świnder and Arkadiusz Bauerek
Minerals 2024, 14(10), 1050; https://doi.org/10.3390/min14101050 - 19 Oct 2024
Cited by 2 | Viewed by 1621
Abstract
Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals [...] Read more.
Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals and critical raw materials. The historical slags associated with the smelting of polymetallic ores originating from Mississippi Valley-type (MVT) deposits consisted primarily of gypsum. The contemporary slags, obtained from industrial waste rich in zinc and lead, were predominantly spinels (magnesium-aluminate and ferric) that exhibited higher iron content (up to 46.6 wt% of Fe2O3) compared to the historical slags (up to 26.1 wt% of Fe2O3). The zinc content was similar for both the slag types (3.5 wt% Zn). The average titanium and arsenic contents in the old and contemporary slags were at the same level as well, with 0.21 wt% (Ti) and 0.13 wt% (As), respectively. The contemporary slags contained higher levels of critical raw materials, such as cobalt, nickel, copper, and manganese, compared to the historical slags. Rare earth elements (REEs) were also more abundant in the contemporary slags, with an average content of 212 ppm, while the historical slags averaged 124 ppm. These findings underscore the potential for recovering valuable metals and critical raw materials from such slags, presenting opportunities for resource optimisation and environmental management. Full article
(This article belongs to the Special Issue Characterization and Reuse of Slag)
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12 pages, 3660 KiB  
Article
Study on the Optimization of the Preparation Process of ZM5 Magnesium Alloy Micro-Arc Oxidation Hard Ceramic Coatings and Coatings Properties
by Bingchun Jiang, Zejun Wen, Peiwen Wang, Xinting Huang, Xin Yang, Minghua Yuan and Jianjun Xi
Metals 2024, 14(5), 594; https://doi.org/10.3390/met14050594 - 19 May 2024
Cited by 3 | Viewed by 1667
Abstract
Hard ceramic coatings were successfully prepared on the surface of ZM5 magnesium alloy by micro-arc oxidation (MAO) technology in silicate and aluminate electrolytes, respectively. The optimization of hard ceramic coatings prepared in these electrolyte systems was investigated through an orthogonal experimental design. The [...] Read more.
Hard ceramic coatings were successfully prepared on the surface of ZM5 magnesium alloy by micro-arc oxidation (MAO) technology in silicate and aluminate electrolytes, respectively. The optimization of hard ceramic coatings prepared in these electrolyte systems was investigated through an orthogonal experimental design. The microstructure, elemental composition, phase composition, and tribological properties of the coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and tribological testing equipment. The results show that the growth of the hard ceramic coatings is significantly influenced by the different electrolyte systems. Coatings prepared from both systems have shown good wear resistance, with the aluminate electrolyte system being superior to the silicate system in performance. The optimized formulation for the silicate electrolyte solution has been determined to be sodium silicate at 8 g/L, sodium dihydrogen phosphate at 0.2 g/L, sodium tetraborate at 2 g/L, and potassium hydroxide at 1 g/L. The optimized formulation for the aluminate electrolyte solution consists of sodium aluminate at 5 g/L, sodium fluoride at 3 g/L, sodium citrate at 3 g/L, and sodium hydroxide at 0.5 g/L. Full article
(This article belongs to the Special Issue Preparation and Processing Technology of Advanced Magnesium Alloys)
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12 pages, 3777 KiB  
Article
MgAl Oxide Coatings Modified with CeO2 Particles Formed by Plasma Electrolytic Oxidation of AZ31 Magnesium Alloy: Photoluminescent and Photocatalytic Properties
by Stevan Stojadinović and Nenad Radić
Metals 2024, 14(3), 366; https://doi.org/10.3390/met14030366 - 21 Mar 2024
Cited by 6 | Viewed by 1651
Abstract
MgAl oxide coatings composed of MgO and MgAl2O4 phases were doped with CeO2 particles via plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy in a 5 g/L NaAlO2 water solution. Subsequently, particles of CeO2 up to 8 [...] Read more.
MgAl oxide coatings composed of MgO and MgAl2O4 phases were doped with CeO2 particles via plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy in a 5 g/L NaAlO2 water solution. Subsequently, particles of CeO2 up to 8 g/L were added. Extensive investigations were conducted to examine the morphology, the chemical and phase compositions, and, most importantly, the photoluminescent (PL) properties and photocatalytic activity (PA) during the photodegradation of methyl orange. The number of CeO2 particles incorporated into MgAl oxide coatings depends on the concentration of CeO2 particles in the aluminate electrolyte. However, the CeO2 particles do not significantly affect the thickness, phase structure, or surface morphology of the coatings. The PL emission spectrum of MgAl oxide coatings is divided into two bands: one in the 350–600 nm range related to structural defects in MgO, and another much more intense band in the 600–775 nm range attributed to the F+ centres in MgAl2O4. The incorporated CeO2 particles do not have a significant effect on the PL intensity of the band in the red spectral region, but the PL intensity of the first band increases with the concentration of CeO2 particles. The PA of MgAl/CeO2 oxide coatings is higher than that of pure MgAl oxide coatings. The MgAl/CeO2 oxide coating developed in aluminate electrolyte with a concentration of 2 g/L CeO2 particles exhibited the highest PA. The MgAl/CeO2 oxide coatings remained chemically and physically stable across multiple cycles, indicating their potential for applications. Full article
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13 pages, 6307 KiB  
Article
Study on the Causes and Control Measures of Mg–Al Spinel Inclusions in U75V Heavy Rail Steel
by Jun Zhu, Lei Ren and Jichun Yang
Appl. Sci. 2024, 14(5), 1718; https://doi.org/10.3390/app14051718 - 20 Feb 2024
Cited by 2 | Viewed by 1801
Abstract
U75V heavy rail steel production uses an aluminum-free deoxidation process; however, large particles of MgO–Al2O3 inclusions form in the steel, which has a great impact on product quality. In this paper, we try to explain how spinel inclusions, which affect [...] Read more.
U75V heavy rail steel production uses an aluminum-free deoxidation process; however, large particles of MgO–Al2O3 inclusions form in the steel, which has a great impact on product quality. In this paper, we try to explain how spinel inclusions, which affect the metallurgical quality of heavy rail steel, are produced by thermodynamic and experimental methods, and then determined measures for avoiding such inclusions. The formation mechanism of spinel inclusions in U75V heavy rail steel was determined through the analysis of nozzle clogging in the pouring process and typical inclusions in steel. The results show that there are two types of spinel inclusions in heavy rail steel: one is pure Mg–Al spinel inclusions and the other is Mg–Al spinel inclusions coated with calcium aluminate. The small, pure Mg–Al spinel inclusions were precipitated during the solidification of the molten steel, and the precipitation temperature was related to the composition of the molten steel. The large spinel inclusions were derived from clogging of the submersed nozzle. Mg–Al spinel inclusions coated with calcium aluminate were transformed from CaO–SiO2–Al2O3–MgO complex inclusions in the steel during cooling, and the formation temperature was related to the content of Al2O3 and MgO in the inclusions. The content of Al2O3 and MgO in the inclusions was the key to the formation of the Mg–Al spinel inclusions. Therefore, in order to control the production of spinel inclusions in steel, it is necessary to strictly control the content of impurity elements such as magnesium and aluminum in the alloy auxiliary materials, to reduce the secondary oxidation of liquid steel and to reduce the erosion of refractory materials. Full article
(This article belongs to the Section Materials Science and Engineering)
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20 pages, 9195 KiB  
Article
Simultaneously Recovery of Thorium and Tungsten through Hybrid Electrolysis–Nanofiltration Processes
by Geani Teodor Man, Paul Constantin Albu, Aurelia Cristina Nechifor, Alexandra Raluca Grosu, Diana Ionela Popescu (Stegarus), Vlad-Alexandru Grosu, Virgil Emanuel Marinescu and Gheorghe Nechifor
Toxics 2024, 12(2), 103; https://doi.org/10.3390/toxics12020103 - 26 Jan 2024
Cited by 4 | Viewed by 2543
Abstract
The recovery and recycling of metals that generate toxic ions in the environment is of particular importance, especially when these are tungsten and, in particular, thorium. The radioactive element thorium has unexpectedly accessible domestic applications (filaments of light bulbs and electronic tubes, welding [...] Read more.
The recovery and recycling of metals that generate toxic ions in the environment is of particular importance, especially when these are tungsten and, in particular, thorium. The radioactive element thorium has unexpectedly accessible domestic applications (filaments of light bulbs and electronic tubes, welding electrodes, and working alloys containing aluminum and magnesium), which lead to its appearance in electrical and electronic waste from municipal waste management platforms. The current paper proposes the simultaneous recovery of waste containing tungsten and thorium from welding electrodes. Simultaneous recovery is achieved by applying a hybrid membrane electrolysis technology coupled with nanofiltration. An electrolysis cell with sulphonated polyether–ether–ketone membranes (sPEEK) and a nanofiltration module with chitosan–polypropylene membranes (C–PHF–M) are used to carry out the hybrid process. The analysis of welding electrodes led to a composition of W (tungsten) 89.4%; Th 7.1%; O2 2.5%; and Al 1.1%. Thus, the parameters of the electrolysis process were chosen according to the speciation of the three metals suggested by the superimposed Pourbaix diagrams. At a constant potential of 20.0 V and an electrolysis current of 1.0 A, the pH is varied and the possible composition of the solution in the anodic workspace is analyzed. Favorable conditions for both electrolysis and nanofiltration were obtained at pH from 6 to 9, when the soluble tungstate ion, the aluminum hydroxide, and solid thorium dioxide were formed. Through the first nanofiltration, the tungstate ion is obtained in the permeate, and thorium dioxide and aluminum hydroxide in the concentrate. By adding a pH 13 solution over the two precipitates, the aluminum is solubilized as sodium aluminate, which will be found after the second nanofiltration in the permeate, with the thorium dioxide remaining integrally (within an error of ±0.1 ppm) on the C–PHF–M membrane. Full article
(This article belongs to the Section Toxicity Reduction and Environmental Remediation)
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12 pages, 9113 KiB  
Article
Unveiling the Structural and Optical Properties of MgAl2O4 Single Crystals Irradiated by Swift Heavy Ions
by Abdirash Akilbekov, Arseny Kiryakov, Alma Dauletbekova, Gulnara Aralbayeva, Aiman Akylbekova and Zhulduz Ospanova
Materials 2024, 17(2), 344; https://doi.org/10.3390/ma17020344 - 10 Jan 2024
Cited by 3 | Viewed by 1449
Abstract
A synthetic single crystal of magnesium-aluminate spinel was irradiated perpendicularly to the (111) plane with swift heavy xenon ions with an energy of 220 MeV. The modified layer was attested based on Raman scattering spectra recorded while focusing on the surface. A decrease [...] Read more.
A synthetic single crystal of magnesium-aluminate spinel was irradiated perpendicularly to the (111) plane with swift heavy xenon ions with an energy of 220 MeV. The modified layer was attested based on Raman scattering spectra recorded while focusing on the surface. A decrease in surface crystallinity was observed, reflected in the changes in fundamental optical characteristics such as the band gap and the energies of static and dynamic disorder. In this study, we demonstrate, along with the modification of optical characteristics and the formation of a disordered layer, the creation of new optically active centers. The luminescent properties of these centers were analyzed. The effect of temperature flare-up in the 3.4 eV band of the excitation spectrum was determined. The low sensitivity of Cr3+ luminescence to SHI is demonstrated. Full article
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8 pages, 2713 KiB  
Proceeding Paper
Temperature-Dependent Dielectric Studies of Copper-and-Magnesium-Doped Zinc Aluminate: Implications for Electrical Behaviour
by Yasmin Jamil, Gracie. P. Jeyakumar and Geetha Deivasigamani
Eng. Proc. 2023, 56(1), 213; https://doi.org/10.3390/ASEC2023-16270 - 15 Nov 2023
Cited by 1 | Viewed by 804
Abstract
Copper (Cu2+)-and-magnesium (Mg2+)-doped Zinc aluminate ZnAl2O4 is a promising material with diverse applications in electronic and energy storage devices. In this study, the synthesis of Zn0.9MxAl2O4 (M = Cu [...] Read more.
Copper (Cu2+)-and-magnesium (Mg2+)-doped Zinc aluminate ZnAl2O4 is a promising material with diverse applications in electronic and energy storage devices. In this study, the synthesis of Zn0.9MxAl2O4 (M = Cu2+ and Mg2+; x = 0.00 and 0.10) was conducted via the sol–gel combined combustion technique. The structural, spectral, optical and dielectric parameters of the synthesized spinel aluminates were analysed to explore the substitution effect of Cu2+ and Mg2+ content. The formation and crystallinity analyses of the single-phase cubic spinel structure in the synthesized spinel aluminates were confirmed using XRD patterns. The lattice parameter and grain size were ascertained from the XRD data. The crystallite size of Cu2+ and Mg2+ substituted into ZnAl2O4 using Scherrer’s formula was found to be around 22 nm. The spinel structure formations in the prepared spinel aluminates were ascertained through an FT-IR study. The UV-Vis spectra exhibited a broad absorption band in the UV-Vis region, indicating the presence of electronic transitions. The band gap energy of the prepared aluminates was estimated from the absorption edge, with values varying between 2.90 eV and 3.03 eV, revealing its suitability for optoelectronic applications. Measurement of the dielectric parameters was performed in the frequency range of 100 Hz to 20 MHz at temperatures ranging from 30 °C to 250 °C. The dielectric constant (ε′) and dielectric loss (ε”) were determined as a function of frequency at different temperatures. The results showed that the dielectric constant decreased with increasing frequency for all the observed temperatures, while the dielectric loss exhibited a peak at a specific temperature. The conductivity results indicate that the conduction mechanism occurred due to polaron hopping. The Arrhenius relation was adopted to calculate the activation energies Ea for all the samples, and the values were between 0.70 eV and 0.38 eV. The obtained results were discussed and interpreted. These findings contribute to our understanding of the electrical behaviour of doped zinc aluminate materials and their useful applications in different electronic and energy systems. Full article
(This article belongs to the Proceedings of The 4th International Electronic Conference on Applied Sciences)
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12 pages, 5200 KiB  
Article
Optical Characteristics of MgAl2O4 Single Crystals Irradiated by 220 MeV Xe Ions
by Abdirash Akilbekov, Arseny Kiryakov, Guldar Baubekova, Gulnara Aralbayeva, Alma Dauletbekova, Aiman Akylbekova, Zhulduz Ospanova and Anatoli I. Popov
Materials 2023, 16(19), 6414; https://doi.org/10.3390/ma16196414 - 26 Sep 2023
Cited by 6 | Viewed by 2462
Abstract
In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: [...] Read more.
In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: transmission spectra in the IR region (190–7000) nm, optical absorption spectra in the range (1.2–6.5) eV, and Raman spectra were measured along the depth of ion penetration from the surface to 30 µm. A peak with a broad shape at approximately 5.3 eV can be observed in the optical absorption spectrum of irradiated spinel crystals. This band is linked to the electronic color centers of F+ and F. Meanwhile, the band with a maximum at ~(3–4) eV is attributed to hole color centers. Apart from the typical Raman modes of an unirradiated crystal, additional modes, A1g* (720 cm−1), and Eg* (385 cm−1), manifested mainly as an asymmetric shoulder of the main Eg mode, are also observed. In addition, the Raman spectroscopy method showed that the greatest disordering of crystallinity occurs in the near-surface layer up to 4 μm thick. At the same time, Raman scattering spectroscopy is sensitive to structural changes almost up to the simulated value of the modified layer, which is an excellent express method for certifying the structural properties of crystals modified by swift heavy ions. Full article
(This article belongs to the Section Optical and Photonic Materials)
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25 pages, 14686 KiB  
Article
Evaluation of Slag Foaming Behavior Using Renewable Carbon Sources in Electric Arc Furnace-Based Steel Production
by Lina Kieush, Johannes Schenk, Andrii Koveria, Andrii Hrubiak, Horst Hopfinger and Heng Zheng
Energies 2023, 16(12), 4673; https://doi.org/10.3390/en16124673 - 12 Jun 2023
Cited by 19 | Viewed by 3571
Abstract
The influence of different carbon sources, including anthracite, calcined petroleum coke, three samples of high-temperature coke, biochar, and a mixture of 50 wt.% biochar and 50 wt.% coke, on slag foaming behavior was studied. The slag’s composition was set to FeO-CaO-Al2O [...] Read more.
The influence of different carbon sources, including anthracite, calcined petroleum coke, three samples of high-temperature coke, biochar, and a mixture of 50 wt.% biochar and 50 wt.% coke, on slag foaming behavior was studied. The slag’s composition was set to FeO-CaO-Al2O3-MgO-SiO2, and the temperature for slag foaming was 1600 °C. The effect of the carbon sources was evaluated using foaming characteristics (foam height, foam volume, relative foaming height, and gas fraction), X-ray diffraction (XRD), chemical analysis of the slag foams, Mossbauer spectroscopy, observation by scanning electron microscope (SEM), and energy-dispersive spectroscopy (EDS) mapping. Different foaming phenomena were found among conventional sources, biochar as a single source, and the mixture of coke and biochar. Biochar showed the most inferior foaming characteristics compared to the other studied carbon sources. Nevertheless, the slag foaming process was improved and showed slag foaming characteristics similar to results obtained using conventional carbon sources when the mixture of 50 wt.% coke and 50 wt.% biochar was used. The XRD analysis revealed a difference between the top and bottom of the slag foams. In almost all cases, a maghemite crystalline phase was detected at the top of the slag foams, indicating oxidation; metallic iron was found at the bottom. Furthermore, a difference in the slag foam (mixture of coke and biochar) was found in the presence of such crystalline phases as magnesium iron oxide (Fe2MgO4) and magnetite (Mg0.4Fe2.96O4). Notwithstanding the carbon source applied, a layer between the foam slag and the crucible wall was found in many samples. Based on the SEM/EDS and XRD results, it was assumed this layer consists of gehlenite (Ca2(Al(AlSi)O7) and two spinels: magnesium aluminate (MgAl2O4) and magnesium iron oxide (Fe2MgO4). Full article
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19 pages, 84491 KiB  
Article
Mechanical Behavior of Transparent Spinel Fabricated by Spark Plasma Sintering
by Khadidja Hoggas, Salim Benaissa, Abdelbaki Cherouana, Sofiane Bouheroum, Abdenacer Assali, Mohamed Hamidouche and Gilbert Fantozzi
Ceramics 2023, 6(2), 1191-1209; https://doi.org/10.3390/ceramics6020072 - 31 May 2023
Cited by 7 | Viewed by 2914
Abstract
In this work, a transparent nanostructured ceramic magnesium aluminate spinel (MgAl2O4) was fabricated by Spark Plasma Sintering (SPS) from commercial spinel nano-powders at different temperatures (1300, 1350 and 1400 °C). The sintered samples were thoroughly examined to assess their [...] Read more.
In this work, a transparent nanostructured ceramic magnesium aluminate spinel (MgAl2O4) was fabricated by Spark Plasma Sintering (SPS) from commercial spinel nano-powders at different temperatures (1300, 1350 and 1400 °C). The sintered samples were thoroughly examined to assess their microstructural, optical, and mechanical properties. Various techniques such as SEM, AFM, spectrophotometer with an integrating sphere, instrumented Vickers indenter, Pin-on-Disk tribometer, scratch tester, and sandblasting device were employed to characterize the sintered samples. The results indicated the significant impact of the sintering temperature on the properties of the spinel samples. Particularly, the samples sintered at T = 1350 °C exhibited the highest Real In-line Transmission (RIT = 72% at 550 nm and 80% at 1000 nm). These samples demonstrated the highest hardness value (HV = 16.7 GPa) compared to those sintered at 1300 °C (HV = 15.6 GPa) and 1400 °C (HV = 15.1 GPa). The measured fracture toughness of the sintered samples increased substantially with increasing sintering temperature. Similarly, the tribological study revealed that the friction coefficient of the sintered spinel samples increased with the sintering temperature, and the spinel sintered at 1350 °C exhibited the lowest wear rate. Additionally, sandblasting and scratch tests confirmed the significant influence of the sintering temperature on the mechanical properties of the fabricated spinels. Overall, the spinel sintered at 1350 °C presented the best compromise in terms of all the evaluated properties. Full article
(This article belongs to the Special Issue Transparent Ceramics—a Theme Issue in Honor of Dr. Adrian Goldstein)
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15 pages, 10194 KiB  
Article
Preparation and Characterization of Polyethersulfone-Ultrafiltration Membrane Blended with Terbium-Doped Cerium Magnesium Aluminate: Analysis of Fouling Behavior
by Gouled Aouled, Saleem Raza, Ehsan Ghasali, Asif Hayat and Yasin Orooji
Molecules 2023, 28(6), 2688; https://doi.org/10.3390/molecules28062688 - 16 Mar 2023
Cited by 6 | Viewed by 3107
Abstract
In this study, various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and water-contact-angle goniometry (WCAG), were used to characterize the crystalline structure and morphological properties of terbium-doped [...] Read more.
In this study, various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and water-contact-angle goniometry (WCAG), were used to characterize the crystalline structure and morphological properties of terbium-doped cerium magnesium aluminate (Ce0.67Tb0.33MgAl11O19 or CMAT) in powder form. The results demonstrated that CMAT was successfully synthesized with a particle size of less than 5 µm and a fully evident distribution of elements, as revealed by the SEM images. This was further confirmed by the XRD and HRTEM images. XPS analysis confirmed the presence of all necessary components in CMAT. Additionally, WCAG results showed that the contact angle of CMAT was more hydrophilic with a value of 8.4°. To evaluate its performance, CMAT particles were dispersed in a Polyethersulfone (PES) solution and used to modify a PES ultrafiltration membrane through a phase-inversion method. The resulting membranes were characterized by SEM, atomic force microscopy (AFM), thermogravimetric analysis (TGA), WCAG, and permeability performance and fouling experiments. The addition of CMAT to the PES membranes did not have a significant effect on the structure of the SEM images of the top layer and cross-section of surface properties. However, increasing the concentration of CMAT improved the membrane surface roughness in AFM, and the modified membranes had the ability to resist fouling. The addition of CMAT did not lead to significant energy loss, indicating that the heat flux loss observed can indeed be explained by the amount of C-OH on the PES membrane’s surface. The contact angle of the membranes became more hydrophilic with increasing concentration of CMAT from PES G0 to PES G7. The PES origin membrane showed a higher permeation than the membranes mixed with CMAT, and the modified membranes with CMAT displayed significant fouling resistance. Full article
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16 pages, 3880 KiB  
Article
Urban Exotic Pollution: The Harmful Environmental Footprint for Health and Historical Architecture
by Cristina Postolachi, Alexandru Cocean, Silvia Garofalide, Bogdanel Silvestru Munteanu, Georgiana Cocean, Nicanor Cimpoesu, Vasile Pelin, Iuliana Cocean and Silviu Gurlui
Int. J. Environ. Res. Public Health 2023, 20(6), 4715; https://doi.org/10.3390/ijerph20064715 - 7 Mar 2023
Viewed by 1805
Abstract
The study in this paper was carried out as a result of the observation of pollution phenomena and foaming effects associated with anthropogenic activities, including street cleaning activity. The processes of dust binding used in order to reduce PM10 and PM 2.5 pollution [...] Read more.
The study in this paper was carried out as a result of the observation of pollution phenomena and foaming effects associated with anthropogenic activities, including street cleaning activity. The processes of dust binding used in order to reduce PM10 and PM 2.5 pollution has been proven to be inefficient, and even contributing to pollution with particulate matter. Our results suggest that the use of dust binders must be integrated in a technique that includes methods of removing agglomerated particle structures resulting from the process of coagulation or flocculation. These are the conclusions of the investigations carried out by spectroscopic methods (FTIR, SEM-EDX) on samples collected from the streets of Iasi on 10 March 2021, and on samples collected from the surface of the Precinct Wall of the historical monument Golia—Iasi Monastery Ensemble (Romania). On the later samples, coloristic analysis was also performed. The alert for investigation was given by the foaming waters that were leaking on the streets. The phenomenon was observed after the streets had been washed by specialized vehicles. Analyses revealed compounds used as dust binders and coagulant type (aluminum sulfate, sodium aluminate and their derivatives, plus anti-skid chemicals such as calcium chlorine and magnesium chlorine), as well as organic compounds included in aggregate type structures, and they showed contamination of the Golia Precinct Wall. The results show that the dust binders or coagulants used as such, or embedded in various products intended for the cleaning process of streets or other outdoor public places, must be subject to regulation. Otherwise, there is a risk of adding more pollutants during an operation with the opposite purpose. The migration of these pollutants on the studied building offers an image on how both our health and all constructions and equipment exposed in the open air are affected. Full article
(This article belongs to the Section Environmental Science and Engineering)
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11 pages, 1550 KiB  
Article
Solid-State Transformations of Mayenite and Core-Shell Structures of C12A7@C Type at High Pressure, High Temperature Conditions
by Sergey A. Gromilov, Anatoly I. Chepurov, Alexander M. Volodin and Aleksey A. Vedyagin
Materials 2023, 16(5), 2083; https://doi.org/10.3390/ma16052083 - 3 Mar 2023
Cited by 3 | Viewed by 2068
Abstract
Calcium aluminate of a mayenite structure, 12CaO∙7Al2O3 (C12A7), is widely applicable in many fields of modern science and technology. Therefore, its behavior under various experimental conditions is of special interest. The present research aimed to estimate the possible impact of [...] Read more.
Calcium aluminate of a mayenite structure, 12CaO∙7Al2O3 (C12A7), is widely applicable in many fields of modern science and technology. Therefore, its behavior under various experimental conditions is of special interest. The present research aimed to estimate the possible impact of the carbon shell in core-shell materials of C12A7@C type on the proceeding of solid-state reactions of mayenite with graphite and magnesium oxide under High Pressure, High Temperature (HPHT) conditions. The phase composition of the solid-state products formed at a pressure of 4 GPa and temperature of 1450 °C was studied. As is found, the interaction of mayenite with graphite under such conditions is accompanied by the formation of an aluminum-rich phase of the CaO∙6Al2O3 composition, while in the case of core-shell structure (C12A7@C), the same interaction does not lead to the formation of such a single phase. For this system, a number of hardly identified calcium aluminate phases along with the carbide-like phrases have appeared. The main product of the interaction of mayenite and C12A7@C with MgO under HPHT conditions is the spinel phase Al2MgO4. This indicates that, in the case of the C12A7@C structure, the carbon shell is not able to prevent the interaction of the oxide mayenite core with magnesium oxide located outside the carbon shell. Nevertheless, the other solid-state products accompanying the spinel formation are significantly different for the cases of pure C12A7 and C12A7@C core-shell structure. The obtained results clearly illustrate that the HPHT conditions used in these experiments lead to the complete destruction of the mayenite structure and the formation of new phases, which compositions differ noticeably depending on the precursor used—pure mayenite or C12A7@C core-shell structure. Full article
(This article belongs to the Special Issue Nonconventional Technology in Materials Processing-Volume 2)
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