Mixed Oxides NiO/ZnO/Al2O3 Synthesized in a Single Step via Ultrasonic Spray Pyrolysis (USP) Method

Mixed oxides have received remarkable attention due to the many opportunities to adjust their interesting structural, electrical, catalytic properties, leading to a better, more useful performance compared to the basic metal oxides. In this study, mixed oxides NiO/ZnO/Al2O3 were synthesized in a single step via the ultrasonic spray pyrolysis method using nitrate salts, and the temperature effects of the process were investigated (400, 600, 800 °C). The synthesized samples were characterized by means of scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and Raman spectroscopy analyses. The results showed Al2O3, NiO–Al2O3 and ZnO–Al2O3 systems with spinel phases. Furthermore, the Raman peaks supported the coexistence of oxide phases, which strongly impact the overall properties of nanocomposite.

CATALYTIC PROPERTIES IN THE HETEROGENEOUS FENTON REACTION OF THE SURFACE OF NANOPOROUS IRON OBTAINED BY ELECTROCHEMICAL DEALOIYNG IN MELTED CHLORIDE MIXTURES

Исследованы образцы частично окисленного микро- и нанопористого железа, полученного методом высокотемпературного деаллоинга железо-марганцевого сплава в солевом расплаве. При помощи электронной микроскопии получены данные о морфологии образцов и составе их поверхности, установлено, что уже после отмывки при комнатной температуре на воздухе образовались оксидные фазы железа в виде вискеров толщиной порядка 10 нм. В ходе получения образцов достигалось количественное удаление марганца из исходного сплава. Оценена каталитическая активность полученных образцов в гетерогенной реакции Фентона по окислению красителя метилового оранжевого пероксидом водорода. На первом этапе протекания реакции, описываемой уравнением реакции первого порядка, ее скорость определялась наиболее активной расходуемой частью образцов, далее реакция переходила в стационарный режим. Более высокой каталитической активностью обладали нанопористые образцы. The samples of partially oxidized micro- and nanoporous iron obtained by high-temperature dealloing of an iron-manganese alloy in a molten salt were investigated. The data concerning the structure of the samples and the composition of their surface were obtained by electron microscopy; it was found that after washing at room temperature in air the oxide phases of iron were formed as whiskers with a thickness of about 10 nm. During the preparation of the samples a quantitative removal of manganese from the initial alloy was achieved. The catalytic activity of the obtained samples in the heterogeneous Fenton reaction was estimated by oxidation of methyl orange by hydrogen peroxide. The rate of the first stage of the reaction, which was described by the first-order equation, was determined by the most active spent part of the samples, and then the reaction passed into the stationary mode. The nanoporous samples possessed a higher catalytic activity.

Platinum-Group Minerals in the Placer of the Kitoy River, East Sayan, Russia

The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os‑Ir‑Ru alloys with a pronounced ruthenium trend. Many of the Os‑Ir‑Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites.

Synthesis and Characterization of α-Fe2O3 Nanoparticles Prepared by PLD at Different Laser Energies

In this paper, ferric oxide nanoparticles) Fe2O3 NPs( were synthesized directly on a quartz substrate in vacuum by pulse laser deposition technique using Nd:YAG laser at different energies (171, 201,363 mJ/pulse). The slides were then heated to 700o C for 1 hour. The structural, optical, morphological, and electrical properties were studied. The optical properties indicated that the prepared thin films have an energy gap ranging from 2.28 to 2.04 eV. The XRD results showed no lattice impurities for other iron oxide phases, confirming that all particles were transformed into the α-Fe2O3 phase during the heating process. The AFM results indicated the dependence of nanoparticles size on the laser energy. As the laser energy increased, the average grain size increased from 72.6 nm to 79.02 nm. Hall effect measurement indicated that the film was an n-type semiconductor.

Can Empirical Biplots Predict High Entropy Oxide Phases?

High entropy oxides are entropy-stabilised oxides that adopt specific disordered structures due to entropy stabilisation. They are a new class of materials that utilises the high-entropy concept first discovered in metallic alloys. They can have interesting properties due to the interactions at the electronic level and can be combined with other materials to make composite structures. The design of new meta-materials that utilise this concept to solve real-world problems may be a possibility but further understanding of how their phase stabilisation is required. In this work, biplots of the composition’s mean electronegativity are plotted against the electron-per-atom ratio of the compounds. The test dataset accuracy in the resulting biplots improves from 78% to 100% when using atomic-number-per-atom Z/a ratios as a biplot parameter. Phase stability maps were constructed using a Voronoi tessellation. This can be of use in determining stability at composite material interfaces.

Systematic study of the synthesis of nanostructured multiferroic films and their structural, electronic and magnetic properties

<p>Multiferroics are unique materials that display multiple ferroic properties (ferroelectricity, ferromagnetism and ferroelasticity) simultaneously. A number of materials containing bismuth have intrinsic multiferroic properties, including BiFeO₃ and BiCrO₃. Among them, BiFeO₃ has attracted widespread attention because BiFeO₃ was the first material to display multiferroic behaviour at ambient temperature. A weak ferromagnetism occurs only at low temperatures depending on synthesis conditions. This thesis reports the structural, magnetic and optical properties of nanostructured BiFeO₃ thin films prepared by two novel approaches of ion beam sputtering and ion implantation techniques. Nanocrystalline BiFeO₃ films were prepared at ambient temperature by sputtering and thermal annealing at 500 °C in an oxygen atmosphere. The annealing resulted in the formation of multiferroic BiFeO₃ phase with a reduction of iron oxide and bismuth phases. Superparamagnetism was observed and could be attributed to magnetite and maghemite nanoparticles. The magnetic properties were mainly due to magnetite and maghemite nanoparticles. The saturation magnetic moment was 60% lower after annealing, which was due to Fe in phases of iron oxide being incorporated into BiFeO₃ nanoparticles. An exchange bias was observed before and after annealing. The exchange bias cannot be attributed to BiFeO₃ structure. Instead, the exchange has likely arisen from magnetite and maghemite cores with spin-disordered shells. Piezoelectric responses measured by piezoelectric force microscopy confirmed the presence of BiFeO₃ ferroelectric material. The Magneto-optical Kerr effect (MOKE) and optical studies were used to calculate an anomalously high Verdet constant. The MOKE and magnetic circular dichroism (MCD) displayed a significant modification in function of the wavelength. Further increasing the annealing temperature lead to an increase in iron oxide phases, while increasing the annealing duration reduced the iron oxide phases, however this increases the fraction of Bi₂Fe₄O₉ and Bi₂O₃. Another approach to synthesise BiFeO₃ thin film was investigated by bismuth ion implantation into iron oxide thin film. An as-made iron oxide film subsequently implanted with bismuth and annealed showed a 6.5% reduction of the ferromagnetic phase fraction. An annealed iron oxide film subsequently implanted with bismuth and annealed show that the ferromagnetic phase was present at less than 4% while Fe₃O₄ and γ-Fe₂O₃ increased to 7%. The coercive field is affected by annealing. However, this field is not affected by the bismuth implantation. For the first-time, a preliminary investigation reporting the implantation of Bi then Fe then O into SiO₂:Si was made with the aim to synthesise BiFeO₃ films and magnetic nanoparticles. The implantation of Fe then O then Bi into SiO₂:Si contained a mix of iron oxides: α-Fe₂O₃ and Fe₃O₄, as confirmed by Raman spectroscopy and X-ray diffraction, while γ-Fe₂O₃ was most likely also present in the film. The as-implanted sample displayed a sign of a superparamagnetic phase that was lost with annealing the sample. Preliminary investigations of another multiferroic material, BiCrO₃, were carried out. Thin films of BiCrO₃ were prepared by ion beam sputtering and annealing the sample in an oxygen atmosphere which lead to BiCrxOy with chromium oxides and bismuth oxide phases. Magnetic enhancement was observed when annealing above 700 °C. Annealing in an oxygen atmosphere followed by an argon atmosphere created a superparamagnetic phase that was not visible under other annealing conditions.</p>

Systematic study of the synthesis of nanostructured multiferroic films and their structural, electronic and magnetic properties

<p>Multiferroics are unique materials that display multiple ferroic properties (ferroelectricity, ferromagnetism and ferroelasticity) simultaneously. A number of materials containing bismuth have intrinsic multiferroic properties, including BiFeO₃ and BiCrO₃. Among them, BiFeO₃ has attracted widespread attention because BiFeO₃ was the first material to display multiferroic behaviour at ambient temperature. A weak ferromagnetism occurs only at low temperatures depending on synthesis conditions. This thesis reports the structural, magnetic and optical properties of nanostructured BiFeO₃ thin films prepared by two novel approaches of ion beam sputtering and ion implantation techniques. Nanocrystalline BiFeO₃ films were prepared at ambient temperature by sputtering and thermal annealing at 500 °C in an oxygen atmosphere. The annealing resulted in the formation of multiferroic BiFeO₃ phase with a reduction of iron oxide and bismuth phases. Superparamagnetism was observed and could be attributed to magnetite and maghemite nanoparticles. The magnetic properties were mainly due to magnetite and maghemite nanoparticles. The saturation magnetic moment was 60% lower after annealing, which was due to Fe in phases of iron oxide being incorporated into BiFeO₃ nanoparticles. An exchange bias was observed before and after annealing. The exchange bias cannot be attributed to BiFeO₃ structure. Instead, the exchange has likely arisen from magnetite and maghemite cores with spin-disordered shells. Piezoelectric responses measured by piezoelectric force microscopy confirmed the presence of BiFeO₃ ferroelectric material. The Magneto-optical Kerr effect (MOKE) and optical studies were used to calculate an anomalously high Verdet constant. The MOKE and magnetic circular dichroism (MCD) displayed a significant modification in function of the wavelength. Further increasing the annealing temperature lead to an increase in iron oxide phases, while increasing the annealing duration reduced the iron oxide phases, however this increases the fraction of Bi₂Fe₄O₉ and Bi₂O₃. Another approach to synthesise BiFeO₃ thin film was investigated by bismuth ion implantation into iron oxide thin film. An as-made iron oxide film subsequently implanted with bismuth and annealed showed a 6.5% reduction of the ferromagnetic phase fraction. An annealed iron oxide film subsequently implanted with bismuth and annealed show that the ferromagnetic phase was present at less than 4% while Fe₃O₄ and γ-Fe₂O₃ increased to 7%. The coercive field is affected by annealing. However, this field is not affected by the bismuth implantation. For the first-time, a preliminary investigation reporting the implantation of Bi then Fe then O into SiO₂:Si was made with the aim to synthesise BiFeO₃ films and magnetic nanoparticles. The implantation of Fe then O then Bi into SiO₂:Si contained a mix of iron oxides: α-Fe₂O₃ and Fe₃O₄, as confirmed by Raman spectroscopy and X-ray diffraction, while γ-Fe₂O₃ was most likely also present in the film. The as-implanted sample displayed a sign of a superparamagnetic phase that was lost with annealing the sample. Preliminary investigations of another multiferroic material, BiCrO₃, were carried out. Thin films of BiCrO₃ were prepared by ion beam sputtering and annealing the sample in an oxygen atmosphere which lead to BiCrxOy with chromium oxides and bismuth oxide phases. Magnetic enhancement was observed when annealing above 700 °C. Annealing in an oxygen atmosphere followed by an argon atmosphere created a superparamagnetic phase that was not visible under other annealing conditions.</p>

Rare Earth Elements Enrichment in the Upper Eocene Tošići-Dujići Bauxite Deposit, Croatia, and Relation to REE Mineralogy, Parent Material and Weathering Pattern

Tošići-Dujići bauxite deposit, situated in Dalmatian inlands, Croatia, contains minor remaining bauxite reserves. The deposit lies on Lower Eocene foraminiferal limestone and is covered by Upper Eocene Promina sediments. Bauxite samples were analyzed for textural, mineralogical, and geochemical features in order to determine absolute REE abundances and their relation to mineralogy, as well as to devise the origin of REE enrichment and to trace weathering and bauxitization paths of the parent material. The samples show total REE abundances up to 3500 mg/kg with significant HREE enrichment in some cases. All samples are gibbsitic with hematite and anatase as major phases. Kaolinite occurs in most of the samples, and goethite, böhmite, and nordstrandite are minor phases. Monazite-(Ce) and xenotime-(Y) were identified as detrital REE minerals as well as authigenic florencite-(Ce). In the REE most abundant sample, REE are most likely bound to Fe- and Ti-oxide phases as suggested by correlation analysis. Chemical weathering proxies show intensive weathering. Geochemical and textural data imply that the REE enrichment is influenced by intensive weathering (CIA 97.87–99.26) of detrital material, and also by possible deposition/redeposition of residual material potentially derived and mobilized from various sedimentary rocks of the area.

Coupling effect of temperature and Cr content on the steam oxidation of Ni-Fe-Cr alloys

Excellent resistance to steam oxidation is a key required property for heat-resistant alloys used in next-generation fossil power plants. In order to clarify the degradation mechanism of Ni-Fe-Cr alloys in high temperature steam, four kinds of Ni-Fe-Cr model alloys with various Cr content were prepared and their long-term steam oxidation were investigated at 650 oC and 700 oC. The microstructure and composition of oxide scales were characterized by SEM equipped with EDS, and the oxide phases were identified by XRD. The results showed significant dependence of temperature and Cr content in alloys on the oxidation kinetics, cross-section morphology and elemental section-distribution. For Ni-Fe-Cr alloys with low Cr contents (12~16 wt.%), the increase of temperature made the oxide scale change from breakaway scale morphology (nodule-crater microstructure with external exfoliation) to protective scale morphology (uniform layer and internal oxidation). For Ni-Fe-Cr alloy with 18wt.% Cr, the effect of temperature was greatly reduced. The oxidation mechanism was discussed from the perspectives of selective oxidation and the effect of alloying elements.

Tungsten-Based Cost-Effective Gas Sensors for H2S Detection

Tungsten trioxide thin films were deposited on silicon substrates by non-reactive RF sputtering from a WO3 target at room temperature. The WO3 films were post-annealed at two different temperatures, 400 °C and 500 °C. The morphological and microstructural properties of these films were analyzed by using atomic force microscopy and X-ray diffraction. X-ray diffraction patterns only show WO3 oxide phases. The AFM images show different morphologies with smaller grains for the film annealed at 400 °C. WO3 sensing films and W heating elements were embedded in commercial cases for the fabrication of cost-effective gas sensors. The sensitivity and dynamic response of the sensors were analyzed under various concentrations of H2S, from 20 to 100 ppm, at SIMTRONICS SAS (3M Company, Saint Paul, MN, USA). A good sensitivity G/G0 of about 6.6 under H2S 100 ppm was obtained with the best sensor. An interesting dynamic response was observed in particular with a short response time. Additionally, the evolution of the sensitivity was studied, and a conduction model was proposed for explaining the conduction mechanism under H2S exposition.