Stoichiometric Composition Research Articles

A comparative study of electric current-assisted and conventional sintering of Inconel 718 superalloy

AbstractIn this study, In718 powder mixtures prepared from elemental powders following stoichiometric composition and supplied as a commercial product were produced by conventional powder metallurgy (1300 °C/4 h) and electric current-assisted sintering (ECAS)(1700-2300A/10 min) methods and followed by a double-aging heat treatment. The characterization studies determined that the best results were the sample produced by the ECAS method using the elemental powder mixture. The targeted precipitate γ′, γ″, and δ phases were obtained after the heat treatment, and a hardness value of 344 ± 41 HV0.5 and a relative density of 98.96% were achieved. The sample preserved its surface integrity by exhibiting high corrosion resistance from hot corrosion studies in the temperature range of 650–850 °C and NaSO4 + 60%V2O5 environment. The corrosion rate of the sample, which was subjected to electrochemical corrosion tests in 3.5% NaCl and 10% NaNO3 solutions, was determined as 45.59 mpy and 10.56 mpy, respectively.

Hydrothermal Synthesis of CuO/WO3 Hybrid Bifunctional Composites with Unprecedented Dark Adsorption and Photocatalysis

AbstractThis study presents the synthesis and characterization of Copper Oxide/Tungsten Oxide (CuO/WO3) hybrid bifunctional composites using a hydrothermal approach. X‐ray diffraction (XRD) analysis confirms the successful synthesis of CuO/WO3 hybrids, exhibiting additional peaks corresponding to WO3 phases. Scanning electron microscopy (SEM) images reveal well‐defined, aggregated particles with a nanoscale pattern and uniform distribution of CuO and WO3 throughout the composite. Energy‐dispersive X‐ray spectroscopy (EDX) confirms the stoichiometric composition of CuO/WO3 hybrids. Evaluation of dark adsorption and sunlight‐assisted photocatalysis using methylene blue (MB) dyes shows a remarkable enhancement in efficiency compared to pristine CuO. The CuO/WO3 hybrids exhibit a dark adsorption capacity of 87 % and a photocatalytic degradation efficiency of 95 % under sunlight illumination, outperforming pure CuO. These results underscore the synergistic interaction between CuO and WO3, facilitating efficient pollutant removal. The study elucidates the structural properties and mechanistic insights driving the superior performance of CuO/WO3 hybrid composites, offering promising prospects for advanced water treatment technologies.

Red Photoluminescence from Fe-Doped MgAl2O4 Crystals

Abstract The influence of variations in composition (x = MgO/Al2O3 = 0.3–1.0), Fe2O3 concentrations (0.05 mol%–2.0 mol%), and O2 concentrations (100 vol% and 0 vol%) in the atmosphere on the PL characteristics of Fe-doped MgAl2O4 crystals were investigated using single phase spinel crystals grown by FZ technique. The peak wavelength shift of photoluminescence at around 730 nm are observed depending on the Fe2O3 concentration and composition. Concentration quenching of red PL occurred at Fe2O3 concentration above 0.1 mol%. PL intensity was higher in samples grown in 100 vol% O2 compared to those grown in 100 vol% Ar. PL intensity from Fe-doped MgAl2O4 increased with increasing compositions x from 0.3 to 1.0. MgAl2O4 doped with 0.1 mol% Fe2O3, and a stoichiometric composition (x = 1.0) grown in 100 vol% O2, demonstrated strong red PL with ultraviolet-C (UVC) lights excitation.

Production of High-Coercive nanostructured ND-fE-B alloy by chemical method

For the first time, a nanostructured alloy powder with high coercive force was obtained by a chemical method without the addition of Dy, which can compete with physical methods of production. The work carried out a study of the influence of stoichiometric composition on the magnetic properties of nanostructured Nd-Fe-B alloys. Alloys with different contents of Nd, Fe, and B were synthesized: Nd12Fe84B6, Nd14Fe80B6, Nd16Fe76B8, and Nd16Fe72B8. With a decrease in the iron content in the first two compositions, a decrease in the iron content in the soft magnetic phase α-Fe was observed, which led to an increase in the coercive force Hc and a decrease in the values of Ms and Mr. Experiments have shown that an increase in the content of Nd and B promotes the formation of the hard magnetic phase Nd2Fe14B and an increase in the coercive force. For example, the nanostructured Nd16Fe76B8 alloy demonstrated a maximum coercive force of Hc = 8439 Oe, while compensating for the values of Ms (109 emu*g−1) and Mr (78 emu*g−1). A comprehensive study of the nanostructured Nd16Fe76B8 alloy was carried out, including structural analysis. XRD using FullProff and Vesta software revealed the tetragonal crystal structure of the Nd2Fe14B phase, providing details of the atomic arrangement. The unit cell contains four layers with Nd and Fe atoms, and boron atoms are embedded in the center of the octahedron of Nd and Fe atoms, playing an important role in the magnetic exchange interaction. The results of Mössbauer spectroscopy confirmed the presence of the Nd2Fe14B phase and revealed details of the state of Fe atoms in the structure of six sextets.

Demonstration of high-impedance superconducting NbRe Dayem bridges

Here, we demonstrate superconducting Dayem-bridge weak-links made of different stoichiometric compositions of NbRe. Our devices possess a relatively high critical temperature, normal-state resistance, and kinetic inductance. In particular, the high kinetic inductance makes this material a good alternative to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the realization of superinductors and high-quality factor resonators, whereas the high normal-state resistance yields a large output voltage in superconducting switches and logic elements realized upon this compound. Moreover, out-of-plane critical magnetic fields exceeding 2 T ensure that possible applications requiring high magnetic fields can also be envisaged. Altogether, these features make this material appealing for a number of applications in the framework of quantum technologies.

Microstructural characterisation and compound formation in rapidly solidified SiGe alloy

Severe Ge segregation to grain boundaries was observed in a Si–14.2 at% Ge thermoelectric alloy rapidly solidified using a drop-tube facility, manifesting itself as a series of regions with uniform stoichiometric compositions. The step change in composition at the interface between adjacent regions was ascribed to the formation of different SiGe pseudocompounds and contradicted the accepted thermodynamic description of the SiGe system as a continuous random solid solution. Rapid solidification increased, rather than decreased, the inhomogeneity degree of the solid product, and the Ge content of the most Ge-rich regions was positively correlated with the cooling rate, which suggested the absence of solute trapping. The transmission electron microscopy/selected area electron diffraction analysis of the most Ge-rich regions revealed superlattice spots indicative of chemical ordering. However, simple chemical ordering within a single diamond cubic unit cell could not explain the fact that most stoichiometries had compositions that were multiples of 5 at% Ge, which indicated the presence of superstructural ordering.

High-temperature CO2 sorption over Li4SiO4 synthesized from diatomite: study of sorption heat and isotherm modeling.

The Li4SiO4 seems to be an excellent sorbent for CO2 capture at post-combustion. Our work contributes to understanding the effect of the natural Algerian diatomite as a source of SiO2 in the synthesis of Li4SiO4 for CO2 capture at high temperature. For this purpose, we use various molar % (stoichiometric and excess) of calcined natural diatomite and pure SiO2. To select the best composition, CO2 sorption isotherms at 500°C on the prepared Li4SiO4 are obtained using TGA measurements under various flows of CO2 in N2. The sorbent having 10% molar SiO2 in diatomite (10%ND-LS) exhibits the best CO2 uptake, probably due to various factors such as the content of the different secondary phases. A comparative study was performed at 400 to 500°C on this selected 10%ND-LS and those with stoichiometric composition obtained with diatomite and pure SiO2. The obtained isotherms show the endothermic character of CO2 sorption. In addition, the evolution of isosteric heat highlights the nature of the involved CO2/Li4SiO4 interactions, by considering the double-shell mechanism. Finally, the experimental sorption isotherms are confronted with some well-known adsorption models to explain the phenomenon occurring over our prepared sorbents. Freundlich and Jensen-Seaton models present a better correlation with the experimental results.

Influence of Sulfurization Time on Sb2S3 Synthesis Using a New Graphite Box Design.

In recent years, antimony sulfide (Sb2S3) has been investigated as a photovoltaic absorber material due to its suitable absorber coefficient, direct band gap, extinction coefficient, earth-abundant, and environmentally friendly constituents. Therefore, this work proposes Sb2S3 film preparation by an effective two-step process using a new graphite box design and sulfur distribution, which has a high repeatability level and can be scalable. First, an Sb thin film was deposited using the RF-Sputtering technique, and after that, the samples were annealed with elemental sulfur into a graphite box, varying the sulfurization time from 20 to 50 min. The structural, optical, morphological, and chemical characteristics of the resulting thin films were analyzed. Results reveal the method's effectivity and the best properties were obtained for the sample sulfurized during 40 min. This Sb2S3 thin film presents an orthorhombic crystalline structure, elongated grains, a band gap of 1.69 eV, a crystallite size of 15.25 Å, and a nearly stoichiometric composition. In addition, the formation of a p-n junction was achieved by depositing silver back contact on the Glass/FTO/CdS/Sb2S3 structure. Therefore, the graphite box design has been demonstrated to be functional to obtain Sb2S3 by a two-step process.

Electrochemical properties of B-site non-stoichiometric layered perovskite SmBa0.5Sr0.5CoxO5+d (x=1.9–2.1) cathodes for IT-SOFC

In this study, layered perovskites were synthesized using a non-stoichiometric synthesis strategy that allowed the variation of the amount of Co substitution in the basic composition of SmBa0.5Sr0.5Co2O5+d (SBSCO), used as a cathode material for Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFCs).SmBa0.5Sr0.5CoxO5+d (x = 1.9–2.1, SBSCO-1.9–2.1), B-site non-stoichiometric layered perovskites, were analyzed to characterize the electrical and electrochemical properties with respect to the Co substitution. Among them, SmBa0.5Sr0.5Co2.05O5+d (SBSCO-2.05) exhibited the best electrical and electrochemical properties with an ASR of 0.082 Ωcm2 and an electrical conductivity of 268.42 S/cm at 700 °C (measured in air within a series of measurements of increasing measuring temperature). Therefore, B-site non-stoichiometric perovskite compositions with increased Co substitution on their B sites represent a key strategy for achieving high performance cathodes compared to cathodes with stoichiometric compositions.

Design and Characterization of a Novel NiAl–(Cr,Mo) Eutectic Alloy

To enhance the mechanical properties of NiAl–(Cr,Mo) in situ composites for high‐temperature structural use, achieving a regular eutectic microstructure is crucial. A novel alloy with a composition of Ni30.6Al36Cr31.4Mo2 is developed that exhibits a significantly reduced solidification interval compared to well‐studied alloys such as Ni33Al33Cr28Mo6. This advancement results from using the in‐house developed alloy design tool PyMultOpt and Calculation of Phase Diagrams analysis to minimize the solidification interval. The refined alloy demonstrates a theoretical solidification interval of 0 K. These results are verified with differential scanning calorimetry measurements at different heating rates for the new alloy and compared with the established alloy Ni33Al33Cr28Mo6. The small solidification interval leads to a uniform eutectic microstructure consisting of a (Cr,Mo) phase embedded in the NiAl matrix without primary NiAl dendrites present. This indicates that deviating from the stoichiometric NiAl composition results in a significantly lower solidification interval and thus in an actual eutectic composition of the NiAl–(Cr,Mo) system.

Synthesis and Properties of Eu and Ni Co-Doped ZnS Nanoparticles for the Detection of Ammonia Gas

Zinc sulfide nanoparticles were synthesized successfully via chemical co-precipitation, both in undoped form and co-doped with Europium (Eu) and Nickel (Ni). All prepared samples exhibited cubic zinc blende structure as confirmed by X-ray diffraction (XRD). The average particle size ranged from 3 to 6 nm for both pure and (Eu, Ni) co-doped ZnS, with no alteration in the crystal structure due to Eu and Ni co-doping. However, increasing the Ni dopant concentration (0, 2, 4, & 6 at%) while maintaining a constant Eu concentration (4 at%) led to an enhancement in the crystallite size. This was further validated by transmission electron microscopy (TEM), which showed particle sizes consistent with the XRD findings (3–5 nm). Microscopic analysis via scanning electron microscopy and TEM revealed spherical agglomerated morphology for the (Eu, Ni) co-doped nanoparticles. Energy-dispersive X-ray spectroscopy spectra confirmed the stoichiometric chemical composition of ZnS: Eu, Ni. Photoluminescence studies demonstrated an increased intensity of green luminescence at 6 at% Ni co-dopant concentration. Moreover, the synthesized samples exhibited promising gas sensing properties, particularly towards ammonia gas, with good selectivity. Notably, both pure and (Eu, Ni) co-doped ZnS nanoparticles showed rapid response and recovery times at room temperature, suggesting their potential applicability in gas sensing applications.

Synthesis, Characterization and Power Factor Estimation of SnSe Thin Film for Energy Harvesting Applications

In this work, a simple, cost-effective successive ionic layer adsorption and reaction (SILAR) deposition technique has been used to deposit a high-quality tin selenide (SnSe) thin film onto a glass substrate. Structural, morphologic, and thermoelectric properties have been characterized for the prepared thin film. X-ray diffraction (XRD) results of the SnSe thin film reveal an orthorhombic structure phase. The morphological properties of the prepared thin films have been studied using field emission scanning electron microscopy (FESEM). The stoichiometric composition of the deposited thin film and the elemental binding energies of the Sn and Se elements have been investigated with energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The Fourier transformation infrared (FTIR) spectrum of the SnSe thin film displays vibrational modes of chalcogenides bonds. These results suggest that the developed thin film is crystalline, uniform, and without impurities and is appropriate for energy harvesting applications. The prepared thin film’s Seebeck coefficient and electrical resistivity were estimated through ZEM-3 from room temperature to 600 K. The power factor was evaluated. A substantially high electrical conductivity is observed, which decreases somewhat with temperature, suggesting a semimetal conducting transport—the absolute values of the Seebeck coefficient increase with temperature. The resulting power factor showed the highest values near room temperature and a somewhat decreasing trend as the temperature increased. Despite lower values of the Seebeck coefficient, the substantially enhanced power factor is due to the higher electrical conductivity of the thin film, superior to that reported previously. This precursor study demonstrates promising results for developing high-performance flexible thermoelectric devices via a simple and facile SILAR strategy.

Mechanism of initiation of ethylene cationic polymerization in the presence of an aluminum chloride aquacomplex in heptane with a stoichiometric composition of 1:1:1:2 at the quantum level

In this paper, the mechanism of ethylene initiation in the presence of an aluminum chloride – water catalyst in a heptane solvent of stoichiometric composition 1:1:1:2 was studied using the ab initio RHF theoretical quantum chemical method. The activation energy and thermal effect of this reaction were obtained. These data can be useful for further research in the field of cationic polymerization, and can also be used in the development of new technological processes of polyethylene with specified physicochemical properties characteristic of fiber optics.

Fingerprint Raman spectroscopy for two-dimensional MoS2x Se2(1−x) alloys

Two-dimensional transition metal dichalcogenides (TMDs) and alloys based on them, is a promising platform for creating opto- and nanoelectronic devices. For layered alloys, there is a strong need to theoretically determine the frequencies of vibrational modes and dependences of their energies on the stoichiometric composition. By comparing experimentally measured Raman modes with theoretical predictions, it becomes possible to determine the stoichiometric composition of the manufactured alloys. In this work, we investigated the vibrational properties of monolayer MoS2x Se2(1−x) alloys utilizing density functional theory method and confirmed them experimentally by Raman spectroscopy. The dependence of A1ʹ and E1 2g ‘dactylographic’ modes on the stoichiometric composition of alloys has been calculated. When in pure MoSe2 structure Se atoms are substituted by S atoms, the in-plane E1 2g (S–Mo), E1 2g (Se–Mo) and out-plane A1ʹ (S–Mo) modes shifted linearly in x to higher frequencies, while the out-plane A1ʹ (Se–Mo) mode did the same in nonlinear way. We also identified the E1 2g (Se–Mo–S) mode, which specific for the MoS2x Se2(1-x) alloys and does not appear in pure two-component TMDs.

Influence of halogen precursors on the growth of InSb nanostructures

The present work highlights the role of halogen compounds in modifying the shape of the InSb nanostructures, while maintaining a high crystalline quality of the nanostructures. One-dimensional (1D) nanowires (NWs) and two-dimensional (2D) nanoplatelets (NPLs) were synthesized by ambient pressure chemical vapor deposition. Our experimental results suggest that at a critical growth temperature of 512 ∘C, InSb NWs grow by the traditional vapor–liquid–solid growth mechanism when gold (Au) nanoparticles are used to initiate growth on an InSb film. The resulting NWs were found to have a cylindrical or tapered shape, were of high crystalline quality, and had stoichiometric composition. In the presence of halogen precursors, a change in morphology was observed and the resulting nanostructures were 2D NPLs and faceted NWs. Using existing models of crystal growth and concepts of volume, surface and edge energies, the experimental results are explained on the basis of chlorine atoms adsorbed on the wide or narrow facets of a nanocrystal, initiating nucleation and facilitating NPL or faceted NW formation. The incorporation of the chlorine atoms add a new degree of freedom to CVD synthesis of nanostructures and the results are promising for the controlled growth of novel 1D and 2D nanostructures for nano-electronic devices.

Surface immobilization mechanisms of cobalt ions on hydroxyapatite catalyst supports

Cobalt deposition in an excess of solution was used to design Co-modified hydroxyapatite materials with various Co loadings and controlled dispersion. It is rationalized how the properties of hydroxyapatite supports (more or less stoichiometric compositions, nanorod or platelet morphologies and crystalline (100) zig-zag termination or non-apatitic hydrated external layer), influence the immobilization processes of Co by operating either with slightly acidic (natural) or basic pH of the suspension media. Four cobalt immobilization mechanisms impacting the final dispersion of Co on hydroxyapatites were identified by combining structural (XRD, 1H and 31P solid-state NMR, UV-Vis, Raman and X-ray fluorescence spectroscopies), surface (XPS) characterizations of Co-modified hydroxyapatites after drying and thermal treatment at 500 °C, and monitoring of the pH and the composition of the supernatant solutions during the Co deposition step. On dried Co-modified crystalline stoichiometric hydroxyapatite nanorods, cobalt is highly dispersed through cationic exchange or strong electrostatic adsorption (SEA) at slightly acidic or basic pH, respectively. After thermal treatment at 500 °C, only cation exchange preserved atomic dispersion of Co(II) ions since Co3O4 nanoparticles were observed on samples for which Co deposition occurred via SEA. On defective hydroxyapatite platelets, cobalt deposited at acidic natural pH could diffuse in an external non-apatitic layer, whereas under basic pH media, this surface layer was hydrolysed, resulting in the formation of a cobalt-substituted hydroxyapatite layer in which only a limited fraction of the surface cobalt species could be probed by XPS.

Investigating the magnetic domain structure and photonics characters of Singled Phased hard ferromagnetic Ferrite MFe3O4 (M= Co2+, Zn2+, Cd2+) Compounds

The impact of transition metals on ferrite (iron (III) oxide) compounds is investigated in this study. Ferrite samples were synthesized using the co-precipitation method. X-ray analysis unveiled the presence of the Fe-phase in the trivalent state, showcasing a single-phased cubic spinel framework with a preferred orientation along the (311) reflection plane. Crystallite sizes were determined for CdFe3O4, ZnFe3O4, and CoFe3O4 utilizing the Scherer equation, yielding values of 10.54 nm, 18.76 nm, and 32.63 nm, respectively. Zinc ferrite displayed an intermediate photonic nature compared to cobalt and cadmium ferrite, with cadmium ferrite showing high optical losses and cobalt ferrite exhibiting minimal optical losses. EDX analysis confirmed the presence of Zn2+, Co2+, Fe3+, Cd2+, and O2? ions in the correct ratios, supporting the intended stoichiometric composition. Optical assessment revealed that CoFe3O4 nanoparticles are well-suited for optoelectronic devices, ultraviolet detectors, and infrared (IR) detectors. VSM measurements of cobalt ferrite exhibited higher coercivity and magnetic saturation compared to other samples. Photoluminescence (PL) spectroscopy revealed multiple colors, including cyan, green, and yellow, at different wavelengths for the ferrite samples. These findings suggest that the synthesized samples are suitable materials for high-frequency devices owing to their robust magnetic properties. Cadmium ferrite displayed a multi-magnetic domain structure, contrasting with the single-magnetic domain structure observed in zinc and cobalt ferrite.

THE EFFECT OF BARIUM SUBSTITUTION WITH COMBINATIONS OF RARE EARTH ON PERMANENT MAGNETIC SURFACE MORPHOLOGY BASED ON BARIUM HEXAFERRITE

The development of hard magnets today is progressing very rapidly. Developing hard magnets based on rare earth metals becomes a severe problem when the raw materials are not readily available. The chosen solution is to replace oxide-based permanent magnets with small amounts of rare earth metals substituted to improve their magnetic properties. This study synthesized a permanent magnet oxide based on barium hexaferrite doped with lanthanum and cerium atoms. In the synthesis of this material, a mechanical wet milling technique is used to obtain a single-phase permanent magnetic Ba1-β-γLaβCeγFe12O19 system with composition (β = 0 - 0.5 and γ = 0 - 0.1). The precursors are weighted according to their stoichiometric composition. Each mixed composition was milled by high energy milling (PW 1000 in the mixer/mill) at a milling speed of 1000 rpm using steel balls with an average diameter of 12 mm. Grinding conditions included a ball-to-powder weight ratio of 2:1, milling time 5 hours, then compacted with 7000 Psi pressure and sintered at 1200oC for 2 hours. The surface morphology and microstructure of the resulting sample particles were observed using scanning electron microscopy (SEM) with the SEM JEOL JED 305 brand. The characterization results show that the particles are hexagonally homogeneous in shape with particle sizes in the range of 1000-2000 nm for β = 0 and γ = 0 (without doping). In general, the four samples with varying concentrations of doping ions La3+ and Ce4+ showed homogeneous hexagonal structures but smaller particle sizes than pure barium hexaferrite. The sample particle sizes ranged from 500-1000 nm for β = 0.02 and 300-1000 nm for β = 0.04.

Unlocking the potential of Cu3SbSe3: Ultralow thermal conductivity and enhanced thermoelectric performance

Cu3SbSe3, with its ultralow thermal conductivity and Earth-abundant elements, has emerged as a promising thermoelectric material. However, synthesizing its pure phase and achieving effective doping have proven to be challenging. In this study, we present our findings on the investigation of thermoelectric properties of stoichiometric and off-stoichiometric Cu3SbSe3 compositions along with various doping strategies. Our results demonstrate that samples with non-stoichiometric compositions and Bi doping further reduces the lattice thermal conductivity of 0.16 W/mK. The consistently moderate Seebeck coefficient leads to a zT value of 0.25 at 650 K across all cation-deficient samples. Furthermore, we observed that 5% Bi doping further enhances the zT value to 0.35, representing a 52% improvement over pristine Cu3SbSe3. We believe that the compositional insensitivity of zT and the enhanced performance achieved through Bi doping offer new opportunities for exploring materials with ultra-low thermal conductivity in the field of thermoelectrics.

Modelling atomic and nanoscale structure in the silicon–oxygen system through active machine learning

Silicon–oxygen compounds are among the most important ones in the natural sciences, occurring as building blocks in minerals and being used in semiconductors and catalysis. Beyond the well-known silicon dioxide, there are phases with different stoichiometric composition and nanostructured composites. One of the key challenges in understanding the Si–O system is therefore to accurately account for its nanoscale heterogeneity beyond the length scale of individual atoms. Here we show that a unified computational description of the full Si–O system is indeed possible, based on atomistic machine learning coupled to an active-learning workflow. We showcase applications to very-high-pressure silica, to surfaces and aerogels, and to the structure of amorphous silicon monoxide. In a wider context, our work illustrates how structural complexity in functional materials beyond the atomic and few-nanometre length scales can be captured with active machine learning.